This document discusses distortion in optical fibers caused by dispersion and attenuation. It describes various types of dispersion including intramodal, material, waveguide, and intermodal dispersion. Material dispersion arises from the refractive index variation of the core with wavelength. Waveguide dispersion depends on fiber design and arises from differences in propagation velocity between spectral components. The document also covers attenuation mechanisms like material absorption and scattering that limit the transmission distance of optical signals in fibers.
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.
Describes Fiber Optics using Optical Ray Theory.
For comments please contact me at solo.hermelin@gmail.com.
For more presentations visit my website at http://www.solohermelin.com.
Optical fiber communication Part 1 Optical Fiber FundamentalsMadhumita Tamhane
Optical fiber systems grew from combination of semiconductor technology, which provided necessary light sources and photodetectors and optical waveguide technology. It has significant inherent advantages over conventional copper systems- low transmission loss, wide BW, light weight and size, immunity to interferences, signal security to name a few. One principle characteristic of optical fiber is its attenuation as a function of wavelength. Hence it is operated in two major low attenuation wavelength windows 800-900nm and 1100-1600nm . Light travels inside optical fiber waveguide on principle of total internal reflection. Fiber is available as single mode and multiple mode, step index and graded index depending on applications and expenditures. Principle of fiber can be understood by ray theory or mode theory. ...
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 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.
Describes Fiber Optics using Optical Ray Theory.
For comments please contact me at solo.hermelin@gmail.com.
For more presentations visit my website at http://www.solohermelin.com.
Optical fiber communication Part 1 Optical Fiber FundamentalsMadhumita Tamhane
Optical fiber systems grew from combination of semiconductor technology, which provided necessary light sources and photodetectors and optical waveguide technology. It has significant inherent advantages over conventional copper systems- low transmission loss, wide BW, light weight and size, immunity to interferences, signal security to name a few. One principle characteristic of optical fiber is its attenuation as a function of wavelength. Hence it is operated in two major low attenuation wavelength windows 800-900nm and 1100-1600nm . Light travels inside optical fiber waveguide on principle of total internal reflection. Fiber is available as single mode and multiple mode, step index and graded index depending on applications and expenditures. Principle of fiber can be understood by ray theory or mode theory. ...
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.
The attached narrated power point presentation describes the principle of working, various configurations, advantages, disadvantages and applications of Erbium Doped Fiber Amplifiers. The material will be useful to KTU final year B tech students who prepare for the subject EC 405, Optical Communications.
Discussion of cutoff wavelength in optical fibres its defination measurements specifications optical fibre refractive index profiles, Total Internal Reflection, specifications for ITU G 657, 655A ,G655A,D
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...
A brief presentation about optical fiber technology. Presented by Abdessalam BENHARIRA and Laurent PANEK.
Summary
1. What is optical fiber ?
2. How it works ?
3. Different types
4. Uses
5. Advantages and disadvantages
6. Conclusion
This topic will provide a detailed study about the optical heterodyne detection and its working. A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called heterodyning.
Heterodyning is used to shift one frequency range into another, new frequency range, and is also involved in the processes of modulation and demodulation.
The two input frequencies are combined in a nonlinear signal-processing device such as a vacuum tube, transistor, or diode, usually called a mixer.
An Antenna is a transducer, which converts electrical power into electromagnetic waves and vice versa.
An Antenna can be used either as a transmitting antenna or a receiving antenna.
A transmitting antenna is one, which converts electrical signals into electromagnetic waves and radiates them.
A receiving antenna is one, which converts electromagnetic waves from the received beam into electrical signals.
In two-way communication, the same antenna can be used for both transmission and reception.
Basic Parameters
Frequency
Wavelength
Impedance matching
VSWR & reflected power
Bandwidth
Percentage bandwidth
Radiation intensity.
The attached narrated power point presentation describes the principle of working, various configurations, advantages, disadvantages and applications of Erbium Doped Fiber Amplifiers. The material will be useful to KTU final year B tech students who prepare for the subject EC 405, Optical Communications.
Discussion of cutoff wavelength in optical fibres its defination measurements specifications optical fibre refractive index profiles, Total Internal Reflection, specifications for ITU G 657, 655A ,G655A,D
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...
A brief presentation about optical fiber technology. Presented by Abdessalam BENHARIRA and Laurent PANEK.
