HETERODYNE RECEIVER HAVING LOW INTERMEDIATE FREQUENCY

摘要

An optical heterodyne receiver converts a received modulated optical signal into an electrical IF signal by an IF converter which includes a local laser, a coupling element and an opto-electrical converter. The IF signal is converted into a demodulated signal by a demodulator having a quadratic transfer characteristic. To permit a relatively low intermediate frequency, the IF converter converts the received signal into two quadrature IF signals and in the demodulator two sub-demodulators recover therefrom two demodulated signals which are then combined. This eliminates unwanted quadratic components in the combined signal.