Table of contents

The strong light–matter interaction between the exciton of atomically thin transition metal dichalcogenides (TMDCs) and photonic nanocavities leads to the formation of unique hybrid light-matter quasiparticles known as exciton-polaritons. The newly formed mixed state has the advantages of the photonic part such as rapid propagation and low effective mass and the highly desirable optical properties of TMDC's exciton, including the interparticle strong interactions nonlinearity and spin-valley polarization. These joint properties make such systems an ideal platform for studying many compelling physics phenomena and open the possibility of designing novel optoelectronic devices. This work reviews recent progress of strong coupling between exciton in TMDC and different resonant photonic structures, such as optical microcavities, plasmonic and all-dielectric nanocavities. Furthermore, we discussed the unique valleytronic and nonlinear properties of TMDC monolayers in the strong coupling regime. Finally, we highlighted some of the challenges and potential future research opportunities in this field.

We present a microscopic study of water–dimethyl sulfoxide (DMSO) binary mixtures using optical tweezers and thermal lens techniques. Binary mixtures of DMSO with water show anomalous behavior due to the specific hydrogen bonding ability of DMSO. We use a tightly focused femtosecond laser at a low average power to optically trap microspheres with diameters of 1 micron for use as probes. The binary mixture exhibits various viscosities, depending on its composition ratio, and hence different trapped particle characteristic frequencies (corner frequencies) due to Brownian motion. The power spectrum density method is used to obtain the corner frequency from forward-scattered data. Thus, using low-power optical tweezer experiments, we find that the maximum viscosity occurs at a DMSO mole fraction of 0.276. At higher powers, the propensity for trapping is highly diminished. It may be surprising to note that these viscosity values obtained from the corner frequencies do not exactly match those published in the literature. However, this deviation can be attributed to the thermal behavior of the binary mixture, which affects the Brownian motion and hence the obtained viscosity values. Studies at the microscopic level can thus provide a newer perspective on these already important binary mixtures. Intensity-dependent measurements further confirm the contribution of thermal effects in this study.

The transformation of normal cervix to cervicitis as well as to cervical cancer is accompanied with biochemical alterations at cellular level. Laser induced fluorescence (LIF) can reflect those changes either as variations in the fluorescence intensity or as shift in the fluorescence maxima of bio fluorophores present in tissues. The curve resolved fluorescence investigation of tissues under 325 nm excitation provides collagen, bound nicotinamide adenine dinucleotide (NADH) and free NADH as the discrimination factors between normal, cervicitis and cervical cancer. Even though the fluorescence emission intensity derived from collagen fiber is comparable in both normal and cervicitis, a considerable reduction was observed for the cervical cancer tissues compared to the former. Fluorescence corresponding to bound NADH is found to be reduced during the progression from normal to cervicitis and to cervical cancer, whereas the free NADH shows an opposite trend. The principal component analysis (PCA) was performed to obtain classification of spectral data from different categories on a reduced dimensional space. Furthermore, to test the usefulness of the recorded fluorescence spectra in discriminating the malignant and non-malignant (cervicitis and normal) samples, a supervised machine learning model based on support vector machine (SVM) was built using the PCA-reduced data. The proposed SVM model was able to detect the malignant samples with a sensitivity of 94.19% and specificity of 96.51%. Moreover, the Raman spectral data from the corresponding tissue sites corroborate well with the observations derived from the fluorescence measurement. The results obtained in the present pilot study strongly suggests the potential of LIF technique combined with multivariate data analysis tool for the diagnosis of cervicitis and cervical malignancy.

Hybrid entangled states exhibit non-local correlations between photons with independent degrees of freedom and are currently gaining much interest. In particular, hybrid entanglement between polarisation and spatial modes of two photons are promising candidates for future heterogeneous quantum channels, but their versatility is limited by current generation methods that rely on static elements. Here, we present a technique that exploits polarisation and spatial mode dependent phase modulation in an all-digital approach using spatial light modulators. We show that we can tailor hybrid entangled states using spatial modes with Cylindrical and Cartesian symmetry, making our approach flexible, dynamic, and adaptable.

Voltage imaging and optogenetics offer new routes to optically detect and influence neural dynamics. Optimized hardware is necessary to make the most of these new techniques. Here we present the Octoscope, a versatile, multimodal device for all-optical electrophysiology. We illustrate its concept and design and demonstrate its capability to perform both 1-photon and 2-photon voltage imaging with spatial and temporal light patterning, in both inverted and upright configurations, in vitro and in vivo.

