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Instrumentation and Measurements|53 Article(s)
Transient long-range distance measurement by a Vernier spectral interferometry
Liang Xu, Kun Wang, Chen Liu, Wenying Chen, Chi Zhang, and Xinliang Zhang
Rapid and long-range distance measurements are essential in various industrial and scientific applications, and among them, the dual-comb ranging system attracts great attention due to its high precision. However, the temporal asynchronous sampling results in the tradeoff between frame rate and ranging precision, and the non-ambiguity range (NAR) is also limited by the comb cycle, which hinders the further advancement of the dual-comb ranging system. Given this constraint, we introduce a Vernier spectral interferometry to improve the frame rate and NAR of the ranging system. First, leveraging the dispersive time-stretch technology, the dual-comb interferometry becomes spectral interferometry. Thus, the asynchronous time step is unlimited, and the frame rate is improved to 100 kHz. Second, dual-wavelength bands are introduced to implement a Vernier spectral interferometry, whose NAR is enlarged from 1.5 m to 1.5 km. Moreover, this fast and long-range system also demonstrated high precision, with a 22.91-nm Allan deviation over 10-ms averaging time. As a result, the proposed Vernier spectral interferometry ranging system is promising for diverse applications that necessitate rapid and extensive distance measurement. Rapid and long-range distance measurements are essential in various industrial and scientific applications, and among them, the dual-comb ranging system attracts great attention due to its high precision. However, the temporal asynchronous sampling results in the tradeoff between frame rate and ranging precision, and the non-ambiguity range (NAR) is also limited by the comb cycle, which hinders the further advancement of the dual-comb ranging system. Given this constraint, we introduce a Vernier spectral interferometry to improve the frame rate and NAR of the ranging system. First, leveraging the dispersive time-stretch technology, the dual-comb interferometry becomes spectral interferometry. Thus, the asynchronous time step is unlimited, and the frame rate is improved to 100 kHz. Second, dual-wavelength bands are introduced to implement a Vernier spectral interferometry, whose NAR is enlarged from 1.5 m to 1.5 km. Moreover, this fast and long-range system also demonstrated high precision, with a 22.91-nm Allan deviation over 10-ms averaging time. As a result, the proposed Vernier spectral interferometry ranging system is promising for diverse applications that necessitate rapid and extensive distance measurement.
Photonics Research
- Publication Date: May. 07, 2024
- Vol. 12, Issue 6, 1107 (2024)
High-speed PGC demodulation model and method with subnanometer displacement resolution in a fiber-optic micro-probe laser interferometer
Yisi Dong, Wenwen Li, Jinran Zhang, Wenrui Luo, Haijin Fu, Xu Xing, Pengcheng Hu, Yongkang Dong, and Jiubin Tan
As the key of embedded displacement measurement, a fiber-optic micro-probe laser interferometer (FMI) is of great interest in developing high-end equipment as well as precision metrology. However, conventional phase-generated carrier (PGC) approaches are for low-speed scenes and local error analysis, usually neglecting the global precision analysis and dynamic effect of system parameters under high-speed measurement, thus hindering their broad applications. We present a high-speed PGC demodulation model and method to achieve subnanometer displacement measurement precision in FMI. This model includes a global equivalent resolution analysis and revelation of the demodulation error mechanism. Utilizing this model, the failure issues regarding the PGC demodulation method under high speed and large range are addressed. Furthermore, an ultra-precision PGC demodulation algorithm based on the combination of static and dynamic delay adaptive regulation is proposed to enable high-speed and large-range displacement measurement. In this paper, the proposed model and algorithm are validated through simulation and experimental tests. The results demonstrate a displacement resolution of 0.1 nm with a standard deviation of less than 0.5 nm when measuring at a high velocity of 1.5 m/s—nearly a tenfold increase of the latest study. As the key of embedded displacement measurement, a fiber-optic micro-probe laser interferometer (FMI) is of great interest in developing high-end equipment as well as precision metrology. However, conventional phase-generated carrier (PGC) approaches are for low-speed scenes and local error analysis, usually neglecting the global precision analysis and dynamic effect of system parameters under high-speed measurement, thus hindering their broad applications. We present a high-speed PGC demodulation model and method to achieve subnanometer displacement measurement precision in FMI. This model includes a global equivalent resolution analysis and revelation of the demodulation error mechanism. Utilizing this model, the failure issues regarding the PGC demodulation method under high speed and large range are addressed. Furthermore, an ultra-precision PGC demodulation algorithm based on the combination of static and dynamic delay adaptive regulation is proposed to enable high-speed and large-range displacement measurement. In this paper, the proposed model and algorithm are validated through simulation and experimental tests. The results demonstrate a displacement resolution of 0.1 nm with a standard deviation of less than 0.5 nm when measuring at a high velocity of 1.5 m/s—nearly a tenfold increase of the latest study.
