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This paper describes an exceptionally high birefringent modified slotted core circular photonic crystal fiber (MSCCPCF). At the 1.55 μm telecommunication wavelength, the proposed fiber structure aims to achieve exceptional birefringence performance through the thoughtful placement of air holes and the incorporation of slots. The optical properties of the proposed MSCCPCF are rigorously simulated using the finite element method (FEM). The FEM simulations show high birefringence of up to 8.795 × 10−2 at 1.55 μm. The suggested fiber exhibits single mode behavior in the E to L communication bands (Veff < 2.405). Numerous geometric factors and their effects on other optical properties, such as birefringence, beat length (17.62 μm) and dispersion coefficient (−310.8 ps/(nm · km)) have been meticulously studied. The proposed fiber’s viability and potential uses are evaluated by analyzing modal features like nonlinearity (21.76 W−1 km−1), confinement loss (5.615 × 10−11 dB/cm), and dispersion. The proposed fiber structure has potential for use in polarization-maintaining devices, sensors, and other photonic applications requiring high birefringence and tailored optical properties.

Orbital Angular Momentum (OAM) multiplexing is a technology of communication systems that enables high-capacity optical communication networks. One of the most important determinants of this technology is the channel capacity, loss of power, and Bit Error Rate (BER) accompanying the transmission. This article proposed an Orbital Angular Momentum (OAM)/Spatial Domain Multiplexing (SDM) Gigabit-capable Passive Optical Network (G-PON) architecture for a Multiple-Input Multiple-Output (MIMO) communication system that supports (OAM/SDM G-PON) technology. The proposed architecture is used to multiplex the downstream OAM channels and the upstream SDM channels, and an OAM multiplexer/demultiplexer (OAM-MUX/DEMUX) is used to multiplex and demultiplex the OAM channels. In the OAM/SDM G-PON system, the signal will propagate through three different mediums, each having its own nature in influencing the power of the signal that passes through that medium. The experiment involves bidirectional transmissions with a DS/US data rate of 2.4 Gbps and Binary Phase Shift Keying (BPSK) downstream and 1.2 Gbps upstream. The observed results showed that the bit-error rate (BER) is a function of coupling angles and increases with the increase in the OAM ring size.

We present the design of composite optical nanofibers (ONF) coated with thin layers of nonlinear materials, Titanium dioxyde (TiO2) and Polymethyl methacrylate (PMMA), for the realization of new all-solid Raman wavelength converters for an emission around 1.5 μm. Our simulations show that Stimulated Raman Scattering can be obtained with moderate input peak powers, typical ONF geometrical parameters, and layer thicknesses deposited which are technologically achievable: a few tens of nm for TiO2 and a few hundreds of nm for PMMA. This study enlarges the field of applications of ONF in nonlinear optics and lasers by opening the way to the coating by other materials such as doped polymers.

A highly sensitive distributed measurement technique is employed to map supercontinuum generation along a tapered silica optical fiber. This technique, which utilizes a confocal Raman micro-spectrometer, relies on analyzing far-field frequency-resolved Rayleigh scattering along the waveguide with micrometer-scale spatial resolution and high spectral resolution. Non-destructive and non-invasive, the mapping system enables observation of every stage of supercontinuum generation along the fiber cone, including cascade Raman scattering, four-wave mixing, and dispersive wave generation. Consequently, it unveils unique nonlinear spatial dynamics that are beyond the reach of standard spectral analyzers.

Industrial processes such as smelting and sintering require stable and precise temperature control of furnaces. To achieve this, accurate temperature measurements are required. Pyrometry allows for contactless measurement of bulk materials and is particularly suitable for high temperature applications. One of the main influences on the accuracy of pyrometric measurements is the knowledge of the emissivity in the spectral measurement range. To reduce this dependence, two-color pyrometers or multi-color pyrometers can be used. With this in mind, the Institute of Space Systems (IRS) is further developing their existing pyrometer technology by designing an advanced multi-channel pyrometer for bulk oven processes in a joint venture with Stange Elektronik GmbH and New Generation Kilns Grün GmbH. The design approach is explained here and the considered methods of achieving emissivity independent temperature measurements are examined.

In this work a three-dimensional diffusion model is used to model photopolymers as a recording media. This model allows us to predict the properties of the Diffractive Optical Elements (DOEs) once we recorded into the photopolymer. This model had never been tested with more complex elements, such as multifocal diffractive lenses, as presented in the following in this work. In addition, the model includes; the estimation of the refractive index modulation, the low-pass filtering effect due to the experimental optical setup, and the evolution of the transverse intensity distribution. In this way, the selection of the appropriate material characteristics depending on the intended DOE application is made possible. Specifically, an acrylamide-based PVA/AA photopolymer is simulated using the proposed model. Moreover, coverplating and index matching systems are considered together to avoid the effects of thickness variation. Furthermore, in order to compare their properties using the proposed model, we focus on Fibonacci lenses (FL), a type of bifocal lenses. This allows us to evaluate the dependence of the focii intensity on the polymerisation rate, the diffusivity parameter, low-pass filtering effect and the use of the index matching system for these lenses. This enables us to know the recording parameters in order to produce this type of multifocal diffractive lenses with higher quality and precision.

