The microstructures on flexible membrane substrate prepared by the traditional methods may introduce large morphology and position errors, making it hard to achieve clear imaging. In this paper, we present a high precision fabrication method composed of two steps: unstressed fixation of the polyimide membrane and high precision fabrication of diffractive microstructures on the flexible membrane substrate

A dual-channel phase-tunable down converter with local oscillator (LO) frequency doubling is proposed by using a commercial dual-polarization dual-drive Mach-Zehnder modulator (DP-DMZM) and a specially designed dual-channel phase modulator (DP-PM). A radio frequency (RF) signal is injected to one of sub-DMZMs in the DP-DMZM, and a LO signal modulates another sub-DPMZM. An optical bandpass filter (OBPF)

We design and integrate four optical phased arrays (OPAs) in a single chip. Each OPA possesses different output grating period. Furthermore, we use optical switches to select one or more OPAs for beam scanning. We demonstrate the longitudinal scanning by tuning the laser wavelength. The experimental results show that the scanning range of the four-lines chip reaches 28.54° when the wavelength ranges

We propose and demonstrate a rectangular optical lattice filter with reconfigurable bandwidth and wavelength. The proposed reconfigurable rectangular lattice filter consists of three-stage cascaded ring-assisted Mach-Zehnder interferometers (RAMZIs), and each RAMZI unit serves as an approximate optical elliptical filter with optimized shape factor. The scheme and design principle are presented with

A single-pixel imaging (SPI) system is often applied to a specific scenario. The target object images may belong to a specific category and have some common features. Fourier or Hadamard illumination patterns can be sub-optimal since they are fixed and non-adaptive. We propose a novel scheme for designing and optimizing the illumination patterns adaptively from an image dictionary by extracting the

Optical multipath RF self-interference cancellation (SIC) based on phase modulation for full-duplex communication is proposed and demonstrated experimentally. Phase modulation is utilized to convert the RF signal into optical domain, in which the time delay tuning, amplitude tuning and phase inversion for multipath RF SIC are completed. The comprehensive theoretical model of the optical multipath RF

In this paper, a tunable graphene-based band-stop filter in the mid-infrared region was demonstrated, which consists of periodic structure based on bilayer graphene nanoribbons. Due to the unique tunable Fermi level of graphene, the resonance wavelength of the filter can be tuned over a wide range (10020 nm–15100 nm) with the applied voltage varying from 1 V to 5 V, realizing selectivity and tunability

In this paper, the pre- and post-nonlinear compensation (NLC) methods based on regular perturbation (RP) theory are contrastively investigated with the original NLC as a bridge for analyses. Firstly, the numerical error functions of pre-NLC and original NLC are derived, revealing that the numerical error of pre-NLC is more severe due to the error accumulation. Secondly, we deduce the relevance of post-NLC

VLC-WIFI heterogeneous networks have become a promising solution, where VLC and WIFI are collaborating on providing services for indoor users. The dense deployment of visible light communication multiple access points (APs) can expand the system capacity, but it leads to complicated inter-cell interference (ICI). In order to arrange users to access the appropriate AP and implement interference management

The transparent window in optical fiber at 2-μm waveband enables a huge potential for fiber optical communications. Intensive efforts have been devoted to pursuit of photonic devices in this new band. The arrayed waveguide grating (AWG) is one of the key components for various functionalities like wavelength multiplexer, optical filter, spectrometer and so forth. However, the integrated and wavelength

Multipath reflection degrades the performance of visible light communications (VLC) based localization systems, where it is often considered as a strong random noise. However, due to the inherent transmission features of light, the optical wireless indoor channel is static; therefore, multipath components can be modeled as deterministic functions of the transceiver location, furnishings, and room geometry

This paper proposes an enhancement of semiconductor optical amplifier (SOA)-based scintillation mitigation by polarization shift on-off keying (PS-OOK) transmission in free-space optical (FSO) communication. The scintillation effect is a critical issue in a vertical FSO link. The issue of the extinction ratio (ER) degradation of the received OOK signal caused by the high dynamic gain frequency of the

Imaging photoplethysmography (IPPG) enables contactless physiological parameters monitoring using a regular video camera, which led to an increasing interest in video health monitoring. However, classical IPPG is unable to accurately measure heart rate over a long-distance motion. In this paper, an IPPG heart rate detection framework is proposed based on an adaptive-zoom system called adaptive-zoom

