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In this paper, multiple tunable Fano resonances are firstly achieved in an end-coupled system composed of a rectangular cavity and an inverted U-shaped groove. Through increasing a coupling path, dual Fano resonances are tuned to four Fano peaks. High figure of merits (FOMs) and high refractive index sensitivities are obtained so that the proposed structure is preferred in the highly integrated optical sensing technology. Besides, a new Fano resonance with high performances occurs through cascading a horizontal rectangular cavity. Additionally, the phase shifts and the group delays are also investigated within the Fano resonant windows. These proposed structures are investigated and analyzed by 2D finite-difference time-domain (FDTD) method and multiple interference coupled mode theory (MICMT) method, respectively, and the results show enormous potential in highly integrated optical area.

In this paper we consider a cavity optomechanics consists of a two-level atom that interacts with a single-mode quantized field in the presence of a strong driving laser. By evaluating the effective Hamiltonian of the whole system which contains the field dissipation, we derive the time-dependent state vector of the system corresponding to particular initial conditions for the cavity field and oscillatory mirror. In the continuation, we pay our attention to the dynamical properties of the considered system by choosing different initial conditions for the atom. In particular, the effects of amplitude of the pump field, various initial atomic states and cavity loss rate on the entanglement, atomic population inversion and photon and phonon statistical properties are numerically analysed. According to the obtained results, maximal entanglement for all chosen initial states of the system is visible as time develops. Moreover, the presence of dissipative field leads to decrease the entanglement and finally tends to a fixed positive value, while the Mandel parameter as well as the population inversion reduce and tend to a fixed value in the negative region. Also, the appearance of non-classicality feature such as typical collapse–revival phenomenon in the (negative values of) Mandel parameter is noticeable.

Surface-enhanced Raman scattering (SERS) has been widely used to realize considerable enhancement of Raman scattering, while most SERS substrates enhance all the Raman signals in a relative wide spectral range. Selective enhancement of specific Raman shifts is also important in order to directly identify a target molecule from numerous background ones. In this paper, we design a SERS substrate with periodic silver nanoholes on silica spacer and silver film. The substrate possesses three resonance modes, which are excited by the localized surface plasmon resonance (LSPR) of nanoholes, the surface plasmon polariton (SPP) of period holes and the Fabry–Perot (FP) resonance between silver film mirror and nanoholes respectively. The interaction between those resonance modes results in higher Q factor, which will be applicable for selective Raman enhancement. With matching the three resonance modes to the exciting frequency and two selected Raman frequencies of R6G (Rhodamine 6G) respectively, experimental results show that the Raman signals with the triple resonance substrate at the matched frequencies can be enhanced ten times larger than the case of periodic silver nanoholes on silica substrate only with single resonance. At the same time, the matched two selected Raman signals can be enhanced about three times larger than the mismatched ones. Therefore, considering the two selectively enhanced Raman signals simultaneously can help to improve the molecule identification about one order of magnitude. This selective enhancement property provides a potential method to directly identify target molecule without spectral spectrophotometry system.

In this work, the up-conversion luminescence of Yb 3 + /Er 3 + doped Gd2O3 phosphors for optical temperature sensing in green and red regions are investigated. The intense green (522 and 562 nm) and red emissions (660 and 682 nm) radiated from Er 3 + /Yb 3 + tri-doped Gd2O3 phosphors are successfully realized via tuning the doping proportion of Er 3 + and Yb 3 + . To evaluate their potential ability of optical thermometry in green light range and the first biological window, the temperature-dependent green and red emissions are investigated. Based on the florescence intensity ratio (FIR) of 522 and 562 nm, the absolute sensing sensitivities of Gd2O3: 1 mol% Er 3 + /4 mol% Yb 3 + and Gd2O3: 1 mol% Er 3 + /6 mol% Yb 3 + phosphors reach 1.16 and 1.2% K−1 (523 K), respectively. In addition, the temperature sensing sensitivities based on the FIR of 660 and 682 nm reach 0.8 and 0.6% K−1 (300 K), respectively. Moreover, the changes of FIR ( Δ R) are smaller than 3% within the cycling heat and cool processes. These results reveal that Gd2O3:1mol%Er/4(6)mol%Yb phosphors are promising for FIR-based temperature sensing in high temperature via green emissions and room temperature via red emissions.

