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The optical topology, which serves as a stable spatial electromagnetic structure, offers a new dimension for applications in the field of optical information processing, transmission, and storage. In recent years, there has been an increasing focus on these spatially structured light fields. By reversing the radiation of orthogonal dipole pairs, we propose an approach to generate Meron topologies within the focused light field while also investigating the evolution of the Meron structure along the longitudinal axis. Through introducing a dipole placed along the z -axis, we achieve precise positioning and fine adjustment of the topological center. The stability of Meron under a high numerical aperture objective lens (NA = 0.95) can be effectively demonstrated. [ABSTRACT FROM AUTHOR]

In this work, we describe a theoretical approach for combined thermal, mechanical and optical simulation and analysis of planar polymer waveguides. We consider a finite element approach for thermal and stress/deformation simulation. Also, a Crank-Nicholson finite difference beam propagation method (CN-BPM) is implemented to perform the optical simulation. The results of the finite element (thermo-mechanical) analysis are coupled with the CN-BPM results to carry out the optical simulation of poly(methyl methacrylate) (PMMA) waveguides as function of temperature. For thermal simulation, a model was designed where a polysilicon microheater was added to the upper cladding of the PMMA waveguides to vary the temperature between 20 °C and 200 °C. Thus, the impact of the induced temperature gradients on the refractive index modulation of the PMMA waveguides and the corresponding change in numerical aperture are obtained. In addition, the temperature gradients influence the beam intensity profiles and the movement of the primary eyes within the optical waveguides, thus, impacting the optical properties. Furthermore, the thermally induced mechanical stress and deformation were calculated for transverse and axial directions. In the next step, validation of the model by systematic experimental studies will be performed. In general, our approach provides a toolbox for more comprehensive multi-physics theoretical analysis of polymer-optical waveguides which, in future, can be extended to more complex and functional structures as required for flexible sensor networks, as example. [ABSTRACT FROM AUTHOR]

Radially polarized beam (RPB) could be focused to a tighter spot than a spatially homogeneous polarized beam with a high numerical aperture (NA) objective lens. However, the traditional objective lens suffers from high cost and bulky size. In this paper, polarization-insensitive nanopillar metalenses were designed to execute tight focusing without the requirement of the incident beams to be specific polarized states. It was found that the focal spot of RPB was potentially smaller than that of a linear polarized beam because of the longitudinal component. Diffraction-limited focusing of RPB was achieved by a high NA polarization-insensitive metalens through an annular aperture illumination. This study may contribute to high-resolution photonics and optoelectronic applications. [ABSTRACT FROM AUTHOR]

Metasurfaces have demonstrated revolutionary capabilities in manipulating the polarization, phase, and amplitude of light. Pancharatnam–Berry (P–B) phase metasurfaces can operate over a broad spectrum and robust phase distributions against fabrication tolerance. However, the conjugated characteristic of the modulated phases for different spin photons introduces an obstacle for multifunctional photonics applications. This problem seriously hinders the development of P–B phase metasurfaces. We proposed a method through symmetry breaking of photonic spin–orbit interactions and achieving spin-independent manipulation of spin–orbit interactions. As a proof-of-principle demonstration, we realized polarization-multiplexed multifunctional metalenses at visible and infrared wavelengths with high numerical aperture, and the focal lengths of different foci can be adjusted independently. The proposed metalens has potential applications in imaging, optical communications and optical trapping, and also the approach of independent manipulation of spin–orbit interactions can facilitate the development of P–B phase metasurfaces toward spin-controlled multifunctional photonics. [ABSTRACT FROM AUTHOR]

Diffractive optical elements (DOEs) remain highly underutilized in broadband optical systems even though different technologies for DOEs including échelette-type gratings (EGs), multilevel DOEs, and metagratings have been introduced. Specifically, nanocomposite-enabled EGs can achieve efficiencies of close to throughout the visible spectrum, but only for relatively small diffraction angles. Therefore, the question remains if they are suitable for high-numerical-aperture (NA) systems. Here we show that this is indeed the case. To this end, we first demonstrate that macroscopic nanocomposite-enabled diffractive lenses (DLs) can achieve perfect broadband focusing up to a NA of 0.03. We then derive analytic relationships and investigate prototypical optical designs to show that this threshold fully covers the requirements of high-end imaging systems with This holistic all-system analysis demonstrates that the individual NA of a DL in a broadband imaging system is one to two orders of magnitude lower than the overall system's NA. This shows that high-NA flat optical elements are not required for high-NA broadband systems. Therefore, nanocomposite-enabled EGs can unlock the full potential of DOEs for broadband optical systems, whereas other technologies cannot fulfill their high efficiency requirements. [ABSTRACT FROM AUTHOR]

