Zoned optical waveplate
View Patent ↗A zoned waveplate has a series of transversely stacked birefringent zones alternating with non-birefringent zones. The birefringent and non-birefringent zones are integrally formed upon an AR-coated face of a single substrate by patterning the AR coated face of the substrate with zero-order sub-wavelength form-birefringent gratings configured to have a target retardance. The layer structure of the AR coating is designed to provide the target birefringence in the patterned zones and the reflection suppression.
1. A zoned optical waveplate (ZWP) comprising:
a substrate that is transparent to light of a target wavelength λ; and
an anti-reflection (AR) structure disposed over the substrate, wherein
the AR structure comprises a series of zones, and
each zone, of the series of zones, comprises a sub-wavelength grating.
2. The ZWP of claim 1 , wherein the sub-wavelength grating is configured to provide a first target retardance for light of the target wavelength.
3. The ZWP of claim 1 , wherein two zones of the series of zones comprise different sub-wavelength gratings.
4. The ZWP of claim 1 , wherein a quantity of zones, of the series of zones, are spaced apart.
5. The ZWP of claim 1 , wherein the series of zones is repeated on the AR structure one or more times.
6. The ZWP of claim 1 , wherein the zones, of the series of zones, are arranged linearly.
7. The ZWP of claim 1 , wherein the AR structure comprises an AR coated face deposited over the substrate, a spacer layer, and an index matching layer deposited over the spacer layer.
8. The ZWP of claim 7 , wherein:
the AR coated face is an etch stop layer, and
wherein, in a particular zone of the series of zones, a plurality of parallel trenches extend through the spacer layer and to the etch stop layer.
9. The ZWP of claim 7 , wherein, in a particular zone of the series of zones, a plurality of gaps extend through the spacer layer and the index matching layer, thereby forming a surface-relief grating.
10. The ZWP of claim 1 , wherein the sub-wavelength grating is a first zero-order form-birefringent sub-wavelength (ZOFBSW) relief grating.
11. A method of fabricating an optical waveplate, the method comprising:
depositing an antireflection (AR) structure upon a substrate of optically transmissive material; and
defining, on the AR structure, a series of zones, including at least one patterned zone,
wherein the at least one patterned zone defines a sub-wavelength grating.
12. The method of claim 11 , wherein the sub-wavelength grating is configured to provide a first target retardance for light of a target wavelength.
13. The method of claim 11 , wherein two zones, of the series of zones, comprise different sub-wavelength gratings.
14. The method of claim 11 , wherein a quantity of zones, of the series of zones, are spaced apart.
15. The method of claim 11 , wherein the series of zones is repeated on the AR structure one or more times.
16. The method of claim 11 , wherein the zones, of the series of zones, are arranged linearly.
17. The method of claim 11 , wherein defining the series of zones includes:
forming a grating mask upon the AR structure comprising a plurality of parallel sub-wavelength strips defining a plurality of grating lines of the sub-wavelength grating;
forming a zone mask over the grating mask, the zone mask having a plurality of zone openings defining the series of zones;
forming a plurality of trenches within the series of zones; and
removing the grating mask and the zone mask.
18. The method of claim 11 , wherein depositing the AR structure includes:
depositing an etch-stop layer over the substrate;
depositing a spacer layer over the etch-stop layer; and
depositing an index matching layer over the spacer layer.
19. The method of claim 18 , wherein a plurality of gaps extend through the spacer layer and the index matching layer, thereby forming a surface-relief grating.
20. The method of claim 11 , wherein the sub-wavelength grating is a first zero-order form-birefringent sub-wavelength (ZOFBSW) relief grating.