Integrated wavelength locker

Patent metadata

Field	Value
Publication number	US-10128634-B2
Application number	US-201715689352-A
Country	US
Kind code	B2
Filing date	Aug 29, 2017
Priority date	Oct 10, 2016
Publication date	Nov 13, 2018
Grant date	Nov 13, 2018

Abstract

Described are various configurations of integrated wavelength lockers including asymmetric Mach-Zehnder interferometers (AMZIs) and associated detectors. Various embodiments provide improved wavelength-locking accuracy by using an active tuning element in the AMZI to achieve an operational position with high locking sensitivity, a coherent receiver to reduce the frequency-dependence of the locking sensitivity, and/or a temperature sensor and/or strain gauge to computationally correct for the effect of temperature or strain changes.

First claim

What is claimed is:

1. A wavelength locker comprising:
an athermal asymmetric Mach-Zehnder interferometer (AMZI) comprising an input coupler, two waveguide arms, and an output coupler having at least two output ports;
placed at the at least two output ports, at least two respective photodetectors for measuring at least two respective optical interference signals exiting the at least two output ports;
a temperature sensor to measure a temperature of the AMZI and a strain gauge to measure a strain in the AMZI; and
circuitry configured to adjust a locking condition based on the measured temperature and strain, and to tune a frequency of light coupled into the AMZI, based on a feedback parameter derived from the measured optical interference signals, to satisfy the adjusted locking condition.

2. The wavelength locker of claim 1 , wherein the output coupler and the at least two photodetectors are configured as a coherent receiver in which relative phase shifts imparted between two signals being interfered to form the optical interference signals differ between at least two of the output ports by a value that is not a multiple of 180°, and wherein the feedback parameter is a filter phase and the locking condition is satisfied if the filter phase matches a target filter phase associated with a specified locking frequency, the target filter phase being adjusted based on the measured temperature and strain.

3. The wavelength locker of claim 1 , wherein the output coupler has four output ports and the wavelength locker comprises four respective photodetectors, and wherein the output coupler and the four photodetectors are configured as a 90-degree hybrid optical receiver measuring balanced in-phase and quadrature signals.

4. The wavelength locker of claim 1 , wherein the AMZI includes in one of the waveguide arms an active tuning element configured to adjust an optical-path-length difference between the two waveguide arms, wherein the at least two photodetectors comprise a pair of photodetectors forming a balanced receiver, wherein the feedback parameter is a balanced photocurrent measured with the balanced receiver, and wherein the locking condition is satisfied if the balanced photocurrent is substantially zero when a setting of the active tuning element matches a target setting associated with a specified locking frequency, the target setting being adjusted based on the measured temperature and strain.

5. The wavelength locker of claim 1 , wherein the locking condition comprises a target parameter, the wavelength locker further comprising memory storing target parameter values or correction coefficients for a plurality of temperatures and strains, the circuitry configured to select one of the stored target parameter values or correction coefficients based on the measured temperature and strain.

6. The wavelength locker of claim 1 , wherein the locking condition comprises a target parameter, and wherein the circuitry is configured to computationally adjust a stored target parameter value associated with a nominal temperature and a nominal strain based on the measured temperature and strain using a stored functional dependence of the target parameter on temperature and strain.

7. The wavelength locker of claim 1 , wherein the strain gauge comprises two resistance temperature detectors made from two respective metals differing in their respective temperature coefficients of resistance.

8. A method for locking a frequency of a light source of a photonic integrated circuit using an integrated wavelength locker comprising an athermal AMZI, the method comprising:
coupling light emitted by the light source into the AMZI at an input of the AMZI;
measuring at least two optical interference signals at an output of the AMZI;
measuring a temperature of the AMZI and a strain in the AMZI;
adjusting a locking condition based on the measured temperature and strain; and
tuning a frequency of the light, based on a feedback parameter derived from the measured optical interference signals, to satisfy the adjusted locking condition.

9. The method of claim 8 , further comprising computing a filter phase of the AMZI from the measured optical signals, the filter phase constituting the feedback parameter, wherein the locking condition is satisfied by tuning the frequency of the light to cause the filter phase to match a target filter phase associated with a specified locking condition and adjusted based on the measured temperature and strain.

10. The method of claim 9 , wherein the at least two optical interference signals comprise balanced in-phase and quadrature signals.

11. The method of claim 8 , further comprising adjusting a setting of an active tuning element included in one waveguide arm of the AMZI to match a target setting associated with a specified locking frequency and adjusted based on the measured temperature and strain, wherein the feedback parameter is a balanced photocurrent resulting from the at least two optical interference signals, and wherein the locking condition is satisfied by tuning the frequency of the light to bring the balanced photocurrent to substantially zero while the setting of the active tuning element matches the target setting.

12. The method of claim 8 , wherein adjusting the locking condition comprises selecting a value of a target parameter included in the locking condition, among target parameter values stored for a plurality of temperature and strains, based on the measured temperature and strain.

13. The method of claim 8 , wherein adjusting the locking condition comprises computationally adjusting a value of a target parameter included in the locking condition based on the measured temperature and strain using a stored functional dependence of the target parameter on temperature and strain.

14. The method of claim 8 , further comprising, prior to use of the integrated wavelength locker for frequency locking, measuring a filter response of the AMZI at multiple wavelengths and temperatures.

Assignees

• Juniper Networks Inc

Inventors

• Parker John
• Bauters Jared
• Roth Jonathan Edgar
• Norberg Erik
• Fish Gregory Alan

Classifications

• H01S5/0612

  controlled by temperature · CPC title

• H01S5/0264

  for monitoring the laser-output · CPC title

• G02B6/29353

  with a wavelength selective element in at least one light guide interferometer arm, e.g. grating, interference filter, resonator · CPC title

• G02B6/12007

  forming wavelength selective elements, e.g. multiplexer, demultiplexer · CPC title

• H01S5/0617

  using memorised or pre-programmed laser characteristics · CPC title