This document discusses optical sources and detectors used in fiber optic communications. It describes light emitting diodes (LEDs) and laser diodes as the main optical sources. LEDs use a double heterostructure to provide carrier and optical confinement for high efficiency. They emit incoherent light without an optical cavity. Laser diodes function as coherent sources using a Fabry-Perot cavity formed by cleaved facets to provide optical feedback, producing highly directional and monochromatic output. Factors such as modulation capability and fiber characteristics must be considered when choosing an optical source.
This document discusses different sources of noise in optical communication systems. It describes thermal noise, shot noise from dark current, and shot noise from photocurrent. Thermal noise is caused by random motion of electrons and is proportional to temperature and bandwidth. Shot noise arises from the discrete nature of electrons and is proportional to current. The total receiver noise is the combination of thermal noise, shot noise from dark current, shot noise from photocurrent, and amplifier noise. The signal to noise ratio takes all these noise sources into account.
Optical fiber communication Part 2 Sources and DetectorsMadhumita Tamhane
For optical fiber communication, major light sources are hetero-junction-structured semiconductor laser diode and light emitting diodes. Heterojunction consists of two adjoining semiconductor materials with different bandgap energies. They have adequate power for wide range of applications. Detectors used are PiN diode and Avalanche Photodiode. Being very small in size and feeding to small core optical fiber, it is very important to study emission characteristics of sources and their coupling to fiber. As it can operate for low power over a long distance, received power is very small, hence study of noise characteristics of detectors is very essential...
This document summarizes several methods for fabricating optical fibers, including glass, plastic, and photonic crystal fibers. The key steps in optical fiber fabrication are producing a preform, drawing fibers from the preform, and applying coatings. Common preform fabrication techniques described are outside vapor-phase oxidation, vapor-phase axial deposition, and modified chemical vapor deposition. The document also provides brief overviews of plastic and photonic crystal fiber properties.
Optical Fiber Communication Part 3 Optical Digital ReceiverMadhumita Tamhane
Current generated by photodetector is very weak and is adversely effected by random noises associated with photo detection process. When amplified, this signal further gets corrupted by amplifiers. Noise considerations are thus important in designing optical receivers.
Most meaningful criteria for measuring performance of a digital communication system is average error probability, and in analog system, it is peak signal to rms noise ratio. ...
The attached narrated power point presentation attempts to explain the methods of computation of total power loss and system rise time in a fiber optic link. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
This document summarizes key aspects of PIN photodiodes. It describes the physical principles of how PIN photodiodes operate by separating photo-generated carriers across a reverse-biased junction to produce a photocurrent. It also discusses photodiode characteristics like quantum efficiency and responsivity. Additionally, it covers noise sources in photodetector circuits including quantum, dark current, leakage current, and thermal noise. The document also examines photodiode response time and how the junction capacitance and absorption coefficient impact the rise and fall times. Finally, it compares different PIN photodiode structures like front vs rear illuminated and diffused vs mesa etched designs.
LED and LASER source in optical communicationbhupender rawat
The document discusses LEDs, lasers, and their use in optical fiber communication. It provides introductions to LEDs and lasers, explaining how they work by converting electrical energy into light. LEDs are suitable for optical fiber due to their small size, high radiance, ability to modulate at high speeds, and long lifetime. Lasers provide more directional, coherent light and are used where higher performance is needed, allowing transmission over greater distances and higher data rates. Both LEDs and lasers can be used to inject light signals into optical fibers for communication.
This document discusses different sources of noise in optical communication systems. It describes thermal noise, shot noise from dark current, and shot noise from photocurrent. Thermal noise is caused by random motion of electrons and is proportional to temperature and bandwidth. Shot noise arises from the discrete nature of electrons and is proportional to current. The total receiver noise is the combination of thermal noise, shot noise from dark current, shot noise from photocurrent, and amplifier noise. The signal to noise ratio takes all these noise sources into account.
Optical fiber communication Part 2 Sources and DetectorsMadhumita Tamhane
For optical fiber communication, major light sources are hetero-junction-structured semiconductor laser diode and light emitting diodes. Heterojunction consists of two adjoining semiconductor materials with different bandgap energies. They have adequate power for wide range of applications. Detectors used are PiN diode and Avalanche Photodiode. Being very small in size and feeding to small core optical fiber, it is very important to study emission characteristics of sources and their coupling to fiber. As it can operate for low power over a long distance, received power is very small, hence study of noise characteristics of detectors is very essential...
This document summarizes several methods for fabricating optical fibers, including glass, plastic, and photonic crystal fibers. The key steps in optical fiber fabrication are producing a preform, drawing fibers from the preform, and applying coatings. Common preform fabrication techniques described are outside vapor-phase oxidation, vapor-phase axial deposition, and modified chemical vapor deposition. The document also provides brief overviews of plastic and photonic crystal fiber properties.
Optical Fiber Communication Part 3 Optical Digital ReceiverMadhumita Tamhane
Current generated by photodetector is very weak and is adversely effected by random noises associated with photo detection process. When amplified, this signal further gets corrupted by amplifiers. Noise considerations are thus important in designing optical receivers.
Most meaningful criteria for measuring performance of a digital communication system is average error probability, and in analog system, it is peak signal to rms noise ratio. ...
The attached narrated power point presentation attempts to explain the methods of computation of total power loss and system rise time in a fiber optic link. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
This document summarizes key aspects of PIN photodiodes. It describes the physical principles of how PIN photodiodes operate by separating photo-generated carriers across a reverse-biased junction to produce a photocurrent. It also discusses photodiode characteristics like quantum efficiency and responsivity. Additionally, it covers noise sources in photodetector circuits including quantum, dark current, leakage current, and thermal noise. The document also examines photodiode response time and how the junction capacitance and absorption coefficient impact the rise and fall times. Finally, it compares different PIN photodiode structures like front vs rear illuminated and diffused vs mesa etched designs.
LED and LASER source in optical communicationbhupender rawat
The document discusses LEDs, lasers, and their use in optical fiber communication. It provides introductions to LEDs and lasers, explaining how they work by converting electrical energy into light. LEDs are suitable for optical fiber due to their small size, high radiance, ability to modulate at high speeds, and long lifetime. Lasers provide more directional, coherent light and are used where higher performance is needed, allowing transmission over greater distances and higher data rates. Both LEDs and lasers can be used to inject light signals into optical fibers for communication.
This document discusses semiconductor optical amplifiers (SOAs). It explains that SOAs use stimulated emission to amplify optical signals, like lasers, but have anti-reflection coatings on the facets so light passes through only once. The main types are traveling-wave amplifiers, which are widely used because they amplify signals with a single pass and have a large bandwidth. SOAs have a core made of InGaAsP for gain and InP cladding layers. External pumping by current injection provides carriers that undergo stimulated emission to amplify optical signals. Amplifier gain increases with length and current but saturates with increasing optical power due to depletion of excited carriers.
These slides give an extensive knowledge about the photo diode. It covers the circuit diagram and its energy band diagram. Also includes important information about noise factors and resoponsitivities.
LEDs are of interest for fibre optics because of five inherent characteristics..
How it works?
Spectrum of an LED
Modulation of LED
LED Vs. Laser diode
disadvantages of LED
This document discusses optical losses associated with fiber optic joints. It describes losses from Fresnel reflection at the interface between fibers due to differences in refractive index. It also discusses losses from various types of geometric misalignments between fibers, including longitudinal offset, lateral offset, and angular misalignment. Finally, it examines losses from variations in optical parameters between fibers, such as core diameter, numerical aperture, and refractive index profile mismatches. Formulas are provided for calculating losses from many of these sources.
Unit II- TRANSMISSION CHARACTERISTIC OF OPTICAL FIBER tamil arasan
Attenuation - Absorption losses, Scattering losses, Bending Losses, Core and Cladding losses, Signal Distortion in Optical Wave guides-Information Capacity determination -Group Delay-Material Dispersion, Wave guide Dispersion, Signal distortion in SM fibers-Polarization Mode dispersion, Intermodal dispersion, -Design Optimization of SM fibers-RI profile and cut-off wavelength.
