Submicron Gratings Research Articles

Plasmonic photodetector with submicron grating for reconstructive spectroscopy of low-intensity broadband light

Reconstructive spectroscopy, a spectroscopic method that derives the spectrum of incident light using photodetection elements with various dispersion characteristics, is emerging as a promising approach for constructing compact spectroscopic devices. The generally adopted approach of simultaneously irradiating spatially distributed multiple elements is not suitable for weak light because the elements divide the total incident power spatially. Temporarily tilting a single-eyed diffraction grating photodetector that couples the light with the surface plasmon resonance can utilize the whole incident optical power, which is advantageous when only weak light is available. However, to perform robust spectroscopy, a carefully designed dispersion relation of surface plasmon resonance is required. In this study, we propose a suitable grating structure for reconstructive spectroscopy of low-intensity broadband near-infrared light. Using an optimal sub-micron pitch of 0.95 µm grating, the reconstruction of the light from a halogen lamp light with an intensity density as small as around 10µW/nm is presented in the 1200–1400 nm wavelength range. The reconstructive spectroscopy with the plasmonic photodetector also allows for the identification of materials such as glass, cycloolefin polymer, and acrylic resin within this wavelength band. The potential for integration with microelectromechanical systems technology opens up possibilities for a compact near-infrared spectroscopic device that is compatible with a variety of light sources, offering applications in various scientific fields.

High-Uniformity Submicron Gratings with Tunable Periods Fabricated through Femtosecond Laser-Assisted Molding Technology for Deformation Detection.

As one of the important diffractive optical elements, the submicron gratings on flexible substrates can actively and precisely control the dispersion and steering characteristics of beams and have been widely applied in deformation detection technologies. Herein, we propose a spatially modulated femtosecond laser-assisted molding technology for efficiently fabricating high-uniformity large-area submicron gratings with tunable periods on flexible substrates. The technology first uses a cylindrically focused femtosecond laser-assisted chemical etching method to form a regular submicron grating on silicon; subsequently, the structure is cast with polydimethylsiloxane, a useful flexible substrate with a small Young's modulus, and cured to obtain a high-uniformity large-area submicron grating with a tunable period. The grating exhibits high mechanical stability and sensitivity and favorable optical properties. In the present study, as the deformation of the grating increased from 0 to 10%, the diffraction angle changed by 6.5°. Under illumination by a broad-band white-light source, distinguishable multicolor diffraction patterns were clearly observed. Drawing on this characteristic, we fabricated a deformation sensor. The grating fabricated by using the proposed technology also has potential applications in optical sensors and soft robots.

Design and Simulation of Waveguide Bragg Grating based Temperature Sensor in COMSOL

With the advancements in the domain of photonics and optical sensors, Fibre Bragg Grating (FBG) sensors, owing to their increased advantages, have been researched widely and have proved to be useful in sensing applications. Moreover, the advent of Photonic Integrated Circuits (PICs) demands the incorporation of optical sensing in waveguides, which can be integrated on silicon photonic chips. In this paper, the design of a sub-micron range Waveguide Bragg Grating (WBG) based temperature sensor with high peak reflectivity and thermal sensitivity is proposed. The flexibility of COMSOL Multiphysics software is explored to simulate the sensor and the results are verified with the analytical values calculated using MATLAB. The simulation is carried out for the proposed design having 16000 gratings and a corresponding peak reflectivity of 0.953 is obtained. A thermal sensitivity of 80 pm/K is achieved, which is approximately eight times better than that of FBG based sensor.

Non-resonant 3D Elliptical Vibration Cutting Induced Submicron Grating Coloring

Surface Submicron grating manufacturing has broad application prospects, which has also been the subject of intensive research and development by scholars with many efforts. In this paper, a grating coloring manufacturing method is proposed based on three-dimensional elliptical vibration cutting and non-resonant piezoelectric actuator. Based on the mechanism of elliptical motion, an effective cutting depth model was established. Nonlinear interaction of machining parameters (overlap rate, nominal cutting speed, vibration frequency) on the geometry of the grating were analyzed and controllable modulation model of grating geometry was established. The geometrical dimensions of the grating were predicted and grooved experiments were performed on brass and aluminum surfaces. A set of angle-adjustable detection device was designed independently to check the diffraction quality of the grating. The quantitative experimental results show that grating distances of copper and aluminum rods are 752 nm and 684 nm, respectively. The average width of the aluminum rod overall grating is 764 nm, the accuracy error is 9.25%. In addition, aluminum rod gratings can diffract red light at non-specific angles, which is more effective at viewing angle of 70°. The experimental results are in agreement with the theory which have positive significance for expanding the functional surface.

