# US 2019/0170500 A1 · Accurate chirped synthetic wavelength interferometer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0170500 A1 - Document ID: US20190170500A1 - Status: Published application - Kind: A1 - Application number: 16/264,346 - Filed: 2019-01-31 - Published: 2019-06-06 - Earliest claimed: 2014-10-29 - Assignees: Bridger Photonics, Inc. - Applicants: Bridger Photonics, Inc. - Inventors: Peter Roos; Michael Thorpe; Jason Brasseur - Web page: https://patentgrep.com/patent/US20190170500A1 ## CPC - G01B 9/02007: {Two or more frequencies or sources used for interferometric measurement (using only beat G01B9/02003)} - G01B 9/02004: using frequency scans - G01B 9/02075: {of particular errors} - G01B 11/026: {by measuring distance between sensor and object (G01B11/0608 takes precedence)} - H04B 10/071: using a reflected signal, e.g. using optical time domain reflectometers [OTDR] - H04B 10/07953: {Monitoring or measuring OSNR, BER or Q} - H04B 10/5165: {Carrier suppressed; Single sideband; Double sideband or vestigial} - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS - H04B: TRANSMISSION ## Abstract A system is provided for measuring distance or displacement, comprising: first and second laser sources configured to provide first and second laser outputs; a beam combiner configured to receive and combine at least part of the first and second laser outputs into a combined laser output; a signal calibrator configured to receive at least part of the first laser output, the second laser output, or the combined laser output, and output a calibration signal; a plurality of optical paths, including a first optical path, a second optical path, the plurality of optical paths being configured to direct at least part of the combined beam onto an optical detector to produce an interference signal; and a signal processor configured to receive the interference signal and determine a pathlength difference between the first and second optical paths. ## Claims ### Claim 1 A system comprising: a first chirped laser source configured to provide a first laser output having a first optical frequency varying at a first chirp rate; a calibration unit comprising at least one gas cell having at least one absorption line, the calibration unit configured to receive a first portion of the first laser output and to output a calibration signal; a first plurality of optical paths configured to direct a second portion of the first laser output onto an optical detector to produce a first interference signal; and a signal processor configured to receive the first interference signal and the calibration signal, the signal processor further configured to: determine a first time based on when the first optical frequency matches a feature of the absorption line of the gas cell during a chirp; and determine an interferometer phase based on the first time. ### Claim 2 (depends on 1) The system of claim 1 additionally comprising: a second chirped laser source configured to provide a second laser output having a second optical frequency varying at a second chirp rate; and a second plurality of optical paths configured to direct a portion of the second laser output onto the optical detector, or a different optical detector, to produce a second interference signal, wherein the signal processor is additionally configured to determine a second time based on when the second optical frequency matches a feature of an absorption line of the gas cell, or a different gas cell, during a chirp. ### Claim 3 (depends on 2) The system of claim 2, wherein the first plurality of optical paths and the second plurality of optical paths share at least one common optical path. ### Claim 4 (depends on 1) The system of claim 1, wherein the signal processor is further configured to determine a distance based, at least in part, on the determined interferometer phase. ### Claim 5 (depends on 1) The system of claim 1, wherein the determined interferometer phase is a standard interferometer phase. ### Claim 6 (depends on 1) The system of claim 1, wherein the determined interferometer phase is synthetic interferometer phase. ### Claim 7 A method comprising: chirping a first laser output having a first optical frequency by varying the first optical frequency at a first chirp rate; directing a first portion of the first laser output to a calibration unit comprising at least one gas cell having at least one absorption line, wherein the calibration unit is configured to output a calibration signal; directing a second portion of the first laser output through a first plurality of optical paths onto a detector to produce a first interference signal; and determining a distance based at least in part on the first interference signal and the calibration signal, wherein determining the distance comprises: determining a first time when the first optical frequency matches a feature of the absorption line of the gas cell during the chirping; and determining an interferometer phase based, at least in part, on the first time. ### Claim 8 (depends on 7) The method of claim 7, additionally comprising: chirping a second laser output having a second optical frequency by varying the second optical frequency at a second chirp rate; and directing a portion of the