HETERODYNE RECEIVER HAVING LOW INTERMEDIATE FREQUENCY

摘要

In an optical transmission system comprising a transmitter (2), an electro-optical converter (4) modulates a transmit signal on an optical carrier. This modulated signal is transferred to a receiver (8) of the heterodyne type through a glass fibre (6). In this receiver (8) the modulated signal is converted into an intermediate frequency signal by a local laser (16), a coupling element (14) and an opto-electrical converter (11). This intermediate frequency signal is converted into a demodulated signal by a demodulator having a quadratic transfer. For selecting a low value intermediate frequency, the received signal is converted into two quadrature signals and two sub-demodulators (22, 24) are used whose output signals are combined.