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Photonics, Volume 10, Issue 3 (March 2023) – 119 articles

Cover Story (view full-size image): The review aims to provide an overview of the optical injection locking technique for visible light communication (VLC) applications. There is growing demand for ultra-high speed and ultra-low latency in wireless communication, and visible light communication is a promising technique for next-generation optical data networks, benefiting from making good use of abundant spectrum resources. High-speed VLC is typically enabled by laser-based transmitters, and optical injection locking technology can significantly improve the modulation bandwidth of laser diodes, including those used in VLC. It is expected that further exploration and research will lead to miniaturized, high efficiency, high-speed injection-locked devices for visible light communication systems. View this paper
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14 pages, 5943 KiB  
Communication
Influence of Off-Axis Noncanonical Vortex on the Dynamics of Energy Flux
by Xinying Zhao, Huijian Liang, Gaofeng Wu and Xiaoyan Pang
Photonics 2023, 10(3), 346; https://doi.org/10.3390/photonics10030346 - 22 Mar 2023
Viewed by 977
Abstract
In this article, we analyze the impact of the off-axis noncanonical vortex on the dynamics of 3D energy flux. The results reveal that the properties of energy flux are significantly influenced by the anisotropy parameter σc of the off-axis noncanonical vortex. It [...] Read more.
In this article, we analyze the impact of the off-axis noncanonical vortex on the dynamics of 3D energy flux. The results reveal that the properties of energy flux are significantly influenced by the anisotropy parameter σc of the off-axis noncanonical vortex. It is demonstrated that by adjusting the anisotropy parameter, we can control the transverse energy flux, from the position of the transverse energy tornado and the distribution of the transverse energy strength to the rotation direction of the transverse energy flux as the beam propagates. The interesting phenomenon, the reversed energy flux, is also closely related to the anisotropy parameter. The position and size of the reversed energy flux region, as well as the production of two energy tornadoes with opposite rotating directions, resembling a Chinese “Taiji” pattern, can be controlled by varying the anisotropy parameter. This result will potentially provide a new freedom for tailoring the 3D optical field and be useful in optical manipulation and processing. Full article
(This article belongs to the Special Issue Coherent and Polarization Optics)
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11 pages, 62214 KiB  
Article
The Effect of GaSb Substrate Oxidation Layer on InAs/GaSb Type II Superlattice
by Jiabo Liu, Lianqing Zhu, Ruixin Gong, Bingfeng Liu, Mingliang Gong, Qingsong Feng, Zhiping Chen, Dongliang Zhang, Xiantong Zheng, Yulin Feng, Lidan Lu and Yuan Liu
Photonics 2023, 10(3), 345; https://doi.org/10.3390/photonics10030345 - 22 Mar 2023
Cited by 1 | Viewed by 1356
Abstract
Type-II superlattices (T2SLs) are emerging as next-generation materials for infrared detectors. The epitaxial quality of T2SLs is of great importance to the performance of infrared detectors such as dark current and detectivity. Herein, we explore the effect of the native GaSb oxide layer [...] Read more.
Type-II superlattices (T2SLs) are emerging as next-generation materials for infrared detectors. The epitaxial quality of T2SLs is of great importance to the performance of infrared detectors such as dark current and detectivity. Herein, we explore the effect of the native GaSb oxide layer on the surface morphology and crystal quality of InAs/GaSb T2SLs grown with molecular beam epitaxy. The experimental results demonstrate that the thickness of the oxidation layer on GaSb substrates gradually increases over time and is saturated at around 73 Å in the natural oxidation condition. Moreover, the oxidation process is sensitive to humidity. As the thickness of the GaSb oxide layer increases from 18.79 Å to 61.54 Å, the full width at half maximum of the first satellite peak increases from 38.44 to 61.34 arcsec in X-ray diffraction measurements, and the root mean square roughness increases from 0.116 nm to 0.171 nm in atomic force microscopy measurements. Our results suggest that the thickness of the GaSb oxide layer should be less than 55 Å to obtain smooth buffer layers and qualified superlattices. The work provides an optimized direction for achieving high-quality superlattices for infrared optoelectronic devices. Full article
(This article belongs to the Special Issue III-V Semiconductors Optoelectronic Materials and Devices)
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10 pages, 4224 KiB  
Communication
Single-Layered Phase-Change Metasurfaces Achieving Polarization- and Crystallinity-Dependent Wavefront Manipulation
by Jie Hu, Yujie Chen, Wenting Zhang, Ziyi Tang, Xiang Lan, Qinrong Deng, Hengyu Cui, Ling Li and Yijia Huang
Photonics 2023, 10(3), 344; https://doi.org/10.3390/photonics10030344 - 22 Mar 2023
Cited by 1 | Viewed by 1260
Abstract
As a promising platform for versatile electromagnetic (EM) manipulations, metasurfaces have drawn wide interest in recent years due to their unique EM properties and small footprints. However, although great efforts have been made to achieve multifunctionalities, the design of tunable metasurfaces with high [...] Read more.
As a promising platform for versatile electromagnetic (EM) manipulations, metasurfaces have drawn wide interest in recent years due to their unique EM properties and small footprints. However, although great efforts have been made to achieve multifunctionalities, the design of tunable metasurfaces with high compactness is still challenging. Here, a simple yet powerful design methodology for single-layered reconfigurable metasurfaces composed of nonvolatile phase-change material Ge2Sb2Se4Te1 (GSST) is proposed with average working amplitudes of 72.6% and 53% at different crystallization levels. The proposed metasurfaces could not only enable independent phase control at different crystallization levels but also introduced another polarization degree of freedom. As a proof of concept, we numerically demonstrate three kinds of metadevices in the infrared region achieving a multi-focus metalens with tunable foci, multistate vortex beam generator with adjustable topological charges and multi-channel meta-hologram with three independent information channels. It is believed that these multifunctional metasurfaces with both tunability and compactness are promising for various applications including information encryption, chiroptical spectroscopy, chiral imaging and wireless communication. Full article
(This article belongs to the Special Issue Terahertz Metamaterials and Device Applications)
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15 pages, 7174 KiB  
Article
275–305 GHz FM-CW Radar 3D Imaging for Walk-Through Security Body Scanner
by Tomofumi Ikari, Yoshiaki Sasaki and Chiko Otani
Photonics 2023, 10(3), 343; https://doi.org/10.3390/photonics10030343 - 22 Mar 2023
Cited by 5 | Viewed by 1993
Abstract
Imaging using millimeter waves (MMW) and terahertz (THz) waves can help inspect hazardous materials hidden beneath clothing in a non-contact and non-invasive manner. A 3D terahertz imaging system for security gate applications in the 275–305 GHz range was developed and experimentally demonstrated to [...] Read more.