We experimentally demonstrate the performance of 16-ary orbital angular momentum shift keying (OAM-SK) decoders based on convolutional neural networks (CNNs) in an underwater optical wireless communication (UOWC) system. We verify the decoding accuracy of the OAM-SK system in a 1-m tank filled with flowing salty water. The oceanic turbulence is emulated by the random phase screen method by a spatial light modulator (SLM). The results show that the decoders are robust to short-distance water fluctuations induced by the water flow, with an accuracy of more than 99% in clean water. In turbid water, the decoders require input images with a greater number of pixels and can reach an accuracy of more than 99% with a pixel number of 64 × 64. The decoders are tolerant to weak turbulence, with accuracies greater than 96.78% and 99.75% for input pixel numbers of 32 × 32 and 64 × 64 in 20-m temperature-induced channels with an equivalent temperature structure parameter of C n 2 = 1 0 − 15 K 2 ⋅ m − 2 ∕ 3 . As the strength of the oceanic turbulence increases, the accuracy decreases to lower than 85.5%. In both turbid channels and turbulent channels, large OAM modes are more likely to be incorrectly recognized. Increasing the pixel number of the input images or decreasing the order of the coding format can improve the decoding accuracy under moderate-to-strong turbulence conditions. This work will be beneficial for the design of UOWC systems.

Traditional Fourier ptychographic microscopy (FPM) requires the acquisition of multiple images, which limits the acquisition speed and increases storage requirements. Here, we present a compressed sampling method for FPM (CSFPM), wherein we randomly switch on a certain number of the source LEDs each time to collect compressed data and use it to recover an FPM low-resolution image set. Subsequently, we utilize a general FPM recovery algorithm to reconstruct a high-resolution image. We conduct simulations and experiments to validate the CSFPM feasibility and acquisition efficiency. Our results demonstrate that CSFPM reduces the acquisition-data amount by 49.59% and acquisition-time by 84.63% relative to traditional FPM.

In this paper, we present a full description of the design and fabrication of a compact spot-size converter (SSC) applied to interferometric fiber optic gyroscopes (IFOGs). The obtained SSC has a length of 500 um and a coupling efficiency of 52%. The polarization dependency of the SSC is less than 0.1 dB, and the variation tendencies of our experimental results agree well with a simulation. The SSC possesses many properties suitable for various optical communication and sensing systems, including small size, high coupling efficiency, integration, and high stability.

In this work, the potential of Li 1 . 8 Na 0 . 2 TiO 3 : Mn 4 + for the lifetime-based luminescence thermometry is assessed. The material is prepared by the solid-state reaction of Li2CO3, Na2CO3, and nanostructured TiO2 at 800 °C, and its monoclinic structure (space group C2/c) is confirmed by X-ray diffraction analysis. In this host, Mn 4 + provides strong absorption around 330 nm and 500 nm due to 4A 2g → 4T 1g and 4A 2g → 4T 2g electric dipole forbidden and spin-allowed electron transitions, respectively, and emits around 679 nm on account of 2E g → 4A 2g spin forbidden electron transition. Temperature dependences of emission intensity and emission decay are measured over the 10–350 K range. Due to the low value of energy of 4T 2g level (20000 cm−1), the strong emission quenching starts at low-temperatures which favors the use of this material for the luminescence thermometry. It is demonstrated that the quite large value of relative sensitivity (2.27% K−1@330 K) facilitates temperature measurements with temperature resolution better than 0.15 K, and with the excellent repeatability.

Two experimental setups to generate multi-mode NOON states are proposed. The first setup is a universal model, which can create a d -mode N -photon NOON state with an arbitrary mode number d and photon number N in principle in a lossless system with perfect optical devices, using states with non-deterministic distributions of photons as the input sources and post-selection of total N photons for detection. The second approach, on the other hand, can generate a 4-mode 4-photon NOON state using single photon sources. The core unit of both setups is the Fock state filter, which is used to filter out an arbitrary Fock state component from an incident state using a beam splitter with proper transmissivity. The intrinsic generation efficiencies of the NOON states produced by both methods, with the first setup particularly focused on using squeezed vacuum states as the inputs, are calculated. They are found to be at least two orders of magnitude larger than and scale more favorably to the previously proposed approach using coherent state inputs. We also show that the second setup has the best performance for the case with d = N = 4 , while the first method scales better for a larger N or d . These results manifest that multi-mode NOON states with 3 or 4 modes and 4 or 6 photons could feasibly be generated in experiments with current photonic technologies.

