# US 11,442,330 B1 · Circuits and methods for correcting DC bias and suppressing optical carrier frequency in electro-optic modulators > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,442,330 B1 - Document ID: US11442330B1 - Status: Granted - Kind: B1 - Application number: 17/182,938 - Filed: 2021-02-23 - Published: 2022-08-25 - Granted: 2022-09-13 - Earliest claimed: 2021-02-23 - Assignees: The Aerospace Corporation - Applicants: The Aerospace Corporation - Inventors: David B. Borlaug - Web page: https://patentgrep.com/patent/US11442330B1 ## CPC - G02F 1/2255: {controlled by a high-frequency electromagnetic component in an electric waveguide structure} - G02F 1/212: {Mach-Zehnder type} - 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 ## Abstract This application relates to circuits and methods for dynamically correcting DC bias and suppressing optical carrier frequency in electro-optic modulators (EOMs). A DC bias voltage for a control path may be determined using a control path DC bias structure. DC bias in a signal path may be corrected by applying the DC bias voltage, or a function thereof, to a signal path DC bias structure. Signal path and control path RF signal structures may be operated for a time period during which their DC biases drift together. An updated DC bias voltage for the control path may be determined using the control path DC bias structure. The drift of DC bias in the signal path may be corrected by applying the updated DC bias voltage, or a function thereof, to the signal path DC bias structure. ## Claims ### Claim 1 A circuit, comprising: a substrate comprising: an input receiving an optical carrier having a frequency; and a waveguide splitting the input into a signal path having a signal path output and a control path having a control path output; a first electro-optic modulator (EOM) comprising: a signal path radio-frequency (RF) structure comprising electrodes disposed along the signal path and configured to receive voltages to impose an RF signal on the optical carrier in the signal path; and a signal path DC bias structure comprising electrodes disposed along the signal path; a second EOM comprising: a control path RF signal structure comprising electrodes disposed along the control path; and a control path DC bias structure comprising electrodes disposed along the control path; a photodetector coupled to the control path output; and a controller comprising circuitry configured to: determine a DC bias voltage for the control path using changes in optical intensity at the photodiode caused by applying voltages to the electrodes of the control path DC bias structure; and correct DC bias in the signal path by applying the DC bias voltage, or a function thereof, to the electrodes of the signal path DC bias structure. ### Claim 2 (depends on 1) The circuit of claim 1, wherein the control path RF signal structure and the control path RF signal structure have approximately the same dimensions, materials, and manufacturing process as one another, and wherein the signal path DC bias structure and the control path DC bias structure have approximately the same dimensions, materials, and manufacturing process as one another. ### Claim 3 (depends on 1) The circuit of claim 1, wherein the signal path and the control path have approximately the same phase velocity, local temperature, and charge accumulation characteristics as one another. ### Claim 4 (depends on 1) The circuit of claim 1, wherein the optical carrier is asymmetrically split between the signal path and the control path. ### Claim 5 (depends on 1) The circuit of claim 1, wherein the signal path DC bias structure is disposed between the signal path RF structure and the signal path output, and wherein the control path DC bias structure is disposed between the control path RF signal structure and the control path output. ### Claim 6 (depends on 1) The circuit of claim 1, wherein the circuitry of the controller is configured to periodically determine an updated DC bias voltage for the control path using the control path DC bias structure, and to correct any drift in the DC bias in the signal path by applying the updated DC bias voltage, or a function thereof, to the signal path DC bias structure. ### Claim 7 (depends on 1) The circuit of claim 1, further comprising a signal path carrier suppression structure comprising electrodes along the signal path and a control path carrier suppression structure comprising electrodes along the control path, wherein the circuitry of the controller further is configured to: determine a carrier suppression voltage for the control path using changes in optical intensity at the photodiode caused by applying voltages to the electrodes of the control path carrier suppression structure; and dynamically suppress the frequency of the optical carrier at the signal path output by applying the carrier suppression voltage, or a function thereof, to the electrodes of the signal path carrier suppression structure. ### Claim 8 (depends on 1) The circuit of claim 1, wherein the waveguide comprises a junction splitting the signal path into first and second sections and a junction combining the first and second sections into the signal path output, a first one of the electrodes of the signal path RF signal structure being between the first and second sections, a second one of the electrodes of the signal path RF signal structure being outside the first section, and a third one of the electrodes of the signal path RF signal structure being outside the second section, and a first one of the electrodes of the signal path DC bias structure being between the first and second sections, a second one of the electrodes of the signal path DC bias structure being outside the first section, and a third one of the electrodes of the signal path DC bias structure being outside the second section; and wherein the waveguide further comprises a junction splitting the control path into first and second sections and a junction combining the first and second sections into the signal path output, a first one of the electrodes of the control path RF signal structure being between the first and second sections, a second one of the electrodes of the control path RF signal structure being outside the first section, and a third one of the electrodes of the control path RF signal structure being outside the second section, and a first one of the electrodes of the control path DC bias structure being between the first and second sections, a second one of the electrodes of the control path DC bias structure being outside the first section, and a third one of the electrodes of the control path DC bias structure being outside the second section. ### Claim 9 A circuit, comprising: a substrate comprising: an input receiving an optical carrier having a frequency; and a waveguide splitting the input into a signal path having a signal path output and a control path having a control path output; a first electro-optic modulator (EOM) comprising a signal path radio frequency (RF) signal structure comprising electrodes disposed along the signal path and configured to receive voltages to impose an RF signal on the optical carrier in the signal path; a signal path carrier suppression structure comprising electrodes disposed along the signal path; a second EOM comprising a control path RF signal structure comprising electrodes disposed along the control path; a control path carrier suppression structure comprising electrodes disposed along the control path; a photodetector coupled to the control path output; and a controller comprising circuitry configured to: determine a carrier suppression voltage for the control path using changes in