Due to the narrow frequency response range of traditional optical microphones based on diaphragm or cantilever beam, and the different frequency ranges of sound waves detected in different environments and requirements, a wideband optical microphone based on a dual diaphragm structure has been designed. This optical microphone is composed of single-mode fiber, metamaterial membrane, and waveguide membrane. Theoretical analysis is conducted on the influence of the structural parameters of two membranes on the performance of the sensor. COMSOL Multiphysics is used for simulation, and the prepared optical microphone is tested. The simulation results show that the designed optical microphone has a flat frequency response within the frequency range of 1~100 kHz, with a resonant frequency of 170 kHz.