# US 10,122,457 B2 · Optical amplifier with closed loop control for scintillation compensation in free space optical communications > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,122,457 B2 - Document ID: US10122457B2 - Status: Granted - Kind: B2 - Application number: 15/629,208 - Filed: 2017-06-21 - Published: 2017-10-05 - Granted: 2018-11-06 - Earliest claimed: 2015-08-05 - Assignees: X Development LLC - Applicants: X Development LLC - Inventors: Chiachi Wang; Christopher Joshua Shiro Ito - Web page: https://patentgrep.com/patent/US10122457B2 ## CPC - H04B 10/118: specially adapted for satellite communication - H04B 10/1125: {using a single common optical path} - H04B 10/1129: {Arrangements for outdoor wireless networking of information} - H04B: TRANSMISSION ## Abstract A method includes receiving a first optical signal at a first communication terminal from a second communication terminal through a free space optical link and determining a receiving power for the optical link based on the first optical signal. The method further includes adjusting an output amplification at the first communication terminal based on the receiving power for the optical link. The output amplification is adjusted to provide a second optical signal with a minimum transmission power for maintaining the optical link. The method transmits the second optical signal from the first communication terminal to the second communication terminal through the optical link. ## Claims ### Claim 1 A method comprising: receiving, at a first communication terminal, a first optical signal from a second communication terminal through a free space optical link, the first optical signal comprising a laser diode signal from a laser diode of the second communication terminal through the free space optical link; filtering, at the first communication terminal, the laser diode signal from the first optical signal; determining, by control hardware of the first communication terminal, a received power of the laser diode signal that is filtered from the first optical signal; determining, by the control hardware, a receiving power for the free space optical link based on the received power of the laser diode signal; adjusting, by the control hardware, an output amplification at the first communication terminal based on the receiving power for the free space optical link, the output amplification adjusted to provide a second optical signal with a minimum transmission power for maintaining the free space optical link; and transmitting the second optical signal from the first communication terminal to the second communication terminal through the free space optical link. ### Claim 2 (depends on 1) The method of claim 1, wherein determining the receiving power for the free space optical link is also based on an error rate of data packets associated with the first optical signal. ### Claim 3 (depends on 1) The method of claim 1, further comprising: when receiving the first optical signal: receiving a telemetry signal at the first communication terminal from the second communication terminal through the free space optical link, the telemetry signal providing the receiving power for the free space optical link at the second communication terminal; and wherein determining the receiving power for the free space optical link is also based on the telemetry signal providing the receiving power for the free space optical link at the second communication terminal. ### Claim 4 (depends on 1) The method of claim 1, wherein the second communication terminal transmits the laser diode signal from the laser diode at a constant output power. ### Claim 5 (depends on 4) The method of claim 4, wherein, when the received power of the laser diode signal differs from the constant output power of the laser diode, adjusting, by the control hardware, the output amplification at the first communication terminal includes adjusting the output amplification by an amount based on the difference between the received power of the laser diode signal and the constant output power of the laser diode. ### Claim 6 (depends on 1) The method of claim 1, wherein the second communication terminal transmits the laser diode signal from the laser diode at a wavelength outside a gain bandwidth associated with the first optical signal. ### Claim 7 (depends on 1) The method of claim 1, further comprising, when transmitting the second optical signal from the first communication terminal to the second communication terminal, transmitting a telemetry signal from the first communication terminal to the second communication terminal through the free space optical link, the telemetry signal providing the receiving power for the free space optical link at the first communication terminal based on at least one of: a received optical power of the first optical signal; or an error rate of data packets associated with the first optical signal. ### Claim 8 (depends on 7) The method of claim 7, wherein the telemetry signal comprises a dedicated channel different than a signal channel associated with the second optical signal. ### Claim 9 (depends on 7) The method of claim 7, wherein the telemetry signal and the second optical signal are co-propagated through an optical amplifier at the first communication terminal prior to transmitting the second optical signal and the telemetry signal to the second communication terminal. ### Claim 10 (depends on 1) The method of claim 1, wherein adjusting the output amplification at the first communication terminal comprises: when the receiving power for the free space optical link is less than a threshold receiving power: increasing the output amplification at the first communication terminal to increase the receiving power for the free space optical link when the second communication terminal receives the second optical signal; or when the receiving power for the free space optical link is greater than the threshold receiving power: decreasing the output amplification at the first communication terminal to decrease the receiving power for the free space optical link when the second communication terminal receives the second optical signal. ### Claim 11 (depends on 10) The method of claim 10, wherein decreasing the output amplification comprises decreasing the output amplification at a rate that avoids oscillations when the first communication terminal transmits the second optical signal. ### Claim 12 (depends on 1) The method of claim 1, wherein the first communication terminal or the second communication terminal comprises a high-altitude platform. ### Claim 13 (depends on 1) The method of claim 1, wherein the first communication terminal and the second communication terminal operate at a common altitude above the earth while maintaining a line of sight between each other. ### Claim 14 A high altitude platform comprising: receiver optics configured to receive a first optical signal from another high altitude platform through a free space optical link, the first optical signal comprising a laser diode signal from a laser diode of the other high altitude platform through the free space optical link; optical filter configured to filter the laser diode signal from the first optical signal; transmitter optics configured to transmit a second optical signal to the other high altitude platform through the free space optical link; and control hardware in communication with the receiver optics and the transmitter optics, the control hardware configured to: determine a received power of the laser diode signal that is filtered from the first optical signal; determine a receiving power for the free space optical link based on the received power of the laser diode signal; and adjust an output amplification at the transmitter optics based on the receiving power for the free space optical link, the output