System and method for optical communication
Mixing between I and Q components in coherent homodyne optical signals can occur due to phase shifts, e.g. relative to the local oscillator, relative to the other signal components. In some examples, the phase shifts can arise due to thermal expansion of the optical waveguides and/or can include polarization mixing. A descrambler functions to correct for mixing between multiple signal components. The descrambler may be configured to at least partially correct for a phase difference between a first plurality of modulated optical data signals and a first local oscillator reference signal; and a controller may be configured for determining a first correction parameter for at least partially correcting for the phase difference, and for transmitting the first correction parameter to the descrambler. The controller may be configured for determining the first correction parameter from a first pilot signal transmitted with the first plurality of modulated optical data signals.
1. An optical system comprising:
a transmitter for transmitting optical signals onto an optical link, comprising:
an optical source configured for generating a first plurality of coherent optical signals, and a first local oscillator reference signal; and
a first optical modulator configured for modulating the first plurality of coherent optical signals forming a first plurality of modulated optical data signals, comprising a first in-phase modulated optical data signal and a first quadrature modulated optical data signal; and
a receiver configured to receive the first plurality of coherent optical signals, and the first local oscillator reference signal, the receiver comprising:
a first optical hybrid configured for generating a first in-phase electrical data signal and a first quadrature electrical data signal from the first in-phase modulated optical data signal, the first quadrature modulated optical data signal and the first local oscillator reference signal;
a phase corrector configured for at least partially correcting for a first phase difference between the first plurality of modulated optical data signals and the first local oscillator reference signal; and
a controller configured for determining a first correction parameter for at least partially correcting for the first phase difference, and for transmitting the first correction parameter to the phase corrector;
wherein the first optical modulator is also configured for generating a first pilot signal for transmission with the first plurality of coherent optical signals; and
wherein the controller is configured for determining the first correction parameter from the first pilot signal.
2. An optical system comprising:
a transmitter for transmitting optical signals onto an optical link, comprising:
an optical source configured for generating a first plurality of coherent optical signals, and a first local oscillator reference signal; and
a first optical modulator configured for modulating the first plurality of coherent optical signals forming a first plurality of modulated optical data signals, comprising a first in-phase modulated optical data signal and a first quadrature modulated optical data signal; and
a receiver configured to receive the first plurality of coherent optical signals, and the first local oscillator reference signal, the receiver comprising:
a first optical hybrid configured for generating a first in-phase electrical data signal and a first quadrature electrical data signal from the first in-phase modulated optical data signal, the first quadrature modulated optical data signal and the first local oscillator reference signal;
a phase corrector configured for at least partially correcting for a first phase difference between the first plurality of modulated optical data signals and the first local oscillator reference signal; and
a controller configured for determining a first correction parameter for at least partially correcting for the first phase difference, and for transmitting the first correction parameter to the phase corrector;
wherein the first plurality of coherent optical signals comprises four coherent optical signals, including a first polarized in-phase modulated optical data signal and a second polarized quadrature modulated optical data signal;
wherein the first optical modulator is further configured for modulating the first polarized in-phase modulated optical data signal and the second polarized quadrature modulated optical data signal;
a first optical multiplexer configured for combining the first plurality of coherent optical signals into a combined optical signal; and
a first optical demultiplexer configured for separating the combined optical signal into the first plurality of modulated optical data signals.
3. The optical system according to claim 1 , wherein the first pilot signal has a frequency greater than or equal to 10 times lower in frequency than the first plurality of coherent optical signals.
4. The optical system according to claim 1 , wherein the phase corrector is configured to receive the first in-phase electrical data signal and the first quadrature electrical data signal, and to perform a virtual rotation for at least partially correcting for the first phase difference by adjusting the first in-phase electrical data signal and the first quadrature electrical data signal based on the first correction parameter.
5. The optical system according to claim 4 , further comprising an optical phase corrector including an optical phase shifter for at least partially correcting for the first phase difference.
6. The optical system according to claim 1 , wherein the phase corrector comprises an optical phase corrector including an optical phase shifter for at least partially correcting the first phase difference.
7. The optical system according to claim 1 , wherein the controller is configured to perform an iterative optimization process to correct for the first phase difference, wherein the first correction parameter provided to the phase corrector is updated by the controller based on an effect the phase corrector has on measurements of the first pilot signal using the first correction parameter.