Alzheimer's disease (AD) is a neurodegenerative disease, characterized by the presence of extracellular deposits (plaques) of amyloid-beta peptide and intracellular aggregates of phosphorylated tau. In general, these hallmarks are studied by techniques requiring chemical pre-treatment and indirect labeling. Imaging techniques that require no labeling and could be performed on tissue in its native form could contribute to a better understanding of the disease. In this article a combination of label-free and non-invasive techniques is presented to study the biomolecular composition of AD human brain tissue. We build on previous research that already revealed the autofluorescence property of plaque, and the presence of carotenoids in cored plaques. Here, we present further results on cored plaques: showing blue and green autofluorescence emission coming from the same plaque location. Raman microscopy was used to confirm the presence of carotenoids in the plaque areas, with clear peaks around 1150 and 1514 cm⁻¹. Carotenoid reference spectra were recorded in hexane solution, but also adsorbed on aggregated Aβ42 peptides; the latter agreed better with the Raman spectra observed in plaques. From the six single carotenoids measured, lycopene matched closest with the peak positions observed in the cored plaques. Lastly, stimulated Raman scattering (SRS) microscopy measurements were performed, targeting the shift of the beta-sheet Amide I peak observed in plaques. Employing SRS in the C–H stretch region we also looked for the presence of a lipid halo around plaque, as reported in the literature for transgenic AD mice, but such a halo was not observed in these human AD brain samples.

Spin–orbit interaction deals with the interaction and coupling of spin and orbital angular momentum degrees of freedom of spinning particles, which manifests in diverse fields of physics, ranging from atomic, condensed matter to optical systems. In classical light beams, this has led to a number of non-trivial optical phenomena like spin and orbital Hall effect of light, optical Rashba effect, photonic Aharonov–Bohm effect, rotational Doppler effect, transverse spin, Belinfante's spin-momentum and spin-momentum locking etc. These have been observed in diverse micro- and nano-scale optical systems. These have generated a new area in photonics, namely, spin-orbit photonics that not only deals with fundamental light–matter interaction effects but also opened up the feasibility of a new generation of miniaturized and on-chip integrable multifunctional photonic devices based on the angular momentum and geometrical phase of light. This paper will introduce the emerging field of spin-orbit photonics and will cover the representative spin-orbit photonic effects in a variety of light-matter interactions with examples. In this regard, we also present proof-of-concept demonstrations of two interesting techniques based on the geometrical phase of light, namely, geometrical phase polarimeter and weak value polarimeter.

The unique three-dimensional (3D) deformations caused by nano-kirigami have enabled a new degree of freedom for reconfigurable optics. Here, we demonstrate a facile nano-kirigami method that can create 3D deformed structures, which can flexibly manipulate optical properties using thermally actuated micro-/nanoscale deformations. By connecting four pairs of thermal actuators to the four sides of a gradient metasurface, large-angle beam steering (∼90°) can be achieved by adjusting the temperature of the actuators. The amplitude of circular dichroism can be adjusted by thermally actuating micro-/nanoscale deformations. The 2D-to-3D transformation of the curved arm structure on metallic substrate results in enhanced structural absorption, inducing an almost perfect absorption at specific wavelengths. Curved asymmetric structures can also be created by thermally actuated micro-/nanoscale deformations, which provides a novel method for cross-polarized light conversion. The proposed design with thermally actuated micro-/nanoscale deformations provides a new methodology to explore versatile reconfigurable functionalities.

The present work aims to understand the signal enhancement observed in nanoparticle (NP)-enhanced laser induced breakdown spectroscopy (NELIBS) due to changes in the plasma parameters as a result of improved atomization and excitation. A systematic study on signal enhancements during NELIBS using simultaneous spectroscopy and imaging is investigated by varying the experimental parameters like particle size and laser fluence. We have observed similar enhancements in spectroscopy and imaging channels regardless of NP size at different laser fluences. Although the plume size in NELIBS was marginally more prominent than the LIBS at the same laser fluence, the corresponding intensity in NELIBS is significantly higher. This agrees with the hypothesis of efficient atomization and excitation of plasma in the case of NELIBS. Therefore, we performed a sensitivity analysis using simulated LIBS signal to understand changes in experimentally observable plasma parameters (excitation temperature and electron number density) on signal enhancement. We have shown that the enhancements in the emission intensities of typically one order of magnitude can be explained as a result of the change in electron number density and plasma temperature. A comparison of the expected enhancement due to this change with experimental observation for a Cu I line is also presented.

