Reflection type diffraction grating

• US 20020044359A1
• Filed: 09/17/2001
• Published: 04/18/2002
• Est. Priority Date: 09/21/2000
• Status: Active Grant

• Current Assignee: Nippon Sheet Glass Company Limited
• Original Assignee: Nippon Sheet Glass Company Limited
• Inventors: Shimmo, Katsuhide, Kawamoto, Shinji, Kunisada, Terufusa, Nakama, Kenichi
• Granted Patent: US 6,839,173 B2
• Time in Patent Office: Days
• US Class Current: 359/572
• CPC Class Codes: G02B 5/1861 Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence

Abstract

A reflection type diffraction grating according to the present invention has a structure in which a metal film as a first layer with reflectance not lower than 30% with respect to the wavelength of incident light and a transparent dielectric film as a second layer are laminated successively on the surface of the reflection type diffraction grating. With respect to the wavelength of incident light, the metal film has a refractive index selected to be not higher than 1.5 and an extinction coefficient selected to be not smaller than 6.0. The transparent dielectric film has a refractive index selected to be in a range of from 1.30 to 1.46, both inclusively, with respect to the wavelength of incident light and has an optical film thickness selected to be in a range of from 0.20λ to 0.38λ, both inclusively, when λis the wavelength of incident light.

Claims

1. In a diffraction grating having a groove period which is 0.1 to 10 times as large as a wavelength of incident light, a reflection type diffraction grating comprising a laminate of a metal film as a first layer with reflectance not lower than 30% and a transparent dielectric film as a second layer, said first and second layers being laminated in order on a surface side of said first-mentioned diffraction grating.

2. A reflection type diffraction grating according to claim 1, wherein:

said metal film has a refractive index not higher than 2.0 and an extinction coefficient not smaller than 6.0 with respect to the wavelength of the incident light; and

said dielectric film has a refractive index in a range of from 1.30 to 1.65, both inclusively, with respect to the wavelength of the incident light and has an optical film thickness 0.20 to 0.80 times, both inclusively, as large as the wavelength of the incident light.

3. A reflection type diffraction grating according to claim 2, wherein said dielectric film has a refractive index in a range of from 1.30 to 1.46, both inclusively, with respect to the wavelength of the incident light and has an optical film thickness 0.20 to 0.38 times, both inclusively, as large as the wavelength of the incident light.

4. A reflection type diffraction grating according to any one of claims 1 through 3, wherein said metal film is constituted by any one selected from Al or an alloy containing Al as a main component, Ag or an alloy containing Ag as a main component, Cu or an alloy containing Cu as a main component, and Al or an alloy containing Au as a main component.

5. A diffraction grating comprising:

a substrate defining a fine roughness structure on a surface, said fine roughness structure being constructed by a large number of fine grooves arranged periodically;

a transparent dielectric layer provided to said substrate as an exposed surface;

at least one metal layer provided to said substrate to be located between said dielectric layer and said fine roughness structure; and

reflectance of said metal layer is not lower than 30%.

6. A diffraction grating according to claim 5, wherein a refractive index of said metal layer is not higher than 2.0 with respect to the wavelength of the incident light.

7. A diffraction grating according to claim 5, wherein an extinction coefficient of said metal layer is not smaller than 6.0 with respect to the wavelength of the incident light.

8. A diffraction grating according to claim 5, wherein a refractive index of said dielectric layer is in a range of from 1.30 to 1.65, both inclusively, with respect to the wavelength of the incident light.

9. A diffraction grating according to claim 5, wherein an optical film thickness of said dielectric layer is 0.20 to 0.80 times, both inclusively, as large as the wavelength of the incident light.