Beam Shaping Optics Research Articles

Magneto-optical trapping using planar optics

Laser-cooled atoms are a key technology for many calibration-free measurement platforms—including clocks, gyroscopes, and gravimeters—and are a promising system for quantum networking and quantum computing. The optics and vacuum hardware required to prepare these gases are often bulky and not amenable to large-volume manufacturing, limiting the practical realization of devices benefiting from the properties of cold atoms. Planar, lithographically produced optics including photonic integrated circuits, optical metasurfaces (MSs), and gratings offer a pathway to develop chip-scale, manufacturable devices utilizing cold atoms. As a demonstration of this technology, we have realized laser cooling of atomic Rb in a grating-type magneto-optical trap (MOT) using planar optics for beam launching, beam shaping, and polarization control. Efficient use of available light is accomplished using MS-enabled beam shaping, and the performance of the planar optics MOT is competitive with Gaussian-beam illuminated grating MOTs.

Active Optical Beam Shaping Based on Liquid Crystals and Polymer Micro-Structures

Emerging applications requiring light beam manipulation, such as high-efficiency sunlight concentrators for solar cells, switchable micro-lens arrays for autostereoscopic displays, tunable lenses for augmented reality goggles, auto-focusing spectacles, and smart contact lenses, mostly depend on one or more active optical components with the desired and controllable beam modifying functionalities, preferably manufactured at relatively low cost. Recent progress in research on components based on the combination of liquid crystals (LCs) and various polymer micro-structures is reviewed in this paper. It is found that such components can address the demands appropriately and have the potential of paving the way for large-scale applications of active optical beam shaping components.

Micro- and nano-fiber probes for optical sensing, imaging, and stimulation in biomedical applications

The flexibile nature of optical fiber enables it to offer remote-access capabilities, which could be used in many biomedical applications. This review focuses on different micro- and nano-structured fiber probes for applications in biosensing, imaging, and stimulations. The modifications to fiber could extend design freedom from waveguide optimization to functional material integration. Fiber probes with optimized waveguide structures or integrated functional materials could achieve enhanced optical mode interaction with biosamples, and hence obtain ultrasensitive biosensors with a remarkably low limit of detection. Furthermore, bioimaging with a high spatial resolution can be obtained by engineering dispersion and nonlinearity of light propagation in the fiber core or designing a metal-coated tapered fiber tip with a sub-wavelength aperture. Flat metasurfaces can be assembled on a fiber tip to achieve a large depth of focus and remove aberrations. Fiber is also a compact solution to realize the precise delivery of light for in vivo applications, such as deep brain stimulation. The optical beam size, shape, and direction could be steered by the probe parameters. Micro- and nano-technologies integrated with fiber contribute to various approaches to further improve detection limit, sensitivity, optical resolution, imaging depth, and stimulation precision.

Nonlinear Beam Shaping with Binary Phase Modulation on Patterned WS2 Monolayer

The capability of controlling the phase of the nonlinear polarization of media is vital for nonlinear optical beam shaping. Achieving this control over nonlinear phase manipulation on the nanoscale...

Novel Optical Linear Beam Shaping Designs for use in Laparoscopic Laser Sealing of Vascular Tissues.

Suture ligation of vascular tissues is slow and skill intensive. Ultrasonic (US) and radiofrequency (RF) devices enable more rapid vascular tissue ligation to maintain hemostasis, than sutures and mechanical clips, which leave foreign objects in the body and require exchange of instruments. However, US and RF devices are limited by excessive collateral thermal damage to adjacent tissues, and high jaw temperatures that require a long time to cool. A novel alternative method using infrared (IR) laser energy is being developed for more rapid and precise sealing of vessels. This study describes design, modeling, and initial testing of several optical beam shaping geometries for integration into the standard jaws of a laparoscopic device. The objective was to transform the circular laser beam into a linear beam, for uniform, cross-irradiation and sealing of blood vessels. Cylindrical mirrors organized in a staircase geometry provided the best spatial beam profile.Clinical Relevance-This study explored several optical designs for potential integration into the standard jaws of a laparoscopic vessel sealing device, transforming a circular laser beam into a linear beam for sealing of vascular structures.

Method to control near-field bowing of laser diode arrays by balancing the thermal-induced stress

Due to the thermal-induced stress during the bonding process, the emitters in a laser diode array (LDA) are vertically displaced, which causes the near-field bowing of a laser diode bar (i.e., the SMILE effect). Near-field bowing degrades the laser beam brightness, adversely affecting optical coupling and beam shaping, resulting in a larger divergence angle and a wider line after focusing and collimation. The mechanism of near-field bowing has been theoretically studied, in which the ratio of tensile strength between submount and heat sink has a great effect on the deformation of LDAs. Arm-wrestling between CuW submount and heat sink vividly describes that the deformation of LDAs changes as a function of the ratio of two materials’ tensile strength. We design a symmetrical structure that bonds another submount on the bottom of the heat sink to control the SMILE effect by balancing the acting force from the top of the heat sink. The deformation of the heat sink and LDAs are approximately zero when the thermal-induced stresses forced on the top and bottom of the heat sink are equal.