Deep neural networks (DNNs) are increasingly employed across diverse fields of applied science, particularly in areas like computer vision and image processing, where they enhance the performance of instruments. Various advanced coherent imaging techniques, including digital holography, leverage different deep architectures like convolutional neural networks (CNN) or Vision Transformers (ViT). These architectures enable the extraction of diverse metrics such as autofocusing reconstruction distance or 3D position determination, facilitating applications in automated microscopy and phase image restitution. In this work, we propose a hybrid approach utilizing an adapted version of the GedankenNet model, coupled with a UNet-like model, for the purpose of accessing micro-objects 3D pose measurements. These networks are trained on simulated holographic datasets. Our approach achieves an accuracy of 98% in inferring the 3D poses. We show that a GedankenNet can be used as a regression tool and is faster than a Tiny-ViT (TViT) model. Overall, integrating deep neural networks into digital holographic microscopy and 3D computer micro-vision holds the promise of significantly enhancing the robustness and processing speed of holograms for precise 3D position inference and control, particularly in micro-robotics applications.

Fluorescence molecular tomographic (FMT) reconstruction is commonly solved based on the Jacobian matrix, which is a first-order sensitivity matrix. Basically, using the second-order derivatives for iterative reconstruction can help improve the performance of convergence. In this paper, a reconstruction method of FMT based on the reduction of the second-order sensitivity matrix is proposed. In addition, the strategy of detectors rotation is combined into the inverse reconstruction to further improve the reconstruction quality. The reconstructed results demonstrate that the proposed method accelerates the reconstruction with high precision of inverse solutions.

This study presents an initiative aimed at developing a real-time optical measurement system for non-contact measurement of airborne fungal spores in protected crops such as strawberries, tomatoes, and cucumbers. The system is based on a customized microscope and an automatic system for trapping fungal spores. It has been tested in the field under real conditions, and image processing algorithms have been developed to identify fungal spores in high-resolution microscope images.

The response of three of the most used commercial polymers (poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET) and polypropylene (PP)) under irradiation with high repetition rate (1 kHz–1 MHz) femtosecond (450 fs) multi-pulse (N = 10–1500) laser at λ = 343 nm, 515 nm (1.40 J/cm2 for both former wavelengths) and 1030 nm (1.70 J/cm2) is reported, obtaining a study on how the absorption mechanism influences the processing efficiency for these materials. Tunable ablation depth and diameters are accomplished by modifying repetition rates at a constant fluence and number of pulses. The results highlight the role of absorption mechanism, repetition rate ranges and thermal properties of the materials for benefiting ablation efficiency. Furthermore, the use of high repetition rates improves the laser processing, reducing extended thermal effects and increasing ablation uniformity.

The actual implementation of on-site analysis of biomarkers, such as miRNAs, depends on the availability of portable and easy-to-handle detection systems that can be used as point-of-care in real life applications. In this work, an automatized microfluidic platform combined with a portable Raman spectrometer is reported and tested for miR-214 detection by surface enhanced Raman scattering (SERS). A multi-chamber SERS-active chip, functionalized according to a previously optimized two-step hybridization assay, was automatically incubated with the analyte solution. Preliminary tests allowed to adjust the portable Raman spectrometer acquisition conditions and to compare the obtained results with those of a bench Raman microscope. Finally, miR-214 at different concentrations was analyzed through an automatic procedure, achieving a limit of detection (LOD) in the picomolar range.

In the present work, the viability of a novel recording geometry to produce reflection holographic couplers is analyzed. Recalling the idea of previous works, photopolymers are used as the recording material because they have been proven to be well-suited for the intended see-through application: the capability to provide a virtual image without compromising the information about the surrounding environment. Moreover, holography fundamentals give us the proper background to examine the proposed design, where no prisms or microlenses arrays are used. Aiming to support the analysis, we provide experimental evidence that the produced reflection holographic gratings exhibit the correct properties to work as a coupler, where the sensitivity of the material and its properties are studied and examined.

