## 2 Literature Review  
Optical plastic lenses that are made of polymer materials have the advantages of low material cost, light weight, high impact resistance, high impact and shatter resistance, and a simple production process for rapid mass production, as aspheric lenses are easier to produce. However, the disadvantages are that it is not easy to control the refractive index as it changes with temperature, which leads to birefringence. Compared with polymer materials, glass materials have a higher molding temperature and a high hardness, so they consume more energy. The optical glass molding process requires cutting and shape forming, and then multiple grinding and polishing processes. Consequently, if polymer material residual stress and distribution effects can be effectively interpreted, process defects can be improved through simulation and correcting machine parameters. Therefore, this research attempts to find a way to interpret the residual stress in polymer molding to determine the force distribution effects. As early as 1995, [PERSON] et al. [1] proposed a new full-field method for the automatic analysis of isochromatic fringes in white light. This RGB photoelasticity method eliminates the typical shortcomings of the classic white light photoelastic methods, which requires subjective analysis of colors and requires experienced analysts to obtain and interpret the results. In 1996, [PERSON] et al. [2] used a digital photoelastic system to measure the birefringence of injection molded parts, which combined digital image analysis technology and a half-fringe photoelastic (HFP) method. The influences of processing conditions, including melt temperature, mold temperature, filling time, and filling pressure, on birefringence development in molded parts were investigated. It was found that temperature and pressure are the two main factors that determine the development of birefringence during the molding process. The frozen-in birefringence of molded parts decreases with the increase in melting temperature, mold temperature, and injection speed. The birefringence of the parts will also increase as the filling pressure increases, especially near the gate area. In 1998, [PERSON] and [PERSON] [3] proposed a new two-dimensional photoelastic analysis method for determining the fringe order and the main direction of birefringence from a single image combined with elliptically polarized white light and color image processing. After determining the fringe order, the main direction of birefringence is obtained by solving a nonlinear equation. In this paper, the output light intensity equation was derived, and the principle of the method was then described. In 1998, [PERSON] and [PERSON] [4] mentioned that photoelasticity is an engineering tool, and as end users, people want to know which technology to choose for a particular application. In these terms, various technologies are reviewed, and the steps involved in each technology are briefly introduced in this paper. This work also mentioned that color images need to be captured for fully automated data collection, as well as emphasizing the future direction of digital photo elasticity research. In 2001, [PERSON] and [PERSON] [5] conducted a statistical experimental study to systematically analyze the influence of various process parameters on lens contour errors. The process parameters studied included injection speed, holding pressure, and mold temperature. As optical lenses require precise control of the surface profile, determination of the processing conditions for lens molding is complicated. The purpose of this work was to experimentally study the influence of molding conditions on the surface profile of injection molded lenses. The contour error is related to the mold shrinkage rate and the residual stress in the molded lens. Before the year 2000, although there have been research studies in the field of optics, it can be seen that most of them are based on traditional physical analysis, such as the well-known two-dimensional photoelastic analysis method.