Showing papers on "Diffraction grating published in 2019"

Dynamic Control of Light Direction Enabled by Stimuli-Responsive Liquid Crystal Gratings.

Abstract: The ability to control light direction with tailored precision via facile means is long-desired in science and industry. With the advances in optics, a periodic structure called diffraction grating gains prominence and renders a more flexible control over light propagation when compared to prisms. Today, diffraction gratings are common components in wavelength division multiplexing devices, monochromators, lasers, spectrometers, media storage, beam steering, and many other applications. Next-generation optical devices, however, demand nonmechanical, full and remote control, besides generating higher than 1D diffraction patterns with as few optical elements as possible. Liquid crystals (LCs) are great candidates for light control since they can form various patterns under different stimuli, including periodic structures capable of behaving as diffraction gratings. The characteristics of such gratings depend on several physical properties of the LCs such as film thickness, periodicity, and molecular orientation, all resulting from the internal constraints of the sample, and all of these are easily controllable. In this review, the authors summarize the research and development on stimuli-controllable diffraction gratings and beam steering using LCs as the active optical materials. Dynamic gratings fabricated by applying external field forces or surface treatments and made of chiral and nonchiral LCs with and without polymer networks are described. LC gratings capable of switching under external stimuli such as light, electric and magnetic fields, heat, and chemical composition are discussed. The focus is on the materials, designs, applications, and future prospects of diffraction gratings using LC materials as active layers.

Three-dimensional femtosecond laser nanolithography of crystals

Abstract: Nanostructuring hard optical crystals has so far been exclusively feasible at their surface, as stress induced crack formation and propagation has rendered high precision volume processes ineffective. We show that the inner chemical etching reactivity of a crystal can be enhanced at the nanoscale by more than five orders of magnitude by means of direct laser writing. The process allows to produce cm-scale arbitrary three-dimensional nanostructures with 100 nm feature sizes inside large crystals in absence of brittle fracture. To showcase the unique potential of the technique, we fabricate photonic structures such as sub-wavelength diffraction gratings and nanostructured optical waveguides capable of sustaining sub-wavelength propagating modes inside yttrium aluminum garnet crystals. This technique could enable the transfer of concepts from nanophotonics to the fields of solid state lasers and crystal optics.

Prospects and challenges in augmented reality displays

Abstract: Augmented reality (AR) displays are attracting significant attention and efforts. In this paper, we review the adopted device configurations of see-through displays, summarize the current development status and highlight future challenges in micro-displays. A brief introduction to optical gratings is presented to help understand the challenging design of grating-based waveguide for AR displays. Finally, we discuss the most recent progress in diffraction grating and its implications.

Understanding diffraction grating behavior: including conical diffraction and Rayleigh anomalies from transmission gratings

Abstract: With the wide-spread availability of rigorous electromagnetic (vector) analysis codes for describing the diffraction of electromagnetic waves by specific periodic grating structures, the insight and understanding of nonparaxial parametric diffraction grating behavior afforded by approximate methods (i.e., scalar diffraction theory) is being ignored in the education of most optical engineers today. Elementary diffraction grating behavior is reviewed, the importance of maintaining consistency in the sign convention for the planar diffraction grating equation is emphasized, and the advantages of discussing “conical” diffraction grating behavior in terms of the direction cosines of the incident and diffracted angles are demonstrated. Paraxial grating behavior for coarse gratings ( d ≫ λ) is then derived and displayed graphically for five elementary grating types: sinusoidal amplitude gratings, square-wave amplitude gratings, sinusoidal phase gratings, square-wave phase gratings, and classical blazed gratings. Paraxial diffraction efficiencies are calculated, tabulated, and compared for these five elementary grating types. Since much of the grating community erroneously believes that scalar diffraction theory is only valid in the paraxial regime, the recently developed linear systems formulation of nonparaxial scalar diffraction theory is briefly reviewed, then used to predict the nonparaxial behavior (for transverse electric polarization) of both the sinusoidal and the square-wave amplitude gratings when the +1 diffracted order is maintained in the Littrow condition. This nonparaxial behavior includes the well-known Rayleigh (Wood’s) anomaly effects that are usually thought to only be predicted by rigorous (vector) electromagnetic theory.