Bound states in the continuum (BICs) are localized states despite in a radiation continuum, rendering the ultra-high quality factor for enhanced light–matter interactions and supporting exotic topological properties. So far, most of studied BICs in photonic crystal (PhC) slabs are only vertically localized, i.e. allowing propagations in the plane of slab therein but forbidding radiations, and the density of optical states (DOS) at their frequencies is limited due to the steep dispersion characteristics. Here, we report a BIC existing on a flatband of symmetry-broken PhC slab. The flatband, associated with largely reduced group velocity, significantly sharpens the DOS at the frequency of BIC, which can be realized via finely controlling broken vertical symmetry in the PhC slab. The effect of broken symmetry is revealed in a simple effective Hamiltonian near the second-order Γ point of such system. Our results show the simultaneous engineering of dispersion and leaky characteristics of modes, offering new opportunities to boost light–matter interactions and to enhance the performance of photonic devices.

Black phosphorus (BP), a new type of two-dimensional material, has attracted extensive attention because of its excellent properties. The anisotropy of BP makes its physical properties vary greatly in different directions, which increases the complexity of the design of BP metamaterials. We present a residual neural network on the basis of the improved adaptive batch normalization algorithm to achieve the inverse design of a multilayer thin film structure based on BP, and we adopt the characteristic matrix method to obtain perfect optical absorption samples. The prediction accuracy of the neural network model is more than 95% for absorbing structures with both single and multiple resonances. This method has the advantages of a fast rate of convergence and high precision of prediction and achieves the design target on the basis of the structure of a BP metamaterial.

The fabrication steps for an air-clad photonic lantern that can excite the first two LP mode groups in a multimode fiber are presented in this paper. A multiplexing crosstalk below −16.8 dB is measured on the fabricated lantern using S² imaging technique over a wavelength of 1525–1575 nm. The de-multiplexing crosstalk is measured for both LP₀₁ and LP₁₁ mode groups as −16.8 dB and −9.4 dB respectively using loss measurements. $2\times40$ Gbs⁻¹ MIMO-less mode division multiplexing (MDM) transmission through 7 m of two mode step index fiber is demonstrated using the fabricated photonic lanterns. $2\times10$ Gbs⁻¹ MIMO-less MDM transmission through 1.6 km standard 50/125 µm multimode fiber is also demonstrated and a Q value higher than 3.7 is obtained for both spatial channels over all input polarizations. Simple intensity modulation and direct detection schemes are used for these MDM transmissions.

We report our studies on ytterbium doped fiber laser passively Q-switched by fiber optic ring resonator in all-fiber format. The Q-switched laser characteristics viz. pulse duration, pulse profile, repetition rate and average power are easily varied not only by pump power but also by changing the polarization state of light inside the laser resonator with the help of polarization controllers. At 330 mW pump power, the laser generates 1.07 μs duration pulses with 0.68 μJ pulse energy at 83.6 kHz repetition rate. The Q-switched laser wavelength is tunable from 1059 to 1069.7 nm by changing the polarization state inside the cavity.

The properties of electron round lenses produced by the ponderomotive potential are investigated in geometrical optics. The potential proportional to the intensity distribution of a focused first-order Bessel or Laguerre–Gaussian (LG) beam is exploited to produce an electron round lens and a third-order spherical aberration (SA) corrector. Several formulas for the focal length and SA coefficients in the thin-lens approximation are derived to set the lens properties and associated light beam parameters. When the mode field of the optical beam is small, the electron trajectory calculation results show properties similar to those obtained using the formulas. Alternatively, large higher-order aberrations are introduced because of the annular distribution of the potential. The second- and higher-order Bessel and LG beams produce no focusing power and no negative third-order SA; however, they can still be used as circularly symmetric higher-order aberration correctors. Results show that the ponderomotive potential–based electron lens or phase plate forms a refractive index medium with a shape that is considerably more flexible than that achieved in the case of conventional electrostatic and magnetic electron optics. The formulas presented herein can serve as guidelines for designing preferred light fields, thus promoting the advancement of a novel technology in electron optics that exploits the electron–light interaction.

