Frequency characteristics of an avalanche photodiode in super-high-speed optical demodulation with electronic mixing

Abstract

An analysis is presented for super-high-speed optical demodulation by an avalanche photodiode (APD) with electronic mixing. A normalized gain is defined to evaluate the performance of the demodulation. Unlike previous work, we include the effect of the non-linear variation of the APD capacitance with bias voltage as well as the effect of parasitic and amplifer input capacitance. As a result, the normalzed gain is dependent on the signal frequency and the frequency difference between the signal frequency and the local oscillator frequency. However, the current through the equivalent resistance of the APD is almost independent of signal frequency. The mixing output is mainly attributed to the nonlineanty of the multiplication factor. We show also that there is an optimal local oscillator voltage at which the normalized gain is maximized for a given avalanche photodiode.