Summary
1. What is optical fiber ?
2. How it works ?
3. Different types
4. Uses
5. Advantages and disadvantages
6. Conclusion
This topic will provide a detailed study about the optical heterodyne detection and its working. A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called heterodyning.
Heterodyning is used to shift one frequency range into another, new frequency range, and is also involved in the processes of modulation and demodulation.
The two input frequencies are combined in a nonlinear signal-processing device such as a vacuum tube, transistor, or diode, usually called a mixer.
An Antenna is a transducer, which converts electrical power into electromagnetic waves and vice versa.
An Antenna can be used either as a transmitting antenna or a receiving antenna.
A transmitting antenna is one, which converts electrical signals into electromagnetic waves and radiates them.
A receiving antenna is one, which converts electromagnetic waves from the received beam into electrical signals.
In two-way communication, the same antenna can be used for both transmission and reception.
Basic Parameters
Frequency
Wavelength
Impedance matching
VSWR & reflected power
Bandwidth
Percentage bandwidth
Radiation intensity.
Signal Degradation In Optical Fiber
Losses in an optical fibre:-
The types of losses in a optical fibre are
Attenuation loss
Absorption
Scattering
Bending loss
Dispersion loss
Coupling loss
As we know Optical communication Network offers
very high potential bandwidth and flexibility. In terms of high
bit-rate transmission. However, their performance slows down
due to some parameter like dispersion, attenuation, scattering. In
long haul application, dispersion is the main parameter which
needs to be compensated in order to provide better service. Fiber
Braggs Grating (FBG) is one of the most widely used element to
compensate it, however its performance slows down with the
increase in distance.
This paper presents an investigation on Pulse distortions due to
the third-order dispersion (TOD) on very high speed long
distance single mode optical fiber communication system using
OptiSystem. Presence of the TOD introduces broadening on the
propagating pulse. The impact of TOD is observed at the
receiving end of transmission line considering the variation of
different factors such as transmission reach, bit rate, duty
cycle.BER performance are also considered here.
Twenty Essential Knowledge of Optical Cable.pdfHYC Co., Ltd
An article about basic knowledge of optical fiber cable, including the wavelength, dispersion of optical fiber, insertion loss, return loss, fiber core diameter, types of optical fiber etc. Including What is the mode field diameter (MFD), What is Numerical Aperture (NA), What is the cutoff wavelength and so on.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Explore the innovative world of trenchless pipe repair with our comprehensive guide, "The Benefits and Techniques of Trenchless Pipe Repair." This document delves into the modern methods of repairing underground pipes without the need for extensive excavation, highlighting the numerous advantages and the latest techniques used in the industry.
Learn about the cost savings, reduced environmental impact, and minimal disruption associated with trenchless technology. Discover detailed explanations of popular techniques such as pipe bursting, cured-in-place pipe (CIPP) lining, and directional drilling. Understand how these methods can be applied to various types of infrastructure, from residential plumbing to large-scale municipal systems.
Ideal for homeowners, contractors, engineers, and anyone interested in modern plumbing solutions, this guide provides valuable insights into why trenchless pipe repair is becoming the preferred choice for pipe rehabilitation. Stay informed about the latest advancements and best practices in the field.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
2. DISTORTION IN OPTICAL FIBERS
▪ When an optical signal is transmitted on an optical fiber, the signal is
distorted due to two phenomena: dispersion and attenuation.
Distortion in optical fiber
Dispersion
▪ Intramodal dispersion
▪ Material dispersion
▪ Waveguide dispersion
▪ Inter modal dispersion
Attenuation
Material attenuation
▪ Absorption
▪ Scattering
Bending loss Radiation
3. DISPERSION
▪ The light is launched into an optical fiber in the form of a light pulse to transmit the
information
▪ The broadening of the transmitted light pulses as they travel along the fiber is known
as dispersion.
▪ the overlap between adjacent pulses, creating
errors in the receiver output (i.e., ISI),
resulting in the limitation of information-
carrying capacity of a fiber.
4.
5. CHROMATIC OR INTRAMODAL DISPERSION
▪ This type of dispersion results from the finite spectral linewidth of the optical
source. Since optical sources do not emit just a single frequency but a band of
frequencies
▪ There may be propagation delay differences between the different spectral
components of the transmitted signal. This causes broadening of each
transmitted mode and hence intramodal dispersion (group velocity dispersion).
