Light Uniformity Optimization and Light Leakage Suppression in the Exit Pupil Plane of Array Waveguide AR Display System
At present,there are many combinations of reflectance parameters of the partial reflector of the array optical waveguide.Manual optimization takes a long time,and it is difficult to obtain the optimal parameter combination,resulting in poor display image quality.On the other hand,there is a widespread problem of light leakage,which will reveal the user's privacy,especially when used as a target in a nighttime military environment.In this paper,the reflectance of each part of the array waveguide is automatically optimized with Python and LightTools,and the simulation model of optical machine-waveguide-human eye all-element AR display is established.The reflectance range of each part of the reflector is set in Python and initialized.By calling the API interface of LightTools in Python,the reflectance of each part of the LightTools simulation model is evaluated according to a specific step size,and the optical uniformity of the pupil plane is automatically simulated and calculated.After the cycle is over,the optical uniformity under all reflectance combinations is sorted.The reflectance combination corresponding to the maximum optical uniformity is the reflectance parameter combination after optimizing the optimal reflectance.The causes of stray light are analyzed in detail,and it is proposed that the light is incident at a specific angle after coupling into the system to avoid stray light Ⅰ1.At the same time,the angle selection film is innovatively proposed to suppress stray light I2.The angle selection film is a partial mirror film with different reflectance characteristics for incident light at different angles,which can simultaneously satisfy the reflection of small angle light and the transmission of large angle light.The parallel tolerance requirements of waveguide substrate,upper and lower surface and partial mirror array are simulated by Monte Carlo method based on the limit requirement of viewing angle resolution.The parallelism of waveguide depends on the parallelism of substrate material,the parallelism of cutting and polishing process and the parallelism of bonding.In the machining process,the machining parallelism of waveguide is ensured by precisely adjusting the parameters of grinding,polishing and gluing.According to the requirements of human eye resolution and waveguide parameters,it is not difficult to calculate the parallel error tolerance of the upper and lower surfaces of the waveguide and the parallel error tolerance of the partial mirror array should be controlled at 6"and 9"respectively.On this basis,according to the characteristics of the optical system,the array waveguide near-eye display system is developed by using the multi-layer film design angle selection film,combined with the optimization of the distance of some mirrors,and an array waveguide augmented reality display prototype with a field of view of 40° is developed by optical cold processing technology.The luminance at different positions of the exit pupil surface of the prototype is measured by the luminance meter in the National Flat Panel Display Center.The uniformity of the exit pupil of the prototype is 83％.The prototype has significant advantages in color uniformity and reducibility,and the illumination uniformity is higher than that of the pupil plane.When the light enters the human eye after many total internal reflections in the waveguide,due to the Fresnel reflection at the interface between the waveguide and the air,part of the light is reflected back to the environment,forming about 4％of the light leakage.An anti-reflection film is plated on the surface of the waveguide near the human eye to inhibit light leakage.The light leakage images of the prototype before and after the anti-reflection film coating were taken with a mobile phone at a distance of about 10 mm from the waveguide and tested.Through comparative analysis,the light leakage of the waveguide is suppressed obviously after coating the anti-reflection film,and the proportion of vertical light leakage is reduced from 4％to 2％.
Array waveguideAugmented realityAutomatic optimizationMonte Carlo analysisUniformityLight leakage
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