Imaging using millimeter waves (MMW) and terahertz (THz) waves can help inspect hazardous materials hidden beneath clothing in a non-contact and non-invasive manner. A 3D terahertz imaging system for security gate applications in the 275–305 GHz range was developed and experimentally demonstrated to detect concealed objects carried by pedestrians. This system performs 3D measurements by combining depth detection using frequency-modulated continuous wave (FM-CW) radar, vertical scanning of the detection spot using a 1D high-speed mechanical beam scanner, and horizontal movement of the irradiated area and detection spot as the pedestrian walks. The high-speed beam scanner comprises an F-Theta telecentric lens and a polygon mirror. It has a vertical line scan rate of 142 lines/s and spatial resolution of ~10 mm, consistent with the design value, and a depth resolution of ~7 mm, which is 40% larger than the theoretical value estimated from the FM-CW radar principle. The depth-dependent lateral distortion in 3D images, known as telecentricity, measured using the body scanner imaging system, was also evaluated. Consequently, images with the same magnification were obtained at a range of more than 500 mm of focus depth. Finally, the detection of concealed objects carried by pedestrians was demonstrated, showing that the system can work for a pedestrian walking at speeds from 4 km/h to 7 km/h. Full article
(This article belongs to the Special Issue Terahertz (THz) Science in Advanced Materials, Devices and Systems)
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12 pages, 6904 KiB  
Article
Lensed Fiber-Optic Two-Photon Endomicroscopy for Field-of-View Enhancement
by Conghao Wang, Huilan Liu, Jianrui Ma, Qiang Fu, Yijun Li, Yanchuan Chen, Yuqian Gao, Jingquan Tian, Xinlei Luo, Fei Yu, Chunzhu Zhao, Runlong Wu, Aimin Wang and Lishuang Feng
Photonics 2023, 10(3), 342; https://doi.org/10.3390/photonics10030342 - 22 Mar 2023
Cited by 2 | Viewed by 1531
Abstract
Two-photon endomicroscopy is a promising technique with the ability to achieve in situ imaging and diagnosis at subcellular resolution. The large field-of-view capability is essential and useful to locate and image suspicious areas of biological tissue. In this work, we report objective-lens-free, lensed [...] Read more.
Two-photon endomicroscopy is a promising technique with the ability to achieve in situ imaging and diagnosis at subcellular resolution. The large field-of-view capability is essential and useful to locate and image suspicious areas of biological tissue. In this work, we report objective-lens-free, lensed fiber-optic two-photon endomicroscopy for field-of-view enhancement. The field of view of this two-photon endomicroscopic probe is 750 μm with a resolution of 3.03 μm. This 1.6 g miniature probe has an integrated outer diameter of 5.8 mm and a rigid length of 33.5 mm. The imaging performance of the lensed-fiber-optic two-photon endomicroscopy was validated by examining an ex vivo mouse heart, kidney, brain, stomach wall tissues, and in vivo brain tissue. Full article
(This article belongs to the Topic Biomedical Photonics)
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12 pages, 8850 KiB  
Article
Rotational Doppler Velocimetry of a Surface at Larger Tilt Angles
by Yanxiang Zhang, Zijing Zhang, Liping Liu and Yuan Zhao
Photonics 2023, 10(3), 341; https://doi.org/10.3390/photonics10030341 - 22 Mar 2023
Cited by 2 | Viewed by 1142
Abstract
Here, we experimentally demonstrate a straightforward-to-implement scheme that enables the rotating velocimetry of a noncooperative target at large deflection angles. This scheme is based upon the combination of digital modal decomposition with the rotational Doppler effect of orbital angular momentum (OAM)-carried light modes. [...] Read more.
Here, we experimentally demonstrate a straightforward-to-implement scheme that enables the rotating velocimetry of a noncooperative target at large deflection angles. This scheme is based upon the combination of digital modal decomposition with the rotational Doppler effect of orbital angular momentum (OAM)-carried light modes. To achieve this, we first theoretically analyzed the tilt effect of a rotating surface on the OAM complex spectra and rotational Doppler spectrum. Our findings validate that the tilted surface causes not only the broadening of OAM power and phase spectra, but also the broadening of the scattered Doppler spectrum. Furthermore, we introduce a compensation phase for tilted OAM light that effectively suppresses the sidebands of the OAM power spectrum, thereby restraining the sideband amplitudes of the Doppler spectrum. As a consequence, the rotating velocimetry can be extended to cover larger tilt angles (as large as 70 degrees) than those of existing systems. Our outcomes have the advantages of providing, in addition to profound insight into the interaction between OAM-carrying light and object motion, potential opportunities for noncontact optical metrology and the telemetry of angular speeds, particularly in meteorological applications. Full article
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16 pages, 1467 KiB  
Article
Crosstalk Classification Based on Synthetically Consider Crosstalk and Fragmentation RMCSA in Multi-Core Fiber-Based EONs
by Yanbo Chen, Nan Feng, Yue Zhou, Danping Ren and Jijun Zhao
Photonics 2023, 10(3), 340; https://doi.org/10.3390/photonics10030340 - 22 Mar 2023
Cited by 2 | Viewed by 1016
Abstract
Space division multiplexing elastic optical networks (SDM-EONs) based on multi-core fiber (MCF) technologies have attracted widespread attention as a potential means of enhancing large capacity and high flexibility. However, inter-core crosstalk (XT) degrades the quality of transmission. The algorithm for minimizing XT leads [...] Read more.
