Electromechanical tuning of double-membrane Photonic Crystal Cavities
PL spectra and peak shift obtained by applying a gradually increasing voltage are shown in Fig. 1b. We report up to 7 nm mode shift when the applied bias reaches 8.6 V. By further increasing the voltage we observe the well-known pull-in phenomenon: the cantilever collapses on the substrate because electrostatic forces win over elastic forces. We attribute the need for high voltages to fabrication issues and imperfections such as the complete erosion of the p-doped InGaAsP layer in the photonic crystal region during the sacrificial layer etching. Further process optimization should result in PCCs with Q factors>10'000, electromechanically tunable over >30 nm.
Optomechanical wavelength and energy conversion in high- double-layer cavities of photonic crystal slabs.
We demonstrate that ultrasmall double-layer photonic-crystal-slab cavities exhibit a very high-Q value for a wide range of the layer spacing, which enables us to realize unique optomechanical coupling. By mechanically varying the separation, we can achieve extraordinarily large wavelength conversion. In addition, the light stored in the cavity can generate a large radiation force. We show that this system exhibits extremely high energy conversion efficiency between optical and mechanical energy, leading to a novel approach for the optomechanical control of light and matter.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.