Graphene-assisted all-optical tunable Mach-Zehnder interferometer based on microfiber

We experimentally demonstrate a compact all-optical tunable Mach-Zehnder interferometer (MZI) based on microfiber. The graphene-assisted sandwich structure (GASS) integrated on the microfiber is adopted to form the all-optical tunable structure. The effective footprint of the fabricated device is about 7.31×8.66 mm2 which is much more compact than other reported all-optical tunable MZIs based on fiber system. An out-fiber 1535 nm continuous-wave pump light is employed to irradiate the GASS vertically, which can produce the strong interaction of light-graphene. As a result, the device's response spectrum occurs red-shift due to the graphene's photothermal effect. Compared with the microfiber MZI with only the bottom graphene film, the tuning efficiency of the microfiber MZI with GASS is improved by 6 times, which is about 0.856 pm/mW. Meanwhile, the red-shift range can exceed one free spectral range (FSR) that means the resonant wavelength can be tuned to arbitrary wavelength in the range of the transparent window. This microfiber MZI with GASS featured with wavelength tunability, all-in-fiber, compact size, easy fabrication, and simple packaging is expected for the fabricated device to be used as all-optical modulator, tunable optical filter and optical switch, etc.