# US 12,768,639 B2 · Three-phase spectral interferometry with improved signal retrieval > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,768,639 B2 - Document ID: US12768639B2 - Status: Granted - Kind: B2 - Application number: 18/525,578 - Filed: 2023-11-30 - Published: 2024-05-16 - Granted: 2026-10-20 - Earliest claimed: 2022-10-17 - Assignees: Lawrence Livermore National Security, LLC - Applicants: Lawrence Livermore National Security, LLC - Inventors: Ryan Douglas Muir; John E. Heebner; Daniel Ernest Mittelberger - Web page: https://patentgrep.com/patent/US12768639B2 ## CPC - G01B 9/02041: {characterised by particular imaging or detection techniques} - G01J 3/45: Interferometric spectrometry - G11B 7/0065: Recording, reproducing or erasing by using optical interference patterns, e.g. holograms - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract Methods, systems and devices are described that enable measurement and characterization of complex laser pulses by relying on three interferograms that are measured simultaneously. The described three-phase spectral interferometry (3PSI) can meet the growing demand for optical recorders with long record and 1 ps or finer resolution. These techniques leverage various calibration and signal retrieval operations that allow improved system performance. An example method for determining characteristics of an input optical signal includes measuring the spectra associated with three interferograms produced at outputs of a three-by-three optical splitter, and determining an amplitude and a phase value of the input optical signal using those measurements and the results of a calibration procedure that characterizes point spread functions across multiple spectrometers and determines corrections factors for the spectrometers. ## Claims ### Claim 1 An interferometric method for determining characteristics of an input optical signal using a three-phase interferometric system, comprising: providing the input optical signal to a first input of a three-by-three optical splitter; providing a reference optical signal to a second input of the three-by-three optical splitter; measuring spectra associated with three interferograms produced at a first, a second and a third output of the three-by-three optical splitter using a plurality of spectrometers; and determining an amplitude value and a phase value of the input optical signal from information obtained from the measured spectra, wherein: prior to providing the input optical signal and the reference optical signal for determining characteristics of an input optical signal, performing a calibration procedure to characterize point spread functions across the plurality of spectrometers used for measuring interferograms output from the three-by-three optical splitter, the calibration operation including, for each interferometer: constructing a regression matrix and determining a correction factor that allow spectra of the input optical signal to be retrieved from a background subtracted image according to a linear fitting model, wherein the regression matrix is constructed from a plurality of calibration images acquired at multiple wavelengths and is configured to compensate for wavelength-dependent point spread function variations and spectral response variations of each spectrometer so that the retrieved spectra are corrected for non-uniform detector response and wavelength-dependent spreading of interferogram energy across detector pixels. ### Claim 2 (depends on 1) The method of claim 1, wherein the correction factor is determined using a white light or broadband source as input to the three-by-three optical splitter, measuring a detected spectra by each spectrometer, and determining a deviation of the measured spectra from a uniform spectra for each spectrometer. ### Claim 3 (depends on 1) The method of claim 1, wherein the correction factor is obtained based on a ratio of a downsampled image to an oversampled image. ### Claim 4 (depends on 1) The method of claim 1, comprising, for each spectrometer in the three-phase interferometric system, deconvolving each local point spread function, normalizing the spectral response, and performing the linear fit at every resolvable wavelength. ### Claim 5 (depends on 1) The method of claim 1, wherein the regression matrix and the correction factor are computed only once per calibration procedure. ### Claim 6 (depends on 1) The method of claim 1, wherein each of the three interferograms is determined based on parameters obtained as part of the calibration procedure, the parameters relating to: polarization mismatch backgrounds of the interferograms, a signal content that is outside of record length, reference spectral response amplitudes for the interferograms, or signal spectral response amplitudes for the interferograms. ### Claim 7 (depends on 1) The method of claim 1, wherein each of the three interferograms is a function of a plurality of parameters including: a first parameter that defines spectral response amplitude of the reference optical signal for the corresponding interferogram, and a second parameter that defines spectral response amplitude of the input optical signal for the corresponding interferogram. ### Claim 8 An interferometric method for determining characteristics of an input optical signal using a three-phase interferometric system, comprising: providing the input optical signal to a first input of a three-by-three optical splitter; providing a reference optical signal to a second input of the three-by-three optical splitter; measuring spectra associated with three interferograms produced at a first, a second and a third output of the three-by-three optical splitter using a plurality of spectrometers, each of the three interferograms being a function of a plurality of parameters including a first parameter that defines a spectral response amplitude of the reference optical signal for the corresponding interferogram and a second parameter that defines a spectral response amplitude of the input optical signal for the corresponding interferogram, and determining an amplitude value and a phase value of the input optical signal from information obtained from the measured spectra, wherein: prior to providing the input optical signal and the reference optical signal for determining characteristics of an input optical signal, performing a calibration procedure to characterize point spread functions across the plurality of spectrometers used for measuring interferograms output from the three-by-three optical splitter, the calibration operation including, for each interferometer: constructing a regression matrix and determining a correction factor that allow spectra of the input optical signal to be retrieved from a background subtracted image according to a linear fitting model; and determining the first and the second parameter values as part of the calibration procedure that injects a broadband source into the first and the second input of the three-by-three optical splitter one at a time and making corresponding