Investigation on the polarization-dependent spectral characteristics of acousto-optic tunable filter for polarization multiplexed mid-infrared spectral imaging

The traditional Mid-wavelength IR(MWIR) acousto-optic enable filter (AOTF)-based spectral imaging systems mostly use a single polarization state detection mode, which leads to a system flux loss of more than 50% during spectral detection. However, one of the challenges in designing a polarization-multiplexed MWIR AOTF-based spectral imaging system is that the traditional AOTF devices are designed for a single polarization state detection mode, and their cutting parameters are designed to meet the parallel tangent principle of a single polarization state, resulting in a large difference in the spectral response of diffracted o light and e light. To reduce the spectral response difference between the diffracted o light and e light in the AOTF device, an optimization model for the AOTF cutting parameters based on the non-parallel tangent principle was developed. Specifically, the difference between the central driving frequencies of the two diffracted beams under the phase matching condition for monochromatic light incident on the AOTF was set as the objective function. Polarization-insensitive AOTF cutting parameters were calculated and the dependence of the central wavelength on the incident angle for the AOTF device was analyzed. The simulation results show that the cutting parameters of non-polarization-dependent AOTF devices areas follows: the ultrasonic cut angle is 8.5°, the incident chamfer angle is 18.55°, the wavelength difference between the two diffracted light matching centers in the 3.7um∼4.8um spectrum is 0.67nm and the spectral drift range of diffraction o light is 54.6nm and the spectral drift range of diffractive e light is 43.1nm in the field of view of ±2°. In addition, we also research the method of adjusting the incident polar angle of the light by rotating the AOTF device with arbitrary cut parameters to optimize the spectral response of two diffracted beams, and the analysis results show that when the incident angle of light entering the AOTF is varied, the absolute value of the difference between the central driving frequencies corresponding to the diffracted o light and e light exhibits a pattern of initially decreasing and then increasing. Simulation results show that when the AOTF driving frequency is set to 9.92 Hz, the peak wavelength difference between the two diffracted conical beams remains within 5 nm, and the difference in spectral FWHM is less than 50 nm. Finally, the effectiveness of the optimization method based on the rotation of AOTF device is verified by experiments.