Free-space optical communication using Hermite-Gaussian modes
View Patent ↗Aspects of the present disclosure describe systems, methods, and structures for free-space optical communications using Hermite-Gaussian modes resulting in advantageous performance over prior art systems particularly with respect to lateral misalignment.
1. A free-space optical communications system comprising:
a data transmitter;
a data receiver; and
a free-space channel optically connecting the data transmitter to the data receiver;
the data transmitter including:
N-lasers that generate N-laser beams;
N-modulators that modulate the N-laser beams producing N-data streams;
a mode multiplexer that converts the N-data streams into N-Hermite-Gaussian modes and combine them into a single laser beam for transmission over the free-space channel to the data receiver;
wherein the N-Hermite-Gaussian modes are spatial patterns of light that are perpendicular to the light's direction of propagation;
wherein the spatial patterns are solutions to an electromagnetic wave equation in rectangular coordinates (x, y, z), and at z=0, and amplitudes of Herrnite-Gaussian modes are given by the equation:
HG
mn
(
x
,
y
)
=
c
mn
H
m
(
x
2
w
)
H
n
(
y
2
w
)
exp
(
-
x
2
-
y
2
w
2
)
,
where c mn are normalized coefficients, H m ( . . . ) and H n ( . . . ) are Hermite polynomials, w is a waist size of the modes, and m and n are indices of the Hermite-Gaussian modes corresponding to the x and y directions, respectively, where m, n=0,1, 2, . . . ;
wherein the N-Hermite-Gaussian modes are a special subset of the Hermite-Gaussian modes and are given by the equation:
[HG m0 (x,y), HG 0n (x,y)],
where the indices of each Hermite-Gaussian mode are given by m=0 and n≠0 or, m≠0 and n=0; and
wherein N is greater than 2.
2. The system of claim 1 wherein the free-space channel includes one or more selected from the group consisting of: an Earth's atmosphere, and outer space.
3. The system of claim 1 wherein the free-space channel introduces a lateral misalignment in the N-Hermite-Gaussian modes.
4. The system of claim 3 wherein the lateral misalignment in the N-Hermite-Gaussian modes is due to atmospheric turbulence or mechanical movement of the data transmitter and/or data receiver.
5. The system of claim 1 wherein the N-Hermite-Gaussian modes are conveyed via the free-space channel as N-data signals.
6. The system of claim 1 wherein the data receiver includes N receiver photodiodes.
7. The system of claim 1 where the mode multiplexer of the data transmitter comprises one selected from the group consisting of: liquid crystal spatial light modulators, digital micromirror spatial light modulators, photonic lanterns, core to core optical fiber coupling, multi-plane light conversion, and liquid crystal q-plates.
8. The system of claim 1 wherein a mode multiplexer of the data receiver comprises one selected from the group consisting of liquid crystal spatial light modulators, digital rnicromirror spatial light modulators, photonic lanterns, core to core optical fiber coupling, multiplane light conversion, and liquid crystal q-plates.
9. The system of claim 1 where at least one of the data transmitter and the data receiver are mounted on an unmanned aerial vehicle, selected from the group consisting of: aerial balloons, satellites, drones, helicopter drones.
10. The system of claim 1 wherein the N-data streams are transmitted only via Herrnite-Gaussian modes.
11. The system of claim 1 wherein the data receiver and the data transmitter are mis-aligned.
12. A free-space optical communications method comprising:
generating, through the effect of N-lasers, N-laser beams;
modulating, through the effect of N-modulators, the N-laser beams to produce N-data streams;
converting, through the effect of a mode multiplexer, the N-data streams into N-Hermite-Gaussian modes and combining them into a single laser beam for transmission over a free-space channel to a data receiver; and
transmitting the N-data streams via the N-Hermite-Gaussian modes to the data receiver;
wherein the N-Hermite-Gaussian modes are spatial patterns of light that are perpendicular to the light's direction of propagation;
wherein the spatial patterns are solutions to an electromagnetic wave equation in rectangular coordinates (x, y, z,), and at z=0, and amplitudes of Hermite-Gaussian modes are given by the equation:
HG
mn
(
x
,
y
)
=
c
mn
H
m
(
x
2
w
)
H
n
(
y
2
w
)
exp
(
-
x
2
-
y
2
w
2
)
,
where c mn , are normalized coefficients, H m ( . . . ) and H n ( . . . ) are Hermite polynomials, w is a waist size of the modes, and m and n are indices of the Hermite-Gaussian modes corresponding to the x and y directions, respectively, where m, n=0,1, 2, . . . ;
wherein the N-Hermite-Gaussian modes are a special subset of the Hermite-Gaussian modes and are given by the equation:
[HG m0 (x,y), HG 0n (x,y)],
where the indices of each Hermite-Gaussian mode are given by m=0 and n≠0 or, m≠0 and n=0; and
wherein N is greater than 2.
13. The method of claim 12 wherein the N-data streams are transmitted exclusively via the N-Hermite-Gaussian modes.