Reasearch On Key Technology Of Laser Projection Display Optical System

With the rapid enrichment of material life,people pay more and more attention to the spirit life.As the main window of human perception to the world,visual experience has always been the focus of people's pursuit.Traditional xenon light source projection display systems are gradual unable to meet the big screen,high resolution,high brightness,true color and other requirements.People have turned their attention to the laser projection display systems.Because of its large color gamut,high brightness,low power consumption and long life,laser projection display technology has been considered as the next generation of display technology,and has become the major development direction and technical competition focus of the domestic and foreign projection manufacturers.The application of laser light source makes the laser projection display system different from the projection system based on conventional light source,and the following issues need to be addressed.The first one is how does the circular Gaussian laser beam fully illuminate the rectangular spatial light modulator,the second one is how to effectively suppress the existence of laser speckle in the projection image,and the third one is how to design a highly energy efficient,compact optical engine structure combined with the above two questions.Based on the above background and problem,this paper focuses on the use of diffractive optical components(DOE)to achieve the laser beam shaping and homogenization.At the same time,methods of simultaneous achieving laser shaping and speckle reduction were studied by combining the DOE.And based on the DOE,a new compact laser projection optical engine was designed.The main research contents are as follows:1.Research on laser beam shaping and homogenization based on DOEs.Combined with the laser projection display system illumination demands,an eight steps DOE with a diameter of 16.5 mm was designed using Fourier iterative algorithm,the designed DOE was fabricated by multi-masks etching process,and the performance of the DOE was tested.The results show that the DOE have good shaping performance,but there are a lot of speckle in the rectangular spot,the RMSE of the spot is 67.67%.In order to suppress the speckle in the spot and further enhance the effect of beam homogenization,a fine design method is proposed to improve the performance of the DOE.The simulation results show that the speckle in the diffraction spot of the DOE designed by the fine design algorithm is well suppressed and the RMSE of the spot is reduced to 21.52%.2.Study on laser speckle suppression method.The causes of laser speckle were analyzed,the first-order statistical properties and second-order statistical properties of laser speckle were described,and the situation of multiple speckle pattern overlay was analyzed.On the basis of reviewing the existing methods of suppressing speckle,three methods of simultaneous achieving laser beam shaping and speckle suppression are proposed in combination with DOE,include the method of vibrating the DOE,the method based on a phase distribution limited DOE,and the method based on a silicon-based liquid crystal.In the method of vibrating the DOE,combined with the DOE,set up the relevant experimental platform,and the relationship between vibration frequency,amplitude and speckle suppression and energy utilization of DOE was studied.In the method based on a phase distribution limited DOE,the relationship between the distribution of the wavefront phase and the contrast of the laser speckle is analyzed theoretically under the condition of uniform phase distribution.In the method based on a silicon-based liquid crystal,the effect of superimposing multiple speckle patterns on speckle suppression was investigated and the effect of the correlation between overlay patterns on speckle reduction was analyzed.3.Design of 3DLP laser projection display optical system based on a DOE.Combined with the above two parts,a novel type of 3DLP laser projection display optical system based on a DOE is proposed.The laser light source,the DOE illumination optical path and the projection lens are designed,and the whole optical system is modeled and simulated.The simulation results are compared with the traditional laser projection system based on light-pipe,and the superiority of the new system is verified by various aspects.