Collimator Lens Research Articles

Polarization-Insensitive Vertically Curved Si Surface Optical Coupler Bent by Ion Implantation

For input coupling from single-mode optical fibers to photoreceivers made with silicon photonics integrated circuits (Si-PICs), we constructed a polarization-insensitive optical surface coupler with a vertically curved silicon waveguide. The polarization insensitivity was attained by the equalization of the radiative transmission losses of TE and TM polarizations in the vertically curved waveguide (VCW) structure while keeping the straight structure of the spot-size converter (SSC) connected above the curved structure. Numerical simulations revealed that the radius of curvature of 6 μm or larger nearly enabled the equalization, and thus we developed a bending technology using ion implantation to realize simultaneously a VCW radius of curvature of 6 μm and a straight SSC of length 7 μm by varying the implantation angles. The bent silicon core was subsequently coated with SiO2 by plasma-enhanced chemical vapor deposition to function as a collimation lens. The coupling properties of the fabricated coupler and the single-mode fiber with a mode-field diameter of 5 μm exhibited a polarization dependence loss of less than 0.25 dB, a 1-dB bandwidth of 180 nm, and coupling losses of about 1.6 dB at 1550 nm wavelength. A sharp inversely tapered Si waveguide that affects these characteristics significantly can be formed by applying ArF-immersion lithography on the 45-nm-node and hence fabrication is compatible with mass production processes.

Design method of diffuse transmission free-form surface combined with collimation lens array

Lighting-emitting diodes are widely applied in lighting systems, and diffusers are commonly used in systems for indirect illumination. In this paper, a design method of diffuse transmission free-form surface combined with collimation lens array is proposed. Based on the Lambertian characteristics of lighting-emitting diodes and the principle of collimation lenses, a mathematical model of diffuser with ideal diffuse transmission free-form surface is established. We propose a method of the preset collimation surface to connect the free-form surface and the collimation lens array, and derive the nonlinear algebraic equation of the diffuse transmission free-form surface according to the connection effect of the preset collimation surface. Then, solving the equation numerically by MATLAB, the profile of the diffuse transmission free-form surface is obtained. Finally, the non-sequential ray tracing software TracePro is used to simulate the irradiance distribution of the target plane. The results show better uniformity and higher efficiency comparing with the lighting system using diffuse transmission free-form surface alone and the traditional diffuse transmission lighting system.

High-NA achromatic diffractive lensing for arbitrary dual-wavelengths enabled by hybridized metal-insulator-metal cavities.

A new type of diffractive lens based on hybridized Fabry-Perot (FP) cavities with high-NA and achromatic features for arbitrary dual-wavelengths is theoretically proposed and demonstrated. We utilize the subwavelength-scale metal-insulator-metal nanocavity to form a Fresnel zone plate (MIM-FZP) that benefits from both spectral selectivity and high numerical aperture (NA > 0.9) to enable lensing functionality. By taking advantage of the different transmission orders from MIM, any arbitrary dual-wavelength achromatic focusing design is achieved. Using this approach, we merge two independent MIM-FZP designs and realize achromatic focusing performance at the selected dual-wavelength of 400/600 nm. Furthermore, the achromatic lens also exhibits a crucial potential for dynamically tuning of the operation wavelengths and focusing lengths as actively scaling the core layer thickness of MIM. The unique MIM-FZP design can be practically fabricated using a grayscale lithography technique. We believe such high-NA and achromatic optical devices enjoy great simplicity for structural design and can easily find applications including high-resolution imaging, new-generation integrated optoelectronic devices, confocal collimation, and achromatic lens, etc.

