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Optical simulation and analysis of a circularly polarization imaging system

V. Dremin 1, E. Zharkikh 1, A. Bykov 2

1 Research & Development Center of Biomedical Photonics, Orel State University, Orel, Russia
2 Optoelectronics and Measurement Techniques Unit, University of Oulu, Oulu, Finland


Due to a high sensitivity of polarized light to scattering variations, the polarized spectroscopy has a great potential to be used for screening malformation and other structural changes in the biological tissue samples. In this work, we analyze the optical scheme of the circularly polarization imaging system in the TracePro software environment. The initial information for solving most problems of computer simulation and development of optical systems is their design parameters. At the analysis stage, the optical system is described by design parameters in an approximation sufficient for mathematical simulation of its operation. The main computational procedure is the calculation of the passage of light rays through the optical system. The purpose of the simulation in this work is to search for design parameters and energy values suitable for providing a given level of signal-to-noise ratio (SNR), forming the necessary spatial structure of the beam, its spectral composition, etc. The interaction of circularly polarized light with biological scattering media was also modeled within the same optical scheme of the setup.
The experimental system consists of two main channels: illumination and detection. In the illumination channel, the linearly polarized light in the range of 450-650 nm was used. The light can be changed by a half-wave plate into the desired state of linear polarization and a quarter-wave plate assures circular polarization. The light beam is focused with the objective lens onto the sample at 55° angle. We use unequal angles of incidence and detection to eliminate specular reflection. The diffusely reflected light from the sample was collected by the measurement channel at 30° angle at a variable distance between two channels. In the detection channel, we use a standard spatial filtering scheme with a pinhole and two doublets. All simulations were performed in the wavelength range of 450-650 nm, which is determined by the range of the acousto-optic tunable filter used in experimental studies to filter the light of a supercontinuum laser.
Using simulations in the TracePro environment, we analyzed the optimal relationship between the pinhole diameter and the system resolution, SNR, the dependence of the signal on the source-detector distance, and the dependence of the polarization pattern on the above parameters.
This study was funded by the Russian Science Foundation (project: №19-79-00082).


Viktor Dremin
Research & Development Center of Biomedical Photonics, Orel State University


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