▪ The delay differences may be caused by the dispersive properties of the
waveguide material (material dispersion) and also guidance effects within
the fiber structure (waveguide dispersion).
6. MATERIAL DISPERSION
▪ This arises due to the variations of the refractive index of the core material as a
function of wavelength.
▪ This refractive index property causes a wavelength dependence of the group
velocity of a given mode; that is, pulse spreading occurs when different
wavelengths follow the same path.
▪ The group velocity is given by 𝑣𝑔 =
𝑑𝜔
𝑑𝛽
; where the propagation constant 𝛽 =
2𝜋𝑛1 𝜆
𝜆
and ω =
2𝜋𝑐
𝜆
▪ A time delay or group delay in the direction of the propagation 𝑡𝑔 =
𝐿
𝑣𝑔
𝑡𝑔 =
𝐿
𝑣𝑔
= 𝐿
𝑑𝛽
𝑑𝜔
𝑜𝑟
𝐿
𝑐
𝑑𝛽
𝑑𝑘
7. MATERIAL DISPERSION
𝑑𝛽
𝑑𝜆
= −
2𝜋
𝜆2
𝑛1 − 𝜆
𝑑𝑛1
𝑑𝜆
𝑎𝑛𝑑
𝑑𝜔
𝑑𝜆
= −
2𝜋𝑐
𝜆2
▪ Therefore
𝑡𝑔 = 𝐿
𝑑𝛽/𝑑𝜆
𝑑𝜔/𝑑𝜆
=
𝐿
𝑐
𝑛1 − 𝜆
𝑑𝑛1
𝑑𝜆
▪ If the spectral width of the optical source is not too wide, then the delay difference per unit
wavelength along the propagation path is approximately
𝑑𝑡𝑔
𝑑𝜆
.
▪ For spectral components which are 𝛿𝜆 apart, symmetrical around center wavelength, the total
delay difference 𝛿𝜏 over a distance L is:
𝛿𝜏 =
𝑑𝑡𝑔
𝑑𝜆
𝛿𝜆 =
𝐿
𝑐
𝜆
𝑑2𝑛1
𝑑𝜆2
𝛿𝜆
▪ The material dispersion of optical fibers is quoted in terms of the material dispersion parameter
Dmat given by
𝐷𝑚𝑎𝑡 =
1
𝐿
𝛿𝜏
𝛿𝜆
=
𝜆
𝑐
𝑑2𝑛1
𝑑𝜆2
Dmat has the units of ps nm–1 km–1.
8. ▪ In the case of optical pulse, if the spectral width of the optical source is
characterized by its rms value of the Gaussian pulse 𝜎𝜆, the pulse
spreading over the length of L, 𝜎𝑚 can be well approximated by:
𝜎𝑚𝑎𝑡 =
𝑑𝑡𝑔
𝑑𝜆
𝜎𝜆 = 𝐿𝐷𝑚𝑎𝑡𝜎𝜆
9.
10. WAVEGUIDE DISPERSION
▪ The degree of waveguide dispersion depends on the fiber design.
▪ Waveguide dispersion usually can be ignored in multimode fibers, but its effect
is significant in single-mode fibers.
▪ This dispersion arises because the difference in core-cladding spatial power
distributions, together with the speed variations of the various wavelengths,
causes a change in propagation velocity for each spectral component.
▪ Waveguide dispersion is due to the dependency of the group velocity of the
fundamental mode as well as other modes on the V number.
▪ In order to calculate waveguide dispersion, we consider that n is not dependent
on wavelength. Defining the normalized propagation constant b as:
𝑏 =
𝛽
𝑘
2
− 𝑛2
2
𝑛1
2 − 𝑛2
2
13. ▪ The wavelength at which the first-order dispersion
is zero λ0 may be extended to wavelengths of 1.55
μm and beyond by a combination of three
techniques. These are:
▪ lowering the normalized frequency (V) for the
fiber;
▪ increasing the relative refractive index
difference Δ for the fiber;
▪ suitable doping of the silica with germanium.
