Enhanced volume phase grating with high dispersion, high diffraction efficiency and low polarization sensitivity

• US 20030007201A1
• Filed: 07/09/2001
• Published: 01/09/2003
• Est. Priority Date: 07/09/2001
• Status: Active Grant

• Current Assignee: Leroy David Dickson
• Original Assignee: Leroy David Dickson
• Inventors: Dickson, LeRoy David
• Granted Patent: US 6,750,995 B2
• Time in Patent Office: Days
• US Class Current: 359/15
• CPC Class Codes: G02B 27/4244 in wavelength selecting devices spectrometry G01J
• CPC Class Codes: G02B 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence
• CPC Class Codes: G02B 5/1857 using exposure or etching means, e.g. holography, photolithography, exposure to electron or ion beams
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02B 6/2706 as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters
• CPC Class Codes: G02B 6/2793 Controlling polarisation dependent loss, e.g. polarisation insensitivity, reducing the change in polarisation degree of the output light even if the input polarisation state fluctuates
• CPC Class Codes: G02B 6/29311 Diffractive element operating in transmission
• CPC Class Codes: G02B 6/29397 Polarisation insensitivity

Abstract

An enhanced volume phase diffraction grating provides high dispersion, uniformly high diffraction efficiency and equal diffraction efficiencies for all polarizations across a wide range of wavelengths. The thickness of the volume phase material and the modulation of its refractive index are jointly established to provide equalization of diffraction efficiencies for all polarizations over a wide range of wavelengths. The equalization occurs where the S and P diffraction efficiencies are both at a maximum.

Claims

1. A diffractive optical device comprising

a transparent support means;

a volume phase medium attached to said transparent support means;

a transparent cover means attached to said volume phase medium with a transparent adhesive to provide a sealant and protectant for said volume phase medium;

the material and geometric parameters of said volume phase medium—

the angle of incidence of an incident beam at a nominal wavelength, the angle of diffraction of the diffracted beam at said nominal wavelength, the average bulk refractive index of said volume phase medium at said wavelength, the refractive index modulation of said volume phase medium at said wavelength and the effective thickness of said volume phase medium—

being substantially simultaneously established for said incident beam at said nominal wavelength such that the S-polarization diffraction efficiency of said volume phase medium at said wavelength and said angle of incidence and the P-polarization diffraction efficiency of said volume phase medium at said wavelength at said angle of incidence are both substantially maximized at substantially the same value of said index modulation of said volume phase medium of said effective thickness;

exterior surfaces of said transparent support means and said transparent cover means being coated with anti-reflection coatings such that the Fresnel reflection losses of said exterior surfaces are substantially minimized and the maximum values of said S-polarization diffraction efficiency and said P-polarization diffraction efficiency are substantially equal;

2. A volume phase grating as defined in claim 1 wherein said anti-reflection coatings are modified to decrease said S-polarization diffraction efficiency, thereby substantially minimizing the maximum difference between said S-polarization diffraction efficiency and said P-polarization diffraction efficiency across a given bandwidth in a single pass through said grating.

3. A volume phase grating as defined in claim 1 wherein a reflective means is used to reflect said diffracted beam back toward said grating.

4. A volume phase grating as defined in claim 3 wherein said anti-reflection coatings are modified to decrease said S-polarization diffraction efficiency, thereby substantially minimizing the maximum difference between said S-polarization diffraction efficiency and said P-polarization diffraction efficiency across a given bandwidth in two passes through said grating.

5. A diffractive optical device comprising

a transparent support means;

a volume phase medium attached to said transparent support means;

a transparent cover means attached to said volume phase medium with a transparent adhesive to provide a sealant and protectant for said volume phase medium;

the material and geometric parameters of said volume phase medium—

the angle of incidence of an incident beam at a nominal wavelength, the angle of diffraction of the diffracted beam at said nominal wavelength, the average bulk refractive index of said volume phase medium at said wavelength, the refractive index modulation of said volume phase medium at said wavelength and the effective thickness of said volume phase medium—

being substantially simultaneously established for said incident beam at said nominal wavelength such that the S-polarization diffraction efficiency of said volume phase medium at said wavelength and said angle of incidence and the P-polarization diffraction efficiency of said volume phase medium at said wavelength at said angle of incidence are both substantially maximized at substantially the same value of said index modulation of said volume phase medium of said effective thickness and the variation of said S-polarization diffraction efficiency with wavelength and said P-polarization diffraction efficiency with wavelength are substantially minimized and the variation of the difference between said S-polarization diffraction efficiency and said P-polarization diffraction with wavelength is substantially minimized;

exterior surfaces of said transparent support means and said transparent cover means being coated with anti-reflection coatings such that the Fresnel reflection losses of said exterior surfaces are substantially minimized and the maximum values of said S-polarization diffraction efficiency and said P-polarization diffraction efficiency are substantially equal.

6. A volume phase grating as defined in claim 5 wherein said anti-reflection coatings are modified to decrease said S-polarization diffraction efficiency, thereby substantially minimizing the maximum difference between said S-polarization diffraction efficiency and said P-polarization diffraction efficiency across a given bandwidth in a single pass through said grating.

7. A volume phase grating as defined in claim 5 wherein a reflective means is used to reflect said diffracted beam back toward said grating.

8. A volume phase grating as defined in claim 7 wherein said anti-reflection coatings are modified to decrease said S-polarization diffraction efficiency, thereby substantially minimizing the maximum difference between said S-polarization diffraction efficiency and said P-polarization diffraction efficiency across a given bandwidth in two passes through said grating.