We present aperiodic multilayer structures with ultrabroadband near-perfect absorption in the visible and near-infrared wavelength range. We use a hybrid optimization algorithm coupled with the transfer-matrix method, to optimize both the material composition and the layer thicknesses of the aperiodic multilayer structures that are composed of infinite slabs of material above a semi-infinite substrate

The eigenmodes of an inverse-parabolic graded index fiber under torsion were investigated by using the finite element method simulation. These eigenstates correspond to orbital angular momentum modes except for the two polarized-vortex modes. The design of appropriate core parameters can lead to the difference in the effective refractive indexes between all adjacent modes being greater than 10 −4 over

A near-infrared (NIR) supercontinuum and ultrashort pulses are generated via phase-mismatched cascaded frequency conversion in DSTMS (4-N, N-dimethylamino-4’-N’-methyl-stilbazolium 2, 4, 6-trimethylbenzenesulfonate) crystal. NIR pulses with a central wavelength of 1.5 μm and 63 fs pulse duration are incident into the crystal, and the spectrum is broadened to over 1200–2100 nm. Compensating the dispersion

In this paper, we proposed a two ports coherent perfect absorber based on antisymmetric metasurface with gain material which is able to effectively regulate the absorption of the coherent incident wave under the condition of unequal incident intensities. This design overcomes the limitation that exists in the previous coherent controller which can only be applied to coherent light of equal intensity

Phase-matched wavelength conversion is achieved in difference frequency generation (DFG) in a structure of gallium arsenide (GaAs) with periodic arrays of nanoholes. Linear properties (refractive indices) of the structure are determined from the S -parameters of the structure. Finite difference time domain (FDTD) simulation is used to calculate the S -parameters. The longest wavelength achieved is

Inspired by the empirical mode decomposition (EMD)-enhanced gas detection work, this paper develops a further improved signal reconstruction method (namely EWT-ASG) for the demodulated harmonics of tunable diode laser absorption spectroscopy (TDLAS), which is mainly based on empirical wavelet transform (EWT) and Savitzky-Golay (S-G) filtering. First, the imported EWT performs better on the decomposition

A novel nanocavity-based polymer-on-insulator (POI) electro-optic modulator (EOM) is proposed. It consists of a polymeric photonic-crystal nanobeam cavity (PCNC) with ultra-low index-contrast ( n$_{\text{cavity}}$/n$_{bg}$ = 1.17). Based on three-dimensional (3D) finite-difference time-domain (FDTD) method, the PCNC design and optimization are investigated theoretically. A high quality-factor ( Q )

An efficient intracavity-frequency-doubled singly resonant optical parametric oscillator (SR-OPO), pumped by a high-maturity 532 nm laser, tunable in the yellow wavelength region is demonstrated. An elaborate V-shaped idler cavity design is employed for a potassium titanyl phosphate (KTP) OPO nonlinear crystal to achieve a 5.06 W idler output at 1151.2 nm at a 10 kHz pulse repetition frequency. Using

In this letter, we report the demonstration of terawatt (TW)-scale femtosecond vortex laser pulses based on noncollinear optical parametric chirped-pulse amplification (OPCPA) centered at 800 nm. To the best of our knowledge, this is the first experimental study of amplification for OPCPA-based vortex pulses to achieve a powerful ultrafast (TW-scale) vortex pulse output. In this experiment, a 0.5-mJ

An all-polarization maintaining mode-locked Yb-doped fiber integrated laser with a nonlinear amplifying loop Mirror (NALM) under the operation regime of dissipative soliton resonance (DSR) has been demonstrated. The mode-locked laser can generate DSR pulses at 1.04 μm at the repetition rate of 2.59 MHz. The output DSR pulses can be tuned in pulse width from hundreds of picoseconds to a few nanoseconds

Intense light-matter interaction is critical for enabling high-sensitivity refractive index sensors, high-efficiency light sources, and high-performance nonlinear devices. A bowtie-hole photonic crystal micro-ring resonator is proposed and numerically demonstrated to enhance the light-matter interaction effectively through achieving strong spatial and temporal light confinement, simultaneously. Through

