Apparatus and method for driving an optical modulator with independent modulator arm bias

Patent metadata

Field	Value
Publication number	US-11650475-B2
Application number	US-202117141672-A
Country	US
Kind code	B2
Filing date	Jan 5, 2021
Priority date	Aug 24, 2018
Publication date	May 16, 2023
Grant date	May 16, 2023

Abstract

Driving an optical modulator is described. A control circuit generates first and second input voltages based on a target phase modulation between first and second optical waveguide arms of the optical modulator. An offset control circuit generates first and second offset signals. A linear modulator driver receives the first and second offset signals, generates a first output voltage for biasing the first optical waveguide arm using the first offset signal, and generates a second output voltage for biasing the second optical waveguide arm using the second offset signal. Feedback circuitry can feed the first and second output voltages to the offset control circuit, which can generate the first and second offset signals using the first and second output voltages. The output voltages bias the waveguide arms so the optical modulator operates close to the target phase modulation, even in the presence of manufacturing errors.

First claim

What is claimed is:

1. An apparatus, comprising:
an optical modulator control circuit configured to generate a first input voltage and a second input voltage, the first input voltage and the second input voltage determined to produce a target phase modulation between a first optical waveguide arm and a second optical waveguide arm of an optical modulator;
an offset control circuit configured to generate a first offset signal and a second offset signal based on the first input voltage and the second input voltage; and
a linear modulator driver configured to
receive the first offset signal and the second offset signal;
generate, using the first offset signal, a first output voltage for biasing the first optical waveguide arm; and
generate, using the second offset signal, a second output voltage for biasing the second optical waveguide arm, wherein at least one of the first output voltage is different from the first input voltage or the second output voltage is different from the second input voltage.

2. The apparatus of claim 1 , wherein
the first offset signal is a first offset current and the second offset signal is a second offset current, and
the linear modulator driver is configured to
receive the first input voltage and the second input voltage;
generate the first output voltage for biasing the first optical waveguide arm by modifying the first input voltage using the first offset current; and
generate the second output voltage for biasing the second optical waveguide arm by modifying the second input voltage using the second offset current.

3. The apparatus of claim 1 , further comprising
a feedback circuit configured to feed the first output voltage and the second output voltage to the offset control circuit, wherein the offset control circuit is configured to generate the first offset signal and the second offset signal using the first output voltage and the second output voltage.

4. The apparatus of claim 1 , wherein the target phase modulation represents a condition wherein the first optical waveguide arm and the second optical waveguide arm exhibit one of a same phase modulation or a defined different phase modulation.

5. The apparatus of claim 1 , further comprising
the optical modulator, the optical modulator comprising a first electrode coupled to the first optical waveguide arm, and a second electrode coupled to the second optical waveguide arm, wherein the linear modulator driver is coupled to each of the first electrode and the second electrode for respectively applying the first output voltage at the first electrode and the second output voltage at the second electrode.

6. The apparatus of claim 1 , wherein the optical modulator is a Mach-Zehnder modulator in a series push-pull configuration.

7. The apparatus of claim 1 , further comprising
an optical modulator feedback circuit that receives an output of the optical modulator and transmits an input signal to the offset control circuit to modify the first offset signal and the second offset signal.

8. The apparatus of claim 1 , wherein the first offset signal and the second offset signal are determined to compensate for one or more of a manufacturing error in the first optical waveguide arm, a manufacturing error in the second optical waveguide arm, a manufacturing error in one or more resistor elements of the linear modulator driver, or a manufacturing error in one or more switching devices of the linear modulator driver.

9. The apparatus of claim 1 , wherein
the first offset signal comprises a first offset current and the second offset signal comprises a second offset current,
the linear modulator driver comprises a differential push-pull driver with an output stage including a single emitter follower or a dual series-stacked emitter follower receiving a DC offset current corresponding to the first offset signal and the second offset signal.

10. An apparatus, comprising:
an optical modulator control circuit configured to generate a first input voltage and a second input voltage, the first input voltage and the second input voltage determined to produce a target phase modulation between a first optical waveguide arm and a second optical waveguide arm of an optical modulator;
an offset control circuit configured to generate a first offset current and a second offset current;
a linear modulator driver configured to receive the first input voltage, the second input voltage, the first offset current, and the second offset current, and to generate a first output voltage for biasing the first optical waveguide arm by modifying the first input voltage using the first offset current and to generate a second output voltage for biasing the second optical waveguide arm by modifying the second input voltage using the second offset current, wherein at least one of the first output voltage is different from the first input voltage or the second output voltage is different from the second input voltage.

11. The apparatus of claim 10 , further comprising
a feedback circuit configured to feed the first output voltage and the second output voltage to the offset control circuit, wherein the offset control circuit is configured to generate the first offset current and the second offset current using the first output voltage and the second output voltage.

12. The apparatus of claim 10 , further comprising
the optical modulator, the optical modulator comprising a Mach-Zehnder (MZ) modulator in a series push-pull configuration, wherein the linear modulator driver is coupled to a first electrode and a second electrode of the MZ modulator to apply the first output voltage to the first electrode and apply the second output voltage to the second electrode.

13. The apparatus of claim 10 , further comprising
an optical modulator feedback circuit that receives an output of the optical modulator, determines a performance measure of the optical modulator using the output, and transmits an input signal to the offset control circuit to modify the first offset current and the second offset current using the performance measure.

14. A method, comprising:
receiving, from an optical modulator control circuit, a first input voltage and a second input voltage, wherein the first input voltage and the second input voltage are determined to produce a target phase modulation between a first optical waveguide arm and a second optical waveguide arm of an optical modulator;
generating, using an offset control circuit, a first offset signal and a second offset signal based on the first input voltage and the second input voltage;
receiving, at a linear modulator driver, the first offset signal and the second offset signal; and
generating, using the linear modulator driver, a first output voltage for biasing the first optical waveguide arm using the first offset signal, and a second output voltage for biasing the second optical waveguide arm using the second offset signal, wherein at least one of the first output voltage is different from the first input voltage and the second output voltage is different from the second input voltage.

15. The method of claim 14 , further comprising
calibrating a voltage offset between the first output voltage and the second output voltage to minimize a difference between the target phase modulation and an actual phase modulation of the optical modulator.

16. The method of claim 15 , wherein calibrating the voltage offset comprises
adjusting a control signal to the offset control circuit that determines the first offset signal and the second offset signal until the first output voltage is equal to the second o

Assignees

• Ciena Corp

Inventors

• Vitic Michael
• Falt Christopher Edgar
• Delisle-Simard Alexandre
• Poulin Michel

Classifications

• G02F1/0123

  Circuits for the control or stabilisation of the bias voltage, e.g. automatic bias control [ABC] feedback loops · CPC title

• G02F1/025 Primary

  in an optical waveguide structure (G02F1/017, {G02F1/2257} take precedence) · CPC title

• G02F1/2255 Primary

  controlled by a high-frequency electromagnetic component in an electric waveguide structure · CPC title

• G02F1/212

  Mach-Zehnder type · CPC title