A series of experiments demonstrate that this bio-inspired multimodal 3D endoscope not only provides surgeons with real-time feedback on the location of tumor tissue and lymph nodes but also creates an immersive experience for surgeons without impeding surgical workflow. Its excellent characteristics and good scalability can promote the further development and application of image-guided and robotic surgery.For a squeezing-enhanced linear (so-called SU(2)) interferometer, we theoretically investigate the possibility to broaden the phase range of sub-shot-noise sensitivity. We show that this goal can be achieved by implementing detection in both output ports, with the optimal combination of the detectors outputs. With this modification, the interferometer has the phase sensitivity independent of the interferometer operation point and, similar to the standard dark port regime, is not affected by the laser technical (excess) noise. Provided that each detector is preceded by a phase-sensitive amplifier, this sensitivity could be also tolerant to the detection loss.This work presents an analytical coupling model for perturbed abrupt fiber tapers in single-mode fibers. In addition to LP0m modes, the modeling predicts the presence of LP11 and LP12 modes for a bent taper. Our model also introduces a perturbation function that can match most cases of bending variations on a taper. We have shown that the tapering and bending effect can be treated separately within one abstract formulation. Agreement amongst the model predictions and experimental results support the viability of our method.In this work, we present an efficient polarization conversion device via using a hollow graphene metasurface. The platform can simultaneously realize a series of excellent performances, including the broadband x-to-y cross polarization conversion (CPC) function with near unity polarization conversion ratio (PCR), dual-frequency linear-to-circular polarization conversion (LTC-PC) function, and highly sensitive polarization conversion function manipulation under wide oblique incidence angle range. For instance, the proposed device obtains an x-to-y CPC function with the bandwidth up to 1.83 THz (χPCR ≥98.8%). Moreover, the x-to-y CPC function can be switched to LTC-PC function via artificially tuning the Fermi energy of graphene. The maximal frequency shift sensitivity (S) of polarization conversion function reaches 23.09 THz/eV, suggesting a frequency shift of 2.309 THz for the LTC-PC function when the chemical potential is changed by 0.1 eV. Based on these superior performances, the polarization converter can hold potential applications in integrated and compact devices, such as polarization sensor, switches and other optical polarization control components.Complex lightwave manipulation such as broadband absorption has been realized with metasurfaces based on laterally arranged metal-dielectric-metal cavities with different geometries. However, application of these metasurfaces for optoelectronic devices by incorporating functional dielectrics remains challenging. Here, we integrate a quantum well infrared photodetector (QWIP) with a metasurface made of a patchwork of square cavities with different dimensions arranged in a subwavelength unit cell. Our detector realizes wideband photoresponse approaching the entire responsivity spectrum of the QWIP-single-sized square cavities can utilize only 60% of the possible bandwidth-and external quantum efficiencies of up to 78% at 6.8 µm. Our highly flexible design scheme enables integration of photodetectors and metasurfaces with arbitrary arrangements of cavities selectively responding to incidence with a specific wavefront.A novel fiber optic localized surface plasmon resonance (LSPR) hydrogen sensor has been developed based on the hetero-core structured with palladium nanoparticles (PdNPs) onto a cylindrical cladding surface. In a light-intensity-based experiment with an LED operating at 850 nm, it has been observed that a transmitted loss change of 0.23 dB was induced with response and recovery times of 1.5 and 3.2 s for 4% hydrogen which are the fastest response times among optical fiber hydrogen sensors. The proposed sensor resolved the inevitable trade-off issue between sensitivity and response time which existed in the previously reported SPR sensors, with keeping the response time below 2.0 s even in a high sensitivity region of interest.Silicon-based Yb-doped Y3Al5O12 garnet nanofilms are fabricated by atomic layer deposition, which are polycrystalline after annealing at 1150 °C. The sub-nanometer compositional regulation and the Yb2O3 cladding layers, which also work as the luminescent dopants, are critical for the crystallization. Characteristic Yb3+ luminescence at 1030 nm and 970 nm is identified under electrical injection, exhibiting the external quantum efficiency of 0.65% and the fluorescence lifetime of 80-200 µs. The doped Yb3+ are impact-excited by hot electrons stemming from Fowler-Nordheim tunneling mechanism within the Y3Al5O12 matrix, with the excitation cross section of 0.7×10-15 to 6.4×10-15 cm2. This work certifies the manipulation of multi-oxide nanofilms with designed composition and crystallinity, revealing the possibility of developing Si-based optoelectronic devices from crystalline garnet films.The study of the optical transmission matrix (TM) of a sample reveals important statistics of light transport through it. The accuracy of the statistics depends strongly on the orthogonality and completeness of the basis in which the TM is measured. While conventional experimental methods suffer from sampling effects and optical aberrations, we use a basis of Bessel modes of the first kind to faithfully recover the singular values, eigenvalues and eigenmodes of light propagation through a finite thickness of air.Metasurface based polarization multiplexing is usually conducted in two orthogonal-polarization states, e.g., linearly polarized along x/y axes, left/right-handed circularly polarized states, etc. Herein, we show metasurfaces can be employed to implement tri-channel polarization multiplexing in three non-orthogonal-polarization states, merely with a single-size nanostructure design approach. Specifically, nanostructured metasurfaces acting as nano-polarizer arrays can modulate the incident light intensity pixel-by-pixel by controlling the orientation angles of nanostructures, governed by Malus’s law. Hence, by inserting a