Light- and Neutron-Optical Properties of Holographic Transmission Gratings from Polymer-Ionic Liquid Composites with Submicron Grating Spacing.

We investigate the applicability of polymer-ionic liquid composites as optical elements for light, as well as for slow neutrons. The gratings are recorded using two-beam mixing and are characterized experimentally based on their diffraction properties. We produced a set of samples differing in their thickness, ranging from 10 μm–100 μm. We demonstrate that it is possible to prepare transmission gratings with a lattice constant of nm, resulting in thick gratings for light, as well as neutrons. The presented samples show low optical losses in the Vis-UV spectrum and exhibit refractive index modulations of about at nm. However, further improvements have to be made to obtain efficient neutron optical components.

Method for Tuneable Homeotropic Anchoring at Microstructures in Liquid Crystal Devices

A simple method for vapour-phase deposition of a silane surfactant is presented, which produces tuneable homeotropic anchoring in liquid crystals. Both the zenithal anchoring energy and surface slip are measured by fitting to the latching threshold versus pulse width characteristic of a zenithal bistable nematic liquid crystal device based on a deep, submicron grating. The method is shown to give microscopic anchoring strength between 5 × 10-5 and 2 × 10-4 J/m2, with a surface slip of about 100 nm. The silanated surfaces are characterized using atomic force microscopy and X-ray photoelectron spectroscopy, which show a direct relationship between the surface coverage of silane groups and the resulting anchoring energy.

Photonic bandpass filter characteristics of multimode SOI waveguides integrated with submicron gratings.

It has been shown that a fundamental mode adiabatically launched into a multimode SOI waveguide with submicron grating offers well-defined flat-top bandpass filter characteristics in transmission. The transmitted spectral bandwidth is controlled by adjusting both waveguide and grating design parameters. The bandwidth is further narrowed down by cascading two gratings with detuned parameters. A semi-analytical model is used to analyze the filter characteristics (1500 nm≤λ≤1650 nm) of the device operating in transverse-electric polarization. The proposed devices were fabricated with an optimized set of design parameters in a SOI substrate with a device layer thickness of 250nm. The pass bandwidth of waveguide devices integrated with single-stage gratings are measured to be ∼24 nm, whereas the device with two cascaded gratings with slightly detuned periods (ΔΛ=2 nm) exhibits a pass bandwidth down to ∼10 nm.

Solar cell efficiency improvement using dip-pen nanolithography

An innovative approach to improve the performance of photovoltaic solar cells is presented. Until recently, the fabrication of grating layers has been well proven using bulk micromachining techniques, but lately low-cost dip-pen nanolithography (DPN) has been proposed as a method for printing nanostructures on different substrates and has matured to become one of the most versatile patterning techniques available at the nanoscale. However, this technique has scarcely been studied and tested for fabricating grating layers. In this research, submicron grating patterns from high refractive index polymers are fabricated on a few types of solar cells, significantly improving their efficiency. The appropriate geometries and materials for the grating patterns are obtained via numerical optimization using rigorous coupled wave analysis for electromagnetic simulations of the grating multilayer. Possible light-confinement schemes are analyzed, and their figures of merit are assessed. The simulation of the electrical characteristics is integrated with postdesign electromagnetic simulation. The corresponding theoretical and experimental studies shed light on the impact of the merger of the grating structure with the light harvester on the device’s optical and electrical properties. Success in using DPN paves pathways to low-cost fabrication of light harvesting devices with improved performance.