This document discusses various types of antennas and antenna arrays. It begins by describing common antenna types including helical antennas, horn antennas, and parabolic reflector antennas. It then discusses how antenna arrays work, noting that they are composed of multiple similar radiating elements whose spacing and excitation determine the array's properties. Examples of linear and 2D arrays are provided. The document also summarizes different array configurations and beamforming techniques as well as applications such as smart antennas and adaptive arrays. Key benefits of arrays like controlling radiation patterns electronically are highlighted.
This narrated power point presentation attempts to explain the various dispersion mechanisms that are observed in optical fibers. Some fundamental terms and concepts are also discussed. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
This document discusses different methods of fibre splicing used to join optical fibers, including fusion splicing, mechanical splicing, and array splicing. Fusion splicing involves heating the fiber ends and fusing them together, while mechanical splicing uses tubes, V-grooves, or other guides to hold the fibers in alignment without heating. Array splicing allows simultaneously splicing multiple fibers in a ribbon using techniques like electric arc fusion or V-groove chips. Average splice losses are typically 0.1 dB or less depending on the splicing technique and fiber type.
Diversity Techniques in Wireless CommunicationSahar Foroughi
This document discusses diversity techniques for wireless communication, including cooperative diversity. It begins by introducing wireless systems and the impairments they face like fading. It then covers various diversity techniques like space, frequency, and time diversity that provide multiple transmission paths to reduce fading. Cooperative diversity is described as allowing single-antenna devices to achieve MIMO-like benefits by sharing antennas. The document outlines cooperative transmission protocols and challenges at different network layers in implementing cooperation. In conclusion, diversity techniques improve performance by providing multiple signal replicas to overcome fading, while cooperation enables reliability and throughput gains with challenges to address across protocol layers.
Erbium-doped fiber amplifiers (EDFAs) were invented in 1987 at the University of Southampton. Erbium ions allow for amplification in the 1540nm band with low fiber loss. Erbium can be excited by 980nm or 1480nm pumps carried by fiber. EDFAs provide high gain, low noise figure, and bit rate transparency for wavelength division multiplexing. They require pump lasers but do not need high-speed electronics.
This document provides an overview of optical amplifiers, including their necessity, basic concepts, types, and applications. Optical amplifiers are needed to compensate for attenuation losses over long transmission distances. The main types discussed are semiconductor optical amplifiers, erbium-doped fiber amplifiers (EDFAs), and Raman amplifiers. EDFAs use stimulated emission in erbium-doped fiber to amplify signals, while Raman amplifiers rely on stimulated Raman scattering in fiber. Both can provide wavelength-independent amplification but have different noise and gain characteristics. Optical amplifiers play a critical role in modern long-haul optical networks by enabling transmission over thousands of kilometers.
An optical fiber coupler is a device that splits light from one fiber into multiple fibers. There are different types of couplers classified by their shape, including Y, T, X, star, and tree couplers. Couplers work by transferring power between fibers through their cores or surfaces. Examples show how to calculate excess loss, insertion loss, crosstalk, and splitting ratios using the measured input and output powers. Optical couplers have applications in splitting and combining optical signals in fiber networks and communication systems.
The attached narrated power point presentation attempts to explain the working principle, types, classifications, merits, demerits, applications,safety and deployment issues related to Raman Amplifiers. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
This narrated power point presentation attempts to examine the losses due to non-linear effects in optical fibers. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
(1) LEDs use a p-n junction made of direct bandgap semiconductors that emits photons when electrically biased through injected minority carrier recombination. (2) Edge emitter LEDs have a thin active layer sandwiched between transparent guiding layers, allowing light to propagate and emit from the end face into smaller NA fibers for high coupling efficiency. (3) Double heterostructure LEDs provide the best performance with internal quantum efficiencies up to 80% due to high radiative recombination in the active region.
The attached narrated power point presentation is an attempt to introduce the WDM Standards framed by International Telecommunications Union as well as to familiarize oneself with the most popular WDM Components in practice. The material will be useful to KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
Optical Amplifiers are devices that amplify the optical light directly without conversion into electrical signals.
There are many types of Optical amplifier, but I am going to introduce to you the Semiconductor Optical Amplifier (SOA).
this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a
This document discusses semiconductor optical amplifiers (SOAs). It explains that SOAs use stimulated emission to amplify optical signals, like lasers, but have anti-reflection coatings on the facets so light passes through only once. The main types are traveling-wave amplifiers, which are widely used because they amplify signals with a single pass and have a large bandwidth. SOAs have a core made of InGaAsP for gain and InP cladding layers. External pumping by current injection provides carriers that undergo stimulated emission to amplify optical signals. Amplifier gain increases with length and current but saturates with increasing optical power due to depletion of excited carriers.
These slides give an extensive knowledge about the photo diode. It covers the circuit diagram and its energy band diagram. Also includes important information about noise factors and resoponsitivities.
LEDs are of interest for fibre optics because of five inherent characteristics..
How it works?
Spectrum of an LED
Modulation of LED
LED Vs. Laser diode
disadvantages of LED
This document discusses optical losses associated with fiber optic joints. It describes losses from Fresnel reflection at the interface between fibers due to differences in refractive index. It also discusses losses from various types of geometric misalignments between fibers, including longitudinal offset, lateral offset, and angular misalignment. Finally, it examines losses from variations in optical parameters between fibers, such as core diameter, numerical aperture, and refractive index profile mismatches. Formulas are provided for calculating losses from many of these sources.
Unit II- TRANSMISSION CHARACTERISTIC OF OPTICAL FIBER tamil arasan
Attenuation - Absorption losses, Scattering losses, Bending Losses, Core and Cladding losses, Signal Distortion in Optical Wave guides-Information Capacity determination -Group Delay-Material Dispersion, Wave guide Dispersion, Signal distortion in SM fibers-Polarization Mode dispersion, Intermodal dispersion, -Design Optimization of SM fibers-RI profile and cut-off wavelength.
This document discusses various types of antennas and antenna arrays. It begins by describing common antenna types including helical antennas, horn antennas, and parabolic reflector antennas. It then discusses how antenna arrays work, noting that they are composed of multiple similar radiating elements whose spacing and excitation determine the array's properties. Examples of linear and 2D arrays are provided. The document also summarizes different array configurations and beamforming techniques as well as applications such as smart antennas and adaptive arrays. Key benefits of arrays like controlling radiation patterns electronically are highlighted.
This narrated power point presentation attempts to explain the various dispersion mechanisms that are observed in optical fibers. Some fundamental terms and concepts are also discussed. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
This document discusses different methods of fibre splicing used to join optical fibers, including fusion splicing, mechanical splicing, and array splicing. Fusion splicing involves heating the fiber ends and fusing them together, while mechanical splicing uses tubes, V-grooves, or other guides to hold the fibers in alignment without heating. Array splicing allows simultaneously splicing multiple fibers in a ribbon using techniques like electric arc fusion or V-groove chips. Average splice losses are typically 0.1 dB or less depending on the splicing technique and fiber type.
Diversity Techniques in Wireless CommunicationSahar Foroughi
This document discusses diversity techniques for wireless communication, including cooperative diversity. It begins by introducing wireless systems and the impairments they face like fading. It then covers various diversity techniques like space, frequency, and time diversity that provide multiple transmission paths to reduce fading. Cooperative diversity is described as allowing single-antenna devices to achieve MIMO-like benefits by sharing antennas. The document outlines cooperative transmission protocols and challenges at different network layers in implementing cooperation. In conclusion, diversity techniques improve performance by providing multiple signal replicas to overcome fading, while cooperation enables reliability and throughput gains with challenges to address across protocol layers.
Erbium-doped fiber amplifiers (EDFAs) were invented in 1987 at the University of Southampton. Erbium ions allow for amplification in the 1540nm band with low fiber loss. Erbium can be excited by 980nm or 1480nm pumps carried by fiber. EDFAs provide high gain, low noise figure, and bit rate transparency for wavelength division multiplexing. They require pump lasers but do not need high-speed electronics.
This document provides an overview of optical amplifiers, including their necessity, basic concepts, types, and applications. Optical amplifiers are needed to compensate for attenuation losses over long transmission distances. The main types discussed are semiconductor optical amplifiers, erbium-doped fiber amplifiers (EDFAs), and Raman amplifiers. EDFAs use stimulated emission in erbium-doped fiber to amplify signals, while Raman amplifiers rely on stimulated Raman scattering in fiber. Both can provide wavelength-independent amplification but have different noise and gain characteristics. Optical amplifiers play a critical role in modern long-haul optical networks by enabling transmission over thousands of kilometers.
