# US 12,222,589 B2 · Thermal stabilization circuit for an optical ring resonator

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 12,222,589 B2
- Document ID: US12222589B2
- Status: Granted
- Kind: B2
- Application number: 17/729,031
- Filed: 2022-04-26
- Published: 2023-10-26
- Granted: 2025-02-11
- Earliest claimed: 2022-04-26
- Assignees: GlobalFoundries U.S. Inc.
- Applicants: GlobalFoundries U.S. Inc.
- Inventors: Michal Rakowski; Vaibhav A. Ruparelia; Riddhi Nandi; Prateek K. Sharma; Avijit Chatterjee; Vasudeva Reddy KuppiReddy; Indranil Som
- Web page: https://patentgrep.com/patent/US12222589B2

## CPC

- G02F 1/0123: {Circuits for the control or stabilisation of the bias voltage, e.g. automatic bias control [ABC] feedback loops}
- G02B 6/12026: {characterised by means for reducing the temperature dependence}
- G02B 6/2934: {Fibre ring resonators, e.g. fibre coils}
- G02F 1/0147: {based on thermo-optic effects (G02F1/132 takes precedence)}
- G02F 2201/58: Arrangements comprising a monitoring photodetector
- G02F 2203/15: involving resonance effects, e.g. resonantly enhanced interaction
- H01S 3/083: Ring lasers {(fibre ring lasers H01S3/06791)}
- H01S 5/0078: {for frequency filtering}
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL

## Abstract

Disclosed is a thermal stabilization circuit including a heater, which is adjacent and thermally coupled to a closed-curve waveguide of an optical ring resonator, and an analog feedback circuit, which includes a fully autonomous analog feedback loop from a drop port of a bus waveguide of the optical ring resonator to the heater. This analog feedback circuit is configured to dynamically control the electrical power provided to the heater and, thereby to dynamically control the thermal output of the heater in order to tune the ring resonance wavelength to the operating laser wavelength. The analog feedback circuit is further configured to be independent of input power, to be power efficient, to have a relatively small footprint, to have a tunable time constant and to facilitate adjustable wavelength locking. Also disclosed is a device (e.g., a ring-based transceiver or the like), which includes multiple optical ring resonators and corresponding thermal stabilization circuits.

## Claims

### Claim 1

A structure comprising:
a heater adjacent to an optical ring resonator; and
an analog feedback circuit configured to detect an optical signal at a drop port of the optical ring resonator, to generate an analog voltage signal using the optical signal, to generate a reference voltage signal using the analog voltage signal, to compare the reference voltage signal to the analog voltage signal to generate a voltage control signal, and to control power provided to a heater based on the voltage control signal.

### Claim 2 (depends on 1)

The structure of claim 1, wherein the optical ring resonator comprises:
a first bus waveguide having an input port and a through port;
a second bus waveguide having the drop port; and
a closed-curve waveguide between the first bus waveguide and the second bus waveguide, wherein the heater is adjacent to the closed-curve waveguide and wherein the power controls a thermal output of the heater so as to tune a ring resonance wavelength.

### Claim 3 (depends on 1)

The structure of claim 1, wherein the analog feedback circuit comprises:
a photosensor configured to receive the optical signal from the drop port and to output an analog current signal;
a current-to-voltage converter configured to receive the analog current signal and to output the analog voltage signal; and
a peak-based reference voltage generator configured to receive the analog voltage signal and to generate the reference voltage signal based the analog voltage signal.

### Claim 4 (depends on 3)

The structure of claim 3, wherein the peak-based reference voltage generator further generates the reference voltage signal based on an offset amount from a drop port transmission peak.

### Claim 5 (depends on 4)

The structure of claim 4, wherein the peak-based reference voltage generator comprises:
a diode having a diode input and a diode output;
a first amplifier comprising: two first amplifier inputs and a first amplifier output, wherein the first amplifier output is connected to the diode input and wherein the two first amplifier inputs are connected to the current-to-voltage converter for receiving the analog voltage signal and to the diode output, respectively;
a second amplifier comprising two second amplifier inputs and a second amplifier output, wherein the two second amplifier inputs are connected to the diode output and to the second amplifier output, respectively;
a capacitor connected to an intermediate node between the diode and the second amplifier and to ground and configured to store a maximum voltage level corresponding to the drop port transmission peak;
an output node; and
a voltage divider connected to the second amplifier output and the output node, wherein the voltage divider is configured to output the reference voltage signal at the output node such that the reference voltage signal is a predetermined fraction of the maximum voltage level given the offset amount.

