Methods, systems, and apparatus for global multiple-access optical communications

Patent metadata

Field	Value
Publication number	US-10128949-B2
Application number	US-201615054546-A
Country	US
Kind code	B2
Filing date	Feb 26, 2016
Priority date	Feb 27, 2015
Publication date	Nov 13, 2018
Grant date	Nov 13, 2018

Abstract

A wide-field telescope and focal plane array (FPA) that look at Earth and satellites in low- and medium-Earth orbit (LEO and MEO) from a satellite in higher orbit, such as geostationary Earth orbit (GEO), can serve as a node in an on-demand, optical multiple access (OMA) communications network. The FPA receives asynchronous low-rate signals from LEO and MEO satellites and ground stations at a signal rate determined in part by the FPA frame rate (e.g., kHz to MHz). A controller tracks the low-rate signals across the FPA as the signal sources orbit Earth. The node also includes one or more transmitters that relay the received information to other nodes via wavelength-division multiplexed (WDM) free-space optical signals. These other signals may include low-rate telemetry communications, burst transmissions, and continuous data relay links.

First claim

The invention claimed is:

1. An optical receiver for multiple-access optical communications at a satellite in geostationary Earth orbit (GEO), the optical receiver comprising:
a first telescope having a first field of view of at least about 20° to receive an inbound free-space optical signal at a first wavelength from a satellite in low-Earth orbit (LEO);
a focal plane array (FPA), disposed in a back focal plane of the first telescope, to detect the inbound free-space optical signal;
a bandpass filter, in optical communication with the first telescope and/or the FPA, to transmit light at the first wavelength and reject light at other wavelengths;
a controller, operably coupled to the FPA, to monitor a trajectory of the inbound free-space optical signal across the FPA as the satellite in LEO moves with respect to the satellite in GEO; and
at least one transmitter, operably coupled to the controller, to transmit an outbound free-space optical signal in response to detection of the inbound free-space optical signal.

2. The optical receiver of claim 1 , wherein the inbound free-space optical signal is modulated at a data rate less than a frame rate of the FPA.

3. The optical receiver of claim 1 , wherein the FPA is configured to simultaneously detect a plurality of inbound free-space optical signals from a plurality of satellites in LEO.

4. The optical receiver of claim 1 , wherein the at least one transmitter is configured to modulate the outbound free-space optical signal at a rate of at least about 1 Megabit per second (Mbps).

5. The optical receiver of claim 4 , wherein the at least one transmitter is configured to modulate the outbound free-space optical signal at a rate of at least about 10 Mbps.

6. The optical receiver of claim 1 , wherein the at least one transmitter comprises:
an array of optical transmitters, each optical transmitter of the array of optical transmitters having a corresponding aperture with a diameter of about 3 cm or less to transmit a corresponding outbound free-space optical signal to a corresponding remote terminal.

7. The optical receiver of claim 1 , further comprising:
a second telescope, having a second field of view smaller than the first field of view, to receive another inbound free-space optical signal from the satellite in LEO, the other free-space optical signal being at a second wavelength different from the first wavelength and being modulated at a rate of at least about 1 Mbps.

8. The optical receiver of claim 7 , wherein the bandpass filter is configured to reject light at the second wavelength.

9. The optical receiver of claim 1 , further comprising:
a buffer, operably coupled to the controller, to store data received from the satellite in LEO prior to transmission of the data via the at least one transmitter at rate greater than 100 kbps.

10. The optical receiver of claim 1 , further comprising:
an actuator, operably coupled to the at least one transmitter, to steer a field of view of the at least one transmitter through an angular range of ±20°.

11. A method of multiple-access optical communications at a satellite in geostationary Earth orbit (GEO), the satellite in GEO comprising a first telescope in optical communication with a focal plane array (FPA), the method comprising:
receiving, via the first telescope from a satellite in low-Earth orbit (LEO), at least one inbound free-space optical signal;
detecting the at least one inbound free-space optical signal at the FPA;
monitoring a trajectory of the at least one inbound free-space optical signal across the FPA as the satellite in LEO moves with respect to the satellite in GEO; and
transmitting an outbound free-space optical signal from the satellite in GEO in response to detection of the at least one inbound free-space optical signal.

12. The method of claim 11 , wherein receiving the at least one inbound free-space optical signal comprises transmitting the at least one inbound free-space optical signal through a bandpass filter.

13. The method of claim 11 , wherein receiving the at least one inbound free-space optical signal comprises receiving a plurality of first free-space optical signals from a plurality of satellites in LEO.

14. The method of claim 11 , wherein detecting the at least one inbound free-space optical signal at the FPA comprises reading out the FPA at rate of greater than a modulation rate of the at least one inbound free-space optical signal.

15. The method of claim 11 , wherein transmitting the outbound free-space optical signal comprises transmitting the outbound free-space optical signal to the satellite in LEO.

16. The method of claim 11 , wherein transmitting the outbound free-space optical signal comprises transmitting the outbound free-space optical signal to a receiver on Earth.

17. The method of claim 11 , wherein transmitting the outbound free-space optical signal comprises modulating the outbound free-space optical signal at a rate of at least about 1 Megabit per second (Mbps).

18. The method of claim 11 , wherein transmitting the outbound free-space optical signal comprises:
modulating the outbound free-space optical signal at a rate of at least about 10 Mbps; and
emitting the outbound free-space optical signal via an aperture having a diameter of at least about 10 cm.

19. The method of claim 11 , further comprising:
receiving, via a second telescope having a second field of view smaller than the first field of view, another inbound free-space optical signal from the satellite in LEO, the other inbound free-space optical signal being modulated at a rate of at least about 1 Mbps.

20. The method of claim 19 , wherein:
the inbound free-space optical signal is at a first wavelength and the other inbound free-space optical signal is at a second wavelength, and
receiving the at least one inbound free-space optical signal comprises transmitting light at the first wavelength to the FPA and rejecting light at the second wavelength with a filter.

21. The method of claim 11 , wherein transmitting the outbound free-space optical signal comprises steering the outbound free-space optical signal through an angular range of ±10°.

22. The method of claim 11 , further comprising:
imaging, with the first telescope, the entire visible portion of the Earth and at least a portion of outer space above a surface of the Earth.

23. The method of claim 11 , wherein detecting the at least one inbound free-space optical signal at the FPA comprises:
detecting a first inbound free-space optical signal at a first pixel in the FPA and a second pixel in the FPA during a first frame integration period; and
at least one of summing or averaging an output of the first pixel with an output of the second pixel.

24. An optical receiver for multiple-access optical communications at a satellite, the optical receiver comprising:
a telescope having a first field of view of at least about 20° to receive a plurality of inbound free-space optical signals, each inbound free-space optical signal in the plurality of inbound free-space optical signals being at a first wavelength;
a bandpass filter, in optical communication with the telescope, to transmit light at the first wavelength and reject light at other wavelengths;
a focal plane array (FPA), in optical communication with the telescope, to detect the plurality of inbound free-space optical signals;
a read-out integrated circuit, operably coupled to the FPA, to read out the

Assignees

• Massachusetts Inst Technology

Inventors

• Boroson Don M
• Robinson Bryan S
• Menrad Robert J
• Rush John
• Perko Kenneth

Classifications

• H04B10/118 Primary

  specially adapted for satellite communication · CPC title

• H04J14/0223

  Conversion to or from optical TDM · CPC title

• H04B10/5161

  Combination of different modulation schemes · CPC title

• H04B10/60

  Receivers · CPC title

• H04B7/195

  Non-synchronous stations · CPC title