Method of producing a diffraction grating element
An optical diffraction grating ( 10 ) is produced by providing a mold ( 50 ) having a plurality of inclined grooves ( 58 ), which have a small clearance angle (γ). The mold ( 50 ) is covered by a curable material (M 1 ). Said material is subsequently cured, i.e. hardened, and separated from the mold ( 50 ) to provide the diffraction grating ( 10 ). The inclined orientation of the grooves ( 58 ) allows expansion or contraction of the grating during the curing and separation steps such that the probability of mold breakage may be reduced. The inclined orientation of the grooves may also facilitate the separation of the grating ( 10 ) from the mold ( 50 ).
1. A method of producing a diffraction grating by using a mold, which mold has a plurality of adjacent microscopic grooves, the inclination (φ) of said grooves being greater than or equal to 20 degrees and smaller than or equal to 70 degrees with respect to the normal (N) of the plane of the mold, the depth (h) of the grooves being greater than or equal to 0.4 times the grating period of the mold, the grating period of said mold being greater than or equal to 0.2 μm and smaller than or equal to 10 μm, and the clearance angle (γ) of said grooves being greater than or equal to 5 degrees and smaller than or equal to 20 degrees,
said method comprising at least:
applying an anti-adhesion layer to said mold to facilitate separation of the diffraction grating from said mold,
applying curable substance to said mold,
curing said substance at least partially to produce the diffraction grating, and
separating said diffraction grating from said mold.
2. The method according to claim 1 , wherein the inclination (φ) of said grooves is greater than or equal to 25 degrees and smaller than or equal to 45 degrees with respect to the normal (N) of the plane of the mold.
3. The method according to claim 1 , wherein the clearance angle (γ) of said grooves is greater than or equal to 5 degrees and smaller than or equal to 12 degrees.
4. The method according claim 1 , wherein the filling factor (c 2 ) of the mold is greater than or equal to 0.2 and smaller than or equal to 0.8.
5. The method according to claim 1 , wherein the depth (h) of the grooves is greater than or equal to 0.6 times the grating period (d).
6. The method according to claim , wherein said substance is cured by heat.
7. The method according to claim 6 wherein said diffraction grating is separated from said mold when the temperature of the substance of the grating is greater than or equal to 50° C.
8. The method according to claim 1 wherein said substance is cured by UV radiation.
9. The method according to claim 1 wherein said diffraction grating is separated from said mold when the substance of the grating is in semi-hardened state.
10. The method according to claim 1 further comprising joining a substrate plate to said diffraction grating.
11. The method according to claim 10 wherein the diffraction grating is separated from said mold by directing a separating force to the corner and/or edge of said substrate plate.
12. The method according to claim 10 wherein said substrate plate is flexible.
13. The method according to claim 10 further comprising treating said substrate plate with an adhesion promoting agent.
14. The method according to claim 1 wherein said mold comprises at least a first groove having a first inclination (φ 1 ), and a second groove having a second inclination (φ 2 ), said first inclination (φ 1 ) being different from said second inclination (φ 2 ).
15. The method according to claim 1 wherein at least one area of the mold comprises curved and/or circular grooves.