State-of-the-art super-resolution microscopy techniques, including Stimulated Emission Depletion (STED), Reversible Saturable Optical Fluorescence Transitions (RESOLFT), and Switching Laser Mode (SLAM) microscopies, implement Laguerre-Gaussian beams, also known as vortex or doughnut beams to capture fluorescence information within a sub-wavelength area of the observed sample, effectively surpassing the diffraction limit and significantly improving the quality of the image. However, these techniques typically operate at point by point basis, involving time-consuming scanning of the sample to construct a complete, meaningful image. Therefore, for real-time live cell imaging purposes, the parallelization of illumination is crucial. In this study, we demonstrate the parallel generation of arbitrary arrays of Gaussian and Laguerre-Gaussian laser foci suitable for super-resolution microscopy. We achieve rapid scanning through the sample using acousto-optic spatial light modulation, a technique we have previously pioneered across various fields. By employing parallelized illumination with both Gaussian and doughnut beams, we aim to capture super-resolution images.

Drosophila melanogaster, better known as the fruit fly, has become a widely used model organism that has allowed us to understand many biological behaviors, from sleep to neurological diseases, behavioral patterns, reproduction, and the circadian cycle, which coordinates biological rhythms in a 24-hour daily cycle through its main Zeitgerber, light, especially blue light. Therefore, the aim of this work was to build an optical setup with a hexagonal design that allowed a large number of D. melanogaster cultures to be irradiated homogeneously with blue light simultaneously. This array can cover an illuminance range from 0 to approximately 600 lux by applying a current variation from 0 to approximately 1 A. It also has a real-time timer to turn the lights on and off, programmed in a 12:12 LD cycle for 24 h. The optical setup with its unique design can become a very useful tool for developing experiments and understanding paradigms related to blue light at genetic, behavioral and neuronal levels, among others that are still unanswered.

This study presents a comparative analysis of AlGalnAs buried heterostructure laser diodes by using dual-channel ridge-waveguides. Different shaped channels, including bowl shaped groove and vertical groove, are explored. Using a vertical groove structure, we achieved an output power of 90 mW at 25 °C with a threshold current of only 4 mA. This represents a 3.6-fold increase in output power compared to the BH-DFB structure. At a high temperature of 85 °C, the laser maintains a side-mode suppression ratio of over 45 dB at the maximum power point. The laser’s relative intensity noise in the 0–40 GHz frequency range is less than −162.8 dB/Hz when operated at 300 mA with the chip butterfly packaged. These findings underscore the robustness, reliability, and high-performance capabilities of the developed DFB laser, highlighting its potential for various practical applications.

In this study, we report the generation of multi-wavelength light sources through enhanced four-wave-mixing processes using a straightforward and adaptable dual-frequency Brillouin fiber laser. This passive optical and nonreciprocal cavity is first tested and analyzed with long fiber lengths up to 1 km in the 1.55 μm telecommunication C band and then in the 2-μm waveband. In the latter case, we demonstrate that our fiber cavity enables efficient multiple four-wave mixings, in the continuous-wave regime, which are commonly inaccessible in long silica-fibers due to increased losses. We also report on the tunable repetition rate from tens of GHz to hundreds of GHz, by simply changing the frequency spacing between the two continuous-wave pumps. The coherence limitations of our all-fiber system are discussed, along with the impact of the dispersion regime of the nonlinear fiber that forms the cavity.

Terahertz radiation has emerged as a prominent solution for imaging and detection beyond visible and infrared. Active terahertz imaging is a widely used technology in this context especially for security applications and screening. Such systems are built around an illuminating source, a detecting module and a beam shaping system to match the detectors geometry. The overall system performance is largely dependent on an optimized choice of these modules. In this work, an active sub-terahertz scanning system working at 100 GHz frequency is proposed to detect concealed objects in parcels and mail. The system is optimized based on an adapted design of the beam shaper and a preprocessing correction of the images to ensure uniformity of response and cleanness. The proposed system demonstrated through experimentation improved resolution with a uniform response along its detection area.

In photometry, spectrally integrated quantities are commonly used, and their uncertainties are calculated using classical approaches. Since determining correlations at different wavelengths and effects on spectrally integrated quantities is rather complex, a noise modification of the spectral value using Monte Carlo simulation was applied to estimate unknown correlations in the uncertainty of total luminous flux based on integrated spectral luminous flux values. For this aim, an LED with 6500 K correlated colour temperature was measured in an integrated sphere flux measurement system. The correlations between the measurements at different wavelengths were analysed, and the uncertainty boundaries of the integrated quantity and total luminous flux were obtained.