Single photon avalanche diodes (SPAD) based on avalanche effect have been widely used in the detection of extremely weak light signals. Conventional SPAD devices manufactured with silicon-based CMOS technology have a high dark count rate (DCR), making it difficult to accurately detect single photon signals. This paper proposes a low dark count rate ring-gate SPAD (RG-SPAD) to solve above problems,

Integral imaging three-dimensional (3D) display provides quasi-continuous viewpoints within a certain viewing angle. A single human eye can obtain several parallax images corresponding to the viewpoints. In this paper, we studied the effect of viewpoints received by a single human eye on the accommodation response when viewing the 3D image reconstructed by integral imaging 3D display. We analyzed the

In this paper, a dual-view integral imaging system is proposed to present two different 3D images for viewers in different viewing zones. For most of the conventional dual-view integral imaging systems, either the viewing angle or the spatial resolution of 3D image is decreased. In the proposed dual-view system, the viewing angle of each viewing zone is enlarged by introducing a switchable mask. Meanwhile

We demonstrate a four-lane wavelength division multiplexing (WDM) intensity modulation and direct detection (IM/DD) system at O-band. The 3-dB bandwidth of directly modulated lasers (DMLs) in this experiment is only 15 GHz. To support 100-Gbit/s/lane PAM-4 transmission in each lane, digital pre-equalization and advanced receiver-side DSPs are adopted to compensate for bandwidth limitation. Moreover

The objective of this paper is to present a microwave photonic system that can measure the angle of arrival (AOA) of multiple microwave signals with improved measurement accuracy. It is based on a photonic mixer approach to down convert the incoming microwave signals into IF signals, which enables a low-frequency electrical spectrum analyser to be used for measuring the power of the IF signals to determine

We put forward and demonstrate a angle-of-arrival (AOA) based visible-light-positioning (VLP) system using quadrant-solar-cell (QSC) and third-order ridge regression machine learning (RRML) to improve the positioning accuracy.

High sampling-rate digital-to-analog converters (DAC) are usually applied in optical fiber communication systems for the signal generation with advanced modulation formats such as four-level pulse amplitude modulation (PAM4). There exist various imperfections for high sampling-rate DACs. Clock tone leakage (CTL) is one of the imperfections and may seriously degrade the bit error rate (BER) performance

A simplified and cost-effective architecture is proposed and experimentally demonstrated with a millimeter wave (MMW) signal over fiber and free-space wireless transmission. The distributed feedback (DFB) laser is operated in optimized settings after measuring its characteristics and thus the 6 Gbps 64–quadrature amplitude modulation (64-QAM) signal can be successfully transmitted after 20- and 50-km

Filter bank multi-carrier (FBMC) using offset quadrature amplitude modulation (OQAM) has recently attracted increasing interests for the next-generation high-speed optical transmission systems, due to the salient FBMC modulation advantages in terms of high spectrum efficiency by completely removing the cyclic prefix. However, high peak-to-average power ratio (PAPR) still plays a key role of constraining

We present a polymer thermo-optic mode switch based on the structure of two vertical Mach-Zehnder interferometers (MZIs). It can achieve a rapid switch between ${E_{00}}$ , ${E_{01}}$ , ${E_{10}}$ and ${E_{11}}$ with the different heaters turning on. In our simulation, we compare two structures (the metal top electrode and the graphene electrode). The Finite element method (FEM) is used to simulate

Gallium Nitride (GaN) based light-emitting diodes (LEDs) suffer from the persistent issue of high resistivity of the p-type layer, due to inefficient dopant activation at room temperature. Here, a novel Electrostatic Field Effect LED (EFELED) is demonstrated to solve this issue by introducing significantly more holes into the LED active region for the first time. An increase in drive current is observed

Seismic-physical-model imaging (SPM), a successful strategy for the research in seismic wave propagation and wave theoretical predictions, effectively bridges the computation modeling and the field exploration and leads to a nearly ideal setting without a rock matrix. However, the current strategy for SPM imaging, the ultrasonic imaging technology, shows a narrow excitation frequency and a low coupling

Electromagnetic waves carrying orbital angular momentum (OAM) have motivated a wealth of applications. Achromatic or broadband OAM beams are preferred in many applications and have been extensively explored in previous research endeavors. In view of the low efficiency of the previous reported broadband OAM generators, this work proposes a metasurface composed of high-refractive-index dielectric resonators