Space division multiplexing elastic optical networks (SDM-EONs) based on multi-core fiber (MCF) technologies have attracted widespread attention as a potential means of enhancing large capacity and high flexibility. However, inter-core crosstalk (XT) degrades the quality of transmission. The algorithm for minimizing XT leads to an increase in spectrum fragmentation in the lightpath, which influences the spectrum utilization. Therefore, the question of how to comprehensively consider the two factors and improve the network performance is an issue worthy of study. This paper focuses on maximizing spectrum resource utilization while satisfying the XT constraints. Firstly, we optimize a three-dimensional metric model to evaluate XT and fragmentation more exactly in SDM-EONs. Furthermore, a crosstalk classification (CC) algorithm, which can adjust the XT constraints according to the actual situation of the network, is proposed. Moreover, to match the CC algorithm, we describe the crosstalk and fragmentation in the network and propose a synthetically consider crosstalk and fragmentation (SCCF) algorithm. Finally, simulation results show that the proposed CC-SCCF routing, modulation, core, and spectrum allocation algorithm reduces the XT on existing lightpaths, and also provides a lower probability of blocking and greater spectrum utilization. Full article
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12 pages, 5571 KiB  
Communication
Second-Order Statistics of Self-Splitting Structured Beams in Oceanic Turbulence
by Liming Liu, Yulu Liu, Hao Chang, Jifei Huang, Xinlei Zhu, Yangjian Cai and Jiayi Yu
Photonics 2023, 10(3), 339; https://doi.org/10.3390/photonics10030339 - 22 Mar 2023
Cited by 7 | Viewed by 1001
Abstract
Free-space optical communication is restricted by random media-stimulated beam degradation. However, partially coherent structured beams modulated by the coherence structure can potentially mitigate this negative effect. By employing the extended Huygens–Fresnel integral, we provide an examination of the second-order statistical features of a [...] Read more.
Free-space optical communication is restricted by random media-stimulated beam degradation. However, partially coherent structured beams modulated by the coherence structure can potentially mitigate this negative effect. By employing the extended Huygens–Fresnel integral, we provide an examination of the second-order statistical features of a common type of partly coherent structured beams, self-splitting structured beams, in a turbulent ocean. The implications of turbulence parameters relating to the ocean and beginning beam parameters corresponding to the progression of such beam propagation attributes are fully investigated. Our numerical outcomes show that, for turbulence with a low-dissipation kinetic energy rate per unit mass of fluid, small Kolmogorov inner scale, large relative strength of temperature to salinity undulations, and large dissipation rate of mean-square temperature has a greater negative effect on the structured beams. In addition, we suggest an effective approach, enhancing the order of the beam and reducing the coherence length of the beams, to lower the oceanic turbulence-induced negative effects, and thus have future extensive possibilities in free-space optical communication. Full article
(This article belongs to the Special Issue Coherent and Polarization Optics)
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13 pages, 3996 KiB  
Article
An Autofocus Method Based on Improved Differential Confocal Microscopy in Two-Photon Lithography
by Zhenyu Yang, Minfei He, Guozun Zhou, Cuifang Kuang and Xu Liu
Photonics 2023, 10(3), 338; https://doi.org/10.3390/photonics10030338 - 21 Mar 2023
Cited by 1 | Viewed by 1677
Abstract
Two-photon lithography (TPL) plays a vital role in microstructure fabrication due to its high processing accuracy and maskless characteristics. To optimize the manufacturing quality deteriorated by the defocus of the substrate, an autofocus approach based on improved differential confocal microscopy (IDCM) is proposed [...] Read more.
Two-photon lithography (TPL) plays a vital role in microstructure fabrication due to its high processing accuracy and maskless characteristics. To optimize the manufacturing quality deteriorated by the defocus of the substrate, an autofocus approach based on improved differential confocal microscopy (IDCM) is proposed in this paper. Through analyzing the intensity response signals from two detectors with symmetrical axial offset, the defocus amount is measured and compensated for with high precision and noise immunity to stabilize the substrate. The verification experiments on the coverslip reported a detection sensitivity of 5 nm, a repetitive measurement accuracy of less than 15 nm, and a focusing accuracy reaching around 5 nm. The consistency between simulation and characterization demonstrated the effectiveness and superior performance of the autofocus system for the high production quality of the metalens array. The proposed autofocus method shows promise for further application to the fabrication of complex structures on various substrates. Full article
(This article belongs to the Special Issue Optical Measurement Systems)
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11 pages, 640 KiB  
Article
Mach–Zehnder Modulator Output in Time and Frequency Domain—Calculation and Experimental Confirmation
by Sander Vervoort, Yannick Saalberg and Marcus Wolff
Photonics 2023, 10(3), 337; https://doi.org/10.3390/photonics10030337 - 21 Mar 2023
Cited by 1 | Viewed by 2530
Abstract
The Mach–Zehnder intensity Modulator (MZM), named after Ludwig Mach and Ludwig Zehnder, is based on the corresponding interferometer. It splits light into two counter-rotating partial beams, which are later recombined with a controlled phase difference. The output of the MZM depends on the [...] Read more.
The Mach–Zehnder intensity Modulator (MZM), named after Ludwig Mach and Ludwig Zehnder, is based on the corresponding interferometer. It splits light into two counter-rotating partial beams, which are later recombined with a controlled phase difference. The output of the MZM depends on the phase difference of the interferometer paths. This phase difference is usually adjusted by an electrical voltage applied to a Phase Shifter (PS) placed in one of the interferometer arms. For MZM applications in which the wavelength is changing, the applied voltage must be adjusted accordingly. We derived the equations describing the MZM output in the frequency domain for the case of a triangular PS voltage (necessary for a sinusoidal output) and compared the analytical results with measurements. Our setup uses an Optical Parametric Oscillator (OPO) with a tunable wavelength from 3.2–3.5 μm as the light source and a Lithium Tantalate (LT)-PS for the MZM’s phase modulation. The novel insights enable new control methods for MZMs particularly suited for spectroscopic applications where the wavelength is scanned or otherwise altered. Full article
(This article belongs to the Special Issue Emerging Frontiers in Photoacoustic Spectroscopy Detection)
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14 pages, 3928 KiB  
Article
Simulation and Design of a PIC-Based Heterodyne Optical Phase Locked Loop
by Xiu Yang, Chanchan Luo, Ben Zhang, Bocang Qiu and Ruiying Zhang
Photonics 2023, 10(3), 336; https://doi.org/10.3390/photonics10030336 - 21 Mar 2023
Viewed by 1395
Abstract
In this paper, we report on our simulation and design of a photonic integrated circuits (PIC)-based heterodyne optical phase-locked loop (OPLL). Our simulation reveals that the OPLL operation can be in one of three states, i.e., absolutely stable, metastable, and unstable states, depending [...] Read more.
