| Research Abstract |
SUMMARY OF RESEARCH RESULTS
1.Development of short wavelength (0.8mum)completely-polarization-independent optical modulator
We made an InGaAs pseudo substraste with larger lattice constant than GaAs on a GaAs substrate by sandwiching GaAs/InGaAs strained super lattice buffer layr between them. On its top, we grew GaAs tensilestained quantum wells with mess-dependent width successfully. The wafer was made into optical intensity modulators and their optical modulation properties were characterized. Consequently, we have achieved complete polarization-independent optical modulation with extinction ratio larger than 10 dB over the wavelength range of 28 nm around 0.8mum band.
2.Epitaxial growth technique toward long wavelength (1.55mum) completely-polarization-independent optical modulator
We studied molecular beam epitaxy of lnGaAs/lnAlAs strained quantum wells on lnP substrates, aiming at completely-polarization-independent optical modulators based on the same principle as above in 1.55mum o
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ptical communication wavelength band. By optimizing growth temperature and by carefully selecting indium source materials and InP substrates, epitaxial growth of strained quantum wells with excellent quality was made possible. Next, we grew double heterostructure, made it into ridge waveguide configuration, and measured its propagation Ioss by using the Fabry-Perot interference.
3.Surface vertical optical switches with low insertion loss
We reduced remaining insertion loss at ON atate in surface-vertical optical bistable devices, namely, SEEDs, by utillzing effective blue shift of band edges in coupled quantum well structures. we also showed, We also showed, experimentally and theoretically, that not only the remaining loss but also the contrast between ON and OFF atate could be improved throved through the use of asymmetric triple coupled quantum wells. On the other hand, utilization of large absorption change in low electric field region was made possible by a special symetric coupled quantum wells. We fabricated transmission-type symmetric SEEDs by making use of a modified potential asymmetric coupled quantum wells and accomplished optical bistable operation in them.
4.Traveling wave quantum well high speed optical modulator
We fabricated a GaAs directional coupler optical modulator with coplanar traveling-wave electrodes, and characterterized its optical modulation performance using the swept-frequency method. Bandwidth of 22 GHz was achieved.
5.Modified-potential five-step asymmetric coupled quantum wells
We found a special quantum well structure where a large index change is obtainable at low electric field without exciting red-shift of absorption edges. Less
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