Plasma produced from molten-tin microdroplets generates extreme ultraviolet light for state-of-the-art nanolithography. Currently, CO₂ lasers are used to drive the plasma. In the future, solid-state mid-infrared lasers may instead be used to efficiently pump the plasma. Such laser systems have promise to be more compact, better scalable, and have higher wall-plug efficiency. In this Topical Review, we present recent findings made at the Advanced Research Center for Nanolithography (ARCNL) on using 1 and 2 µm wavelength solid-state lasers for tin target preparation and for driving hot and dense plasma. The ARCNL research ranges from advanced laser development, studies of fluid dynamic response of droplets to impact, radiation-hydrodynamics calculations of, e.g. ion 'debris', (EUV) spectroscopic studies of tin laser-produced-plasma as well as high-conversion efficiency operation of 2 µm wavelength driven plasma.

Bound states in the continuum (BICs) have emerged as a significant design principle for producing systems with high-quality (Q) factor states to enhance light–matter interactions. As a particular case, symmetry-protected BICs are flexible to be designed, commonly by utilizing two identical lossless dielectric elements. Herein, different from previous studies, we propose symmetry-protected BICs in a plasmonic structure of two contacting graphene nanoribbons (GNRs), in which two GNRs are not identical and lossy. We show that BICs are achieved when two GNRs are perpendicular to each other, and as the vertical GNR deviates from the vertical direction (inversion symmetry breaking), it will evolve into quasi-BICs, with a new resonance dip appearing in the transmission spectrum. The spectrum curve can be well described by the coupled-mode theory, from which the variation of two fundamental states is clearly seen. Since in the presence of internal loss, the Q-factor of quasi-BICs does not follow the linear formula that is generally valid for symmetry-protected BICs. Alternatively, an extended formula is derived, which predicts exactly the behavior of the Q-factor of quasi-BICs. Besides BICs, the structure can also support plasmonically induced transparency (PIT) like effects, through rotating the vertical GNR to a particular angle. Therefore, a mechanically tunable switch, from BIC to PIT, is achieved here. Our work demonstrates an alternative scheme for BICs, and a new degree of freedom for tuning plasmonic coupling related effects.

Although numerous studies showcase the capability of metalenses to serve as crucial elements of miniaturized optical systems, tunable focusing remains an ongoing challenge. Here, we propose a doublet zoom lens based on a Ge₂Sb₂Te₅ (GST) metasurface at a wavelength of 1.55 μm. Multistep zooming is realized by the joint control of incident circular polarization inversion and GST phase transition. Three tight focal spots, 0.91 λ, 1.09 λ and 0.89 λ, are achieved from the composite lens. The devised highly-integrated doublet lens, with advantages such as as being multi-foci, easily operated and responding quickly, can find applications in fields that require ultracompact zoom imaging and beam focusing.

Terahertz sensing is one of the most promising methods for label-free and noninvasive detection of refractive index changes. However, the figure of merit (FOM) of terahertz sensors in practical applications has been low. In this paper, a metamaterial sensor based on simple stacking of gold and silicon dioxide is proposed, through whose structure not only narrow-band absorption with five absorption peaks is realized, but FOM is also improved to 1792. The excellent sensing performance and the mature manufacturing technology of this kind of structure provide a platform for the design of multi-band photodetectors and high-sensitivity sensors.

Leveraging the traditional transfer matrix and stationary phase methods, the nonreciprocal Goos–Hänchen (GH) phenomena for the electromagnetic (EM) waves reflected at the surface of the one-dimensional photonic crystals with ferrite layers and dielectric layers are investigated numerically. The GH effect (the peak of the lateral shift value up to over 200 times the wavelength) produced by the forward and backward incidence of EM waves under the transverse electric wave is identified to arise at significantly different frequency positions in the terahertz (THz) regime, whereas the transverse magnetic wave produces almost no GH effect under the same condition. Based on such a nonreciprocal phenomenon, the effect of the incident angle on the nonreciprocal properties is covered initially, for every 20° increase in the angle of the incident TE wave, the frequency span at which the two GH shift peaks emerge will decrease by 0.1 THz. In addition, the thicknesses of dielectric layers are modified separately, and distinct sensitivities of them to the nonreciprocal phenomenon are displayed. Lastly, through the regulation of the external magnetic fields of ferrite layers, the nonreciprocal effect can be selectively presented in multiple forms, which provides a novel pathway to design nonreciprocal sensors.

