A multiple-image encryption method based on two-step phase-shifting interferometry （PSI） and spatial multiplexing of a smooth compressed signal is proposed. In the encoding and encryption process, with the help of f...A multiple-image encryption method based on two-step phase-shifting interferometry （PSI） and spatial multiplexing of a smooth compressed signal is proposed. In the encoding and encryption process, with the help of four index matrices to store original pixel positions, all the pixels of four secret images are firstly reordered in an ascending order; then, the four reordered images are transformed by five-order Haar wavelet transform and performed sparseness operation. After Arnold transform and pixels sampling operation, one combined image can be grouped with the aid of compressive sensing （CS） and spatial multiplexing techniques. Finally, putting the combined image at the input plane of the PSI encryption scheme, only two interferograms ciphertexts can be obtained. During the decoding and decryption, utilizing all the secret key groups and index matrices keys, all the original secret images can be successfully decrypted by a wave-front retrieval algorithm of two-step PSI, spatial de-multiplexing, inverse Arnold transform, inverse discrete wavelet transform, and pixels reordering operation.展开更多
An accurate and fast three-step self-calibrating generalized phase-shifting interferomertry(SGPSI) is proposed. In this approach, two new phase-shifting signals are constructed by the difference interferograms normali...An accurate and fast three-step self-calibrating generalized phase-shifting interferomertry(SGPSI) is proposed. In this approach, two new phase-shifting signals are constructed by the difference interferograms normalization and noise suppressing, then the unknown phase shift between the two difference phase-shifting signals is estimated quickly through searching the minimum coefficient of variation of the modulation amplitude, a limited number of pixels are selected to participate in the search process to further save time, and finally the phase is reconstructed through the searched phase shift. Through the reconstruction of phase map by the simulation and experiment, and the comparison with several mature algorithms, the good performance of the proposed algorithm is proved, and it eliminates the limitation of requiring more than three phase-shifting interferograms for high-precision SGPSI. We expect this method to be widely used in the future.展开更多
By the mathematic models of flexible hinge,the accurate relationship between the phase-shifting and pressure acting on the hinge is deduced and verified by experimental results.Through the optimization of the geometri...By the mathematic models of flexible hinge,the accurate relationship between the phase-shifting and pressure acting on the hinge is deduced and verified by experimental results.Through the optimization of the geometric parameter of flexible hinge,a phase-shifting generator is developed to determine the length of an object precisely by interferometry.The experiments show that the triple phase-shifting produced using this generator is up to 1 m.With this generator,an example for the application in length measurement is introduced.The result shows the length uncertainty is 0.5 nm when the temperature uncertainty is limited in 2 mK.This paper provides a novel technique to measure the dimension of an object,especially to the diameter of a silicon sphere for Avogadro constant project.展开更多
We propose a novel spatial phase-shifting interferometry that exploits a genetic algorithm to compensate for geometric errors. Spatial phase-shifting interferometry is more suitable for measuring objects with properti...We propose a novel spatial phase-shifting interferometry that exploits a genetic algorithm to compensate for geometric errors. Spatial phase-shifting interferometry is more suitable for measuring objects with properties that change rapidly in time than the temporal phase-shifting interferometry. However, it is more susceptible to the geometric errors since the positions at which interferograms are collected are different. In this letter, we propose a spatial phase-shifting interferometry with separate paths for object and reference waves. Also, the object wave estimate is parameterized in terms of geometric errors, and the error is compensated by using a genetic algorithm.展开更多
Understanding the plasma dynamics of advanced energetic materials is crucial for their application.For the first time,this study presents a quantitative,two-dimensional mapping of the electron density distribution in ...Understanding the plasma dynamics of advanced energetic materials is crucial for their application.For the first time,this study presents a quantitative,two-dimensional mapping of the electron density distribution in plasma plumes generated by the laser ablation of glycidyl azide polymer(GAP)-coated nano-aluminum(Al@GAP).We employed a timeresolved,full-field polarizing shear interferometer to capture the plume's spatiotemporal evolution.By analyzing interference fringe shifts with an Abel inversion,we systematically investigated the effects of laser fluence(5.8-24.6 J/cm^(2))and ambient pressure(10-75 kPa).The results reveal peak electron densities on the order of 10^(16)cm^(-3)and complex plume structures governed by interactions with the ambient gas.Notably,we observed a non-monotonic relationship between laser fluence and central electron density,with higher fluences promoting radial expansion and reducing central density.These findings provide unprecedented quantitative insight into the energy release mechanisms and fluid dynamics of Al@GAP plasmas,offering a critical dataset for optimizing high-performance propellants,laser propulsion systems,and other energy-release applications.展开更多
