Free-space optical communication system using a backchannel for power optimization

1. A device comprising:

an optical modulator configured to generate an optical beam, wherein the optical beam encodes network data and has a beam intensity, a beam direction and a carrier frequency;

an optical power amplifier configured to adjust a transmitted power of the optical beam;

a transmit beam angle mechanism, configured to:

adjust the beam direction; and

transmit the optical beam to a remote receiver over a free-space optical link; and

a controller, configured to:

receive backchannel data from the remote receiver comprising a received power, a bit error rate, and a carrier frequency offset between local oscillator frequencies used by the device and the remote receiver; and

modify a plurality of characteristics of the optical beam based on the backchannel data, the plurality of characteristics comprising:

adjustment of the beam intensity to maintain the bit error rate at a level that is correctable by the remote receiver while not further increasing the beam intensity; and

adjustment of the carrier frequency to reduce the carrier frequency offset,

wherein the carrier frequency offset is a difference between a local oscillator frequency of the device and a second local oscillator frequency of the remote receiver and is minimized to reduce the transmitted power of the optical beam for the bit error rate.

2. The device of claim 1 , wherein the controller comprises at least one of a transmit frequency controller configured to adjust the carrier frequency, a transmit power controller, or a transmit beam angle controller.

3. The device of claim 1 , wherein:

the controller comprises a transmit power controller configured to modify a beam power of the optical beam based on the received power of the optical beam by the remote receiver.

4. The device of claim 1 , wherein:

the controller comprises a transmit beam angle controller configured to adjust the beam direction of the optical beam using the transmit beam angle mechanism based on the backchannel data.

5. The device of claim 1 , wherein the free-space optical link is bidirectional, and the device is configured to receive the backchannel data over the free-space optical link.

6. The device of claim 1 , wherein the backchannel data includes a beam pointing error determined by the remote receiver.

7. The device of claim 1 , wherein the device is configured to receive the backchannel data over a radio-frequency link.

8. A device comprising:

an optical amplifier, configured to receive an optical beam from a remote transmitter over a free-space optical link;

an optical demodulator, configured to demodulate the optical beam and generate network data from the optical beam; and

a terminal controller, configured to:

determine at least one characteristic of the optical beam; and

transmit backchannel data to the remote transmitter including the at least one characteristic of the optical beam, wherein the backchannel data comprises a received power, a bit error rate, and a carrier frequency offset between local oscillator frequencies used by the device and the remote transmitter; and

wherein the device is further configured to:

transmit a second optical beam to the remote transmitter; and

receive remote backchannel data from the remote transmitter, and based on the remote backchannel data:

adjust a second beam intensity of the second optical beam to maintain a second bit error rate that is correctable by the remote transmitter while not further increasing the beam intensity; and

adjust a second carrier frequency of the second optical beam to reduce the carrier frequency offset, wherein:

the carrier frequency offset is a difference between a local oscillator frequency of the device and a second local oscillator frequency of the remote receiver and is minimized to reduce the transmitted power of the optical beam for the bit error rate.

9. The device of claim 8 , wherein the free-space optical link is bidirectional, and the device is configured to transmit the backchannel data to the remote transmitter over the free-space optical link.

10. The device of claim 8 , wherein the device is configured to determine a beam pointing error from the received power of the optical beam, and the at least one characteristic of the optical beam includes the beam pointing error.

11. The device of claim 8 , wherein the device is configured to transmit the backchannel data to the remote transmitter over a radio-frequency link.

12. The device of claim 8 , wherein:

the remote backchannel data comprises remote received power.

13. A method, comprising:

receiving, at a communication terminal, a communication signal over a free-space optical link from a remote communication terminal;

determining, at the communication terminal, at least one characteristic of the communication signal;

transmitting, from the communication terminal to the remote communication terminal, backchannel data including an indication of the at least one characteristic of the communication signal, wherein the backchannel data comprises a received power, a bit error rate, and a carrier frequency offset between a local oscillator frequencies used by the communication terminal and the remote communication terminal; and

modifying, at the remote communication terminal, the communication signal based on the backchannel data, wherein:

the communication signal comprises an optical beam;

modifying the communication signal comprises:

adjustment of a beam intensity of the optical beam to maintain the bit error rate at a value that is correctable by the communication terminal while not further increasing the beam intensity; and

adjustment of the carrier frequency of the optical beam to reduce a carrier frequency offset between the communication terminal and the remote communication terminal; and

the carrier frequency offset is a difference between a local oscillator frequency of the device and a second local oscillator frequency of the remote receiver and is minimized to reduce the transmitted power of the optical beam for the bit error rate.

14. The method of claim 13 , further comprising correcting, by the communication terminal, bit errors using forward error correction.

15. The method of claim 13 , wherein modifying, at the remote communication terminal, the communication signal based on the backchannel data comprises adjusting a beam carrier frequency of the free-space optical link to reduce the carrier frequency offset.