SiN integrated optical phased arrays for two-dimensional beam steering at a single near-infrared wavelength

Abstract: In this work, we present two-dimensional beam steering in the near-infrared using a SiN integrated circuit, containing optical phased arrays. Beam steering was achieved over a range of 17.6° × 3°, at a fixed wavelength of 905 nm. The first dimension was steered via phase differences between the optical phased array channels. The second dimension was accessed by actively switching between various optical phased array sub-devices containing output diffraction gratings with different periods. The characterisation was performed on a wafer-level test station.

Generalized Space-Time-Periodic Diffraction Gratings: Theory and Applications

Abstract: Unlike a conventional diffraction grating, a space-time-periodic (STP) grating produces spatial diffraction orders, each of which is formed by an infinite set of temporal diffraction orders. STP gratings offer enhanced functionalities and exotic characteristics, such as asymmetric diffraction patterns, nonreciprocal and asymmetric transmission and reflection, and an enhanced diffraction efficiency. Here a rigorous, general theory of diffraction by STP gratings is formulated, and a particular practical application in wireless communication is proposed: an inventive multiple-access communication system, featuring full duplex operation and high data-transmission rate.

Enhancing the Output Performance of Triboelectric Nanogenerator via Grating‐Electrode‐Enabled Surface Plasmon Excitation

Abstract: As energy crisis has become a serious problem in the world, intensive research efforts have been devoted to explore new energy resources. Triboelectric nanogenerators (TENGs) as a new energy harvesting technology with unprecedented output The surface charge density and the output impedance of triboelectric nanogenerators (TENGs) are two critical factors for TENGs to speed up their commercialization, so it is important to explore unique methods to reduce the output impedance and increase the surface charge density. Here, an approach is demonstrated to effectively boost the output performance of TENG while reducing the output impedance of TENGs by utilizing gratingelectrode-enabled surface plasmon excitation. A sustainable and enhanced output performance of about 40 μA (short-circuit current) and 350 V (peak-topeak voltage at a resistance of 10 MΩ) is produced via grating-coupled surface plasmon resonance on the TENG with the aluminum grating electrode in the line density of 600 lines mm−1, and it delivers a peak output power of 3.6 mW under a loading resistance of 1 MΩ, giving over 4.5-fold enhancement in output power and a 75% reduction in the output impedance. Finally a self-powered ultrasonic ranging system is utilized to verify the capability of the TENG in powering portable electrics.

Stretchable, flexible, rollable, and adherable polarization volume grating film

Abstract: Volume Bragg gratings (VBGs) have many applications, including filters, wavelength multiplexing devices, and see-through displays. As a kind of VBGs, polarization volume gratings (PVGs) based on liquid crystal polymer have the advantages of nearly 100% efficiency, large deflection angle, and high polarization selectivity. However, previous reports regarding PVGs did not address high efficiency, tunable periodicity, and flexibility. Here, we report a stretchable, flexible, and rollable PVG film with high diffraction efficiency. The control of PVG by mechanical stretching is investigated, while the Bragg reflection band shift is evaluated quantitatively. Moreover, we quantified the deflection angle change's behavior, which has promising potential for laser beam steering applications. The mechanical robustness under stretch-release cycles is also scrutinized.

Realization of alignment-tolerant grating couplers for z-cut thin-film lithium niobate.

Abstract: We present the design, modeling, fabrication, and characterization of grating coupler devices for z-cut lithium niobate near 1550 nm. We first experimentally measure the sensitivity of the insertion loss of a conventional grating coupler to translational misalignment through a three-factor full factorial design of experiment. Next, we design grating couplers that are significantly less sensitive to misalignment. The fabricated devices experienced less than 7 dB of excess insertion loss for combined misalignments of up to ± 5 μm in plane and up to −2 μm or + 10 μm out of plane.

Engineered Diffraction Gratings for Acoustic Cloaking

Abstract: The authors demonstrate, both theoretically and experimentally, that engineered diffraction gratings can modulate the acoustic wavefront more efficiently than can traditional devices based on complex metamaterials and metasurfaces. To demonstrate the feasibility of this approach, a three-dimensional conical ground cloak is fabricated and tested, with remarkable results, compared to other cloaks based on different physical mechanisms. This achievement shows a path to advanced control of mechanical waves by means of simpler, more efficient principles.

