Лекция 18: Оптические телекоммуникационные системы
Фотоприемники
Базовые элементы оптической линии
Точка – точка (Point – to – point)
Приемник: Фотодиоды
Приемник: Фотодиоды
Различные структуры фотодиодов
MSM
(Metal Semiconductor Metal)
PIN
APD
Layer Structure |
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Features |
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Simple, Planar, |
Semiinsulating GaAs |
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Low Capacitance |
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Low Quantum Efficiency |
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Contact |
InGaAsP p |
5x1018 |
Trade-off Between |
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Absorption |
InGaAs |
n- |
5x1014 |
Quantum efficiency |
Contact |
InP |
n |
1x1019 |
and Speed |
Contact |
InP |
p |
1x1018 |
Gain-Bandwidth: |
Multiplication |
InP |
n |
5x1016 |
120GHz |
Transition |
InGaAsP n |
1x1016 |
Low Noise |
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Absorption |
InGaAs |
n 5x1014 |
Difficult to make |
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Contact |
InP |
n |
1x1018 |
Complex |
Substrate |
InP |
Semi insulating |
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Waveguide
Absorption Layer |
High efficiency |
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High speed |
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Guide Layers |
Difficult to couple into |
Key: |
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Absorption Layer |
Contact layers
Принцип работы PIN диода
ВАХ
needed sic “I”
V
Carriers absorbed here must diffuse to the intrinsic layer before they recombine if they are to contribute to the photocurrent. Slow diffusion can lead to slow “tails” in the temporal response.
Основные характеристики фотодиода
• Internal
Quantum Efficiency
•External
Quantum efficiency
• Responsivity
•Photocurrent
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Number of Collected electrons |
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W |
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i |
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1 e |
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Number of Photons *Entering* detector |
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Number of Collected electrons |
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iph / q |
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W |
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e |
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1 Rp 1 e |
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Number of Photons *Incident* on detector |
Po / h |
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R |
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Photo Current (Amps) |
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iph |
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q |
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1 Rp 1 e |
W |
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Incident Optical Power (Watts) |
Po |
h |
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Fraction Transmitted into Detector
P |
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W |
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iph q |
o |
1 Rp |
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1 e |
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RPo |
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h |
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Incident Photon Flux |
Fraction absorbed in |
(#/sec) |
detection region |
Чувствительность фотодиода
R he M
Выходной ток на 1Вт световой мощности (типичная величина 0.5 A/Вт)
Спектральные характеристики
Absorption coefficient vs. Wavelength |
Photodiode Responsivity vs. Wavelength |
for several materials |
for various materials |
(Bowers 1987) |
(Albrecht et al 1986) |