Mitigation of atmospheric scintillation for communication
The present application is directed to an optical terminal including two linearly polarized optical transmit beams configured to exhibit a time-delay therebetween. The optical terminal may include a quarter-wave plate such that the linearly polarized transmit beam becomes circularly polarized. The optical terminal may also include a receiving ground terminal including a properly oriented quarter-wave plate for separating and directing the two recovered linearly polarized beams. The application is also directed to a method for reconstructing an originally transmitted data stream.
1. A device for free space communication comprising:
a quarter wave plate configured to receive a circularly polarized optical signal and output a linearly polarized optical signal;
a polarization beam splitter configured to receive the linearly polarized optical signal and output a first optical signal comprising data and a second optical signal comprising the data delayed by a time period;
at least two photodetectors configured to convert the first optical signal to a first data signal and the second optical signal to a second data signal;
a delay element configured to cause the first data signal to be delayed based on the time period;
at least two forward error correction decoders configured to convert the first data signal to first data and the second data signal to second data; and
a decision element configured to receive the first data and the second data and output the first data or the second data.
2. The device of claim 1 , wherein the decision element is configured to output one of the first data and the second data based on a determination of which of the second data or the first data has fewer errors.
3. The device of claim 1 , wherein the decision element is configured to determine, on a packet-by-packet basis, to output the one of the first data or the second data.
4. The device of claim 1 , wherein the time period is of a time length that allows correction of transmission errors due to atmospheric scintillation.
5. The device of claim 1 , wherein the time period is of a time length in a range of about 5 ms to about 15 ms.
6. The device of claim 1 , further comprising a controller configured to update a parameter to cause a change in the time period based on a plurality of measurements of optical intensity over time.
7. The device of claim 1 , wherein the circularly polarized optical signal comprises a first sub-channel comprising the data and a second sub-channel comprising the data delayed based on time period.
8. A method comprising:
converting a circularly polarized optical signal to a linearly polarized optical signal;
splitting the linearly polarized optical signal to a first optical signal comprising data and a second optical signal comprising the data delayed by a time period;
converting the first optical signal to a first data signal and the second optical signal to a second data signal;
causing the first data signal to be delayed based on the time period;
converting the first data signal to first data and the second data signal to second data; and
outputting, based on analysis of the first data and the second data, the first data or the second data.
9. The method of claim 8 , wherein the analysis of the first data and the second data comprises a determination of which of the second data or the first data has fewer errors.
10. The method of claim 8 , wherein outputting, based analysis of the first data and the second data, the first data or the second data is performed on a packet-by-packet basis.
11. The method of claim 8 , wherein the time period is of a time length that allows correction of transmission errors due to atmospheric scintillation.
12. The method of claim 8 , wherein the time period is of a time length in a range of about 5 ms to about 15 ms.
13. The method of claim 8 , further comprising:
determining a plurality of measurements of optical intensity over time; and
updating a parameter to cause a change in the time period based on the plurality of measurements of optical intensity.
14. The method of claim 8 , wherein the circularly polarized optical signal comprises a first sub-channel comprising the data and a second sub-channel comprising the data delayed based on the time period.
15. A system for free space communication comprising:
a transmitter configured to:
generate a first optical signal comprising data and a second optical signal comprising the data delayed by a time period;
combine the first optical signal and the second optical signal into a combined linearly polarized signal;
convert the combined linearly polarized signal into a circularly polarized signal; and
output, into free space, the circularly polarized signal; and
a receiver configured to receive, from free space, the circularly polarized signal and output an indication of the data.
16. The system of claim 15 , where the receiver is configured to:
receive the circularly polarized signal;
split the circularly polarized signal into two linearly polarized signals;
correct for a time delay between the two linearly polarized signals based on the time period; and
output, based on analysis of data from the two linearly polarized signals corrected for the time delay, a portion of the data.
17. The system of claim 16 , wherein the analysis of the data from the two linearly polarized signals corrected for the time delay comprises a determination of which portion of the data has fewer errors.
18. The system of claim 16 , wherein the receiver is configured to output, based on the analysis of the data from the two linearly polarized signals corrected for the time delay and on a packet-by-packet basis, the portion of the data.
19. The system of claim 15 , wherein the time period is of a time length that allows correction of transmission errors due to atmospheric scintillation.
20. The system of claim 15 , wherein the first optical signal is rotated 90 degrees along a direction transverse to a direction of travel of the first optical signal and second optical signal in comparison to the second optical signal.