Grating Structure Research Articles

Fabrication of slanted gratings by using glancing angle deposition

Slanted gratings, commonly used for manipulating light in various applications, are typically fabricated using conventional top-down methods. However, these methods have limitations on material choice. This paper explores the use of glancing angle deposition (GLAD) to fabricate slanted gratings with various materials and slant angles on silicon (Si) and quartz (SiO2) substrates. The process involves the first step of creating a template using electron beam lithography, lift-off, and dry etching, and the second step of electron beam evaporation at a glancing angle on the prefabricated template. The template consists of grating structures with very shallow trenches. Different materials, such as chromium (Cr), copper (Cu), aluminum oxide (Al2O3), and titanium oxide (TiO2), were used in the GLAD process to create slanted grating structures on Si or SiO2 substrates, showcasing their versatility. Here, the formation of the slanted grating is due to the shadowing effect that leads to deposition onto the protruded grating lines but not into the trench. Using TiO2 as the source material, the GLAD technique can produce slanted gratings with various angles by adjusting the deposition angle. The optical characteristics of the slanted grating prepared using GLAD were verified through simulations with COMSOL software, confirming its excellent light guide performance.

Bidirectional Littrow double grating interferometry for quadruple optical interpolation

Although grating interferometers are considered high-performance optical displacement sensors, higher requirements are being demanded for displacement sensing. Furthermore, the TGIS (traditional grating interferometry system) cannot achieve high-fold optical subdivision in the case of single-diffraction, which restricts the improvement of measurement resolution. In this paper, a BLDGIS (bidirectional Littrow double grating interferometry system) is demonstrated, combining Littrow heterodyne detection technology with the double grating structure and providing a quadruple optical subdivision in the case of single-diffraction. Additionally, the use of planar mirror for beam deflection in the optical path is unnecessary, and the sensitivity to angular error is greatly reduced. The experiment results show that the error of the BLDGIS in the linear displacement range of 10 mm in the X direction is within ±15 nm, and the actual resolution reaches 2 nm. Compared with TGIS, the error was reduced by 30 % and the resolution was increased by 50 %.

Highly sensitive plasmonic-grating PCF biosensor for cancer cell detection

Highly sensitive biosensor based on D-shaped photonic crystal fiber (PCF) with plasmonic grating is introduced and analyzed. The suggested structure is tested using four different grating structures (rectangular, triangular, circular, or elliptical) on the polished surface of the D-shaped PCF. The sensing operation depends on surface plasmon resonance mechanism where the analyte refractive index (RI) is utilized to control the coupling between the core mode and surface plasmon mode via phase matching phenomenon. Rhodium is employed as a plasmonic material to induce the SPMs. The resonance (i.e., phase matching) wavelength is a function of the analyte RI. The geometrical parameters of the proposed structure are optimized using full vectorial finite element method to enhance the sensor sensitivity. The proposed biosensor can be utilized in the detection of different cancerous Basel, Breast and Cervical cells. The performance of the reported biosensor is investigated in terms of sensitivity, linear response, and fabrication tolerance. The reported biosensor has high sensitivities of 19,750 nm/RIU, 20,428 nm/RIU and 20,041 nm/RIU for the detection of Basel, Breast and Cervical cancer cells, respectively. The presented biosensor is a good candidate for biological sample detection and organic chemical sensing.

Few-Cycle Surface Plasmon Polaritons.

Surface plasmon polaritons (SPPs) can confine and guide light in nanometer volumes and are ideal tools for achieving electric field enhancement and the construction of nanophotonic circuitry. The realization of the highest field strengths and fastest switching requires confinement also in the temporal domain. Here, we demonstrate a tapered plasmonic waveguide with an optimized grating structure that supports few-cycle surface plasmon polaritons with >70 THz bandwidth while achieving >50% light-field-to-plasmon coupling efficiency. This enables us to observe the─to our knowledge─shortest reported SPP wavepackets. Using time-resolved photoelectron microscopy with suboptical-wavelength spatial and sub-10 fs temporal resolution, we provide full spatiotemporal imaging of co- and counter-propagating few-cycle SPP wavepackets along tapered plasmonic waveguides. By comparing their propagation, we track the evolution of the laser-plasmon phase, which can be controlled via the coupling conditions.

Holographic nanodiamond–polymer composite grating with unprecedented slow-neutron refractive index modulation amplitude

We demonstrate exceptionally high slow-neutron diffraction efficiency (≈ 70% of transmitted intensity diffracted to the first order) from a holographic nanodiamond–polymer composite grating of only tens of micrometers thickness at the average neutron wavelength of 5.3 nm. By meticulous choice of materials for extreme refractive index modulation in a thin grating structure, we overcome typical wavelength and angular selectivity issues usually encountered when pursuing high diffraction efficiencies with a thick grating. This achievement paves the way for the implementation of flux-efficient diffractive elements, well-suited for polychromatic beams, and weakly collimated slow-neutron beams.