A controllable multi-frequency absorption structure predicated on a one-dimensional magnetized ferrite photonic crystals (MFPCs) that achieves coherent perfect absorption is designed and further analyzed by utilizing the transfer matrix method. By introducing the filter structures to the MFPC and using the gradient descent optimization algorithms to optimize its layer parameters, the multi-frequency coherent absorption curve is obtained. The suggested MFPC brings out about six absorption peaks whose absorptance can be higher than 0.99 at the same time under the transverse electric mode. Moreover, the absorptance can be regulated from 0.99 to less than 0.1 by merely changing the phase deviation between the two incident waves to the front and rear surfaces. Besides, the studied results demonstrate that the intensity of coherent absorption and the position of absorption peaks can be adapted by altering the magnetic field and the thicknesses of ferrite layers. It follows that the absorption peaks can cover most frequency points from 58.6 to 65.9 THz via changing the thicknesses of the external magnetic field and ferrite layers. Moreover, the structure also has the potential for wide-angle absorption. This research furnishes a significant reference for the design of the multi-frequency absorption optoelectronic device and phase sensor.

Hyperspectral resolution, high spatial resolution, and a wide field of view (FOV) are the targets of optical spectral microscopy imaging. However, hyperspectral microscopy imaging technology cannot provide a wide FOV and a high spatial resolution at the same time. Fourier ptychographic microscopy (FPM) is a novel microscopy imaging technique that uses LEDs at varying angles to capture a series of low-spatial-resolution images that are used to recover images that have both high spatial resolution and a wide FOV. Since FPM cannot obtain the spectral resolution of the sample, in this paper, an efficient strategy based on the FPM system is proposed for the reconstruction of hyperspectral images. First, the traditional FPM setup is optimized, with a new experimental setup based on halogen lamp illumination and a narrow band-pass filter to capture a series of low-spatial-resolution images at different wavelengths. Second, a new algorithm, combining hyperspectral resolution imaging using interpolation compensation and a phase retrieval algorithm, is proposed to reconstruct high-spatial-resolution, wide FOV, and hyperspectral resolution images. Finally, we verified the feasibility and effectiveness of our experimental setup and algorithm by both simulation and experiment. The results show that our method can not only reconstruct high-spatial-resolution and wide FOV images, but also has a spectral resolution of 5 nm.

Hybrid optical elements, which combine refractive and diffractive optical components to enhance optical performance by taking advantage of the optical characteristics of the individual components, have enormous potential for next-generation optical devices. However, there have not been many reports on the simulation methodology to characterize such hybrid optical systems. Here, we present a method for simulating a hybrid optical element realized by attaching an ultra-thin, flexible diffractive optics array onto a refractive optical element. The ultra-thin diffractive optical element is fabricated by direct-laser-writing using a femtosecond pulsed laser as the light source. A systematic investigation of the proposed simulation method, which does not require extensive hardware resources or computational time, but retains resolution and accuracy, is presented. The proposed scheme is validated by comparing simulation and experimental results. The simulation and experimental results on the spot size and focal length for the diffractive Fresnel zone plate (FZP) match well, with typical errors of less than 6%. The aspect ratio of the focal spot sizes at the compound and FZP focal planes of the hybrid optical system from the simulation and experiment also match quite well, with typical errors below 7%. This simulation scheme will expedite the designs for novel hybrid optical systems with optimal optical performances for specific applications, such as microfluidics and aberration-controlled optics.

We address the dynamics of two-dimensional (2D) truncated Airy waves (TAWs) and three-component solitons in the system of two fundamental-frequency (FF) and second-harmonic (SH) fields, coupled by quadratic ($\chi ^{(2)}$) terms. The system models second–harmonic-generating optical media and atomic-molecular mixtures in Bose–Einstein condensates. In addition to stable solitons, the system maintains truncated-Airy-waves states in either one of the FF components, represented by exact solutions, which are stable, unlike the Airy waves in the degenerate (two-component) $\chi ^{(2)}$ system. It is also possible to imprint vorticity onto the 2D Airy modes. By means of systematic simulations, we examine interactions between TAWs originally carried by different FF components, which are bending in opposite directions, through the SH field. The interaction leads to fusion of the input into a pair of narrow solitons. This is opposed to what happens in the 1D system, where the interacting Aity waves split into a large number of solitons. The interaction of truncated Aity waves carrying identical imprinted vorticities creates an additional pair of solitons, while opposite vorticities create a set of small-amplitude 'debris' in the output. Slowly moving solitons colliding with a heavy TAW bounce back, faster ones are absorbed by it, and collisions are quasi-elastic for fast solitons. Soliton-soliton collisions lead to merger into a single mode, or elastic passage, for lower and higher velocities, respectively.

