Optimal design of an optical receiver using avalanche photodiode as both photodetector and electronic mixer

Abstract

The design principle of an optical receiver for super-high-speed signal demodulation using an avalanche photodiode (APD) as both the photodetector and the electronic mixer (mixing detection) is presented. A simple theory is provided to evaluate the signal and noise properties with frequency-down conversion. Expressions for the signal to noise ratio (SNR) and the receiver sensitivity are given. The SNR and the receiver sensitivity for mixing detection are dependent on both the local oscillator voltage and DC bias voltate of the photodiode. There is an optimal condition (an optimal local oscillator voltage and an optimal DC bias voltage) to maximize the SNR or to minimize the receiver sensitivity for a given APD. A comparison between mixing detection and direct detection is presented and the results show that the optimal bias voltage of the APD for best SNR and receiver sensitivity for mixing detection is ess than that for direct detection, making for more stable operation. The optimal design of a receiver for direct detection is only related to the APD multiplication factor, whereas for mixing detection it is related to this factor and its derivatives.