Full-duplex optical transmission using self-heterodyne lasertransceivers

The use of semiconductor diode lasers simultaneously as heterodyne receivers and lightwave transmitters in a full-duplex single optical fiber transmission system is reported. A transmission distance of 16 km, limited by Rayleigh backscattering, is obtained at a bit rate of 40 Mb/s for this simple system, which requires no optical couplers or photodiodes. The proposed operation is analogous to that of the so-called autodyne radio receiver in which the local oscillator circuit also performs the heterodyne mixing. The optical counterpart is called a self-heterodyne mixer and offers the same frequency selectivity and tunability as a conventional heterodyne detector but with reduced receiver complexity. In the self-heterodyne receiver, an optical signal to be detected is introduced directly into the lasing cavity by coupling the signal into the laser through an uncoated cleaved end facet. Changes in the optical cavity field, which result from interference between the lasing mode and the injected signal, modulate the rate of stimulated carrier recombination and thus produce a change in the injection current. This alternating current component is detected and amplified in the laser active region bias