The present disclosure provides a semiconductor optical signal amplifier for amplifying a light having an energy smaller than a band gap energy. The semiconductor optical signal amplifier includes: a first end surface; a second end surface, arranged apart from the first end surface; a first semiconductor region and a second semiconductor region, arranged between the first end surface and the second end surface; an active layer, arranged between the first end surface and the second end surface, and sandwiched between the first semiconductor region and the second semiconductor region, made of an indirect transition type semiconductor that amplifies a signal intensity of an input light by stimulated emission; a first electrode, connected to the first semiconductor region; and a second electrode, connected to the second semiconductor region and detecting a change in a carrier density in the active layer by a potential difference from the first electrode.

Devices, methods and techniques related to the use of a photoconductive semiconductor switch (PCSS) to drive a high-power laser diode for a wide range of pulse widths are disclosed. In one example aspect, a circuit for driving one or more laser diodes includes an input port configured to be coupled to a voltage input, one or more inductors that are configured to be in series with the one or more laser diodes, a photoconductive switch coupled with the one or more inductors, and an output port configured to be coupled to the one or more laser diodes.