An optical fiber coupler is a device that splits light from one fiber into multiple fibers. There are different types of couplers classified by their shape, including Y, T, X, star, and tree couplers. Couplers work by transferring power between fibers through their cores or surfaces. Examples show how to calculate excess loss, insertion loss, crosstalk, and splitting ratios using the measured input and output powers. Optical couplers have applications in splitting and combining optical signals in fiber networks and communication systems.
The attached narrated power point presentation attempts to explain the working principle, types, classifications, merits, demerits, applications,safety and deployment issues related to Raman Amplifiers. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
This narrated power point presentation attempts to examine the losses due to non-linear effects in optical fibers. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
(1) LEDs use a p-n junction made of direct bandgap semiconductors that emits photons when electrically biased through injected minority carrier recombination. (2) Edge emitter LEDs have a thin active layer sandwiched between transparent guiding layers, allowing light to propagate and emit from the end face into smaller NA fibers for high coupling efficiency. (3) Double heterostructure LEDs provide the best performance with internal quantum efficiencies up to 80% due to high radiative recombination in the active region.
The attached narrated power point presentation is an attempt to introduce the WDM Standards framed by International Telecommunications Union as well as to familiarize oneself with the most popular WDM Components in practice. The material will be useful to KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
Optical Amplifiers are devices that amplify the optical light directly without conversion into electrical signals.
There are many types of Optical amplifier, but I am going to introduce to you the Semiconductor Optical Amplifier (SOA).
this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a presentation on photo diode it can be very useful for engineering students as well as undergraduate this is a
The document discusses optical sources for fiber optic communications, including light emitting diodes (LEDs) and laser diodes. It describes the basic structures and operating principles of LEDs and laser diodes. LEDs have a wide spectral width and beam width, while lasers can achieve coherent, highly directional beams with narrow spectral width using stimulated emission in an optical cavity. The document covers considerations for optical sources used in fiber communications and reviews semiconductor physics concepts relevant to LED and laser operation.
An optical transmitter converts an electrical input signal into an optical signal using an optical source such as a light emitting diode (LED) or laser diode. LEDs are better suited for optical communication systems with bit rates under 100-200 Mb/s and optical powers in the tens of micro watts range. A key component of LEDs is a double heterostructure which confines both holes and electrons to a narrow active layer, improving recombination efficiency. Edge emitting LEDs have a more directional emission pattern than surface emitting LEDs, providing better coupling efficiency into an optical fiber.
The document provides an introduction to optoelectronic devices, including their operation and key properties. It discusses:
1) The wave nature of light and how it is described by Maxwell's equations.
2) Polarization and the electromagnetic spectrum, including visible, infrared, and ultraviolet light ranges.
3) Types of optoelectronic devices like p-n junction diodes, heterojunction diodes, laser diodes, photoconductive cells, pin photodiodes, avalanche photodiodes, and photovoltaic cells. It provides details on their principles, structures, and applications.
This document provides information on optical sources and detectors. It discusses various optical sources like LEDs and lasers. For LEDs, it describes the structures of surface emitting LEDs and edge emitting LEDs. It also discusses laser diodes, the principle of population inversion required for lasing, and the formation of an optical cavity using mirrors. For detectors, it mentions PIN photodetectors and avalanche photodiodes. It provides a high-level overview of the key topics in optical sources and detectors.
This document discusses optical sources, specifically lasers. It begins with an overview of lasers and their basic concepts like stimulated emission. It then discusses semiconductor injection lasers in more detail, including their structure, characteristics like threshold current and temperature variation, and coupling lasers to optical fibers. Key aspects covered include population inversion, optical cavities, stripe geometry, and techniques for fiber coupling like butt coupling and lens systems.
A novel C+ L band erbium doped fiber broadband light so urce w ith hig h power was introduced. In the ex periment, a fiber loop mirr or made fr om 3 dB coupler was employed, mean while, power controlling circuit made fiber output steady. Single stage fiber and two pump LDs of 980 nm was used, and C band amplified spontaneous emission of backw ard again enhanced the efficiency of LD and stability o f output of fiber. Mean while, selecting appropriate Erbium doped fiber length simultaneously g ot output of C+ L band with power higher than 26.67 mW ( 14.26 dBm) , whose average wavelength was 1 550.887 nm.
The document discusses the basic structure and types of optical fibers. It describes how optical fibers carry light through total internal reflection using their core and cladding structure. Multi-mode fibers have a larger core diameter than single-mode fibers and can support multiple light propagation paths. Graded-index multi-mode fibers reduce dispersion by having a decreasing refractive index from the core center to cladding. Attenuation and coupling loss in optical fibers are also examined, with absorption and scattering identified as primary causes of signal loss over fiber length. Experimental procedures are outlined to characterize fiber properties including numerical aperture and attenuation measurements.
Adding quantum wells to the intrinsic region of a p-i-n solar cell improves its conversion efficiency in the following ways:
1. Quantum wells allow a wider range of photon energies to be absorbed by shifting electrons to higher energy levels. This improves the solar spectrum absorption.
2. Electron-hole pairs generated in the quantum wells have a longer lifetime, increasing the probability that they will separate and be collected before recombining.
3. The quantum wells act as intermediate energy levels, allowing photons of lower energy to still promote electrons provided the energy difference is matched by the quantum well transition.
However, limitations include the solar spectrum not being truly monochromatic, so not all energies can be utilized.
Circuits for Optical Based Line of Sight Voice CommunicationjournalBEEI
We present here line of sight communication between a person and his neighbour with the help of optical signal produced by a laser torch which act as a carrier. It is therefore a wireless communication and the transmission can go up to 500 meters. We used photodiode to receive the signal at the receiver. The transmitter circuit comprises condenser microphone transistor amplifier BC547 followed by an op-amp stage built around µA741. When we give a voice signal from the mike, it converts the voice signal into the electrical signal. This electrical signal is fed to IC741 (op-amp) for amplification. The gain of the op-amp can be controlled with the help of 1-mega-ohm potentiometer. The AF output from IC is coupled to the base of a class B amplifier which, in turn, modulates the signal. The transmitter uses 5V power supply. However, the 3-volt laser torch (after removal of its battery) can be directly connected to the circuit-with the body of the torch connected to the class B. The photodiode converts the optical signal into electrical signal and again this signal is amplified using IC741 and a combination of class B push pull amplifiers. The receiver circuit uses an NPN photodiode as the light sensor that is followed by a two-stage transistor preamplifier and IC741 based audio Power amplifier. The receiver does not need any complicated alignment. Just keep the photodiode oriented towards the remote transmitter’s laser point and adjust the volume control for a clear sound. The sensor must not directly face the sun.
Recent research shows the tremendous potential for the development of optical devices viz. photo-detector, optical sources, connectors and applications etc. This is mainly because of the success of optical communication in the recent for gigabit transmission and is intended for terabits transmission in future. In this paper, mathematical model for the optical dependence of I-V, C-V characteristics of MISFET structure (to be used as photo-detector) is reported. Model is based on solution of Poisson‟s and current continuity equation. Proposed structure of MISFET includes, In0.53Ga0.47As used as substrate material and InP as insulator. Light is made to incident perpendicular to the surface. Drain current can be controlled optically by means of varying light intensity of incident radiation. There is significant effect of intensity modulation on IV and CV characteristics of MISFET. As a result of intensity modulation, drain current increases significantly in presence of illumination mainly due to change in carrier concentration of channel results from photo-generated carriers. Simulation of mathematical model is carried out in MATLAB.
Optical antennas are devices designed to efficiently convert between propagating optical radiation and localized energy. Like radio frequency antennas, optical antennas can increase the interaction area of local absorbers or emitters with free radiation. Key aspects of optical antennas include their operation based on plasmonics and impedance matching. They can be fabricated using electron beam lithography or focused ion beam milling at the nanoscale. Applications include imaging, photovoltaics, and coherent control. Optical antennas provide opportunities for new optoelectronic architectures and devices by controlling light-matter interactions at the nanoscale.
