An α-cyanostilbene crystal showing optical nonlinearity was examined to be compared with a non-optically active crystal, with emphasis on the structural aspect. It was suggested that the introduction of bulky substituents such dimethylamino and methoxy groups into the cyanostyrene conjugation system was effective to get macroscopic optical nonlinearity, based on the chemical synthesis and structural analysis. It was also stressed that the quadrupole interaction in α-cyanostilbenes was one of the important factors responsible for a nonsymmetric molecular arrangement for the second order optical nonlinearity.

Self-oscillations of V-channeled substrate inner stripe (VSIS) lasers with index guiding and the influence of external feedback on low-frequency noise generation are presented. The self-oscillation is induced by means of shortening a cavity length of VSIS laser to 110 μm. VSIS lasers with self-oscillation have the fundamental linewidth of 0.56 Å below 3 mW and are not sensitive to both phase and amplitude of the externally reflected light. Signal to noise ratio of short-cavity VSIS laser at 1 MHz with a 10-KHz bandwidth was 97 dB at 0.05% optical feedback.

The interface disorder of quantum wells grown by molecular beam epitaxy at high substrate temperature is investigated by low-temperature photoluminescence. The excitonic emission from a single quantum well is a single sharp peak, and the well width precisely determined from the emission peak energy does not equal to integral multiples of one-monolayer width in almost all samples. These results indicate that the lateral size of growth islands with a one-monolayer height is much smaller than the exciton diameter and a one-monolayer interface acts as a layer with smaller AlAs mole fraction than the barrier layer.

A phased array with an integrated phase shifter which can convert a 180° phase mode into an in-phase mode was demonstrated. An Al2O3 facet coating with a different thickness on each array element was performed. It should act as the phase shifter. A stable single-lobed far-field pattern was obtained from the array with the phase shifter.

High-purity Al0.3Ga0.7As is grown by molecular beam epitaxy at a high substrate temperature using a superlattice buffer layer in order to trap residual impurities. The unintentionally doped layer is p type with p < 5×1014 cm−3. Photoluminescence spectra at 10 K showed the strong bound-exciton emission to be 3.8 meV wide and extremely weak emission due to residual C and Si. Photoluminescence spectra of successively grown single-quantum wells with different widths demonstrate that residual C and Si are mainly trapped at the interface of the first-grown well.