Fabrication of One-Dimensional Photonic Crystal with Large Dispersion in SiO₂ Glass Substrate Using Deep Dry Etching Technique

Binary gratings with high first-order transmission diffraction efficiency were covered with a thin SiO₂ film without the filling in the grooves by plasma enhanced chemical vapor deposition. The diffraction efficiencies of about 90% were attained for transverse-electric (TE) and transverse-magnetic (TM) polarized lights at a wavelength of 1.55 µm when the period and depth were 1.5 and 2.8 µm, respectively. The grating was used for the integrated spectrographic chip. A four-channel demultiplexer with 20-nm spacing was fabricated on a silica substrate of 5.1 x 9.2 mm², in which a buried grating, a pair of parabolic mirrors and channel waveguides were integrated. It was confirmed by the numerical calculation that the angular dispersion of the grating was increased drastically if the input and output surfaces were tilted against its grating vector, which should be effective to minimize the device size.