Photonics Research
- Publication Date: May. 01, 2024
- Vol. 12, Issue 5, 921 (2024)
Dead-zone-free atomic magnetometer based on hybrid Poincaré beams
Ke Tian, Weifeng Ding, and Zhaoying Wang
In this paper, we present the experiment and the theory scheme of light-atom interaction in atomic magnetometers by using a hybrid Poincaré beam (HPB) to solve an annoying problem, named “dead zone.” This kind of magnetometer can be sensitive to arbitrary directions of external magnetic fields. The HPB has a complex polarization distribution, consisting of a vector radially polarized beam and a scalar circularly polarized beam in our experiment. These two kinds of beams have different directions of dead zones of external magnetic fields; thereby, the atomic magnetometer with an HPB can avoid the non-signal area when the direction of the external magnetic field is in the plane perpendicular to the light polarization plane. Furthermore, the optical magnetic resonance (OMR) signal using an HPB still has no dead zones even when the direction of the external magnetic field is in the plane parallel to the polarization plane in our scheme. Our work has the potential to simplify and optimize dead-zone-free atomic magnetometers. In this paper, we present the experiment and the theory scheme of light-atom interaction in atomic magnetometers by using a hybrid Poincaré beam (HPB) to solve an annoying problem, named “dead zone.” This kind of magnetometer can be sensitive to arbitrary directions of external magnetic fields. The HPB has a complex polarization distribution, consisting of a vector radially polarized beam and a scalar circularly polarized beam in our experiment. These two kinds of beams have different directions of dead zones of external magnetic fields; thereby, the atomic magnetometer with an HPB can avoid the non-signal area when the direction of the external magnetic field is in the plane perpendicular to the light polarization plane. Furthermore, the optical magnetic resonance (OMR) signal using an HPB still has no dead zones even when the direction of the external magnetic field is in the plane parallel to the polarization plane in our scheme. Our work has the potential to simplify and optimize dead-zone-free atomic magnetometers.
Photonics Research
- Publication Date: May. 01, 2024
- Vol. 12, Issue 5, 1093 (2024)
Optical colorimetric LiTaO3 wafers for high-precision lithography on frequency control of SAW devices
Ming Hui Fang, Yinong Xie, Fangqi Xue, Zhilin Wu, Jun Shi, Sheng Yu Yang, Yilin Liu, Zhihuang Liu, Hsin Chi Wang, Fajun Li, Qing Huo Liu, and Jinfeng Zhu
Surface acoustic wave (SAW) resonators based on lithium tantalate (LT, LiTaO3) wafers are crucial elements of mobile communication filters. The use of intrinsic LT wafers typically brings about low fabrication accuracy of SAW resonators due to strong UV reflection in the lithography process. This hinders their resonance frequency control seriously in industrial manufacture. LT doping and chemical reduction could be applied to decrease the UV reflection of LT wafers for high lithographic precision. However, conventional methods fail to provide a fast and nondestructive approach to identify the UV performance of standard single-side polished LT wafers for high-precision frequency control. Here, we propose a convenient on-line sensing scheme based on the colorimetry of reduced Fe-doped LT wafers and build up an automatic testing system for industrial applications. The levels of Fe doping and chemical reduction are evaluated by the lightness and color difference of LT-based wafers. The correlation between the wafer visible colorimetry and UV reflection is established to refine the lithography process and specifically manipulate the frequency performance of SAW resonators. Our study provides a powerful tool for the fabrication control of SAW resonators and will inspire more applications on sophisticated devices of mobile communication. Surface acoustic wave (SAW) resonators based on lithium tantalate (LT, LiTaO3) wafers are crucial elements of mobile communication filters. The use of intrinsic LT wafers typically brings about low fabrication accuracy of SAW resonators due to strong UV reflection in the lithography process. This hinders their resonance frequency control seriously in industrial manufacture. LT doping and chemical reduction could be applied to decrease the UV reflection of LT wafers for high lithographic precision. However, conventional methods fail to provide a fast and nondestructive approach to identify the UV performance of standard single-side polished LT wafers for high-precision frequency control. Here, we propose a convenient on-line sensing scheme based on the colorimetry of reduced Fe-doped LT wafers and build up an automatic testing system for industrial applications. The levels of Fe doping and chemical reduction are evaluated by the lightness and color difference of LT-based wafers. The correlation between the wafer visible colorimetry and UV reflection is established to refine the lithography process and specifically manipulate the frequency performance of SAW resonators. Our study provides a powerful tool for the fabrication control of SAW resonators and will inspire more applications on sophisticated devices of mobile communication.
