Half-Duplex Fiber-Optic Data Transmission With A Semiconductor Junction Transceiver

Much of the data transfer in computer and process control systems takes place by half duplex data transmission. Conventional approaches to implementation of half duplex fiber optic links use a separate fiber for each transmission direction or a single fiber for both directions and a Y branch. If an LED is used as a semiconductor junction transceiver (SJT) for both emission and detection of optical signals, half duplex data transmission links can be implemented with a single fiber and a single optoelectronic device at each end of the fiber. Investigation of the suitability of reverse biased LED's for use as detectors shows that responsivities higher than 1/5 that of a PIN diode can be achieved. Although the reverse biased capacitance of the LED is larger than the PIN diode, rise times as short as 3 nanoseconds have been measured for LED's used in the detector mode. Comparison of Burrus, edge emitting and large area surface emitting diodes shows that the Burrus and large area surface emitting diodes offer the best detector performance. Experimental results for a half duplex transceiver using an SJT will be presented.