amplification adjusted to provide the second optical signal with a minimum transmission power for maintaining the free space optical link. ### Claim 15 (depends on 14) The high altitude platform of claim 14, wherein the control hardware determines the receiving power for the free space optical link further based on an error packet rate of data packets associated with the first optical signal when the receiver optics receive the first optical signal. ### Claim 16 (depends on 14) The high altitude platform of claim 14, wherein: the receiver optics, when receiving the first optical signal, are configured to receive a telemetry signal from the other high altitude platform through the free space optical link, the telemetry signal providing the receiving power for the free space optical link at the other high altitude platform; and the control hardware is configured to determine the receiving power for the free space optical link based on the receiving power for the free space optical link at the other high altitude platform. ### Claim 17 (depends on 14) The high altitude platform of claim 14, further comprising an optical amplifier in communication with the control hardware and the transmitter optics, the optical amplifier configured to adjust the output amplification at the high altitude platform by an amount based on a difference between the received power of the laser diode signal and a constant output power of the laser diode signal when the laser diode at the other high altitude platform transmits the laser diode signal. ### Claim 18 (depends on 14) The high altitude platform of claim 14, wherein the transmitter optics, when transmitting the second optical signal to the other high altitude platform, transmit a telemetry signal to the other high altitude platform through the free space optical link, the telemetry signal providing the receiving power for the free space optical link at the high altitude platform based on at least one of: a received optical power of the first optical signal; or an error rate of data packets associated with the first optical signal. ### Claim 19 (depends on 18) The high altitude platform of claim 18, further comprising a telemetry transmitter in communication with the control hardware and the transmitter optics, the telemetry transmitter providing the telemetry signal with a dedicated channel different than a signal channel associated with the second optical signal. ### Claim 20 (depends on 18) The high altitude platform of claim 18, further comprising an optical amplifier in communication with the control hardware and the transmitter optics, the optical amplifier configured to co-propagate the telemetry signal and the second optical signal prior to the transmitter optics transmitting the telemetry signal and the second optical signal to the other high altitude platform. ### Claim 21 (depends on 14) The high altitude platform of claim 14, further comprising an optical amplifier in communication with the control hardware and the transmitter optics, the optical amplifier configured to: when the receiving power for the free space optical link is less than a threshold receiving power: increase the output amplification at the transmitter optics to increase the receiving power for the free space optical link when the other high altitude platform receives the second optical signal; or when the receiving power for the free space optical link is greater than the threshold receiving power: decrease the output amplification at the transmitter optics to decrease the receiving power for the free space optical link when the other high altitude platform receives the second optical signal. ### Claim 22 (depends on 21) The high altitude platform of claim 21, wherein the optical amplifier is configured to decrease the output amplification at a rate that avoids oscillations when the transmitter optics transmit the second optical signal. ### Claim 23 A communication system comprising: a first communication terminal comprising: first receiver optics configured to receive a first optical signal comprising a first laser diode signal through a free space optical link; optical filter configured to filter the first laser diode signal from the first optical signal; first transmitter optics configured to transmit a second optical signal comprising a second laser diode signal through the free space optical link; and first control hardware in communication with the first receiver optics and the first transmitter optics, the control hardware configured to: determine a received power of the first laser diode signal that is filtered from the first optical signal; determine a receiving power for the free space optical link based on the received power of the first laser diode signal; and adjust an output amplification at the first transmitter optics based on the receiving power for the free space optical link, the output amplification adjusted to provide the second optical signal with a minimum transmission power for maintaining the free space optical link; and a second communication terminal comprising: second receiver optics configured to receive the second optical signal from the first transmitter optics through the free space optical link; second transmitter optics configured to transmit the first optical signal to the first receiver optics through the free space optical link; and second control hardware in communication with the first receiver optics and the first transmitter optics, the control hardware configured to: determine a received power of the second laser diode signal; determine a receiving power for the free space optical link based on the received power of the second laser diode signal; and adjust an output amplification at the second transmitter optics based on the receiving power for the free space optical link, the output amplification adjusted to provide a subsequent optical signal for transmission from the second transmitter optics with a minimum transmission power for maintaining the free space optical link. ### Claim 24 (depends on 23) The communication system of claim 23, wherein at least one of the first or second control hardware determines the receiving power for the free space optical link further based on at least one of: an optical power of the associated one of the first or second optical signals when the associated one of the first or second receiver optics receives the associated one of the first or second optical signals; or an error packet rate of data associated with the associated one of the first or second optical signals when the associated one of the first or second receiver optics receives the associated one of the first or second optical signals. ### Claim 25 (depends on 23) The communication system of claim 23, wherein: one of the first or second receiver optics of the associated one of the first or second communication terminals, when receiving the associated one of the first or second optical signals, are configured to receive a telemetry signal from the other one of the first or second communication terminals through the free space optical link, the telemetry signal providing the receiving power for the free space optical link at the other one of the first or second communication terminals; and one of the first or second control hardware associated with the one of the first or second receiver optics that receives the telemetry signal is configured to determine the receiving power for the free space optical link based on the receiving power for the free space optical link at the other one of the first or second communication terminals. ### Claim 26 (depends on 23) The communication system of claim 23, wherein the first and second communication terminals comprise high altitude platforms operating at a common altitude above the earth while maintaining a line of sight between each other.