Enhancing surface sensing performance of cascaded high contrast gratings using bound states in the continuum.

We proposed the cascaded high contrast grating (CHCG) structure to enhance surface sensing capabilities through bound states in the continuum (BICs). Utilizing the finite element method (FEM) and rigorous coupled-wave analysis (RCWA), we studied the dispersion relations, far-field contribution CHCGs, and near-field distributions of BICs corresponding to resonance peaks at different wavelengths. Results demonstrate the ability to precisely control symmetry-protected BIC (SP-BIC) and Friedrich-Wintgen BIC (FW-BIC) resonance peaks by altering incident angles and structural parameters, enhancing structure robustness and tunability. Significantly, modes 1 and 2 have demonstrated substantial enhancement in surface refractive index sensing, achieving highest sensitivities at 51 nm/RIU and the figure of merit reaching 490.8 RIU-1, indicating notable advancement in detecting subtle surface changes. In contrast, mode 3 has shown robust performance in bulk refractive index sensing, achieving a sensitivity of 602 nm/RIU and a figure of merit of 5189.65 RIU-1. These findings underscore the significant potential of the structure as a high-performance integrated sensor, particularly for precise environmental and biological monitoring in surface refractive index sensing.

Small Footprint and High Extinction Ratio Cladding-Modulated Bragg Grating Structure as a Wideband Bandstop Filter

This study presents a comprehensive numerical investigation of silicon Bragg grating (BG) waveguide structures with cladding modulation. The device design features a uniform silicon ridge waveguide with corrugated cladding on both sides. Two distinct architectures are explored: one where silicon serves as the cladding and another where gold (Au) is employed. Our detailed analysis uncovers compelling results for both configurations. The silicon corrugated cladding BG waveguide demonstrates a bandstop bandwidth of ~50 nm, accompanied by an extinction ratio (ER) of 7.98 dB. The device footprint is compact, measuring approximately 16.4 × 3 µm2. In contrast, the Au corrugated cladding BG waveguide exhibits exceptional performance, boasting a wideband bandstop bandwidth of ~143 nm and an impressive ER of 19.96 dB. Despite this enhanced functionality, the device maintains a reasonably small footprint at around 16.9 × 3 µm2. This investigation underscores the potential of Au corrugated cladding BG waveguides as ideal candidates for achieving high-spectral-characteristic bandstop filters. The significant improvement in bandstop bandwidth and ER makes them promising for advanced optical filtering applications.

High-directivity far-field radiation of quantum dot-based single-photon emitter coupled to polymeric circular waveguide resonant grating

Solid-state single-photon emitters (SPEs) commonly encounter the limitation of quasi-omnidirectional radiation patterns, which poses challenges in utilizing their emission with conventional optical instruments. In this study, we demonstrate the tailoring of the far-field radiation patterns of SPEs based on colloidal quantum dots (QDs), both theoretically and experimentally, by employing a polymer-based dielectric antenna. We introduce a simple and cost-effective technique, namely low one-photon absorption direct laser writing, to achieve precise coupling of a QD into an all-polymer circular waveguide resonance grating. By optimizing the geometry parameters of the structure using 3D finite-difference time-domain simulations, resonance at the emission wavelength of QDs is achieved in the direction perpendicular to the substrate, resulting in photon streams with remarkably high directivity on both sides of the grating. Theoretical calculations predict beam divergence values below 2°, while experimental measurements using back focal plane imaging yield divergence angles of approximately 8°. Our study contributes to the evaluation of concentric circular grating structures employing low refractive index polymer materials, thereby expanding the possibilities for their application.

Structural design and photoelectron emission characteristics of a new Cs2Te photocathode based on surface plasmon polaritons

Surface plasmon polaritons (SPPs) have been introduced into Cu and K2CsSb photocathodes to substantially improve their quantum efficiency, while no similar studies have been reported on Cs2Te photocathode. In this paper, SPPs were introduced into Cs2Te photocathode by means of micro-nano grating structure, which successfully stimulated local enhanced field to improve photon absorption rate and regulate initial distribution of the excited photoelectrons. In order to explore the effect of SPPs on the performance of Cs2Te photocathode, Monte Carlo method was used to simulate the photoemission process of Cs2Te photocathode before and after the introduction of SPPs. The results showed that the quantum efficiency of Cs2Te photocathode with SPPs was improved by 60% while the thermal emittance remained basically unchanged. The results are of great significance for the development of high-brightness electron sources that are required in the field of particle accelerators.

Enabling Waveguide Optics in Rhombohedral-Stacked Transition Metal Dichalcogenides with Laser-Patterned Grating Couplers.