Необходимые условия физической реализуемости бифокального линзового коллиматора

The conditions of physical realizability of one of the varieties of aplanitic lens collimators, a bifocal lens collimator, which has two points of perfect focus and do not lie on the main optical axis, are considered. Based on the relationship of the parameters specified during the design of the bifocal lens collimator (aperture size, thickness, focal length, distance from the main optical axis to the focal point, tilt of the phase front in the aperture), conditions that are necessary for the synthesis of a physically feasible collimator are formulated. The solution of this problem is based on the properties of an ellipse of equal edges and the geometry of a bifocal lens collimator. The graphic dependencies of the obtained expressions are given and analyzed. Based on this analysis, the mutual dependence of the parameters specified at the beginning of the calculation of the lens surface is determined. Systems of inequalities that establish the conditions for the realizability of a bifocal lens collimator are written. A number of restrictions on the initial parameters of the bifocal lens collimator are recorded. The fulfillment of the inequalities obtained in the article is a necessary condition for the physical realizability of the bifocal lens collimator.

Angular sensing system based on Y-type twin-core fiber and reflective varied-line spacing grating fabricated by electron beam lithography

A varied-line spacing grating (VLSG) inscribed by electron beam lithography was proposed and used for an experimental demonstration of angular sensing. The designed VLSG central groove density was 655 L/mm, and it had an aluminized surface to reflect light. A Y-type twin-core fiber of 600 μm diameter cores connected with a collimator lens was used to input and collect reflected light from the VLSG. The Y-type fiber input and output paths were connected to a white light source and an optical spectrum analyzer, respectively. The fabricated quasi-continuous VLSG size was 70 × 30 mm, with a fixed 23° input angle. The reflected wavelength changed from 917.3 to 1656.9 nm as the incident light spot moved to different grating positions, with a displacement sensitivity of 14.812 nm/mm. As the input angle was adjusted from 23° to 35° in 1° increments, the spot location on the VLSG changed simultaneously, and the reflection wavelength peak positions changed from 917.3 to 1584.5 nm, with a sensitivity of 57.544 nm/° and linearity of 0.993.

Modified structural Luneburg lens for broadband focusing and collimation

Luneburg lens is a symmetric gradient-index lens with a refractive index that increases from the outer surface to the center in a radial manner. It has the ability to focus and collimate waves, which makes it useful for energy harvesting, waveguiding and as a component in transducers. An ideal Luneburg lens should be easy to fabricate, has broadband and omnidirectional characteristics, as well as a focal length that can be easily tuned. However, existing structural Luneburg lenses based on phononic crystals can hardly achieve these requirements. Here, we propose an alternative structural Luneburg lens which has a refractive index that varies smoothly with its radial distance as a result of a changing thickness. Theoretical calculations, numerical simulations and experimental measurements of flexural wave propagation through the lens showed that flexural wave focusing can be obtained inside, at the edge and outside of the variable thickness lens for different frequencies and propagation directions. Flexural wave collimation was also demonstrated when a point source was placed at the respective focal points for each lens. Furthermore, it was shown that flexural waves that were focused onto a piezoelectric energy harvester by the Luneburg lens can lead to a significant increase in the harvested voltage compared to that obtained without focusing.

System design and error correction for 300 mm aperture vertical Fizeau spatial-temporal phase-shifting interferometer.

With the development of high-power lasers for aerospace, electronics, etc., the demand for large-aperture planar optical elements has become more urgent, along with the demand for measurement methods. In this paper, the design of a 300 mm aperture vertical Fizeau spatial-temporal phase-shifting interferometer is discussed. Based on position difference between laser sources, the spatial phase-shifting technique is achieved by generating a laser source array on the focal plane of the collimation lens, and four pairs of coherent beams with different phase shifts are integrated in a vertical Fizeau interference system. Combined with a tunable laser diode, a temporal phase-shifting technique can be realized in any pair of coherent beams through wavelength tuning. The key techniques, which include laser duplication to introduce different phase shifts, conjugate imaging, and separation for interferograms, and assembly for a transmission flat, are demonstrated. The systematic error and position mismatch error of interferograms are eliminated. Comparison experiments are conducted between spatial and temporal phase-shifting techniques. A dynamic water surface is also measured to verify its capacity for detecting dynamic objects.

