Abstract: A laser amplifier operable such that at the commencement of each output pulse the carrier level has recovered from depletion by the previous pulse. Under these conditions output power commensurate with a much higher carrier density than is usually available is possible. The mode of operation is especially useful as a way of providing high power pulses, for example for use in optical time domain reflectometry. Using a travelling wave amplifier in conjunction with return to zero format data pulses is also disclosed.

Abstract: An optical amplifier having a saturable absorption region is operated below the lasing threshold for the device. Non-linear effects and bistability are observable at temperatures above room temperature. A selected input wavelength .lambda..sub.i within the gain spectrum of the device is amplified and an output at the same wavelength .lambda..sub.i is produced. This is in contrast to the normal operation at threshold, where there is a wavelength shift to the lasing wavelength and, depending on the laser used for the naturable absorption device, the output may be multimode for a monomode input. Best gain is achieved by tuning the input wavelength to a peak of a Fabry-Perot mode in the gain spectrum for the amplifier.The amplifier may be used as wavelength controlled optical switch, when operated bistably, or as a regenerative amplifier when operated in the non-linear region without hysteresis effects.

Abstract: A semiconductor travelling wave optical amplifier in presented in a new configuration. An amplifier chip (20) has the rear facet (23) provided with a reflective coating. Optical signals are input and amplified signals are output via optical fibers (21, 35, 30) and directional coupler (24). A single fiber-to-amplifier alignment is required between fibre tail (25) and the front facet (22) is provided with a very low reflectivity coating. In this configuration the amplification is increased in comparison with the conventional in-line amplifier configuration.