Conventional refractive lenses concentrate the incident light at focal distance. A narrow beam waist can be achieved by increasing the lens numerical aperture, but strongly reduces the depth of focus. In this work, we explore diffractive lenses designs, with fast angular variation of the focal distance, that produce both a narrow beam waist and a long depth of focus. We predict the focusing properties of the diffractive lenses with a simple analytical model based on an incoherent superposition of standard lenses with different focal distances. The histogram of the local focal distances is used to determine the weights in the superposition. Our model optimizes the shape of the diffractive lenses, in order to extend the depth of focus, which corresponds to the lotus lens. We verify our results with numerical simulations based on Rayleigh–Sommerfeld approach. Experimentally, we validate our analytical and numerical solutions with a spatial light modulator. We have found configurations for the lotus lens where the depth of focus is significantly incremented with only a slight increment of the focal width. For example, we increased the depth of focus from 7.6 mm to 37.2 mm while the beam waist varied from 35.0 microns to 51.6 microns for a lens with diameter D = 4 mm, and focal distance f' = 125 mm. These results may find applications in the design of contact and intraocular lenses with extended depth of focus, laser focus generators, and imaging applications where extended depth of focus is needed. [ABSTRACT FROM AUTHOR]

The flow of a fluid around an optically trapped particle forces the particle to move out of its equilibrium position. The particle will escape the trap if the fluid velocity exceeds a certain limit. Accordingly, we propose a novel and accurate method to sort the particles due to a difference in their escape velocities that depends on the size and refractive index of the particles. Here, the influence of the numerical aperture of the microscope objective and laser power on the escape velocities are studied for calibration. In addition, the method is used to sort various pairs of the particles; polystyrene beads with diameters of 1.48 and 2.18 micron, 1.65 and 3.0 micron, and 3.0 micron silica and polystyrene beads. The results show an efficiency of about 95% to locate the particles into the desired region. To verify the capability of the method for cell sorting, we have accomplished this technique to sort thalassemia red blood cells from healthy ones. Our presented method, as an accurate, high throughput and ease-of-use technique, could be used in the development of microfluidic-based devices and it is of critical importance to different areas in biotechnology and cellular biology. [ABSTRACT FROM AUTHOR]

Lateral resolution enhancement is demonstrated in a confocal imaging system with amplitude-modulated radially polarized (RP) light at the wavelength Annular pupil fields and optimized amplitude distribution functions can be realized with a spatial light modulator. By comparing images obtained with full and amplitude modulated apertures of RP illuminations using a high numerical aperture (NA = 0.9), spatial resolution of has been achieved experimentally. This result agrees very well with theoretical simulation results and will be helpful in improving performance of the non-fluorescent imaging systems. [ABSTRACT FROM AUTHOR]

Nanosheets, nanoparticles, and microstructures of ZnO were synthesized via a wet chemical method. ZnO films with a thickness of 44–46 μm were fabricated by spray coating, and these have been investigated for their potential use in turbid lens applications. A morphology-dependent comparative study of the transmittance of ZnO turbid films was conducted. Furthermore, these ZnO turbid films were used to enhance the numerical aperture (NA) of a Nikon objective lens. The variation in NA with different morphologies was explained using size-dependent scattering by the fabricated films. A maximum NA of around 1.971 of the objective lens with a turbid film of ZnO nanosheets was achieved. [ABSTRACT FROM AUTHOR]

In this paper, we numerically demonstrate that the negative refraction of a photonic crystal immersion lens can bend a beam by unconventionally large convergence angles over π/2 in free space. This super-convergence feature leads to constructive interference of high-spatial-frequency waves in both lateral and axial directions and forms super-resolution focal areas beyond the evanescent fields. As such, a 57% reduction in the focal area compared with the diffraction-limited case of an objective with numerical aperture of 0.95 has been numerically achieved at a normalized frequency of 0.3 in a photonic crystal immersion lens, corresponding to a lateral resolution of 0.32λ as well as an axial resolution of 0.70λ. [ABSTRACT FROM AUTHOR]

