Methods and apparatus for dual polarisation optical communication

Patent metadata

Field	Value
Publication number	US-2020007263-A1
Application number	US-201616465177-A
Country	US
Kind code	A1
Filing date	Dec 12, 2016
Priority date	Dec 12, 2016
Publication date	Jan 2, 2020
Grant date	—

Abstract

A method for dual polarisation optical transmission is disclosed. The method comprises splitting a continuous wave light source into first and second sub-channels, optically modulating each sub-channel with a data signal, and superimposing a first pilot tone onto the first optically modulated sub-channel and a second pilot tone, different from the first pilot tone, onto the second optically modulated sub-channel. The method further comprises polarisation multiplexing the first and second sub-channels to form a polarisation multiplexed signal, in which the first and second sub-channels have orthogonal states of polarisation, and transmitting the polarisation multiplexed signal.

First claim

1 . A method for dual polarisation optical transmission, the method comprising:
splitting a continuous wave light source into first and second sub-channels; optically modulating each sub-channel with a data signal; superimposing a first pilot tone onto the first optically modulated sub-channel and a second pilot tone, different from the first pilot tone, onto the second optically modulated sub-channel; polarisation multiplexing the first and second sub-channels to form a polarisation multiplexed signal, in which the first and second sub-channels have orthogonal states of polarisation; and transmitting the polarisation multiplexed signal.

2 . A method as claimed in claim 1 , wherein a frequency of each of the first and second pilot tones is selected from a frequency range at which power spectral density of the corresponding optically modulated sub-channel is negligible.

3 . A method for dual polarisation optical reception, the method comprising:
splitting a received polarisation multiplexed signal onto first and second optical paths, the received polarisation multiplexed signal comprising first and second sub-channels, the first sub-channel having superimposed a first pilot tone and the second sub-channel having superimposed a second pilot tone; and on each of the first and second paths:
using maximisation of power of one of the first or second pilot tones for polarisation recovery of one of the first or second sub-channels.

4 . A method as claimed in claim 3 further comprising using a minimisation of power of the other of the first or second pilot tones as a convergence condition for polarisation recovery of one of the first or second sub-channels.

5 . A method as claimed in claim 4 , wherein the pilot tone for which power is maximised on the first optical path is the pilot tone for which power is minimised on the second optical path.

6 . A method as claimed in claim 3 , further comprising, on each of the first and second paths:
using direct detection to receive the polarisation recovered sub-channel.

7 . A method as claimed in claim 3 , wherein using maximisation of power of one of the first or second pilot tones and minimisation of power of the other of the first or second pilot tones as a convergence condition for polarisation recovery of one of the first or second sub-channels comprises:
passing the received polarisation multiplexed signal on the path through a polarisation recovery device, the polarisation recovery device having at least one control variable; on output from the polarisation recovery device, extracting the first and second pilot tones; estimating a power of the pilot tones; and adjusting a value of the control variable of the polarisation recovery device until a power of one of the first or second pilot tones reaches a convergence threshold.

8 . A method as claimed in claim 7 , wherein extracting the first and second pilot tones comprises one of:
tapping the signal output from the polarisation recovery device; and on a low power output of the optical tap, photodetecting and filtering the signal to retain only the first and second pilot tones; or
photodetecting the signal output from the polarisation recovery device; and
isolating the first and second pilot tones.

9 . A method as claimed in claim 7 , wherein extracting the first and second pilot tones comprises tapping the signal output from the polarisation recovery device; and, on a low power output of the optical tap, photodetecting and filtering the signal to retain only the first and second pilot tones;
and wherein using direct detection to receive the polarisation recovered sub-channel comprises:
when the power of one of the first or second pilot tones reaches a convergence threshold,
performing direct detection a signal output from a high power output of the optical tap.

10 . A method as claimed in claim 7 , wherein adjusting a value of the control variable of the polarisation recovery device until a power of one of the first or second pilot tones reaches a convergence threshold comprises:
for a reference value of the control variable:
adding an offset to the reference value of the control variable and estimating a resulting power of the extracted first and second pilot tones;
removing the offset from the reference value of the control variable and estimating a resulting power of the extracted first and second pilot tones; and
if, after addition or removal of the offset to the reference value of the control variable, an estimated power of one of the first or second pilot tones is greater than when the control variable is at the reference value, and a power of the other of the first or second pilot tones is less than or equal to when the control variable is at the reference value:
updating the reference value of the control variable by an adjustment value.

11 . A method as claimed in claim 10 , wherein adjusting a value of the control variable of the polarisation recovery device until a power of one of the first or second pilot tones reaches a convergence threshold further comprises:
if, the condition of if, after addition or removal of the offset to the reference value of the control variable, an estimated power of one of the first or second pilot tones is not greater than when the control variable is at the reference value, or a power of the other of the first or second pilot tones is not less than or equal to when the control variable is at the reference value then: updating the reference value of the control variable to be a selected value within a setting range for the control variable.

12 . A method as claimed in claim 10 , wherein adjusting a value of the control variable of the polarisation recovery device until a power of one of the first or second pilot tones reaches a convergence threshold further comprises:
repeating the steps of adding, removing and updating until an estimated power of one of the first or second pilot tones reaches a convergence threshold.

13 . A method as claimed in claim 7 , wherein the polarisation recovery device has a plurality of control variables, and wherein using maximisation of power of one of the first or second pilot tones and minimisation of power of the other of the first or second pilot tones as a convergence condition for polarisation recovery of one of the first or second sub-channels further comprises:
adjusting a value of each of the control variables of the polarisation recovery device until a power of one of the first or second pilot tones reaches a convergence threshold.

14 . A method as claimed in claim 7 , further comprising:
if a power of one of the first or second pilot tones does not reach a convergence threshold within a target number of adjustments, updating the reference value of the control variable to be a selected value within a setting range for the control variable.

15 . A method as claimed in claim 7 , wherein if, after adjustment of a value of the control variable, a power of both pilot tones increases or decreases, the method further comprises concluding that an orthogonality of the first and second sub-channels has been lost.

16 . A method as claimed in claim 7 , wherein if, after multiple adjustments of a value of the control variable, a power of the first and second pilot tones remains substantially unchanged, the method further comprises concluding that an orthogonality of the first and second sub-channels has been lost.

17 . A computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out a me

Assignees

• Ericsson Telefon Ab L M

Inventors

• Cavaliere Fabio
• Meloni Gianluca
• Fresi Francesco
• Sorianello Vito

Classifications

• H04J14/06 Primary

  Polarisation multiplex systems · CPC title

• H04B10/532 Primary

  Polarisation modulation · CPC title

• H04B10/67

  Optical arrangements in the receiver · CPC title