Generalized Space-Time Periodic Diffraction Gratings: Theory and Applications

Abstract: This paper studies the theory and applications of the diffraction of electromagnetic waves by space-time periodic (STP) diffraction gratings. We show that, in contrast with conventional spatially periodic grating, a STP diffraction grating produces spatial diffraction orders, each of which is formed by an infinite set of temporal diffraction orders. Such spatiotemporally periodic gratings are endowed with enhanced functionalities and exotic characteristics, such as asymmetric diffraction pattern, nonreciprocal and asymmetric transmission and reflection, and an enhanced diffraction efficiency. The theory of the wave diffraction by STP gratings is formulated through satisfying the conservation of both momentum and energy, and rigorous Floquet mode analysis. Furthermore, the theoretical analysis of the structure is supported by time and frequency domain FDTD numerical simulations for both transmissive and reflective STP diffraction gratings. Additionally, we provide the conditions for Bragg and Raman-Nath diffraction regimes for STP gratings. Finally, as a particular example of a practical application of the STP diffraction gratings to communication systems, we propose an original multiple access communication system featuring full-duplex operation. STP diffraction gratings are expected to find exotic practical applications in communication systems, especially for the realization of enhanced-efficiency or full-duplex beam coders, nonreciprocal beam splitters, nonreciprocal and enhanced-resolution holograms, and illusion cloaks.

Inverse Grating Problem: Efficient Design of Anomalous Flexural Wave Reflectors and Refractors

Abstract: To obtain a desired profile of transmitted wave modes, what must a diffraction grating look like? This work presents a generalized, systematic method to design devices for control of the flow of wave energy. This control is achieved by engineering the diffraction properties of gratings, and simplified configurations are found, compared to similar gradient-metasurface devices. Although focused on flexural waves in thin elastic plates, this approach can be easily applied to other domains, such as optics, electronics, or fluid acoustics, as the diffraction principles are the same in all of these contexts.

Sub-decibel silicon grating couplers based on L-shaped waveguides and engineered subwavelength metamaterials.

Abstract: The availability of low-loss optical interfaces to couple light between standard optical fibers and high-index-contrast silicon waveguides is essential for the development of chip-integrated nanophotonics. Input and output couplers based on diffraction gratings are attractive coupling solutions. Advanced grating coupler designs, with Bragg or metal mirror underneath, low- and high-index overlays, and multi-level or multi-layer layouts, have proven less useful due to customized or complex fabrication, however. In this work, we propose a rather simpler in design of efficient off-chip fiber couplers that provide a simulated efficiency up to 95% (−0.25 dB) at a wavelength of 1.55 µm. These grating couplers are formed with an L-shaped waveguide profile and synthesized subwavelength grating metamaterials. This concept jointly provides sufficient degrees of freedom to simultaneously control the grating directionality and out-radiated field profile of the grating mode. The proposed chip-to-fiber couplers promote robust sub-decibel coupling of light, yet contain device dimensions (> 120 nm) compatible with standard lithographic technologies presently available in silicon nanophotonic foundries. Fabrication imperfections are also investigated. Dimensional offsets of ± 15 nm in shallow-etch depth and ± 10 nm in linewidth’s and mask misalignments are tolerated for a 1-dB loss penalty. The proposed concept is meant to be universal, which is an essential prerequisite for developing reliable and low-cost optical couplers. We foresee that the work on L-shaped grating couplers with sub-decibel coupling efficiencies could also be a valuable direction for silicon chip interfacing in integrated nanophotonics.

Single-beam Zeeman slower and magneto-optical trap using a nanofabricated grating.

Abstract: We demonstrate a compact (0.25 L) system for laser cooling and trapping atoms from a heated dispenser source. Our system uses a nanofabricated diffraction grating to generate a magnetooptical trap (MOT) using a single input laser beam. An aperture in the grating allows atoms from the dispenser to be loaded from behind the chip, increasing the interaction distance of atoms with the cooling light. To take full advantage of this increased distance, we extend the magnetic field gradient of the MOT to create a Zeeman slower. The MOT traps approximately 106 7Li atoms emitted from an effusive source with loading rates greater than 106 s-1. Our design is portable to a variety of atomic and molecular species and could be a principal component of miniaturized cold-atom-based technologies.

The ROGUE: a novel, noise-generated random grating.

Abstract: We propose a novel device defined as Random Optical Grating by Ultraviolet or ultrafast laser Exposure (ROGUE), a new type of fiber Bragg grating (FBG), exhibiting a weak reflection over a large bandwidth, which is independent of the length of the grating. This FBG is fabricated simply by dithering the phase randomly during the writing process. This grating has an enhanced backscatter, several orders of magnitude above typical Rayleigh backscatter of standard SMF-28 optical fiber. The grating is used in distributed sensing using optical frequency domain reflectometry (OFDR), allowing a significant increase in signal to noise ratio for strain and temperature measurement. This enhancement results in significantly lower strain or temperature noise level and accuracy error, without sacrificing the spatial resolution. Using this method, we show a sensor with a backscatter level 50 dB higher than standard unexposed SMF-28, which can thus compensate for increased loss in the system.