Chirality, an intrinsic property of certain entities in the universe, is characterized by the absence of mirror symmetry. Understanding chirality is crucial as it influences molecular interactions and properties. Circular dichroism (CD), measured using circularly polarized light, is a standard technique for probing chirality, but its sensitivity is often limited. Here, we explore extrinsic chirality (i.e. a property arising from asymmetric achiral materials when observed from out of normal incidence directions), using photo-acoustic spectroscopy (PAS). PAS allows direct measurement of local absorption, by monitoring the heat produced and transferred to the surrounding air, regardless the transmitted, reflected, and scattered light that flows away from the sample. In conventional techniques, the CD is usually measured by taking into account only the extinction as transmitted (or reflected) light. In this study, we introduce a new PAS setup that employs an oblique-incidence laser to study extrinsic chirality in silver-coated self-assembled metasurfaces. Our experimental results reveal intriguing CD trends dependent on the angle of incidence and wavelength, indicative of extrinsic chirality. This study expands the application of PAS, enabling simultaneous analysis of multiple wavelengths and providing valuable insights into chiral metasurfaces.

We report on the experimental investigation, by means of spatially-resolved cathodoluminescence spectroscopy, of rectangular all-dielectric Ge nanoantennas sustaining Fabry-Perot resonances. The combination of spatial and spectral resolution allows us to directly image the standing-wave pattern of the local density of optical states inside the nanoantennas, which is the fingerprint of the resonant Purcell contribution to the overall emission enhancement previously reported in the literature for the same structures. Our results confirm that the emission properties of Ge nanostructures can be effectively tuned by engineering the local density of optical states and that cathodoluminescence provides valuable information to experimentally address such modulation in their emission properties.

Biosensors are becoming ubiquitous in the study of biomolecules, as, by modifying shape size and environment of metallic nanostructures it is now possible to engineer the field so to monitor subtle transient changes in molecular conformation at the level of a single biolayer. In this paper, we present a first step towards a polarization-resolved study of light-induced conformational changes of transmembrane proteins. We exploit a platform of self-organized gold nanorods on SiO2 substrates to enhance the infrared reflection absorption spectroscopy and to perform difference spectroscopy (i.e., spectrum under visible light ON minus spectrum under visible light OFF) on a light-sensitive transmembrane protein with simultaneous visible light illumination from the backside of the chip. The broad size distribution of nanorods allows us to probe with high sensitivity the modifications of the vibrational peaks over the entire fingerprint region. We show that it is possible to identify dissimilarities in the difference spectra, which in turn implies that we are monitoring over a broadband spectrum not only the chemical bonds with the dipole moment aligned orthogonally to our substrate/nanorod surface but also those with different orientation.

An improved algorithm for diffractive optical element (DOE) with high imaging quality is proposed in this paper. The algorithm is designed based on amplitude division between signal and noise regions, further subdivides the noise region into two distinct parts. The image quality in the signal region will be effectively improved by employing a partition-constraint strategy, which imposes amplitude freedom on the first noise region while enforcing strict amplitude constraints on the second noise region. The principle of the algorithm, simulation analysis, and experimental results are presented. The simulation and experimental results demonstrate that the algorithm is feasible.

We present a comprehensive review of recent developments in Spin Orbit Interactions (SOIs) of light in photonic materials. In particular, we highlight progress on detection of Spin Hall Effect (SHE) of light in hyperbolic metamaterials and metasurfaces. Moreover, we outline some fascinating future directions for emergent applications of SOIs of light in photonic devices of the upcoming generation.

Three-dimensional (3D) reconstruction technology is the key technology to establish and express the objective world by using computer, and it is widely used in real 3D, automatic driving, aerospace, navigation and industrial robot applications. According to different principles, it is mainly divided into methods based on traditional multi-view geometry and methods based on deep learning. This paper introduces the above methods from the perspective of three-dimensional space representation. The feature extraction and stereo matching theory of traditional 3D reconstruction methods are the theoretical basis of 3D reconstruction methods based on deep learning, so the paper focuses on them. With the development of traditional 3D reconstruction methods and the development of deep learning related theories, the explicit deep learning 3D reconstruction method represented by MVSNet and the implicit 3D reconstruction method represented by NeRF have been gradually developed. At the same time, the dataset and evaluation indicators for 3D reconstruction were introduced. Finally, a summary of image based 3D reconstruction was provided.

Line-field confocal optical coherence tomography (LC-OCT) is an optical technique based on low-coherence interference microscopy with line illumination, designed for tomographic imaging of semi-transparent samples with micrometer-scale spatial resolution. A theoretical model of the signal acquired in LC-OCT is presented. The model shows that a refractive index mismatch between the sample and the immersion medium causes a dissociation of the coherence plane and the focal plane, leading to a decrease in the signal amplitude and a degradation of the image’s lateral resolution. Measurements are performed to validate and illustrate the theoretical predictions. A mathematical condition linking various experimental parameters is established to ensure that the degradation of image quality is negligible. This condition is tested experimentally by imaging a phantom. It is verified theoretically in the case of skin imaging, using experimental parameters corresponding to those of the commercially available LC-OCT device.