In this paper, we report on our simulation and design of a photonic integrated circuits (PIC)-based heterodyne optical phase-locked loop (OPLL). Our simulation reveals that the OPLL operation can be in one of three states, i.e., absolutely stable, metastable, and unstable states, depending on the relative position of the initial phase reversal point to the loop bandwidth. By systematically optimizing all of the loop parameters involved, the loop bandwidth of 247.8 MHz and the residual phase noise variance of 0.012 rad2 are theoretically obtained in such a PIC-OPLL system, which are better than any reported counterparts. In addition, the lowest required power of the master laser is also evaluated, assuming that the largest acceptable residual phase noise variance is 0.02 rad2, and it is found that the lowest master laser power is −54 dBm in our current OPLL system, and this value can be reduced to −56 dBm, providing that the summed linewidth is reduced to 10 kHz. Full article
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11 pages, 3680 KiB  
Article
Extra-High Pressure in the Core of Silica-Based Optical Fiber Preforms during the Manufacturing Process
by Galina Bufetova, Alexey Kosolapov, Mikhail Yashkov, Andrey Umnikov, Vladimir Velmiskin, Vladimir Tsvetkov and Igor Bufetov
Photonics 2023, 10(3), 335; https://doi.org/10.3390/photonics10030335 - 21 Mar 2023
Viewed by 1132
Abstract
The core refractive index n2 of silica-based optical fiber preform heated to 2000 °C was determined experimentally for the first time. The measurements were carried out in the process of preform temperature reduction. It was shown that n2 could increase up [...] Read more.
The core refractive index n2 of silica-based optical fiber preform heated to 2000 °C was determined experimentally for the first time. The measurements were carried out in the process of preform temperature reduction. It was shown that n2 could increase up to ~1.75 in the visible spectral range at temperatures of ~2000 °C (n2 ≈ 1.46 at room temperature). This fact suggests that pressures close to or exceeding the ultimate strength of silica glass (~20 GPa) occur in the preform core region. The local extra pressure is argued to be a possible cause of the well-known “starburst” phenomenon at the core–cladding interface of preforms with certain core compositions. The observed effect of radial cracks can be interpreted as the result of silica cladding destruction under the action of extra-high pressure in the core. Full article
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7 pages, 2695 KiB  
Communication
A Novel α-BaTeMo2O9 Acousto-Optic Switch for Generating Stable 639 nm Pulsed Laser
by Ke Zhang, Feifei Guo, Yicheng Jin, Kuan Li, Lihua Meng, Peifu Wang, Shande Liu, Zeliang Gao and Xutang Tao
Photonics 2023, 10(3), 334; https://doi.org/10.3390/photonics10030334 - 21 Mar 2023
Viewed by 1171
Abstract
In this paper, an acousto-optic (AO) Q-switch based on α-BaTeMo2O9 (α-BTM) crystal is designed and further applied to generate a laser pulse at 639 nm for the first time. The α-BTM AO Q-switch demonstrates a large [...] Read more.
In this paper, an acousto-optic (AO) Q-switch based on α-BaTeMo2O9 (α-BTM) crystal is designed and further applied to generate a laser pulse at 639 nm for the first time. The α-BTM AO Q-switch demonstrates a large diffraction angle of 0.93° and a high diffraction efficiency of 85% at 639 nm. In the experiment, a maximum AO Q-switched output power of 362 mW is achieved at a repetition rate of 30 kHz, under a maximum absorbed pump power of 3.60 W, corresponding to a slope efficiency of 15.2%. With transmittance of T = 3%, the shortest Q-switching pulse width of 54.7 ns is generated at a repetition rate of 1 kHz. Meanwhile, the beam quality factor M2 of the above laser is measured, presenting the magnitude of 1.14 at both x and y directions. Our findings indicate that α-BTM AO Q-switch could act as an excellent switching device at 639 nm which may help to explore potential applications in the visible field. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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9 pages, 2314 KiB  
Communication
Transmission Properties in Plasma Photonic Crystal Controlled by Magnetic Fields
by Hailu Wang, Jianfei Li, Liang Guo, Dongliang Ma, Jingfeng Yao and He-Ping Li
Photonics 2023, 10(3), 333; https://doi.org/10.3390/photonics10030333 - 20 Mar 2023
Viewed by 1157
Abstract
The transmission properties in two-dimensional plasma photonic crystal composed of plasma and yttrium–iron–garnet rods with square lattices are demonstrated under different electron densities and external magnetic fields. The TE and TM modes respond to the permittivity tensor and the permeability tensor produced by [...] Read more.
The transmission properties in two-dimensional plasma photonic crystal composed of plasma and yttrium–iron–garnet rods with square lattices are demonstrated under different electron densities and external magnetic fields. The TE and TM modes respond to the permittivity tensor and the permeability tensor produced by the magnetic field. For TM polarization, two distinct attenuation peaks appear in the ranges of 3.4–3.62 GHz and 3.78–4 GHz, induced by the external magnetic fields, and the location of these attenuation peaks can be modulated by modifying the electron densities. For TE polarization, a flat transmission spectrum was obtained in the range of 4–4.6 dB by increasing the electron density to 3×1012 cm3. Then, a Y-shaped plasma photonic crystal waveguide is designed. The transmission path can be modulated by changing the direction of the external magnetic field. By regulating the electron density, switching the Y-shaped waveguide on and off can be achieved. Full article
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14 pages, 2320 KiB  
Article
A Novel Measurement Method for Spin Polarization Three Axis Spatial Distribution in Spin-Exchange Relaxation Free Atomic Magnetometer
by Xiujie Fang, Jin Li, Yanning Ma, Kai Wei, Wenfeng Fan, Yueyang Zhai, Wei Quan and Zhisong Xiao
Photonics 2023, 10(3), 332; https://doi.org/10.3390/photonics10030332 - 20 Mar 2023
Viewed by 1407
Abstract
The measurement of atomic spin polarization distribution in spin-exchange relaxation free (SERF) magnetometer is an important topic for improving the sensitivity and consistency of multi-channel magnetic field measurement applications. A novel spin polarization spatial distribution measurement method is presented based on the transient [...] Read more.