Lop-sided Raman–Nath diffraction in PT-antisymmetric atomic lattices

Abstract: Two-dimensional (2D) optical lattices of driven cold atoms can provide a useful platform to construct 2D electromagnetically induced grating (EIG) with parity-time (PT) antisymmetry. This atomic grating is achieved by the spatial modulations of the atomic density and frequency detunings in the four-level double-Λ atomic system. Gain-assisted PT antisymmetry allows us to realize lop-sided Raman–Nath diffraction with high diffraction efficiency at the exception point. It is shown that the nontrivial phenomenon originates from non-Hermitian degeneracy of PT antisymmetry. Our scheme may provide the possibility for active all-optical control and conversion of the spatial beam in optics.

Experimental Verification of a Bigrating Beam Rider.

Abstract: An optical beam rider making use of a light sail comprising two opposing diffraction gratings is experimentally demonstrated for the first time. We verify that the illuminated space-variant grating structure provides an optical restoring force, exhibiting stable oscillations when the bigrating is displaced from equilibrium. We further demonstrate parametric cooling by illuminating the sail with synchronized light pulses. This experiment enhances the technical feasibility of a laser-driven light sail based on diffractive radiation pressure.

Plug-and-play fiber to waveguide connector.

Abstract: The mass production and commercialization of integrated photonics have been slowed down by the high cost of packaging its optical interfaces We show a plug-and-play connector between a fiber and a nanophotonic waveguide consisting of a 3D polymer structure with a fiber entrance port that simultaneously achieves mechanical and optical passive alignment with tolerance beyond ±10 μm to the fiber input position We take advantage of a mechanical and optical co-design, analogous to commercial fiber-to-fiber connectors We fabricate the plug-and-play couplers using 3D nanoprinting directly on foundry fabricated diffraction grating couplers We measure an average of only 005 dB excess coupling loss between a single mode fiber and a high confinement silicon waveguide in addition to the inherent grating coupler loss Our coupling platform offers a passive plug-and-play solution for scalable integrated photonics fiber-chip packaging

Experimental Demonstration of an Acoustic Asymmetric Diffraction Grating Based on Passive Parity-Time-Symmetric Medium

Abstract: Acoustic asymmetric transport is important for noise control and communication acoustics. Recent progress on non-Hermitian systems has yielded a scheme to realize asymmetric transport without nonlinear effects or mode conversion. The authors report the experimental realization of an asymmetric diffraction grating based on a cleverly designed passive $P\phantom{\rule{0}{0ex}}T$-symmetric medium, in which loss is introduced as an extra modulation factor, and the energy distribution can be adjusted more freely. Moreover, the designed structure is helpful for further research on non-Hermitian acoustic systems.

Numerical investigation of imaging-free terahertz generation setup using segmented tilted-pulse-front excitation.

Abstract: Recently a hybrid-type terahertz (THz) pulse source was proposed for high energy terahertz pulse generation. It is the combination of the conventional tilted-pulse-front setup and a nonlinear crystal with a transmission stair-step echelon of period in the hundred-micrometer range etched into the front face. The tilt angle introduced by the conventional tilted-pulse-front setup (pre-tilt) was chosen to be equal to the tilt-angle needed inside the nonlinear crystal (62° for lithium niobate (LN)) in order to fulfill velocity-matching. In this case, plane-parallel nonlinear optical crystals can be used. The possibility of using a plane-parallel nonlinear optical crystal for producing good-quality, symmetric THz beams was considered the most important advantage of this setup. In the present paper, a thorough numerical investigation of a modified version of that setup is presented. In the new version, the tilted pulse-front is created by a transmission grating without any imaging optics, and a wedged nonlinear optical crystal with a small wedge angle is supposed. According to a 1D numerical code, significantly higher THz generation efficiency can be achieved with a transmission stair-step echelon-faced nonlinear crystal having a 5 – 15-degree wedge angle than with a plane-parallel one or with the conventional tilted-pulse-front setup. Because of the spatially-dependent group-delay dispersion introduced by the transmission grating, a small wedge in the nonlinear crystal improves the spatial homogeneity of the THz-generation process, resulting in higher efficiencies and better beam profiles. At 100 K temperature, and by using 800 nm pump pulses with 20 mJ pulse energy, 100 fs pulse length and 8 mm beam spot radius, approximately 4.5% conversion efficiency and close to 1 mJ terahertz pulse energy can be reached with the newly-proposed setup.

