Optical amplifier with closed loop control for scintillation compensation in free space optical communications

Patent metadata

Field	Value
Publication number	US-9716551-B2
Application number	US-201514818706-A
Country	US
Kind code	B2
Filing date	Aug 5, 2015
Priority date	Aug 5, 2015
Publication date	Jul 25, 2017
Grant date	Jul 25, 2017

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.

First claim

What is claimed is:

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;
determining, by control hardware of the first communication terminal, a receiving power for the optical link at the first communication terminal based on the received first optical signal;
adjusting, by the control hardware, an output amplification at the first communication terminal using the receiving power for the optical link at the first communication terminal, the output amplification adjusted to provide a second optical signal with a minimum transmission power for maintaining the optical link; and
transmitting the second optical signal from the first communication terminal to the second communication terminal through the optical link,
wherein 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 optical link, the telemetry signal providing the receiving power for the 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, and

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.

2. The method of claim 1 , wherein determining the receiving power for the optical link is based on an optical power of the first optical signal when the first communication terminal receives the first optical signal.

3. The method of claim 1 , wherein determining the receiving power for the optical link is based on an error rate of data packets associated with the first optical signal.

4. The method of claim 1 , further comprising:
when receiving the first optical signal:
receiving a laser diode signal at the first communication terminal from a laser diode of the second communication terminal through the optical link; and
determining, by the control hardware, a received power of the laser diode signal; and

determining, by the control hardware, the receiving power for the optical link at the first communication terminal based on the received power of the laser diode signal.

5. The method of claim 4 , wherein the second communication terminal transmits the laser diode signal from the laser diode at a constant output power.

6. The method of claim 5 , further comprising, 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 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.

7. The method of claim 4 , 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.

8. The method of claim 1 , wherein the telemetry signal comprises a dedicated channel different than a signal channel associated with the second optical signal.

9. The method of claim 1 , wherein adjusting the output amplification at the first communication terminal comprises:
when the receiving power for the optical link at the first communication terminal is less than a threshold receiving power:
increasing the output amplification at the first communication terminal to increase the receiving power for the optical link when the second communication terminal receives the second optical signal; or

when the receiving power for the optical link at the first communication terminal is greater than the threshold receiving power:
decreasing the output amplification at the first communication terminal to decrease the receiving power for the optical link when the second communication terminal receives the second optical signal.

10. The method of claim 9 , 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.

11. The method of claim 1 , wherein the first communication terminal or the second communication terminal comprises a high-altitude platform.

12. 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.

13. 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;
transmitter optics configured to transmit a second optical signal to the other high altitude platform through the optical link, 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 optical link, the telemetry signal providing the receiving power for the 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;

control hardware in communication with the receiver optics and the transmitter optics, the control hardware configured to:
determine a receiving power for the optical link at the receiver optics based on the received first optical signal; and
adjust an output amplification at the transmitter optics using the receiving power for the optical link at the receiver optics, the output amplification adjusted to provide the second optical signal with a minimum transmission power for maintaining the optical link; and

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.

14. The high altitude platform of claim 13 , wherein the control hardware determines the receiving power for the optical link based on at least one of:
an optical power of the first optical signal when the receiver optics receive the first optical signal; or
an error packet rate of data packets associated with the first optical signal when the receiver optics receive the first optical signal.

15. The high altitude platform of claim 13 , wherein:
the receiver optics, when receiving the first optical signal, are configured to receive a laser diode signal from a laser diode of the other high altitude platform through the optical link; and
the control hardware is configured to determine a received power of the laser diode signal and determine the receiving power for the optical link at the receiver optics based on the received power of the laser diode signal.

16. The high altitude platform of claim 15 , 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

Assignees

• Google Inc

Inventors

• Wang Chiachi
• Ito Christopher Joshua Shiro

Classifications

• H04B10/07955

  Monitoring or measuring power · CPC title

• H04B10/118 Primary

  specially adapted for satellite communication · CPC title

• H04B10/1125

  using a single common optical path · CPC title

• H04B10/11

  Arrangements specific to free-space transmission, i.e. transmission through air or vacuum · CPC title

• H04B10/564 Primary

  Power control · CPC title