The measurement of atomic spin polarization distribution in spin-exchange relaxation free (SERF) magnetometer is an important topic for improving the sensitivity and consistency of multi-channel magnetic field measurement applications. A novel spin polarization spatial distribution measurement method is presented based on the transient response of the magnetometer after modulating the pumped light with a chopper. Polarization is obtained by a slow-down factor based on the fast spin-exchange interaction effects. Longitudinal and transverse polarization distributions are measured simultaneously without interrupting the operation of the SERF status. Under different oscillating magnetic fields, the spin polarization is measured at the cell centroid. Residual magnetic field inside the magnetometer is obtained from the linear relationship between the precession frequency and the oscillating magnetic field. The one-dimensional polarization distributions in the x, y, and z axes are measured using a digital micromirror device with a resolution of 0.25 cm. The measurement results conform to the Lambert-Bier absorption law and the Gaussian distribution law. Furthermore, 7 × 7 two-dimensional spatial distribution measurements of polarization on the xy and yz planes are performed. Nonuniformity of 1.04 in the xy plane and 1.82 in the yz plane in the built magnetometer. Compared with other measurement methods, the distribution measurement method proposed is independent of optical depth and suitable for low polarization and high polarization applications. Based on the results of the proposed measurement method of spin polarization spatial distribution, further compensation can improve the application consistency of multi-channel magnetic field measurements and improve the sensitivity of single-channel differential measurements. Full article
(This article belongs to the Special Issue Optically Pumped Magnetometer and Its Application)
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13 pages, 4379 KiB  
Article
Non-Collinear Attosecond Streaking without the Time Delay Scan
by Peng Xu, Xianglin Wang, Huabao Cao, Hao Yuan, Liang-Wen Pi, Yishan Wang, Yuxi Fu, Yonglin Bai and Wei Zhao
Photonics 2023, 10(3), 331; https://doi.org/10.3390/photonics10030331 - 20 Mar 2023
Viewed by 2376
Abstract
Attosecond streaking provides an extremely high temporal resolution for characterizing light pulses and photoionization processes with attosecond (10−18 s) accuracy, which employs a laser as a streaking field to deflect electrons generated by photoionization. The current attosecond streaking requires a time delay [...] Read more.
Attosecond streaking provides an extremely high temporal resolution for characterizing light pulses and photoionization processes with attosecond (10−18 s) accuracy, which employs a laser as a streaking field to deflect electrons generated by photoionization. The current attosecond streaking requires a time delay scan between the attosecond pulses and streaking field with attosecond accuracy and a femtosecond range, which is difficult to realize real-time measurement. In this study, we theoretically propose a non-collinear attosecond streaking scheme without the time delay scan, enabling real-time and even the potential to perform single-shot attosecond pulse measurement. In the proposal, time-delay information is projected into longitudinal space, both horizontally and vertically, enabling attosecond pulse characterization with temporal-spatial coupling. From our calculation, down to 70 as pulses with pulse front and wavefront tilt are characterized with high accuracy. Our study not only provides a method toward real-time attosecond pulse measurement, but also an approach for attosecond pump-probe experiments without time delay scan. Full article
(This article belongs to the Special Issue Ultrafast Optics and Applications)
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8 pages, 1989 KiB  
Communication
Performance Analysis of LDPC-Coded OFDM in Underwater Wireless Optical Communications
by Jianzhong Guo, Jinpeng Xiao, Jing Chen, Xin Shan, Dejin Kong, Yan Wu and Yong Ai
Photonics 2023, 10(3), 330; https://doi.org/10.3390/photonics10030330 - 20 Mar 2023
Cited by 2 | Viewed by 1503
Abstract
The performance of Low-Density Parity-Check (LDPC)-coded Orthogonal Frequency Division Multiplexing (OFDM) is investigated over turbulence channels in underwater wireless optical communications (UWOC). The relation between the bit error ratio (BER) and parameters such as the scintillation coefficient, signal-to-noise ratio (SNR), length of LDPC [...] Read more.
The performance of Low-Density Parity-Check (LDPC)-coded Orthogonal Frequency Division Multiplexing (OFDM) is investigated over turbulence channels in underwater wireless optical communications (UWOC). The relation between the bit error ratio (BER) and parameters such as the scintillation coefficient, signal-to-noise ratio (SNR), length of LDPC code, and order of OFDM is quantified by simulation. Results show that while the OFDM with subcarrier quadrature amplitude modulation (QAM-OFDM) has slightly better anti-turbulence performance than the OFDM with subcarrier phase shift keying modulation (PSK-OFDM), the LDPC-coded QAM-OFDM has a much better performance than the QAM-OFDM and the LDPC-coded PSK-OFDM, and, at SNR = 12, it decreases the BER by four orders of magnitude compared to the 16QAM-OFDM system when the scintillation coefficient σξ2 = 0.05. Full article
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17 pages, 3632 KiB  
Article
Wheel-Based MDM-PON System Incorporating OCDMA for Secure Network Resiliency
by Meet Kumari, Vivek Arya and Hamza Mohammed Ridha Al-Khafaji
Photonics 2023, 10(3), 329; https://doi.org/10.3390/photonics10030329 - 19 Mar 2023
Cited by 6 | Viewed by 1458
Abstract
Wheel-based network resilience passive optical network (PON) based on mode division multiplexing (MDM) can be integrated with optical code division multiple access (OCDMA) schemes efficiently for the fixed and backhaul traffic under normal and break/failure fiber operating conditions. In this work, a bidirectional [...] Read more.
Wheel-based network resilience passive optical network (PON) based on mode division multiplexing (MDM) can be integrated with optical code division multiple access (OCDMA) schemes efficiently for the fixed and backhaul traffic under normal and break/failure fiber operating conditions. In this work, a bidirectional 10/2.5 Gbit/s hybrid MDM-OCDMA-PON system using multi-weight zero cross-correlation (MWZCC) code is proposed. Donut modes 0 and 1 are incorporated by the MDM technique in the proposed system. The benefit of this work is to offer an inexpensive, high-bandwidth and advanced long-haul network with satisfactory resource utilization ability for fiber links with protection against faults and to improve the reliability along with survivability of the network. The simulation results show the successful realization of the multimode fiber (MMF) link at 1.6 km in the uplink and 1.2 km in the downlink directions under an acceptable bit error rate (BER). The minimum accepted received power of −31 dBm in uplink and −27 dBm in downlink over 1 km link at 10/2.5 Gbit/s rate is obtained. Moreover, the minimum received power of −20 dBm in uplink and −30 dBm downlink is achieved by using MWZCC code compared to other codes handling 58 simultaneous end users. Further, the influence of fiber impairments and connected devices on the proposed approach is numerically evaluated. Moreover, it is shown that the wheel based proposed approach performs well than other topologies for the bidirectional network resilience transmission. Full article
(This article belongs to the Special Issue Advances in Optical Communication and Network)
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12 pages, 8941 KiB  
Communication
Exclusive Effect in Rydberg Atom-Based Multi-Band Microwave Communication
by Shuhang You, Minghao Cai, Haoan Zhang, Zishan Xu and Hongping Liu
Photonics 2023, 10(3), 328; https://doi.org/10.3390/photonics10030328 - 19 Mar 2023
Cited by 4 | Viewed by 1674
Abstract
We have demonstrated a Rydberg atom-based two-band communication with the optically excited Rydberg state coupled to another pair of Rydberg states by two microwave fields, respectively. The initial Rydberg state is excited by a three-color electromagnetically-induced absorption in rubidium vapor cell via cascading [...] Read more.
