Ch7Sec1 - i A W P(7.1 Joseph C Palais 7.1 7 2 Spectral...

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THE FIBER FORUM Fiber Optic Communications JOSEPH C. PALAIS PRESENTED BY
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Joseph C. Palais 7.1 2 Chapter 7 Light Detectors
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Joseph C. Palais 7.1 3 Section 7.1 Photodetection Mechanisms Detectors convert light signals into electrical signals. Internal Photoelectric Effect Generation of mobile charge carriers in semiconductors by absorption of photons.
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Joseph C. Palais 7.1 4 Section 7.1 Photodetection Mechanisms Devices: pn photodiode PIN photodiode avalanche photodiode (APD)
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Joseph C. Palais 7.1 5 External Photoelectric Effect Generation of free electrons when photons strike the surface of a metal. Electrons are emitted from the surface. Devices: Vacuum Photodiode Photomultiplier tube LIGHT DETECTORS
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Joseph C. Palais 7.1 6 PHOTODETECTION MECHANISMS Important Detector Properties 1. Responsivity: Power Optical Input Current Output = ρ P i Optical Power Photodetector Electrical Current
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Unformatted text preview: / i A W P (7.1) Joseph C. Palais 7.1 7 2. Spectral Response: Range of optical wavelengths over which the detector is useful. It is often displayed as a curve of responsivity versus wavelength. An example appears on the next slide. PHOTODETECTION MECHANISMS Joseph C. Palais 7.1 8 PHOTODETECTION MECHANISMS 0.5 0.7 0.9 1.1 0.5 λ ( μ m) ( / ) A W ρ Silicon Photodiode Response Joseph C. Palais 7.1 9 3. Speed of Response: Range of modulation frequencies over which the detector is useful. As before, if t r is the rise time, the bandwidth is (approximately) r dB t f 35 . 3 =-(7.2) P i 10% 90% t r PHOTODETECTION MECHANISMS Input Output Joseph C. Palais 7.1 10 Other Important Properties: Size, temperature sensitivity, gain, lifetime, circuit complexity, and cost. PHOTODETECTION MECHANISMS...
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