Characterized by high accuracy and operational simplicity,oil-film interferometry(OFI)has served as an effective wall-shear stress(WSS)measurement technique over the past decades.It utilizes the monochromatic light in...Characterized by high accuracy and operational simplicity,oil-film interferometry(OFI)has served as an effective wall-shear stress(WSS)measurement technique over the past decades.It utilizes the monochromatic light interference principle to measure the temporal variation of oil-film thickness caused by WSS,and calculates time-averaged WSS based on the variation of interference fringe width.However,small-scale noise,which is caused by defects on the target surface,ambient dust,and local oil-film non-uniformity,contaminates the interference fringe patterns and directly increases the measurement uncertainty.One practical way is to apply denoising methods to improve the accuracy of identifying the centroids of fringes.In the present study,quasi-bivariate variational mode decomposition(QBVMD)is proposed as a self-adaptive denoising method to remove small-scale noise.Since no characteristic information of fringe patterns is required in the QBVMD-based denoising method,it has higher accuracy and lower uncertainty than the conventional OFI denoising methods,which need to pre-set the mask signal or the bandpass frequency,i.e.,cross-correlation or spectral filtering.Thus,it facilitates the automatic identification of time-varying inhomogeneous fringes.Two sets of experiments,i.e.,WSS measurement on either a canonical flat-plate turbulent boundary layer(TBL)or a TBL perturbed by micro vortex generators(MVG),were conducted to validate the applicability of this QBVMD-OFI method.The former experiment shows that the accuracy of QBVMD-OFI is equivalent to near-wall high-resolution particle image velocimetry,and is considerably higher than that of a dual hot-film sensor.As for the latter,QBVMD-OFI provides sufficient spatial resolution to resolve fine WSS structures generated by MVG.展开更多
A phase-shifting digital holography scheme developed to investigate internal defects in artworks is described. Phase-shifting is utilized to obtain a clear reconstructed object wave from a rough surface texture. A rev...A phase-shifting digital holography scheme developed to investigate internal defects in artworks is described. Phase-shifting is utilized to obtain a clear reconstructed object wave from a rough surface texture. A reverse-transform algorithm is employed to reconstruct the object wave on its original position of unknown distance or the imaging position from the object wave information on the holographic plane. To get the clearest reconstruction the exact registration of the unknown distance is determined by applying the intensity sum as the auto-focusing function, The spatial resolution of the reconstruction image is also investigated for a variety of affecting factors. Laboratory results of reconstruction images under deformation are presented.展开更多
Digital structured light （SL） profilometry is increasingly used in three-dimensional （3D） measurement technology. However, the nonlinearity of the off-the-shelf projectors and cameras seriously reduces the measure...Digital structured light （SL） profilometry is increasingly used in three-dimensional （3D） measurement technology. However, the nonlinearity of the off-the-shelf projectors and cameras seriously reduces the measurement accuracy. In this paper, first, we review the nonlinear effects of the projector-camera system in the phase-shifting structured light depth measurement method. We show that high order harmonic wave components lead to phase error in the phase-shifting method. Then a practical method based on frequency domain filtering is proposed for nonlinear error reduction. By using this method, the nonlinear calibration of the SL system is not required. Moreover, both the nonlinear effects of the projector and the camera can be effectively reduced. The simulations and experiments have verified our nonlinear correction method.展开更多
In this paper, we propose an encryption scheme based on phase-shifting digital interferometry. According to the original system framework, we add a random amplitude mask and replace the Fourier transform by the Fresne...In this paper, we propose an encryption scheme based on phase-shifting digital interferometry. According to the original system framework, we add a random amplitude mask and replace the Fourier transform by the Fresnel transform. We develop a mathematical model and give a discrete formula based on the scheme, which makes it easy to implement the scheme in computer programming. The experimental results show that the improved system has a better performance in security than the original encryption method. Moreover, it demonstrates a good capability of anti-noise and anti-shear robustness.展开更多
A deterministic phase-encoded encryption system is proposed. A lenticular lens array (LLA) sheet with a particular LPI (lenticular per inch) number is chosen as a modulator (key) instead of the random phase molator. T...A deterministic phase-encoded encryption system is proposed. A lenticular lens array (LLA) sheet with a particular LPI (lenticular per inch) number is chosen as a modulator (key) instead of the random phase molator. The suggested encryption scheme is based on arbitrary two-step phase-shift interferometry (PSI), using an unknown phase step. The encryption and decryption principle is based on an LLA in arbitrary unknown two-step PSI. Right key holograms can be used to theoretically show that the object wavefront is the only one left in the hologram plane and that all accompanying undesired terms are eliminated. The encrypted image can therefore be numerically and successfully decrypted with the right key in the image plane. The number of degrees of freedom of the encryption scheme increases with the distance from the object and the LLA to the CCD, and also with the unknown phase-step and the LLA LPI number. Computer simulations are performed to verify the encryption and decryption principles without a key, with the wrong key and with the right key. Optical experiments are also performed to validate them.展开更多
Fresnel incoherent correlation holography(FINCH)has the ability to generate three-dimensional images with a superresolution by using incoherent sources.However,there are unwanted direct current term and twin image in ...Fresnel incoherent correlation holography(FINCH)has the ability to generate three-dimensional images with a superresolution by using incoherent sources.However,there are unwanted direct current term and twin image in interferograms,so it is of great significance to find a method to eliminate them.Phase-shifting technology is a most widely used technique for this task,but its three-step phase-shifting is not suitable for the instantaneous measurement of dynamic objects,and the quality of reconstructed image with the traditional two-step phase-shifting is lower.In this paper,we present a method of enhancing the resolution through using a two-step phase-shifting technology based on the discrete wavelet transform.After two-step phase-shifting,the resulting hologram is a superposition of multiple forms.The frequency of the resulting hologram is decomposed into different levels through using discrete wavelet transform,then the image is reconstructed after retrieving the low frequency band.Various experiments have verified the effectiveness of this method.展开更多