The document summarizes key information about optical sources used for fiber optic communications. It describes how semiconductor laser diodes and light-emitting diodes (LEDs) use a pn junction to emit light via radiative recombination of electrons and holes. LEDs emit incoherent light, while laser diodes emit coherent light confined within an optical cavity. The document discusses characteristics of LEDs and laser diodes, including their structures, materials used, emission properties, and applications in optical communication systems.
A novel C+ L band erbium doped fiber broadband light so urce w ith hig h power was introduced. In the ex periment, a fiber loop mirr or made fr om 3 dB coupler was employed, mean while, power controlling circuit made fiber output steady. Single stage fiber and two pump LDs of 980 nm was used, and C band amplified spontaneous emission of backw ard again enhanced the efficiency of LD and stability o f output of fiber. Mean while, selecting appropriate Erbium doped fiber length simultaneously g ot output of C+ L band with power higher than 26.67 mW ( 14.26 dBm) , whose average wavelength was 1 550.887 nm.
This document provides an overview of various optical sources used for fiber optic communication, including LEDs, semiconductor lasers, and laser diodes. It describes the basic operation of LEDs and lasers, and discusses key laser diode structures like double heterostructure lasers, distributed feedback lasers, quantum well lasers, and vertical-cavity surface-emitting lasers. The document outlines requirements for optical sources in fiber optic systems and explains characteristics like emission wavelength, spectral width, output power, and modulation capabilities for different source types.
The document discusses quantum dot solar cells (QDSCs). QDSCs use quantum dots as the light-absorbing material instead of bulk semiconductors like silicon. Quantum dots have tunable bandgaps based on their size, allowing different energy levels to be harvested from the solar spectrum. This could enable higher efficiency multi-junction solar cells. The document outlines the history of QDSCs, describes how quantum dots exhibit quantum confinement effects, and discusses methods for fabricating quantum dots with different bandgaps through controlling their size and composition.
This document provides an overview of optical nano antennas. It begins by defining nano antennas and their role in transmitting and receiving optical signals at the nanoscale. Next, it discusses the characteristics of metallic and dielectric nano antennas, including their directivity, radiation efficiency, gain, and ability to enhance localized electric fields. Applications mentioned include medicine, photovoltaics, spectroscopy, and near-field microscopy. The document concludes by introducing seebeck nano antennas for solar energy harvesting and discusses limitations of current photovoltaic technology.
The document discusses optical fiber transmission and its advantages over other transmission mediums. It describes how optical fibers conduct light using total internal reflection. It also summarizes the key components used in optical fiber communication systems including optical sources like LEDs and lasers, photodetectors, and various types of optical fibers and their characteristics such as attenuation and dispersion. The document highlights how optical fiber transmission provides high bandwidth and capacity.
This document summarizes an online seminar about antenna basics and design concepts. It discusses the historical development of antennas from the 19th century works of scientists like Maxwell and Hertz to modern applications. Key antenna topics are defined, like radiation patterns, polarization, directivity and gain. Specific antenna types are described, such as dipoles, loops, Yagi-Uda arrays. The presentation outlines antenna parameters that influence performance, including materials, size, efficiency and impedance matching.
Similar to Unit 3- OPTICAL SOURCES AND DETECTORS (20)
The document discusses the Fast Fourier Transform (FFT) algorithm. It explains that FFT reduces the number of computations needed to calculate the Discrete Fourier Transform (DFT) of a sequence by decomposing the DFT into successive DFTs of smaller sizes. Specifically, it breaks down the N point DFT into multiple N/2 point DFTs recursively until it reaches DFTs of size 1. This decomposition reduces the complexity from O(N^2) for DFT to O(NlogN) for FFT.
The program demonstrates linear and circular convolution of sequences using MATLAB. For linear convolution, the conv function is used to convolve two input sequences and plot the results. For circular convolution, the FFT of each sequence is taken, multiplied together and inverse FFT applied to obtain the output, which is also plotted. The program thus allows generation and visualization of linear and circular convolution.
1. The document describes the syllabus for the VLSI Design Laboratory course for the academic year 2017-2018 at Erode Sengunthar Engineering College.
2. The syllabus includes experiments involving HDL-based design and simulation of basic components like counters and adders using FPGA tools. It also includes layout design and simulation of basic CMOS gates using CAD tools.
3. The listed experiments will be carried out in two cycles. Cycle 1 involves the implementation of components like adders, multipliers and counters on FPGA. Cycle 2 involves the design and simulation of CMOS gates using EDA tools and their layout using other CAD tools.
This document discusses sequential circuits and their design. It covers:
1. The difference between combinational and sequential logic and examples like finite state machines and pipelines that require sequential logic.
2. Methods for sequencing tokens through pipelines using flip-flops, latches, and pulsed latches and the associated timing diagrams.
3. Design considerations for sequential circuits like max/min delays, time borrowing, and clock skew.
4. Circuit designs for various latches and flip-flops including transparent latches, CMOS transmission gate latches, dynamic flip-flops, and true single phase clock elements.
The document discusses various techniques for encrypting messages to provide security in communication. It describes:
1. Traditional encryption techniques like the Caesar cipher, monoalphabetic ciphers, the Playfair cipher, and polyalphabetic ciphers like the Vigenere cipher. These techniques encrypt messages by substituting or transposing letters.
2. The importance of keeping encryption algorithms and keys secret to prevent cryptanalysis attacks. Brute force attacks try every possible key to decrypt messages.
3. How more advanced techniques like using multiple cipher alphabets and large keys spaces make cryptanalysis much more difficult compared to simple ciphers like the Caesar cipher.
The document discusses stream ciphers and block ciphers. It explains that stream ciphers encrypt data bit-by-bit or byte-by-byte, requiring a randomly generated keystream, while block ciphers encrypt fixed-length blocks, allowing for broader applications. It then focuses on the Feistel cipher structure for block ciphers, proposed by Feistel to approximate an ideal block cipher for large block sizes. The Feistel structure uses a product cipher approach involving substitutions and permutations to provide diffusion and confusion and resist statistical cryptanalysis.
1. Digital signatures provide authentication of digital documents by using asymmetric cryptography techniques. A digital signature is generated using a private key and can be verified by anyone using the corresponding public key.
2. There are various types of attacks against digital signature schemes like key-only attacks, generic chosen message attacks, and adaptive chosen message attacks. The security goals are to prevent total key breaks or the ability to forge signatures selectively or existentially.
3. A secure digital signature scheme must produce signatures that depend on the message, use secret information to prevent forgery and denial, be efficient to generate and verify, and make forgery computationally infeasible. Timestamps can be included to require message freshness.
Filter- IIR - Digital signal processing(DSP)tamil arasan
1. The document discusses and compares analog and digital filters. Digital filters are described as processing digital data/signals using elements like adders and multipliers, while analog filters use electronic components.
2. It also summarizes different types of common digital filters like Butterworth and Chebyshev filters. Butterworth filters have a monotonic magnitude response while Chebyshev filters exhibit ripple in the passband or stopband.
3. The document outlines different methods to convert analog filters to digital filters, including bilinear transformation which maps the s-plane jΩ axis to the unit circle in the z-plane to avoid aliasing.
1. DSP algorithms are realized using special or general purpose digital hardware where numbers are stored using a finite number of bits. Quantization errors are introduced during truncation or rounding of coefficients and numbers.
2. There are three main types of quantization errors: input quantization error from A/D conversion, product quantization error from multiplier outputs being rounded to a finite number of bits, and coefficient quantization error that deviates the frequency response from the desired response.
3. Fixed point and floating point representations are used to represent numbers in digital computers, with fixed point using a fixed binary point and floating point having a variable binary point to increase dynamic range at the cost of more complex hardware.