Fabrication of micron and submicron gratings by using plasma treatment on the curved polydimethylsiloxane surfaces

Here, a simple and low-cost fabrication strategy to efficiently construct well-ordered micron and submicron gratings on polymeric substrates by oxygen plasma treatment is reported. The Polydimethylsiloxane (PDMS) substrate is prepared on the polyethylene (PET) by spin-coating method, then the curved PDMS-PET substrates are processed in oxygen plasma. After appropriate surface treatment time in plasma the curved substrates are flattened, and well-ordered wrinkling shape gratings are obtained, due to the mechanical buckling instability. It is also demonstrated that changing the curvature radius of PDMS-PET substrates and the time of plasma treatment, the period of the wrinkling patterns and the amplitude of grating also change accordingly. It is found the period of the wrinkling patterns increased with the radius of curvature; while the amplitude decreased with that. It also shows good optical performance in transmittance diffraction testing experiments. Thus the well-ordered grating approach may further develop portable and economical applications and offer a valuable method to fabricate other optical micro strain gauges devices.

Compact mirror-tunable laser interference system for wafer-scale patterning of grating structures with flexible periodicity

This paper presents a novel mirror-tunable laser interference system for the wafer-scale patterning (>4-in.) of submicron grating structures with a flexible periodicity (200–1000 nm) in a compact and cost-effective manner. The proposed system guides and splits the laser beam into two expanded light beams propagating in a downward direction to be reflected by rotatable ultraviolet mirrors to produce interference patterns. The incident angle of two light beams can be controlled by rotating the mirrors until they match the targeted periodicity of the grating, without the need to reconfigure the optical paths. The fact that light polarization changes with the rotation angle of the mirrors necessitates the use of a half-wave plate along each optical path to adjust the direction of polarization perpendicular to the plane of incident light. The proposed system enables large-area fabrication and wide-range grating tunability, making it highly useful for applications that require wafer-scale patterning of submicron periodic structures, such as flexible wire-grid polarizers for displays, patterned sapphire substrates for light-emitting diodes, and Bragg gratings for distributed feedback lasers.

High surface mobility and fast surface enhanced crystallization of metallic glass

The surface viscosity and self-diffusion of a Pd-based metallic glass were measured using annealing-induced decay of its surface submicron gratings. Strong surface dynamics and surface diffusion with the value of more than 105 times faster than bulk diffusion are found at temperatures below glass transition. The high surface dynamic induces a fast crystallization below glass transition temperature at the free surface which is more than 100 times faster than that in bulk.

A simple and wide-range refractive index measuring approach by using a sub-micron grating

This paper presents the design and simulation results of a high-precision low-cost refractometer that demonstrates the main advantage of a wide measurement range (1 ≤ n ≤ 2). The proposed design is based on the diffractive properties of sub-micron gratings and Snell's Law. The precision and uncertainty factors of the proposed system were tested and analyzed, revealing that the proposed refractometer demonstrates a wide measurement range with sensitivity of 10−4.

Sub-micron structuring of silicon using femtosecond laser interferometry

We report the fabrication of planar sub-micron gratings in silicon with a period of 720 nm using a modified Michelson interferometer and femtosecond laser radiation. The gratings consist of alternated stripes of laser ablated and unmodified material. Ablated stripes are bordered by parallel ridges which protrude above the unmodified material. In the regions where ridges are formed, the laser radiation intensity is not sufficient to cause ablation. Nevertheless, melting and a significant temperature increase are expected, and ridges may be formed due to expansion of silicon during resolidification or silicon oxidation. These conclusions are consistent with the evolution of the stripes morphology as a function of the distance from the center of the grating.

Long Wavelength {greater than or equal to}1.9 μm Germanium for Optoelectronics Using Process Induced Strain

The photoluminescence of tensile strained germanium nanostructures is reported. Sub-micron gratings and pillars were fabricated before bein embedded in a strained silicon nitride films. Using different deposition conditions and different sizes of structures the stress in the nanostructures can be controlled. The measured optical properties of the samples show that the direct band-gap is shifted drastically towards higher wavelength over 1.9 um wavelength. This process of local control of the stress in germanium nanostructures is compatible with integrated photonic devices in waveguides geometry. That opens the route for both emitters and photo-detectors above 1.6 um wavelength which are not easily available and also potentially towards a germanium laser.

