We propose and analyze a new type of intersectional optical switch using positive refractive index variation in quantum well structure. The switch structure has a built-in refractive index difference in the waveguide, due to which the incident light is reflected to cross port at the OFF state. When the electric field applied to the electrode (ON state), the built-in refractive index difference vanishes by the positive refractive index variation in the quantum well, and the light transmits to straight port. Low insertion loss of lesser than 1 dB and high extinction ratio of more than 20 dB can be obtained at both cross and straight port.

The permissible optical input power of a semiconductor optical switch/modulator for maintaining high performances was derived by taking account of reduction of internal electric field due to absorption-induced photo-current. It was found that the extinction ratio degrades with the increase of absorbed optical power. The permissible optical input power, at which the extinction ratio decreases 3 dB, was found to be higher than 20 mW for reflection type optical switch/modulator.

We have successfully demonstrated a GaInAs/InP multiple quantum well (MQW)-based wavelength switch composed of the straight arrayed waveguide with linearly varying refractive index distribution by changing the refractive index using thermo-optic effect. Since optical path length differences between waveguides in the array were achieved through refractive index differences that were controlled by SiO2 mask design in selective metal-organic vapor phase epitaxy (MOVPE), wavelength demultiplexing, and the output port switching in each wavelength of light by the refractive index change in the array waveguides through the thermo-optic effect were achieved. We have obtained the wavelength switching and the change of transmission spectra in each output ports.

We have demonstrated switching characteristics in a wavelength switch based on multiple GaInAs/InP quantum wells. It consisted of straight arrayed waveguides with a linearly varying refractive index distribution. The refractive index can be changed via the thermo-optic (TO) effect. Using a Ti/Au thin-film heater to generate the TO effect, we realized four-port switching at four demultiplexed wavelengths. In addition, by changing the structure of the heater from rectangular to triangular, the power consumption for four-port switching was reduced by half.

Mass-transport and conventional buying techniques were combined to fabricate narrow active stripe lasers. Lowest threshold current of 9.6 mA was obtained under CW operation for the active layer width of 1µm in 1.5 µm wavelength region. The maximum light output power and differential quantum efficiency were 10.6 mW and 17 percent/facet, respectively. With this structure, complete single transverse mode operation was achieved both for Fabry-Perot (FP) type and bundle-integrated-guide distributed Bragg reflecter (BIB-DBR) type lasers.

An intersectional optical switch structure based on the field induced refractive index variation was fabricated by the use of LPE grown GaInAsP/InP MQW wafer. The first switching operation in a MQW intersectional switch structure was achieved. The field induced refractive index variation in quantum well was estimated to be around 0.45% at the applied field of 13 V/µm from the experimentally obtained switching ratio. Finally a small X-type modulator with low chirp, low power saturation is proposed which make use of the reflection phenomenon caused by field induced rafractive index variation instead of absorption phenomenon as in conventional absorption type modulators.

A GaInAs/InP multiple quantum well (MQW)-based wavelength demultiplexer composed of a waveguide array in which the refractive index varies across the array yielded successful results of wavelength demultiplexing and optical deflection. Since optical path length differences between waveguides in the array are achieved through refractive-index differences controlled by the SiO2 mask design in selective metal-organic vapor phase epitaxy (MOVPE), a straight waveguide grating can be formed with reduced optical propagation losses. A straight waveguide array device with a 1.4% refractive-index difference was fabricated. The fabrication of a preliminary wavelength demultiplexer was also achieved, for which a wavelength separation with an approximately 25 nm spacing and free spectral range (FSR) of approximately 100 nm were obtained. Moreover, an optical deflector was investigated and primitive deflection was achieved at 1460 and 1490 nm incident wavelengths.

Wavelength demultiplexed light switching is numerically calculated in the variable index arrayed waveguide. Wavelength demultiplexed light is switched in 4 output ports by changing the refractive index of variable index arrayed waveguide with 16 array waveguides. In the calculation, the phase differences in each arrayed waveguide, and the diffraction in the star coupler are considered. In 4 output ports switching, numerically calculated the refractive index changes of 16 array waveguides are numerically calculated to obtain the 24 switching pattern, and also calculated the crosstalk of each switching.