Electric vehicle and photovoltaic advanced roles in enhancing the financial p...IJECEIAES
Climate change's impact on the planet forced the United Nations and governments to promote green energies and electric transportation. The deployments of photovoltaic (PV) and electric vehicle (EV) systems gained stronger momentum due to their numerous advantages over fossil fuel types. The advantages go beyond sustainability to reach financial support and stability. The work in this paper introduces the hybrid system between PV and EV to support industrial and commercial plants. This paper covers the theoretical framework of the proposed hybrid system including the required equation to complete the cost analysis when PV and EV are present. In addition, the proposed design diagram which sets the priorities and requirements of the system is presented. The proposed approach allows setup to advance their power stability, especially during power outages. The presented information supports researchers and plant owners to complete the necessary analysis while promoting the deployment of clean energy. The result of a case study that represents a dairy milk farmer supports the theoretical works and highlights its advanced benefits to existing plants. The short return on investment of the proposed approach supports the paper's novelty approach for the sustainable electrical system. In addition, the proposed system allows for an isolated power setup without the need for a transmission line which enhances the safety of the electrical network
Comparative analysis between traditional aquaponics and reconstructed aquapon...bijceesjournal
The aquaponic system of planting is a method that does not require soil usage. It is a method that only needs water, fish, lava rocks (a substitute for soil), and plants. Aquaponic systems are sustainable and environmentally friendly. Its use not only helps to plant in small spaces but also helps reduce artificial chemical use and minimizes excess water use, as aquaponics consumes 90% less water than soil-based gardening. The study applied a descriptive and experimental design to assess and compare conventional and reconstructed aquaponic methods for reproducing tomatoes. The researchers created an observation checklist to determine the significant factors of the study. The study aims to determine the significant difference between traditional aquaponics and reconstructed aquaponics systems propagating tomatoes in terms of height, weight, girth, and number of fruits. The reconstructed aquaponics system’s higher growth yield results in a much more nourished crop than the traditional aquaponics system. It is superior in its number of fruits, height, weight, and girth measurement. Moreover, the reconstructed aquaponics system is proven to eliminate all the hindrances present in the traditional aquaponics system, which are overcrowding of fish, algae growth, pest problems, contaminated water, and dead fish.
Advanced control scheme of doubly fed induction generator for wind turbine us...IJECEIAES
This paper describes a speed control device for generating electrical energy on an electricity network based on the doubly fed induction generator (DFIG) used for wind power conversion systems. At first, a double-fed induction generator model was constructed. A control law is formulated to govern the flow of energy between the stator of a DFIG and the energy network using three types of controllers: proportional integral (PI), sliding mode controller (SMC) and second order sliding mode controller (SOSMC). Their different results in terms of power reference tracking, reaction to unexpected speed fluctuations, sensitivity to perturbations, and resilience against machine parameter alterations are compared. MATLAB/Simulink was used to conduct the simulations for the preceding study. Multiple simulations have shown very satisfying results, and the investigations demonstrate the efficacy and power-enhancing capabilities of the suggested control system.
Software Engineering and Project Management - Introduction, Modeling Concepts...Prakhyath Rai
Introduction, Modeling Concepts and Class Modeling: What is Object orientation? What is OO development? OO Themes; Evidence for usefulness of OO development; OO modeling history. Modeling
as Design technique: Modeling, abstraction, The Three models. Class Modeling: Object and Class Concept, Link and associations concepts, Generalization and Inheritance, A sample class model, Navigation of class models, and UML diagrams
Building the Analysis Models: Requirement Analysis, Analysis Model Approaches, Data modeling Concepts, Object Oriented Analysis, Scenario-Based Modeling, Flow-Oriented Modeling, class Based Modeling, Creating a Behavioral Model.
Embedded machine learning-based road conditions and driving behavior monitoringIJECEIAES
Car accident rates have increased in recent years, resulting in losses in human lives, properties, and other financial costs. An embedded machine learning-based system is developed to address this critical issue. The system can monitor road conditions, detect driving patterns, and identify aggressive driving behaviors. The system is based on neural networks trained on a comprehensive dataset of driving events, driving styles, and road conditions. The system effectively detects potential risks and helps mitigate the frequency and impact of accidents. The primary goal is to ensure the safety of drivers and vehicles. Collecting data involved gathering information on three key road events: normal street and normal drive, speed bumps, circular yellow speed bumps, and three aggressive driving actions: sudden start, sudden stop, and sudden entry. The gathered data is processed and analyzed using a machine learning system designed for limited power and memory devices. The developed system resulted in 91.9% accuracy, 93.6% precision, and 92% recall. The achieved inference time on an Arduino Nano 33 BLE Sense with a 32-bit CPU running at 64 MHz is 34 ms and requires 2.6 kB peak RAM and 139.9 kB program flash memory, making it suitable for resource-constrained embedded systems.
The CBC machine is a common diagnostic tool used by doctors to measure a patient's red blood cell count, white blood cell count and platelet count. The machine uses a small sample of the patient's blood, which is then placed into special tubes and analyzed. The results of the analysis are then displayed on a screen for the doctor to review. The CBC machine is an important tool for diagnosing various conditions, such as anemia, infection and leukemia. It can also help to monitor a patient's response to treatment.
Batteries -Introduction – Types of Batteries – discharging and charging of battery - characteristics of battery –battery rating- various tests on battery- – Primary battery: silver button cell- Secondary battery :Ni-Cd battery-modern battery: lithium ion battery-maintenance of batteries-choices of batteries for electric vehicle applications.
Fuel Cells: Introduction- importance and classification of fuel cells - description, principle, components, applications of fuel cells: H2-O2 fuel cell, alkaline fuel cell, molten carbonate fuel cell and direct methanol fuel cells.
Redefining brain tumor segmentation: a cutting-edge convolutional neural netw...IJECEIAES
Medical image analysis has witnessed significant advancements with deep learning techniques. In the domain of brain tumor segmentation, the ability to
precisely delineate tumor boundaries from magnetic resonance imaging (MRI)
scans holds profound implications for diagnosis. This study presents an ensemble convolutional neural network (CNN) with transfer learning, integrating
the state-of-the-art Deeplabv3+ architecture with the ResNet18 backbone. The
model is rigorously trained and evaluated, exhibiting remarkable performance
metrics, including an impressive global accuracy of 99.286%, a high-class accuracy of 82.191%, a mean intersection over union (IoU) of 79.900%, a weighted
IoU of 98.620%, and a Boundary F1 (BF) score of 83.303%. Notably, a detailed comparative analysis with existing methods showcases the superiority of
our proposed model. These findings underscore the model’s competence in precise brain tumor localization, underscoring its potential to revolutionize medical
image analysis and enhance healthcare outcomes. This research paves the way
for future exploration and optimization of advanced CNN models in medical
imaging, emphasizing addressing false positives and resource efficiency.
2. Light Sources:
1. Heterojunction -structured semiconductor Laser diodes
(injection laser diodes or ILDs)
2. Light-emitting diodes(LEDs)
Heterojunction two adjoining semiconductor materials with different
band-gap energies.
They have adequate output power for a wide range of applications
High efficiency
Light emitting region LEDs and LASER diodes pn junction
Direct band gap III-V semiconductor materials.
Junction forward baised electron and holes are injected into the p
and n regions.
Injected minority carriers can recombine either radiatievely ,
Photon energy hv emittd
This pn junction is active or recombination region.
3. LED:
Output incoherent
No optical cavity exists output radiation broad spectral width.
LASER:
Output coherent
Coherent source optical resonant cavity highly monochromatic
output beam very directional.
Choosing optical source:
Optical waveguide, Characteristics of optical fiber like geometry,
attenuation as a function of wavelength, Group delay distortion, modal
characteristics
Interplay of these factors optical source power , spectral width,
radiation pattern, and modulation capability.
Laser use single or multi mode fiber.
LED use only Multimode.
4. a) Energy level diagrams showing the excitation of an electron from the valence band to the conduction band.
The resultant free electron can freely move under the application of electric field.
b) Equal electron & hole concentrations in an intrinsic semiconductor created by the thermal excitation of
electrons across the band gap
-123
JK1038.1
Bk
Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
5. Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
-
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Si -
-
-
-
• Inject Arsenic into the crystal with an implant step.
• Arsenic is Group5 element with 5 electrons in its outer shell, (one more than
silicon).
• This introduces extra electrons into the lattice which can be released through
the application of heat and so produces and electron current
• The result here is an N-type semiconductor (n for negative current carrier)
Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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-
Si -
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-
Si -
-
-
-
-
+
+
+
As -
-
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- -
As -
-
-
- -
As -
-
-
- -
+
-
-
-
6. a) Donor level in an n-type semiconductor.
b) The ionization of donor impurities creates an increased electron concentration distribution.
Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
7. Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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-
Si -
-
-
-
• Inject Boron into the crystal with an implant step.
