Wide-range linear attenuation via elliptical mirror for variable attenuator application

This paper proposes an improved design of variable optical attenuator (VOA) using a micromachined elliptical mirror as the movable reflector. We compared the attenuation performances of the three different types of VOAs, which were fabricated by the same deep reactive ion etching process. It is noticed that the proposed VOA (EVOA) has superior performance than the common shutter-type VOA (SVOA) and the flat-mirror reflection-type VOA (FVOA). Based on the focus property of the ellipse, this reflection-type EVOA enjoys low insertion loss while using the normally-cleaved single mode fibers. It achieves a large attenuation of 44 dB at 10.7 V driving voltage. The PDL is 0.8 dB at the 40 dB attenuation level and the WDL is 1.2 dB at the 20 dB level for 100 nm wavelength change. More importantly, the attenuation increases nearly linearly with the mirror displacement. The EVOA also has low polarization dependence loss (PDL), low wavelength dependence loss (WDL) and low back reflection.