We propose a transceiver design method based on an autoencoder (AE) network for multi-color visible light communication (VLC) systems. Taking into account the chromaticity constraint described by MacAdam ellipses and the peak-value constraint of transmitted signals, the proposed AE network utilizes a peak-value constraint layer and an integrated loss function which different from previous AE designs

This paper proposes a novel approach to provide a privately secured multiple-input and multiple-output visible light communication (VLC) in the mobility conditions. In the proposed system, a private secured VLC link is adaptively allocated to a mobile user all the time thanks to the movement tracking assistance by a camera-based detection system. The generation of the dynamic location-based scrambling

Iterative Fourier transform algorithm (IFTA) has been widely applied to achieve holograms in diffractive optical elements, however it is insufficient for designing holograms uploaded on liquid crystal on silicon (LCOS) to steer multi-beams in a wavelength selective switch (WSS). In this paper, a three-step hybrid algorithm including IFTA, Symmetrical IFTA with both phase and amplitude freedoms (SIFTA-2)

This paper reports an intracavity terahertz parametric source based on the stimulated polariton scattering in RbTiOPO 4 crystal with a high repetition rate and a high average power. The side pumping for the gain medium by laser diodes is adopted to get a higher fundamental power and a larger fundamental laser beam size than those in the diode-end-pumping in order to improve the THz output power. A

We present a novel concept for the stabilization of the carrier-envelope offset (CEO) frequency of femtosecond pulse trains from thin-disk laser oscillators by exploiting gain depletion modulation in the active gain region. We shine a small fraction of the laser output power back onto the thin disk allowing the population inversion in the gain medium to be controlled. We employ this technique in our

Agile mode switching between LP 01 and LP 11 modes in an all-fiber laser is demonstrated by exploiting an acoustically induced fiber grating within the laser cavity. The laser exploits a cladding pump configuration and can deliver up to 5.85 W of stable output power in LP 11 mode at 1070.07 nm and 6.06 W in LP 01 mode at 1070.48 nm, with a slope efficiency near 50%. Complete mode-switching speed with

An ultrafine frequency linearly tunable single-frequency fiber laser based on the intracavity active tuning is demonstrated. Single-frequency operation can be achieved by an ultrashort cavity and ultranarrow polarization-maintaining fiber Bragg grating. A sub-nanometer-accuracy piezoelectric ceramic actuator with closed-loop mode has been employed to realize the cavity-length active tuning scheme,

In this paper, a passively mode-locked Tm-doped fiber laser by employing lead sulfide (PbS) nanoparticles as the saturable absorber (SA) is successfully demonstrated in the 2 μm region for the first time, to the best of our knowledge. Measured by a home-made balanced twin-detector setup at 2 μm, the PbS SA was characterized by the modulation depth of 10.69%, the non-saturable loss of 74.27%, and the

Here we report on the exfoliation of graphene by using femtosecond pulsed laser with the highly oriented pyrolytic graphite (HOPG) immersed in water. The size of the graphene flakes was demonstrated to be well regulated by controlling the peak-power density of the femtosecond laser irradiation on the HOPG. The transmission electron microscopy (TEM) and Raman spectroscopy were used to identify the morphology

A high power Ho:YAP laser in-band pumped by a home-constructed Tm doped all fiber master oscillator power amplifier (MOPA) is reported. The optically polished and uncoated Ho:YAP laser yielded over 107 W of output power at ~2117.1 nm with 215.4 W of absorbed pump power, corresponding to a slope efficiency of 50.6% with respect to the absorbed pump power. The beam quality M 2 parameter was measured

The experiment reports a kind of L-band dissipative soliton resonance (DSR) nanosecond Er-doped fiber laser. The passive mode-locked L-band DSR pulse is achieved in a figure-eight structure by using the nonlinear-amplifying-loop-mirror (NALM). The repetition rate of pulse is 468 kHz. At the maximum pump power of 398 mW, the output power is 25 mW with a pulse energy of 45 nJ. By adjustment of polarization

Recent research on nonlinear multimode interference (NL-MMI) based mode-locking method provides a new approach for ultrafast all-fiber lasers. Here, we report on the polarization dynamics of group velocity locked vector solitons (GVLVSs) and noise-like vector pulses (NLVPs) in a graded-index multimode fiber (GIMF) based all-fiber laser. Due to the non-polarization sensitive characteristic of the NL-MMI