We apply time dependent spectral phase modulation to generate pulse trains that are spectrally and temporally partially coherent in an ensemble averaged sense. We consider, in particular, quadratic spectral phase modulation of Gaussian pulses, and demonstrate two particular types of nonuniformly correlated pulse trains. The controlled partial temporal coherence of the nonstationary fields is generated using a pulse compressor and experimentally verified with frequency resolved optical gating (FROG). We show that the correlation characteristics of such pulse trains can be retrieved directly from the FROG spectrograms provided one has certain a priori knowledge of the pulse train. Our results open a pathway for experimental confirmation of several correlation induced effects in the temporal domain.

A highly nonlinear single mode anomalous dispersion silicon-core fiber is designed and optimized at the operating wavelength of 2.2 µm for the purpose of generating stable temporal pulse doublets. To designate the output pulse pair as a perfect Gaussian doublet, two new parameters, dissimilarity factor (${\rho _g}$) and co-similarity index (μ_cs) are introduced. Different input pulse parameters such as power, pulse width and chirp are optimized to obtain Gaussian temporal doublets at the shortest optimum length (∼few cm) which is sufficiently smaller in comparison to silica fibers reported earlier. The output pulse pairs remain as a doublet for quite a good stability length. In view of serving practical purposes, the possibilities of fluctuations of input power and pulse width are included to investigate the changes in stability length and effective repetition rate (ERR). The change in ERR along the fiber length produces a remarkable change in free carrier concentration in core, which has also been taken into account for the first time as per our knowledge to obtain the temporal pulse doublet in the so designed Si-core fiber.

This article presents the generation and propagation dynamics of a high power Gaussian soliton beam through a highly nonlocal nonlinear media having cubic-quintic nonlinearity. Solitons are also generated with lesser explored Hermite super-Gaussian, Hermite cosh-Gaussian and Hermite cosh-super-Gaussian beam profiles. The governing nonlocal nonlinear Schrödinger equation yields matching solitons analytically using variational method as well as numerically using split-step Fourier method. Linear stability analysis identifies the parametric space for stability of the solitons against small perturbation. The variation of the system parameters leads to the bifurcation of the beam beyond a critical point. A parametric zone of bifurcation is identified. Some of the solitons are bistable too. The influence of quintic nonlinearity on generation, propagation and bifurcation is highlighted.

As a beam splitter, multi-value phase grating (MVPG) has a higher diffraction efficiency than the traditional Damman grating (DG) due to its increased number of phase values within one period of the grating. In this paper, two MVPGs are numerically designed within a 120 μm × 120 μm area, which generate 4 * 4 and 5 * 5 focal spot arrays in the far field. Both gratings are fabricated by direct laser writing (DLW) technology. Their diffraction efficiencies reach 68.58% and 63.4%, respectively. To compare, DGs with the same size and focal spot arrays are designed and fabricated, whose diffraction efficiencies are tested to be 29.55% and 35.04%, respectively. The results demonstrate the better optical properties of multi-value phase gratings and the capability of DLW in three-dimensional nano-scale diffractive optical element fabrication.

In this paper, the radially polarized (RP) new kind of power-exponent-phase vortex (NPEPV) beam, with rotationally symmetrical phase structure, was introduced and the tightly focused properties of the RP NPEPV beam passing through a high numerical aperture objective lens were studied numerically. The results show that with the increase of topological charge l, there are multiple intensity points in the focal region, and the number is consistent with the topological charge. In addition, as the power order n increases, the light intensity gradually concentrates on the central optical axis and the surrounding intensity points gradually disappear, which finally presents a Gaussian intensity distribution with the dark cores gradually move away from the optical axis and disappear. These unique properties will have potential applications in particle trapping and laser fabrication, especially for simultaneous trapping of multiple particles and fabrication of chiral microstructures.