14. INTER-MODAL DISPERSION
▪ The light rays travel different paths inside the core of an optical fiber because
different light rays are incident on the tip of the optical fiber at different angles
within the acceptance cone and lead to the broadening of the actual time-width of
the pulse. This phenomenon is called as inter-modal dispersion
▪ Intermodal dispersion or modal delay appears only in multimode fibers.
15. INTER-MODAL DISPERSION
▪ This broadening is simply obtained from ray tracing and for a fiber of length L
is given by
Δ𝑇 = 𝑇𝑚𝑎𝑥 − 𝑇𝑚𝑖𝑛
𝑇𝑚𝑖𝑛 =
𝐿
𝑐
𝑛1 𝑎𝑛𝑑 𝑇𝑚𝑎𝑥 =
𝐿
𝑐 cos 𝜃
𝑛1
sin 𝜙𝑐 = cos 𝜃 =
𝑛2
𝑛1
Δ𝑇 =
𝐿
𝑐
𝑛1
𝑛1
𝑛2
− 1 ≈
𝐿
𝑐
𝑛1Δ
The rms pulse broadening due to
intermodal dispersion
16. PROBLEMS
A 6 km optical link consists of multimode step index fiber with a core refractive index of
1.5 and a relative refractive index difference of 1%. Estimate:
(a) the delay difference between the slowest and fastest modes at the fiber output;
(b) the rms pulse broadening due to intermodal dispersion on the link;
(c) the maximum bit rate that may be obtained without substantial errors on the link
assuming only intermodal dispersion
Sol:
(a) The delay difference
∆𝑇 =
𝐿
𝑐
𝑛1Δ = 6 × 1.5 ×
0.01
3 × 105
= 300 𝑛𝑠
(b) The rms pulse broadening due to intermodal dispersion
𝜎𝑠 =
𝐿
2 3𝑐
𝑛1Δ = 86.7 𝑛𝑠
(c) The maximum bit rate may be estimated in two ways:
𝐵𝑇,𝑚𝑎𝑥 =
1
2∆𝑇
= 1.7 𝑀𝑏𝑝𝑠 or 𝐵𝑇,𝑚𝑎𝑥 =
0.2
𝜎𝑠
= 2.3 𝑀𝑏𝑝𝑠
17. PROBLEMS
▪ A glass fiber exhibits material dispersion given by |λ2(d2n1/dλ2) | of 0.025.
Determine the material dispersion parameter at a wavelength of 0.85 μm, and
estimate the rms pulse broadening per km for a good LED source with an rms
spectral width of 20 nm at this wavelength.
Sol:
Given that 𝜆2 𝑑2𝑛1
𝑑𝜆2 = 0.025
Operating wavelength λ = 850 nm
RMS spectral width 𝜎𝜆 = 20 𝑛𝑚
The material dispersion
𝐷𝑚𝑎𝑡 =
𝜆
𝑐
𝑑2
𝑛1
𝑑𝜆2
=
1
𝑐𝜆
𝜆2
𝑑2
𝑛1
𝑑𝜆2
=
0.025
3 × 105 × 850
= 98.04 ps nm−1 km−1
The rms pulse broadening per km
𝜎𝑚𝑎𝑡
𝐿
= 𝐷𝑚𝑎𝑡𝜎𝜆 = 1.96 𝑛𝑠/𝑘𝑚
18. PROBLEMS
▪ A manufacturer’s data sheet lists the material dispersion Dmat of a GeO2-
doped fiber to be 110 ps/(nm-km) at a wavelength of 860 nm. Find the rms
pulse broadening per km due to material dispersion if the optical source is a
GaAlAs LED that has a spectral width of 40 nm at an output wavelength of
860 nm.
19. ATTENUATION
▪ Signal attenuation (fiber loss) largely determines the maximum repeaterless
separation between optical transmitter & receiver (i.e., maximum
transmission distance between a transmitter and a receiver)
▪ Signal attenuation is usually expressed in the logarithmic unit of the decibel.
