Optical communication method and system

Patent metadata

Field	Value
Publication number	US-10819461-B2
Application number	US-201615750959-A
Country	US
Kind code	B2
Filing date	Aug 5, 2016
Priority date	Aug 7, 2015
Publication date	Oct 27, 2020
Grant date	Oct 27, 2020

Abstract

The invention relates to optical communication methods and systems. In particular, the invention relates to an optical communication method and system which is configured to create a multiplexed beam from an incident beam, wherein the multiplexed beam comprises a predetermined number of spatial modes simultaneously generated and multiplexed together in a fashion that is independent of wavelength. The spatial modes have two degrees of spatial freedom. The multiplexed beam is de-multiplexed downstream from multiplexing thereof in the communication system in a simultaneous fashion independent of wavelength to yield the predetermined number of spatial mode. The modes are used in optical communication as channels or as bits in a bit (de) encoding scheme.

First claim

The invention claimed is:

1. A method of optical communication, wherein the method comprises:
receiving at least one incident light beam having one or more wavelengths;
acting on the received at least one incident light beam with a first optical element to create a single multiplexed light beam comprising a multiplex of a predetermined number of spatial modes per one or more wavelengths of the received at least one incident light beam in a manner which is independent of the one or more wavelengths of the received at least one incident light beam, wherein each of the predetermined number of spatial modes have at least two spatial degrees of freedom; and
using the single multiplexed light beam for optical communication wherein the predetermined number of spatial modes are used as one or both of carrier channels and bits in a bit coding scheme, wherein the first optical element comprises a single hologram operable to generate the predetermined number of spatial modes irrespective of the one or more wavelengths of the received at least one incident light beam, wherein the single hologram is a superposition of a plurality of holograms, wherein each of the plurality of holograms has a different carrier frequency corresponding to each of the predetermined number of modes, and wherein each different carrier frequency has a substantially saw-tooth shaped phase function.

2. The method as claimed in claim 1 , wherein the method comprises acting on the single multiplexed light beam with the first optical element to:
create the predetermined number of spatial modes, each having two degrees of spatial freedom, wherein the two spatial degrees of freedom is two degrees of freedom in spatial pattern; and
apply a phase gradient to each of the spatial modes during creation thereof resulting in a grating; and
use only a first order of diffraction for creating the predetermined number of spatial modes.

3. The method as claimed in claim 1 , further comprising selecting the two spatial degrees of freedom from a group comprising radial and azimuthal indices of Laguerre Gaussian beams, and X and Y axis indices of Hermite-Gaussian beams in Cartesian symmetry.

4. The method as claimed in claim 1 , further comprising receiving the at least one incident light beam in the form of a data carrying light beam.

5. The method as claimed in claim 1 , further comprising complex-amplitude modulating the received at least one incident light beam with the first optical element to create the single multiplexed light beam in a manner that is mode selective but independent of the wavelength of the received at least one incident light beam.

6. The method as claimed in claim 1 , wherein each mode and wavelength of the single multiplexed light beam is spatially separate in the Fourier plane.

7. The method as claimed in claim 1 , further comprising transmitting the single multiplexed light beam across an optical channel selected from a group comprising one or more optical fiber/s and free space.

8. The method as claimed in claim 1 , wherein the first optical element is selected from a group consisting of a diffractive optical element, an aspherical optical element, and a phase only spatial light modulator.

9. The method as claimed in claim 1 , further comprising:
receiving the single multiplexed light beam;
acting on the received single multiplexed light beam with a second optical element to de-multiplex the received single multiplexed light beam to constituent spatially separate modes in a simultaneous fashion independent of the associated wavelength(s) thereof; and
using the de-multiplexed modes as one or both of carrier channels and bits in a bit coding scheme.

10. The method as claimed in claim 9 , further comprising complex-amplitude modulating the received at least one incident light beam with the second first optical element to de-multiplex the single multiplexed light beam in a manner that is mode selective but independent of the wavelength(s) of the single multiplexed light beam.

11. The method as claimed in claim 9 , wherein the second optical element is selected from a group consisting of a diffractive optical element, an aspherical optical element, and a phase only spatial light modulator.

12. The method as claimed in claim 9 , wherein the second optical element comprises a single hologram to de-multiplex the received single multiplexed light beam, wherein the single hologram is a superposition of a plurality of holograms corresponding to the predetermined number of modes, wherein each hologram of the plurality of holograms has a spatial frequency matched to spatially separate a particular mode from the single multiplexed light beam irrespective of the wavelength(s) of the single multiplexed light beam, wherein each spatial frequency has a substantially saw-tooth shaped phase function.

13. The method as claimed in claim 9 , further comprising transmitting the single multiplexed beam from the first optical element to the second optical element.

14. The method as claimed in claim 9 , wherein the method comprises the step of modal decomposition, wherein modal weightings of the de-multiplexed modes are determined so as to detect a signal for each mode.

15. The method as claimed in claim 1 , further comprising one or both of the steps of:
adjusting a phase function for each mode to correct for distortions and aberrations;
and
applying a linear grating across each mode and use only a first diffraction order thereof for each of the predetermined number of modes.

16. A method of optical communication, further comprising:
receiving a single multiplexed light beam comprising a multiplex of a predetermined number of spatial modes per one or more wavelengths, wherein each of the predetermined number of spatial modes per one or more wavelengths have at least two spatial degrees of freedom;
acting on the received single multiplexed light beam with a second optical element to de-multiplex the received single multiplexed light beam to constituent spatially separate de-multiplexed spatial modes in a simultaneous fashion and independent of the wavelength(s); and
use the spatially separate de-multiplexed spatial modes as one or both of carrier channels and bits in a bit coding scheme, wherein the second optical element comprises a single hologram to de-multiplex the received single multiplexed light beam, wherein the single hologram is a superposition of a plurality of holograms corresponding to the predetermined number of spatial modes, wherein each hologram of the plurality of holograms has a spatial frequency matched to spatially separate a particular spatially separate de-multiplexed mode from the single multiplexed light beam irrespective of the wavelength(s) of the multiplexed light beam, wherein each spatial frequency has a substantially saw-tooth shaped phase function.

17. The method as claimed in claim 16 , further comprising the step of modal decomposition, wherein modal weightings of the de-multiplexed modes are determined so as to detect a signal for each mode.

18. An optical communication system, wherein the optical communication system comprises:
an optical transmitter comprising a first optical element, the optical transmitter being configured to:
receive at least one incident light beam having one or more wavelengths;
and
act on the received at least one incident light beam with the first optical element to create a single multiplexed light beam comprising a multiplex of a predetermined number of modes per one or more of the wavelengths of the received at least one incident light bea

Assignees

• Univ Johannesburg Witwatersrand
• Csir
• Univ Of The Witwaterstrand Johannesburg

Inventors

• Forbes Andrew
• Dudley Angela
• Guzmán Carmelo Guadalupe Rosales

Classifications

• H04B10/516 Primary

  Details of coding or modulation · CPC title

• H04J14/04 Primary

  Mode multiplex systems · CPC title

• H04J14/0201

  Add-and-drop multiplexing · CPC title

• H04J14/06

  Polarisation multiplex systems · CPC title

• H04B10/66

  Non-coherent receivers, e.g. using direct detection · CPC title