Design Of Ultra-short Focal Projection Optical System

With the advent of the information age,large-screen display,as an effective means of information transmission,plays an increasingly important role in people’s life and work.Projection display is a mainstream technology to realize large-screen display.Projection technology is that the image produced by the display device is amplified by the optical system and projected onto the screen to produce a clear image.Image projection display is favored for its intuitive,convenient and high-definition features.Ultra-short focus projection display technology is the mainstream research direction of projection display technology in recent years.Its advantages lie in ultra-short focal length,super-large image,ultra-high definition picture and high space utilization rate.The key of ultra-short focus projection display technology is to design high-definition wide-field optical system,including the design of projection lens and illumination system.The key difficulty lies in projecting a large-size,high-brightness and high-resolution image in a short distance,which is embodied in:(1)determining the structure and surface shape to correct various aberrations caused by large viewing angle,and reducing the difficulty of processing and assembling ultra-short focus projection lens;(2)ensure the illumination uniformity and sufficient brightness of the lighting system.Aiming at the above research background and technical difficulties,the design of ultra-short focus projection optical system is studied in this paper.The main research contents include the following aspects:Firstly,the mainstream projection display technology and existing mainstream products are studied,and the basic aberration theory and Seidel aberration theory are used to guide the design of projection imaging lens.By comparing the three structural forms of ultra-short focus projection and analyzing the parameters,the specific design method is determined.Secondly,the design concept of matching refraction and reflection is adopted to construct the initial structure,focusing on the calculation and calculation process of the mirror surface parameters.The zero view point of the object plane is used as the coordinate origin,and the aspheric equation is projected onto a two-dimensional plane to establish a coordinate system.According to the refraction propagation trajectory of the principal ray,the coordinate formula of the intersection point between the principal ray and the aspheric surface is derived by using the reflection law and the conjugate relation of the object and image.According to the coordinates of discrete points on the aspheric surface,the initial surface shape of the mirror is obtained by least square fitting.Thirdly,a projection lens composed of 15 spherical lenses and an even aspheric mirror is designed by using optical design software simulation optimization,which can project a100-inch image at 500 mm.The MTF in the full field of view of 148 is greater than 0.5 at the cut-off frequency,the horizontal TV distortion is 0.52%,and the vertical TV distortion is0.62%,which meets the visual requirements of human eyes.Fourthly,the tolerance and manufacturability of the designed optical system are analyzed.The results show that the projection lens has good tolerance and machining feasibility.Compared with most projection lenses in the market,the projection ratio is about0.3.The lens designed in this paper reduces the projection ratio to 0.22,and the spherical lens and even aspheric mirror which are easy to process can effectively reduce the processing cost,and the coaxial design result can also effectively reduce the assembly difficulty.Fifthly,in the design of lighting system,the theory of non-imaging optics and optical expansion is used to guide the design,and the overall light path is determined as a square bar lighting system using laser as lighting source.According to the tricolor mixed white light technology and the tristimulus value of tricolor laser light source,the power ratio of tricolor laser light source is calculated.In order to couple the mixed-color white light into the square rod,a collimating lens and a coupling lens are designed in combination with the laser divergence angle.Sixthly,in the design,considering the principle that the optical expansion only increases but not decreases,and taking into account the maximum utilization of energy,the optical expansion of the spatial light modulator is used to determine the size of the square rod homogenizer.And the light spot emitted by the square rod is irradiated to the spatial light modulator through the relay system.The Light Tools software is used to simulate the lighting system,and to simulate the light distribution and transmission effect of the lighting system.The results show that all of the light can be received by the spatial light modulator,and the illumination uniformity of the spot can reach more than 90%,which has a good light energy utilization rate.Compared with the lighting system using LED light source,using laser as light source in this paper can obtain images with richer levels and fuller colors.