focus of all countries.As an effective new energy,the fuel cell has attracted the attention of scholars.However,due to the particularity of proton exchange membrane fuel cell(PEMFC),the performance of traditional PI c...focus of all countries.As an effective new energy,the fuel cell has attracted the attention of scholars.However,due to the particularity of proton exchange membrane fuel cell(PEMFC),the performance of traditional PI controlled phase-shifted full-bridge power electronics DC-DC converter cannot meet the needs of practical application.In order to further improve the dynamic performance of the converter,this paper first introduces several main topologies of the current mainstream front-end DC-DC converter,and analyzes their performance in the fuel cell system.Then,the operation process of the phase-shifted fullbridge power electronics DC-DC converter is introduced,and the shortcomings of the traditional PI control are analyzed.Finally,a double closed-loop adaptive fuzzy PI controller is proposed,which is characterized by dynamically adjusting PI parameters according to different working states to complete the intelligent control of phase-shifted full-bridge DC-DC converter.The simulation results in MATLAB/Simulink show that the proposed algorithm has good a control effect.Compared with the traditional algorithm,the overshoot and stabilization time of the system are shorter.The algorithm can effectively suppress the fluctuation of the output current of the fuel cell converter,and is a very practical control method.展开更多
In this paper, the principle of phase-shift interferometry is first briefly introduced. Then it is used as an illustration to measure small surface deformation, and the measurement accuracy of 0.02μis obtained. This ...In this paper, the principle of phase-shift interferometry is first briefly introduced. Then it is used as an illustration to measure small surface deformation, and the measurement accuracy of 0.02μis obtained. This demonstrates that the technology has great significance for strain analysis in experimental mechanics.展开更多
The effect of phaseshift error in phase shifting interferometry is investigated. A new algorithm with two sets of 4 samples for eliminating phase shift error is presented. The computer simulation and experiment resul...The effect of phaseshift error in phase shifting interferometry is investigated. A new algorithm with two sets of 4 samples for eliminating phase shift error is presented. The computer simulation and experiment result show that the phase shift offset should be π when the algorithm is used, and this algorithm has gotten better result than the original 4 sample algorithm.展开更多
We demonstrate a silicon nitride photonics-based imaging system that can perform one-dimensional interferometric imaging around the 1550-nm wavelength.The magnetograph using interferometric and computational imaging f...We demonstrate a silicon nitride photonics-based imaging system that can perform one-dimensional interferometric imaging around the 1550-nm wavelength.The magnetograph using interferometric and computational imaging for remote observations(MICRO)design uses silicon nitride on a Si platform to replace the bulky free-space optics of traditional magnetograph imaging systems with nanofabricated structures of a fraction of the size.The photonic integrated circuit(PIC)uses an array of lenslets that couple light into four input waveguides with spacing arranged along a Golomb ruler,where each aperture pair formed has a unique length.Each aperture is mixed with a 13-dBm reference laser and separated inside a 2×4 optical hybrid to generate in-phase and quadrature-phase signals to be detected in balanced detectors at the output of the PIC.We use a field programmable gate array(FPGA)board to digitize and process the measurements.The FPGAs and PIC are combined to reduce the overall size,weight,and power of the system,paving the way for a compact imaging system.We demonstrate a PIC-based imager design and experimental testbed for spectrometry applications.展开更多
Single-wavelength interferometry achieves high resolution for smooth surfaces but struggles with rough industrially relevant ones due to limited unambiguous measuring range and speckle effects.Multiwavelength interfer...Single-wavelength interferometry achieves high resolution for smooth surfaces but struggles with rough industrially relevant ones due to limited unambiguous measuring range and speckle effects.Multiwavelength interferometry addresses these challenges using synthetic wavelengths,enabling a balance between extended measurement range and resolution by combining several synthetic wavelengths.This approach holds immense potential for diverse industrial applications,yet it remains largely untapped due to the lack of suitable light sources.Existing solutions are constrained by limited flexibility in synthetic-wavelength generation and slow switching speeds.We demonstrate a light source for multiwavelength interferometry based on electro-optic single-sideband modulation.It reliably generates synthetic wavelengths with arbitrary values from centimeters to meters and switching time below 30 ms.This breakthrough paves the way for dynamic reconfigurable multiwavelength interferometry capable of adapting to complex surfaces and operating efficiently even outside laboratory settings.These capabilities unlock the full potential of multiwavelength interferometry,offering unprecedented flexibility and speed for industrial and technological applications.展开更多
Laser frequency combs,which are composed of a series of equally spaced coherent frequency components,have triggered revolutionary progress in precision spectroscopy and optical metrology.Length/distance is of fundamen...Laser frequency combs,which are composed of a series of equally spaced coherent frequency components,have triggered revolutionary progress in precision spectroscopy and optical metrology.Length/distance is of fundamental importance in both science and technology.We describe a ranging scheme based on chirped pulse interferometry.In contrast to the traditional spectral interferometry,the local oscillator is strongly chirped which is able to meet the measurement pulses at arbitrary distances,and therefore,the dead zones can be removed.The distances can be precisely determined via two measurement steps based on the time-of-flight method and synthetic wavelength interferometry,respectively.To overcome the speed limitation of the optical spectrum analyzer,the spectrograms are stretched and detected by a fast photodetector and oscilloscope and consequently mapped into the time domain in real time.The experimental results indicate that the measurement uncertainty can be well within±2μm,compared with the reference distance meter.The Allan deviation can reach 0.4μm at 4 ns averaging time and 25 nm at 1μs and can achieve 2 nm at 100μs averaging time.We also measured a spinning disk with grooves of different depths to verify the measurement speed,and the results show that the grooves with about 150 m∕s line speed can be clearly captured.Our method provides a unique combination of non-dead zones,ultrafast measurement speed,high precision and accuracy,large ambiguity range,and only one single comb source.This system could offer a powerful solution for field measurements in practical applications in the future.展开更多