8. The optical system according to claim 1 , wherein the transmitter is configured to transmit the first pilot signal on only one of the first in-phase modulated optical data signal and the first quadrature modulated optical data signal; and
wherein, when a portion of the first pilot signal is detected by the receiver with the other of the first in-phase modulated optical data signal and the first quadrature modulated optical data signal, the controller is configured to adjust the first correction parameter based on a deviation of the first pilot signal received by the receiver from the first pilot signal transmitted by the transmitter.
9. The optical system according to claim 1 , wherein the phase corrector is configured to separate the first pilot signal from the first plurality of modulated optical data signals.
10. The optical system according to claim 1 , further comprising:
a second optical source configured for generating a second plurality of coherent optical signals at a different wavelength than the first plurality of coherent optical signals, and a second local oscillator reference signal;
a second optical modulator configured for modulating the second plurality of coherent optical signals forming a second plurality of modulated optical data signals, comprising a second in-phase modulated optical data signal and a second quadrature modulated optical data signal, and for generating a second pilot signal;
a first optical multiplexer configured for combining the first plurality of modulated optical data signals and the second plurality of modulated optical data signals into a combined optical signal;
a second optical multiplexer configured for combining the first local oscillator reference signal and the second local oscillator reference signal into a combined reference signal;
an optical link for transmitting the combined optical signal, the combined reference signal, the first pilot signal and the second pilot signal;
a first optical demultiplexer configured for separating the combined optical signal into the first plurality of modulated optical data signals and the second plurality of modulated optical data signals;
a second optical demultiplexer configured for separating the combined reference signal into the first local oscillator reference signal and the second local oscillator reference signal; and
a second optical hybrid configured for generating a second in-phase electrical data signal and a second quadrature electrical data signal from the second in-phase modulated optical data signal, the second quadrature modulated optical data signal and the second local oscillator reference signal;
wherein the phase corrector is also configured for at least partially correcting a second phase difference between the second plurality of modulated optical data signals and the second local oscillator reference signal; and
wherein the controller is also configured for determining a second correction parameter from the second pilot signal for at least partially correcting for the second phase difference, and for transmitting the second correction parameter to the phase corrector.
11. The optical system according to claim 2 , wherein the first optical modulator is also configured for generating a first pilot signal for transmission with the first plurality of coherent optical signals; and
wherein the controller is configured for determining the first correction parameter from the first pilot signal.
12. An optical system comprising:
a receiver comprising:
a first optical hybrid configured for generating a first in-phase electrical data signal and a first quadrature electrical data signal from a first in-phase modulated optical data signal, a first quadrature modulated optical data signal and a first local oscillator reference signal;
a phase corrector configured for at least partially correcting a first phase difference between the first plurality of modulated optical data signals and the first local oscillator reference signal; and
a controller configured for determining a first correction parameter for at least partially correcting for the first phase difference, and for transmitting the first correction parameter to the phase corrector;
wherein the controller is also configured for determining the first correction parameter from a first pilot signal transmitted with the first quadrature modulated optical data signal and the first local oscillator reference signal.
13. The optical system according to claim 12 , wherein the first pilot signal has a frequency greater than or equal to 10 times lower in frequency than the first in-phase modulated optical data signal and the first quadrature modulated optical data signal.
14. The optical system according to claim 12 , wherein the phase corrector is configured to receive the first in-phase electrical data signal and the first quadrature electrical data signal, and to perform a virtual rotation for at least partially correcting for the first phase difference by adjusting the first in-phase electrical data signal and the first quadrature electrical data signal based on the first correction parameter.
15. The optical system according to claim 14 , further comprising an optical phase corrector including an optical phase shifter for at least partially correcting for the first phase difference.
16. The optical system according to claim 12 , wherein the phase corrector comprises an optical phase corrector including an optical phase shifter for at least partially correcting for the first phase difference.
17. The optical system according to claim 12 , wherein the controller is configured to perform an iterative optimization process to correct for the first phase difference, wherein the first correction parameter provided to the phase corrector is updated by the controller based on an effect the phase corrector has on measurements of the first pilot signal using the first correction factor.
18. The optical system according to claim 12 , wherein the first pilot signal is transmitted with only one of the first in-phase modulated optical data signal and the first quadrature modulated optical data signal; and
wherein, when a portion of the first pilot signal is detected with the other of the first in-phase modulated optical data signal and the first quadrature modulated optical data signal, the controller is configured to adjust the first correction parameter based on a deviation of the first pilot signal received by the receiver from the first pilot signal transmitted by a transmitter.
19. The optical system according to claim 12 , wherein the phase corrector is configured to separate the first pilot signal from the first in-phase modulated optical data signal and the first quadrature modulated optical data signal.