Method and device for producing a coupling grating for a waveguide

• US 20040042724A1
• Filed: 07/10/2003
• Published: 03/04/2004
• Est. Priority Date: 11/29/2000
• Status: Abandoned Application

• Current Assignee: Andreas Gombert, Hansjorg Lerchenmuller, Michael Niggemann
• Original Assignee: Andreas Gombert, Hansjorg Lerchenmuller, Michael Niggemann
• Inventors: Lerchenmuller, Hansjorg, Gombert, Andreas, Niggemann, Michael
• Application Number:
  US10/415,469
• Publication Number:
  US 20040042724A1
• Time in Patent Office: Days
• US Class Current: 385/37
• CPC Class Codes: G02B 2006/12107 Grating
• CPC Class Codes: G02B 2006/12173 Masking
• CPC Class Codes: G02B 6/124 Geodesic lenses or integrated gratings
• CPC Class Codes: G02B 6/136 by etching

Abstract

The invention relates to a method and a device for producing a coupling grating (5) for a waveguide. The method relies on the technique of interference lithography, whereby an interference pattern on a light-sensitive layer (2) is exposed by superimposing two coherent light beams (3, 4) on said light-sensitive layer (2). Said pattern is then transferred onto the surface of the substrate (1) that lies underneath by subsequent developing and an etching process. The method is characterized in that it uses a shadow mask (6) that is mounted at minimum clearance relative to the surface of the light-sensitive layer (2). By observing said minimum clearance, the Fresnel diffraction images of both light beams (3, 4) are separated on the edge(7). The thickness of the light-sensitive layer (2) is selected in such a way that the superimposition of the Fresnel diffraction pattern of one light beam with the other undisturbed light beam suffices to uncover areas of the substrate (1) during subsequent developing of the layer (2). The method makes it possible to avoid transfer of unwanted diffraction effects on the edge of the shadow mask to the substrate. The method provides a cost-effective solution for the production of large-surface coupling grating matrices.

Claims

1. A method for producing a coupling grating for a waveguide utilizing interference lithography, in which a light-sensitive layer (2) on a substrate (1) is exposed with an interference pattern by superimposing two coherent light beams (3,4) and said light-sensitive layer (2) is subsequently developed, the regions of said substrate (1) which said development laid bare or nearly laid bare are subjected to an etching process and said light-sensitive layer (2) is then removed from said substrate,

wherein,

to set the outer boundaries of said to-be-produced coupling grating (5) during said exposure, a shadow mask (6) is disposed while maintaining a minimum distance d_min from the surface of said light-sensitive layer (2), said distance permitting a spatial separation of the Fresnel diffraction patterns of the two light beams (3,4) on the surface due to an inner edge (7) of said shadow mask (6), with the thickness of said light-sensitive layer (2) being selected in such a manner that said superimposition of said Fresnel diffraction pattern of one said light beam with the undisturbed other said light beam (3,4) for exposure of said light-sensitive layer (2) just suffices to be able to etch regions of said substrate (1) following said subsequent development of said layer (2).

2. A method according to claim 1,

wherein,

said minimum distance d_min is selected in such a manner that the relationship

$d_{\min }\ge$

2tan2

θ

i·

λ

0

is fulfilled, with λ

₀ standing for the central wavelength and θ

_i for the, if required averaged, angle of incidence of said two light beams.

3. A method according to claim 1 or 2,

wherein,

a photoresist layer is utilized as said light-sensitive layer (2).

4. A method according to one of the claims 1 to 3,

wherein,

said distance of said shadow mask (6) from said surface of said light-sensitive layer (2) is altered during said exposure of said layer (2).

5. A method according to one of the claims 1 to 4,

wherein,

a shadow mask (6) having one or a plurality of slot-shaped mask openings (8) is utilized.

6. A method according to one of the claims 1 to 5,

wherein,

a shadow mask (6) is utilized whose inner edges (7), which are to effect setting the boundaries of said coupling grating parallel to the grating lines, are designed as cuttings edges having a cutting angle α

in relation to a main surface of said shadow mask, said cutting angle fulfilling the condition θ

_i+2α

≦

90°

, with θ

_i being the angle of incidence of the two light beams.

7. A method according to one of the claims 1 to 6,

wherein,

using a shadow mask (6) having a plurality of mask openings (8) disposed in a matrix manner produces a multiplicity of coupling gratings simultaneously on said substrate (1).

8. A method according to one of the claims 1 to 7,

wherein,

following removal of said light-sensitive layer (2) the substrate is coated with a waveguide layer the refraction index of which is higher than that of said substrate (1).

9. A method according to one of the claims 1 to 7,

wherein,

the substrate having one or a plurality of coupling gratings is utilized as an imprinting mask for producing further coupling gratings.

10. A device for carrying out the method according to one or a multiplicity of the preceding claims having a holding means for a substrate (1), a shadow mask (6), which can be set at a defined distance from the surface of a substrate (1) inserted in said holding means, as well as a source of coherent laser light having a beam splitting and beam widening optic as well as beam guiding elements in order to be able to superimpose two split beams (3, 4) at defined angles of incidence on the surface of a substrate (1) inserted in said holding means, with said shadow mask (6) being provided with mask openings (8) having edges (7) running perpendicular to the plane formed by said split beams (3, 4) and which are designed in a cutting-edge manner.

11. A device according to claim 10,

wherein,

a drive is provided with which said shadow mask (6) is moved perpendicular to the substrate surface during exposure.

12. A device according to claim 10 or 11,

wherein said shadow mask (6) is provided with one or a plurality of slot-shaped mask openings (8).