optical intensity at the photodiode caused by applying voltages to the electrodes of the control path carrier suppression structure; and suppress the frequency of the optical carrier at the signal path output by applying the carrier suppression voltage to the electrodes of the signal path carrier suppression structure. ### Claim 10 (depends on 9) The circuit of claim 9, wherein the signal path RF signal structure and the control path RF signal structure have approximately the same dimensions, materials, and manufacturing process as one another, and wherein the signal path carrier suppression structure and the control path carrier suppression structure have approximately the same dimensions, materials, and manufacturing process as one another. ### Claim 11 (depends on 9) The circuit of claim 9, wherein the signal path and the control path have approximately the same phase velocity, local temperature, and charge accumulation characteristics as one another. ### Claim 12 (depends on 9) The circuit of claim 9, wherein the optical carrier is asymmetrically split between the signal path and the control path. ### Claim 13 (depends on 9) The circuit of claim 9, wherein the signal path carrier suppression structure is disposed between the signal path RF signal structure and the signal path output, and wherein the control path carrier suppression structure is disposed between the control path RF signal structure and the control path output. ### Claim 14 (depends on 9) The circuit of claim 9, wherein the circuitry of the controller is configured to periodically determine an updated carrier suppression voltage using the control path carrier suppression structure, and to correct any changes to the optical carrier frequency at the signal path output by applying the updated carrier suppression voltage, or a function thereof, to the signal path carrier suppression structure. ### Claim 15 (depends on 9) The circuit of claim 9, further comprising a signal path DC bias structure comprising electrodes along the signal path and a control path DC bias structure comprising electrodes along the control path, wherein the circuitry of the controller further is configured to: determine a DC bias voltage using changes in optical intensity at the photodiode caused by applying voltages to the electrodes of the control path DC bias structure; and correct DC bias in the EOM by applying the DC bias voltage, or a function thereof, to the electrodes of the signal path DC bias structure. ### Claim 16 (depends on 9) The circuit of claim 9, wherein the waveguide further comprises a junction splitting the signal path into first and second sections and a junction combining the first and second sections into the signal path output, a first one of the electrodes of the signal path RF signal structure being between the first and second sections, a second one of the electrodes of the signal path RF signal structure being outside the first section, and a third one of the electrodes of the signal path RF signal structure being outside the second section, and a first one of the electrodes of the signal path carrier suppression structure being between the first and second sections, a second one of the electrodes of the signal path carrier suppression structure being outside the first section, and a third one of the electrodes of the signal path carrier suppression structure being outside the second section; and wherein the waveguide further comprises a junction splitting the control path into first and second sections and a junction combining the first and second sections into the signal path output, a first one of the electrodes of the control path RF signal structure being between the first and second sections, a second one of the electrodes of the control path RF signal structure being outside the first section, and a third one of the electrodes of the control path RF signal structure being outside the second section, and a first one of the electrodes of the control path carrier suppression structure being between the first and second sections, a second one of the electrodes of the control path carrier suppression structure being outside the first section, and a third one of the electrodes of the control path carrier suppression structure being outside the second section. ### Claim 17 A method, comprising: determining a DC bias voltage for a control path using a control path DC bias structure; correcting DC bias in a signal path by applying the DC bias voltage, or a function thereof, to a signal path DC bias structure; operating a signal path radio-frequency (RF) signal structure and a control path RF signal structure for a time period during which DC biases in the signal path and in the control path drift; determining an updated DC bias voltage for the control path using the control path DC bias structure; and correcting the drift of the DC bias in the signal path by applying the updated DC bias voltage, or a function thereof, to the signal path DC bias structure. ### Claim 18 (depends on 17) The method of claim 17, wherein the signal path DC bias structure and the signal path RF signal structure are disposed along a signal path provided by a waveguide within a substrate, and wherein the control path DC bias structure and the control path RF signal structure are disposed along a control path provided by the waveguide within the substrate. ### Claim 19 A method, comprising: determining a carrier suppression voltage for a control path using a control path carrier suppression structure; suppressing a carrier frequency at a signal path output by applying the carrier suppression voltage, or a function thereof, to a signal path carrier suppression structure; operating a signal path radio-frequency (RF) signal structure for a time period during which the carrier frequency changes or carrier suppression voltages in the signal path or in the control path otherwise drift; determining an updated carrier suppression voltage for the control path using the control path carrier suppression structure; and suppressing the carrier frequency at the signal path output by applying the updated carrier suppression voltage, or a function thereof, to the signal path carrier suppression structure. ### Claim 20 (depends on 19) The method of claim 19, wherein the signal path carrier suppression structure and the signal path RF signal structure are disposed along a signal path provided by a waveguide within a substrate, and wherein the control path carrier suppression structure and the control path RF signal structure are disposed along a control path provided by the waveguide within the substrate. ### Claim 21 A method, comprising: determining a DC bias voltage for a control path using a control path DC bias structure; correcting DC bias in a signal path by applying the DC bias voltage, or a function thereof, to a signal path DC bias structure; determining a carrier suppression voltage for the control path using a control path carrier suppression structure; suppressing a carrier frequency at a signal path output by applying the carrier suppression voltage, or a function thereof, to a signal path carrier suppression structure; determining an updated DC bias voltage for the control path using the control path DC bias structure; correcting the DC bias in the signal path by applying the updated DC bias voltage, or a function thereof, to the signal path DC bias structure; determining an updated carrier suppression voltage for the control path using the control path carrier suppression structure; and suppressing the carrier frequency at the signal path output by applying the updated carrier suppression voltage, or a function thereof, to the signal path carrier suppression structure.