Wide beam steering by slow-light waveguide gratings and a prism lens

A lattice-shifted photonic crystal waveguide (LSPCW) maintains slow light as a guided mode and works as an optical antenna when a kind of double periodicity is introduced. Selecting one LSPCW from its array and converting the fan beam to a spot beam using a collimator lens allows non-mechanical, two-dimensional beam steering. We employed a shallow-etched grating into the LSPCW as the double periodicity to increase the upward emission efficiency and designed a bespoke prism lens to convert the steering angle in a desired direction while maintaining the collimation condition for the steered beam. As a result, a sharp spot beam with an average beam divergence of 0.15° was steered in the range of40∘×4.4∘without precise adjustment of the lens position. The number of resolution points obtained was 4256. This method did not require complicated and power-consuming optical phase control like that in optical phased arrays, so it is expected to be applied in complete solid-state light detection and ranging.

Enhanced daylight system with acrylic based collimator

High rise buildings or office cubicles constitute the modern living and work places. Rapid pace of urbanization has led to population concentration in cities. Due to space constraints, multi-story buildings in these cities often lack proper access to natural lightening. This necessitates the increasing use of artificial light for illumination even during daytime, leading to higher energy usage in this era of energy crisis. A well-designed Daylight System can deliver daylight to interior parts of buildings, thus reducing dependence on artificial lightening system and to cut energy consumption during the daytime. A daylight illumination system has been presented in this work that made it possible to use PMMA based fiber optic bundle and acrylic lenses as collimator lens reduces heat concentration that arises due to infrared rays at focal point. Numerical simulation for ray tracing and illumination analysis using Trace Pro 7 software has been done. Illumination maps and Polar iso candela have been plotted for collimated and non-collimated beam and it has been observed that collimator lens results in uniform distribution of light rays without any hot spot formation.

Tunable metallic and topological properties in two-dimensional ligand-functionalized antimonene films

Using first-principle calculations, we predict that fully-hydroxyl-decorated antimonene (SbOH) is a two-dimensional topological insulator with extraordinarily global gap of 330 meV, and incompletely hydroxyl-decorated antimonene films show metallic properties. The ligand OH on top side of SbOH@SiC(1 1 1) heterostructure can be veered by external electric field, which induces a switchable in-plane spontaneous polarization. Moreover, the asymmetry and strong spin-orbit coupling of SbOH leads to spin polarization of edge states and a pair of unequal valleys that have opposite Berry curvatures near the vertices (K and K’) of Brillouin zone. The tunable of valley polarization in SbOH is useful to realize quantum valley Hall effect. In the case, SbOH shows the dual TI with coexisting switchable ferroelectric and valley polarization. Ferroelectric topological materials provide a new paradigm for device engineering, such as perfect-focusing Veselago lens and spin-selective electron collimator. Based on spin polarization of edge states, we suggest a transistor model using the spin direction as a switch. We can tune the material to be metal, TI, or ferroelectric TI according to SbO film partially or completely hydroxylated. Our findings not only broaden the family of the 2D ferroelectric topological materials, but also offer a promising platform for novel electronic and spintronic applications.

Implementation of Integrated VCSEL-Based Optical Feedback Interferometry Microfluidic Sensor System with Polymer Microoptics

Using the optical feedback interferometry (OFI) technique, we demonstrated a miniaturized and compact sensor system based on a dedicated optical source for flowmetry at the micro-scale. In the system, polymer microlenses were integrated directly on a VCSEL (vertical-cavity surface-emitting laser) chip and the microfluidic channel chip surface using polymer-based micro-fabrication technologies. In particular, at a post-process stage, we integrated a collimation lens on a VCSEL chip of small dimensions (200 µm × 200 µm × 150 µm). This process was enabled by the soft-printing of dry thick resist films and through direct laser writing technology. We performed flow rate measurements using this new compact system, with a conventional bulk glass lens configuration for system performance evaluation. A maximum 33 dB signal-to-noise ratio was achieved from this novel ultra-compact system. To our knowledge, this is the highest signal level achieved by existing OFI based flowmetry sensors.

