Beam combiner and a combiner depolarizer
The invention relates to a beam combiner for a Raman pump unit. The beam combiner is configured to receive and propagate at least two orthogonally polarized collimated light beams. The beam combiner comprises a birefringent prism and an optically isotropic prism. Each of the prisms is located in the path of the beams and configured so that the beams are substantially parallel to each other when they emanate from the beam combiner.
1. A beam combiner depolarizer for a Raman pump unit, the beam combiner depolarizer configured to receive and propagate at least two orthogonally polarized collimated light beams, and comprising:
a beam combiner comprising a birefringent prism and an optically isotropic prism, each located in the path of the beams and configured so that the beams are substantially parallel to each other when they emanate from the beam combiner; and
a depolarizing birefringent prism, optically downstream of the beam combiner, wherein, an optical path length of the depolarizing birefringent prism varies across a diameter of each of the beams emanated from the beam combiner.
2. The beam combiner depolarizer according to claim 1 , wherein the birefringent prism and the optically isotropic prism are configured so that the beams are aligned when the beams emanate from the beam combiner.
3. The beam combiner depolarizer according to claim 1 , wherein the birefringent prism is configured to alter a relative angle between the beams such that the beams are substantially parallel when the beams emanate from the birefringent prism.
4. The beam combiner depolarizer according to claim 1 , wherein the isotropic prism is configured to decrease a spatial separation between the beams such that the beams substantially overlap in cross section when the beams emanate from the isotropic prism.
5. The beam combiner depolarizer according to claim 1 claim, wherein the isotropic prism is configured to maintain a relative angle between the beams.
6. The beam combiner depolarizer according to claim 1 , wherein the birefringent prism is configured to refract at least one of the beams by spatial walk-off.
7. The beam combiner depolarizer according to claim 6 , wherein an optical axis of the birefringent prism is angled with respect to a direction of propagation of the at least one beam as it enters the birefringent prism.
8. The beam combiner depolarizer according to claim 1 , wherein a face of the isotropic prism is angled to refract input beams.
9. The beam combiner depolarizer according to claim 1 , wherein the birefringent prism abuts the isotropic prism.
10. The beam combiner depolarizer according to claim 9 , wherein the birefringent and isotropic prisms are cemented together.
11. The beam combiner depolarizer according to claim 1 , wherein the birefringent prism is spaced apart from the isotropic prism.
12. The beam combiner depolarizer according to claim 11 , wherein an air gap between the birefringent prism and the isotropic prism is 1 mm or less.
13. The beam combiner depolarizer according to claim 1 , wherein beams output from the beam combiner are substantially co-axially aligned to each other.
14. The beam combiner depolarizer according to claim 1 , wherein the optical axis of the depolarizing birefringent prism is substantially perpendicular to an optical axis of the birefringent prism of the beam combiner.
15. The beam combiner depolarizer according to claim 1 , wherein the depolarizing birefringent prism abuts the beam combiner.
16. The beam combiner depolarizer according to claim 1 , wherein the depolarizing birefringent prism is spaced apart from the beam combiner.
17. An optical assembly comprising a beam combiner depolarizer according to claim 1 , the optical assembly further comprising an input gradient index microlens optically upstream of the beam combiner and for collimating input beams.
18. The optical assembly according to claim 17 , wherein the beam combiner abuts the input gradient index microlens.
19. The optical assembly according to claim 18 wherein the beam combiner is cemented to the input gradient index microlens.
20. The optical assembly according to claim 17 , wherein the isotropic prism is optically upstream from the birefringent prism and is integrated into the input gradient index microlens.
21. The optical assembly according to claim 17 further comprising an output gradient index microlens optically downstream of the beam combiner and configured to focus the beams emanating from the beam combiner to a same focus point.