Theoretical Design of Mid-Infrared Graphene Optical Gas Sensor Based on Slot Si Core Fiber

Silicon core optical fibers are promising for realizing all-in-fiber optical processing and sensing applications in the mid-infrared spectral region. However, this approach requires integration with other optoelectronic materials to realize various functions. Here, we theoretically designed a graphene optical gas sensor based on silicon fibers at 8-μm wavelengths. Gas molecules adsorbed on graphene serving as the charge-carrier donors or acceptors change graphene's optical conductivity, which leads to the change in the optoelectronic properties of graphene-integrated devices. We first optimized the Fermi level of graphene and the operating wavelength so that the gas molecules can effectively change graphene's optical conductivity. Then, we proposed a silicon slot fiber structure to enhance the optical interaction in graphene-on-silicon fiber devices. Based on the optimized silicon slot fiber structure, we designed a fiber-integrated graphene Bragg grating structure, in which the 3-dB bandwidth of the central reflection band increases linearly with the gas concentration. Our proposed device has a detection limit below one part per million and 90-fold improvement of sensitivity compared with the designed graphene-on-silica microfiber gas sensors for gaseous nitrogen dioxide detection. This letter paves the way for the mid-infrared silicon optical fiber sensors.