Development of Photonic Crystals for Radiation-Field Control

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1. We have successfully fabricated three-types of two-dimensional (2D) photonic-crystal slabs or quasi-three dimensional ones from Al_xGa_<1-x> As by using the state-of-art semiconductor micro-machining technique. Then, we have charified optical responses of those samples, such as the transmittance spectrum and reflectance at specific wavelengths observed using a femtosecond light pulse. Thus, we have characterized, from the vewpoint of controlling the radiation field and light propagation, those samples with the help of the corresponding photonic band-structure calculated.(1) Optical-waveguide slab perforated periodically down to midway the lower cladding-layer ; it is clarifed that although no guided modes exist, the samples with an air-filling factor smaller than 0.3 and the number of air-hole's row smaller than 10 should work for the above purpose.(2) Air-bridge slab without any cladding-layer ; it is found that the guided modes exist, where the transmittance is almost 100%, and that this type of sample is superior.(3) Slab with the lower cladding-layer oxidized for reducing the refractive index ; this type of sample is also found to be good, since the guided modes exist in a limited energy region.2. We have experimentally demonstrated a few novel aspects of interaction between matter and light in a photonic crystal, by utilizing either a slab sample described above or a 2D capillary-type of air-rod crystal made of PbO fibers.(1) We have developed a 2D photonio-crystal laser, which is based on a small group-velocity(2) We have shown in the second-harmonic generation phenomenon that a phase-matching condition is easily fulfilled with use of a unique photonic band-structure, and that the signal is enhanced due to a small group-velocity.(3) By observing propagation time of a femtosecond light pulse through a photonic crystal, we have for the first time clarified that the group-velocity becomes smaller by almost two orders of magnitude than that in vacuum.