Non-imaging lens assembly design for efficient power coupling from multimode fiber to small-area photodetectors
An optical communication device is provided that includes a first lens having a first surface and a second surface, a second lens having a third surface and a fourth surface, an optical fiber configured to output light including a plurality of ray bundles, and a photodetector located at the fourth surface of the second lens. The first lens is configured to cause the light output from the optical fiber to form an image at an image plane located at the third surface of the second lens. The second lens is configured to cause subsets of the ray bundles received at the third surface of the second lens to intersect or overlap at the photodetector in a smaller cross-sectional area than at the third surface of the second lens.
1. An optical communication device comprising:
a first lens having a first surface and a second surface;
a second lens having a third surface and a fourth surface;
an optical fiber configured to output light including a plurality of ray bundles; and
a photodetector located at the fourth surface of the second lens,
wherein:
the first lens is configured to cause the light output from the optical fiber to form an image at an image plane located at the third surface of the second lens; and
the second lens is configured to cause subsets of the ray bundles received at the third surface of the second lens to intersect or overlap at the photodetector in a smaller cross-sectional area than at the third surface of the second lens.
2. The optical communication device of claim 1 , wherein the first lens is configured to receive the light output from the optical fiber, and
wherein a diameter of the first lens is at least 2 tan(θ)d, where θ is a numerical aperture of the optical fiber and d is a distance between an output plane of the optical fiber and the first lens.
3. The optical communication device of claim 1 , wherein the second lens is configured to receive the light output from the first lens and to output light having a cross-sectional area at the fourth surface of the second lens that is smaller than a cross-sectional area at the first surface of the first lens.
4. The optical communication device of claim 1 , wherein the first surface is a first convex surface, the second surface is a second convex surface, the third surface is a third convex surface, and the fourth surface is a fourth planar surface.
5. The optical communication device of claim 1 , wherein the fourth surface is positioned at a focal length of the second lens.
6. The optical communication device of claim 5 , wherein the second lens has a thickness between the third surface and the fourth surface that is equal to the focal length of the second lens.
7. The optical communication device of claim 1 , wherein the optical communication device is configured for free-space optical communication.
8. A method of processing an optical signal, the method including:
outputting, by an optical fiber, light including a plurality of ray bundles through a first lens having a first surface and a second surface, and a second lens having a third surface and a fourth surface;
causing, by the first lens, the light output from the optical fiber to form an image at an image plane located at the third surface of the second lens; and
causing, by the second lens, subsets of the ray bundles received at the third surface of the second lens to intersect or overlap at a photodetector located at the fourth surface of the second lens in a smaller cross-sectional area than at the third surface of the second lens.
9. The method of claim 8 , further comprising receiving, at the first lens, the light output from the optical fiber,
wherein a diameter of the first lens is at least 2 tan(θ)d, where θ is a numerical aperture of the optical fiber and d is a distance between an output plane of the optical fiber and the first lens.
10. The method of claim 8 , further comprising receiving, at the second lens, the light output from the first lens; and
outputting, from the second lens, light having a cross-sectional area at the fourth surface of the second lens that is smaller than a cross-sectional area at the first surface of the first lens.
11. The method of claim 8 , wherein the first surface is a first convex surface, the second surface is a second convex surface, the third surface is a third convex surface, and the fourth surface is a fourth planar surface.
12. The method of claim 11 , wherein the fourth surface is positioned at a focal length of the second lens.
13. The method of claim 12 , wherein the second lens has a thickness between the third surface and the fourth surface that is equal to the focal length of the second lens.
14. The method of claim 8 , further comprising deriving, by one or more processors, data from the light received at the photodetector.
15. An optical transceiver comprising:
an optical fiber configured to receive and transmit light;
a lens system including a first lens having a first surface and a second surface, and a second lens having a third surface and a fourth surface;
a photodetector located at the fourth surface of the second lens, the photodetector configured to receive the light and convert the received light into an electrical signal using a photoelectric effect; and
one or more processors configured to use the photodetector to derive data from the received light,
wherein the lens system is positioned between the optical fiber and the photodetector,
wherein the received light converges as it passes through the first lens due to a greater refractive index of the first lens and a curvature of the first lens,
wherein light output from the optical fiber includes a plurality of ray bundles, and
wherein subsets of the ray bundles received at the third surface of the second lens to intersect or overlap at the photodetector in a smaller cross-sectional area than at the third surface of the second lens.
16. The optical transceiver of claim 15 , wherein the first lens is configured to receive the light output from the optical fiber, and
wherein a diameter of the first lens is at least 2 tan(θ)d, where θ is a numerical aperture of the optical fiber and d is a distance between an output plane of the optical fiber and the first lens.
17. The optical transceiver of claim 15 , wherein the second lens is configured to receive the light output from the first lens and to output light having a cross-sectional area at the fourth surface of the second lens that is smaller than a cross-sectional area at the first surface of the first lens.
18. The optical transceiver of claim 17 , wherein the first surface is a first convex surface, the second surface is a second convex surface, the third surface is a third convex surface, and the fourth surface is a fourth planar surface.
19. The optical transceiver of claim 18 , wherein the fourth surface is positioned at a focal length of the second lens.
20. The optical transceiver of claim 19 , wherein the second lens has a thickness between the third surface and the fourth surface that is equal to the focal length of the second lens.