Mach-Zehnder modulator bias control for arbitrary waveform generation

Patent metadata

Field	Value
Publication number	US-9281898-B2
Application number	US-201414183767-A
Country	US
Kind code	B2
Filing date	Feb 19, 2014
Priority date	Feb 19, 2014
Publication date	Mar 8, 2016
Grant date	Mar 8, 2016

Abstract

A method comprising applying an In-phase (I) offset to an I component of an orthogonal pseudo-random coded direct current (DC) bias signal, applying a Quadrature-phase (Q) offset to a Q component of the orthogonal pseudo-random coded DC bias signal, applying an I dither signal to an I Mach-Zehnder modulator (MZM), wherein the I dither signal is based on the I component of the orthogonal pseudo-random coded DC bias signal, applying a Q dither signal to a Q MZM, wherein the Q dither signal is based on the Q component of the orthogonal pseudo-random coded DC bias signal, and performing arbitrary waveform generation (AWG) by modulating an analog data signal onto an optical carrier signal via the MZMs, wherein the I offset and the Q offset are selected to mitigate crosstalk between the I MZM and the Q MZM due to a finite extinction ratio.

First claim

What is claimed is:

1. An optical transmitter comprising:
a plurality of Mach-Zehnder modulators (MZMs) configured to modulate analog data signals onto an optical carrier signal for transmission;
an MZM bias controller coupled to at least one of the MZMs and configured to bias the MZMs with orthogonal pseudo-random code based dither signals to suppress noise associated with operation of the MZMs,
wherein the MZM bias controller comprises:
an orthogonal pseudo-random code generator for generating digital signals comprising orthogonal pseudo-random codes;
a digital to analog converter (DAC) coupled to the orthogonal pseudo-random code generator and an MZM bias controller output and configured to:
receive the digital signals of orthogonal pseudo-random codes as input; and
based on the input, output analog signals of the orthogonal pseudo-random codes to an MZM of the plurality of MZMs for use as orthogonal pseudo-random code based dither signals; and

a pseudo-noise code generator coupled to the DAC, wherein pseudo-noise code signals from the pseudo-noise code generator are combined with the digital signals of orthogonal pseudo-random codes as input to the DAC.

2. The optical transmitter of claim 1 , wherein the MZM bias controller further comprises a direct current (DC) bias module for generating offset DC bias signals, wherein the offset DC bias signals are combined with the digital signals of orthogonal pseudo-random codes as input to the DAC.

3. The optical transmitter of claim 2 , wherein the MZMs comprise an In-phase (I) MZM and a Quadrature-phase (Q) MZM, wherein the DC bias module comprises an I offset module and a Q offset module, wherein the I offset module and the Q offset module each:
receive control signals;
offset the received control signals by a value selected to mitigate crosstalk between the I MZM and Q MZM associated with a finite extinction ratio; and
forward the offset control signals toward the DAC as offset DC bias signals.

4. The optical transmitter of claim 3 , further comprising an optical receiver configured to:
receive a portion of the optical carrier signal transmitted from the MZMs; and
forward the optical carrier signal portion toward the I offset module and the Q offset module.

5. The optical transmitter of claim 4 , further comprising a synchronous orthogonal pseudo-random code generator for generating a synchronous signal of orthogonal pseudo-random codes, wherein the synchronous signal of orthogonal pseudo-random codes are combined with the optical carrier signal portion to generate the control signals.

6. The optical transmitter of claim 5 , further comprising a synchronous pseudo-noise code generator for generating a synchronous pseudo-noise code signal, wherein the optical carrier signal portion is further combined with the synchronous pseudo-noise code signal to generate the control signals.

7. A method comprising:
generating an In-phase (I) bias signal by:
receiving a measured I portion of a control signal from an I Mach-Zehnder modulator (MZM);
offsetting the I portion of the control signal by an I offset;
applying an I dither signal to the I portion of the control signal, wherein the I dither signal is based on orthogonal pseudo-random codes; and
apply a pseudo-noise code signal to the I portion of the control signal;

generating a Quadrature-phase (Q) bias signal by:
receiving a measured Q portion of the control signal from a Q MZM;
offsetting the Q portion of the control signal by a Q offset;
applying a Q dither signal to the Q portion of the control signal, wherein the Q dither signal is based on the orthogonal pseudo-random codes; and
apply a pseudo-noise code signal to the Q portion of the control signal;

applying the I bias signal to the I MZM;
applying the Q bias signal to the Q MZM; and
performing arbitrary waveform generation (AWG) by modulating an analog data signal onto an optical carrier signal via the I and Q MZMs,
wherein the I offset and the Q offset are selected to mitigate crosstalk between the I MZM and the Q MZM due to a finite extinction ratio.

8. The method of claim 7 , wherein the optical carrier signal is split between the Q MZM and the I MZM, wherein the finite extinction ratio describes the ratio of the optical carrier signal received by each MZM, and wherein the finite extinction ratio is a result of MZM manufacturing process imperfections.

9. The method of claim 7 , further comprising:
generating a phase bias signal by:
receiving a measured phase portion of the control signal from at least one of the MZMs; and
applying a phase dither signal to the phase portion of the control signal, wherein the phase dither signal is based on the orthogonal pseudo-random codes; and

applying the phase bias signal to at least one of the I and Q MZMs.

10. The method of claim 9 , wherein the phase portion of the control signal, when generating the phase bias signal, is absent an offset.

11. The method of claim 9 , wherein the I offset is described by the equation:

I
⁢

⁢
Offset

∝

1

ER
Q

×

〈

cos
⁡

(

π
2

⁢

υ

Q
,
RF

)

〉

〈

cos
⁡

(

π
2

⁢

υ

I
,
RF

)

〉

,

wherein ER Q is an extinction ratio of the Q MZM, ν Q,RF is a driving signal of the Q MZM normalized to v π , ν I,RF is a driving signal of the I MZM normalized to vπ, and vπ is a driving voltage that causes a phase shift of π in the Q portion.

12. The method of claim 9 , wherein the Q offset is described by the equation:

Assignees

• Futurewei Technologies Inc

Inventors

• Guo Qing
• Wang Jianfeng
• Zhu Fei

Classifications

• H04B10/50575

  to control the modulator DC bias · CPC title

• H04B10/5161

  Combination of different modulation schemes · CPC title

• H04B10/5053 Primary

  using a parallel, i.e. shunt, combination of modulators · CPC title

• H04B3/464

  Electricity · mapped topic

• H04B10/5561

  Digital phase modulation · CPC title