A micromachined 2 × 2 optical switch aligned with bevel-ended fibers for low return loss

This paper presents the design and optical performance characteristics of a micromachined 2 × 2 optical switch with low return loss for an optical add-drop application. The switch is equipped with four optical fibers beveled at 8°. An intentional lateral offset was introduced to align the refracted light at the input fiber-air interface with output fibers. A micromirror was actuated into the optical path by an electrostatic comb actuator to change the direction of the input optical signal. The optical switch was fabricated using silicon deep reactive ion etching (DRIE) of silicon-on-insulator (SOI) wafers. Optical performance measurements of the fabricated optical switch revealed that the time dependent loss (TDL), polarization dependent loss (PDL), and wavelength dependent loss (WDL) were -0.04 dB, -0.05 dB and -0.71 dB, respectively. The switching time was within 5 ms for a 24-V electrical step signal. Because the beveled ends of the optical fibers kept the propagated light from reflecting backward into the input fiber, the return losses were just -43 dB. This return loss was used to theoretically analyze a model of the beveled end by considering backscattering due to the surface roughness, which thereby was determined to be about 41 nm.