Method and apparatus for large spectral coverage measurement of volume holographic gratings
View Patent ↗The present invention relates to methods of measuring the optical characteristics of volume holographic gratings with high resolution and with a large spectral coverage using a spectrally broad band source in conjunction with instruments that measure the spectrum such as spectrometers, imaging spectrometers, and spectrum analyzers.
1. A system for measuring the characteristics of a volume holographic grating, the system comprising: a spectrally broad band light source for generating an output beam via a coupled fiber; a collimating lens element for collimating the output beam received from the spectrally broad band light source via the coupled fiber, wherein the volume holographic grating is disposed in a path of the collimated output beam and filters the collimated output beam into a transmitted beam; and an apparatus disposed in the path of the transmitted beam, the apparatus receiving the transmitted beam and generating a spectrum of the transmitted beam, wherein each pixel in the generated spectrum corresponds to a spectral measurement, wherein the characteristics of the volume holographic grating include diffraction efficiency, grating spacing, slant angle, and bulk transmission.
2. The system of claim 1 wherein the volume holographic grating is a wafer.
3. The system of claim 1 wherein the spectrally broad band light source is a supercontinuum white light source.
4. The system of claim 1 wherein the spectrally broad band light source is a superluminescent light emitting diode (SLED).
5. The system of claim 1 further including a lens element disposed between the volume holographic grating and the apparatus.
6. The system of claim 1 wherein the volume holographic grating is oriented at a pre-determined angle with respect to the collimated output beam.
7. The system of claim 1 wherein an aperture is positioned in the path of the transmitted beam between the volume holographic grating and the apparatus.
8. The system of claim 1 wherein the collimated lens element is disposed on a translation stage so that the collimated output beam can be collimated over a wide spectral range.
9. The system of claim 1 wherein the volume holographic grating is removable to acquire reference measurements.
10. The system of claim 1 wherein the apparatus is a high resolution spectrometer.
11. The system of claim 1 wherein the apparatus is a high resolution spectrum analyzer.
12. The system of claim 1 wherein the apparatus is an imaging spectrometer.
13. A method of determining characteristics of a volume holographic grating, the method comprising: placing the volume holographic grating in a path of an output beam, wherein the volume holographic grating filters the output beam into a transmitted beam; and generating a spectrum of the transmitted beam, wherein each pixel in the spectrum corresponds to a spectral measurement, wherein the characteristics of the volume holographic grating include diffraction efficiency, grating spacing, slant angle, and bulk transmission.
14. A method of determining characteristics of a volume holographic grating, the method comprising: placing the volume holographic grating in a path of an output beam, wherein the volume holographic grating filters the output beam into a transmitted light beam, a facet of the volume holographic grating; and measuring a spectrum of the transmitted light beam pixel by pixel with an imaging spectrometer, wherein each pixel in the spectrum corresponds to a spectral measurement, wherein the characteristics of the volume holographic grating include diffraction efficiency, grating spacing, slant angle, and bulk transmission.
15. A method of determining characteristics of a volume holographic grating, the method comprising: placing the volume holographic grating in a path of an output light beam, wherein the volume holographic grating filters the output light beam into a first transmitted light beam, a facet of the volume holographic grating being at a fixed angle with respect to the output light beam; placing an aperture in a path of the first transmitted light beam, wherein the aperture reduces a size of the first transmitted light beam; translating the aperture in two-dimensions perpendicularly to a direction of the first transmitted light beam to provide a second transmitted beam; and measuring a spectrum of the second transmitted beam, wherein each pixel in the spectrum corresponds to a spectral measurement, wherein the characteristics of the volume holographic grating include diffraction efficiency, grating spacing, slant angle, and bulk transmission.
16. A method of determining characteristics of a volume holographic grating, the method comprising: placing the volume holographic grating in the path of an output beam, wherein the volume holographic grating filters the output beam into a transmitted light beam, a facet of the volume holographic grating being at a fixed angle with respect to the output beam; placing a selectable aperture array in a path of the transmitted light beam, wherein each aperture selected from the aperture array reduces a size of the transmitted light beam; and measuring a spectrum of the transmitted light beam, wherein each pixel in the spectrum corresponds to a spectral measurement, wherein the characteristics of the volume holographic grating include diffraction efficiency, grating spacing, slant angle, and bulk transmission.