A full duplex dense-wave-division-multiplexing radio-over-multicore fiber system based on the multiple frequency multiplication technique at 60 GHz between multiple micro Base Stations (BSs) with multiple-input multiple-output (MIMO) technique is proposed and demonstrated with simulation experiment. The generation and transmission of optical millimeter waves are analyzed theoretically. This study is an initial attempt to combine multi-core fiber and multiple V-band millimeter waves based on the multiple frequency multiplication for applying in the Radio-over-Fiber system. And the effective combination of heterogeneous 7-core optical fiber with ultra-low crosstalk and 28 micro BSs with 2 × 2 MIMO technology can be well adapted to the propose system for the dense micro BSs technology of the fifth-generation mobile communication (5G), which can realize multiple micro BSs to transmit different data simultaneously and satisfy the demand of huge bandwidth and high speed of the 5G.

A dual digital micromirror devices (DMDs) camera for high dynamic range imaging is presented. The dual DMDs camera consists of two DMDs, an objective imaging lens, and a reimaging lens, both of which were connected by a symmetric relay imaging lens whose responsibility is to correct the off-axis aberrations caused by the two tilted DMDs. The dual DMDs camera can meet a dynamic range of 216 dB in maximum when the gray level of imaging sensor (CMOS) is 12 bits, comparing with the single DMD camera whose dynamic range, on the same terms, is only 144 dB in maximum. In our final design, the aberration is well corrected and the modulation transfer function values across the entire field of the whole system are above 0.3 at 37 line pairs/mm.

To improve the grating ruling efficiency and success rate, this report documents a method to indirectly measure the error trajectory of space coordinates produced by ruling and indexing systems. The errors were corrected based on the proposed active control system. According to the residual errors after correction, a mathematical model of the full aperture grating diffraction wavefront with high frequency error information was reconstructed in real time. Based on this mathematical model, two gratings were ruled with or without the aid of an error correction system, respectively, and the reconstructed grating diffraction wavefront values were obtained to verify the effectiveness of this method. For larger gratings, the grating diffraction wavefront can also be reconstructed in real time with long time ruling. The experimental result demonstrated that the grating quality can be judged by monitoring the grating diffraction wavefront in real time.

An antireflective coating made by TiO2 nanocone array is designed on an ultrathin multilayer GaAs substrate (the thickness of GaAs is 300 nm). The intrinsic light trapping, carrier recombination and photoconversion are simulated by a complete photoelectric simulation. The results show that the optimized light trapping design can enhance the electromagnetic resonance in active layer and lead to an extraordinary enhancement of both absorption and power conversion capabilities in GaAs solar cell. The short-circuit current density increases by 51.12%, from 12.01 mA/cm2 to 18.15 mA/cm2 and power conversion efficiency increases by 52.83%, from 11.00% to 16.81% compared to the reference benchmark.

We demonstrate a highly-stable laser-based underwater radio frequency transfer with electronic phase compensation technique. A 100 MHz radio-frequency signal has been transferred over a 5-m underwater link with this frequency transfer scheme. To evaluate the quality of the transferred frequency signal, timing jitter power spectral, timing fluctuations and instabilities were all measured. The transferred frequency signal over 5-m underwater link with electronic phase compensation achieved 2.1 ps of root-mean-square (RMS) timing fluctuations, meanwhile, the relative fractional frequency instability is 5 × 1 0 − 13 at 1 s and 7 × 1 0 − 16 at 1000 s for phase-compensated link. The transmission link achieved higher stability than Cs and H-master clocks, which gives this proposed transfer scheme the potential of disseminating these atomic clocks signal over the underwater transmission link.