metasurface between a bulk-optic polarizer and an analyzer, and elaborately controlling their polarization combinations, we show that the Malus-assisted metasurface can simultaneously record a continuous gray-image and two independent binary-patterns in three different information channels. We experimentally demonstrate this concept by recording three independent gray-images right at the metasurface surface. With the advantages of high information density, high security, high compatibility and ultracompactness, the proposed gray-imaging meta-device can play a significant role in the field of optical storage, anti-counterfeiting, and information multiplexing, etc.Signal enhancement of spectroscopies including terahertz time-domain spectroscopy (THz-TDS) and surface-enhanced Raman scattering (SERS) is a critical issue for effective molecular detection and identification. In this study, the sensing performance between THz-TDS and SERS individually accompanied by the proper plasmonic subwavelength structures was compared. For the precisely quantitative study on the optical properties of rhodamine 6G (R6G) dyes, SERS incorporates with the non-linearly enhanced Raman emissions at the molecular characteristic peaks while THz-TDS refers to the transmittance change and the shift of the spectral resonance. The local molecular density-dependent trade-off relationship between limit-of-detection and quenching was observed from both measurements. The specificity for two samples, R6G and methylene blue, is determined by the discriminations in spectral features such as the intensity ratio of assigned peaks in SERS and transmittance difference in THz-TDS. The comprehension of field enhancement by the specific nanostructures was supported by the finite-element method-based numerical computations. As a result, both spectroscopic techniques with the well-tailored nanostructures show great potential for highly sensitive, reproducible, label-free, and cost-effective diagnosis tools in the biomedical fields.Owing to the characteristics of existing spatial light modulators (SLMs), the computer-generated hologram (CGH) with continuous complex-amplitude is conventionally converted to a quantized amplitude-only or phase-only CGH in practical applications. The quantization of CGH significantly affects the holographic reconstruction quality. In this work, we evaluated the influence of the quantization for both amplitude and phase on the quality of holographic reconstructions by traversing method. Furthermore, we considered several critical CGH parameters, including resolution, zero-padding size, reconstruction distance, wavelength, random phase, pixel pitch, bit depth, phase modulation deviation, and filling factor. Based on evaluations, the optimal quantization for both available and future SLM devices is suggested.In this work, we explore the interrogation of an array of fiber Bragg gratings as part of a laser cavity. A semiconductor optical amplifier in a sigma-shaped fiber cavity provides gain and is gated periodically at a rate that matches the roundtrip time associated with each grating of the array. The interrogator exhibits clear laser properties such as a threshold and linewidth narrowing. Besides improving the signal-to-noise ratio and enabling the re-use of wavelengths, it is found that this interrogation scheme enables monitoring of weak gratings spaced by less than 1 cm. Intracavity grating interrogation studied here is found to be a simple and powerful way to increase the number of sensor points for industrial applications.We demonstrate a comprehensive characterization of the diode-pumped YbBi4Si3O12 laser operating in the continuous-wave and soliton mode-locked regimes. Pumping with a 650 mW, single-transverse mode, fiber-coupled laser diode, a maximum continuous-wave output power amounted to 213 mW with a slope efficiency up to 57.6%. A broadband wavelength tuning range of more than 70 nm was achieved in CW regime with a fused silica prism. Applying a SESAM as mode locker, nearly transform-limited pulses as short as 113 fs were generated for a maximum average power of 53 mW and a pulse repetition rate of ∼106 MHz. To the best of our knowledge, this is the first report on passively mode-locked operation with the YbBi4Si3O12 crystal.Using porous silicon (PSi) interferometer sensors, we show the first experimental implementation of the high contrast cleavage detection (HCCD) mechanism. HCCD makes use of dramatic optical signal amplification caused by cleavage of high-contrast nanoparticle labeled reporters instead of the capture of low-index biological molecules. An approximately 2 nm reflectance peak shift was detected after cleavage of DNA-quantum dot reporters from the PSi surface via exposure to a 12.5 nM DNase enzyme solution. This signal change is 20 times greater than the resolution of the spectrometer used for the interferometric measurements, and the interferometric measurements agree with the response predicted by simulations and fluorescence measurements. These proof of principle experiments show a clear path to achieving a real-time, highly sensitive readout for a broad range of biological diagnostic assays that generate a signal via nucleic acid cleavage triggered by specific molecular binding events.Sub-aperture tool polishing of precision optics requires a detailed understanding of the local material removal [tool influence function (TIF)] at the contact spot between the workpiece and tool to achieve high removal determinism and hence precision of the optic relative to the desired/design surface figure. In this study, the mechanisms influencing and the quantitative prediction of the removal rate and shape of TIF spots during polishing of fused silica glass with cerium oxide slurry using a rotating hemispherical pad-foam tool for a wide variety of process conditions (including tool properties, kinematics, and applied displacements) are investigated. The TIF volumetric removal rate can be estimated utilizing the average relative velocity and contact area using a simple analytical model. In addition, stability of the volumetric removal rate for fixed process conditions is shown to be greatly dependent on the pad preparation and amount of tool use (affecting both pad topography and slurry buildup), whose general behavior shows an increase in removal rate followed by stabilization with polishing time. The determination of the TIF removal shape is more complex. An extended