Double-Sided Freeform Lens for Light Collimation of Light Emitting Diodes

A double-sided freeform lens is proposed for collimating light emitted from light emitting diodes (LEDs). The surface profiles of the lens are mathematically characterized and precisely determined based on a point-source assumption and differential geometry theory. The proposed lens design method is straightforward, flexible, and effective. Moreover, the optical performance of the lens can be intuitively adjusted by tuning just a small number of design parameters. The simulation results showed that the proposed lens achieved an excellent collimating effect for a commercial ultraviolet (UV) LED. A prototype lens is fabricated in UV-grade poly(methyl methacrylate) material using a standard injection molding process. The light collimating effect of the lens/UV-LED assembly was measured experimentally and was shown to be in good agreement with the simulation results. The collimating angle at the half-energy level was equal to 1.88°. The performance of the UV-LED is thus comparable to that of conventional lithography UV light sources based on mercury arc lamps. Consequently, the proposed double freeform lens showed significant potential for photolithography applications within the industry.

Prism lens for beam collimation in a silicon photonic crystal beam-steering device.

The doubly periodic Si photonic crystal waveguide operates as a nonmechanical beam-steering device that can be applied in light detection and ranging. In this Letter, we develop and describe a prism lens that collimates a fan-shaped beam, emitted from the waveguide independent of the steering angle. Its fundamental profile is investigated using a theoretical analysis for thick lenses, and then, its detailed aspherical design is obtained. In ray tracing, this prism lens suppresses the beam divergence to less than the diffraction limit in most of the targeted beam-steering range. The prism lens is fabricated by acrylic cutting, and its expected characteristics are observed.

Improved spherical mirror multipass-cell-based interband cascade laser spectrometer for detecting ambient formaldehyde at parts per trillion by volume levels.

We report the development of an improved spherical mirror multipass-cell-based interband cascade laser (ICL) spectrometer for ambient formaldehyde (HCHO) detection. The multipass cell consists of two easily manufactured spherical mirrors that are low cost, and have a simple structure, large mirror area utilization, and dense spot pattern. Optical interference caused by the multipath cell was largely reduced, resulting in good sensitivity. Using wavelength modulation spectroscopy (WMS), a detection precision (${1} \sigma $1σ) of 51 pptv in 10 s was achieved with an absorption pathlength of 96 m, which compared favorably with the performance of other state-of-the-art instruments. The precision can be further improved by using a long absorption pathlength configuration and by removing fringe-like optical noise caused by the collimation lens. Ambient application of the developed spectrometer was demonstrated.

Wavefront sensing for low-coherent sources through spatial coherence revival

An interferometry based wavefront sensing scheme applicable to low-coherent light sources is proposed and demonstrated. Using a pair of cascaded Sagnac interferometers, spatial frequency multiplexed interference of three sheared copies of the wavefront is recorded. The independent vector gradients obtained are used to reconstruct the wavefront. We overcome the spatio-temporal coherence limitations of the light source through the choice of spatial and spectral distribution of the light source. A Gaussian spectral distribution enables the measurement of the phase gradient corresponding to the central wavelength. Introduction of aperture for controlling the spatial distribution of the extended light source, we revive the spatial coherence of the optical field at the detector plane. We revive the spatial coherence of the field for the set value of lateral shear to maintain the visibility of the interference at the detectable level. Validating the scheme through measurement of changes in wavefront as a function of a collimation lens position, we apply it to reconstruct the wavefront of a light beam passing through a pseudo random phase plate, an atmospheric turbulence simulator.

Automated UV-Epoxy-Based Micro-Optic Assembly for Kilowatt-Class Laser-Diode Arrays and Modules

This paper outlines the numerous interdisciplinary activities required to implement two ultraviolet (UV) epoxy-based automated micro-optic assembly tools within a “smart factory” for high-power semiconductor laser manufacturing. After a brief overview of the motivation and approach, two examples of automated micro-optic assembly tools [e.g., fast-axis collimation (FAC) lens attach and mirror stripe alignment] for kilowattclass laser-diode arrays and modules are given that demonstrate the breadth of automation activities required within a modern factory. For each system, the complete assembly sequence is outlined, and the steps that presented fully automated challenges are highlighted. In contrast, to the previous published results that focused on the details of the automated micro-optic alignment, the largest challenges primarily involved automation and repeatability of the UV-epoxy dispense and attach processes for these high-power semiconductor devices. These were solved by precise and stable mechanical design, customized lighting, and machine vision solutions. Finally, the complete integration of the tools into a “smart-factory” system is outlined.

