Invention:
This invention is concerned with improving manufacturing accuracy and speed of Volume Holographic Elements (VHOEs) through more accurate diffraction efficiency measurement in real-time measurement conditions. Diffraction efficiency is an important characteristic of VHOEs, and the most basic technique for controlling the diffraction efficiency during fabrication is to use separate beams to expose the holographic material and measure the material’s efficiency. However, this technique is time consuming and requires additional equipment. Ideally, a measurement technique that used the exposure beam would reduce both these limitations.
The technique proposed in this invention works by periodically blocking an exposing beam during the fabrication and measuring the power of the diffracted beam using a power meter. Once the diffraction efficiency of the VHOE is measured to reach the desired value, the exposing beams can be shut off. Since this measurement is performed in real-time, the method has potential to account for the local variations in the material or laser power variation that cause the necessary exposure time to fluctuate between samples.
Background:
Most Volume Holographic Elements (VHOEs) must attain certain diffraction efficiency depending on the design. In many designs the diffraction efficiency should be maximized, while in other designs, such as exit pupil expanders in waveguide display systems, the diffraction efficiency is intentionally a lower value. In other setups, light from a separate laser at a different wavelength from the construction wavelength and at a separate incident angle is used to measure the diffraction efficiency. The diffraction efficiency at the construction wavelength can then be obtained through mathematical approximations. However, this method requires additional equipment and complicated experimental setups and the mathematical approximations reduce the accuracy of the method.
In this invention, a new technique for monitoring the diffraction efficiency of VHOEs in real-time is proposed that has potential for higher accuracy and greater simplicity than previous setups. The invention has potential for fabricating VHOEs that have precise tolerance in the required diffraction efficiency.
Applications:
- Industrial manufacturing of volume holographic elements
Advantages:
- Simpler/less equipment
- Precise and real-time