The orbital angular momentum (OAM) of light has garnered significant interest in recent years owing to its various applications, and extensive creative research has been conducted to generate OAM. However, the particular helical phase structure of an optical vortex leads to nonsmooth and discontinuous phase profiles and hinders the accurate recovery of the phase distribution of the vortex beam. Significantly, the existence of a wavefront dislocation leads to the failure of the traditional phase unwrapping algorithm. At the same time, it is essential to detect the wavefront of OAM modes in real-time for free-space optical communication and optical precision measurement. Therefore, we designed conformal mapping–spatial phase-shifting interferometry and achieved rapid and high-precision wavefront measurements for the OAM modes. The wavefront of the OAM modes with a topological charge of 1, 2, 4 and 6 were measured, respectively. The results were significantly consistent with the anticipated results based on simulations. This study reveals the mathematical mechanism behind the forked fringe patterns and presents a method for demodulating the helical wavefront from the forked fringe patterns.

Image quality evaluation is a key factor in the advancement and improvement of display technology, which could lead to effective improvement through the evaluation result from various aspects to achieve the better result further. However, display principles and image characteristics should be considered for Image quality evaluation. For three-dimensional (3D) holograms, charge-coupled devices are mainly applied to capture and record reconstructed images for analysis. 3D holograms have multiple depths and thus can lead to varying light intensities at the information points of the reconstructed images during image acquisition. Finally, it will lead to poor analysis results. Aiming at the previously mentioned problem, an algorithm called three-dimensional structural similarity (3D-SSIM) is proposed in this study. It is expected to optimize hologram evaluation and analysis. A fixed-focus shooting system matching silhouette sampling and SSIM is proposed to sample objects with 360° in order to implement 3D SSIM evaluation. This study successfully optimized the hologram evaluation method, leading to more accurate image evaluation results of hologram algorithms or holographic display systems.

In this research, a fast method to calculate the color rainbow holographic stereogram (CRHS) by taking full advantage of the sparsity of the frequency domain is demonstrated. The CRHS is a novel color rainbow hologram containing a large number of elemental CRHSs, where each elemental CRHS only reproduces the color light field information of local 3D color object. The color of the reconstructed color 3D image perceived by the human eye is determined by the spectrum of the reproduced dispersion of different elemental CRHSs that enter the human eye. The calculation of the CRHS is implemented with parallel computing by inversely Fourier transforming the frequency of each elemental CRHS. With the proposed method, the computation time for a resolution of 200k × 200k pixels and size of 64 × 64 mm CRHS is only 15.4 min for a color 3D model with 406k object points. The optical reconstruction with a white LED light illumination proves the effectiveness of our proposed method, which can be applied to the field of color holographic 3D display, advertising or holographic packaging.

In this paper, we propose an arc-remodified long period fiber grating (AR-LPFG) and introduce the ratios of shift-distance of two resonant dips (RSRDs) as a novel distinguishing index to monitor bending absolute condition which refers to detect the curvature and directions of fiber under a stationary status. The AR-LPFG is configured by arc-remodifying the LPFG that prepared from CO₂ laser. The refractive index of the fiber is modulated again by the arc-remodification method which results in new resonant dips. Two orthogonal bending directions are distinguished by comparing the RSRDs, which are calculated to be 0.51 and 1.42 for 0° and 90°, respectively. Two opposite bending directions are distinguished by the opposite shift directions of two resonant dips. The stability and reliability of the novel distinguishing method are verified by a series of comparative experiments. The AR-LPFG still contains a conspicuous performance for bending variation sensing with a maximum sensitivity of 17.02 nm m⁻¹. The AR-LPFG, together with the orientation distinguishing index, can be widely applied at the fields that the bending relative variation or absolute condition need to be monitored.

In this manuscript, we experimentally demonstrate a parity-time-symmetric optoelectronic oscillator (OEO) with polarization multiplexed channels. We obtained a microwave single-mode oscillation at 9.5 GHz with phase noise values of −116.2 and −122.3 dBc Hz⁻¹ at 10 kHz offset frequencies, and side mode suppression values below −68 and −75 dBc Hz⁻¹, by utilizing a 1 km long and 5 km long single mode fiber delay lines, respectively. Our experimental results suggest that parity-time-symmetric OEOs with polarization multiplexed channels are simple and cost-efficient alternatives to their more complex counterparts.