| 研究実績の概要 |
In order to solve the problems of low coupling efficiency with fiber and poor mechanical stability, a new type free-standing waveguide with subwavelength grating cladding has been proposed and demonstrated. By using SOI as test substrate, these waveguides, together with fiber-to-waveguide grating couplers and microdisk resonators have been fabricated. Coupling efficiency of over 10% was achieved, which is 4 times higher than last year’s results and enables us easily to perform the further spectrum measurement.
Due to change of institute, fabrication process of Ge-based devices and MIR transmission measurement system were re-established. Reactive-ion etching of Ge has been optimized that vertical and smooth sidewalls could be obtained. The design for SOI waveguide devices can be readily applied to Ge-on-Si. For measurement, an MIR differential-frequency generation laser with ~3.3 μm wavelength was used as light source, whose wavelength could be tuned over a range >10 nm, and thus more suitable for spectrum measurement.
The sensitivity of CH4 gas detection by using microdisk resonators has been analyzed. The effective absorption path length (Leff) could be significantly enhanced when microdisk was operating near critical coupling. The maximum Leff is also found to be increased as the intrinsic Q-factor of microdisk increases. For a feasible Q-factor of 1000, Leff of longer than 1 meter can be readily achieved in a microdisk with radius of 100 μm. These results indicate that the proposed platform is very promising for high sensitivity on-chip gas detection.
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