Adaptive orthogonal frequency division multiplexing (OFDM) systems are promising for high-bit-rate short-reach communication by optimizing the allocation of modulation format and power to each subcarrier. Because adaptive OFDM systems involve multiple modulation formats, automatic modulation format identification (AMFI) is significant for subsequent signal processing and symbol decision of OFDM receivers. In this work, we proposed and experimentally demonstrated a blind modulation format identification technique based on constellation diagrams achieved from channel estimation of OFDM system. In the proposed AMFI scheme, the identification feature is the number of signals’ constellation clusters. First, we use the peak-density clustering algorithm to track the centers of signals’ constellation clusters by plotting the density–distance graph, where the clusters’ centers have much larger density and distance values than that of the other clusters’ points. Then, we use the K nearest neighbor regression algorithm to automatically calculate the number of signals’ constellation clusters. Finally, we evaluated and measured the identification accuracies of QPSK, 8-QAM, 8-PSK, 16-QAM, 64-QAM and 128 QAM signals in simulation and experiment.

A three-dimensional plasmonic wavelength demultiplexer is investigated using slit- and stub-type filters consisting of metal–insulator–metal waveguides. To achieve a narrow bandwidth of the slit-type filter, a dielectric material is inserted into the slit section and the metal thickness is deliberately chosen to be 0 . 2 μ m . Then, a demultiplexer is considered with the two filters being placed in parallel. Numerical results show that a separation of 18.9 dB between the two output ports is obtained at 1 . 31 μ m , while it is only 9.8 dB at 1 . 55 μ m . To improve the separation, stub sections forming an attenuation pole are introduced into the waveguides. It is found that the separation is successfully improved to more than 20 dB at both wavelengths. All calculations are performed using the finite-difference time-domain method based on the trapezoidal recursive convolution technique.

A novel constellation shaped 11-QAM signaling scheme based on geometric shaping (GS) and probabilistic shaping (PS) is proposed in this paper. The 11-QAM signals are obtained by Huffman coding with an optimized 11-QAM constellation structure. Then the non-uniform 11-QAM signals are generated by bit-interleaved coded modulation (BICM), which can get a better performance of bit error ratio (BER) and approach the Shannon limit. An experiment of the proposed 11-QAM constellation is carried out to transmit data over 25-km standard single-mode fiber (SSMF) in the polarization division multiplexed coherent optical communication system. Results show that when the data rate reaches 33Gbps, the proposed GS/PS 11-QAM scheme respectively outperforms the traditional uniformly distributed star 8-QAM and the traditional PS 9-QAM by 2.9dB and 1.2dB in OSNR.

Traditionally, the 980 nm laser is used as the excitation source for Yb 3 + /Er 3 + codoped phosphors. Different from this conventional way, it is shown here that the as-prepared CaWO4:Yb 3 + /Er 3 + (5/1 mol %) phosphors can be effectively triggered by the commonly used and cheap 405 nm laser diode. On such excitation, the Er 3 + ion’s characteristic green emission, which is ascribed to the 2H 11∕2 ∕ 4 S 3∕2 -4I 15∕2 transitions, is successfully detected with a good signal to noise ratio. The green emission’s response to the temperature change is investigated in the 93–813 K range. It is confirmed that the 2H 11∕2 -4I 15∕2 and 4S 3∕2 -4I 15∕2 transitions obey the Boltzmann distribution well, which are thus suitable for optical ratiometric temperature measurement. Their maximum relative sensitivity is found to be 10.41% K−1 at 93 K.

The development of communication technologies has led to an ever-increasing demand for higher dimension and higher speed of optical coding technology. The orbital angular momentum (OAM) of vortex beams provides a new degree of freedom for optical coding in recent years. In this paper, we propose a novel high-dimensional vortex beam encoding/decoding scheme for high-speed free-space communication. An off-axis 4f-configuration with a digital micromirror device (DMD) and a MIP-based pattern formation algorithm are employed to generate fast switchable, accurate vortex beams (arrays) that can be used for encoding. Interference is introduced to efficiently decode data information. We experimentally demonstrate a high-quality communication link based on 64-ary vortex beam encoding/decoding and zero bit error rate is observed, which shows the validity of the proposed high-dimensional scheme. Owing to enhancement of encoding dimension and employment of high-speed DMDs, the proposed scheme enjoys a higher transfer rate exceeding other communication technologies. What is more, the data transfer rate can be further improved by introducing vortex arrays, which is demonstrated by the rapid transmission of a 24-bit true color bitmap.