version of the Preston removal model is developed to explain a comprehensive set of measured TIF removal shapes to within ∼22%. This model incorporates a number of phenomena impacting the TIF removal shape including (a) temporal and spatial dependent relative velocity between the workpiece and tool; (b) an elastic mechanics based, as well as hydrodynamic, pressure distribution; (c) a spatially dependent friction coefficient possibly caused by both reduced slurry replenishment in low velocity regions and pad slurry islands (100 µm scale) and porosity (millimeter scale); and (d) a shear-based removal mechanism on the periphery of the contact spot.In this work, we present an accurate polarization reconstruction method based on the coherence demodulation technique, which is different from the previous windowing method operating in the optical path difference domain. The proposed method uses a signal multiplier and a low-pass filter to reconstruct Stokes parameters without performing any Fourier transform. Because this method does not require a Fourier transform, the Stokes reconstruction could be finished in the spectral domain. For calibrating the waveplate phase error, coherence demodulation allows for establishing an analytical model to describe the influence of waveplate imperfections on the polarization measurement process. The phase error will result in a channel shift and Fourier broadening, both of which cause serious errors during Stokes reconstruction. With the model, a method based on a linear polarizer was proposed for calibrating the phase deviation of waveplate. After that, the accurate reconstruction of polarization parameters could be achieved. An experiment was performed to check the ability of the proposed method. The experimental result showed that it has the same excellent performance of reconstructing Stokes parameters using the traditional windowing method. Finally, a series of simulations was carried out to verify the robustness of this method, which showed that the reconstruction technique is robust to misalignment and additional noise.A high-gain two-stage double-pass off-axis NdYVO4 picosecond laser amplifier has been developed. The comprehensive influence of crystal doping concentration and pump beam quality on the small-signal gain of the NdYVO4 amplifier is theoretically analyzed with a model developed by considering energy transfer upconversion and pump light absorption saturation effect. The thermal effect of NdYVO4 crystal with different doping concentrations, undoped end cap lengths, and pump beam quality is investigated as well. Based on the theoretical analysis, a high-gain two-stage and double-pass off-axis NdYVO4 amplifier based on picosecond fiber seed source is realized by choosing long-composite low-doping NdYVO4 crystal and with high brightness laser diode pumping, delivering a gain of 28 dB and an output pulse energy of 67.5 µJ at a repetition rate of 200 kHz.In this paper, a hybrid method of physical optics (PO) shooting and bouncing ray (SBR) physical theory of diffraction (PTD), is adopted to investigate the composite scattering of a vehicle target on the ground. Where the scattering of ground is calculated by the PO method, the scattering of the vehicle target is computed by the SBR-PTD method, and the mutual couplings between them are solved by the ray tracing technique. In addition, an octree data structure is used to accelerate the ray tracing progress. A forward-backward ray tracing technique is employed to ensure the accuracy of the illuminated facet identification. In numerical simulation, the monostatic and bistatic scattering of a reduced-scale vehicle target are calculated by the SBR-PTD method and compared with the simulation results with the multilevel fast multipole method (MLFMM) in commercial software FEKO. And the composite scattering from a reduced-scale vehicle target on the planar ground by our PO-SBR-PTD method is also compared with the MLFMM. The results show that our methods can greatly reduce the computational time and memory requirement while keeping a satisfactory accuracy. Finally, the composite scattering from the vehicle target on the rough ground is demonstrated and analyzed for different incident parameters.Dynamic laser speckle analysis (DLSA) can obtain useful information about the scene dynamics. Traditional implementations use intensity-based imaging sensors such as a complementary metal oxide semiconductor and charge-coupled device to capture time-varying intensity frames. We use an event sensor that measures pixel-wise asynchronous brightness changes to record speckle pattern sequences. Our approach takes advantage of the low latency and high contrast sensitivity of the event sensor to implement DLSA with high temporal resolution. We also propose two evaluation metrics designed especially for event data. Comparison experiments are conducted in identical conditions to demonstrate the feasibility of our proposed approach.Single-point diamond turning is a high-efficiency, low-cost method for manufacturing harmonic diffractive optical elements (HDOEs). Generally, in order to ensure high diffraction efficiency of HDOEs, a half-round tool is used to reduce surface-relief profile errors and a super small feed rate is selected to control surface roughness when hard-brittle materials are turning. However, this method is no longer suitable for soft-brittle materials, which have a strict requirement for the range of the feed rate. It limits the types of materials available for HDOEs. Therefore, according to the range of the feed rate and the cutting depth for soft-brittle materials, an optimized turning model is proposed in this paper. It overcomes the high surface roughness caused by the half-round tool; meanwhile, the advantage of the half-round tool is kept in terms of surface-relief profile errors. On this basis, a mathematical model is proposed to reveal the relationship among diffraction efficiency, period widths, tool radius, and feed rate with different soft-brittle optical materials. As a typical soft-brittle material, barium fluoride (BaF2) was selected to be the material for manufacturing HDOEs. By using the optimized model, the turning experiment of BaF2 HDOEs was completed, and then the BaF2 HDOEs with Ra=2.75nm were obtained. The optimized model is verified to be effective and further provides theory guidance and engineering application in the optical manufactory field of soft-brittle materials