Influence of high overload on the collimating lenses of laser ranging systems

Collimating lenses are an important component of laser ranging systems, and high overload environments severely affect the beam shaping effect of such lenses. This study proposes a buffer isolation method on the basis of impact stress wave attenuation theory for collimating lens spacers. ANSYS finite element software was applied to simulate the high load dynamics of collimating lenses, and the buffer isolation performance of different materials and composite structures was compared and analysed. Optical simulation analysis of the collimating lenses under different buffer conditions was performed using ZEMAX software to study the mechanism by which a high overload affects the collimating lenses. High overload and optical shaping experiments based on theoretical analysis were further conducted. Results showed the superiority of butadiene rubber to polytetrafluoroethylene after application of 70000 g impact acceleration. The combination-gasket method was superior to the single-gasket method, and the sandwich combination-gasket method was superior to the double-layer combination-gasket method.

Prismatic mass analyzer with the conical achromatic prism and transaxial lenses

The conical achromatic prism (CAP) has a record angular dispersion equal to about 50 radians on per 100% of mass variation. In CAP, electric and magnetic fields are realized whose potentials in a spherical coordinate system depend only on angular variables. The particles of a homogeneous planar parallel ion beam move in the mean plane of the CAP along similar trajectories and maintain parallelism at the exit from the CAP. The CAP also possesses by energy focusing, and the parallelism of the volume beam is maintained due to its telescopiс in the vertical direction. CAP can be used in a prismatic mass spectrometer, which in its scheme is like to a prismatic light-optical spectrometer equipped with a collimating and focusing lenses. The linear dispersion of the prismatic spectrometer is equal to the angular dispersion of the CAP multiplied by the focal length of the focusing lens. A prismatic device is designed in which three-electrode transaxial lenses are used as a collimating and focusing lenses. By using a positional detector located in the focal plane of the focusing lenses, the instrument can also be used as a mass spectrograph.

Anomalous Photothermoelectric Transport Due to Anisotropic Energy Dispersion in WTe2.

Band structures are vital in determining the electronic properties of materials. Recently, the two-dimensional (2D) semimetallic transition metal tellurides (WTe2 and MoTe2) have sparked broad research interest because of their elliptical or open Fermi surface, making distinct from the conventional 2D materials. In this study, we demonstrate a centrosymmetric photothermoelectric voltage distribution in WTe2 nanoflakes, which has not been observed in common 2D materials such as graphene and MoS2. Our theoretical model shows the anomalous photothermoelectric effect arises from an anisotropic energy dispersion and micrometer-scale hot carrier diffusion length of WTe2. Further, our results are more consistent with the anisotropic tilt direction of energy dispersion being aligned to the b-axis rather than the a-axis of the WTe2 crystal, which is consistent with the previous first-principle calculations as well as magneto-transport experiments. Our work shows the photothermoelectric current is strongly confined to the anisotropic direction of the energy dispersion in WTe2, which opens an avenue for interesting electro-optic applications such as electron beam collimation and electron lenses.

A freeform collimator lens design for the Natural Light Illumination System

This paper presents the design of a collimator lens for use with the Lightbrick that uses total internal reflection as well as convex and concave surfaces. The Lightbrick is a light collector for the Natural Light Illumination System. The collimator lens is constructed using freeform surfaces which can be calculated through geometric-optics. Verified by optical simulation, using the collimator lens can achieve 90.3% luminous flux within ±2°, and optical efficiency improves by 48% in the collimator lens output. The collimator lens converges the light distribution of the Lightbrick and enhances the transmission efficiency of the Natural Light Illumination System.