We analysis the noncollinear Spontaneous Parametric Down Conversion (SPDC) and compare the biphotons generated by the chirped Quasi-Phase-Matching (QPM) between the Periodically Poled Lithium Niobate (PPLN) and Periodically Poled KTiOPO4 (PPKTP) crystals. Due to the chirping of the crystals, the frequency response range of the biphotons would be greatly increased. For nonlinear SPDC, angular variation is limited (less than 0.06° in this paper), and the angle would narrow the frequency response range of the biphotons. We compare the effect of angle in PPLN crystals and PPKTP crystals for biphotons. Both the two crystals with chirped QPM, the single-cycle biphotons can be generated during noncollinear SPDC within a suitable angle range, which is favorable for wider applications in experiments.

Surface Plasmon Polaritons (SPPs) in Au thin films are nowadays intensively exploited for sensing applications that leverage the strong optical field confinement at the metal/dielectric interface and the easy functionalization of the Au surface. Moreover, Au thin films represent one of the common starting points for the top-down nanofabrication of plasmonic nanostructures supporting localized resonances. In this framework, strategies for the growth of high-quality Au films on transparent substrates are crucial and not yet fully established. In this study, we exploit MgO(001) substrates for the growth of thin (about 45 nm) Au films, also including an additional buffer layer of Fe. We successfully demonstrate Au samples with reduced roughness and presenting Low-Energy Electron Diffraction (LEED) features, indicating a high degree of crystalline ordering. This is supported by the experimental evidence of an increased (by almost a factor of 3) propagation length compared to a reference Au sample grown on standard glass slides, which is however still significantly lower than the one expected from first principles.

Tailoring nonlinear optical properties at the nanoscale is a hot topic in nowadays nanophotonics, promising for applications spanning from sensing to ultrafast optical communications. Here we present a numerical approach of designing a simple semiconductor nanostructure able to tailor second harmonic emission in the near- and far-field. We start from linear simulations of ZnO nanospheres, which reveal multipolar nature of the scattering. Next, we show how the same nanospheres, with radii in 30–130 nm range, excited at 800 nm, manipulate the directivity of the emitted second harmonic. We observe that the nanospheres which exhibit Kerker condition at 400 nm, emit the second harmonic field in the forward direction. We further investigate how the asymmetry (ellipsoid geometry) tailors the second harmonic directivity. We finally introduce geometry with low chiro-optical response, and observe that the second harmonic far-field depends on the handedness of the light exciting the nanostructure at 800 nm.

A wearable sweat sensor chip based on surface-enhanced Raman spectroscopy (SERS) is here presented. The plasmonic core of the chip, obtained by deposition of silver nanowires on a polytetrafluoroethylene (PTFE) porous membrane, permits the direct and label-free detection of urea and lactate at physiologic concentrations in combination with the pH measurement in the range between 5 and 9. Once integrated with commercial biocompatible and adhesive tape layers, the as produced SERS-active chip provides a low-cost, flexible and wearable sensing device for rapid and reliable human sweat analysis. The chip was finally tested on real sweat samples to estimate lactate and urea during medium-intense exertions.

A spectrophotometric method is demonstrated for refractive index and thickness determination of thin and ultrathin metallic films. The method involves a three-layer stack where the metallic layer of interest is deposited on an opaque Si wafer coated with SiO2. This stack creates oscillations in the reflectance spectrum, which are highly sensitive to the index of the metallic film, allowing precise determination of the index of layers down to 1 nm. Experimental index values are given for Ag and Au over the wavelength range of 370–835 nm. These results are correlated with Atomic force microscopy (AFM) images of the films, which reveal dramatic changes in structure for layers of different thickness.

We study the coupling of a finite number of Bloch Surface Waves (BSWs) propagating in different directions at the surface of a dielectric multilayer. These surface waves arise from a set of diffraction orders associated to a grating on the bottom surface of the substrate that is illuminated by a normally incident beam. Simultaneous excitation of multiple BSWs is possible with a set of diffraction orders having the same radial spatial frequency. Using rigorous electromagnetic theory, we design gratings for simultaneous excitation of two, four and six BSWs propagating in directions separated by π, π/2 and π/3 azimuthal intervals, respectively.

