Eye-tracking Super Multi-view 3D Display Based On Pixelated Nanogratings

Three-dimensional display(3D)technology can provide audiences with visual information with deep clues without auxiliary equipment.It has the characteristics of intuitiveness,interaction and immersion,and can be widely used in commercial entertainment,medical assistance,cultural relic protection,military exercise and other fields.Free stereoscopic 3D display can be integrated with existing planar display devices,and the complete light field information can be discretized into multiple views,which can be projected to the specified position in space through the view modulator.It is considered to be the fastest commercialized naked eye 3D display technology.In this display scheme,the observer is prone to visual fatigue,because the intersection of the optic axis after binocular convergence is located on the reconstructed virtual stereo image,while the lens of a single eyeball still determines the diopter according to the relative position of the display device.This has resulted in Vergence-accommodation conflict(VAC).In essence,the convergence contradiction is due to the insufficient density of information received in one eye.However,the existing display screen resolution is limited,and there is inherent contradiction between single view resolution,Angle resolution and field Angle.In this paper,nano-grating is used to produce non-uniform viewpoint distribution in accordance with human characteristics,which is characterized by high precision of ray regulation and large degree of freedom,so as to reduce information redundancy.Moreover,the angular interval between viewpoints is smaller than the pupil diameter,which effectively increases the angular resolution of the system.With the design of a multi-angle directional backlight system and the synchronization control circuit developed based on Field Programmable Gate Array(FPGA),the view point distribution generated by backlight switching can be synchronized with the observer’s motion track,and the observation area of both eyes can be completely covered.At the same time,the LCD screen provides amplitude information corresponding to the Angle of view.In this paper,a prototype of color naked eye 3D display was built to verify the feasibility of the 3D naked eye display based on pixelated nanogratings for human eyes tracking super many views.The main research work of this paper is as follows:(1)A 3D display scheme of vector light field based on directional backlight is proposed,and the light producing mechanism of nanogratings is studied.The design results of a view modulator composed of pixelated nanogratings matrix are given.The left and right eyes correspond to 8 view points respectively,and the view point interval is 0.45°.A directional backlight system with horizontal deflection angles of ±3°,±60 and ±9° is designed according to the view Angle modulation board.The influence of incident light deflection on the view point distribution is analyzed,and the predicted view point distribution results of the 3D display system are given.(2)The hardware scheme of synchronization control based on FPGA is designed.A human eye tracking module is developed based on Harr Cascade algorithm to input position signals for synchronization control system.Verilog HDL program is used to design each module and realize the collimating backlight switching and parallax image refresh synchronously.(3)By building a prototype,the 3D display effect with a large number of viewpoints is verified.A pixelated nano grating view modulation plate was fabricated by using a four-variable output UV lithography system,and its optical properties were tested.By aligning and fitting it with LCD pixel by pixel,a nude eye 3D display prototype with super many viewpoints was built.Combined with the pointing backlight system,the color stereoscopic display information output with refresh rate of 60 Hz,spatial resolution of 480×270 and view interval of 0.45° is realized.The stereoscopic display system has a field Angle of 26.9°,smooth motion parallax,and achieves a single-eye focusing effect of ±8 cm.