Image Evaluation Of The Optical Transmission Through Inhomogeneous Medium

In the application fields like laser communication, aerial photo-mapping and remote sensed imaging, how dose an optical wave be transmitted through the random medium is a critical problem. Meanwhile, in other industries like laser medicine, and biological engineering, the imaging through a random medium is also a basic knowledge for the researchers and scientists.In solving the problem of imaging through the random medium, this paper mainly applies the method of ray tracing, combined with the technology of wavefront calculations in the field of physical optics, so as to obtain a series of image evaluation results. During the ray trace process, the refractive index and its gradient information of the random medium are frequently used, how to storage the mass refractive information is one of the biggest problems in the research. This paper presented the method, namely self-adaptive grid, effectively describing the arbitrary refractive distribution in the random medium. By applying the local-subdivision algorithm, the storage volume can get its full usage under the circumstances that the ray trace accuracy is guaranteed.This paper firstly overviews the relationship between the random medium and optical wave transmission, and its application background, emphasizing on the principle and realization method of ray tracing through the inhomogeneous medium. Secondly, the data structure and the corresponding algorithm of self-adaptive grid is explained in detail, so as to achieve the optimum situation that the grid is divided into smaller ones in the area where the refractive index changes vastly, and the grid size is larger in the area where the refractive index changes smoothly. And then, the paper also presented the method of vary-step ray trace method, that combining the ray trace step with the local adaptive grid size, so as to achieve an optimum ray trace model. In addition, this paper also describes various image evaluation methods concerning the application of ray trace through random medium, such as MTF, spot diagram, PSF and Strehl, etc.. In order to verify the correctness of self-adaptive grid algorithm and the corresponding ray trace codes, one simple model is taken as an example, or say, the refractive index distribution of GRIN lens can be described by a sort of equations, so that numerous refractive index information at discrete sample locations can be obtained, and input into the self-adaptive grid software. The ray trace calculations based on such an algorithm can be easily compared with that from the commercially available software Zemax. The results illustrate that the algorithm of self-adaptive grid has very high accuracy, and such a method can greatly reduce the storage consumption under a reasonable threshold setting, so as to make the high-accuracy image simulation through the random medium come possible. Meanwhile, this paper also takes a real random medium as an example, and the results show that the vary-step ray trace method can effectively reduce the ray tracing time and greatly improve the image simulation efficiency.