Research On Key Technologies Of Optical Engine Of Pico Projector Based On LED

Projection display technology has been widely used in daily life and work of human beings, however, weight and volume of the traditional projectors will limit the mass acceptance of them to some extent. Suppose that projector can be miniature and portable, it will further satisfy the demand for customers to use. Pico-projector is a newly emerged technology which corresponds to this requirement, thus, it should be light and small enough to be easy to carry. As the core element of projector, how to reduce the size of optical engine is the most critical step to obtain a miniature projector. The major components constitute an optical engine include:light source, spatial light modulator, illumination system and projection system.Currently, pico-projector can be classified as stand-alone style and embedded style. For a portable product, especially that embedded in other mobile devices must possess the features of small size and low power consumption. Obviously, light sources used in traditional projectors are not suitable for the application of pico-projector. However, with the advantages of small size, low voltage, long life, high luminance efficiency, short response time and environment protection, LED becomes the optimal light source of pico-projector. For that a large part of light energy is attenuated by inner optical components, output efficiency of most pico-projectors is very low. To improve the problem, amout of researches about increasing lumen efficiency of LED has been done. In this thesis, after analyzing light-emitting mechanism and light energy loss mechanism of LED, methods to enhance lumen efficiency of LED by improving the band structure of material, layer structure of chip and package mode are presented, respectively. Referring to the accurate layer structures of face-up chip, vertical chip and flip chip, we make a comparison of the output efficiency of the three types of LED chip by modeling and simulation. Simulation results show that layer structures of face-up chip and flip chip provide more benefit for light rays to escape. To improve the output efficiency of flat package module, the method of manufacturing micro-structure on the surface of silicone is proposed. Improvement of output efficiency of LED with different micro-structures is discussed.A novel illumination system design on the basis of freeform lens is proposed for pico-projector. This design overcomes the disadvantage of refraction freeform surface to control output light rays into small angle, and can achieve high collection efficiency. To deal with the problem of extended light source, optimization method is also given in detail. Final optimization results show that, under the condition that the size of light source and SLM are1.6×lmm2and0.45inch, light efficiency and illumination uniformity achieve57%、92%, respectively. Besides, with23%light efficiency increasment, experimental results show that a real freeform illuminaton lens is much better on light performance than the original illumination lens of a commercial pico projector. Compared to the traditional methods of illumination system design, our design is not only good at light performance, but also owns great advantages on size and weight.A projection lens with fixed focal length is designed using traditional imaging design method. By analyzing the inner construction of optical engine, we combine retro focus structure and telecentric beam path on image space to achieve effective back focal length and increasing transmissivity of chief ray, respectively. The algorithm to calculate technical parameters of projection lens including system focal length, the maximum field angle and resolution ratio are stated in this thesis. After determining technical parameters according to practical requirements, an initial projection lens structure is chosen from an existing patent accordingly. We use Zemax to assist the optimization, and shorten the focal length to the desired value. Aberration curves show that:MTF value of maximum field angle at the resolution ratio of321p/mm is bigger than80%, that of0and0.707field angles at the resolution ratio of321p/mm are bigger than85%. Distortion between0field angle and0.707field angle are corrected very well, that of the full field angle is also lower than1%which satisfies technical requirements.