Tunable optical microresonators using micro-electro-mechanical-system (MEMS) technology

Two monolithically integrated MEMS-actuated optical microresonators were fabricated and experimentally demonstrated for the first time. One is the photonic crystal (PC) switch and the other is the tunable microdisk resonator. They show the potential to be building blocks for a variety of wavelength-division-multiplexed (WDM) photonic integrated circuits (PICs). The photonic crystal switch is composed of a combdrive microactuator, input and output waveguides, and a slider with two PC states: (1) a reflection state realized by 1-D photonic crystals and (2) a transmission state corresponding to a defect in the PCs. The two PC states are switched by physically moving slider between the input and an output waveguides using a combdrive actuator. ON-OFF is achieved. The device is fabricated on a silicon-on-insulator substrate. The experimental results show an 11-dB extinction ratio and a 0.5-ms time constant. The transmission window extends from 1530 nm to 1600 nm, which covers the C-band of the wavelength-division-multiplexed (WDM) networks. If the device is connected with a circulator in the input end, a 1x2 optical switch is achieved.; The tunable microdisk resonator is based on a gap-controlled mechanism, which varies the gap spacing between a microdisk and a waveguide by MEMS actuators. It can be realized by deforming the waveguides which are suspended around the microdisk edges. Two types of realization are demonstrated. One is lateral coupling, in which the waveguides and the microdisk are on the same plane. The other is vertical coupling, in which the waveguides are vertically coupled to the microdisk. The former can be fabricated with a single mask. However, for thin waveguides and microdisks as in the case of high index-contrast material systems, vertical coupling is favorable to overcome mechanical instability resulting from waveguide buckling in vertical direction. The measured data show the microdisk resonator can operate in under-coupling, critical coupling and over-coupling regimes, controlled by MEMS actuators. A dynamic dispersion compensator with a tunable range from 185 to 1200 ps/nm was successfully demonstrated. In addition, a reconfigurable add-drop filter based on this device was achieved with an extinction ratio of 20 dB.; To make a low-loss optical microresonator in silicon, reducing surface roughness is essential. A surface roughness of less than 1 nm is necessary to achieve a good optical performance. However, it is challenging to achieve that using conventional dry etch process. In this work, a fast, effective process using hydrogen annealing is developed to reduce sidewall roughness on silicon surfaces. Utilizing this technique, we observed the root-mean-square (rms) sidewall roughness dramatically reduced from 20 nm to 0.26 nm. This process can potentially improve the performance of several devices, including low-loss optical waveguides, vertical micromirrors and smooth microfluidic channels.