A theoretical study is carried out for investigating the first- and third-order susceptibilities in a four-level Y-type atomic system. In this work, we present the wavelength mismatching effect on linear and nonlinear susceptibilities by considering three different wavelength regimes, i.e., near matching, partial mismatching and complete mismatching of wavelengths. Thereafter, in the case of near matching regime, the two upper excited states are coupled by a microwave field that makes a closed-loop of transitions. Therefore, a relative phase factor among fields becomes responsible for significant modification of susceptibilities of atomic medium. An enhanced Kerr nonlinearity with smaller linear absorption is obtained under specific parametric conditions. We attribute the enhanced Kerr nonlinearity to the quantum interference between the transition pathways.

We experimentally demonstrate an optical transmitter with embedded Auxiliary Management and Control Channel (AMCC) and in-service Optical Time Domain Reflectometer (OTDR) for Long Term Evolution-Advanced (LTE-A) data transmission in mobile fronthaul section of radio access networks. The concept is tested on a direct modulation analog radio over fiber system. The OTDR and AMCC signals are time-multiplexed without interfering with each other or affecting data transmission. The coexistence of the three functionalities is achieved through proper modulation index distribution across the AMCC/OTDR and LTE-A data signals.

Quantum communication via seawater channels has attracted much attention. Here, we present the design and implementation of a prototype for space-to-underwater quantum key distribution (QKD). The influence of the fluctuating atmosphere–seawater interface is theoretically analyzed. The setup consists of a specially designed optical source working in the blue–green band and a receiving optical antenna with large field-of-view (FOV). To achieve a larger FOV, photomultipliers with 25 mm active area are adopted to measure the single photon signals. The proof-of-principle experiment of QKD was implemented in the laboratory with near-coast seawater to verify the performance of the devices. This study provides a first step towards space-to-underwater quantum communication.

We propose a novel scheme to generate THz signal based on cascaded phase modulator and I/Q modulator. We experimentally demonstrate 392-GHz THz vector signal generation based on this scheme. Our scheme has these advantages such as dispersion-immunity, good flexibility in frequency and modulation. In our experiment, we realized the THz fiber-wireless link at 392-GHz transmitting 18.4-Gbaud QPSK signal or 4-Gbaud 16QAM signal with BER less than 2.0 × 10−2, the third generation FEC threshold.

Based on the digital bipolar serrodyne and sine phase modulations, a closed-loop RFOG with two LiNbO3 phase modulators is proposed and studied. Through theoretical simulation, the bipolar serrodyne waveform is optimized to improve the detection sensitivity. By the characteristic analysis of the practical serrodyne phase modulation spectrum, the sine modulation frequency is optimized to reduce the two loops’ spectrum overlapping, which would lead to the backscatter noise. The optimization result is verified by the gyro output signal tests under the different sine phase modulation frequencies. It is concluded that in order to avoid the spectrum overlapping, the difference between the sine modulation frequency and serrodyne modulation reset frequency should be properly increased, and the sine modulation frequency is required to be close to an even multiple of the serrodyne modulation repetition frequency. Finally, using the optimized phase modulation parameters, the gyro output signal is tested with an integration time of 0.1 s over 1 h, and the bias stability around 7.1 deg/h based on the Allan deviation analysis is obtained.

A high-sensitivity magnetic field sensor based on dual-core photonic crystal fiber (PCF) is proposed and demonstrated. Two microholes are introduced into the two fiber cores which form two defect cores and the two microholes are assumed to be filled with nano-magnetic fluid. The transmission characteristics of the dual-core PCF are analyzed by finite element method (FEM). The transmission principle of light beam in the fiber cores is proposed and the feasibility of light beam transmission in the defect cores is demonstrated. We analyze the influences of the microhole diameter and magnetic field on the refractive index, effective mode area, birefringence and coupling length of the fiber modes. The influences of the structural parameters and fiber length on the sensitivity are also studied. The sensitivity increases firstly and then decreases with the increasing microhole diameter. And the sensitivity increases with the increasing fiber length. The resonance wavelength red shifts with the increasing magnetic field under the certain structural parameters and fiber length. The fringe spacing between adjacent magnetic fields becomes narrower as the magnetic field increases, in other words, the sensitivity decreases. The highest sensitivity is 948 pm/Oe at the magnetic field 50 Oe.