We have demonstrated a Rydberg atom-based two-band communication with the optically excited Rydberg state coupled to another pair of Rydberg states by two microwave fields, respectively. The initial Rydberg state is excited by a three-color electromagnetically-induced absorption in rubidium vapor cell via cascading transitions, with all of them located in infrared bands: a 780 nm laser servers as a probe to monitor the optical transmittancy via transition 5S1/25P3/2, 776 nm and 1260 nm lasers are used to couple the states 5P3/2 and 5D5/2 and states 5D5/2 and 44F7/2. Experimentally, we show that two channel communications carried on the two microwave transitions influence each other irreconcilably, so that they cannot work at their most sensitive microwave-optical conversion points simultaneously. For a remarkable communication quality for both channels, the two microwave fields both have to make concessions to reach a common microwave-optical gain. The optimized balance for the two microwave intensities locates at EMW1=6.5 mV/cm and EMW2=5.5 mV/cm in our case. This mutual exclusive influence is theoretically well-explained by an optical Bloch equation considering all optical and microwave field interactions with atoms. Full article
(This article belongs to the Special Issue Signal Processing and Transmission Enabled by Microwave Photonics)
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15 pages, 4633 KiB  
Article
Analysis of the Emission Features in CdSe/ZnS Quantum Dot-Doped Polymer Fibers
by Xuefeng Peng, Zhijian Wu, Chen Ye, Yang Ding and Wei Liu
Photonics 2023, 10(3), 327; https://doi.org/10.3390/photonics10030327 - 18 Mar 2023
Viewed by 1499
Abstract
The emission features of Cdse/ZnS quantum dots doped step-index polymer optical fibers are computationally analyzed in this paper. Spontaneous emission and amplified spontaneous emission were calculated by a theoretical model based on the rate equations in terms of time, fiber length, and wavelength. [...] Read more.
The emission features of Cdse/ZnS quantum dots doped step-index polymer optical fibers are computationally analyzed in this paper. Spontaneous emission and amplified spontaneous emission were calculated by a theoretical model based on the rate equations in terms of time, fiber length, and wavelength. All the calculated parameters are derived from experiments. Through the comparative analysis of the calculated and experimental results of spontaneous emission, we found that the pump power and overlap between the emission and absorption cross-sections may be the two main reasons for the red shift of the output spectra. When the pump power exceeds the threshold of amplified spontaneous emission, the width of the output spectra will rapidly decrease, the output wavelength will fall back toward the maximum emission cross-section, and the final output wavelength will still be affected by the doping concentration and pump power, while amplified spontaneous emission will not be generated when the total number of doped quantum dots is less than 1.27 × 1012. Full article
(This article belongs to the Special Issue Advances in Photonic Materials and Technologies)
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14 pages, 5548 KiB  
Article
Broad Tunable and High-Purity Photonic Microwave Generation Based on an Optically Pumped QD Spin-VCSEL with Optical Feedback
by Zhenye Shen, Yu Huang, Xin Zhu, Pei Zhou, Penghua Mu and Nianqiang Li
Photonics 2023, 10(3), 326; https://doi.org/10.3390/photonics10030326 - 18 Mar 2023
Cited by 2 | Viewed by 1301
Abstract
Spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) with birefringence-induced polarization oscillations have been proposed to generate desired photonic microwave signals. Here, we numerically investigate the generation of photonic microwave signals in an optically pumped quantum dot (QD) spin-VCSEL. First, the influence of intrinsic key parameters [...] Read more.
Spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) with birefringence-induced polarization oscillations have been proposed to generate desired photonic microwave signals. Here, we numerically investigate the generation of photonic microwave signals in an optically pumped quantum dot (QD) spin-VCSEL. First, the influence of intrinsic key parameters on period-one (P1) oscillations and microwave properties is discussed. Second, the difference between microwave generation based on the quantum well (QW) and QD spin-VCSELs is analyzed by controlling the carrier capture rate that is described in the spin-flip model. The QD spin-VCSEL shows superior microwave quality in the low-frequency range (e.g., 10 GHz~20 GHz) compared with the QW spin-VCSEL. Finally, to boost the performance of the generated photonic microwave signal, optical feedback is introduced. The results show that dual-loop feedback can simultaneously narrow the microwave linewidth and suppress the side modes that are derived from the external cavity mode. Full article
(This article belongs to the Special Issue Advancements in Semiconductor Lasers)
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9 pages, 2974 KiB  
Communication
Orbital Angular Momentum Resonances Arising from Mode Coupling in Hollow-Core Fibers
by Grigory Alagashev and Andrey Pryamikov
Photonics 2023, 10(3), 325; https://doi.org/10.3390/photonics10030325 - 17 Mar 2023
Viewed by 1016
Abstract
It is known that the growth of the orbital part of the angular momentum of the fundamental air core mode of the negative curvature hollow-core fibers (NCHCFs) with circular polarization occurs at the edge of the transmission bands due to the spin–orbit interaction. [...] Read more.
It is known that the growth of the orbital part of the angular momentum of the fundamental air core mode of the negative curvature hollow-core fibers (NCHCFs) with circular polarization occurs at the edge of the transmission bands due to the spin–orbit interaction. In this paper, we consider the resonant behavior of orbital angular momentum (OAM) for a linearly polarized fundamental air core mode in straight and bent NCHCF. The resonant growth of OAM is associated with coupling between the linear polarized fundamental air core mode and the cladding capillary wall modes. The coupling between the modes arises due to crossing and anti-crossing. This OAM growth can be explained by a complex interaction of energy fluxes of the coupled modes under crossing. This phenomenon may be useful for a deeper understanding of the processes arising from mode coupling in fiber optics and nanophotonics, as well as for generating and transmitting OAM modes in micro-structured optical fibers. Full article
(This article belongs to the Special Issue Recent Advances in Optical Diffraction and Imaging)
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10 pages, 1375 KiB  
Communication
Precise RF Phase Measurement by Optical Sideband Generation Using Mach–Zehnder Modulators
by Qingchuan Huang and Tetsuya Kawanishi
Photonics 2023, 10(3), 324; https://doi.org/10.3390/photonics10030324 - 17 Mar 2023
Viewed by 1130
Abstract
A novel radio frequency (RF) phase measurement method that uses optical modulation was proposed. The mathematical model of Mach–Zehnder modulator (MZM) characterization was reviewed. By measuring the output sideband power of the optical modulator, the phase difference of the electric signals fed to [...] Read more.