second laser output through a second plurality of optical paths onto the optical detector, or a different optical detector, to produce a second interference signal, wherein determining the distance is also based on the second interference signal, and wherein determining the distance further comprises determining a second time when the second optical frequency matches a feature of an absorption line of the gas cell, or a different gas cell, during a chirp. ### Claim 9 (depends on 8) The method of claim 8, wherein the first plurality of optical paths and the second plurality of optical paths share at least one common optical path. ### Claim 10 (depends on 8) The method of claim 8, wherein the first chirp rate is different from the second chirp rate. ### Claim 11 (depends on 8) The method of claim 8, wherein the first chirp rate is the same as the second chirp rate. ### Claim 12 A method comprising: producing a laser output; chirping the optical frequency of the laser output over a chirp bandwidth to produce a chirped beam; directing a portion of the chirped beam through a plurality of optical paths onto a detector; producing an interference signal comprising a first interference signal based on a first optical path and a second interference signal based on a second optical path, wherein the first interference signal and the second interference signal are sub-resolved; and determining a distance based on the interference signal, wherein determining the distance comprises applying a fitting operation to the interference signal based on fitting parameters, wherein the fitting parameters comprise at least an RF frequency of the first interference signal or the second interference signal and an RF phase of the first interference signal or the second interference signal. ### Claim 13 (depends on 12) The method of claim 12, wherein determining the distance further comprises applying a fast Fourier transform or related transform to the interference signal. ### Claim 14 (depends on 13) The method of claim 13, further comprising producing a range profile based on applying the fast Fourier transform or related transform to the interference signal, wherein the range profile comprises a first range peak based on the first interference signal and a second range peak based on the second interference signal, wherein the first range peak and the second range peak are sub-resolved. ### Claim 15 (depends on 13) The method of claim 13, wherein determining the distance further comprises applying a Hilbert or related transform to the interference signal. ### Claim 16 (depends on 13) The method of claim 13, wherein the determining the distance further comprises applying an electronic or digital filter to the interference signal. ### Claim 17 A method comprising: producing a first laser output; producing a second laser output; chirping the optical frequency of the first laser output at a first chirp rate over a first chirp bandwidth to produce a first chirped beam; chirping the optical frequency of the second laser output at a second chirp rate over a second chirp bandwidth to produce a second chirped beam; directing at least a portion of the first chirped beam through a plurality of optical paths onto a detector to produce a first interference signal; directing at least a portion of the second chirped beam through a plurality of optical paths onto the detector to produce a second interference signal peak, wherein the first interference signal and the second interference signal are sub-resolved; producing an interference signal based, at least in part, on interference between the first interference signal and the second interference signal; and determining a distance based on the interference signal, wherein determining the distance comprises applying a fitting operation to the interference signal based on fitting parameters, wherein the fitting parameters comprise at least an RF frequency of the first interference signal or the second interference signal and an RF phase of the first interference signal or the second interference signal. ### Claim 18 (depends on 17) The method of claim 17, wherein determining the distance further comprises applying a fast Fourier transform or related transform to the interference signal. ### Claim 19 (depends on 17) The method of claim 17, wherein determining the distance further comprises applying a Hilbert or related transform to the interference signal. ### Claim 20 (depends on 17) The method of claim 17, wherein determining the distance further comprises applying an electronic or digital filter to the interference signal. ### Claim 21 (depends on 17) The method of claim 17, wherein the first chirp rate is different from the second chirp rate. ### Claim 22 (depends on 17) The method of claim 17, wherein the first chirp rate is the same as the second chirp rate. ### Claim 23 (depends on 17) The method of claim 17, further comprising producing a range profile based on applying the fast Fourier transform or related transform to the interference signal, wherein the range profile comprises a first range peak based on the first interference signal and a second range peak based on the second interference signal, wherein the first range peak and the second range peak are sub-resolved.