AN OPTICAL DETECTOR

摘要

An optical detector for use in detecting digital optical signals has an optical fibre coupler (2) which splits a received optical signal into two signal portions. The coupler (2) has unequal length output fibres (8, 10) so that one signal portion impinges an associated photodetector (12, 14) delayed relative to the other. The photodetectors (12, 14) are connected in series non-opposed. When the delay is equal to the bit period of the optical signal the output of the detector is the differential code (dicode) of the received signal which can be recovered by a high input impedance, i.e. integrating, amplifier. By forming the dicode in the optical domain in this manner large DC and AC dynamic ranges are obtained without linearity constraints on the optical transmission source that apply when the optical signal is transmitted as a dicode.