Optical wavelength diversity techniques for free-space optical communication
A free-space optical communication terminal includes a first transmitter configured to transmit data using a first light beam in a short-wavelength infrared band (e.g., around 1.5 μm), a second transmitter configurable to transmit data using a second light beam in a mid-wavelength or long-wavelength infrared band (e.g., around 10 μm), an optical multiplexer coupled to the first transmitter and the second transmitter and configured to multiplex the first light beam and the second light beam into a multiplexed light beam, and a reflective optical antenna configured to transmit the multiplexed light beam into atmosphere. In some implementations, the reflective optical antenna includes one or more telescopes formed by mirrors, and the mirrors are characterized by a reflective band covering at least the short-wavelength infrared band and the long-wavelength infrared band.
1 . A free-space optical communication terminal comprising:
a first transmitter configured to transmit data using a first light beam in a short-wavelength infrared band;
a second transmitter configurable to transmit data using a second light beam in a mid-wavelength or long-wavelength infrared band;
an optical multiplexer coupled to the first transmitter and the second transmitter and configured to multiplex the first light beam and the second light beam into a multiplexed light beam; and
a reflective optical antenna configured to transmit the multiplexed light beam into atmosphere.
2 . The free-space optical communication terminal of claim 1 , wherein:
the first light beam is characterized by wavelengths around 1.5 μm; and
the second light beam is characterized by wavelengths around 10 μm.
3 . The free-space optical communication terminal of claim 1 , wherein:
the reflective optical antenna comprises one or more telescopes formed by mirrors; and
the mirrors are characterized by a reflective band covering at least the short-wavelength infrared band and the long-wavelength infrared band.
4 . The free-space optical communication terminal of claim 1 , further comprising a controller configure to:
in response to determining that a transmission loss of the first light beam in the atmosphere is greater than a threshold, activate the second transmitter; and
in response to determining that the transmission loss of the first light beam in the atmosphere is at or below the threshold, deactivate the second transmitter.
5 . The free-space optical communication terminal of claim 1 , further comprising a deformable mirror configured to scan and/or modify a wavefront of the multiplexed light beam before the multiplexed light beam is transmitted by the reflective optical antenna into the atmosphere.
6 . The free-space optical communication terminal of claim 5 , wherein the deformable mirror is characterized by a reflective band covering the short-wavelength infrared band and the long-wavelength infrared band.
7 . The free-space optical communication terminal of claim 1 , wherein the reflective optical antenna comprises a Cassegrain telescope.
8 . The free-space optical communication terminal of claim 7 , wherein the reflective optical antenna further comprises a second reflective telescope configured to magnify the multiplexed light beam.
9 . The free-space optical communication terminal of claim 1 , wherein the first transmitter comprises:
a plurality of transmitters configured to transmit data using light in respective sub-bands of the short-wavelength infrared band; and
a wavelength-division multiplexer configured to multiplex the light in the respective sub-bands of the short-wavelength infrared band.
10 . The free-space optical communication terminal of claim 1 , wherein the second transmitter comprises:
a plurality of transmitters configured to transmit data using light in respective sub-bands of the mid-wavelength or long-wavelength infrared band; and
a wavelength-division multiplexer configured to multiplex the light in the respective sub-bands of the mid-wavelength or long-wavelength infrared band.
11 . A free-space optical communication terminal, comprising:
a reflective optical antenna configured to receive a laser beam from atmosphere through a first aperture, the laser beam including at least a first light beam in a short-wavelength infrared band and a second light beam in a mid-wavelength or long-wavelength infrared band;
a deformable mirror configurable to correct aberrations of the received laser beam;
a power selector configurable to split the received laser beam into the first light beam and the second light beam;
a wavefront sensor configured to measure a wavefront profile of the first light beam;
a controller configured to control the deformable mirror to correct the aberrations of the received laser beam based on the wavefront profile of the first light beam measured by the wavefront sensor;
an optical demultiplexer configured to demultiplex the first light beam and the second light beam;
a first optical receiver configured to receive the first light beam from the optical demultiplexer and demodulate data transmitted in the light in the short-wavelength infrared band; and
a second optical receiver configured to receive the second light beam from the optical demultiplexer and demodulate data transmitted in the light in the mid-wavelength or long-wavelength infrared band.
12 . The free-space optical communication terminal of claim 11 , wherein:
the light in the short-wavelength infrared band is characterized by wavelengths around 1.5 μm; and
the light in the mid-wavelength or long-wavelength infrared band is characterized by wavelengths around 10 μm.
13 . The free-space optical communication terminal of claim 11 , wherein the wavefront sensor includes a Shack-Hartmann wavefront sensor.
14 . The free-space optical communication terminal of claim 13 , wherein:
the Shack-Hartmann wavefront sensor is sensitive to light in the short-wavelength infrared band but not sensitive to light in the mid-wavelength or long-wavelength infrared band; and
the controller is configured to correct aberrations of the light in the mid-wavelength or long-wavelength infrared band based on the wavefront profile of the first light beam measured by the Shack-Hartmann wavefront sensor using the light in the short-wavelength infrared band measured.
15 . The free-space optical communication terminal of claim 11 , wherein the wavefront sensor includes a holographic optical element and a camera sensitive to light in the mid-wavelength or long-wavelength infrared band.
16 . The free-space optical communication terminal of claim 11 , wherein the controller is configured to control the deformable mirror to correct residual aberrations in the light in the long-wavelength infrared band using a stochastic parallel gradient descent (SPGD) algorithm, a statistical historic data-based method, a machine-learning model, a model-based method, or a model-free method.
17 . The free-space optical communication terminal of claim 11 , wherein the first optical receiver comprises:
a wavelength-division multiplexer configured to demultiplex the light in the short-wavelength infrared band into a plurality of sub-bands; and
a plurality of optical receivers configured to receive light in respective sub-bands of the plurality of sub-bands.
18 . The free-space optical communication terminal of claim 11 , wherein the second optical receiver comprises:
a wavelength-division multiplexer configured to demultiplex the light in the mid-wavelength or long-wavelength infrared band into a plurality of sub-bands; and
a plurality of optical receivers configured to receive light in respective sub-bands of the plurality of sub-bands.
19 . A free-space optical communication terminal comprising:
a first transceiver configured to transmit and/or receive data using light in a short-wavelength infrared band;
a second transceiver configured to transmit and/or receive data using light in a mid-wavelength or long-wavelength infrared band;
an optical multiplexer coupled to the first transceiver and the second transceiver, the optical multiplexer configured to:
multiplex the light in the short-wavelength infrared band from the first transceiver and the light in the mid-wavelength or long-wavelength infrared band from the second transceiver into a multiplexed light beam; and
demultiplex light in a light beam received from atmosphere into light in the short-wavelength infrared band and light in the mid-wavelength or long-wavelength infrared band; and
a reflective optical antenna configured to receive the light beam from the atmosphere and/or transmit the multiplexed light beam into the atmosphere.
20 . The free-space optical communication terminal of claim 19 , further comprising a deformable mirror configured to modify wavefront of the multiplexed light beam or the light beam received from the atmosphere, the deformable mirror characterized by a reflective band covering the short-wavelength infrared band to the long-wavelength infrared band.