Acoustic detection has many applications across science and technology from medicine to imaging and communications.However,most acoustic sensors have a common limitation in that the detection must be near the acoustic...Acoustic detection has many applications across science and technology from medicine to imaging and communications.However,most acoustic sensors have a common limitation in that the detection must be near the acoustic source.Alternatively,laser interferometry with picometer-scale motional displacement detection can rapidly and precisely measure sound-induced minute vibrations on remote surfaces.Here,we demonstrate the feasibility of sound detection up to 100 kHz at remote sites with≈60 m optical path length via laser homodyne interferometry.Based on our ultrastable hertz linewidth laser with 10-15 fractional stability,our laser interferometer achieves 0.5 pm/Hz1/2 displacement sensitivity near 10 kHz,bounded only by laser frequency noise over 10 kHz.Between 140 Hz and 15 kHz,we achieve a homodyne acoustic sensing sensitivity of subnanometer/Pascal across our conversational frequency overtones.The minimal sound pressure detectable over 60 m optical path length is≈2 mPa,with dynamic ranges over 100 dB.With the demonstrated standoff picometric distance metrology,we successfully detected and reconstructed musical scores of normal conversational volumes with high fidelity.The acoustic detection via this precision laser interferometer could be applied to selective area sound sensing for remote acoustic metrology,optomechanical vibrational motion sensing,and ultrasensitive optical microphones at the laser frequency noise limits.展开更多
Null compensation interferometry is the primary testing method for the manufacture of ultra-high-precision aspheric mirrors.The crosstalk fringes generated by stray light in interferometry can affect accuracy and pote...Null compensation interferometry is the primary testing method for the manufacture of ultra-high-precision aspheric mirrors.The crosstalk fringes generated by stray light in interferometry can affect accuracy and potentially prevent the testing from proceeding normally.Position errors include the decenter error,tilt error,and distance error.During the testing process,position errors will impact the testing accuracy and the crosstalk fringes generated by stray light.To determine the specific impact of position errors,we use the concept of Hindle shell testing of a convex aspheric mirror,and propose the simulation method of crosstalk fringes in null compensation interferometry.We also propose evaluation indices of crosstalk fringes in interferometry and simulate the influence of position errors on the crosstalk fringes.This work aims to help improve the design of compensation interferometry schemes,enhance the feasibility of the design,reduce engineering risks,and improve efficiency.展开更多
Laser frequency microcombs provide a series of equidistant,coherent frequency markers across a broad spectrum,enabling advancements in laser spectroscopy,dense optical communications,precision distance metrology,and a...Laser frequency microcombs provide a series of equidistant,coherent frequency markers across a broad spectrum,enabling advancements in laser spectroscopy,dense optical communications,precision distance metrology,and astronomy.Here,we design and fabricate silicon nitride,dispersion-managed microresonators that effectively suppress avoided-mode crossings and achieve close-to-zero averaged dispersion.Both the stochastic noise and mode-locking dynamics of the resonator are numerically and experimentally investigated.First,we experimentally demonstrate thermally stabilized microcomb formation in the microresonator across different mode-locked states,showing negligible center frequency shifts and a broad frequency bandwidth.Next,we characterize the femtosecond timing jitter of the microcombs,supported by precise metrology of the timing phase and relative intensity noise.For the single-soliton state,we report a relative intensity noise of−153.2 dB∕Hz,close to the shot-noise limit,and a quantum-noise–limited timing jitter power spectral density of 0.4 as 2∕Hz at a 100 kHz offset frequency,measured using a self-heterodyne linear interferometer.In addition,we achieve an integrated timing jitter of 1.7 fs±0.07 fs,measured from 10 kHz to 1 MHz.Measuring and understanding these fundamental noise parameters in high clock rate frequency microcombs is critical for advancing soliton physics and enabling new applications in precision metrology.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61775121,61307003,61405122,and 11574311)Key R&D Program of Shandong Province,China(Grant No.2018GGX101002)+1 种基金the Natural Science Foundation of Shandong Province,China(Grant No.R2016FM03)the Fundamental Research Funds of Shandong University,China(Grant No.2015GN031)
文摘A multiple-image encryption method based on two-step phase-shifting interferometry （PSI） and spatial multiplexing of a smooth compressed signal is proposed. In the encoding and encryption process, with the help of four index matrices to store original pixel positions, all the pixels of four secret images are firstly reordered in an ascending order; then, the four reordered images are transformed by five-order Haar wavelet transform and performed sparseness operation. After Arnold transform and pixels sampling operation, one combined image can be grouped with the aid of compressive sensing （CS） and spatial multiplexing techniques. Finally, putting the combined image at the input plane of the PSI encryption scheme, only two interferograms ciphertexts can be obtained. During the decoding and decryption, utilizing all the secret key groups and index matrices keys, all the original secret images can be successfully decrypted by a wave-front retrieval algorithm of two-step PSI, spatial de-multiplexing, inverse Arnold transform, inverse discrete wavelet transform, and pixels reordering operation.