• Boron is Group3 element is has 3 electrons in its outer shell (one less than silicon)
• This introduces holes into the lattice which can be made mobile by applying heat. This
gives us a hole current
• The result is a P-type semiconductor (p for positive current carrier)
Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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Si -
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B -
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B -
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B -
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8. a) Acceptor level in an p-type semiconductor.
b) The ionization of acceptor impurities creates an increased hole concentration distribution
Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
9. Intrinsic material: A perfect material with no impurities.
Thermal generation process produce free electron hole pair.
Recombination Process free electron releases its energy and
drops into a free hole in the valence band.
Extrinsic material: donor or acceptor type semiconductors.
Mass action law two types of carriers constant
Majority carriers: electrons in n-type or holes in p-type.
Minority carriers: holes in n-type or electrons in p-type.
The operation of semiconductor devices is essentially based on
the injection and extraction of minority carriers.
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10. Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
Electron diffusion across a pn junction
creates a barrier potential (electric field)
in the depletion region.
11. Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
A reverse bias widens the depletion region, but allows minority carriers to move freely with the applied field.
12. Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
Lowering the barrier potential with a forward bias allows majority carriers to diffuse across the junction.
18. Optical communication requiring data rate(bit rate)
100-200 Mb/s with multimode fibre
Coupled optical power tens of microwatts,
LEDs are usually the best choice.
LED less complex than laser diode.
Since no thermal or optical stabilization.
LED have:
1.High radiance output.
2.Fast emission response time.
3.High quantum efficiency.
19. Radiance(brightness):is a measure ,in watts, of the optical power
radiated into a unit solid angle per unit area of the emitting surface.
High radiances necessary to couple sufficiently high optical power
levels into fiber.
Emission response time: the time delay between the application of
current pulse and the onset of optical emission.
Quantum efficiency: the fraction of injected electron hole pairs that
recombine radiatively.
To achieve High Radiance & High Quantum efficiency :
• confining the charge carriers
• stimulated optical emission to the active region of the pn junction,
where radiative recombination takes place.
20. 1.Carrier confinement :
used to achieve a high level of radiative recombination
yields high quantum efficiency
2.Optical confinement:
Prevent absorption of the emitted radiation by material surrounding the
pn junction.
Achieve carrier and optical confinement
LED configurations Homojunctions and single and double
heterojunctions
Mostly double heterostructure used two different alloy layers on
each side of active region .
Dual confinement leads to both high efficiency and high radiance.
21. Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
Cross-section drawing of a typical
GaAlAs double heterostructure light
emitter. In this structure, x>y to
provide for both carrier confinement
and optical guiding.
b) Energy-band diagram showing the
active region, the electron & hole
barriers which confine the charge
carriers to the active layer.
c) Variations in the refractive index;
the lower refractive index of the
material in regions 1 and 5 creates an
optical barrier around the waveguide
because of the higher band-gap
energy of this material.
22. Active light emitting region perpendicular to the axis of the fiber
Well is etched through the substrate of the device which fiber is then
cemented accepted emitted light.
Circular active area50μm diameter,2.5μm thick
Emission Pattern120°half power beam width.
23. Isotropic pattern from surface emitter is called a Lambertian
pattern.
In this pattern source is equally bright when viewed from any
direction.
But power decrease as cosƟ
Ɵ angle between the viewing direction and the normal to the
surface
Power is down to 50% of its peak
when Ɵ=60° so that total half power beam width is 120°
24. Active junction Region incoherent light
Two guiding Layers.
Refractive index of guiding layer < Active region. But higher than
surrounding material
This structure forms waveguide channel that directs the optical
radiation towards the fiber core.
25. Fiber core diameter50-100 μm
Contact stripes edge emitter 50-70μm
Length of active region 100-150μm
Emitted radiation pattern is more directional.
No wave guide effect.
Half power beam width is 120
26. Semiconductor material used active layer of optical source
direct band gap.
Direct band gap electron and hole recombine directly
without needing third particle.
Optical radiation high.
None of the normal single element semiconductor
direct –gap materials many binary compounds are.
Materials: Group III element Al, Ga, In
Group V Element P, As, Sb
Various ternary and quaternary combinations of binary
compounds Direct band gap materials
800-900 nm spectrum ternary alloy used.
Ratio x of alumininum arsenide to gallium arsenide
determines the band gap of alloy and wave length of peak emitted
radiation.
AsAlGa xx1
27. Full width half maximum:
The width of the spectral pattern at its half power point.
For LED FWHM36nm
Relation between energy and wavelength:
E=hv=hc/ λ
Eis energy, is in joules. λ wavelength
)eV(
240.1
m)(
gE
28.
29. Quantum Efficiency and LED Power
Due carrier injection at devices contact excess electrons and holes in
p-type and n-type material respectively.
When carrier injection stops carrier density returns equilibrium value.
Generally excess carrier density decays exponentially
n0 initial injected excess electron density.
τ--> Carrier life time.(Milliseconds to fraction of nano seconds)
Excess carrier recombine radiatively or nonradiatively.
Radiative Recombination photon energy =bandgap energy.
Non radiative recombination includes self absorption carrier
recombination in hetero junction interfaces and auger process.
30. Constant current flow into an LED equilibrium condition
established
Total Rate(Carrier Generated)=Externally supplied+ thermally
generated rates.
J/qd Externally supplied
J current density
qelectron charge
d thickness of recombination region.
n/τthermal generation rate.
Rate Equation is
The equilibrium condition
31. Internal quantum efficiency= Ratio of the radiative recombination rate to
the total recombination rate.
τr radiative recombination life time
τnr radiative recombination life time
Recombination life time:
32. Quantum efficiency:
Simple homo junction LEDs50%
Double hetro junction60-80%
if Current injected into the LED I,
total no.of recombination is Rr+Rnr=I/q
Rr total no.of photons generated per second and each photon has hv
energy.
optical power is
33. To find the emitted power consider External quantum efficiency ηext
The ratio of the photons emitted from the LED to the number of internally
generated photons.
Consider reflection effects
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34. The frequency response of an LED depends on:
1- Doping level in the active region
2- Injected carrier lifetime in the recombination region, .
3- Parasitic capacitance of the LED
If the drive current of an LED is modulated at a frequency of the
output optical power of the device will vary as:
Electrical current is directly proportional to the optical power, thus we
can define electrical bandwidth and optical bandwidth, separately.
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37. Laser comes many forms entire room size to grain of salt.
Lasing medium
Gas,
Liquid,
insulating crystal(Solid state),
Semiconductor.
For optical fiber laser sources Semiconductor laser diode.
its similar to other lasers conventional solid state and gas Lasers.
Emitted radiation Spatial and temporal coherence
output radiation highly monochromatic and the light beam very
directional.
Laser action 3 key Process
Photon absorption
Spontaneous emission
Stimulated emission
39. The meta stable state E2 has greater lifetime than the lower energy state
or ground state E1. Hence, more electrons are accumulated in the energy
state E2 than the lower energy state E1.
40.
41. Optical communication system Requiring Bandwidth > 200MHz.
Laser diode
Response time <1 ns.
Optical bandwidths 2nm or less
Coupling several tens of milliwatts power into optical fiber.
MFD small.
Multi layered hetero junction devices
LED
Double hetro junction achieve optical and carrier confinement.
simpler construction.
Small temperature dependence of the emitted optical power
Absence of catastrophic degradation
Laser
Construction more complicated
Additional requirement current confinement
42. Radiation in the laser diode generated within a Fabry perot resonator
cavity.
43. Pair of flat partially reflecting mirrors directed toward each other to
enclose the cavity.
Mirror facets constructed by making two parallel clefts along natural
cleavage planes of the semiconductor material.
Purpose of these mirror provide strong optical feedback in the longitudinal
direction.
Converting device to oscillator compensates for optical losses in the cavity.
Laser cavity many resonant frequency.
Device will oscillate those frequency gain is sufficient to overcome the
losses.
Sides of cavity formed by roughening the edges reduce unwanted
emission in this direction.
44.
45. Cleaved facets not required for optical feedback.
Lasing action from bragg reflectors or periodic variations of the
refractive index.
Which are incorporated into the multilayer structure along the length of
the diode.
