PPT on Optical sources:LED & LASER for Optical Communication

1. Optical Sources:LED & LASER
By:-
•Dharit Unadkat -130870111039
•Jenish Thumar -130870111038
•Siddhant Vaghani-130870111040
Guided By:-
•Prof.Jwolin Patel
•Prof.A.O.Gupta
Class:-
EC-6th sem,
Parul Institute of Technology,
Limda.
Optical Communication

2. Overview
• What is an Optical Source
• LEDs
• SLEDs – Surface Emitting LEDs
• ELEDs – Edge Emitting LEDs
• LDs – Laser Diodes
• Tunable Lasers
• Conclusion
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3. What is an Optic Source?
• The heart of a fiber optical data system
• A Hybrid Device
– Converts electrical signals into optical signals
– Launches these optical signals into an optical
fiber for data transmission.
• Device consists of an interface circuit, drive
circuit, and components for optical source. (LEDs,
ELEDs, SLEDs, LDs, etc)
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4. LEDs – Light Emitting Diode
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•Emits incoherent light
through spontaneous
emission.
•Used for Multimode
systems w/ 100-200 Mb/s
rates.
•Broad spectral width and
wide output pattern.
850nm region: GaAs and
AlGaAs
1300–1550nm region:
InGaAsP and InP
•Two commonly used
types: ELEDs and SLEDs

5. SLEDs – Surface Emitting LEDs
• Primary active region is a small circular area located
below the surface of the semiconductor substrate, 20-
50µm diameter and up to 2.5µm thick.
• Emission is isotropic and in lambertian pattern.
• A well is etched in the substrate to allow the direct
coupling of emitted light to the optical fiber
• Emission area of substrate is perpendicular to axis of
optical fiber
• Coupling efficiency optimized by binding fiber to the
substrate surface by epoxy resin with matching
refractive index
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6. Surface Emitting LED
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7. ELEDs – Edge Emitting LEDs
• Primary active region is a narrow strip that lies beneath
the semiconductor substrate
• Semiconductor is cut and polished so emission strip
region runs between front and back.
• Rear face of semiconductor is polished so it is highly
reflective while front face is coated with anti-reflective,
light will reflect from rear and emit through front face
• Active Regions are usually 100-150µm long and the
strips are 50-70µm wide which are designed to match
typical core fibers of 50-100µm.
• Emit light at narrower angle which allows for better
coupling and efficiency than SLEDs
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8. Edge Emitting LED
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9. LDs – Laser Diodes
• Emit coherent light through
stimulated emission
• Mainly used in Single Mode
Systems
• Light Emission range: 5 to
10 degrees
• Require Higher complex
driver circuitry than LEDs
• Laser action occurs from
three main processes:
photon absorption,
spontaneous emission, and
stimulated emission.
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10. Laser Diode Optical Cavity
• One reflecting mirror is at one end while the other end
has a partially reflecting mirror for partial emission
• Remaining power reflects through cavity for amplification
of certain wavelengths, a process known as optical
feedback.
• Construction very similar to the ELEDs.
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11. Lasing Characteristics
• Lasing threshold is minimum
current that must occur for
stimulated emission
• Any current produced below
threshold will result in
spontaneous emission only
• At currents below threshold
LDs operate as ELEDs
• LDs need more current to
operate and more current
means more complex drive
circuitry with higher heat
dissipation
• Laser diodes are much more
temperature sensitive than
LEDs
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12. Tunable Laser
• Tunable Laser
– Employed in broad-band interconnections and
broadcast networks where the need for high power,
narrow line width, and a tunable single-frequency
emission is a must.
– Laser that is able to produce controllable multiple
wavelengths within single cavity.
– Able to switch transmission of different wavelengths
without using multiplexer for transmission to many
different channels at by tuning the output frequency to
its designated channel.
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13. Tunable Laser Operation
• Current is injected into the Active Region causing the
entire optical cavity to oscillate in a single longitudinal
mode.
• A current is then injected into the grating control
region causing a refractive index decrease which
induces a shift of the Bragg wavelength and variation in
the mode.
• The phase region with the injected phase current
allows for recovery in Bragg wavelength in order to
keep the same mode in the center of the filter band.
• This results in an output with variable wavelength.
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14. Tunable Laser Cavity
• Consists of an Active Region, and two passive regions:
Phase Control and Grating
• Active region is a double heterostructure of a low bandgap
between two high gap low index claddings.
• Two passive regions made from semiconductor with
intermediate bandgap between active and cladding.
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15. Summary
• Optical light sources convert electrical signals into optical
signals and launch them.
• Commonly used light sources include LEDs, ELEDs, SLEDs,
and LDs.
• LEDs produce nonlinear incoherent light whereas a Laser
Diode produces linear coherent light.
• Incoherent light sources used in multimode systems as
where Laser Diodes/Tunable Lasers in single mode systems
• Laser diodes must operate above their threshold region to
produce coherent light, otherwise operating as ELED.
• Laser diodes are much faster in switching response than
LEDs
• Tunable laser is able to produce coherent light output with
controlled variable wavelength
• Tunable laser is used in multi wavelength systems by
replacing a system where many sources are coupled into a
multiplexing device system
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16. Thank You
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