Optical Low Pass Filter Spot Test System

Optical Low Pass Filter (OLPF), which can improve the graphic quality and obtain the vivid effect, is widely used in the front end of digital imaging device, e.g. digital video cameras, digital video monitor, camcorder.OLPF uses the light-splitting character of birefringent crystal. A light spot can be separated into two divergent light spots after passing a birefringent crystal. Besides principle, the analysis and design of OLPF, composed of a single or multiple crystals, are also discussed in detail in this paper.This paper analyzes and simulates the characteristics of frequency response, dispersion and broad-angle-incident of the OLPF in theory and in experiment. Several birefringent crystals with proper alignment are introduced into OLPF to get a better frequency response. Compared with the OLPF with one crystal, its side-lobe is suppressed to a great extent without obvious deterioration in the main-lobe. In addition, the dispersion can reach its minimum by changing one of the material. The simulation shows that, the maximum errors of dispersion and broad-angle-incident is 8.5% and 25% (the incident angle is ±14° ) of the ideal offset respectively. Consequently, regular OLPF can meet the requirements of wide spectral range and broad-angle-incident optical system.We developed an OLPF recognition system, named as Double Refractive Pattern Recognition System for OLPF. The principle and structure of the system is introduced in this paper. The system, with high precision and large-scale detection, can measure the thickness and angles between optical axes accurately and quickly. In addition, the system has a good compatibility, i.e. standard microscope objective can substitute the digital microscope adapter, which is specially designed for the system. The software of the system is also very powerful: in addition to the basic function image caption and scan, it can automatically detect the light spots number, distance and angles between light spots.