Virtual Retinal Display III

Type: Semester thesis
Students: Cyril Stutz, Andreas Grüter

How good human and computers collaborate with each other depends on the display to some degree . In a Virtual Retinal Display (VRD) a tiny laser beam scans an image from a VGA source directly on the retina. To project the image exactly on the retina two mirror scanners, a horizontal and a vertical one, are used to deflect the beam. Using the VRD technology allows to build a high resolution, wide field-of-view personal display device that is light weight and will operate in a high brightness environment.

This project was a further work with the objective of improvement of the existing prototype. One of the main problems of the prototype was its instability. The horizontal resonance-scanner had been operated with the VGA clock instead of its own resonance frequency. An exactly adjustment of the VGA signal with the resonance frequency of the horizontal scanner is pretty difficult to achieve. Applying the VRD system to different VGA sources (PC, TV, etc.) makes the adjustment even impossible. The remaining frequency mismatch leads to an instable operation of the horizontal scanner.

Our goal was to decouple the VGA source and the scanner. This can be done with an image buffer where the VGA data are stored with an other frequency than the data are read out and transfered to the laser. The image buffer is controlled by a FPGA (Field Programmable Gate Array) where also the rest of the implementation is done. The FPGA makes the complete system very flexible. A reprogramming of the FPGA can change the system to a new application.

There is still continuative work to do. One disadvantage is that the laser does not follow the eye. To guarantee a proper work of the VRD the laser beam should enter the eye in the middle of the pupil. Hence, a combination of the VRD with a pupil tracking system would be an interesting issue. Another work to do is the miniaturisation of the whole system so that it can be used as a wearable system.