In this paper, we describe the design principles of serpentine springs with high reliability for the micro-electromechanical systems (MEMS) optical switches with large mirror mass. The most often seen failure mode of the MEMS optical switches under reliability tests is the breaking of these springs, which provide the restoring force for the MEMS actuators. The breaking points are usually at the turning corner of the serpentine springs when the MEMS optical switches are under a high G shock test or a vibration test. In order to overcome the difficulties, we redesigned the corner shapes of the springs with careful consideration. We will discuss the theoretical analysis and simulation modeling for the corner shapes of serpentine springs. MEMS optical switches with redesigned serpentine springs are fabricated and tested to prove the proposed design. The results show that the MEMS optical switches with new serpentine springs can pass rigorous reliability tests.
The design, fabrication and test results of an electromagnetic-actuated micromachined variable optical attenuator (VOA) are reported in this paper. Optical attenuation is achieved by moving a shutter into the light path between a pair of single mode fiber collimators. The shutter, consisting of a 500 µm × 1200 µm vertical micromirror, is monolithically integrated with an actuation flap. The micromirror was made by tetra-methyl ammonium hydroxide (TMAH) anisotropic wet etching with a sharp edge and a smooth reflecting surface. By arranging fiber collimators in different configurations, the reported VOA can be used as either normally-on or normally-off modes due to its relatively large shutter surface. The insertion loss of the VOA is 0.2 dB and 0.4 dB for normally-on and normally-off modes, respectively. Both optical and mechanical simulation models of the device were discussed, and the theoretical calculations based on these models offered an efficient way to predict the performance of the shutter-type VOA. The controllable attenuation range is approximately 40 dB with a driving voltage less than 0.5 V, and the driving power is less than 2 mW. A response time of 5 ms is achieved by applying proper driving waveform.
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