B.S.T.J. Briefs: Optically Powered Speech Communication Over a Fiber Lightguide

The photovoltaic conversion of optical power transmitted over a fiber lightguide can supply electrical power to low-drain semiconductor devices in remote locations. Acoustic powers comparable to those of using a fiber-coupled GaAlAs photovoltaic detector 2 to excite an electroacoustic tone generator. It was conjectured 1 that the electrical power for other telephone functions--transmit/receive, dialing, and hook-status recognition--could also be optically supplied, but the signaling techniques appropriate to a dielectric fiber were left unspecified. This note describes the implementation of two-way speech communication between an electrically powered local station and an optically powered station located at the remote end of a 1.1-km-long, single-strand, optical fiber. The remote-station sound alerter has also been operated over this link. II. SPEECH SIGNALING METHOD conventional telephone ringers have been produced' in t h i s w a y by The method used for two-way optically powered speech signaling is illustrated in Figs. 1 and 2. Figure 1 depicts schematically the electronics in an optically powered remote station and the optics in an electrically powered local station. Speech-modulated optical power was launched into the local station end of the fiber from a GaAs injection laser emitting at w a v e l e n g t h T h e remote station contained a fiber-coupled GaAlAs double heterostructure transceiver,'1 denoted PV/LED in Fig. 1, which functioned as a photovoltaic detector when 1735