Ch7Sec4 - THE FIBER FORUM Fiber Optic Communications...

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THE FIBER FORUM Fiber Optic Communications JOSEPH C. PALAIS PRESENTED BY
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Joseph C. Palais 7.4 2 Section 7.4 PIN Photodiode hf p n + - E i Intrinsic Layer PIN Photodiode Thin Layer V + - R L v
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Joseph C. Palais 7.4 3 PIN PHOTODIODE The intrinsic layer is on an insulator. Most of the photons are absorbed in that layer because it is long. Most of the voltage drop is across the intrinsic layer. This creates a high electric field in the intrinsic layer. Now there is no delay caused by diffusion and the response time is much faster that that of a pn photodiode.
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Joseph C. Palais 7.4 4 7.4.1 Cutoff Wavelength A condition for detection is that the photon energy be greater than the bandgap energy: g W hf h W f g
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Joseph C. Palais 7.4 5 Cutoff Wavelength At cutoff, then g c W 24 . 1 = λ (7.11) h W c g c = g c W hc = or
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Joseph C. Palais 7.4 6 Cutoff Wavelength Example: Compute the cutoff wavelength for Silicon. The bandgap energy for silicon is W g = 1.1 eV m c μ λ 1 . 1 1 . 1 24 . 1 = =
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Joseph C. Palais 7.4 7 7.4.2 Materials Material Wavelength Range ( μ m) Peak Response λ ( μ m) Silicon 0.3 – 1.1 0.8 0.5 Germanium 0.5 – 1.8 1.55 0.7 InGaAs 1.0 – 1.7 1.7 1.1 Peak Responsivity ρ (A/W) PIN PHOTODIODE
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Joseph C. Palais 7.4 8 v d + - i d PIN PHOTODIODE Photodetector Circuit n V + - R L v p
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Joseph C. Palais 7.4 9 Silicon Photodiode P = 10 μ W 20 30 40 -5 -10 -15 -20 -20 -10 0 0.5 Diode Voltage v d (volts) Diode Current i d ( μ A) I D Photoconductive Region Photovoltaic Region 7.4.3 Current-Voltage Characteristic
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Joseph C. Palais
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This note was uploaded on 05/11/2010 for the course EEE EEE-448 taught by Professor Palais during the Fall '09 term at ASU.

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Ch7Sec4 - THE FIBER FORUM Fiber Optic Communications...

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