The Cherenkov radiation induced by megavolt X-ray beams of a medical linear accelerator is highly intense in blue and ultraviolet lights. This poses a challenge for in vivo imaging, which favors longer wavelengths. However, using quantum dots with a large Stokes shift, we converted the Cherenkov photons to fluorescent photons in the second near-infrared (NIR-II) window. A system was designed to provide shielding for the NIR-II camera, and high quality NIR-II CELI signal was acquired. The NIR-II CELI of X-ray beams was shown at various depths, and the condition to trigger it was also studied. Animal experiments showed this technique could visualize the delivery of X-ray radiation in mice qualitatively. We concluded that CELI induced by megavolt X-ray beams in the NIR-II window possesses a great potential as a quality control tool in radiotherapy.

A four-state modulation scheme is proposed to improve the stability performance of a dual-polarization fiber optic gyroscope (IFOG) operating under an open-loop configuration, overcoming the dead-zone issue that occurs in a closed-loop configuration and achieving a better signal-to-noise ratio (SNR) than conventional sinusoidal modulation. We prove theoretically and demonstrate experimentally that owing to the cross-coupling between the two orthogonal light polarizations co-existing in the dual-polarization IFOG, the rotation rate is not rigorously solvable under square-wave modulation. Instead, four-state modulation accurately extracts the rotation rate, even when the cross-coupling strength varies in time. An improved angular random walk (ARW) of 2 . 2 × 1 0 − 4 ∘ ∕ h and bias instability (BI) of 3 . 5 × 1 0 − 4 ∘ ∕ h were achieved in detecting the rotation rate of the Earth, verifying the effectiveness of the proposed method.

A novel nonlinear optical switch based on a single mode fiber – graded index multimode fiber (GIMF) – single mode fiber (SMS) twined into polarization controller (PC) was proposed as a saturable absorber (SA), to generate ultrashort pulse in fiber laser. The SA device geometry, where a sandwiched GIMF section spliced to two standard SMF at both ends of GIMF, was coiled into a PC. By properly tuning the paddles of PC, mode-locking can be easily realized and the nonlinear saturable absorption characteristics of SMS-SA was changed. In the experiment, the modulation depth of the SMS-SA containing 0.6 m GIMF can be observed 9%, 10.5%, 21.7%, respectively. Based on SMS-SA mode-locking, the stable ultrafast pulse duration of 559 fs, with the FWHM bandwidth of 6.84 nm were generated. The fundamental repetition rate of 25 MHz and wavelength-tuning range of 14 nm can be obtained by adjusting the paddles. The SMS-SA excellent tunable nonlinear optical properties and all-fiber structure have strong potential application in the field of ultrafast photonics.

We propose a bilayer structure made of two twisted hexagonal boron nitride (hBN) slabs for realizing tunable chirality in this work. Our numerical results show that a maximum circular dichroism as high as 0.84 can be achieved with the bilayer structure. The chiral response of the proposed structure comes from the combined effects of polarization conversion of circularly polarized wave with the top slab and selective transmission of linearly polarized wave with the bottom slab. Besides, the chirality can be actively controlled by adjusting the optic axis orientation of the top hBN slab. Finally, the bilayer structure is possible to be built with other suitable materials, metamaterials and microstructures for functioning chiral response in different wavebands. Therefore, the results in this work may provide some important hints for the design of novel chiral response sensors for optical, chemical and biological sensing.