We experimentally demonstrated a novel repetition rate adjustable SBS-based Q-switched fiber laser. An inserted Fabry-Perot interferometer formed by two non-contact end faces of two FC/PC fiber connectors was inserted to help the system stabilize the random output of SBS-based Q-switching. By mechanically fine-tuning the length of the inserted Fabry-Perot interferometer, a linear and continuous repetition

We propose and demonstrate a cladding-pumped, erbium-ytterbium co-doped fiber amplifier (EYDFA) scheme based on dual wavelength auxiliary signal injection technique to solve the issue of the backward Yb-ASE self-lasing under strong pumping for the high-power fiber amplification of 1.5-μm kHz-linewidth linearly-polarized laser signal. With the dual wavelength auxiliary signal of 1030 and 1040 nm injection

An actively Q-switched all-solid-state YVO 4 Raman laser, which used a 885-nm side-pumped Nd:YAG laser as the fundamental wavelength and delivered yellow output, is demonstrated. An in-band pump scheme is adopted to mitigate the thermal effects in the laser crystal and a Z-shaped laser cavity is used to compensate thermal lensing further. By intracavity frequency doubling of the Stokes wave with KTP

Two types of GaN vertical-cavity surface-emitting lasers (VCSELs), with and without lateral optical confinement (LOC) structure, were fabricated and their performances were compared. Compared with the VCSEL without LOC, the device with LOC showed a great improvement in threshold current, slope efficiency, output power and differential quantum efficiency, which was mainly due to the reduction of internal

Polarization-maintaining (PM) all-fiber cavity is always essential to realize stable ultrafast-pulse generation. With the help of five sections of PM fibers with independently specific splicing angles, we successfully obtain a femtosecond pulse output from a PM Ytterbium-doped fiber laser (YDFL) mode-locked by the nonlinear polarization evolution (NPE) technique. Using a hybrid component, the PM all-fiber

We studied the optical signal amplification properties of coumarin 460 (C460) in solution. An optical signal amplification experiment was performed using a side-pumping setup. Amplification of more than 7 dB was achieved over a 13-nm spectral width in the signal wavelength range of 448–461 nm with gains above 10 dB at 448 nm and in the 455–461-nm range. The signal-to-noise ratio (SNR) of the entire

The temperature dependency of erbium doped distributed feedback fiber laser output performance is experimentally and theoretically investigated with two major pump schemes. The output power declined linearly as temperature increased from 30 °C to 120 °C for 980 nm and 1480 nm pumped test laser while the later exhibited stronger heat susceptibility. Further experiment and analysis identified the temperature

A prism-based self-injection locked seamlessly tunable blue InGaN/GaN laser diode composite cavity system is presented. A rigorous analysis of this external cavity diode laser (ECDL) system is performed at two different optical feedback powers. At 130 mA low injection, the high reflection system (HRS) exhibits a record wideband tuning span of ∼12.11 nm with a side-mode-suppression-ratio (SMSR) ≥ 15

In the present work, we report a path of RF stabilization versus delay subject to self-mode-locked (SML) two-section quantum-dash (QDash) lasers emitting at ∼1.55 μm and operating at ∼21 GHz repetition rate using a feedback ratio controlled and optical delay phase-dependent symmetric dual-loop optical feedback. For symmetric dual-loops (equal arms of external loops), we identify the three key parameters:

We conducted a systematic investigation of the light extraction efficiency (LEE) of GaN-based vertical micro-scale light-emitting diode (μ-LED) structures using three-dimensional finite-difference time-domain (FDTD) simulations. The LEE of μ-LED structures was found to have a strong dependence on structural parameters such as the shape of the chip cross section, chip dimension, and p-GaN thickness

We propose designs of silicon nitride (Si 3 N 4 ) waveguides with enhanced nonlinear parameter and engineered anomalous group velocity dispersion (GVD) by addition of tellurium oxide (TeO 2 ) top-coating layers of various thicknesses. The proposed waveguides have calculated nonlinear parameters of up to three times that of stoichiometric Si 3 N 4 and exhibit anomalous GVD at near infrared wavelengths