spectral measurements, wherein the first and the second parameter values are determined based on the following relationships: A RN = R N - ⁢ Measured / R Retrieved , and A SN = S N - ⁢ Measured / S Retrieved wherein: ARN represents the first parameter for the Nth spectrometer, where N has values of 1, 2 and 3, ASN represents the second parameter for the Nth spectrometer, where N has values of 1, 2 and 3, SN_Measured and RN_Measured are respectively spectra of the broadband source measured on spectrometer N at the corresponding output of the three-by-three optical splitter, SRetrieved is a retrieved signal spectra computed using all N spectral measurements associated with the broadband source that is injected into the first input of the three-by-three optical splitter, and RRetrieved is a retrieved reference signal spectra computed using all N spectral measurements associated with the broadband source that is injected into the second input of the three-by-three optical splitter. ### Claim 9 (depends on 8) The method of claim 8, wherein the retrieved signal spectra and the retrieved reference spectra are computed by setting all ARN and ASN to one. ### Claim 10 (depends on 1) The method of claim 1, wherein the reference optical signal originates from a stable optical source, and wherein prior to, or at the same time as, determining the amplitude value and the phase value of the input optical signal, measuring spectra of the reference optical signal and using the measured spectra of the reference optical signal to determine spectra and a phase value of the input optical signal at a plurality of wavelengths. ### Claim 11 (depends on 10) The method of claim 10, further including determining a jitter value. ### Claim 12 A device for determining characteristics of an input optical signal, comprising: a processor and a non-transitory memory with instructions stored thereon, wherein the instructions upon execution by the processor cause the processor to: measure spectra associated with three interferograms produced at a first, a second and a third output of a three-by-three optical splitter using a plurality of spectrometers, wherein the three-by-three optical splitter is configured to receive a reference optical signal and the input optical signal at two different input ports thereof; and determine an amplitude value and a phase value of the input optical signal from information obtained from the measured spectra, wherein: prior to determining an amplitude value and a phase value of the input optical signal, the instructions upon execution by the processor configure the processor to perform a calibration procedure to characterize point spread functions across the plurality of spectrometers used for measuring interferograms output from the three-by-three optical splitter, the calibration operation including, for each interferometer: constructing a regression matrix and determining a correction factor that allow spectra of the input optical signal to be retrieved from a background subtracted image according to a linear fitting model, wherein the regression matrix is generated from calibration images acquired at multiple wavelengths and is configured to compensate for wavelength-dependent point spread function distortions and non-uniform spectral response of each spectrometer in retrieving spectra associated with the interferograms. ### Claim 13 (depends on 12) The device of claim 12, wherein the instructions upon execution by the processor cause the processor to determine the correction factor, when a white light or broadband source is provided as input to the three-by-three optical splitter, by determining a deviation of a measured spectra by each spectrometer from a uniform spectra. ### Claim 14 (depends on 12) The device of claim 12, wherein the correction factor is obtained based on a ratio of a downsampled image to an oversampled image for application at every pixel in the image. ### Claim 15 (depends on 12) The device of claim 12, wherein the instructions upon execution by the processor cause the processor to, for each spectrometer in the three-phase interferometric system, deconvolve each local point spread function, normalize the spectral response, and perform the linear fit at every resolvable wavelength. ### Claim 16 (depends on 12) The device of claim 12, wherein the instructions upon execution by the processor cause the processor to determine each of the three interferograms based on parameters obtained as part of the calibration procedure, the parameters relating to: polarization mismatch backgrounds of the interferograms, a signal content that is outside of record length, reference spectral response amplitudes for the interferograms, or signal spectral response amplitudes for the interferograms. ### Claim 17 (depends on 12) The device of claim 12, wherein each of the three interferograms is a function of a plurality of parameters including: a first parameter that defines spectral response amplitude of the reference optical signal for the corresponding interferogram, and a second parameter that defines spectral response amplitude of the input optical signal for the corresponding interferogram. ### Claim 18 (depends on 17) The device of claim 17, wherein the instructions upon execution by the processor cause the processor to: determine the first and the second parameter values as part of the calibration procedure that injects a broadband source into the first and the second input of the three-by-three optical splitter one at a time and obtain corresponding spectral measurements, wherein the first and the second parameter values are determined based on the following relationships: A RN = R N - ⁢ Measured / R Retrieved , and A SN = S N - ⁢ Measured / S Retrieved wherein: ARN represents the first parameter for the Nth spectrometer, where N has values of 1, 2 and 3, ASN represents the second parameter for the Nth spectrometer, where N has values of 1, 2 and 3, SN_Measured and RN_Measured are respectively spectra of the broadband source measured on spectrometer N at the corresponding output of the three-by-three optical splitter, SRetrieved is a retrieved signal spectra computed using all N spectral measurements associated with the broadband source that is injected into the first input of the three-by-three optical splitter, and RRetrieved is a retrieved reference signal spectra computed using all N spectral measurements associated with the broadband source that is injected into the second input of the three-by-three optical splitter. ### Claim 19 (depends on 18) The device of claim 18, wherein the retrieved signal spectra and the retrieved reference spectra are computed by setting all ARN and ASN to one. ### Claim 20 (depends on 12) The device of claim 12, wherein for a reference optical signal that originates from a stable optical source, the instructions upon execution by the processor cause the processor to use a measured spectra of the reference optical signal to determine spectra and a phase value of the input optical signal at a plurality of wavelengths.