for HDOEs. The range of application materials for HDOEs is enriched, and the freedom of advanced optical design is broadened.The crosstalk noise produced in the multiplexing technology of curved computer-generated holograms has caused great damage to reconstructed objects. In order to solve this problem, we propose a method to realize three-dimensional object reconstruction with low crosstalk noise impact. By multiplexing the spherical holograms in the horizontal and vertical directions, the complex amplitudes of the multiple spherical holograms with different curvatures are added to form a composed hologram. The generated hologram records many unrelated scenes of the object. According to the different angles used to generate the hologram, the original object under different viewpoints can be rebuilt, and the multiview multiplexing and reconstruction of three-dimensional objects can be realized. Simulation and optical experiments verify the feasibility of this method.An optical parametric oscillator (OPO) is developed and characterized for the simultaneous generation of ultraviolet (UV) and near-UV nanosecond laser pulses for the single-shot Rayleigh scattering and planar laser-induced-fluorescence (PLIF) imaging of methylidyne (CH) and nitric oxide (NO) in turbulent flames. The OPO is pumped by a multichannel, 8-pulse NdYAG laser cluster that produces up to 225 mJ/pulse at 355 nm with pulse spacing of 100 µs. The pulsed OPO has a conversion efficiency of 9.6% to the signal wavelength of ∼430nm when pumped by the multimode laser. Second harmonic conversion of the signal, with 3.8% efficiency, is used for the electronic excitation of the A-X (1,0) band of NO at ∼215nm, while the residual signal at 430 nm is used for direct excitation of the A-X (0,0) band of the CH radical and elastic Rayleigh scattering. The section of the OPO signal wavelength for simultaneous CH and NO PLIF imaging is performed with consideration of the pulse energy, interference from the reactant and product species, and the fluorescence signal intensity. The excitation wavelengths of 430.7 nm and 215.35 nm are studied in a laminar, premixed CH4-H2-NH3-air flame. Single-shot CH and NO PLIF and Rayleigh scatter imaging is demonstrated in a turbulent CH4-H2-NH3 diffusion flame using a high-speed intensified CMOS camera. Analysis of the complementary Rayleigh scattering and CH and NO PLIF enables identification and quantification of the high-temperature flame layers, the combustion product zones, and the fuel-jet core. Considerations for extension to simultaneous, 10-kHz-rate acquisition are discussed.A decrease in photon intensity due to carbon contamination on optical elements is a serious issue in synchrotron radiation (SR) beamlines. Photon intensity can be regained by refurbishment of optical elements using suitable techniques. In the literature, three suitable techniques [radio frequency (RF) plasma, ultraviolet (UV) radiation (λ=172nm), and infrared (IR) laser (λ=1064nm) exposure] are reported to remove carbon contaminations from optical elements. These techniques are used independently to remove carbon, and, to the best of our knowledge, no systematic study is available on their relative efficiencies and effects on a mirror surface. We have applied these techniques independently for removal of carbon contamination from a gold surface, and detailed surface characterizations are carried out using soft x-ray reflectivity, x-ray photoelectron spectroscopy, Raman spectroscopy, and atomic force microscopy techniques. Characterization results suggest that all three techniques are capable of removing carbon contamination with certain limitations. Here, detailed relative effects on a gold surface after cleaning experiments with three techniques are discussed.We propose a practical secure key generation and distribution (SKGD) scheme for actual application. Based on the experiment results of the polarization properties of the actual optical-fiber link, we propose a SKGD method by the active modulation of the state of polarization of the optical-fiber by two polarization scramblers placed at the local end of the legal users in the point-to-point communication system. Experiment results prove that the signals received by legal users share high correlation using 20 km standard single-mode fiber and 1 KHz polarization scrambling rate, and the bit generation rate can reach to 1216 bit/s with a bit error rate of ∼0.33%. Security of the system is also analyzed in terms of the polarization properties of the system; the theoretical and experimental results indicate that the proposed scheme possesses high security due to the invisibility of the key signal and the technical difficulty of the recovery of the key sequence.Transmittance and fluorescence optical projection tomography can offer high-resolution and high-contrast visualization of whole biological specimens; however, applications are limited to samples exhibiting minimal light scattering. Our previous work demonstrated that angular-domain techniques permitted imaging of ∼1cm diameter noncleared lymph nodes because of their low scattering nature. Here, an angle-restricted transmittance/fluorescence system is presented and characterized in terms of geometric and fluorescence concentration reconstruction accuracy as well as spatial resolution, depth of focus, and fluorescence limits of detection. Using lymph node mimicking phantoms, results demonstrated promising detection and localization capabilities relevant for clinical lymph node applications.Imaging the high-precision magnetic distribution generated by the surface current of chips and chip-like structures is an important way to measure thermal parameters of core components. Based on a high-concentration nitrogen-vacancy color center ensemble in diamond, the imaging magnetic field distribution is performed in a wide-field microscope. The magnetic vector detection and reduction model is verified first with continuous wave optical detection of magnetic resonance technology. By systematically measuring the distribution of the electromagnetic field generated on the surface of the micro-wire under different microwave power and different laser power conditions, the imaging quality of the wide-field imaging system can be optimized by adjusting the experimental parameters. Then, the electromagnetic field distribution imaging on the wire surface under different current intensities is obtained. In this way, accurate