In recent times, coherent Fourier scatterometry has been considered as an emerging optical grating scatterometry technique for semiconductor metrology since it shows large sensitivity owing to its scanning ability. However, further utilization of coherence is possible by making additional measurements using the principle of temporal phase-shifting interferometry. In this paper, through numerical simulation, we show how scanning and interferometry can be coupled together to improve the sensitivity of coherent Fourier scatterometry, to extend its range of applicability and to obtain sufficient information to calculate the complex scattering matrix for all angles of incidences inside the numerical aperture of a microscope objective. [ABSTRACT FROM AUTHOR]

In order for satellite camera installations to make microsize observations at a working distance of hundreds of millimeters, a microscope with a super-long working distance is designed and established for the precise stitching assemblage of multi-window wide spectrum detectors and also for rigorous achromatic aberration. For the case of a numerical aperture of 0.23 the actual working distance is 225 mm and the wavelength ranges from 400 to 900 nm. This system highlights more potential applications for mirror and mirror lens based hybrid microscopy in industrial inspections by challenging the size of traditional optical microscopes. [ABSTRACT FROM AUTHOR]

We report on the investigation of large energy dissipative soliton resonance (DSR) pulse generation in a simple linear cavity Tm3+-doped fiber laser (TDFL), by using semiconductor saturable absorption mirror as saturable absorber. This DSR TDFL is implemented by utilizing ultra-high numerical aperture 4 (UHNA4) fiber for dispersion compensation. With further dispersion management, the DSR TDFL can generate an average output power of 242 mW with corresponding pulse energy of ~61 nJ. Moreover, the soliton molecules mode-locked operation has also been demonstrated in this TDFL. Our results can provide an easily accessible way to develop large energy TDFLs. [ABSTRACT FROM AUTHOR]

In this paper, according to the inverse Faraday effect, a pure longitudinal magnetization field induced by 4π tightly focusing of two linearly polarized vortex beams (LPVBs) is investigated. We find that the orbital angular momentum (OAM) of these two LPVBs could be transformed into spin angular momentum in the tightly focusing condition, and a longitudinal magnetization with purity of 100% is generated, if the topological charges of the two counterpropagating LPVBs are two identical odd numbers. In addition, the distribution and strength of induced longitudinal magnetization could be regulated by turning the OAM of the two counterpropagating LPVBs and numerical aperture of the two focal lenses, respectively. Besides, the local polarization states of the light field and a three-dimensional magnetization array in the focal region is surveyed. We believe that this 4π setup of generating a pure longitudinal magnetization could potentially be used to the field of storage technology especially for the using of massively parallelized all-optical magnetic recording. [ABSTRACT FROM AUTHOR]

We present a simple method for controlling the polarisation state of light at the waist of a single-mode optical nanofibre. The method consists of complete polarisation compensation based on imaging scattered light from inherent inhomogeneities both on the fibre surface and in the glass material itself. In contrast to the recently reported protocol exploiting two imaging systems oriented at 45° to each other, our method requires only one lens and a video camera. It is particularly useful for nanofibre-based applications with severe geometric constraints, such as inside vacuum chambers for experiments with cold atoms. The measured fidelity of the achieved control is about 98% using lenses with moderate numerical apertures. [ABSTRACT FROM AUTHOR]

Many laser applications utilise a focused laser beam having a single-lobed intensity profile in the focal plane, ideally with the highest possible on-axis intensity. Conventionally, this is achieved with the lowest-order Laguerre–Gaussian mode (LG00), the Gaussian beam, in a tight focusing configuration. However, tight focusing often involves significant spherical aberration due to the high numerical aperture of the systems involved, thus degrading the focal quality. Here, we demonstrate that a high-order radial LGp0 mode can be tailored to meet and in some instances exceed the performance of the Gaussian. We achieve this by phase rectification of the mode using a simple binary diffractive optic. By way of example, we show that the focusing of a rectified LG50 beam is almost insensitive to a spherical aberration coefficient of over three wavelengths, in contrast with the usual Gaussian beam for which the intensity of the focal spot is reduced by a factor of two. This work paves the way towards enhanced focal spots using structured light. [ABSTRACT FROM AUTHOR]

Grating coupled near-field interference lithography has the ability to produce deep-subwavelength interference patterns. Simulations of these systems is very computationally intensive. An inverse design procedure employing a genetic algorithm is utilized here to massively reduce the computational load and allow for the design of systems capable of interfering extremely high numerical apertures. This method is used to optimize systems with an interference patterns with a half pitch of corresponding to a numerical aperture of 20. It is also used to demonstrate interference of higher diffraction orders. [ABSTRACT FROM AUTHOR]