Femtosecond 78-nm Tunable Er:Fibre Laser Based on Drop-Shaped Resonator Topology

Abstract: We report for the first time on study of a passively mode-locked Er-doped fibre laser with ultra-wide tuning (from 1524 to 1602 nm) of the central wavelength of its femtosecond output (503–940 fs). The recently proposed drop-shaped cavity topology for fibre lasers enabled a compact widely tuneable femtosecond laser with a single discrete element, a reflective diffraction grating used for wavelength tuning of the output radiation. The key features of the proposed laser are: spectral tuning does not require adjustment of any other cavity elements; stable generation with a single pulse per round trip is provided over the entire wavelength tuning range; and the output pulses are close to transform limited and feature relatively high (>58 dB) signal-to-noise ratio of laser inter-mode beats indicating high quality of mode locking across the entire wavelength tuning range. The proposed laser configuration relying on the new drop-shaped cavity topology simultaneously delivers stability and reliability of mode locking, possibility of broad-range wavelength tunability, and adjustability of the output pulse repetition rate of the laser (which is important in various metrological and other applications).

Transient grating spectroscopy: An ultrarapid, nondestructive materials evaluation technique

Abstract: Structure–property relationships are the foundation of materials science and are essential for predicting material response to driving forces, managing in-service material degradation, and engineering materials for optimal performance. Elastic, thermal, and acoustic properties provide a convenient gateway to directly or indirectly probe materials structure across multiple length scales. This article will review how using the laser-induced transient grating spectroscopy (TGS) technique, which uses a transient diffraction grating to generate surface acoustic waves and temperature gratings on a material surface, nondestructively reveals the material’s elasticity, thermal diffusivity, and energy dissipation on the sub-microsecond time scale, within a tunable subsurface depth. This technique has already been applied to many challenging problems in materials characterization, from analysis of radiation damage, to colloidal crystals, to phonon-mediated thermal transport in nanostructured systems, to crystal orientation and lattice parameter determination. Examples of these applications, as well as inferring aspects of microstructural evolution, illustrate the wide potential reach of TGS to solve old materials challenges and to uncover new science. We conclude by looking ahead at the tremendous potential of TGS for materials discovery and optimization when applied in situ to dynamically evolving systems.

Unidirectional and controllable higher-order diffraction by a Rydberg electromagnetically induced grating

Abstract: A method for diffracting the weak probe beam into unidirectional and higher-order directions is proposed via a Rydberg electromagnetically induced grating, providing a way for the implementations of quantum devices with cold Rydberg atoms. The proposed scheme utilizes a suitable position-dependent adjustment to the two-photon detuning besides the modulation of the standing-wave coupling field, producing an in-phase modulation which can change the parity of the dispersion. We observe that when the modulation amplitude is appropriate, a perfect unidirectional diffraction grating can be realized. In addition, due to the mutual effect between the van der Waals (vdW) interaction and the atom-field interaction length that deeply improves the dispersion of the medium, the probe energy can be counterintuitively transferred into higher-order diffractions as increasing the vdW interaction, leading to the realization of a controllable higher-order diffraction grating via a strong blockade.

Color LED DMD holographic display with high resolution across large depth.

Abstract: Holographic displays employing digital micromirror devices (DMDs) reconstruct 3D images at high diffraction orders. For LED displays, this geometry introduces large dispersion at the DMD surface, reducing image resolution and depth. This work proposes a color DMD LED holographic display with dispersion compensation utilizing an additional diffraction grating in an illumination module. The solution allows to obtain image depth up to 100 mm, which is comparable to the one achieved by a liquid crystal spatial light modulator, where the limiting factor is spatial coherence of the source. Experimental comparison of the results obtained with the laser and LED source gives evidence of effective speckle noise reduction, even from a single frame.