A novel radio frequency (RF) phase measurement method that uses optical modulation was proposed. The mathematical model of Mach–Zehnder modulator (MZM) characterization was reviewed. By measuring the output sideband power of the optical modulator, the phase difference of the electric signals fed to the modulator was experimentally measured, and picosecond-level accuracies were achieved. This technique is expected to be useful for radio-over-fiber-based antenna array systems. Full article
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13 pages, 7900 KiB  
Communication
Suppression of Nonlinear Optical Effects in DWDM-PON by Frequency Modulation Non-Coherent Detection
by Lei Xin, Xiao Xu, Liuge Du, Chonglei Sun, Feng Gao and Jia Zhao
Photonics 2023, 10(3), 323; https://doi.org/10.3390/photonics10030323 - 17 Mar 2023
Cited by 1 | Viewed by 1276
Abstract
We propose a simple and cost-effective method, using a direct frequency modulation (FM) and noncoherent detection (NCD) scheme, to suppress the nonlinear optical effects in dense wavelength division multiplexed (DWDM) optical communication. The FM transmitter comprises a directly modulated distributed feedback laser and [...] Read more.
We propose a simple and cost-effective method, using a direct frequency modulation (FM) and noncoherent detection (NCD) scheme, to suppress the nonlinear optical effects in dense wavelength division multiplexed (DWDM) optical communication. The FM transmitter comprises a directly modulated distributed feedback laser and a saturable semiconductor optical amplifier. In the NCD receiver, an optical slope filter as the FM to intensity modulation (IM) signal convertor is placed before a conventional photodetector. Because the FM signal has more evenly distributed optical power, bit-pattern-dependent nonlinear effects are consequently suppressed. After analyzing the nonlinear effects in the FM-NCD system and traditional IM direct detection (IM-DD) system, we found that the minimum achievable BER of the proposed FM-NCD scheme is 40 dB smaller. Moreover, a 2 Tbps (10 Gb/s × 200 channels) capacity was achieved by the FM-NCD system in 100 km DWDM passive optical networks (PONs), which is twice the capacity of the IM-DD system (10 Gb/s × 100 channels) under the same condition. These results indicate that WDM-PONs with the cost-effective FM-NCD scheme are strong candidates for future broad access networks and show great potential for the combination of optical access and metro networks for future generations of PONs. Full article
(This article belongs to the Special Issue Optical Fiber Transmission Systems)
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16 pages, 8377 KiB  
Article
Sixty-Nine-Element Voice Coil Deformable Mirror for Visible Light Communication
by Lv Jiang, Lifa Hu, Qili Hu, Xingyu Xu, Jingjing Wu, Lin Yu and Yang Huang
Photonics 2023, 10(3), 322; https://doi.org/10.3390/photonics10030322 - 17 Mar 2023
Cited by 1 | Viewed by 1236
Abstract
To overcome the atmospheric turbulence aberration, and improve the quality of light beam in visible light communication (VLC), a compact 69-element deformable mirror (DM) using micro voice coil actuators was designed based on systematic theoretical analysis. The structural parameters of the micro voice [...] Read more.
To overcome the atmospheric turbulence aberration, and improve the quality of light beam in visible light communication (VLC), a compact 69-element deformable mirror (DM) using micro voice coil actuators was designed based on systematic theoretical analysis. The structural parameters of the micro voice coil actuator were optimized by electromagnetic theory and the finite element method. The DM was optimized from the aspects of thermal deformation, response time, coupling coefficient, and other parameters. Finally, wavefront fitting and residual calculation were completed according to the influence function. The optimized voice coil deformable mirror (VCDM) has a large phase stroke, good thermal stability, a short response time of less than 0.7 ms, and a large first resonance of 2045 Hz. The fitting residuals of the VCDM for the first 10 Zernike modes with a PV value of 8 μm are all below 10 nm (RMS). Compared with a similar DM, the obtained results from our compact VCDM indicate that it has a higher wavefront fitting precision. VCDM corrected complex random aberrations in the VLC scenario and improved the coupling efficiency of the signal beam, proving that the compact VCDM with high performance and low cost has a good application prospect in VLC systems. Full article
(This article belongs to the Special Issue Visible Light Communications)
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14 pages, 4931 KiB  
Article
Optimization of Sampling Mode in Macro Fourier Ptychography Imaging Based on Energy Distribution
by Runbo Jiang, Dongfeng Shi and Yingjian Wang
Photonics 2023, 10(3), 321; https://doi.org/10.3390/photonics10030321 - 16 Mar 2023
Viewed by 1097
Abstract
Fourier ptychography imaging technology is a method developed in recent years to achieve high-resolution imaging. In the traditional macro Fourier ptychography technology, the scanning method when the camera captures low-resolution images mostly uses the rectangular linear grid format. These acquired images contain a [...] Read more.
Fourier ptychography imaging technology is a method developed in recent years to achieve high-resolution imaging. In the traditional macro Fourier ptychography technology, the scanning method when the camera captures low-resolution images mostly uses the rectangular linear grid format. These acquired images contain a small amount of complementary information, and a large number of low-resolution images are needed to achieve high-resolution imaging. Redundant measurements will extend the sampling and reconstruction time, and require more computing resources. In this paper, we propose to obtain the target image spectral energy distribution by pre-sampling. And according to the energy distribution, we use irregular and non-uniform sampling modes to restore the target image. With the same number of samples and same reconstruction time, higher resolution imaging can be achieved compared with traditional methods. Simulation and experimental studies are carried out in this paper, and the results confirm the effectiveness of the proposed methods. Compared with the traditional sampling mode, the two sampling modes proposed in this paper increase the resolution from 4.49 lp/mm to 5.66 lp/mm and 5.04 lp/mm respectively. Full article
(This article belongs to the Special Issue Advances and Applications in Computational Imaging)
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20 pages, 5969 KiB  
Article
Wavefront Sensing by a Common-Path Interferometer for Wavefront Correction in Phase and Amplitude by a Liquid Crystal Spatial Light Modulator Aiming the Exoplanet Direct Imaging
by Andrey Yudaev, Alexander Kiselev, Inna Shashkova, Alexander Tavrov, Alexander Lipatov and Oleg Korablev
Photonics 2023, 10(3), 320; https://doi.org/10.3390/photonics10030320 - 16 Mar 2023
Cited by 1 | Viewed by 1381
Abstract
We implemented the common-path achromatic interfero-coronagraph both for the wavefront sensing and the on-axis image component suppression, aiming for the stellar coronagraphy. A common-path achromatic interfero-coronagraph has its optical scheme based on a nulling rotational-shear interferometer. The angle of rotational shear can be [...] Read more.