Characterizing the number of sheets in a stack of paper typically involves mechanical separation of the individual sheets. Here, we explore an nondestructive method that can be applied to the intact paper stack. Namely, terahertz time-of-flight tomography, together with post signal-processing technique sparse deconvolution based on a two-step iterative shrinkage-thresholding algorithm (SD/TWIST), is employed to reconstruct the stratigraphy of stacks of sheets of paper with multilayered structure in a nondestructive and noncontact manner. The double-Gaussian mixture model (DGMM) is also incorporated to suppress dispersion in the reflected THz echoes. The effectiveness and accuracy of the proposed adaptive sparse-deconvolution method are verified experimentally and numerically. Compared with the commonly used frequency wavelet-domain deconvolution (FWDD) method and previous implementations of sparse deconvolution based on an iterative-shrinkage and thresholding algorithm (SD/IST), the proposed sparse-deconvolution approach can provide a clearer and rapid stratigraphic reconstruction of the paper stacks studied, while ensuring accurate thickness information for each paper sheet in the presence of noise, revealing the potential usage of real-time THz tomographic-image processing.

This work presents a complete Mueller matrix imaging polarimeter that uses three liquid-crystal retarders and a pixelated polarization camera. The polarimeter is characterized and optimized with a standard correction procedure here adapted to be performed fully in-situ, without any additional element, based on considering the polarization camera as the reference. The accuracy limit caused by the extinction ratio in the camera micro-polarizers is analyzed. Finally, the imaging polarimeter is tested experimentally by analyzing well-known samples for structured light applications such as patterned retarders, a patterned polarizer, and a liquid-crystal depolarizer. The work is presented in a tutorial style useful to reproduce the procedure by non-experts in polarimetry.

We demonstrate the generation of broadband tunable and synchronized pulses exceeding the microjoule level using the new concept of Fiber Optical Parametric Chirped-Pulse Oscillation (FOPCPO). The oscillator is based on a collapsed-ends photonic crystal fiber pumped in the normal dispersion regime by an ytterbium fiber laser delivering highly-chirped pulses. The experimental results are compared with the results of numerical simulations and highlight that the feedback ratio appears as a key parameter for optimizing the system’s efficiency and dynamics.

In this work, we introduce a new bispectral optical cavity concept for which we design twin pairs of highly reflective, ultra-low noise metamirrors. Metasurfaces, artificial structures composed of periodic or quasi-periodic arrays of nanostructures, offer unprecedented control over light properties, paving the way for new applications in areas from high-precision optical metrology to quantum science. Custom phase and an ultra-high reflection coefficient make these metasurfaces an ideal candidate to surpass traditional multilayer mirrors as metamirrors in precision interferometry, particularly by also minimizing thermal noise. The focusing metamirrors designed in this study expect to reflect 99.95% and 99.96% of the incoming light at both, 1064 nm and 1550 nm wavelength. Their planar counterparts even reach theoretical reflectivities of 99.9999% (1064 nm) and 99.9995% (1550 nm). These specialized metamirrors enable bispectral low-noise optical cavities, which would reduce the number of cavities in optical experiments or could be used as a versatile transfer cavity for frequency locking.

In this article we describe the implementation of Freeform Optics Raytracer with Manufacturable Imaging Design cApaBiLitiEs (FORMIDABLE): an optical design library capable of simulating optical systems by ray-tracing. Optical performance can be quantified and optimised using third-party optimisation algorithms. Compared to available commercial optical design software and similarly to fast accurate NURBS optimization (FANO), our code can simulate and optimise Non-uniform rational B-Spline (NURBS). It also implements generalized differential capabilities that allows faster convergence compared to state-of-the-art. The implementation of FORMIDABLE and its innovative capabilities are described and illustrated with a representative case-study. The source code is available to eligible third-parties under the ECSL licence.

Considering the serious risks posed by the heavy metals present in pig diets, monitoring and controlling the amount of these metals is crucial. The laser-induced breakdown spectroscopy (LIBS) is a promising technique for performing elemental analysis due to its unique advantages, such as rapid, in situ, nondestructive, and online detection of various minerals. In order to improve the detection accuracy and detection limit (LOD) of elements, the spatial constraint combined with laser-induced breakdown spectroscopy (CC-LIBS) is used to detect the quantity of zinc in pig feed and achieve the detection of samples with lower concentrations. Zn I 480.86 nm is selected as the characteristic spectral line, and the effects of different two-dimensional (cylindrical) and three-dimensional (hemispherical, truncated cone) cavities on the enhancement factor are compared under different time delays. The results show that the optimal conditions include a truncated cone cavity D5H3, a delay time of 2.08, and an enhancement factor of 3.01 associated with the analytical spectral line. The detection limit of zinc in samples under CC-LIBS is 62.67 mg/kg (the recommended quantity of zinc in pig diet mentioned in the safe use of feed additives is 43–80 mg/kg), which is 35.65% lower than that under the LIBS (97.39 mg/kg). Therefore, this work provides a new test basis and idea for the detection of zinc in pig feed.