*********************************************************
Optical output needed only from front facet of the laser. one to be
aligned with an optical fiber.
Dielectric reflector can be deposited on the rear facet to reduce the
optical loss in cavity.
To reduce threshold current density and to increase external quantum
efficiency.
Reflectivities >98% have been achieved six layer reflector.
Distributed Feedback Laser
46. Modes of the cavity optical radiation within cavity of a laser diode sets up
a pattern of electric and magnetic field lines.
Two independent sets of TE and TM modes.
Each set of modes can described in terms of the
1. Longitudinal modes
Related to length L of the cavity.
Determine the principal structure of frequency spectrum of emitted
optical radiation.
L much larger than lasing wavelength(1 um)
Many longitudinal mode exist.
2. Lateral Modes
lie in the plane of pn junction.
Depend on the side wall preparation and the width of the cavity
Determine the shape of the lateral profile of the laser beam.
3. Transverse modes
are associated with electromagnetic field and beam profile in the
direction perpendicular to the plane of the pn junction.
These modes important determine laser characteristics.
47. Determine lasing condition and the resonant frequencies
Electro magnetic wave propagating in longitudinal direction(in-terms of
electric field phasor )
I(z)optical field intensity.
W optical radian frequency
Lasing condition at which light amplification becomes possible in
laser diode.
Requirement lasing population inversion achieved
Understood optical field intensity I, absorption co efficient αλ
Gain coefficient –g
Stimulation emission rate proportional to intensity of the radiation.
The radiation intensity at a photon energy hV varies
48. ā effective absorption coefficient of the material
Г optical confinement factor fraction of optical power in the active
layer.
Optical amplification feedback mechanism of the optical cavity.
Repeated passes between two partially reflecting mirror portion
of the radiation associated in these modes highest optical gain.
Further amplified each trip through the cavity.
Lasing occurs when gain of one or several guided modes is sufficient to
exceed the optical loss during one roundtrip through the cavity
Z=2L. R1,r2 fraction of optical radiation at lasers end 1& 2.
Reflection coefficient
49. At Lasing Threshold steady state oscillation take place magnitude and
the phase of the wave must be equal to original wave.
Amplitude I(2L)=I(0)
Phase exp(-j2βL)=1
lasing at threshold optical gain =total loss αt
αend mirror loss in the lasing cavity.
Lasing occur must g≥gth
Means pumping source maintain population inversion must be strong
to support.
50. Only spontaneous radiation is emitted
low diode current
Spectral range& lateral beam emission
broad like LED
Lasing occur dramatic & sharply
increase power.
Spectral range& lateral beam both
narrow with increasing drive current.
Final spectral width 1nm
Threshold current Ithextrapolation of the lasing region of the power vs
current currve
High power output slope of the curve decrease because junction heating.
Lasing threshold optical gain
gth=β Jth
Β constant
51. Laser diode rate equation
Total carrier population determined by carrier injection,
spontaneous recombination & stimulated emission
Rate equation in terms no. of photons
=stimulated emission+ spontaneous emission + photon loss.
in terms no. of electrons
=injection + spontaneous recombination +stimulated emission
C coefficient senrength of optical emission & absorption.
Rsp rate of Spontaneous emission.
τph--> photon life time
τs-->spontaneous recombination life time injection current density.
52. Steady state condition
dΦ/dt=dn/dt=0
n,Φ non zero.
Rsp negligible,
dΦ/dt positive when Φ is small.
N must exceed a threshold value nth in order for Φ to increase and
threshold value for the electron density nth
The above threshold value(nth) interms of Jth
54. External quantum efficiency
The no.of photons emitted per radiative electron –hole pair
recombination above the threshold level.
Experimentally
dP incremental change in the emitted optical power
dIincremental change in the drive current
55. Resonant Frequency
Lasing threshold equation
The cavity resonates when an integer number m of half wavelength spans
the region between the mirrors.
Gain function of frequency or wavelength
In terms of gaussian form.
56. G(0) maximum gain proportional to population inversion
σ--> spectral width
λ0 wavelength.
Consider frequency or wavelength ,specing betwwen the modes of
multimode fiber.
We consider only logitudional modes.
Find frequency spacing consider two successive modes of frequency
57.
58. Laser Diode Structures and Radiation Patterns
Basic Requirement of laser diodes
1. optical and carrier Confinement between hetro junction layers.
2. The current flow must be restricted laterally to a narrow stripe along
the length of the laser.
To achieve this Many methods proposed.
but are limiting No. of lateral modes
so that lasing confined single filament,
stabilizing the lateral gain
& ensuring relatively low threshold current.
Three optical confinement methods used for bounding laser light
in the lateral direction.
59. GAIN GUIDED LASER
Narrow electrode stripe less than 8μm wide
Runs along the length of the diode.
The injection of electrons and holes into the device
alters the refractive index of the active layer directly below the stripe.
Injected carrier creates weak ,complex waveguide that confines the
light laterally.
This Lasers can emit optical powers exceeding 100mW
Strong instabilities
High astigmatic
60. Index guided Lasers
More stable structure
Dielectric waveguide fabricated in the lateral direction
Variations of real refractive index of various material control the lateral
modes
This lasers supports fundamental transverse and longitudinal modes.
it is known as single mode laser
Emits single ,well collimated beam light intensity profile which is bell
shaped Gaussian curve.
Types 1. positive index wave confining Structures.
2. Negative index wave confining Structures.
In Positive index waveguide
central region higher refractive index than the outer regions
All of the guided light is reflected at the dielectric boundary(just as core
cladding interfaces)
Proper choice change in the refractive index and width of the higher index
region can make device supports fundamental lateral mode.
61. In negative index wave guide
Central region of the active layer lower refractive index than the outer
regions
Dielectric boundaries part of the light is reflected and rest is refracted into
surrounding material and thus lost.
Radiative loss will be appear in far field radiation pattern.
Positive index is more popular.
62. Index guided lasers can be made using any one of fundamental
structures.
1. Buried hetero structure
2. Selectively diffused construction
3. Varying thickness structure
4. Bent layer configuration
Buried hetero structure:
One etches a narrow mesa stripe(1-2 um wide) in double hetero structure
material
Then mesa is embedded in -> high resistivity lattice matched n-type
material with an appropriate band gap and low refractive index.
800- 900 nm laser GaAlAs material with GaAs active layer
1300-1600nm laser InP material with InGaAsP active layer
This configuration strongly traps generated light in a lateral
waveguide.
63.
64. Selectively diffused construction
Chemical dopant zinc for GaAlAs Lasers and
Cadmium for InGaAsP Laser
Is diffused into the active layer immediately below the metallic contact
stripe.
The dopant changes the refractive index of the active layer to form a lateral
wave guide Channel
65. Varying thickness structure
A channel(mesa or terrace) etched into the substate
Layers of crystal are then regrown into channel using liquid phase
epitaxy
This process fills depressions and partially dissolves the protrusions
This creating variations in the thickness of active region
66. Bent layer structure
This structure forms using vapor phase epitaxy to exactly replicate the
mesa configuration.
Active layer constant thickness with lateral bends
Optical wave travels along flat top of the mesa in the active area
Lower index in outside of the material.
67. In addition to optical wave confinement,
Also restrict the drive current tightly to the active layer so more than
60% of the current contributes to lasing.
Current confine methods 4 methods
1.Preferential dopant diffusion
2. Proton implantation
3. Inner stripe confinement
4. Regrowth of back biased pn junction.
Device architecture blocks current on both sides of the lasing region
Achieved by high resitivity or reverse biased pn junction.
Which prevent the current from flowing while the devices is forward biased
under normal conditions.
Continuous active layer current can be confined either above or below
the lasing region.
68.
69. Single Mode Laser
High speed long distance communication Needs single mode laser
Which must contain only single longitudinal mode and a single
transverse mode
So thatSpectral width of the optical emission is very narrow.
One way is only one longitudinal modes is reduce the length L of the
lasing cavity to the point
But reduce l (example 250um to 25 um In 1300nm region) spacing will
increase 1 um to 10um.
However these lengths make device hard to handle limited to optical
output power only few milliwatts.
Another method developed vertical cavity surface emitting laser
That have built in frequency selective grading and tunable lasers.
70. The special feature of vertical cavity surface emitting laser is light
emission is perpendicular to the semiconductor surface.