基金Project supported by the National Natural Science Foundation of China (Grant No. 61905039)Jilin Scientific and Technological Development Program, China (Grant No. 20190701018GH)+1 种基金Education Department of Jilin Province, China (Grant No. JJKH20190691KJ)State Key Laboratory of Applied Optics.
文摘An accurate and fast three-step self-calibrating generalized phase-shifting interferomertry(SGPSI) is proposed. In this approach, two new phase-shifting signals are constructed by the difference interferograms normalization and noise suppressing, then the unknown phase shift between the two difference phase-shifting signals is estimated quickly through searching the minimum coefficient of variation of the modulation amplitude, a limited number of pixels are selected to participate in the search process to further save time, and finally the phase is reconstructed through the searched phase shift. Through the reconstruction of phase map by the simulation and experiment, and the comparison with several mature algorithms, the good performance of the proposed algorithm is proved, and it eliminates the limitation of requiring more than three phase-shifting interferograms for high-precision SGPSI. We expect this method to be widely used in the future.
基金supported by the National Key Technology R&D Program of China (Grant No. 2006BAF06B06)
文摘By the mathematic models of flexible hinge,the accurate relationship between the phase-shifting and pressure acting on the hinge is deduced and verified by experimental results.Through the optimization of the geometric parameter of flexible hinge,a phase-shifting generator is developed to determine the length of an object precisely by interferometry.The experiments show that the triple phase-shifting produced using this generator is up to 1 m.With this generator,an example for the application in length measurement is introduced.The result shows the length uncertainty is 0.5 nm when the temperature uncertainty is limited in 2 mK.This paper provides a novel technique to measure the dimension of an object,especially to the diameter of a silicon sphere for Avogadro constant project.
基金supported by the National Research Foundation and the Ministry of Education, Science and Engineering of Korea through the National Creative Re-search Initiative Program (R16-2007-030-01001-0)
文摘We propose a novel spatial phase-shifting interferometry that exploits a genetic algorithm to compensate for geometric errors. Spatial phase-shifting interferometry is more suitable for measuring objects with properties that change rapidly in time than the temporal phase-shifting interferometry. However, it is more susceptible to the geometric errors since the positions at which interferograms are collected are different. In this letter, we propose a spatial phase-shifting interferometry with separate paths for object and reference waves. Also, the object wave estimate is parameterized in terms of geometric errors, and the error is compensated by using a genetic algorithm.
基金supported by the National Key R&D Program of China under the project“Development of High-Precision Propulsion Calibration Systems and Performance Testing Technologies”(Grant No.2021YFC2202800)。
文摘Understanding the plasma dynamics of advanced energetic materials is crucial for their application.For the first time,this study presents a quantitative,two-dimensional mapping of the electron density distribution in plasma plumes generated by the laser ablation of glycidyl azide polymer(GAP)-coated nano-aluminum(Al@GAP).We employed a timeresolved,full-field polarizing shear interferometer to capture the plume's spatiotemporal evolution.By analyzing interference fringe shifts with an Abel inversion,we systematically investigated the effects of laser fluence(5.8-24.6 J/cm^(2))and ambient pressure(10-75 kPa).The results reveal peak electron densities on the order of 10^(16)cm^(-3)and complex plume structures governed by interactions with the ambient gas.Notably,we observed a non-monotonic relationship between laser fluence and central electron density,with higher fluences promoting radial expansion and reducing central density.These findings provide unprecedented quantitative insight into the energy release mechanisms and fluid dynamics of Al@GAP plasmas,offering a critical dataset for optimizing high-performance propellants,laser propulsion systems,and other energy-release applications.
