# US 2008/0186578 A1 · Transmission type diffraction grating

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- Number: US 2008/0186578 A1
- Document ID: US20080186578A1
- Status: Published application
- Kind: A1
- Application number: 12/018,043
- Filed: 2008-01-22
- Published: 2008-08-07
- Earliest claimed: 2004-07-26
- Assignees: Nippon Sheet Glass Co., Ltd.
- Inventors: Naoko Hikichi; Kenichi Nakama
- Web page: https://patentgrep.com/patent/US20080186578A1

## CPC

- G02B 5/1866: {Transmission 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)}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A transmission diffraction optical element is presented in which ridges having a roughly rectangular cross-section shape are disposed parallel to each other at a regular pitch at the surface of a substrate. Striped thin-film layers are formed on these ridges and a thin-film layer is inserted between the substrate and the ridges. The thin-film layers are arranged at a regular pitch identical to the regular pitch of the ridges and the thin-film layer does not have a periodic pattern oriented in the same direction as the periodic pattern of the ridges.

## Claims

### Claim at position 1

1-4. (canceled)

### Claim 5

A transmission diffraction optical element comprising:
a substrate layer;
a plurality of parallel ridge-shaped projections formed in a periodic pattern and disposed on the substrate layer, said ridge-shaped projections having roughly rectangular cross-section shapes perpendicular to a longitudinal axis;
a plurality of parallel striped thin-film layers with a uniform composition being arranged at a pitch matching a pitch at which said ridge-shaped projections are arranged and with an orientation identical to an orientation of an arrangement of said ridge-shaped projections, said plurality of parallel striped thin-film layers formed parallel to said substrate layer and at a fixed distance from said substrate layer or on a plane parallel to said substrate layer with a boundary surface within said ridge-shaped projections; and
a thin-film layer being disposed parallel to said substrate layer, having a boundary surface either parallel to the surface of said substrate layer or on said substrate layer, and formed with a uniform composition within a plane parallel to said substrate layer, said thin-film layer being formed without a periodic pattern in a direction identical to that of said periodic pattern of said ridge-shaped projections and having wavelength-selective transmission properties;
wherein said striped thin-film layer is disposed on top surfaces of said ridge-shaped projections and on bottom surfaces of grooves between said ridge-shaped projections.

### Claim 6 (depends on 5)

A transmission diffraction optical element according to claim 5, wherein, when said ridge-shaped projections are formed from a material with an index of refraction nH, and a groove depth for which desired characteristics for a transmission diffraction grating are achieved is h, a following condition is met:
nH×h=nH×hH+nLu×hLu−nLd×hLd
where nLu is an index of refraction of said striped thin-film layers disposed on said top surfaces of said ridge-shaped projections, hLu is a film thickness thereof, nLd is an index of refraction of said striped thin-film layers disposed on said bottom surfaces of the grooves between said ridge-shaped projections, hLd is a film thickness thereof, and hH is a height of said ridge-shaped projections formed from said material with an index of refraction nH.

### Claim 7 (depends on 6)

A transmission diffraction optical element according to claim 6, wherein:
at least one set of said striped thin-film layers is formed as a multilayer structure with at least two layers formed from at least two types of materials; and
said nL is replaced with nLa and said hLu is replaced with hLt or said hLd is replaced with hLt, where nLa is an average index of refraction of one set of said multilayer film and hLt is a total film thickness,

### Claim at position 5

8-11. (canceled)

### Claim 12

A transmission diffraction optical element further comprising:
a striped thin-film layer disposed on each bottom groove surface between adjacent ridge-shaped projections.

### Claim at position 7

13-14. (canceled)

### Claim 15

A transmission diffraction optical element further comprising:
a first striped thin-film layer disposed on the top surface of each ridge-shaped projection and a second striped thin-film layer disposed on each bottom groove surface between adjacent ride-shaped projections.

### Claim 16 (depends on 15)

A transmission diffraction optical element according to claim 15, wherein, when said ridge-shaped projections are formed from a material with an index of refraction nH, and a groove depth for which desired characteristics for a transmission diffraction grating are achieved is h, a following condition is met:
nH×h=nH×hH+nLu×hLu−nLd×hLd
where nLu is an index of refraction of said first striped thin-film layer, hLu is a film thickness thereof, nLd is an index of refraction of said second striped thin-film layer, hLd is a film thickness thereof, and hH is a height of said ridge-shaped projections formed from said material with an index of refraction nH.

### Claim 17 (depends on 16)

A transmission diffraction optical clement according to claim 16,
wherein at least said first or second striped thin-film layer is formed as a multilayer structure with at least two layers formed from at least two types of materials; and
said nL is replaced with nLa and said hLu is replaced with hLt or said hLd is replaced with hL1, where nLa is an average index of refraction of one set of said multilayer film and hLt is a total film thickness.

### Claim 18

(canceled)