Abstract Binary defocusing technique can effectively break the limitation of hardware speed, which has been widely used in the real-time three-dimensional (3D) reconstruction. In addition, fusion technique can reduce captured images count for a 3D scene, which helps to improve real-time performance. Unfortunately, it is difficult for binary defocusing technique and fusion technique working simultaneously. To this end, our research established a novel system framework consisting of dual projectors and a camera, where the position and posture of the dual projectors are not strictly required. And, the dual projectors can adjust defocusing level independently. Based on this, this paper proposed a complementary decoding method with unconstrained dual projectors. The core idea is that low-resolution information is employed for high-resolution phase unwrapping. For this purpose, we developed the low-resolution depth extraction strategy based on periodic space-time coding patterns and the method from the low-resolution order to high-resolution order of fringe. Finally, experimental results demonstrated the performance of our proposed method, and the proposed method only requires three images for a 3D scene, as well as has strong robustness, expansibility, and implementation.

Abstract Two simulation programs of a stimulated Raman scattering microscopy (SRS) imaging system with lock-in amplifier (LIA) detection were developed. SRS is an imaging technique based on the vibrational Raman cross-section as the contrast mechanism and enables fast, label-free imaging. Most SRS implementations are based on LIA detection of a modulated signal. However, building and operating such SRS set-ups still poses a challenge when selecting the LIA parameter settings for optimized acquisition speed or image quality. Moreover, the type of sample, e.g. a sparse sample vs. a densely packed sample, the required resolution as well as the Raman cross-section and the laser powers affect the parameter choice. A simulation program was used to find these optimal parameters. The focal spot diameters of the individual lasers (pump and Stokes) were used to estimate the effective SRS signal focal spot and the (optical) spatial resolution. By calibrating the signal and noise propagation through an SRS system for a known molecule, we estimated the signal and noise input to the LIA. We used a low pass filter model to simulate the LIA behavior in order to find the optimal parameters (i.e. filter order and time constant). Optimization was done for either image quality (expressed as contrast to noise ratio) or acquisition time. The targeted object size was first determined as a measure for the required resolution. The simulation output consisted of the LIA parameters, pixel dwell time and contrast to noise ratio. In a second simulation we evaluated SRS imaging based on the same principles as the optimal setting simulation, i.e. the signals were propagated through an imaging system and LIA detection. The simulated images were compared to experimental SRS images of polystyrene beads. Finally, the same software was used to simulate multiplexed SRS imaging. In this study we modeled a six-channel frequency-encoded multiplexed SRS system demodulated with six LIA channels. We evaluated the inter-channel crosstalk as a function of chosen LIA parameters, which in multiplex SRS imaging also needs to be considered. These programs to optimize the contrast to noise ratio, acquisition speed, resolution and crosstalk will be useful for operating stimulated Raman scattering imaging setup, as well as for designing novel setups.

Abstract One of the unique properties of metamaterials is the ability to manipulate electromagnetic waves at subwavelength scales, made possible by their structure on these scales. Here, rather than consider effective bulk properties, we consider the properties of microscopic features based on considering resonant unit cells. We used wire array metamaterials to form localized resonant cavities by changing the resonance frequency of one or more unit cells, surrounded by unchanged unit cells that do not support resonance for the propagating mode (i.e. forming a band gap). We validate our approach experimentally with electromagnetic waves in the terahertz range, demonstrating and characterizing subwavelength resonant cavities in this range. These resonant cavities can pave the way for ultra-compact subwavelength waveguides and other optical components.

Abstract Inorganic metal halide perovskites are relevant semiconductors for optoelectronic devices. The successful deposition of thin films of CsPbBr3 and CsPbCl3 has recently been obtained by Radio-Frequency magnetron sputtering. In this work we compare the morphological, structural and optical characteristics of the two materials obtained with this deposition technique. A detailed photoluminescence (PL) spectroscopy study of the as-grown samples was conducted at the macro and micro scale in a wide temperature range (10-300 K) to fully characterize the PL on sample areas of square centimeters, to assess the origin of the inhomogeneous broadening and to quantify the PL quantum yield quenching. Our results prove that this technique allows for the realization of high quality nanometric films with controlled thickness of relevance for optoelectronic applications.

Abstract In this work, a scheme of combining an aspheric reflector and a primary packaging freeform lens in phosphor-converted lighting-emitting diode (pc-LED) based lighting system design was developed. In contrast to most of previous works in which the color and illumination uniformity of the pc-LED lighting systems were improved one by one, the developed scheme can improve both indicators simultaneously. To demonstrate the feasibility of the developed design scheme, an initially designed pc-LED optical model, with an average correlated color temperature (CCT) of about 5000 K, was constructed as the light source of the illumination system. The key ingredient to the color uniformity of the illumination system was investigated at first, and then several instances with the cut-off angle ranging from 40 to 60 degrees were further discussed. Detailed analysis shows: for each case, the CCT variation decreases from over 4000 K to smaller than 300 K and the illumination uniformity increases from a very low level to better than 80% on the target region.

