Polarisation-independent, optical multiplexing and demultiplexing systems based on ferroelectric liquid crystal phase modulators for spatial mode division multiplexing and demultiplexing

Patent metadata

Field	Value
Publication number	US-10761392-B2
Application number	US-201515537485-A
Country	US
Kind code	B2
Filing date	Dec 16, 2015
Priority date	Dec 19, 2014
Publication date	Sep 1, 2020
Grant date	Sep 1, 2020

Abstract

We describe a multimode reconfigurable optical spatial mode multiplexing system having first and second first and second input beams and a beam combiner to combine these into an optical output. At least one of the paths comprises a polarisation-independent reconfigurable phase modulator to impose a controllable phase profile on an input beam in an input beam phase modulating optical path, to controllably convert a spatial mode order of the input beam from a lower to a higher order spatial mode. The system also has a control input to control the phase modulator to configure the phase profile for the mode conversion. The input beams are combined into a multiple spatial mode combined beam output independent of a polarisation of the input beams. The number of spatial modes of the combined beam can be more than a number of spatial modes in either of the first and second input beams separately.

First claim

The invention claimed is:

1. A multimode reconfigurable optical spatial mode multiplexing system, the system comprising:
a first optical path to carry a first input beam from a first optical input;
a second optical path to carry a second input beam from a second optical input;
a beam combiner to combine beams from said first and second optical paths and provide a combined beam optical output;
wherein at least one of said first and second optical paths is a phase modulating optical path and comprises a polarisation-independent reconfigurable phase modulator to impose a controllable phase profile on an input beam in the phase modulating optical path to controllably convert a spatial mode order of the input beam from a lower order spatial mode to a higher order spatial mode; and
further comprising a control input to control said polarisation-independent reconfigurable phase modulator to configure said controllable phase profile to alter said conversion of said spatial mode order of said input beam;
wherein said first and second input beams are combined into a multiple spatial mode combined beam fibre optical output independent of a polarisation of said first and second input beams;
wherein a number of spatial modes of said combined beam is controllable with said control input to increase a number of spatial modes in said combined beam to more than a number of spatial modes in either of said first and second input beams separately;
wherein said polarisation-independent reconfigurable phase modulator comprises a ferroelectric liquid crystal (FLC) spatial light modulator (SLM); and
wherein said ferroelectric liquid crystal (FLC) spatial light modulator (SLM) comprises exactly 4 pixels tiling an active area of the SLM, one in each quadrant of the modulator.

2. A system as claimed in claim 1 wherein said phase modulating optical path is arranged to carry a multiple polarisation beam, said multiple polarisation beam comprising two different polarisations; and
wherein the same or overlapping regions of said polarisation-independent reconfigurable phase modulator receive and modulate said two different polarisations of said multiple polarisation of beam.

3. A system as claimed in claim 1 wherein FLC SLM said has a switching angle of greater than 80°.

4. A system as claimed in claim 1 wherein at an operating wavelength, λ, of the device

sin
2

⁢
2
⁢
θs
⁢

⁢

in
2

⁢

k
⁢

⁢
Δ
⁢

⁢
nd

2

is greater than 0.5, where in 2θ is the switching angle of the FLC material in the SLM in a direction of light propagation through the SLM, and

k
=

2
⁢
π

λ

.

5. A system as claimed in any one of claim 1 wherein said optical output is couplable to a multimode optical fibre, wherein said pixels are responsive to said control input to configure said controllable phase profile, and wherein said phase profile is configurable to select one of a plurality of phase profiles each corresponding to a respective spatial LP mode of said multimode optical fibre.

6. A system as claimed in claim 5 further comprising a controller, responsive to a mode-select signal on said control input, to select one of said plurality of phase profiles and to control said FLC SLM to impose the selected phase profile on said beam in said phase modulating optical path such that at said optical output said beam has a spatial LP mode selected by said mode select signal.

7. A system as claimed in claim 1 wherein said controllable phase profile has four adjacent regions each switchable between a relative phase delay of 0 and a relative phase delay of π to convert an LP 01 spatial mode beam of any polarisation into an LP 11 beam of any polarisation.

8. A system as claimed in claim 1 wherein said controllable phase profile is configurable to alter said conversion of said spatial mode order of said input beam between no conversion of said spatial mode order from one spatial mode to another and conversion of said spatial mode order from a lower spatial mode to a higher spatial mode order in said combined beam spatial output.

9. A system as claimed in claim 1 further comprising a third optical path to carry a third input beam from a third optical input;
wherein each of said first, second and third optical paths comprises a respective said polarisation-independent reconfigurable phase modulator;
wherein said fibre optical output is arranged to couple to a fibre optic; and
wherein the system further comprises demagnifying optics between said beam combiner and said fibre optical output.

10. An optical communication system comprising the system of claim 1 , and a reconfigurable optical spatial mode demultiplexing system, the demultiplexing system comprising:
an optical input to receive a multimode optical input beam, comprising a plurality of different optical spatial modes;
a beam splitter to split said input beam into at least first and second split beams;
first and second optical outputs;
first and second optical paths between said beam splitter and respective said first and second optical outputs;
wherein at least one of said first and second optical paths is a phase modulating optical path and comprises a polarisation-independent reconfigurable phase modulator to impose a controllable phase profile on a split beam in the phase modulating optical path to controllably convert a spatial mode order of the split beam from a higher order spatial mode to a lower order spatial mode;
further comprising a control input to control said polarisation-independent reconfigurable phase modulator to configure said controllable phase profile to alter said conversion of said spatial mode order of said split beam;
wherein said polarisation-independent reconfigurable phase modulator comprises a ferroelectric liquid crystal (FLC) spatial light modulator (SLM); and
wherein said ferroelectric liquid crystal (FLC) spatial light modulator (SLM) comprises exactly 4 pixels tiling an active area of the SLM, one in each quadrant of the modulator;
the optical communication system further comprising:
a plurality of input optical fibres;
a plurality of output optical fibres;
an optical transmission system between said input optical fibres and said optical output fibres;
an optical spatial mode multiplexing system coupled between said plurality of input optical fibres and said optical transmission system, to encode optical signals on said input optical fibres into a plurality of different optical spatial modes on a multiplexed multimode optical fibre; and
an optical demultiplexing system coupled between said optical transmission system and said plurality of output optical fibres, to decode an optical spatial mode multiplexed signal on a

Assignees

• Cambridge Entpr Ltd

Inventors

• Chu Daping
• Yang Haining

Classifications

• G02F2203/06

  Polarisation independent · CPC title

• H04J14/021

  Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM] · CPC title

• G02F1/141 Primary

  using ferroelectric liquid crystals · CPC title

• G02F2203/12

  spatial light modulator · CPC title