A germanium photodiode incorporated into an optical fiber receiver working at a wavelength of 1.55 m has

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Question:

A germanium photodiode incorporated into an optical fiber receiver working at a wavelength of 1.55 m has a dark current of 500 nA at the operating temperature. When the incident optical power at this wavelength is 10-6 W and the responsitivity of the device is 0.6 A/W, shot noise dominates in the receiver. Determine the SNR (in dB) at the receiver when the post-detection bandwidth is 100 MHz.

2.2 An optical receiver incorporates a high impedance integrating front-end amplifier in parallel with a detector bias resistor of 15 Mohm. The effective input resistance of the amplifier is 9 Mohm and the total capacitance of the detector and amplifier is 8 pF (Assume T = 300 K).

2.2.1 Calculate the bandwidth and RMS thermal noise current for the high-impedance front-end amplifier.

2.2.2 If the high-impedance front-end amplifier is replaced with a trans-impedance front-end amplifier, determine the corresponding bandwidth and RMS thermal noise current. The trans-impedance amplifier incorporates a 250 kohm feedback resistor, has an open loop gain of 100, and a capacitance of 8 pF (the detector bias resistor may be omitted).

2.3 The signal-to-noise ratio of an optical communication system is 45 dB. A pin photodiode receiver with a quantum efficiency of 60% and an operating wavelength of 900 nm is used. The operating bandwidth is 20 MHz, the device dark current is 20 nA, the load resistance is 86 ohm, the amplifier noise figure, Fn = 1 and the operating temperature is 300 K.

2.3.1 Determine the photocurrent, Ip to maintain a SNR of 45 dB. (8) 2.3.2 Calculate the corresponding incident optical power.

2.3.3 Calculate the rms shot noise current.

2.3.4 Calculate the rms thermal noise current.