Method and apparatus for large spectral coverage measurement of volume holographic gratings

• US 8,049,885 B1
• Filed: 05/15/2009
• Issued: 11/01/2011
• Est. Priority Date: 05/15/2008
• Status: Active Grant

• Current Assignee: Coherent Inc (Coherent Corp.)
• Original Assignee: Ondax Incorporated (Coherent Corp.)
• Inventors: Havermeyer, Frank, Moser, Christophe
• Primary Examiner(s): Chowdhury; Tarifur
• Assistant Examiner(s): Nur; Abdullahi
• Application Number:
  US12/454,279
• Time in Patent Office: 900 Days
• Field of Search: 356/326, 356/328
• US Class Current: 356/326
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51

Abstract

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.

Claims

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.