We implemented the common-path achromatic interfero-coronagraph both for the wavefront sensing and the on-axis image component suppression, aiming for the stellar coronagraphy. A common-path achromatic interfero-coronagraph has its optical scheme based on a nulling rotational-shear interferometer. The angle of rotational shear can be chosen at a small angular extent of about 10 deg. Such a small angular shear maintains the coronagraphic contrast degradation known as the stellar leakage effect, caused by a finite stellar size. We study the phase and amplitude wavefront control by a liquid crystal spatial light modulator of reflection type which is used as the pixilated active adaptive optics unit. Therefore, adaptive optics perform a wavefront-correcting input toward a stellar interfero-coronagraph aiming at the direct exoplanet imaging. Presented here are both the numeric evaluations and the lab experiment stand to prove the declared functionality output. Full article
(This article belongs to the Special Issue Optical Systems for Astronomy)
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14 pages, 4464 KiB  
Article
Adaptive Weighted K-Nearest Neighbor Trilateration Algorithm for Visible Light Positioning
by Kaiyao Wang, Yi He, Xinpeng Huang and Zhiyong Hong
Photonics 2023, 10(3), 319; https://doi.org/10.3390/photonics10030319 - 16 Mar 2023
Viewed by 1486
Abstract
An adaptive weighted K-nearest neighbor (AWKNN) trilateration positioning algorithm fused with the channel state information (CSI) is proposed to optimize the accuracy of the visible light positioning. The core concept behind this algorithm is to combine the WKNN algorithm with ranging based on [...] Read more.
An adaptive weighted K-nearest neighbor (AWKNN) trilateration positioning algorithm fused with the channel state information (CSI) is proposed to optimize the accuracy of the visible light positioning. The core concept behind this algorithm is to combine the WKNN algorithm with ranging based on the CSI. The direct path distance estimated by the CSI is utilized to construct a position set consisting of multiple positions and a corresponding distance database containing multiple distance vectors. The error parameters of the weighted combinations of different distance vectors are calculated iteratively to evaluate the impact of different K-values and weights on the positioning accuracy. The proposed algorithm can achieve high-precision trilateration positioning by adaptively selecting the K-value and weight. A typical 4 m × 4 m × 3 m indoor multipath scene with four LEDs is established to simulate the positioning performance. The simulation results reveal that the mean error of the CSI-based AWKNN algorithm achieves 1.84 cm, with a root mean square error (RMSE) of 2.13 cm. Compared with the CSI-based least squares (LS) method, the CSI-based nonlinear LS method, and the CSI-based WKNN method, the average error of this method is decreased by 29%, 16%, and 17%, whereas the RMSE is reduced by 35%, 14%, and 19%. Full article
(This article belongs to the Special Issue Optical Wireless Communications and Applications)
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21 pages, 6631 KiB  
Article
Three-Dimensional Mapping Technology for Structural Deformation during Aircraft Assembly Process
by Yue Liu, Dongming Yan, Lijuan Li, Xuezhu Lin and Lili Guo
Photonics 2023, 10(3), 318; https://doi.org/10.3390/photonics10030318 - 16 Mar 2023
Cited by 3 | Viewed by 1200
Abstract
Owing to the assembly state changes during aircraft assembly processes, assembly force-deformation problem occurs. To obtain the structure shape in the product assembly process efficiently and accurately, a three-dimensional (3D) mapping technology for the structural deformation during the aircraft assembly process is proposed [...] Read more.
Owing to the assembly state changes during aircraft assembly processes, assembly force-deformation problem occurs. To obtain the structure shape in the product assembly process efficiently and accurately, a three-dimensional (3D) mapping technology for the structural deformation during the aircraft assembly process is proposed combined with a fiber Bragg grating (FBG) optical fiber sensor and binocular vision measurement system. First, this study established a curvature transformation model using optical fiber monitoring data, obtained the 3D spatial deformation of the product, and completed the unification of the optical fiber wavelength change and spatial 3D point coordinate heterogeneous data. Second, a mesh deformation optimization algorithm based on point-cloud optimization was established. Subsequently, the deformation effects of four mesh deformation models were compared to verify the feasibility and accuracy of HEC-Laplace, and the 3D mapping of the product structure shape in the assembly process was realized. Finally, a cantilever wing model was used to verify the deformation of different loading modes. The results show that the product structure changes can be accurately obtained through the proposed technology, thereby improving the accuracy control and overall assembly quality in the aircraft assembly process and providing a theoretical basis for intelligent aircraft assembly. Full article
(This article belongs to the Topic Manufacturing Metrology)
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18 pages, 15580 KiB  
Article
Plasmonic Metasurfaces for Superposition of Profile-Tunable Tightly Focused Vector Beams and Generation of the Structured Light
by Lianmeng Li, Xiangyu Zeng, Manna Gu, Yuqin Zhang, Rui Sun, Ziheng Zhang, Guosen Cui, Yuxiang Zhou, Chuanfu Cheng and Chunxiang Liu
Photonics 2023, 10(3), 317; https://doi.org/10.3390/photonics10030317 - 15 Mar 2023
Cited by 3 | Viewed by 1515
Abstract
Vector beams (VBs) and their superposition have found important applications in versatile fields such as optical communications, super-resolution microscopy and quantum information, and metasurfaces have enabled the miniaturization and integration of the optical systems manipulating the vector beams, providing potential applications to subwavelength [...] Read more.
Vector beams (VBs) and their superposition have found important applications in versatile fields such as optical communications, super-resolution microscopy and quantum information, and metasurfaces have enabled the miniaturization and integration of the optical systems manipulating the vector beams, providing potential applications to subwavelength regimes. In this work, we propose a metasurface to realize the superposition of profile-tunable tightly focused VBs, with the novel structured light fields generated. The metasurface is composed of two sets of orthogonal-nanoslit pairs arranged on the inner and outer rings. By realizing the chiral conversion of circularly polarized light with the slit-pairs which act as half-wave plates, and by creating helical phase profiles of optical vortices with the geometrical phase of rotational nano-slit pairs, two focused Bessel VBs are formed. By finely varying the diameters of two sets of rings, the doughnuts of the two Bessel VBs of different orders are tuned to be of the same size, and the superposition of the two VBs is realized. The theoretical analyses of the superimposed fields were presented, the FDTD simulations were performed to optimize the designed metasurfaces, and the experimental measurements were carried out to validate feasibility of the metasurface. The novel and interesting characteristics of the superposed fields different from those of the conventional VBs were demonstrated. This work will be of significance for classical and quantum applications of VBs in various fields. Full article
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