文摘Characterized by high accuracy and operational simplicity,oil-film interferometry(OFI)has served as an effective wall-shear stress(WSS)measurement technique over the past decades.It utilizes the monochromatic light interference principle to measure the temporal variation of oil-film thickness caused by WSS,and calculates time-averaged WSS based on the variation of interference fringe width.However,small-scale noise,which is caused by defects on the target surface,ambient dust,and local oil-film non-uniformity,contaminates the interference fringe patterns and directly increases the measurement uncertainty.One practical way is to apply denoising methods to improve the accuracy of identifying the centroids of fringes.In the present study,quasi-bivariate variational mode decomposition(QBVMD)is proposed as a self-adaptive denoising method to remove small-scale noise.Since no characteristic information of fringe patterns is required in the QBVMD-based denoising method,it has higher accuracy and lower uncertainty than the conventional OFI denoising methods,which need to pre-set the mask signal or the bandpass frequency,i.e.,cross-correlation or spectral filtering.Thus,it facilitates the automatic identification of time-varying inhomogeneous fringes.Two sets of experiments,i.e.,WSS measurement on either a canonical flat-plate turbulent boundary layer(TBL)or a TBL perturbed by micro vortex generators(MVG),were conducted to validate the applicability of this QBVMD-OFI method.The former experiment shows that the accuracy of QBVMD-OFI is equivalent to near-wall high-resolution particle image velocimetry,and is considerably higher than that of a dual hot-film sensor.As for the latter,QBVMD-OFI provides sufficient spatial resolution to resolve fine WSS structures generated by MVG.
文摘A phase-shifting digital holography scheme developed to investigate internal defects in artworks is described. Phase-shifting is utilized to obtain a clear reconstructed object wave from a rough surface texture. A reverse-transform algorithm is employed to reconstruct the object wave on its original position of unknown distance or the imaging position from the object wave information on the holographic plane. To get the clearest reconstruction the exact registration of the unknown distance is determined by applying the intensity sum as the auto-focusing function, The spatial resolution of the reconstruction image is also investigated for a variety of affecting factors. Laboratory results of reconstruction images under deformation are presented.
基金Project supported by the Science and Technology Major Projects of Zhejiang Province,China(Grant No.2013C03043-5)
文摘Digital structured light （SL） profilometry is increasingly used in three-dimensional （3D） measurement technology. However, the nonlinearity of the off-the-shelf projectors and cameras seriously reduces the measurement accuracy. In this paper, first, we review the nonlinear effects of the projector-camera system in the phase-shifting structured light depth measurement method. We show that high order harmonic wave components lead to phase error in the phase-shifting method. Then a practical method based on frequency domain filtering is proposed for nonlinear error reduction. By using this method, the nonlinear calibration of the SL system is not required. Moreover, both the nonlinear effects of the projector and the camera can be effectively reduced. The simulations and experiments have verified our nonlinear correction method.
基金supported by the National Basic Research Program of China(Grant No.2011CB302903)the National Natural Science Foundation of China(Grant Nos.61272084 and 61202004)the Key Project of Natural Science Research of Jiangsu University,China(Grant No.11KJA520002)
文摘In this paper, we propose an encryption scheme based on phase-shifting digital interferometry. According to the original system framework, we add a random amplitude mask and replace the Fourier transform by the Fresnel transform. We develop a mathematical model and give a discrete formula based on the scheme, which makes it easy to implement the scheme in computer programming. The experimental results show that the improved system has a better performance in security than the original encryption method. Moreover, it demonstrates a good capability of anti-noise and anti-shear robustness.
文摘A deterministic phase-encoded encryption system is proposed. A lenticular lens array (LLA) sheet with a particular LPI (lenticular per inch) number is chosen as a modulator (key) instead of the random phase molator. The suggested encryption scheme is based on arbitrary two-step phase-shift interferometry (PSI), using an unknown phase step. The encryption and decryption principle is based on an LLA in arbitrary unknown two-step PSI. Right key holograms can be used to theoretically show that the object wavefront is the only one left in the hologram plane and that all accompanying undesired terms are eliminated. The encrypted image can therefore be numerically and successfully decrypted with the right key in the image plane. The number of degrees of freedom of the encryption scheme increases with the distance from the object and the LLA to the CCD, and also with the unknown phase-step and the LLA LPI number. Computer simulations are performed to verify the encryption and decryption principles without a key, with the wrong key and with the right key. Optical experiments are also performed to validate them.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51175479 and U1704155)the Natural Science Foundation of Henan Province,China(Grant Nos.16A140035 and 18A140032)the Program for Innovative Research Team(in Science and Technique)in the University of Henan Province,China(Grant No.18IRTSTHN016)。
文摘Fresnel incoherent correlation holography(FINCH)has the ability to generate three-dimensional images with a superresolution by using incoherent sources.However,there are unwanted direct current term and twin image in interferograms,so it is of great significance to find a method to eliminate them.Phase-shifting technology is a most widely used technique for this task,but its three-step phase-shifting is not suitable for the instantaneous measurement of dynamic objects,and the quality of reconstructed image with the traditional two-step phase-shifting is lower.In this paper,we present a method of enhancing the resolution through using a two-step phase-shifting technology based on the discrete wavelet transform.After two-step phase-shifting,the resulting hologram is a superposition of multiple forms.The frequency of the resulting hologram is decomposed into different levels through using discrete wavelet transform,then the image is reconstructed after retrieving the low frequency band.Various experiments have verified the effectiveness of this method.