Photonics Research
- Publication Date: Feb. 01, 2024
- Vol. 12, Issue 2, 341 (2024)
Linear group delay spectral interferometry for full-range precision absolute length metrology
Jindong Wang, Jingsheng Huang, Qihua Liu, Wei Du, Fumin Zhang, and Tao Zhu
The optical frequency comb serves as a powerful tool for distance measurement by integrating numerous stable optical modes into interferometric measurements, enabling unprecedented absolute measurement precision. Nonetheless, due to the periodicity of its pulse train, the comb suffers from measurement dead zones and ambiguities, thereby impeding its practical applications. Here, we present a linear group delay spectral interferometer for achieving precise full-range distance measurements. By employing a carefully designed linear group delay (LGD) device for phase modulation of the comb modes, interference can occur and be easily measured at any position. Our approach effectively eliminates the dead zones and ambiguities in comb-based ranging, without the need for cumbersome auxiliary scanning reference devices or reliance on complex high-repetition-rate combs or high-resolution spectrometers. We conducted length metrology experiments using a mode-locked comb referenced to a rubidium clock, achieving a large nonambiguity range up to 0.3 m, covering the entire measurement period. The maximum deviation compared to a laser interferometer was less than 1.5 μm, and the minimum Allan deviation during long-term measurements reached 5.47 nm at a 500 s averaging time. The approach ensures high accuracy while maintaining a simple structure, without relying on complex external devices, thereby propelling the practical implementation of comb-based length metrology. The optical frequency comb serves as a powerful tool for distance measurement by integrating numerous stable optical modes into interferometric measurements, enabling unprecedented absolute measurement precision. Nonetheless, due to the periodicity of its pulse train, the comb suffers from measurement dead zones and ambiguities, thereby impeding its practical applications. Here, we present a linear group delay spectral interferometer for achieving precise full-range distance measurements. By employing a carefully designed linear group delay (LGD) device for phase modulation of the comb modes, interference can occur and be easily measured at any position. Our approach effectively eliminates the dead zones and ambiguities in comb-based ranging, without the need for cumbersome auxiliary scanning reference devices or reliance on complex high-repetition-rate combs or high-resolution spectrometers. We conducted length metrology experiments using a mode-locked comb referenced to a rubidium clock, achieving a large nonambiguity range up to 0.3 m, covering the entire measurement period. The maximum deviation compared to a laser interferometer was less than 1.5 μm, and the minimum Allan deviation during long-term measurements reached 5.47 nm at a 500 s averaging time. The approach ensures high accuracy while maintaining a simple structure, without relying on complex external devices, thereby propelling the practical implementation of comb-based length metrology.
