Subcarrier modulated optical transceiver

Abstract

A coherent optical modulated sensor for use with missiles and the like wherein a series of pulses of optical energy which are intensity modulated by a radio frequency sub-carrier are transmitted to a preselected target having relative motion thereto and wherein returned pulses from the target are received. Phase coherence is effectively maintained by utilizing a single continuously operating local oscillator for down-converting the received detected pulses to a Doppler frequency signal. Target velocity information may be extracted from the Doppler frequency shift induced on the coherent radio frequency sub-carrier of the return pulses. A first channel, or radio frequency sub-carrier channel is provided for receiving the Doppler signal and generating a threshold signal in response to the magnitude of the Doppler signal being equal to or greater than a predetermined magnitude. A second channel (baseband) detects the average direct current power of the received pulse. The average direct current power is compared to the threshold signal for providing a firing control signal when the magnitude of the threshold signal is greater than the magnitude of the detected average current power. The coherent optical modulated sensor may thus be used for detecting preselected targets while discriminating against pulse returns from aerosols.