基金This work was supported in part by the Natural Science Foundation of Jiangsu Province under Grant BK20200969(L.Z.,URL:http://std.jiangsu.gov.cn/)in part by the Natural Science Foundation for Universities of Jiangsu Province under Grant 20KJB520008(Y.Y.,URL:http://jyt.jiangsu.gov.cn/)+2 种基金in part by the Nantong Science and Technology Plan Project under Grant JC2020148(Y.Y.,URL:http://kjj.nantong.gov.cn/)JC2020151(Y.C.,URL:http://kjj.nantong.gov.cn/)JC2019095(L.R.,URL:http://kjj.nantong.gov.cn/).
文摘focus of all countries.As an effective new energy,the fuel cell has attracted the attention of scholars.However,due to the particularity of proton exchange membrane fuel cell(PEMFC),the performance of traditional PI controlled phase-shifted full-bridge power electronics DC-DC converter cannot meet the needs of practical application.In order to further improve the dynamic performance of the converter,this paper first introduces several main topologies of the current mainstream front-end DC-DC converter,and analyzes their performance in the fuel cell system.Then,the operation process of the phase-shifted fullbridge power electronics DC-DC converter is introduced,and the shortcomings of the traditional PI control are analyzed.Finally,a double closed-loop adaptive fuzzy PI controller is proposed,which is characterized by dynamically adjusting PI parameters according to different working states to complete the intelligent control of phase-shifted full-bridge DC-DC converter.The simulation results in MATLAB/Simulink show that the proposed algorithm has good a control effect.Compared with the traditional algorithm,the overshoot and stabilization time of the system are shorter.The algorithm can effectively suppress the fluctuation of the output current of the fuel cell converter,and is a very practical control method.
文摘In this paper, the principle of phase-shift interferometry is first briefly introduced. Then it is used as an illustration to measure small surface deformation, and the measurement accuracy of 0.02μis obtained. This demonstrates that the technology has great significance for strain analysis in experimental mechanics.
文摘The effect of phaseshift error in phase shifting interferometry is investigated. A new algorithm with two sets of 4 samples for eliminating phase shift error is presented. The computer simulation and experiment result show that the phase shift offset should be π when the algorithm is used, and this algorithm has gotten better result than the original 4 sample algorithm.
基金supported by the National Aeronautics and Space Administration(Grant No.80NSSC20K0914)the Lockheed Martin Internal Research Funds(IRAD).
文摘We demonstrate a silicon nitride photonics-based imaging system that can perform one-dimensional interferometric imaging around the 1550-nm wavelength.The magnetograph using interferometric and computational imaging for remote observations(MICRO)design uses silicon nitride on a Si platform to replace the bulky free-space optics of traditional magnetograph imaging systems with nanofabricated structures of a fraction of the size.The photonic integrated circuit(PIC)uses an array of lenslets that couple light into four input waveguides with spacing arranged along a Golomb ruler,where each aperture pair formed has a unique length.Each aperture is mixed with a 13-dBm reference laser and separated inside a 2×4 optical hybrid to generate in-phase and quadrature-phase signals to be detected in balanced detectors at the output of the PIC.We use a field programmable gate array(FPGA)board to digitize and process the measurements.The FPGAs and PIC are combined to reduce the overall size,weight,and power of the system,paving the way for a compact imaging system.We demonstrate a PIC-based imager design and experimental testbed for spectrometry applications.
基金supported by the German Federal Ministry of Education and Research,Research Program Quantum Systems(Grant No.13N16774).
文摘Single-wavelength interferometry achieves high resolution for smooth surfaces but struggles with rough industrially relevant ones due to limited unambiguous measuring range and speckle effects.Multiwavelength interferometry addresses these challenges using synthetic wavelengths,enabling a balance between extended measurement range and resolution by combining several synthetic wavelengths.This approach holds immense potential for diverse industrial applications,yet it remains largely untapped due to the lack of suitable light sources.Existing solutions are constrained by limited flexibility in synthetic-wavelength generation and slow switching speeds.We demonstrate a light source for multiwavelength interferometry based on electro-optic single-sideband modulation.It reliably generates synthetic wavelengths with arbitrary values from centimeters to meters and switching time below 30 ms.This breakthrough paves the way for dynamic reconfigurable multiwavelength interferometry capable of adapting to complex surfaces and operating efficiently even outside laboratory settings.These capabilities unlock the full potential of multiwavelength interferometry,offering unprecedented flexibility and speed for industrial and technological applications.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFC2204601)the National Natural Science Foundation of China(Grant Nos.11925503 and 12275093)+1 种基金the Natural Science Foundation of Hubei Province(Grant No.2021CFB019)the State Key Laboratory of Applied Optics(Grant No.SKLAO2022001A10).