measurement and characterization of the magnetic distribution on the surface of the micro-wire is realized. Finally, at the field of view in the range of 480µm×270µm, the magnetic intensity is an accurate characterization in 0.5-10 Gs, and the magnetic detection sensitivity can be increased from 100 to 20µT/Hz1/2. The results show the accurate magnetic distribution imaging for chips and chip-like structures, which provide a new method for chip function detection and fault diagnosis based on precision quantum measurement technology.It is established in the optical feedback interferometry (OFI) theory that the shape of the interferometric fringe has an impact on the detector’s response to very small displacement measurements. In this paper, we validate-for the first time, to the best of our knowledge, based on experimental results-this statement by comparing experiments to an established model implementation. Through these experiments, we show that the amplitude of the signals induced by sub-λ/2 optical path variations is linearly dependent on the slope of the underlying fringe. Thus, careful control of the phase allows us to maximize the detection amplitude of very small displacements by positioning the phase where the fringe slope is the steepest. These results are directly applicable to established OFI applications that measure sub-λ/2 optical path variations, such as OFI vibrometers or acoustic imaging though the acousto-optic effect.Today, a large number of targets operate in space, and there are mainly four kinds of attitude targets triaxial stabilized targets, spin stabilized targets, triaxial stabilized targets on tumbling, and spin stabilized targets on tumbling. It is of great significance to classify and identify these targets. First, the infrared radiation characteristic model of the target is established, taking different attitude targets into account, which, to the best of our knowledge, has seldom been considered. Then, through the simulation of specific example targets, the differences in infrared characteristics of four kinds of attitude targets are analyzed and explained. Finally, according to the orbit distribution and typical geometry structure of space targets, the infrared characteristic data sets of four kinds of attitude targets are simulated, and a classifier is established to classify and recognize these targets. The results show that the infrared characteristics of different attitude targets are obviously different, and the classifier can successfully classify and recognize different attitude targets.A method for visualizing the air flow from the mouths of vocalists and wind musical instruments is presented. The method is based on a modification of electronic speckle pattern interferometry that incorporates the interference of a transmitted object beam rather than the standard method using a reflected object beam. The resulting whole-field real-time images are a valuable resource for both scientific and pedagogical use.Sandstorms can severely affect the reliability of outdoor optical wireless communications (OWC) by diminishing large regions’ visibility. In this work, the effect of a real sandstorm on optical camera communications (OCC) links is experimentally evaluated. Two link ranges are essayed using a cost-efficient telescope-based camera setup with commercial LEDs. Using on-off keying modulation, a data rate of 1035 and 630 bps with error probabilities of 9.14⋅10-5 and 4.1⋅10-3 for 100 m and 200 m, respectively, can be achieved. The signal-to-noise ratio of the links was optimized by tuning the analog amplifier’s gain of the camera, increasing it by up to 9 dB. It is shown that scattering due to the sandstorm can even be beneficial for increasing the data rate in OCC (contrary to classical photodetector-based OWC links), thanks to an increment of 33% on the region of interest dimensions compared to the expected clear air link.We propose spectroscopic imaging ellipsometry that can measure spectral ellipsometric signals in the entire field of view simultaneously without areal scanning or operation of polarization devices. The proposed imaging ellipsometry is configured in a coaxial optical structure so that the high magnification objective lens is applicable and the spatial resolution is highly increased. Without the operation of polarization components and to efficiently obtain the spectral data in the object plane, the ellipsometric parameters are encoded into the high frequency in the spectral domain and are measured by an imaging Michelson interferometer. The volumetric thickness measurement by the proposed method was verified by comparing the thickness results of the SiO2/Si sample that has four different thicknesses with commercial ellipsometer results.In the present paper, a new 2-bit analog-to-digital converter (ADC) was designed and simulated by using 2D photonic crystal (PC) structures to create a relatively faster and smaller structure. For this purpose, a PC structure with a square lattice and silicon rods in the air bed was used. In the proposed structure, a combination of an optical filter with a linear waveguide, optical nanoresonators, and interference effects was used to create a 2-bit ADC. To create a structure in optimal conditions with maximum output optical power, the size of nanoresonators was scanned to reach the best size. The proposed structure operated at the operating wavelength of 1550 nm with a response time of about 1.63 ps, a sampling rate of about 613 GS/s, and a resolution sampling rate product (RSRP) value of about 2453 ks. Additionally, the size of the structure was about 194µm2, which is small compared with other structures proposed in this field; it also enjoys high simplicity and flexibility like structures with other functions, including 4-bit converters. The amount of power used to create different logic states was at the rate of mW/µm2, which is much lower than the amount used in similar structures and is achieved using nonlinear effects and materials. Therefore, due to the excellent results obtained, this structure is recommended to be used in optical integrated circuits. The plane wave expansion method was used to extract the photonic bandgap, and the finite-difference time-domain method was used to obtain the results related to the output spectrum of the designed structures.Grazing incidence interferometry has been applied to plane, cylindrical, acylindrical, and general rod-like surfaces using