Diffraction element

• US 7,430,076 B2
• Filed: 03/12/2004
• Issued: 09/30/2008
• Est. Priority Date: 09/13/2001
• Status: Expired due to Fees

• Current Assignee: Asahi Glass Company, Limited (AGC, Inc.)
• Original Assignee: Asahi Glass Company, Limited (AGC, Inc.)
• Inventors: Sato, Hiromasa, Ooi, Yoshiharu
• Primary Examiner(s): Chang; Audrey Y
• Application Number:
  US10/798,556
• Publication Number:
  US 20040169929A1
• Time in Patent Office: 1,663 Days
• Field of Search: 359/576, 359/566, 359/569, 359/571, 359/15, 359/572, 359/495, 359/34, 356/305, 356/328, 385/37, 372/102, 372/50.1, 372/43, 369/112.03, 369/112.05
• US Class Current: 359/569
• CPC Class Codes: G02B 27/4244 in wavelength selecting devices spectrometry G01J
• CPC Class Codes: G02B 5/1819 Plural gratings positioned on the same surface, e.g. array of gratings plural diffractive elements positioned sequentially along the optical path G02B27/4272
• 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
• CPC Class Codes: G02B 5/1871 Transmissive phase gratings
• CPC Class Codes: G11B 2007/0006 adapted for scanning different types of carrier, e.g. CD & DVD
• CPC Class Codes: G11B 7/1275 Two or more lasers having different wavelengths
• CPC Class Codes: G11B 7/1353 Diffractive elements, e.g. holograms or gratings diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44

Abstract

A diffraction element having concave/convex-like diffraction gratings in its two surfaces from which at least two separated light beams can be taken in the same direction without changing largely the propagating direction of diffracted light even if the temperature of the operating environment changes. A diffraction grating having a concave/convex shape in cross-section is formed in the incoming-side surface of the transparent substrate and two diffraction gratings of concave/convex shape in cross-section are formed in the outgoing-side surface wherein the grating pitch of the first one is made equal to the grating pitch of one of the second ones.

In addition, a reflection type diffraction element exhibiting a good wavelength dependence of diffraction efficiency without being dependent largely on the direction of polarization of an incoming light is provided. A pseudo sawtooth-like diffraction grating is formed in either surface of the transparent substrate, a reflective film is formed on a diffraction grating portion, and an antireflective film is formed on the opposite surface.

Claims

1. A diffraction element comprising:

a substrate with an incoming-side surface opposite to an outgoing-side surface, the incoming-side surface configured to receive light from a light source external to the substrate;

an incoming-side diffraction grating having a concave/convex shape in cross-section disposed in a central region of the incoming-side surface;

a first outgoing-side diffraction grating having a concave/convex shape in cross-section disposed in the outgoing-side surface and configured to receive light not diffracted by the incoming-side diffraction grating; and

a second outgoing-side diffraction grating covered by a reflective layer and having a concave/convex shape in cross-section, the second outgoing-side diffraction grating positioned on a light path of a light diffracted by said incoming-side diffraction grating, a grating pitch of the incoming-side diffraction grating being substantially equal to a grating pitch of the second outgoing-side diffraction grating,

wherein the incoming-side diffraction grating is configured relative to the light source such that only a center portion of the external light, having a stronger intensity than a peripheral portion of the external light, is not diffracted by the incoming side diffraction grating.

2. The diffraction element according to claim 1, wherein the second outgoing-side diffraction grating forms a reflection type diffraction grating.

3. The diffraction element according to claim 2, wherein the second outgoing-side diffraction grating has a saw-tooth concave/convex portion or a pseudo sawtooth diffraction grating wherein a saw-tooth shape is approximated by stairs.

4. The diffraction element according to claim 2, wherein the second outgoing-side diffraction grating comprises a pseudo sawtooth diffraction grating having a saw-tooth shape approximated by stairs, and a height or depth of a first step of the stairs is different from a height or depth of a second step of the stairs.

5. The diffraction element according to claim 1, wherein the incoming side diffraction grating and the first outgoing-side diffraction grating are arranged in a main axis of the external light, both diffraction gratings being centered on the substrate.