### Claim 6 (depends on 5)

The structure of claim 5, wherein the voltage divider comprises:
a programmable resistor connected in series between the second amplifier output and the output node; and
an additional resistor connected between the output node and ground.

### Claim 7 (depends on 3)

The structure of claim 3, wherein the analog feedback circuit further comprises:
a comparator configured to receive the analog voltage signal and the reference voltage signal and to output the voltage control signal;
an integrator configured to receive the voltage control signal and to output an adjusted voltage signal proportional to a time integral of the voltage control signal; and
a current mirror configured to receive the adjusted voltage signal and to control the power provided to the heater.

### Claim 8 (depends on 7)

The structure of claim 7, wherein the heater and the integrator have approximately equal time constants.

### Claim 9 (depends on 7)

The structure of claim 7, wherein the analog feedback circuit further comprises: a reset device connected between the peak-based reference voltage generator and the comparator, wherein the reset device is operable in one of an operational mode and a reset mode in response to a mode control signal, wherein in the operational mode the reset device passes the reference voltage signal to the comparator, and wherein in the reset mode the reset device passes a positive supply voltage signal to the comparator.

### Claim 10

A structure comprising:
optical ring resonators; and
thermal stabilization circuits for the optical ring resonators, wherein each thermal stabilization circuit for each optical ring resonator comprises:
a heater adjacent to the optical ring resonator; and
an analog feedback circuit configured to detect an optical signal at a drop port of the optical ring resonator, to generate an analog voltage signal using the optical signal, to generate a reference voltage signal using the analog voltage signal, to compare the reference voltage signal to the analog voltage signal to generate a voltage control signal, and to control power provided to the heater based on the voltage control signal.

### Claim 11 (depends on 10)

The structure of claim 10,
wherein each optical ring resonator comprises:
a portion of a first bus waveguide, wherein the first bus waveguide has an input port and a through port;
a second bus waveguide having the drop port; and
a closed-curve waveguide between the first bus waveguide and the second bus waveguide,
wherein the heater of the thermal stabilization circuit for each optical ring resonator is adjacent to the closed-curve waveguide of the optical ring resonator, and
wherein the power provided to the heater controls a thermal output of the heater so as to tune a resonance wavelength.

### Claim 12 (depends on 10)

The structure of claim 10, wherein the analog feedback circuit of the thermal stabilization circuit for each optical ring resonator comprises:
a photosensor configured to receive the optical signal from the drop port and to output an analog current signal;
a current-to-voltage converter configured to receive the analog current signal and to output the analog voltage signal;
a peak-based reference voltage generator configured to receive the analog voltage signal and to generate the reference voltage signal based the analog voltage signal and on an offset amount from a drop port transmission peak;
a comparator configured to receive the analog voltage signal and the reference voltage signal and to output the voltage control signal;
an integrator configured to receive the voltage control signal and to output an adjusted voltage signal proportional to a time integral of the voltage control signal, wherein the heater and the integrator have approximately equal time constants; and
a current mirror configured to receive the adjusted voltage signal and to output the current output signal to the heater.

### Claim 13 (depends on 12)

The structure of claim 12,
wherein the peak-based reference voltage generator of the corresponding analog feedback circuit comprises:
a diode having a diode input and a diode output;
a first amplifier comprising: two first amplifier inputs and a first amplifier output, wherein the first amplifier output is connected to the diode input and wherein the two first amplifier inputs are connected to the current-to-voltage converter for receiving the analog voltage signal and to the diode output, respectively;
a second amplifier comprising two second amplifier inputs and a second amplifier output, wherein the two second amplifier inputs are connected to the diode output and to the second amplifier output, respectively;
a capacitor connected to an intermediate node between the diode and the second amplifier and to ground and configured to store a maximum voltage level corresponding to the drop port transmission peak;
an output node; and
a voltage divider connected to the second amplifier output and the output node, wherein the voltage divider is configured to output the reference voltage signal at the output node such that the reference voltage signal is a predetermined fraction of the maximum voltage level given the offset amount, and
wherein the corresponding analog feedback circuit further comprises a reset device connected between the peak-based reference voltage generator and the comparator, wherein the reset device is operable in one of an operational mode and a reset mode in response to a mode control signal, wherein in the operational mode the reset device passes the reference voltage signal to the comparator, and wherein in the reset mode the reset device passes a positive supply voltage signal to the comparator.