▪ The decibel, which is used for comparing two power levels, may be defined
as the ratio of the input (transmitted) optical power Pi into a fiber to the
output (received) optical power Po from the fiber
𝑃𝑜𝑤𝑒𝑟 𝑟𝑎𝑡𝑖𝑜𝑛 𝑖𝑛 𝑑𝐵𝑠 = −10 log10
𝑃𝑜
𝑃𝑖
= 10 log10
𝑃𝑖
𝑃𝑜
▪ In optical fiber communications the attenuation is usually expressed in
decibels per unit length (i.e. dB/km)
𝛼 =
1
𝐿
10 log10
𝑃𝑖
𝑃𝑜
𝑖𝑛 𝑑𝐵/𝑘𝑚
20. EXAMPLE
When the mean optical power launched into an 8 km length of fiber is 120 μW, the mean optical
power at the fiber output is 3 μW. Determine:
(a) the overall signal attenuation or loss in decibels through the fiber assuming there are no
connectors or splices;
(b) the signal attenuation per km for the fiber.
(c) the overall signal attenuation for a 10 km optical link using the same fiber with splices at 1 km
intervals, each giving an attenuation of 1 dB;
Sol:
(a) The overall signal loss/attenuation
𝛼 𝑑𝐵 = 10 log10
𝑃𝑖
𝑃
𝑜
= 16 𝑑𝐵
(b) The signal attenuation per km
𝛼 𝑑𝐵/𝑘𝑚 =
16
8
= 2 𝑑𝐵/𝑘𝑚
(c) the link also has nine splices (at 1 km intervals) each with an attenuation of 1 dB. Therefore, the
loss due to the splices is 9 dB. Hence, the overall signal attenuation for the link is: 29 dB
21. ATTENUATION IN FIBERS
▪ A number of mechanisms are responsible for the signal attenuation within
optical fibers. These mechanisms are influenced by the material composition,
the preparation and purification technique, and the waveguide structure.
▪ The basic attenuation mechanisms in a fiber are material absorption,
material scattering (linear and nonlinear scattering), curve and micro-
bending losses, mode coupling radiation losses and losses due to leaky modes.
There are also losses at connectors and splices
22. MATERIAL ABSORPTION LOSS
▪ Material absorption is related to the material composition and the fabrication process
for the fiber, which results in the dissipation of some of the transmitted optical power as
heat in the waveguide.
▪ Absorption by atomic defects in the glass composition (i.e., imperfections in the atomic
structure of the fiber material).
▪ these defects include missing molecules, high-density clusters of atom groups, or oxygen
defects in the glass structure
▪ Absorption is caused by the following mechanisms:
▪ Intrinsic absorption
▪ Extrinsic absorption
23. INTRINSIC AND EXTRINSIC ABSORPTION LOSS
▪ Intrinsic absorption caused by the interaction with one or more of the major components of the
glass or fiber material.
▪ electronic absorption bands (associated with the band gaps of the amorphous glass materials)
in the ultra violet (UV) region and from atomic vibration bands in the near-infrared (IR)
region
▪ The UV loss contribution in dB/km at any wave length (given in µm) can be expressed
empirically (derived from observation or experiment) as a function of the mole fraction x
𝛼𝑢𝑣 =
154.2𝑥
46.6𝑥 + 60
× 10−2 exp
4.63
𝜆
▪ In the near-infrared region above 1.2 µm,
𝛼𝐼𝑅 = 7.81 × 1011 exp
−48.48
𝜆
▪ Extrinsic absorption by impurity atoms in the glass material.
24.
25. SCATTERING LOSS
▪ Small (compared to wavelength) variation in material density, chemical composition, and
structural inhomogeneity scatter light in other directions and absorb energy from guided
optical wave.
▪ The essential mechanism is the Rayleigh scattering. Since the black body radiation classically
is proportional to 𝜆−4, the attenuation coefficient due to Rayleigh scattering is approximately
proportional to 𝜆−4
.
e
Temperatur
:
,
JK
10
3806
.
1
Js,
10
626
.
6 -1
23
34
T
k
h B
−
−
=
=
where p is the photo-elastic coefficient
βT is the isothermal compressibility of the material
26.
27. BENDING LOSS
▪ An optical fiber tends to radiate propagating power
whenever it is bent. Two types of bends
▪ macro-bends with radii much larger than the fiber
diameter and
▪ random micro-bends of the fiber axis that may arise
because of faulty cabling.
▪ Every guided core mode has a modal electric-field
distribution that has a tail extending into the cladding.
This evanescent field decays exponentially with
distance from the core.
▪ the optical energy in the tail beyond rc is lost through
radiation
▪ The amount of optical radiation from a bent fiber depends on the field strength at rc and on the
radius of curvature R.
