Research On Illumination System Of High Power Laser Projector

In recent years,with the development of diode-pumped solid-state laser technology,it is possible to manufacture lasers with high-power,low cost and various wavelengths.Compared with cathode ray tubes,halogen lamps,LED and other projection equipment,the laser source has significant advantages in terms of dichroism,brightness,beam directionality,photoelectric conversion efficiency,and lifetime.These advantages make it possible for the projection products of pure laser sources to achieve greater color gamut,clearer,larger size image display capabilities and longer device life.As the fourth generation display technology after digital display,laser display has made significant breakthroughs in three elements of high-fidelity image display,such as large gamut,dual high-definition,real 3D and so on,which provides a technical approach to the human eye resolution limit.Thanks to the good monochromaticity of the laser,laser display can achieve a wide color gamut coverage,but at the same time this characteristic also brings the display noise,namely laser speckle.The contradiction between high saturation of laser light and display noise(laser speckle)is a key issue that restricts the development of laser projection display at present.Another problem that restricts the development of laser projection technology is the contradiction between the limited power of a single light source and the unlimited demand for the projection brightness.Although laser projection can achieve very high brightness output in theory,the output will be unstable due to temperature rise after a certain period of operation,which affects the quality of the display.Therefore,laser projection products on the market generally use a single or few laser diodes as the light source at present,and the actual output brightness is limited.In this paper,how to realize the beam shaping of the array laser source in the high power laser projection display system was studied,mainly from two aspects:light source system based on laser array and the shaping device based on freeform surface array.On the basis of traditional related patents and papers,a new design scheme for high-power laser projection was presented.The related ideas were simulated by software to demonstrate its feasibility.The main research results of the paper are as follows:Firstly,the principle of the collimated beam expanding of the light emitted by the semiconductor laser diode with two cylindrical mirrors was introduced,and the detailed calculation method of the relevant parameters was given.Secondly,the method of how to realize the efficient uniformity of the array light source in the array homogenization device was studied.When the lens array is used for collimating array light source directly,only the size of lens array unit is sufficiently small enough,can we get a better uniformity of the target surface.To solve this existing problem,we put forward that using circular bar to mix multiple light sources to eliminate the periodicity of incident light in space,simplify the design and processing difficulty of subsequent homogenization systems,and achieve the suppression of laser speckle at the same time.The simulation results showed that for the same laser illumination system,the uniformity of the target surface was increased from 77.59%to 91.91%after using round-bar mixed light.Thirdly,the function of free-form surface array in laser projection display device was studied,and the principle of beam smoothing and shaping by free surface array was analyzed.The design principle of free form surface based on parallel incident light to achieve uniform illumination in prescribed area of target surface was introduced,and the derivation process of corresponding first order partial differential equation was presented.The principle and process of solving free-form surface by geometric structure method were introduced,and the corresponding error analysis was given.Fourthly,the corresponding optical element parameters in the optical system were optimized,and the whole lighting system was modeled and simulated in software.Comparing multiple sets of simulation data,we found that using the array of free-form surface units with the same shape as the target surface and the ring light source arrangement can achieve higher uniformity.At the same time,the superiority of the proposed system was demonstrated in many aspects.Lastly,the experimental system of laser illumination based on array light source was set up.The parameters of related optical devices in the system were introduced and the relevant performance parameters of the actual system were tested.The results showed that the output power of the system was 740mW,the uniformity of the target surface was 88.57%,and the optical efficiency was 89.02%.At the same time,a certain degree of speckle suppression had been realized...