Elastic Phased Diffraction Gratings for Manipulation of Ultrasonic Guided Waves in Solids

Abstract: Lamb waves and surface acoustic waves (SAWs) are of great interest for frontier technologies, including structural health monitoring, energy harvesting, sensors, and acoustic tweezers. This work presents elastic phased diffraction gratings, passive structures for controlling guided ultrasonic waves in solids. Such a grating adopts an array of interchangeable superstrates to modulate wave dispersion, and thus the diffraction wave field. Experiments demonstrate the ability to modulate antisymmetric and symmetric Lamb waves at 100 kHz, and Rayleigh SAWs at 100 MHz. These gratings are comparatively easy to fabricate, interchangeable, and theoretically feasible for all Rayleigh-Lamb modes.

Reflection grating concept for the Lynx X-Ray Grating Spectrograph

Abstract: The Lynx X-ray Grating Spectrograph (XGS) is responsible for providing high throughput and spectral resolution for soft x-ray energies. This instrument will help characterize the formation of galaxies and a large-scale structure in the universe. Such goals require large effective areas, >4000 cm2, and high resolving power, R > 5000, over much of the low-energy band, 0.2 to 2.0 keV. A concept design for the XGS using reflection gratings has the potential to achieve these requirements. The design uses achievable grating parameters, efficient packing of the grating array, and a compact detector layout. The concept is presented along with a detailed discussion of the considerations made in its determination.

Diffusion dynamics of valley excitons by transient grating spectroscopy in monolayer WSe2

Abstract: The transient grating spectroscopy is widely used to determine the diffusion coefficients of valley excitons or spins in low-dimensional semiconductor materials. Here, we present the investigation on the diffusion dynamics of the valley excitons in a high-quality large-scale mechanically exfoliated tungsten diselenide (WSe2) monolayer by this technique at room temperature. Collinearly polarized laser excitation (at a photon energy of 1.66 eV resonant to the energy of valley A-excitons) was used to introduce a spatially periodic density of valley excitons. Through probing the spatial and temporal evolution of the initial density of valley excitons, we find that the signals of transient grating exhibit an nonexponential decay, and its decay rate is independent of the period of optical grating Λ. Combined with the transient reflection measurements, we show that the exciton-exciton annihilation plays a key role in decay processes of the transient grating spectroscopy, which results in the distortion of sinusoidal gratings. Based on Einstein relationship, we estimate the diffusion coefficient of valley exciton DX = 0.7 cm2/s.

Global tool path optimization of high-resolution image reproduction in ultrasonic modulation cutting for structural coloration

Abstract: Diffraction gratings are capable of splitting and diffracting parallel white light into a wide diffractive spectrum containing light with different wavelengths travelling in different directions. The apparent angle-dependent color effect is a form of structural coloration. In this paper, a rendering strategy for grating-induced high-resolution image reproduction has been demonstrated based on tool path optimization. The grating structures are generated by ultrasonic modulation cutting due to the cutting depth modulation. The high-resolution image rendering is accomplished by tailoring the interaction between visible light and grating structures through the design and optimization of the distribution of machined grating arrays. Fabricating the desired grating arrays requires a complex objective tool path with ever-changing discontinuous step velocity profiles, which is not achievable for any existing machine tools considering the limited acceleration capability. Unlike conventional toolpath optimization methods, the proposed research aims to relate the cutting process to high-resolution image rendering performance and optimize the quality of machined images through optimally approximating the objective tool velocity-location curve with a series of parametric splines in terms of minimum overall velocity error. A recursive optimization method has been developed to ensure the global optimum of the tool velocity profile considering the physical limitation of motion axes. The fitting performance of proposed method is quantitatively analyzed and evaluated through the simulation and experiment by comparing the real-time velocity-location profiles to the objective curves. In addition, the reproduction quality of machined images is evaluated by measuring the similarity between the reproduced and original images with both simulation and experimental results.

Nanopillar Diffraction Gratings by Two-Photon Lithography

Abstract: Two-dimensional photonic structures such as nanostructured pillar gratings are useful for various applications including wave coupling, diffractive optics, and security features. Two-photon lithography facilitates the generation of such nanostructured surfaces with high precision and reproducibility. In this work, we report on nanopillar diffraction gratings fabricated by two-photon lithography with various laser powers close to the polymerization threshold of the photoresist. As a result, defect-free arrays of pillars with diameters down to 184 nm were fabricated. The structure sizes were analyzed by scanning electron microscopy and compared to theoretical predictions obtained from Monte Carlo simulations. The optical reflectivities of the nanopillar gratings were analyzed by optical microscopy and verified by rigorous coupled-wave simulations.