校正梯形畸变，同时采集到清晰的图像是光学式指纹识别系统的重要指标。采用面光源全反射采集方式，棱镜的材料选用廉价的k9玻璃。用三片球面镜片作为成像系统，其中两片小透镜可通过光学设计软件CODEV设计成同一片镜片，得到的光学调制传递函数全视场大于0.5，无梯形畸变，且光照均匀。相比于市场上其他无梯形畸变的产品，该方案体积较小，成本较低，且容易装配，适合生产的需要。

Trapezoidal distortion correction and clear images collection are important indexes of an optical fingerprint identification system. Total internal reflection acquisition method of surface light source is adopted and cheap k9 glass is chosen as the material of prism. Three pieces of spherical lens is used as an imaging system in which two pieces of small lens can be designed into the same lens by optical design software CODEV. The whole field of view of optical modulation transfer function (MTF) is more than 0.5. There is no trapezoidal distortion and illumination is uniform. Comparing with other non-trapezoidal distortion productions on market, the product has smaller volume and lower cost. It is easy to fit and can meet the needs of production.