This feature facilitates integration of multiple lasers onto a single chip in
one or two dimensional array.
Which make them attractive for WDM applications
Active region very small leads to low threshold current
Equivalent output power compare edge emitting lasers
Modulation bandwidth much larger higher photon densities reduce
radiative lifetimes.
71. The frequency selective reflector is a
corrugated gating which is a passive
waveguide layer adjacent to the active region
Optical wave propagates parallel to this gating.
Operation distributed Bragg phase gating reflector.
Phase gating periodically varying refractive index
ne effective refractive index, k order of the gating
Laser Configurations using built in frequency selective reflector
Distributed Feedback (DFB)Laser Distributed Bragg Reflector (DBR)Laser
Distributed Reflector (DR)Laser
72. 1st order mode(k=1) provides strongest coupling
But some times 2nd order gratings used larger corrugation Fabrication
easier.
73. Modulation of Laser Diode
Process of imposing information on light steam modulation.
1. Directly varying the laser drive current with information stream.
produce varying optical output power.
2. External modulator modify a steady optical power level emitted by
the laser.
External modulation needed for high speed systems(> 2.5 Gb/s)
Varity of external modulator available either separate device or
integral part of the laser transmitter package.
Limitations on direct modulation
Modulation rate depends on spontaneous (radiative) & stimulated
carrier life times and photon life times.
Spontaneous lifetime function of semiconductor band structure and
carrier concentration.
At room temperature Radiative lifetime 1 ns, GaAs material dopant
concentration10^19 cm^-3.
Stimulated carrier lifetime depends on optical density in the lasing
cavity order of 10ps.
74. Photon Life time average time that the photon resides in the lasing cavity
before being lost either by absorption or by emission through the facets.
Laser diode pulse modulated photon life time is much smaller than
carrier lifetime.
If the laser is completely turned off each pulse spontaneous carrier life
time will limit the modulation rate.
Is needed to achieve population inversion necessary to produce gain
sufficient to overcome the optical losses in the cavity.
Pulse modulation carried out by modulating laser only in operating
region above threshold.
Carrier life time is shorten to stimulated lifetime high modulation rates
are possible.
75. When using directly modulated laser diode in high speed system
Modulation frequency can be no larger than the frequency of the
relaxation oscillation of the laser field.
Relaxation oscillation both spontaneous lifetime and photon life time.
Analog Modulation carried out by making drive current above
threshold proportional to baseband information signal.
77. Lasing threshold changes laser ages.
If constant output power level is to be maintained temperature changes
or laser ages
Necessary to adjust dc bias current level
Possible Methods:
Optical feedback
Feedforward schemes
Temperature matching transistor
Predistortion technique
78.
79.
80. Photodetectors senses the luminescent power falling upon and it
converts the variation of this optical power into correspondingly
varying electric current.
Types:
Photomultipliers large size
Pyroelectric detectors speed is limited by detector cooling rate
Semiconductor based photoconductor
Phototransistors
Photodiodes small size, suitable material ,high sensitivity & fast
response time.
Types:pin photodetector & avalanche photodiode
81. The pin Photodetector
Generation of free electron hole pair Photocarriers
Photocurrent with one electron flowing for every carrier pair generated
Diffusion Legthcharge carrier move a distance Ln,Lp
Time takes to electron recombine carrier lifetime τ
D diffusion Coefficient
83. Quantum Efficiency
No.of electron hole pair generated per incident photon of energy
hv
η=No.of electron hole pair generated/No. of incident photon
η= (Ip/q) /(P0/hv)
Responsitivity R=Ip/P0
= ηq/hv
84. Avalanche Photodiodes
APDs internally multiply the primary signal photocurrent before it
enters the input circuitry of the following amplifier.
This increase sensitivity photo current is multiplied before
encountering the thermal noise associated with receiver circuit.
Photogenerated carriers high electric field present
In this high field region photogenerated electron or hole can gain
enough energy so that it ionizes bound electrons in the valance
band upon colliding with them.
This carrier multiplication impact ionization
Newly created carriers accelerated by high electric field.
Thus gaining enough energy to cause further impact ionization
avalanche effect.
85. Reach-through arise from photo diode operation.
When low reverse bias voltage is applied most potential drop is across
in pn+ junction
The depletion layer widens with increasing bias until certain voltage is
reached at which the peak electric field at the pn+ junction about 5-10%
below that needed to cause avalanche breakdown.
At this point depletion layer just reaches through to the nearly intrinsic
π region.
Reach through
Construction
High resistivity p
type material
Deposited on
epitaxial layer on
a p+ substrate
Configuration
is p+πpn+ reach
through
structure
86. Normal usage RAPD fully depleted mode
Light enter p+ region absorbed in the π material it acts as a
collection region for the photogenerated carriers.
Absorbed photon gives up its energy creating electron hole pairs
Separated by electric field in the π region.
The photogenerated electrons drift through the π region in the pn+
junction where high electric field exists.
High field region carrier multiplication takes place.
Ionization rate The average no. of electron hole pairs created by a
carrier per unit distance traveled.
87. PHOTODETECTOR NOISE
In Optical communication system photodiode generally required detect
weak optical signals.
Its required to amplification circuitry optimized ,so that given SNR
maintained
The power signal to noise ratio S/N at the output of an optical receiver
Photodetector noises arise from photon-to-electron conversion process.
Amplifier noise due to thermal noise in amplifier circuitry.
To achieve High SNR
1.Photodetector must have high quantum efficiency
2.The photodetctor and amplifier noises should be kept as low as possible.
88. Noise Sources
If modulated signal of optical power P(t) falls on the detector ,the primary
photocurrent generated is
Pin/ APD photodiode the mean square signal current is
89. Noise Source:
1.Quantum noise
Arises from statistical nature of production and collection of
photoelectrons, when optical signal is incident on a photo detector.
F(M) Noise figure
2.Photodiode dark current current that continues to flow
through the bias circuit of the device.
When no light is incident on the photodiode.
It is combination of bulk and surface currents.
3.Surface dark current or surface leakage current simply
leakage current.
It is dependent on surfaces defects ,cleanliness, bias voltage, and
surface AREA.
Reducing surface dark current through the use of guard ring
structure
90. The photodetector load resistor contributes a mean square thermal
noise current
Signal to Noise Ratio:
91. DETECTOR RESPONSE TIME
Light enters through p layer and Produce electron hole pair.
Those electron hole pair generated in the depletion region or within diffusion
length it will be separated by reverse bias voltage induced electric field.
Leading current flow in the external circuit.
Depletion Layer Photocurrent
94. Response Time
Depends on
1.Transit time of the pohotocarriers
2.Diffusion time of the photocarriers generated outside the depletion region
3. RC time constant of the photodiode and its associated circuit
Photodiode parameter:
1.Absorption coefficient αs
2.Depletion region width w
3. Photodiode junction and package capacitance
4. Amplifier capacitance
5.Detector load resistance
6.Amplifier input resistance
7.Photodiode series resistance
Photodiode series resistance generally only a few ohms can be neglected
(comparison with 5 & 6)
First transit time
The response speed of a photodiode is limited by time takes
photogenerated carriers to travel across the depletion region.
95. Typical high speed silicon photodiode 10um depletion layer width
Response time 0.1ns.
Second diffusion time
Photocarriers should be generated in the depletion region or close to it that
the diffusion times are less than or equal to the carrier drift times.
Response time described by rise time and fall time of the detector output
when the detector is illuminated by step input of optical radiation.
Rise time 10 to 90% change
Fall time 90% to 10% change.
96. Electron hole pairs generated in
the n and p regions must slowly
diffuse to the depletion region
before they can be separated
and collected.
The fast carriers allow the device output to rise to 50% of its maximum value
Slow carriers cause a relatively long delay before the output reaches its
maximum value
To achieve high quantum efficiency
depletion layer width must be much
larger than 1/αs, so that most of the light
will be absorbed.
98. Avalanche Multiplication Noise
Avalanche multiplication process statistical in nature
Since not every photogenerated carrier pair undergoes the same
multiplication.
Avalanche noise
Excess noise factor
The ratio of excess noise generated in avalanche photodiode to the noise
that would exist if all carrier pairs were multiplied by exactly M