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We propose and demonstrate a novel scheme to reduce the recovery time of optical nonlinearity in a semiconductor laser optical amplifier driven under a loss condition for the signal light pulse. Additional light, which is set at a transparency wavelength in the active layer, promotes stimulated recombination of excess carriers induced by the absorption of the signal light. This scheme excludes any additional carrier transport mechanism and nonradiative recombination and hence generation of heat. The principle of operation is experimentally verified by measuring time-domain transmission variance using a pump–probe method. A drastic reduction of the excess-carrier lifetime to less than 70 ps was confirmed.

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GaSb and GaSbxAs1-x single crystal thin films were successfully grown by molecular beam epitaxy. Undoped GaSb showed p-type conduction, and Te was found to be effective as a donor impurity for the MBE-grown GaSb. An in-depth profile of the electrical property of these films revealed that many defects are contained in the epitaxial layer near the interface between the grown layer and the substrate. GaSbxAs1-x films with entire composition were prepared, and the energy gap measured by photoabsorption shows a downward bowing as a function of the composition.

In this study, we investigated quantum dot intermixing (QDI) for InAs/InGaAlAs highly stacked QDs on an InP(311)B substrate with low-temperature annealing at 650 °C in order to realize integrated photonic devices with QDs and passive waveguides. In particular, we adopted the method of introducing point defects by ICP-RIE to realize a blue shift of the PL peak wavelength by about 150 nm. Moreover, we successfully fabricated double micro-ring resonators by QDI. The output power contrasts of the devices were found to be 9.0 and 8.6 dB for TE and TM modes, respectively.

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