diffractive beam splitters. Here, in a first step towards measuring aspherics, we demonstrate that also rough convex steep rotationally symmetric spherics can be measured along one meridian in a single step using diffractive beam splitters and phase shifting techniques. The measurement of rough surfaces is possible, i.e., without the need to polish the surfaces, due to the large effective wavelength (λeff≈10µm) of the test. We include, besides the short recapitulation of the measurement principle and experimental setup, a presentation of the measured data of one small meridian region for the special case of spherical objects under test. The subsequent data analysis combined with suitable simulations focuses on elimination of the misalignment aberrations from the results caused by specimen displacements in the setup.A new method of measuring external cylindrical surfaces is proposed, making use of a ring beam transform unit. The unit is composed of three cone mirrors, with which a parallel beam can be transformed into annular and convergent beams. The method has advantages over classic methods It avoids physical contact with the cylinder surface and is fast and stitching-free. In experiments using a dynamic interferometer to demonstrate the feasibility of the method, the RMS difference of the axis contour from results using a Luphoscan is 0.0282 µm, while the roundness difference of the circumferential contour is 0.0962 µm.To accurately determine the optical axis cut error of a nonlinear uniaxial crystal, a measurement method based on dual-optical path second-harmonic energy (SHE) rocking curve acquisition is presented in, of which the measurement uncertainty can be controlled within 3.20 µrad , 26 times higher than that of a high-precision commercial x-ray diffractometer (XRD). To meet the measurement requirements, a Type I potassium dihydrogen phosphate reference crystal (RC) is first made, and its optical axis cut error is considered as a reference. Then, the optical axis cut error of a measured crystal (MC) with an aperture of 25mm×25mm and a thickness of 10 mm is determined by simultaneously recording the SHE scatter plots of the RC and the MC, where the measurement repeatability of 10 consecutive measurements is only 4.48 µrad and the measurement speed is within 20 s. During data processing, a third-order Fourier polynomial is proposed to fit the scatter plots into smooth curves, of which the regression coefficients are greater than 0.9975. The experimental method not only overcomes the shortcomings that XRDs will introduce scratches and defects to the crystal surface and are unable to measure large-aperture crystals, but can be used to guide the production of precise cutting of a nonlinear uniaxial crystal, thus ensuring the maximum conversion efficiency of a frequency multiplication system.The frequency characteristics of spherical photon density waves excited in media with different degrees of scattering anisotropy are studied. Statistical modeling of the frequency and phase responses of the spatial irradiance of the light field emitted by a point-sized isotropic source were performed employing the Monte Carlo technique. The scattering anisotropy of the medium was determined by the Henyey-Greenstein phase function with different values of the mean scattering cosine. It is shown that the scattering anisotropy factor determines the frequency range, in which the effect of the photon path length distribution on the magnitude of the photon density wave dispersion is maximal. In media with quasi-isotropic scattering, dispersion effects are manifested at lower frequencies as compared to those for anisotropic media. The simulation results are compared with the analytical solution for the asymptotic regime of the light field in an isotropically scattering medium.The security of medical image transmission in telemedicine is very important to patients’ privacy and health. A new asymmetric medical image encryption scheme is proposed. The medical image is encrypted by two spiral phase masks (SPM) and the lower-upper decomposition with partial pivoting, where the SPM is generated from the iris, chaotic random phase mask, and amplitude truncated spiral phase transformation. The proposed scheme has the following advantages First, the iris is used for medical image encryption, which improves the security of the encryption scheme. Second, the combination of asymmetric optical encryption and three-dimensional Lorenz chaos improves the key space and solves the linear problem based on double-random phase encoding. Third, compared with other encryption schemes, the proposed scheme has advantages in occlusion attacks, key space, correlation, and information entropy. Numerical simulation and optical results verify the feasibility and robustness of the encryption scheme.We present the characterization of high extinction ratio (ε) square optical pulses using a photon counting technique, as other techniques only offer a limited range of measurement up to 60 dB. High-ε pulses are generated by applying a square pulse modulation on sinusoidally modulated optical signals, then inducing self-phase modulation (SPM) using the nonlinear Kerr effect and extracting an SPM-generated sideband. We measured a 10 ns Kerr-generated optical pulse exhibiting a 120.1 dB extinction ratio, originating from a conventional electro-optic modulator delivering a pulse with a 20-dB extinction ratio, by counting the number of photons at the peak and the pedestal of the generated pulse. These proven high-ε pulses allow for long-range distributed vibration sensing in optical time-domain reflectometry systems and open new horizons in high-Q microring sensors.This paper proposes an unwrapping algorithm based on deep learning for inertial confinement fusion (ICF) target interferograms. With a deep convolutional neural network (CNN), the task of phase unwrapping is transferred into a problem of semantic segmentation. A method for producing the data set for the ICF target measurement system is demonstrated. The noisy wrapped phase is preprocessed using a guided filter. Postprocessing is introduced to refine the final result, ensuring the proposed method can still accurately unwrap the phase even when the segmentation result of the CNN is not perfect. Simulations and actual interferograms show that our method has better accuracy and antinoise ability than some classical unwrapping approaches. In addition, the generalization