The water-flow like behavior of liquid metals at room temperature has always been fascinating with enabling novel applications towards portable and flexible devices. Many liquid metal alloys based studies have been done but fundamental liquid metals are not much studied due to their tendency towards toxicity/oxidation during applications. In the present study, Mie theory based theoretical model simulated Gallium (Ga) and Cesium (Cs) liquid metals with their core–shell nanospheres coated with Silver (Ag) of different size spectra are used to investigate their localized surface plasmon resonance (LSPR) wavelength and sensitivity of the peak position to the particle size and shell thickness. We assess that the optical properties (absorption and scattering efficiencies) of liquid metal nanoparticles (NPs) (Ga and Cs) coated with noble metal (Ag) can be effectively tuned with controlled size of core and shell layers. The resonance peaks are found in UV–Visible–NIR region for bare NPs and UV–Visible region for core–shell NPs. It is observed that the absorption efficiency increases with increasing the core size as well as shell thickness. These results can be used in the application of UV plasmonics for biosensor devices, solar cells, reformable plasmonic devices, therapeutic agents and certain light absorption/scattering based applications.

All dielectric grating absorbers due to the high potential of providing reliable applications in modern devices and technology are being investigated. Periodic structures based on high-index all dielectric materials are particularly attractive due to the low ohmic loss. In this work, we have proposed and investigated all dielectric grating absorbers by an analytical model. Firstly, we have compared the results of the proposed analytical method with the existent experimental outcomes. Secondly, using the impedance matching concept we have proposed another structure of a hemisphere shape and compared the results of the proposed method with those of the full-wave simulations. With this novel structure, we have achieved high absorptance of approximately 100% and high-quality factor (Q=14.23). Additionally, our proposed method reduces the calculation time and needs less memory compared to the full-wave simulations. The results of the analytical method have an acceptable agreement with the experimental data and those of the full-wave simulations.

In order to design a five-port grating with good uniformity, a single-groove reflective beam splitter with an incident wavelength of 1550 nm is designed. The incident structure is under normal incidence. We get better optimized parameters by rigorous coupled waves. The five diffraction order efficiencies of the grating are each close to 20%. The optimized data shows that grating structure has high efficiency and high tolerance, which will have good application value in the field of beam splitter. Furthermore, by investigating the coupling overlap integration and field distribution, the mechanism can be well explained for such a grating.

A real-time visible light communication (VLC) system is proposed and experimentally demonstrated for simultaneous high-speed wireless communication and positioning beacon transmission realization. Through proposed 2 amplitude shift keying-constant envelope-orthogonal frequency division multiplexing (2ASK-CE-OFDM) coding, the transmitter can integrate 2ASK positioning beacon signal onto the envelope of CE-OFDM communication signal. The communication and positioning signals can be demodulated at the receiver, respectively. The mathematical derivations of 2ASK-CE-OFDM and implementation details of the field programmable gate array (FPGA) based real-time VLC system are introduced in this paper. The real-time VLC system transmission performance is verified with different light radial distances. Compared with directly modulating the 2ASK signal onto the envelope of OFDM, our proposed system has a better performance in terms of the light radial distance . The experimental result shows that the bit error rates (BERs) of 2ASK based positioning beacon and CE-OFDM based communication signal transmission are 4.3 × 10−7 and 6.8 × 10−4 when the wireless radial distance is 3.5 m.

The dual-channel phase-shifting interferometry (DC-PSI) has been focused widely in the dynamic measurement field because of its outstanding advantages. The interferograms matching between two channels is a key factor to the high precision phase retrieval. Suffered from the relative poses of different channel cameras in six-degree of freedom (S-DOF), the interferograms matching between two channels, including translation, rotation and scaling, is always a difficult problem in the DC-PSI. Aiming at the only translation mismatching is here considered and the iterations are needed to get the translation parameters in the translation method, a simplified matching method based on the transformation matrix is proposed, minding all kinds of interferograms mismatching. In the proposed method, only one shot to the calibration plate is needed to obtain the adjustment parameters and the interferograms is matched quickly and precisely. Both the simulation and experimental results demonstrate that the proposed method can improve the phase retrieval accuracy and interferograms matching efficiency.