Colocalized dark-field scattering, atomic force and surface-enhanced Raman scattering microscopic (DFSM, AFM and SERS) imaging of single gold nanoparticles is presented using a home-made instrument. A high numerical aperture total internal reflection objective allows us to probe the polarization-dependence of DFSM spectra associated with individual nanoparticles, which reveal their degree of anisotropy and reflect the morphology and orientation observed on AFM images. Under convenient light excitation, the SERS enhancement efficiency reaches 106–107 for the investigated gold nanorod and ellipsoid, in good agreement with the 103–105 electromagnetic enhancement factor assessed from finite-difference-time-domain (FDTD) calculations and a 102–103 chemical contribution. FDTD calculations also confirm the possibility to reproduce nicely anisotropic behaviours disclosed by DFSM studies using SERS measurements. [ABSTRACT FROM AUTHOR]

A solution to a general problem for 4-channel liquid crystal (LC) modulator (LC focusing device) of the formation of specified-equipotential-line voltage distribution and on its movement along the aperture is presented. The modulator’s capabilities for the formation and control of light fields in the form of circles, line segments and ellipses of an arbitrary orientation are demonstrated numerically and experimentally. [ABSTRACT FROM AUTHOR]

We report the use of sub-wavelength confinement of light using dielectric microspheres for enhancing transmission through the cantilever-based hollow probes used in a near-field scanning optical microscope. With an appropriate choice of the dielectric microsphere, an order of magnitude enhancement was achieved in transmission through the probe. In addition, transmission through such a tip was also found to be less sensitive to the axial and lateral offset between the beam waist and symmetry axis of the probe tip. [ABSTRACT FROM AUTHOR]

A donut-shaped laser that is simultaneously impacted by the coma, astigmatism and spherical aberrations in a high NA focusing system is numerically simulated based on the vectorial diffraction theory. The full-width half-maximum, intensity characters, and dimensions of the dark cores of the donut-shaped laser on the focal plane are quantitatively analyzed. The results are highly consistent with the annular-shaped nano-patterns that are experimentally fabricated by our purpose-built laser direct writing system. The mechanism of asymmetric nano-patterns fabricated through laser writing lithography is also revealed. [ABSTRACT FROM AUTHOR]

The Fourier scatterometry model was used to measure the ZEP 520A electron beam resist lines with specific line edge roughness (LER). By obtaining the pupils via an objective lens, the angle-resolved diffraction spectrum was collected efficiently without additional mechanical scanning. The concavity of the pupil was considered as the weight function in specimen recognition. A series of white noises was examined in the model, and the tolerant white noise levels for different system numerical apertures (NAs) were reported. Our numerical results show that the scatterometry model of a higher NA can identify a target with a higher white noise level. Moreover, the fabricated ZEP 520A electron beam resist gratings with LER were measured by using our model, and the fitting results were matched with scanning electron microscope measurements. [ABSTRACT FROM AUTHOR]

The three dimensional intensity distribution of focused spatial-variant polarized vector Bessel–Gauss beams is investigated in the vicinity of the focal plane by using the Richards–Wolf vectorial diffraction method. The local polarized states of the incident beams vary between linearity and ellipse, and can be easily controlled in real time by a new parameter, namely the phase delay angle, which is introduced by a liquid crystal variable retarder. Our analysis proves the existence of a focal shift toward the focusing objective for this type of beam. The dependence of the focal shift on the different parameters of the beams is discussed in detail. Numerical results indicate that the magnitude of the focal shift is associated with the mode number, the local polarization, the beam width and the wavelength of the incident beams. The controllability of the focal shift indirectly caused by the phase delay angle will have great potential applications in optical micro-manipulation. [ABSTRACT FROM AUTHOR]

We propose to use a pure-phase filter in combination with a high NA lens axicon to achieve a sub-wavelength magnetic focal spot with large uniform magnetization depth when illuminated by a circularly polarized beam. The magnetization distributions are derived and evaluated based on the vector diffraction theory and the inverse Faraday effect of the isotropic and non-magnetically ordered material. With this kind of system, the longitudinal magnetization depth is increased to 12.82λ and the magnetic spot size has been reduced to 0.38λ. However, in the conventional lens with the same NA, the FWHM of the magnetic spot is found to be 0.43λ and its corresponding magnetization depth is only 0.89λ. We expect such a sub-wavelength strong longitudinal magnetic field with large magnetization depth can be widely used in high density magneto-optic recording and the scanning near-field magnetic microscope for studies of magnetic responses of sub-wavelength elementary cells of metamaterials. [ABSTRACT FROM AUTHOR]