Antireflection and Scattering Properties of Two-Dimensional Hexagonal AZO Gratings on Glass Substrates

With photoresist dot arrays fabricated by a two-beam interference lithography as an etch mask, two-dimensional (2-D) hexagonal aluminum-doped zinc oxide（AZO）submicron gratings (SMG) with 160nm height (h) and different periods (P) were produced using lift-off transfer process. Results show that as P decreased to 487nm, SMG exhibited excellent antireflection properties, which reduced the average total reflectivity (Rtotal) from 11.8% of AZO thin film to 4.7% in the wavelength range of 400nm-1050nm, and promoted the total transmittance (Ttotal) significantly, especially in the long spectral range of 750nm-1050nm. On the other hand, as P increased from 487nm to 985nm, the haze parameters of reflectance (HR) or transmittance (HT) improved from 25.5% to 40.2% or from 15.1% to 36.8%, respectively. Nevertheless, P increased from 985nm to 1435nm, both Rtotal (or Ttotal) and HR (or HT) varied very slightly. Bidirectional distribution functions at normal incidence not only verified that the larger the P was, the part of diffuse reflectance (or transmittance) were much higher, but also further demonstrate the larger the P, the smaller the diffaction angle. In summary, 2-D hexagonal AZO SMG show promising antireflection effects at P less than 487nm, and show promising scattering abilities at P about 985nm.

Micron and Sub-Micron Gratings on Glass by UV Laser Ablation

Abstract ArF excimer laser ablation is applied for the generation of surface relief gratings on various glass materials. At the laser wavelength of 193 nm even highly transparent borosilicate glasses exhibit sufficient absorption for the fabrication of precise, crack free ablation patterns. Gratings with periods down to 3 μm are created in a line by line process by projecting a laser illuminated slit onto the glass surface. Micron- and sub-micron-periodic gratings are made by projecting a transmission grating using a Schwarzschild objective. Such gratings can be applied for surface functionalization or diffractive marking.

Grazing-incidence dynamic X-ray diffraction from a crystal with a shaped surface

The dynamic grazing-incidence X-ray diffraction from a crystal with a shaped surface in the form of one-dimensional submicron grating has been investigated. The interaction between the specularly reflected and diffracted waves and grating harmonics is taken into account for noncoplanar diffraction under the conditions of total external reflection. It is shown that this approximation exhibits good convergence in the number of harmonics taken into account. The influence of the angular divergence of the incident beam on the rocking-curve shape is shown.

Long Wavelength ≥1.9 μm Germanium for Optoelectronics Using Process Induced Strain

not Available.

Tunable behavior of reflectance minima in periodic Ge submicron grating structures

The periodic bullet-like and cone-like submicron grating (SMG) structures on germanium (Ge) substrates were fabricated by dry etching processes via laser interference lithography. Their optical reflectance characteristics as well as the wettability of the surface were investigated. The wide cone-like Ge SMG structure exhibited a lower reflectance than that of the narrow bullet-like Ge SMG structure at wavelengths of 300–1100 nm due to its relatively high volume fraction and the more linearly graded effective refractive index distribution between air and the Ge substrate. As the period of cone-like Ge SMGs was increased, the low reflectance band of <10% was shifted toward the longer-wavelength region and its minimum value became slightly higher. The fabricated Ge SMG structures showed a hydrophobic surface property with contact angles of 90.7–102.5°. For theoretical analysis, the reflectance calculations were also performed by a rigorous coupled-wave analysis simulation, which indicated a similar trend to the experimental results.

Longitudinal stitching of sub-micron periodic fringes on a roller

In this work, a servo-assisted system for fabricating sub-micron gratings on a roller-type mold is developed. The fringes are produced by optical interference lithography and have period of about 800 nm. A supporting and precision manipulating system for roller mold is established so that seamless longitudinal fringe stitching can be achieved. Analysis of the measurement system and stitching error are given. Also, beam-steering concept is introduced into this system for correction of relative motion between the roller and the optical system. Exposure experiment is initiated on a 50 mm-diameter roller. The grating structure is directly and indirectly examined by microscopic equipments.