Variable optical attenuator based on a reflective Mach–Zehnder interferometer

A low power-consuming variable optical attenuator (VOA) on silicon is demonstrated by using a reflective Mach–Zehnder interferometer (MZI), which consists of broadband highly-efficient Bragg-grating reflectors at the ends of the MZI arms. The present reflective-MZI VOA enables an ultra-high extinction ratio intrinsically even when the 2×2 3 dB coupler is not balanced perfectly, which make it very robust to realize a VOA array. The power consumption is reduced by half in comparison with the regular MZI-type VOA. For the fabricated reflective MZI-type VOA with 125 μm-long heaters, the power consumption is only about 10.8 mW for a high attenuation of 35.5 dB.