Photonics Research
- Publication Date: Feb. 01, 2024
- Vol. 12, Issue 2, 313 (2024)
Review on the terahertz metasensor: from featureless refractive index sensing to molecular identification
Jiaming Lyu, Lihao Huang, Lin Chen, Yiming Zhu, and Songlin Zhuang
The terahertz (THz) wave is at the intersection between photonics and electronics in the electromagnetic spectrum. Since the vibration mode of many biomedical molecules and the weak interaction mode inside the molecules fall in the THz regime, utilizing THz radiation as a signal source to operate substance information sensing has its unique advantages. Recently, the metamaterial sensor (metasensor) has greatly enhanced the interaction between signal and substances and spectral selectivity on the subwavelength scale. However, most past review articles have demonstrated the THz metasensor in terms of their structures, applications, or materials. Until recently, with the rapid development of metasensing technologies, the molecular information has paid much more attention to the platform of THz metasensors. In this review, we comprehensively introduce the THz metasensor for detecting not only the featureless refractive index but also the vibrational/chiral molecular information of analytes. The objectives of this review are to improve metasensing specificity either by chemical material-assisted analyte capture or by physical molecular information. Later, to boost THz absorption features in a certain frequency, the resonant responses of metasensors can be tuned to the molecular vibrational modes of target molecules, while frequency multiplexing techniques are reviewed to enhance broadband THz spectroscopic fingerprints. The chiral metasensors are also summarized to specific identification chiral molecules. Finally, the potential prospects of next generation THz metasensors are discussed. Compared to featureless refractive index metasensing, the specific metasensor platforms accelerated by material modification and molecular information will lead to greater impact in the advancement of trace detection of conformational dynamics of biomolecules in practical applications. The terahertz (THz) wave is at the intersection between photonics and electronics in the electromagnetic spectrum. Since the vibration mode of many biomedical molecules and the weak interaction mode inside the molecules fall in the THz regime, utilizing THz radiation as a signal source to operate substance information sensing has its unique advantages. Recently, the metamaterial sensor (metasensor) has greatly enhanced the interaction between signal and substances and spectral selectivity on the subwavelength scale. However, most past review articles have demonstrated the THz metasensor in terms of their structures, applications, or materials. Until recently, with the rapid development of metasensing technologies, the molecular information has paid much more attention to the platform of THz metasensors. In this review, we comprehensively introduce the THz metasensor for detecting not only the featureless refractive index but also the vibrational/chiral molecular information of analytes. The objectives of this review are to improve metasensing specificity either by chemical material-assisted analyte capture or by physical molecular information. Later, to boost THz absorption features in a certain frequency, the resonant responses of metasensors can be tuned to the molecular vibrational modes of target molecules, while frequency multiplexing techniques are reviewed to enhance broadband THz spectroscopic fingerprints. The chiral metasensors are also summarized to specific identification chiral molecules. Finally, the potential prospects of next generation THz metasensors are discussed. Compared to featureless refractive index metasensing, the specific metasensor platforms accelerated by material modification and molecular information will lead to greater impact in the advancement of trace detection of conformational dynamics of biomolecules in practical applications.
Photonics Research
- Publication Date: Jan. 29, 2024
- Vol. 12, Issue 2, 194 (2024)
Mutual aid instead of mutual restraint: interactive probing for topological charge and phase of a vortex beam of large aberrations
Shengyang Wu, Benli Yu, and Lei Zhang
An imperfect propagation environment or optical system would introduce wavefront aberrations to vortex beams. The phase aberrations and orbital angular momentum in a vortex beam are proved to be mutually restrictive in parameter measurement. Aberrations make traditional topological charge (TC) probing methods ineffective while the phase singularity makes phase retrieval difficult due to the aliasing between the wrapped phase jump and the vortex phase jump. An interactive probing method is proposed to make measurements of the aberrated phase and orbital angular momentum in a vortex beam assist rather than hinder each other. The phase unwrapping is liberated from the phase singularity by an annular shearing interference technique while the TC value is determined by a Moiré technique immune to aberrations. Simulation and experimental results proving the method effective are presented. It is of great significance to judge the characteristics of vortex beams passing through non-ideal environments and optical systems. An imperfect propagation environment or optical system would introduce wavefront aberrations to vortex beams. The phase aberrations and orbital angular momentum in a vortex beam are proved to be mutually restrictive in parameter measurement. Aberrations make traditional topological charge (TC) probing methods ineffective while the phase singularity makes phase retrieval difficult due to the aliasing between the wrapped phase jump and the vortex phase jump. An interactive probing method is proposed to make measurements of the aberrated phase and orbital angular momentum in a vortex beam assist rather than hinder each other. The phase unwrapping is liberated from the phase singularity by an annular shearing interference technique while the TC value is determined by a Moiré technique immune to aberrations. Simulation and experimental results proving the method effective are presented. It is of great significance to judge the characteristics of vortex beams passing through non-ideal environments and optical systems.