▪ Since higher-order modes are bound less tightly to the fiber core than lower order modes, the
higher-order modes will radiate out of the fiber first.
28. EXAMPLE PROBLEM
▪ Consider a graded-index multimode fiber for which the index profile α = 2.0, the core index
n1= 1.480, the core-cladding index difference Δ = 0.01, and the core radius a = 25 µm. If the
radius of curvature of the fiber is R = 1.0 cm, what percentage of the modes remain in the
fiber at a 1300-nm wavelength?
Thus 42 percent of the modes remain in this fiber at a 1.0-cm bend radius.
29. MICRO-BENDING LOSS
▪ The micro-bends are caused by manufacturing defects which are in the form of non-uniformities in
the core radius or in the lateral pressure created by the cabling of the fiber. The effect of mode
coupling in multimode fibers on pulse broadening can be significant for long fibers.
▪ Micro-bend losses in single-mode fibers can also be excessive if proper care is not taken to minimize
them. One way to reduce such losses in single-mode fibers is to choose the V -value near the cut-off
value of Vc (e.g., 2.405 for the step-index profile), so that the mode energy is confined mainly to the
core.
30. EXAMPLE
▪ A certain optical fiber has an attenuation of 0.6 dB/km at 1310 nm and 0.3 dB/km at
1550 nm. Suppose the following two optical signals are launched simultaneously into
the fiber: an optical power of 150 µW at 1310 nm and an optical power of 100 µW at
1550 nm. What are the power levels in mW of these two signals at (a) 8 km and (b) 20
km?
Sol:
Given data: At λ1 = 1310 nm:
𝛼1 = 0.6 𝑑𝐵/𝑘𝑚
𝑃1 = 150 𝜇𝑊
𝑃1𝑖𝑛 𝑑𝐵𝑚 = 10 log10 150 × 10−3
= −8.24 𝑑𝐵𝑚
At λ2 = 1550 nm:
𝛼2 = 0.3 𝑑𝐵/𝑘𝑚
𝑃2 = 100 𝜇𝑊
𝑃1𝑖𝑛 𝑑𝐵𝑚 = 10 log10 100 × 10−3
= −10 𝑑𝐵𝑚
(a) At 8 km:
𝑃1 8𝑘𝑚 = 𝑃1 − 𝛼1𝐿 = −8.24 − 4.8 = −13.04 𝑑𝐵𝑚 = 49.66 𝜇𝑊
𝑃2 8𝑘𝑚 = 𝑃2 − 𝛼2𝐿 = −10 − 2.4 = −12.4 𝑑𝐵𝑚 = 57.54 𝜇𝑊
(b) At 8 km:
𝑃1 20 𝑘𝑚 = 𝑃1 − 𝛼1𝐿 = −8.24 − 12 = −20.24 𝑑𝐵𝑚 = 9.46 𝜇𝑊
𝑃2 20𝑘𝑚 = 𝑃2 − 𝛼2𝐿 = −10 − 6 = −16 𝑑𝐵𝑚 = 25.12 𝜇𝑊
31. EXAMPLE
A continuous 40-km-long optical fiber link has a loss of 0.4 dB/km.
(a) What is the minimum optical power level that must be launched into the fiber to
maintain an optical power level of 2.0 µW at the receiving end?
(b) What is the required input power if the fiber has a loss of 0.6 dB/km?
Sol:
Given that L = 40 km; α = 0.4 dB/km; Pout = 2 µW
(a) 𝑃𝑖𝑛 = 𝑃𝑜𝑢𝑡 × 10𝛼𝐿/10
= 2 𝜇𝑊 × 100.4×40
= 79.6 𝜇𝑊
(b) ) 𝑃𝑖𝑛 = 𝑃𝑜𝑢𝑡 × 10𝛼𝐿/10 = 2 𝜇𝑊 × 100.6×40 = 1.004 𝑚𝑊
32. TEXT BOOKS
▪ Gerd Keiser, Optical Fiber Communications, TMH India, Fourth Edition,
2010.
▪ Senior John M., Optical Fiber Communications, Pearson Education India,
Third Edition,2009.
▪ R.P. Khare, Fiber optics and optoelectronics, Oxford University Press 2004