OTSLM toolbox for Structured Light Methods

We present a new Matlab toolbox for generating phase and amplitude patterns for digital micro-mirror device (DMD) and liquid crystal (LC) based spatial light modulators (SLMs). This toolbox consists of a collection of algorithms commonly used for generating patterns for these devices with a focus on optical tweezers beam shaping applications. In addition to the algorithms provided, we have put together a range of user interfaces for simplifying the use of these patterns. The toolbox currently has functionality to generate patterns which can be saved as an image or displayed on a device/screen using the supplied interface. We have only implemented interfaces for the devices our group currently uses but we believe that extending the code we provide to other devices should be fairly straightforward. The range of algorithms included in the toolbox is not exhaustive. However, by making the toolbox open sources and available on GitHub we hope that other researchers working with these devices will contribute their patterns/algorithms to the toolbox. Program summaryProgram Title: OTSLM Toolbox for Structured Light MethodsProgram Files doi:http://dx.doi.org/10.17632/8sc66m9r7s.1Licensing provisions: GPLv3Programming language: MatlabNature of problem: There are many algorithms for generating computer controlled holograms however the code and descriptions for these algorithms is often provided as supplementary material to research publications which use these methods, and in some cases only the description is provided without code to reproduce the pattern. Furthermore, implementation of these algorithms can be a time consuming task. Even for simple patterns with simple analytical expressions for the far-field phase or amplitude, such as the Laguerre-Gaussian and Hermite-Gaussian beams, time is often wasted by researchers having to re-implement and test these patterns. Existing libraries for generation of SLM patterns focus on specific tasks, methods of pattern generation, or target specific hardware. These libraries are not general purpose or easily modifiable for general use by researchers working with computer controlled holograms in fields such as beam shaping and optical tweezers.Solution method: We have assembled a toolbox containing many methods commonly used with these devices. The number of methods available makes assembling a complete toolbox impossible, instead we have focused on putting together a general collection of methods, in the form of an open source toolbox, with the hope that other researchers will contribute patterns/algorithms they use. The toolbox currently includes a range of simple and iterative methods for beam shaping and steering as well as some of the methods our group currently uses for SLM control, calibration, imaging and optical tweezers beam shaping. To make the tools we have developed easy to use, we have tried to maintain a consistent well documented interface to each of the functions and provided graphical user interfaces to many of the simpler functions enabling code-free pattern generation.Additional comments: Some of the features require the Optical Tweezers Toolbox [1], in particular, the non-paraxial beam visualisation and optimisation routines. Certain functions require components from other Matlab packages such as the image acquisition toolbox, these can be licensed and installed from Mathworks. There is also interest from the authors in providing a Python version that requires no proprietary components depending on interest from the community. A public repository for the toolbox is available on GitHub [2].

Liquid Lens with Large Focal Length Tunability Fabricated in a Polyvinyl Chloride/Dibutyl Phthalate Gel Tube

Usually, an adaptive liquid lens only has a positive focal length, which severely limits its application in imaging and other fields. Therefore, a liquid lens consisting of polyvinyl chloride/dibutyl phthalate (PVC/DBP) gel, glycerol solution, and a glass substrate is proposed to extend the dynamic focal length range. A spherical tube is formed by the PVC/DBP gel under the effect of hydrostatic and surface tensions, which is used to restrict the glycerol solution. The PVC/DBP gel does not deform under the effect of an electric field, so the tangent line at the three-phase junction changes with the change of contact angle, which leads to an enlargement of the dynamic focal length range. At different voltage values, the proposed lens can be configured to work in three different schemes, namely, converging light, nondeflecting light, and diverging light. Here, the proposed lens has high imaging quality; the resolution is better than 114 lp/mm. A lens with a reconfigurable focal length holds great promise in diverse applications such as fluorescence detection, beam shaping, and adaptive optics.

Angular momentum properties of hybrid cylindrical vector vortex beams in tightly focused optical systems.

Optical angular momenta (AM) have attracted tremendous research interest in recent years. In this paper we theoretically investigate the electromagnetic field and angular momentum properties of tightly focused arbitrary cylindrical vortex vector (CVV) input beams. An absorptive particle is placed in focused CVV fields to analyze the optical torques. The spin-orbit motions of the particle can be predicted and controlled when the influences of different parameters, such as the topological charge, the polarization and the initial phases, are taken into account. These findings will be helpful in optical beam shaping, optical spin-orbit interaction and practical optical manipulation.

