Double-pass diffraction grating
View Patent ↗An optical assembly for double passing a transmission grating may include a prism having first, second and third surfaces. A transmission grating may be bonded to the first surface. A first mirror coating may be bonded to the second surface and a second mirror coating to the third surface. The first, second and third surfaces, the transmission grating and the first and second mirror coatings are configured such that light of a predetermined wavelength entering the prism that is incident on the transmission grating is diffracted a first time by the transmission grating towards the second surface, reflected from the second surface to the third surface, reflected from the third surface back to the transmission grating, and diffracted a second time by the transmission grating as the light exits the prism.
1. An optical assembly, comprising:
a prism having first, second and third surfaces;
a transmission grating bonded to the first surface;
a first mirror coating bonded to the second surface;
a quarter waveplate disposed between the first mirror coating and the second surface; and
a second mirror coating bonded to the third surface, wherein the first, second and third surfaces, the transmission grating and the first and second mirror coatings are configured such that light of a predetermined wavelength entering the prism that is incident on the transmission grating is diffracted a first time by the transmission grating towards the second surface, reflected from the second surface to the third surface, reflected from the third surface back to the transmission grating, and diffracted a second time by the transmission grating as the light exits the optical assembly.
2. The optical assembly of claim 1 wherein the first, second and third surfaces and the transmission grating are oriented such that the light of the predetermined wavelength undergoes an even number of reflections between being diffracted the first time by the transmission grating being diffracted the second time by the transmission grating.
3. The optical assembly of claim 1 wherein the transmission grating is bonded to the first surface by epoxy or optical contacting.
4. The optical assembly of claim 1 , wherein the first surface includes an anti-reflection coating between the transmission grating and the prism.
5. The optical assembly of claim 1 wherein the first or second mirror coating is made by depositing a reflective material directly onto the second or third surfaces of the prism respectively.
6. The optical assembly of claim 1 wherein the first and second mirror coatings are made by bonding mirrors to the second and third surfaces of the prism.
7. The optical assembly of claim 1 wherein the quarter wave plate (QWP) is bonded to the second surface of the prism.
8. The optical assembly of claim 1 wherein the first mirror coating comprises a reflective material bonded to the quarter wave plate.
9. The optical assembly of claim 1 wherein the quarter waveplate includes first and second surfaces, wherein the first surface of the quarter waveplate is attached to the second surface of the prism and wherein the first mirror coating is formed on the second surface of the quarter waveplate.
10. The optical assembly of claim 1 wherein the transmission grating is made of a material having the same index of refraction as the prism.
11. The optical assembly of claim 1 wherein the transmission grating includes a grating substrate made of a different material than the prism.
12. The optical assembly of claim 1 wherein the materials used for the transmission grating and prism are selected such that a temperature dependence of a grating spacing of the grating is counteracted by a temperature dependence of the index of refraction of the prism.
13. The optical assembly of claim 1 wherein the transmission grating includes a substrate made of borosilicate glass and the prism is made of N-PK52.
14. The optical assembly of claim 1 wherein the grating spacing of the transmission grating, the index of refraction of the transmission grating, and the index of refraction of the prism are selected such that the optical assembly suppresses reflection and transmission of diffraction orders other than a predetermined diffraction order.
15. The optical assembly of claim 1 wherein materials used for the substrate of the transmission grating and prism are selected such that a temperature dependence of a grating spacing of the grating is counteracted by a temperature dependence of the substrate and the temperature dependence of the index of refraction of the prism.
16. The optical assembly of claim 1 wherein optical materials used for a substrate of the transmission grating, that is attached or bonded to another substrate, and then bonded to the prism are selected such that a temperature dependence of a grating spacing of the grating is counteracted by a temperature dependence of the substrate of the transmission grating, the other substrate and prism, and a temperature dependence of the index of refraction of the optical materials.
17. The optical assembly of claim 1 wherein the quarter waveplate is configured such that the light that is diffracted a first time by the transmission grating towards the second surface and reflected from the second surface passes through the quarter waveplate twice.