The marine environment is complex and changeable. To meet the urgent needs of accurate detection and identification of oil spills, a visible/infrared dual-band common-aperture polarization imaging optical system based on a defocused plane polarization detector is designed. The optical system is evaluated by ZEMAX simulation software, and we carried out the polarization imaging oil species discrimination experiment based on the split focal plane polarization detector, which proved that for some oil species that cannot be distinguished by intensity information, the polarization information can be distinguished. It verifies the feasibility of polarization detection in the discrimination of marine oil spills, which is of great practical significance in the field of marine oil spill detection.

Superresolution (SR) imaging technology based on compression coding has always been considered as the key to break through the geometric resolution of the detector. In addition to factors such as the reconstruction algorithm and mounting platform vibrations, the impact of inherent errors in the optical system itself on the reconstruction results of SR imaging is also obvious. To address this issue, a study on the design of the SR optical system and the influence of optical alignment errors on SR imaging was conducted. The design of the SR optical system based on digital micro-mirror device (DMD) for long-wave infrared wavelength was completed, and an athermal analysis of the system was carried out. The design results showed that the SR optical system has good imaging quality in the operating temperature range. The imaging model of the DMD SR imaging optical system is established according to the designed SR optical system. We investigated the influence of various alignment errors, including decenter, tilt, lens interval error and defocus, on the imaging properties of the SR optical system. Various random combinations of alignment errors were introduced into the optical system, respectively, and the SR reconstructed image quality of the imaging system was analyzed using the inverse sensitivity method to obtain the tolerance limits when the system was assembled. Finally, the effectiveness of the method to obtain the alignment tolerance limit of the compression coding SR imaging optical system was verified through a desktop demonstration experiment.

At present, polarization imaging detection experiments of underwater objects mainly focus on the degree of polarization but lack of Stokes vector imaging effect of each element. Based on the principle that the polarization characteristics of different materials are different, the experiment of underwater target detection by laser pulse polarization is carried out in this paper, and the influence of different depths of an underwater object and material factors on polarization imaging detection is studied. The results show that in air, the average degree of polarization of iron sheet is 0.56, that of ceramic tile is 1.00, and that of plastic is 0.48. In water, the average degree of polarization of iron sheet is 0.3625 at 7.5 m, the average degree of polarization of ceramic tile at 7.5 m is 0.359, and that of plastic at 7.5 m is 0.3805. The medium will change the degree of polarization of the measured object. The targets made of different materials have different polarization characteristics, and the polarization information is of great value in improving the detection performance of man-made targets. Polarization detection can obtain better information about underwater objects than traditional radiation intensity detection and can effectively suppress the absorption and scattering of light by water.

In this Letter, a polarization-insensitive high-order mode pass filter is presented, designed, and experimentally demonstrated. When TE0, TM0, TE1, and TM1 modes are injected into the input port, TM0 and TE0 modes are filtered, and TE1 and TM1 modes exit from the output port. To attain compactness, broad bandwidth, low insertion loss, excellent extinction ratio, and polarization-insensitive property, the finite difference time domain method and direct-binary-search or particle swarm optimization algorithm are employed for the optimization of structural parameters of the photonic crystal region and the coupling region in the tapered coupler. Measurement results reveal that, for the fabricated filter working at TE polarization, the extinction ratio and insertion loss are 20.42 and 0.32 dB at 1550 nm. In the case of TM polarization, the corresponding extinction ratio and insertion loss are 21.43 and 0.30 dB. Within a bandwidth from 1520 to 1590 nm, insertion loss smaller than 0.86 dB and extinction ratio larger than 16.80 dB are obtained for the fabricated filter working at TE polarization, while in the case of TM polarization, insertion loss lower than 0.79 dB and extinction ratio greater than 17.50 dB are realized.

A polarization analysis method based on a multi-parameter model is proposed to address the polarization effect analysis and calibration requirements of a dual-coded snapshot spectral polarization imaging system. A full-link polarization effect model for a spectral polarization imaging system is established that includes a digital micromirror array (DMD), prism grating prism (PGP), micro-polarizer array detector (MPA), and multi-film. The influence of parameters such as the refractive index, incident angle, grating refractive index, constant, prism refractive index, vertex angle, multi-layer film complex refractive index, and film thickness on the optical transmittance of the system are analyzed. Using a dynamic data exchange mechanism to perform full-link, full-FOV, and full-pupil ray tracing on the optical system, the polarization effect distribution of the system under different degrees of polarization (DOP) and wavelengths is obtained. A calibration experiment for the controllable incident wavelength and DOP using narrowband filters and glass stacks is established. The experimental results show that in the 420 nm, 532 nm, and 635 nm wavelength bands, the MSEs of the calibrated values are 1.3924 × 10−4, 1.6852 × 10−4, and 1.6735 × 10−4, respectively. It is proven that the calibration method based on a multi-parameter model is feasible. Finally, the spectral polarization image at 532 nm is calibrated. The contrast ratio of metallic aluminum is calibrated from 7.13 to 15.33. This study provides a theoretical basis for the analysis and calibration of polarization effects in a dual-coded snapshot spectral polarization imaging system.