capability of our method is verified by successfully applying it to an aspheric nonnull test system. By adjusting the data set, the proposed method may be transferred to other systems.We show an in-line digital holographic image reconstruction from subsampled holograms with resolution improvement and lensless magnification with high noise immunity by a compressive sensing approach. Our method treats the sensed field as subsampled, low-pass filtered and projected on a Fresnel-Bluestein base in an inverse problem approach to image reconstruction with controlled lensless magnification. So, we have demonstrated by simulation and experimental results that the approach can reconstruct images with quality even when used in holograms obtained from unusual subsampling schemes.Outgoing Editor-in-Chief Ron Driggers shares his parting thoughts and hopes for the Applied Optics community in the coming year.We experimentally demonstrate Nyquist wavelength-division-multiplexed (WDM) channels with a low signal-to-noise ratio (SNR) difference based on flat electro-optic combs (EOCs), which reduce the interchannel crosstalk penalty in Nyquist-WDM transmission with no guard band. The five Nyquist-WDM channels are generated through the insertion of uniform and coherent lines around each line of the EOCs from a dual-parallel Mach-Zehnder modulator. For the five channels, the normalized root-mean-square error of optical sinc-shaped pulses at a repetition rate of 9 GHz is between 1.23% and 2.04%. The SNRs of the Nyquist signal can be better than 30 dB by using flat EOCs with a narrow linewidth as WDM sources, and the difference in SNR is less than 0.6 dB for the WDM channels. The transmission performance of five Nyquist-WDM channels with no guard band is compared in a 56 km fiber link. The results show that our scheme provides a minimum interchannel sensitivity penalty of 0.7 dB at the forward-error-correction limit. The Nyquist-WDM channels with low SNR difference can effectively improve the communication performance of the Nyquist-WDM system.During welding of glass with ultrafast lasers, an irregular formation of weld seams was prevented by modulation of the average laser power and spatial beam shaping. The formation of individual molten volumes in regular intervals was achieved by means of power modulation, resulting in a predictable and reproducible weld seam with a regular structure. At constant average power, a homogeneous weld seam without a periodic signature was alternatively achieved by means of a shaped beam generating an elongated interaction volume and resulting in a continuous melting of the material. The influence of the two approaches, and their combination on the process dynamics, was analyzed by means of high-speed videos of the plasma emission and of the formation of the seams.The time transformation (TT) technique is used to study the nonlinear pulse reshaping towards triangular pulse (TP) generation by efficiently optimizing the pulse parameters in an erbium-doped chalcogenide fiber amplifier (EDCFA), for the first time, to the best of our knowledge. The effects of input chirp parameter, optical gain, and dipole relaxation time are also depicted in the context of TP generation. The results obtained from the TT approach when compared with that from the nonlinear Schrodinger equation show excellent agreement. The study also reveals that spectral pulse doubling can be achieved at a shorter length when a pre-chirped Gaussian pulse is propagated through the proposed EDCFA.This paper proposes a novel spiral-scanning laser differential confocal measurement method (SSLDCM) for fast and precise measurement of surface topography with microstructures. Spiral plane scanning is used to eliminate frequent acceleration and deceleration problems in traditional raster-scanning differential confocal measurement systems and helps to keep the measuring process efficient and stable. To solve the problem of uneven sampling distribution during spiral scanning, a variable sampling rate method is adopted to distribute the sampling points at equal intervals, which would help to reduce the time of the 3D imaging process. A denoising method based on an adaptive wavelet threshold is proposed to filter the existing noise during the measuring process. An experimental measurement platform based on SSLDCM is constructed, and the axial response curve is tested and analyzed. The linear region range of the experimental platform reaches 13 µm, and the slope is about 164.15 mV/µm. In addition, the measurement results of a silicon wafer specimen by SSLDCM show good consistency with a commercial high-precision microscope, and the largest deviation is less than 2.71%. The SSLDCM has great potential to be used in various noncontact surface measurement applications with high efficiency and accuracy.Robust detection and classification of multimodal self-mixing (SM) signals emanating from the optical feedback-based SM interferometric laser sensor are necessary for accurate retrieval of sensing information. An abrupt shift in the modality of SM signals can occur due to different operating conditions; consequently, an unidentified modality shift can cause severe measurement errors. Therefore, it is necessary to detect and identify the type of multimodality so that relevant adjustments could then be made, either in the SM sensor setup or in the relevant signal processing, to avoid the errors caused by the shift in modality. In this work, SM modality identification and classification techniques based on the machine learning classifier algorithms of linear regression, XGB regressor, and decision tree regressor are proposed. The distinguishing feature values, which are used to train and test the classifiers, are extracted from the given SM signal by applying techniques such as principal component analysis, peak width, and linear discriminant analysis. Proposed methods are tested on an SM signal dataset containing a total of 45 unseen SM signals, acquired experimentally from the SM sensor. The identification and classification accuracy of the three classifiers of linear regression, XGB regressor, and decision tree regressor is 76%, 96%, and 100%, respectively.Robust detection of interferometric fringes is critical for accurate sensing by self-mixing interferometric (SMI) displacement sensors. Mode-hopping of a laser diode (LD) can potentially diversify SMI fringes, transforming them from mono-modal to multimodal. Thus, fringe