| Optical fiber links are rapidly replacing electrical cables in the communications industry. While their performance is decidedly superior to their electrical counterparts, full utilization of their potential for certain applications is hampered by the absence of a single optical device that can efficiently accept the signal from the fiber and launch it again if necessary.;This work presents a novel device that can efficiently perform complementary tasks of light emission and detection. While any commercial laser could be used to perform these two tasks, its efficiency in the detection mode is, at best, extremely poor. The special diode designed and fabricated in this work utilizes a lightly doped waveguide region adjacent within the active layer of the device. In other respects the structure resembles that of a standard double heterostructure diode, which yields efficient carrier and optical confinement to the junction region. In the forward biased mode, light generated in the active region is radiated into the passive waveguide. This reduces the photon flux incident on the end facets of the device. The chances of catastrophic failure are reduced and the lifetime and reliability of the device are increased. In the reverse biased mode, the waveguide increases detection area. The presence of a strong electric field in this region brings about enhanced interband absorption of incident radiation due to the Franz-Keldysh Effect, producing significant photocurrent. If reverse biased close to breakdown, avalanche multiplication provides gain to the photocurrent.;These devices have been fabricated by growing GaAs/AlGaAs heterostructures on GaAs substrates using liquid phase epitaxy. The waveguide should not significantly affect the performance of the device as a laser. Threshold current densities and external quantum efficiencies are expected to be comparable to commercially available double heterostructure laser diodes. When biased close to breakdown, high responsivity values were obtained even at low values of breakdown voltages and inefficient end-coupling of the source to the waveguide.;Further modifications to the design and the implementation of the device in systems are discussed, with a view to improving the performance of the device. These modifications will also simplify the use of the device in a number of half-duplex communication networks. |