Abstract In this publication, the Luneberg integrals are revisited and the conditions of the using of such integrals have been recalled. Additivity law of Luneberg’s integrals and the link with the Frenel kernel for the propagation are discussed. By means of the definition of the Luneberg’s integrals, the propagation of a vectorial electromagnetic field (Hertz potentials) is developed and a new approach of the computation have been proposed based on Zernike polynomials. With this new approach simulations of holograms is illustrated in the case of the digital in-line holography with an opaque disk.

Abstract We report on the design, growth, fabrication, and performance of InAs/InP quantum dash (QD) multi-wavelength lasers (MWLs) developed by the National Research Council (NRC) Canada. The key technical specifications investigated include optical and RF beating spectra, relative intensity noise (RIN), and optical phase noise of each individual wavelength channel. Data bandwidth transmission capacity of 5.376 Tbit/s and 10.8 Tbit/s respectively in the PAM-4 and 16-QAM modulation formats are demonstrated using only a single C-band QD 34.2-GHz MWL chip. We have also developed a monolithic InAs/InP QD dual-wavelength (DW) DFB laser as a compact optical beat source to generate millimeter-wave (MMW) signals. Due to the common cavity, highly coherent and correlated optical modes with optical linewidth as low as 15.83 kHz, spectrally pure MMW signals around 46.8 GHz with a linewidth down to 26.1 kHz were experimentally demonstrated. By using this QD DW-DFB laser, a one GBaud (2 Gbps) MMW over-fiber transmission link is demonstrated with PAM-4 signals. The results show that the demonstrated device is suitable for high speed high capacity MMW fiber-wireless integrated fronthaul of 5G networks.

Abstract In modern high resolution optical systems like astronomical telescopes or lithographic objectives, performance degradations can be caused by various disturbances. Holistic optical system simulation is required to predict the performance or the high precision systems. In this paper a method for transient dynamical-thermal-optical system modeling and simulation is introduced. Thereby, elastic deformation, rigid body motion, and mechanical stresses due to dynamical excitation are calculated using elastic multibody system simulation and temperature changes are determined using thermal finite element analysis. The deformation, the motion, and the mechanically and thermally induced stress index changes are then considered in a gradient-index ray tracing. Finally, the presented method is applied in a dynamical-thermal single lens system.

Abstract This study proposes using double-layer wire-grid structures to create narrow-band, perfect plasmonic absorbers, which depend on polarization, for the short-wavelength visible and near-ultraviolet regions of the electromagnetic spectrum. A rigorous coupled-wave analysis reveals that the maximum absorption attained using Ag and Al is ~ 90% at 450 and 375 nm. Experiments using Ag yielded results similar to those predicted by simulations. These results demonstrate that narrow-band perfect plasmonic absorbers, which depend on the polarization, can be realized at 450 and 375 nm using Ag or Al.

Abstract In this report we present a confocal Raman system to identify the unique spectral features of two proteins, Interleukin-10 and Angiotensin Converting Enzyme. Characteristic Raman spectra were successfully acquired and identified for the first time to our knowledge, showing the potential of Raman spectroscopy as a non-invasive investigation tool for biomedical applications.

Abstract Polarizing beamsplitters have numerous applications in optical systems, such as systems for freeform surface metrology. They are classically manufactured from birefringent materials or with stacks of dielectric coatings. We present a binary subwavelength-structured form-birefringent diffraction grating, which acts as a polarizing beamsplitter for a wide range of incidence angles −30∘…+30∘. We refine the general design method for such hybrid gratings. We furthermore demonstrate the manufacturing steps with Soft-UV-Nanoimprint-Lithography, as well as the experimental verification, that the structure reliably acts as a polarizing beamsplitter. The experimental results show a contrast in efficiency for TE- and TM-polarization of up to 1:18 in the first order, and 34:1 in the zeroth order. The grating potentially enables us to realize integrated compact optical measurement systems, such as common-path interferometers.

Abstract In this work, we present our results about the thermal crystallization of ion beam sputtered hafnia on 0001 SiO2 substrates and its effect on the laser-induced damage threshold (LIDT). The crystallization process was studied using in-situ X-ray diffractometry. We determined an activation energy for crystallization of 2.6 ± 0.5 eV. It was found that the growth of the crystallites follows a two-dimensional growth mode. This, in combination with the high activation energy, leads to an apparent layer thickness-dependent crystallization temperature. LIDT measurements @355 nm on thermally treated 3 quarter-wave thick hafnia layers show a decrement of the 0% LIDT for 1 h @773 K treatment. Thermal treatment for 5 h leads to a significant increment of the LIDT values.