Dreams Come True

AbstractExperienced CO2 laser beam users once modified the given beam guiding systems and related optics to achieve tailored beam parameters for their applications. This included M2 or k values, power density, the power density distribution and / or the complete beam profile, the Rayleigh Length and more sophisticates' ones like twin spot, triple spot, line spot, homogenized profiles or even assist gas performance and additional relevant process conditions. Different elements, like beam expanders, beam splitters, different focal lengths or even zoom optics or beam shaping optics enable and support such tailoring.

InAsSb-based heterostructures for infrared light modulation

We demonstrate the strong modulation of the long wave infrared transmission of GaInSb/InAsSb/AlInAsSb heterostructures under carrier injection. This results in the population of states in the conduction band of the narrow-gap layer and changes the absorption and refractive index over a broad wavelength range. At λ = 8.6-μm, a single-pass intensity modulation depth up to 9% was demonstrated at T = 77 K for a 1-μm–thick InAs0.58Sb0.42 absorber. By modeling the structure, we show that this corresponds to the electron quasi-Fermi level rising up to 30 meV above the conduction band edge. Due to the strong band-to-band absorption, the change in the quasi-Fermi level is accompanied by a modulation of the refractive index by up to 0.06 in the spectral range below the energy gap of the alloy. This change is orders of magnitude greater than what is achievable in conventional electro-optic materials and allows, for example, the external intensity modulation of long-wave infrared laser sources with a high extinction ratio and a nanosecond-scale time response. Low power requirements make it possible to develop arrays of integrated devices for optical beam steering and shaping.

Anamorphic Shaping of Laser Beams

AbstractAnamorphic beam shaping optics are, e.g., used to transform elliptical laser beams to a round shape before coupling them to single‐mode optical fibers. Conversely, there are cases where originally round laser beams need to be transformed into an elliptical shape. The article describes some sample applications and discusses several concepts of anamorphic beam shaping and their respective advantages and disadvantages.

Use of beam-shaping optics for wafer-scaled nanopatterning in laser interference lithography

Laser interference lithography is a widely used technology for large-area patterning of surfaces on the micro- and nanoscale. It is mostly used for research purposes due to the limited area that can be uniformly patterned due to the Gaussian intensity profile of the laser. In the scope of this work, the lithography system was extended by a freeform refractive glass which provided a spatially uniform energy distribution for a homogenous structuring process. The energy variation of the introduced light was reduced to 2.6% for the exposed area (4 × 9 cm), which is one magnitude lower than the energy variation of a Gaussian beam. With the refractive beam shaper, it was possible to produce a uniform nanopattern with an absolute linewidth variation of 7 nm over an area of 4 × 9 cm2. The structurable area is limited by the mirror size of the Lloyd’s mirror device. The demonstrated LIL system was also able to generate variable light fields from Gaussian to flat-top as well as inverse Gaussian profiles. This paper demonstrates nanopatterning of negative resist with a square homogenous output profile of the beam shaper. The square shape of the beam profile gives the opportunity to efficiently structure substrates with a square shape. Apart from standard silicon-based photolithographic processes, this technique is also attractive for nanopatterning of organic light-emitting diodes on glass or graduated grid structures like polarizers. Consequently, the advantages of the LIL fabrication (high-throughput and low-cost fabrication) are extended by the opportunity to scale the single-exposure process to large areas with only small variations in the detail.

Shaping Airy beams by using tunable polarization holograms

Optical beam shaping has emerged as an important tool in optics and photonics applications. Here we present the generation of Airy beams by means of the spatial-light-modulator-assisted polarization holography technique. The polarization holograms (PHs) are recorded in a polarization-sensitive nematic liquid crystal cell. By exploiting the advantages of the PH’s diffraction properties, such as the achromatic behavior, the high diffraction efficiency, and the polarization dependence, we experimentally generated Airy beams with diffraction efficiency of 91% at a wavelength of 633 nm.

Directive and tunable graphene based optical leaky wave radiating structure

We realize graphene optical leaky wave radiating structure for tuning the wavelength and radiation response. The use of graphene in designing optical leaky wave radiating structure provides efficient dynamic tuning and directive response. This tuning can be used for frequency switching of an optical antenna and beam shaping. In order to create switching mode, graphene perturbations are added in Si3N4 waveguide. Our results lead to graphene based design in the third window of optical communication. In addition, graphene based leaky wave design gives enhancement in different radiating structure parameters like reflection coefficient, transmission coefficient and far field radiation. The proposed graphene based designs have tunable directive response with high efficiency and are envisioned to become building blocks of several infrared systems which is going to be applicable in infrared wireless communication, medical imaging and switching.

Environmental influences on autocollimator-based angle and form metrology.

