Abstract: An optical fibre communications system includes an exchange (E) and a plurality of subscriber lines (1). The exchange (E) provides a plurality of services in different subcarrier frequencies (6,8,9,10). Each subscriber line (1) is provided with terminal apparatus (5) operable at different subscriber frequencies, and a control (11) at the exchange (E) tunes the terminal apparatus to transmit and/or receive on a particular frequency in response to a request. The request may be a signal from the terminal apparatus (5), or an incoming service request addressed to the particular terminal apparatus.

Abstract: An optical communications system comprises a transceiver arranged to provide two-way communication over an optical communications channel (3). The transceiver comprises a semiconductor light source (4) and a detector (5). The semiconductor light source (4) provides optical signals for transmission via the optical communications channel (3), and the detector (5) detects optical signals received via the optical communications channel and converts said optical signals into electrical signals. Means (2)a, (2)b) are provided for modulating the output of the semiconductor light source (4) with an RF carrier having a first frequency. Said electrical signals are passed through filter (8) adapted to filter out signals at said first frequency.

Abstract: A regenerator 10 is provided with a tuning recovery facility 15 which has a multiple passband capability. The regenerator can operate with several line bit rates each corresponding to one of the passbands.