detection of a multimodal SMI signal becomes a bigger challenge as the relative strength of each mode may be different, leading to further diversity in the fringes belonging to each regime. Also the SMI signals from each mode are incoherently added, so the composite multimodal SMI signal is of complex nature. In this paper, a robust method is proposed for the detection of multimodal fringes, which is also able to detect traditionally encountered mono-modal fringes. Since fringes are actually peaks of SMI signals, the proposed method detects all of these peaks and separates the genuine peaks that correspond to true fringes from the falsely detected peaks, corresponding to false fringes. An experimental dataset of 60 SMI signals was acquired by using two different LDs to validate our proposed method. The proposed method has correctly detected the SMI fringes with an accuracy of 99.6%. However, at the same time, 0.7% false fringes were also detected while 0.3% true fringes were undetected by the proposed method.We report on two-dimensional (2D) hexagonal boron nitride (hBN) as saturable absorber (SA) material in a passively Q-switched erbium-doped fiber laser (EDFL) operating at 1.5 µm. The 2D hBN film as an SA is fabricated and transferred onto the optical fiber tip by natural deposition technology. In the Q-switched operation, we obtain stable Q-switched laser operation with a maximum average 10% output power of 2.25 mW, corresponding to a repetition frequency of 55.5 kHz, shortest pulse width of 6.77 µs, and single pulse energy of 40.49 nJ. The achieved PQS at 1.5 µm EDFL with 2D hBN as an SA may have potential applications in many novel 2D materials and all-fiber lasers.A spatial axial shearing interferometer is proposed to obtain a mutual coherence function representing longitudinal spatial coherence of natural light. The modulation of the quadratic phase distribution displayed on a spatial light modulator generates a spatial axial shear without a radial one. Because the optical path lengths along the optical axis on the two paths are identical, the spatial axial shear can be greater than the coherence length derived by temporal coherence. Experimental results are given to confirm that the mutual coherence function obtained by the proposed interferometer has spatial distribution expected by the relation between coherence and diffraction formula.The polarization-maintaining fiber-based Sagnac loop interferometer (PSLI) is frequently applied in directional torsion measurement, but may suffer from a large temperature cross talk. In this study, a novel method was proposed for fabrication of side-tapered PSLI by a two-step arc-discharge technique at the splicing point. The energy distribution of the taper region was characterized, and comprehensive tests were performed in terms of torsion and temperature. The experimental results showed that, through bias twisting, the measuring areas were effectively gapped and highly sensitive torsion and temperature responses were gained simultaneously. With a small wavelength shift, the torsion sensitivity reached 13.54 dB/rad in the range from -30 to 30 rad/m. Moreover, the temperature sensitivity was found to be -1.579nm/∘C, with a near-zero intensity fluctuation. Therefore, the sensor fabricated herein successfully achieves simultaneous measurement of directional torsion and temperature with high sensitivity and ultralow cross talk. The proposed scheme has the merits of practicality, low cost, and ease of operation, and is very promising for multiparameter engineering monitoring.An ultra-sensitive fiber optic sensor based on a HO(Me2SiO)nH (silicone rubber) Fabry-Pérot (FP) resonant cavity is fabricated through a simple method of dipping, which has high linearity, high sensitivity, and a wide response range to temperature. The silicone rubber can form a smooth sphere without wire drawing, and it has strong heat resistance and aging resistance. Its favorable waterproof performance enables it to work efficiently in different humid environments. A method of synchronizing the detection and wavelength sweeping signal is applied to analyze the wavelength shifts of the interference signal. The sensitivity of the fabricated FP sensor is almost 400 pm/°C in the range of 50-190°C with a linearity of 0.999, and the resolution is 0.002 nm. In addition, the testing results at room temperature can also satisfy the linear relationship, providing the possibility of applications in the biological field.Camera modeling and calibration are essential tasks in modern optics. Conventionally, the pinhole model is adopted with a further extension for lens distortion. However, pinhole and distortion models are mutually dependent; thus, the standard approach induces systematic camera calibration errors. This research presents a unifying distorted pinhole camera model that includes a telecentric, distortion-free pinhole, and radial lens distortion as particular cases. An iterative calibration method based on the derived distorted pinhole model is proposed, and experimental evaluation by calibrating a camera with high radial distortion is performed. The calibration results are compared with the standard and fisheye models using a well-known commercial camera calibrator software. The proposed method outperforms the standard model and achieves accuracy comparable to the fisheye model, and the proposed approach is a versatile and accurate tool for diverse optical metrology applications.The dispersion degree of polarization, a new definition of the depolarization degree of partially polarized beams, is first proposed, to the best of our knowledge, to measure the performance of fiber depolarizers. First, the description of the polarization based on the Poincaré sphere is introduced. Then, the modified Delaunay triangulation algorithm is introduced, and the calculation formula of the dispersion degree of polarization is given based on this algorithm. The experimental device was set up, and the dispersion degree of polarization of the depolarized light after the fiber depolarizer was measured to be 47.3%. The components and proportions of polarization in the depolarized light were also obtained. Compared with the degree of polarization, the dispersion degree of polarization can quantitatively analyze the light polarization evaluation in the time dimension and provide a numerical reference for improving the depolarizer, thus increasing the fiber sensor’s accuracy.