Study On Hybrid Refractive/diffractive Optical System Design For Head-mounted Projective Display

The modern head-mounted display (HMD) is required to have good performance, be light in weight, simple in structure and comfortable for wearing. But the HMD based on eyepiece can't realize these requests at one time. Binary optics element (BOE) brings a new idea to optical design of HMD. The introduction of BOE can simplify the structure, lighten the weight, reduce the volume, and improve the imaging quality to a certain extent. However,there are limitations for BOE to do these things.Head-mounted projective display (HMPD) is a new type of head-mounted display, which were originated at the end of 1990s and developed at the beginning of this century. HMPD can realize good performance with a compact design. The usage of projection lens and retro-reflective screen makes HMPD distinguish form conventional HMD in nature. The projection lens makes HMPD easier to get larger field of view (FOV), less optical distortion and other aberrations than HMD based on eyepiece. Nowadays, HMPD has an important application in the fields of medical visualization for training, wearable computers, soldier equipped with digital system, and so on. And now it is becoming an emerging hot area of high-tech industries in the field of optical display.Based on HMPD, we make some studies on the optical system design, and application in the field of low light night vision, which are as follows:1. Analyzed the disadvantages of HMD based on eyepiece, and showed the advantages of HMPD; A refractive lens and a hybrid refractive/diffractive lens are designed. Later, a projective head-mounted display based on the hybrid refractive/diffractive lens has been designed. The miniature display is a 1.3-in. color LCD, and the system is with 50-deg FOV, 12mm exit pupil diameter and 25mm eye relief. The analyses of the aberrations show that the three systems can satisfy the requirements of the applications. They can display VGA mode images. The refractive projection system has 27.4g of weight and the hybrid refractive/diffractive system weights 13g only, which proves that the usage of BOE can lighten the weight effectively. Their diameters showed that it is very convenient to realize binocular design for HMPD. 2. The optical system has been designed for low light night vision goggles. The object lens, with±1 8 FOV, f/1.43 and 18mm image size, is consisted of six lenses, one of which is hybrid refractive/diffractive singlet. It can match the second generation image intensify tube. The projective structure, which has 36 FOV, 18mm image size, 10mm exit pupil and 25mm eye relief, has been applied into night vision goggles to act as visual system. It is very useful to reduce the volume, lower the center of gravity, lighten the neck supports, and improve the imaging quality. It provides new idea and concept for visual system design in night vision goggles.