Optical spatial mode-multiplexer

1. An apparatus, comprising:

an optical fiber bundle comprising a plurality of input optical fibers and a tapered segment, one end of each of the input optical fibers physically connecting to a wide end of the tapered segment, the optical fiber bundle being an integral unit; and

wherein the input optical fibers are multimode optical fibers;

wherein fundamental optical propagating modes of at least two of the multimode optical fibers have different velocities; and

wherein the plurality of input optical fibers includes multi-mode optical fibers with axially symmetric optical cores of, at least, three different diameters.

2. The apparatus of claim 1 , one or more of the input optical fibers having an optical core with a radially graded refractive index profile.

3. The apparatus of claim 1 , wherein extensions of the input optical fibers in the tapered segment taper in diameter along the tapered segment.

4. The apparatus of claim 3 , wherein distances between the extensions decrease at distances farther from the wide end.

5. The apparatus of claim 1 , wherein distances between extensions of the input optical fibers in the tapered segment decrease at distances farther from the wide end.

6. The apparatus of claim 3 , wherein at least one of the input optical fibers has an optical core with a laterally graded index profile.

7. The apparatus of claim 1 , further comprising a multimode optical fiber whose end face is optically end-coupled to a nearby narrower end of the tapered segment.

8. An apparatus, comprising:

an optical fiber bundle comprising a plurality of input optical fibers and a tapered segment, one end of each of the input optical fibers physically connecting to a wide end of the tapered segment, the optical fiber bundle being an integral unit; and

wherein the input optical fibers are multimode optical fibers having axially symmetric cores;

wherein fundamental optical propagating modes of at least two of the multimode optical fibers have different velocities; and

wherein the apparatus further comprises an optical transmitter having an array of optical data modulators, optical outputs of the optical data modulators being optically coupled to the input optical fibers.

9. The apparatus of claim 8 , wherein at least one of the input optical fibers has an optical core with a radially graded refractive index profile.

10. An apparatus, comprising:

an optical fiber bundle comprising a plurality of input optical fibers and a tapered segment, one end of each of the input optical fibers physically connecting to a wide end of the tapered segment, the optical fiber bundle being an integral unit; and

wherein the input optical fibers are multimode optical fibers having axially symmetric optical cores;

wherein fundamental optical propagating modes of at least two of the multimode optical fibers have different velocities; and

wherein the apparatus further comprises an optical receiver having an array of optical data demodulators, optical inputs of the optical data demodulators being optically coupled to the input optical fibers.

11. The apparatus of claim 10 , wherein at least one of the input optical fibers has an optical core with a radially graded refractive index profile.

12. An apparatus, comprising:

an optical fiber bundle comprising a plurality of input optical fibers and a tapered segment, one end of each of the input optical fibers physically connecting to a wide end of the tapered segment, the optical fiber bundle being an integral unit; and

wherein the input optical fibers are multimode optical fibers having axially symmetric optical cores;

wherein fundamental optical propagating modes of at least two of the multimode optical fibers have different velocities; and

wherein the apparatus further comprises an optical device having first and second Mx1 optical spatial mode multiplexers and M optical processing units, each optical processing unit optically coupling a corresponding optical input of one of the Mx1 optical spatial mode multiplexers to a corresponding optical input of the other of the Mx1 optical spatial mode multiplexers, one of the Mx1 optical spatial mode multiplexers including the optical fiber bundle.

13. The apparatus of claim 12 , wherein some of the optical processing units are configured to correct for differential group delay between different optical spatial modes.

14. The apparatus of claim 12 , wherein at least one of the input optical fibers has an optical core with a radially graded refractive index profile.

15. The apparatus of claim 8 , wherein the plurality of input optical fibers includes multi-mode optical fibers with optical cores of, at least, three different diameters.

16. The apparatus of claim 10 , wherein the plurality of input optical fibers includes multi-mode optical fibers with optical cores of, at least, three different diameters.

17. The apparatus of claim 12 , wherein the plurality of input optical fibers includes multi-mode optical fibers with optical cores of, at least, three different diameters.