RF frequency down-conversion with quadratic electro-optic effect

The frequency down-converter is an essential element of a photonic radar frontend. In this paper we describe a new photonic frequency down-conversion approach employing a quadratic optical phase modulator. When paired with an OPLL linear phase demodulator, this approach can potentially achieve a large dynamic range and a low conversion loss. A preliminary experiment has been performed to verify frequency down-conversion with an InP MQW optical phase modulator. It has been found that the unwanted 4^th order electro-optic effect that exists in phase modulator results in spurious distortion for the down-converted RF signal. The techniques for mitigation are discussed.