Systems and methods for analog electronic polarization control for coherent optical receivers

Patent metadata

Field	Value
Publication number	US-2019349093-A1
Application number	US-201916379302-A
Country	US
Kind code	A1
Filing date	Apr 9, 2019
Priority date	May 8, 2018
Publication date	Nov 14, 2019
Grant date	—

Abstract

Described herein are systems and methods that manage polarization in coherent optical receivers by using analog signal processing that eliminates the need for ultra-fast, power-hungry ADCs and DSPs and that would require digitization of the full-bandwidth signal path and result in bulky and expensive circuit designs. Various embodiments of the invention provide polarization correction by using an analog polarization correction circuit that implements the equivalent of two matrix operations. This is accomplished by using analog electronics that comprises a combination of variable and unity gain amplifiers to align polarizations of input signals to generate a polarization-corrected output signal that is further aligned with the polarization frame of reference of the receiver.

First claim

What is claimed is:

1 . An analog polarization control circuit comprising:
a first set of amplifiers that, in response to receiving a first component of a first polarization signal having a first phase, rotates the first phase by a first phase angle; a second set of amplifiers that, in response to receiving a second component of the first polarization signal having a second phase, rotates the second phase by the first phase angle; a third and fourth set of amplifiers that, in response to receiving components of a second polarization signal, output unrotated signals; and a fifth set of amplifiers that rotate, by a second phase angle, one or more of the unrotated signals and the first and second components of the first polarization signal to obtain a set of rotated signals that reduces at least one component of the second polarization signal from the first polarization signal.

2 . The analog polarization control circuit according to claim 1 , wherein the second phase angle aligns the set of rotated signals with a polarization frame of reference of a receiver.

3 . The analog polarization control circuit according to claim 2 , wherein the second phase angle is chosen such that components resolved into X- and Y-polarization branches of the receiver are restored to be substantially orthogonal to each other.

4 . The analog polarization control circuit according to claim 3 , wherein the fifth set of amplifier cross-multiplies the X- and Y-polarizations to obtain the set of rotated signals to align the set of rotated signals with the polarization frame of reference of the receiver.

5 . The analog polarization control circuit according to claim 1 , wherein at least one of the first and second set of amplifiers has a variable gain that is positive or negative.

6 . The analog polarization control circuit according to claim 5 , wherein the variable gain is implemented as a predefined set of trigonometric functions.

7 . The analog polarization control circuit according to claim 5 , wherein the variable gain is programmed to reduce computations of trigonometric weights and signs that correspond to the first and second phase angles.

8 . The analog polarization control circuit according to claim 1 , wherein the analog polarization control circuit comprises signal paths that independently process the first and second polarization signals and carries analog signals that represent magnitude and phase within each polarization signal component in a predefined coordinate system.

9 . A method for analog polarization control, the method comprising:
in response to receiving a first set of polarization signals having a first phase and a second set of polarization signals having a second phase, rotating, by a first phase angle, the first phase of one or more signals in the first set of polarization signals relative to the second phase of one or more signals in the second set of polarization signals to generate a set of rotated signals; and rotating the set of rotated signals by a second phase angle to align the set of rotated signals with a polarization frame of reference.

10 . The method according to claim 9 , wherein rotating the set of rotated signals reduces at least a component of the set of second polarization signals from the first set of polarization signals.

11 . The method according to claim 9 , wherein the set of rotated signals compensates for a polarization rotation of at least one of a first and second component of the first set of polarization signals relative to the second set of polarization signals.

12 . The method according to claim 9 , wherein rotating the first phase comprises adjusting a gain that is defined by a set of trigonometric functions.

13 . The method according to claim 12 , further comprising adjusting a polarity of the gain by adjusting relative transconductances of parallel differential amplifiers that are coupled in opposite polarities.

14 . The method according to claim 9 , wherein the second phase angle is chosen such that components resolved into X- and Y-polarization branches of a receiver are restored to be substantially orthogonal to each other.

15 . A system for analog, electronic polarization control, the system comprising:
an optical front-end that converts an optical signal to a first and second set of polarization components that have respective first and second phases; an analog polarization control circuit that, in response to receiving the first and second set of polarization components:
rotates, by a first phase angle, the first phase of one or more signals in the first set of polarization components relative to the second phase of one or more signals in the second set of polarization components to generate a set of rotated signals;
rotates the set of rotated signals by a second phase angle to align the set of rotated signals with a polarization frame of reference; and
outputs separated polarization signals; and
a differential modulation circuit that performs a set of non-linear operations on the separated polarization signals.

16 . The system according to claim 15 , wherein the analog polarization control circuit uses amplifiers having variable gain and trigonometric weights that correspond to the first and second phase angles, one or more of the trigonometric weights comprising a scalar value that has a positive or negative sign.

17 . The system according to claim 16 , wherein the analog polarization control circuit controls the amplifiers by adjusting the trigonometric weights that control the first and second phase angles.

18 . A system according to claim 15 , wherein the analog polarization control circuit rotates the set of rotated signals by adjusting gains of one or more amplifiers or attenuators in a plurality of signal paths representing a Cartesian or Complex Number representation of amplitude and phase of each polarization component.

19 . A system according to claim 15 , wherein the second phase angle is chosen such that components resolved into X- and Y-polarization branches are restored to be substantially orthogonal to each other.

20 . A system according to claim 19 , wherein the analog polarization control circuit cross-multiplies the X- and Y-polarizations to obtain the set of rotated signals to align the set of rotated signals with the polarization frame of reference of a receiver.

Assignees

• Maxim Integrated Products

Inventors

• Razzell Charles John

Classifications

• H04B10/6151

  comprising a polarization controller at the receiver's input stage · CPC title

• H04B10/614

  comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers (H04J14/06 takes precedence) · CPC title

• H04B10/5561

  Digital phase modulation · CPC title

• H03G3/3084

  in receivers or transmitters for electromagnetic waves other than radiowaves, e.g. lightwaves (H03G3/32, H03G3/34 take precedence) · CPC title

• H04B10/6166

  Polarisation demultiplexing, tracking or alignment of orthogonal polarisation components · CPC title