Photonics Research
- Publication Date: Dec. 22, 2023
- Vol. 12, Issue 1, 172 (2024)
Distributed phase-matching measurement for dynamic strain and temperature sensing based on stimulated Brillouin scattering enhanced four-wave mixing
Yuan Wang, Pedro Tovar, Juntong Yang, Liang Chen, and Xiaoyi Bao
A Brillouin dynamic grating (BDG) can be used for distributed birefringence measurement in optical fibers, offering high sensitivity and spatial resolution for sensing applications. However, it is quite a challenge to simultaneously achieve dynamic measurements with both high accuracy and high spatial resolution. In this work, we propose a sensing mechanism to achieve distributed phase-matching measurement using a chirped pulse as a probe signal. In BDG reflection, the peak reflection corresponds to the highest four-wave mixing (FWM) conversion efficiency, and it requires the Brillouin frequency in the fast and slow axes to be equal, which is called the phase-matching condition. This condition changes at different fiber positions, which requires a range of frequency injection for the probe wave. The proposed method uses a chirped pulse as a probe wave to cover this frequency range associated with distributed birefringence inhomogeneity. This allows us to detect distributed phase matching for birefringence changes that are introduced by temperature and strain variations. Thanks to the single shot and direct time delay measurement capability, the acquisition rate in our system is only limited by the fiber length. Notably, unlike conventional BDG spectrum recovery-based systems, the spatial resolution here is determined by both the frequency chirping rate of the probe pulse and the birefringence profile of the fiber. In the experiments, an acquisition rate of 1 kHz (up to fiber length limits) and a spatial resolution of 10 cm using a 20 ns probe pulse width are achieved. The minimum detectable temperature and strain variation are 5.6 mK and 0.37 με along a 2 km long polarization-maintaining fiber (PMF). A Brillouin dynamic grating (BDG) can be used for distributed birefringence measurement in optical fibers, offering high sensitivity and spatial resolution for sensing applications. However, it is quite a challenge to simultaneously achieve dynamic measurements with both high accuracy and high spatial resolution. In this work, we propose a sensing mechanism to achieve distributed phase-matching measurement using a chirped pulse as a probe signal. In BDG reflection, the peak reflection corresponds to the highest four-wave mixing (FWM) conversion efficiency, and it requires the Brillouin frequency in the fast and slow axes to be equal, which is called the phase-matching condition. This condition changes at different fiber positions, which requires a range of frequency injection for the probe wave. The proposed method uses a chirped pulse as a probe wave to cover this frequency range associated with distributed birefringence inhomogeneity. This allows us to detect distributed phase matching for birefringence changes that are introduced by temperature and strain variations. Thanks to the single shot and direct time delay measurement capability, the acquisition rate in our system is only limited by the fiber length. Notably, unlike conventional BDG spectrum recovery-based systems, the spatial resolution here is determined by both the frequency chirping rate of the probe pulse and the birefringence profile of the fiber. In the experiments, an acquisition rate of 1 kHz (up to fiber length limits) and a spatial resolution of 10 cm using a 20 ns probe pulse width are achieved. The minimum detectable temperature and strain variation are 5.6 mK and 0.37 με along a 2 km long polarization-maintaining fiber (PMF).