文摘Laser frequency combs,which are composed of a series of equally spaced coherent frequency components,have triggered revolutionary progress in precision spectroscopy and optical metrology.Length/distance is of fundamental importance in both science and technology.We describe a ranging scheme based on chirped pulse interferometry.In contrast to the traditional spectral interferometry,the local oscillator is strongly chirped which is able to meet the measurement pulses at arbitrary distances,and therefore,the dead zones can be removed.The distances can be precisely determined via two measurement steps based on the time-of-flight method and synthetic wavelength interferometry,respectively.To overcome the speed limitation of the optical spectrum analyzer,the spectrograms are stretched and detected by a fast photodetector and oscilloscope and consequently mapped into the time domain in real time.The experimental results indicate that the measurement uncertainty can be well within±2μm,compared with the reference distance meter.The Allan deviation can reach 0.4μm at 4 ns averaging time and 25 nm at 1μs and can achieve 2 nm at 100μs averaging time.We also measured a spinning disk with grooves of different depths to verify the measurement speed,and the results show that the grooves with about 150 m∕s line speed can be clearly captured.Our method provides a unique combination of non-dead zones,ultrafast measurement speed,high precision and accuracy,large ambiguity range,and only one single comb source.This system could offer a powerful solution for field measurements in practical applications in the future.
基金supported by the Office of Naval Research(Grant Nos.N00014-16-1-2094 and N00014-24-1-2547)the Lawrence Livermore National Laboratory(Grant No.B622827)the National Science Foundation.Y.-S.J.acknowledges support from KRISS(Grant Nos.25011026 and 25011211).
文摘Acoustic detection has many applications across science and technology from medicine to imaging and communications.However,most acoustic sensors have a common limitation in that the detection must be near the acoustic source.Alternatively,laser interferometry with picometer-scale motional displacement detection can rapidly and precisely measure sound-induced minute vibrations on remote surfaces.Here,we demonstrate the feasibility of sound detection up to 100 kHz at remote sites with≈60 m optical path length via laser homodyne interferometry.Based on our ultrastable hertz linewidth laser with 10-15 fractional stability,our laser interferometer achieves 0.5 pm/Hz1/2 displacement sensitivity near 10 kHz,bounded only by laser frequency noise over 10 kHz.Between 140 Hz and 15 kHz,we achieve a homodyne acoustic sensing sensitivity of subnanometer/Pascal across our conversational frequency overtones.The minimal sound pressure detectable over 60 m optical path length is≈2 mPa,with dynamic ranges over 100 dB.With the demonstrated standoff picometric distance metrology,we successfully detected and reconstructed musical scores of normal conversational volumes with high fidelity.The acoustic detection via this precision laser interferometer could be applied to selective area sound sensing for remote acoustic metrology,optomechanical vibrational motion sensing,and ultrasensitive optical microphones at the laser frequency noise limits.
基金the National Key Research and Development Program of China(2022YFB3403404)the Youth Innovation Promotion Association,CAS(2022213)the National Natural Science Foundation of China(62127901 and 62305334).
文摘Null compensation interferometry is the primary testing method for the manufacture of ultra-high-precision aspheric mirrors.The crosstalk fringes generated by stray light in interferometry can affect accuracy and potentially prevent the testing from proceeding normally.Position errors include the decenter error,tilt error,and distance error.During the testing process,position errors will impact the testing accuracy and the crosstalk fringes generated by stray light.To determine the specific impact of position errors,we use the concept of Hindle shell testing of a convex aspheric mirror,and propose the simulation method of crosstalk fringes in null compensation interferometry.We also propose evaluation indices of crosstalk fringes in interferometry and simulate the influence of position errors on the crosstalk fringes.This work aims to help improve the design of compensation interferometry schemes,enhance the feasibility of the design,reduce engineering risks,and improve efficiency.
基金support from the Lawrence Livermore National Laboratory(Grant No.B622827)the National Science Foundation(Grant Nos.1824568,1810506,1741707,and 1829071)the Office of Naval Research(Grant No.N00014-16-1-2094).
文摘Laser frequency microcombs provide a series of equidistant,coherent frequency markers across a broad spectrum,enabling advancements in laser spectroscopy,dense optical communications,precision distance metrology,and astronomy.Here,we design and fabricate silicon nitride,dispersion-managed microresonators that effectively suppress avoided-mode crossings and achieve close-to-zero averaged dispersion.Both the stochastic noise and mode-locking dynamics of the resonator are numerically and experimentally investigated.First,we experimentally demonstrate thermally stabilized microcomb formation in the microresonator across different mode-locked states,showing negligible center frequency shifts and a broad frequency bandwidth.Next,we characterize the femtosecond timing jitter of the microcombs,supported by precise metrology of the timing phase and relative intensity noise.For the single-soliton state,we report a relative intensity noise of−153.2 dB∕Hz,close to the shot-noise limit,and a quantum-noise–limited timing jitter power spectral density of 0.4 as 2∕Hz at a 100 kHz offset frequency,measured using a self-heterodyne linear interferometer.In addition,we achieve an integrated timing jitter of 1.7 fs±0.07 fs,measured from 10 kHz to 1 MHz.Measuring and understanding these fundamental noise parameters in high clock rate frequency microcombs is critical for advancing soliton physics and enabling new applications in precision metrology.
