Methods and apparatus for detecting and compensating power imbalance and modulation imperfection for a coherent optical transmitter

Patent metadata

Field	Value
Publication number	US-9979472-B1
Application number	US-201615394280-A
Country	US
Kind code	B1
Filing date	Dec 29, 2016
Priority date	Dec 29, 2016
Publication date	May 22, 2018
Grant date	May 22, 2018

Abstract

In some embodiments, a non-transitory processor-readable medium storing code representing instructions to be executed by a processor comprises code to cause the processor to determine, during a calibration of a coherent optical transmitter, a set of parameters associated with each tributary channel by sending a first signal to a digital signal processor (DSP) to adjust a scale factor of that tributary channel. The scale factor is associated with a tap characteristic of a finite impulse response (FIR) filter of the DSP. The code further causes the processor to determine a power imbalance between two tributary channels based on the set of parameters associated with each tributary channel. The code further causes the processor to send a second signal to the coherent optical transmitter to adjust a set of operational settings of the coherent optical transmitter based on the power imbalance and the set of parameters associated with each tributary channel.

First claim

What is claimed is:

1. A non-transitory processor-readable medium storing code representing instructions to be executed by a processor, the code comprising code to cause the processor to:
determine, during a calibration of a coherent optical transmitter, a set of parameters associated with each tributary channel from a set of tributary channels by sending a first signal to a digital signal processor (DSP) to adjust a scale factor of that tributary channel from the set of tributary channels,
the coherent optical transmitter having an optical modulator and the DSP operatively coupled to the optical modulator, the coherent optical transmitter configured to output an optical signal processed by the DSP and modulated by the optical modulator via the set of tributary channels, the set of tributary channels including a first tributary channel and a second tributary channel, the scale factor associated with a tap characteristic of a finite impulse response (FIR) filter of the DSP,

determine, during the calibration of the coherent optical transmitter, a power imbalance between the first tributary channel and the second tributary channel based on the set of parameters associated with the first tributary channel and the set of parameters associated with the second tributary channel,
send a second signal to the coherent optical transmitter to adjust a set of operational settings of the coherent optical transmitter based on (1) the power imbalance between the first tributary channel and the second tributary channel and (2) the set of parameters associated with the first tributary channel or the set of parameters associated with the second tributary channel, such that the power imbalance between the first tributary channel and the second tributary channel is reduced.

2. The non-transitory processor-readable medium of claim 1 , wherein the set of tributary channels includes an X polarization channel (X channel) and a Y polarization channel (Y channel), the X channel including an in-phase channel (XI channel) and a quadrature channel (XQ channel), the Y channel including an in-phase channel (YI channel) and a quadrature channel (YQ channel).

3. The non-transitory processor-readable medium of claim 1 , wherein:
the first tributary channel is an X polarization channel (X channel), the X channel including an in-phase channel (XI channel) and a quadrature channel (XQ channel),
the second tributary channel is a Y polarization channel (Y channel), the Y channel including an in-phase channel (YI channel) and a quadrature channel (YQ channel),
the code further comprising code to cause the processor to determine a power imbalance between the XI channel and the XQ channel, and a power imbalance between the YI channel and the YQ channel.

4. The non-transitory processor-readable medium of claim 1 , wherein for each tributary channel from the set of tributary channels:
the set of parameters includes a first parameter, a second parameter, and a third parameter,
the first parameter is associated with a raw power value in that tributary channel,
the second parameter is associated with a peak-peak voltage swing applied by a radio frequency (RF) amplifier for that tributary channel,
the third parameter is associated with a bias voltage applied by a bias control circuit of the optical modulator for that tributary channel.

5. The non-transitory processor-readable medium of claim 1 , wherein for each tributary channel from the set of tributary channels:
the set of parameters includes a first parameter, a second parameter, and a third parameter,
the first parameter is associated with at least one of a variable optical attenuator (VOA), a variable optical amplifier, and a tunable optical coupler (TOC),
the second parameter is associated with at least one of a radio frequency (RF) amplifier and the tap characteristic of the FIR filter of the DSP,
the third parameter is associated with a bias voltage applied by a bias control circuit for that tributary channel,
the coherent optical transmitter includes the VOA, the variable optical amplifier, the TOC, the RF amplifier, and the bias control circuit for that tributary channel.

6. The non-transitory processor-readable medium of claim 1 , wherein the processor is configured to receive, from the coherent optical transmitter, a third signal associated with a total output power of the optical signal.

7. The non-transitory processor-readable medium of claim 1 , wherein:
the power imbalance between the first tributary channel and the second tributary channel is a first power imbalance,
the code comprises code to cause the processor to
determine, during a signal transmission phase of the coherent optical transmitter, a second power imbalance between the first tributary channel and the second tributary channel, and

send a third signal to the coherent optical transmitter to adjust at least one operational setting from the set of operational settings of the coherent optical transmitter based on the second power imbalance such that the second power imbalance between the first tributary channel and the second tributary channel is reduced during the signal transmission phase of the coherent optical transmitter.

8. The non-transitory processor-readable medium of claim 1 , wherein for each tributary channel from the set of tributary channels:
the adjusting the scale factor of that tributary channel includes adjusting the scale factor of that tributary channel within a first predetermined range,
the power imbalance between the first tributary channel and the second tributary channel is a first power imbalance,
the code further comprises code to cause the processor to determine, during a signal transmission phase of the coherent optical transmitter, a second power imbalance between the first tributary channel and the second tributary channel by changing the scale factor of that tributary channel within a second predetermined range that is less than the first predetermined range.

9. The non-transitory processor-readable medium of claim 1 , wherein the coherent optical transmitter includes a RF amplifier,
the RF amplifier is configured to be in a manual gain control (MGC) mode during the calibration of the coherent optical transmitter.

10. The non-transitory processor-readable medium of claim 1 , wherein the code further comprises code to cause the processor to:
receive a third signal from an optical receiver to adjust at least one operational setting from the set of operational settings of the coherent optical transmitter such that the power imbalance between the first tributary channel and the second tributary channel is reduced,
the optical receiver configured to receive the optical signal from the coherent optical transmitter.

11. A method, comprising:
sending, to an optical transmitter and during an operational phase of the optical transmitter, a first signal to adjust a scale factor of each tributary channel from a set of tributary channels of an optical modulator within a predetermined range, the optical transmitter including the optical modulator and a finite impulse response (FIR) filter operatively coupled to the optical modulator, the scale factor of each tributary channel from the set of tributary channels associated with a tap characteristic of the FIR filter, the set of tributary channels including a first tributary channel and a second tributary channel;
determining, in response to the scale factor of the first tributary channel and the scale factor of the second tributary channel being adjusted and during the operational phase of the optical transmitter, a power imbalance between the first tributary channel and the second tributary channel; and
sending, to the

Assignees

• Juniper Networks Inc

Inventors

• Wang Qiang
• Yue Yang
• He Xuan

Classifications

• H04B10/07955 Primary

  Monitoring or measuring power · CPC title

• H04B10/5161

  Combination of different modulation schemes · CPC title

• H04B10/532

  Polarisation modulation · CPC title

• H04B10/564

  Power control · CPC title

• H04B10/541 Primary

  Digital intensity or amplitude modulation · CPC title