Photonics Research
- Publication Date: Dec. 22, 2023
- Vol. 12, Issue 1, 141 (2024)
Multidimensional optical tweezers synthetized by rigid-body emulated structured light
Liuhao Zhu, Yuping Tai, Hehe Li, Huajie Hu, Xinzhong Li, Yangjian Cai, and Yijie Shen
Structured light with more extended degrees of freedom (DoFs) and in higher dimensions is increasingly gaining traction and leading to breakthroughs such as super-resolution imaging, larger-capacity communication, and ultraprecise optical trapping or tweezers. More DoFs for manipulating an object can access more maneuvers and radically increase maneuvering precision, which is of significance in biology and related microscopic detection. However, manipulating particles beyond three-dimensional (3D) spatial manipulation by using current all-optical tweezers technology remains difficult. To overcome this limitation, we theoretically and experimentally present six-dimensional (6D) structured optical tweezers based on tailoring structured light emulating rigid-body mechanics. Our method facilitates the evaluation of the methodology of rigid-body mechanics to synthesize six independent DoFs in a structured optical trapping system, akin to six-axis rigid-body manipulation, including surge, sway, heave, roll, pitch, and yaw. In contrast to previous 3D optical tweezers, our 6D structured optical tweezers significantly improved the flexibility of the path design of complex trajectories, thereby laying the foundation for next-generation functional optical manipulation, assembly, and micromechanics. Structured light with more extended degrees of freedom (DoFs) and in higher dimensions is increasingly gaining traction and leading to breakthroughs such as super-resolution imaging, larger-capacity communication, and ultraprecise optical trapping or tweezers. More DoFs for manipulating an object can access more maneuvers and radically increase maneuvering precision, which is of significance in biology and related microscopic detection. However, manipulating particles beyond three-dimensional (3D) spatial manipulation by using current all-optical tweezers technology remains difficult. To overcome this limitation, we theoretically and experimentally present six-dimensional (6D) structured optical tweezers based on tailoring structured light emulating rigid-body mechanics. Our method facilitates the evaluation of the methodology of rigid-body mechanics to synthesize six independent DoFs in a structured optical trapping system, akin to six-axis rigid-body manipulation, including surge, sway, heave, roll, pitch, and yaw. In contrast to previous 3D optical tweezers, our 6D structured optical tweezers significantly improved the flexibility of the path design of complex trajectories, thereby laying the foundation for next-generation functional optical manipulation, assembly, and micromechanics.
Photonics Research
- Publication Date: Aug. 22, 2023
- Vol. 11, Issue 9, 1524 (2023)
1.5-m flat imaging system aligned and phased in real time|Spotlight on Optics
Zongliang Xie, Kaiyuan Yang, Yang Liu, Tianrong Xu, Botao Chen, Xiafei Ma, Yong Ruan, Haotong Ma, Junfeng Du, Jiang Bian, Dun Liu, Lihua Wang, Tao Tang, Jiawei Yuan, Ge Ren, Bo Qi, and Hu Yang
Flat optics has been considered promising for constructions of spaceborne imaging systems with apertures in excess of 10 m. Despite recent advances, there are long-existing challenges to perform in-phase stitching of multiple flat optical elements. Phasing the segmented planar instrument has remained at the proof of concept. Here, we achieve autonomous system-level cophasing of a 1.5-m stitching flat device, bridging the gap between the concept and engineering implementation. To do so, we propose a flat element stitching scheme, by manipulating the point spread function, which enables our demonstration of automatically bringing seven flat segments’ tip/tilt and piston errors within the tolerance. With phasing done, the 1.5-m system has become the largest phased planar instrument ever built in the world, to our knowledge. The first demonstration of phasing the large practical flat imaging system marks a significant step towards fielding a 10-m class one in space, also paving the way for ultrathin flat imaging in various remote applications. Flat optics has been considered promising for constructions of spaceborne imaging systems with apertures in excess of 10 m. Despite recent advances, there are long-existing challenges to perform in-phase stitching of multiple flat optical elements. Phasing the segmented planar instrument has remained at the proof of concept. Here, we achieve autonomous system-level cophasing of a 1.5-m stitching flat device, bridging the gap between the concept and engineering implementation. To do so, we propose a flat element stitching scheme, by manipulating the point spread function, which enables our demonstration of automatically bringing seven flat segments’ tip/tilt and piston errors within the tolerance. With phasing done, the 1.5-m system has become the largest phased planar instrument ever built in the world, to our knowledge. The first demonstration of phasing the large practical flat imaging system marks a significant step towards fielding a 10-m class one in space, also paving the way for ultrathin flat imaging in various remote applications.
Photonics Research
- Publication Date: Jun. 28, 2023
- Vol. 11, Issue 7, 1339 (2023)
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