In this paper, a V-shape photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR) effect is proposed. With the full vector finite element method, the V-shape photonic crystal fiber polarization filter is designed, and the coupling characteristics between the core mode and surface plasmon polariton mode are analyzed. The simulation results show that the fiber parameters have significant effects on the shift and strength of the SPR wavelength. Moreover, the losses of the core modes along the Y and X polarization directions are 68904 dB/m and 858 dB/m at the SPR wavelength of 1550 nm, respectively. Finally, the extinction ratio and error-tolerant rate of extinction ratio are also analyzed. The proposed V-shape PCF polarization filter can achieve good filtering effect in the communication band and is easy to integrate with existing optical fiber communication and sensing systems.

Obtaining the analytical expression of focusing off-axis hollow vortex Gaussian (HVG) beams by solving the (2 + 1) dimensionless linear Schrodinger-like equation, we perform the propagation path, the intensity and phase distributions, the center of mass, the peak intensity and the beam width with different potential widths α , different hollow orders n , different topological charges m , different off-axis coordinates ( X 0 , Y 0 ). In general, the off-axis HVG beams are swirled counterclockwise and periodically focus during the propagation. The topological charge m separates the focusing center but the hollow order n concentrates the focusing area. Moreover, the off-axis coordinate ( X 0 , Y 0 ) significantly increases the focusing intensity and the potential width α can also increase the focusing frequency during the propagation. Interestingly, the influences of the hollow order n , the topological charge m and off-axis coordinate ( X 0 , Y 0 ) are the same on the peak intensity, which are different with the beam width. Furthermore, we also discuss the Poynting vector, angular momentum and radiation forces. In terms of the radiation forces, we can easily explore the position trapping particles stably regardless of the off-axis coordinate ( X 0 , Y 0 ) selection.

In this paper, to increase the data rate of free-space optical (FSO) links, we consider multiple parallel FSO links arranged over a specified space (transceivers arranged over two rings with specified radius). Due to its ease of implementation, stability, and low cost, intensity modulation with direct detection (IM/DD) based on On–Off-Keying (OOK) is widely employed in practical terrestrial FSO links. For long-haul FSO links, avalanche photo diodes (APDs) are commonly used, which provide an internal gain in photo-detection, allowing larger transmission ranges, as compared with PIN photo-detector counterparts. Over the considered general case, firstly, we propose maximum likelihood (ML)-based detection methods when the receivers are aware of the instantaneous channel fading coefficients (CSI). Secondly, we propose an efficient OOK data detection method for a more practical case when the instantaneous CSI is not available at the receiver. For this state, initially, the channel coefficients are estimated by employing some pilot symbols and then, we use the channel estimated coefficients to detect OOK signals. For a specified space, due to crosstalk between parallel channels and pointing errors, performance of proposed data detection methods depends on the optimum value for beam waist. By providing Monte-Carlo simulation results, the optimum value of beam waist is obtained for various channel conditions. To evaluate the BER performance, we also provide analytical results and derive an analytical expression for the considered MIMO multiplexing scheme. The validity of our analytical results are confirmed by Monte-Carlo simulations.

A new parameterized anomalous diffraction theory (PADT) is proposed, in which the effects of reflection and refraction are included to calculate the orientation-averaged absorption efficiency of arbitrarily shaped particles accurately. Using the PADT, integral transform technique, data mapping approach, and Gaver–Stehfest inversion method, the discretely real summation formula for retrieval of the particle size distribution (PSD) based on absorption data is developed. The spectral representations of moments of PSD are also presented. The retrieval experiments show that the truncation number has a significant impact on the accuracy of PSD inversion, and the relative error reaches the its minimum at the critical truncation number. Compared with the double precision algorithm, the extended precision algorithm can produce more accurate and reliable results at the cost of high CPU time. In addition, the relative error increases with the increase of noise level, but it will be significantly reduced when a smoothing technique is applied.

A dual sub-pulse train 1064 nm picosecond radially polarized beam pump KGW single-pass Raman generator was designed. The Stokes lines of both the 768 cm−1 and 901 cm−1 vibrational modes of the KGW Raman-active crystal were excited simultaneously. The Raman generator radiated up to seven Stokes lines in the infrared spectrum, which covered multiple optical communication channels. The overall Stokes average power reached 1.01 W, and the maximum Raman overall conversion efficiency was 23.1%. The interaction between the optical field and the Raman crystal was discussed from two perspectives of line width compression and beam quality.