Deflectometric profilometers are indispensable tools for the precision form measurement of beam-shaping optics of synchrotrons and x-ray free electron lasers. They are used in metrology labs for x-ray optics worldwide and are crucial for providing measurement accuracy dictated by the form tolerances for modern state-of-the-art x-ray optics. Deflectometric profilometers use surface slope (angle) to assess form, and they utilize commercial autocollimators for the contactless slope measurement. In this contribution, we discuss the influences of environmental parameters, such as temperature and air pressure, including their gradients, on high-accuracy metrology with autocollimators in profilometers. They can cause substantial systematic errors in form measurement, especially in the case of large and strongly curved optical surfaces of high dynamic range. Relative angle and form measuring errors of the order of 10-4 are to be expected. We characterize environmental influences by extended theoretical and experimental investigations and derive strategies for correcting them. We also discuss the possibility to minimize the contributions of some errors by the application of sophisticated experimental arrangements and methods. This work aims at approaching fundamental limits in autocollimator-based slope and form metrology.

Recent Progress in All-Fiber Non-Gaussian Optical Beam Shaping Technologies

The rapid development of fiber lasers is being followed by wide ranges of applications in laser processing technologies. One of the key parameters to determine the laser–matter interaction is beam shape and there have been intense research activities on beam shaping using bulk optics. However, fiber optic solutions would take clear advantages over bulk optics especially for fiber laser sources in terms of the beam conversion efficiency, the throughput power, and the compact footprint. In this study, all-fiber optical beam shaping technologies are reviewed and they are categorized as the phase front modification on the fiber facet, the surface plasmonics on fiber, all-fiber Fourier transformation, and multimode interference. Their physical principles, beam shaping capability, and some of the novel applications are explained.

Effect of submount thickness on near-field bowing of laser diode arrays.

Near-field bowing a laser diode bar (i.e., the "SMILE" effect) degrades the laser beam brightness, adversely affecting optical coupling and beam shaping. Due to thermally induced stress during the bonding process, the emitters in a laser diode array (LDA) are vertically displaced, which causes the SMILE effect. The mismatch between the coefficients of thermal expansion of an LDA (GaAs with 6.4 ppm/K) and a heat sink (Cu with 16.4 ppm/K) is a large obstacle in the LDA bonding process, because it provokes thermal stress and a large SMILE value, resulting in a larger divergence angle and a wider line after focusing and collimation. In this paper, the changes in stress and strain (SMILE value) and their effects on the laser bar as a function of the copper-tungsten (CuW) submount thickness were theoretically and experimentally studied. The finite element modeling simulations and experimental results show that the compression stress on the laser bar decreases with increasing CuW submount thickness because the CuW submount works as a buffer layer and can absorb stress. However, the laser bar out-of-plane strain (SMILE value) is approximately zero when the LDA is directly bonded onto the heat sink without a submount; the SMILE value is maximized when the CuW submount thickness is increased to approximately one half or 44% of the heat sink. Beyond that, the SMILE value decreases with increasing CuW submount thickness.

Silicon Nitride Metalenses for Close-to-One Numerical Aperture and Wide-Angle Visible Imaging

As one of nanoscale planar structures, metasurface has shown excellent superiorities on manipulating light intensity, phase and/or polarization with specially designed nanoposts pattern. It allows to miniature a bulky optical lens into the chip-size metalens with wavelength-order thickness, playing an unprecedented role in visible imaging systems (e.g. ultrawide-angle lens and telephoto). However, a CMOS-compatible metalens has yet to be achieved in the visible region due to the limitation on material properties such as transmission and compatibility. Here, we experimentally demonstrate a divergent metalens based on silicon nitride platform with large numerical aperture (NA~0.98) and high transmission (~0.8) for unpolarized visible light, fabricated by a 695-nm-thick hexagonal silicon nitride array with a minimum space of 42 nm between adjacent nanoposts. Nearly diffraction-limit virtual focus spots are achieved within the visible region. Such metalens enables to shrink objects into a micro-scale size field of view as small as a single-mode fiber core. Furthermore, a macroscopic metalens with 1-cm-diameter is also realized including over half billion nanoposts, showing a potential application of wide viewing-angle functionality. Thanks to the high-transmission and CMOS-compatibility of silicon nitride, our findings may open a new door for the miniaturization of optical lenses in the fields of optical fibers, microendoscopes, smart phones, aerial cameras, beam shaping, and other integrated on-chip devices.

P‐12.1: Tunable Dammann Grating Based on Patterned Photoalignment

A tunable spatial light modulator, dammann grating, based on patterned photoalignment is demonstrated in this paper. Key to the fabrication of it, which is photo‐aligned with azo‐type material, is the ability of the material to be rewritable, i.e. it usually realigns upon rewriting. By adjusting electrical field, the grating can be switched between diffractive state showing 7 by 7 optical spots array and non‐diffractive state. Because of its diffractive property, it can be used in many optical applications such as optical communication, beam shaping, optical imaging and transparent displays.