Waveguides play a key role in the implementation of on-chip optical elements and, therefore, lie at the heart of integrated photonics. To add the functionalities of layered materials to existing technologies, dedicated fabrication protocols are required. Here, we build on laser writing to pattern grating structures into bulk noncentrosymmetric transition metal dichalcogenides with grooves as sharp as 250 nm. Using thin flakes of 3R-MoS2 that act as waveguides for near-infrared light, we demonstrate the functionality of the grating couplers with two complementary experiments: first, nano-optical imaging is used to visualize transverse electric and magnetic modes, whose directional outcoupling is captured by finite element simulations. Second, waveguide second-harmonic generation is demonstrated by grating-coupling femtosecond pulses into the slabs in which the radiation partially undergoes frequency doubling throughout the propagation. Our work provides a straightforward strategy for laser patterning of van der Waals crystals, demonstrates the feasibility of compact frequency converters, and examines the tuning knobs that enable optimized coupling into layered waveguides.

The enhanced nonreciprocal radiation in a grating structure containing a Weyl semimetal film under conical incidence

The enhanced nonreciprocal radiation in grating structure for light under conical incidence is investigated. The basic structure is composed of a one-dimensional grating on a continuous Weyl semimetal planar and a thick metallic mirror. The results show that near-perfect nonreciprocal radiation can be observed for transverse electric wave, which cannot be achieved for light in traditional incidence. Such effect results from the guided mode resonance (GMR) excited inside the grating, demonstrated by studying the electromagnetic field amplitude distribution. Moreover, the strong nonreciprocity is also stable for the geometric parameters in a wide varying range, lowering the cost of manufacture. Most of important, the proposed scheme could be employed to realize enhanced nonreciprocity for both TM polarization and TE polarization with different resonant wavelengths along with the same resonant wavelength. The concepts proposed here should pave the way to the development of polarization-dependent and polarization-independent as well as dual-polarization nonreciprocal emitters.

Colourful cholesteric liquid crystal polymer network gratings prepared through nanoimprinting

ABSTRACT Both the colourful cholesteric liquid crystal polymer network (CLCN) patterns and the gratings have attracted much attention for their applications as optical materials. Herein, the photochromic cholesteric liquid crystal (CLC) mixtures were prepared using a photoisomerizable chiral dopant. The structural colour of the CLC mixtures was tunable by changing the chiral dopant concentration and the intensity of the 365-nm irradiation light. The CLCN gratings with a structural colour were prepared using the UV nanoimprinting lithography method. The structural colours of the CLCN gratings originate from both the cholesteric and the grating structures. Moreover, a patterned CLCN grating was prepared using a photochromic CLC mixture, which could be applied for decoration and anti-counterfeiting.

Blue-light-enhanced avalanche photodiode with amulti-finger grating structure for fluorescence detection.

The responsiveness of the photodetectors is critical to the accuracy of the fluorescent fiber optical temperature sensor. However, the current gain and signal-to-noise ratio (SNR) of traditional photodiodes (PDs) is low, which makes it difficult to meet the high-precision detection requirements of the system. In response to the above problems, this paper achieves a novel, to the best of our knowledge, multi-finger grating (MFG) avalanche photodiode (APD). The device combines the polysilicon gate and the space charge region formed by P+/N-Well to detect photon signals. The conversion capability of the photodetector can be significantly enhanced by the MFG structure. The principle of the device is simulated and verified by technology-computer-aided design (TCAD). The standard grating APD (SG-APD), 2-finger grating APD (2FG-APD), 3-finger grating APD (3FG-APD), and 4-finger grating APD (4FG-APD) are fabricated based on 0.18µm CMOS process. The optoelectronic detection characteristics of these devices are analyzed by establishing an optoelectronic test platform. At 480nm, the responsivity of 2FG-APD, 3FG-APD, and 4FG-APD increases by 79.3%, 96.9%, and 70.2%, respectively, compared to SG-APD (4.021A/W). The test results indicate that 3FG-APD exhibits a strong photon response in the blue light range. The device has broad application prospects in the field of fluorescence detection.

Diffraction characteristics and formation mechanism of nanogratings in tip-based down-milling

Structural coloration of metal surfaces based on the diffraction mechanism of blazed gratings has considerable value for use in anti-counterfeiting and information encryption applications. When the grating period is comparable to the wavelength of the incident light, the diffraction process will generate only two propagating orders, comprising the 0th order and the −1st order, resulting in lower dispersion. Improvement of the diffraction efficiency of the −1st order spectrum, which has a light splitting ability, is essential to improve the colouring quality of the diffraction structure. Such improvement of efficiency is closely related to the geometric features of the structure, but the relationship is insufficiently clear at present. The novelty of the approach in this paper lies in its use of a combination of optical and mechanical analyses of nano grating structures fabricated by tip-based nanoscale down-milling with the aim of establishing a connection between the diffraction characteristics of the structure and its processing formation. First, profiles of the nanograting structures are generated numerically by taking both the trajectory shape and the cutting edge radius into account. Using the finite-difference time-domain method, a diffraction model is then established to simulate the far-field spectral distributions of the generated profiles. It is concluded from these analyses that the grating height is an important factor that affects the −1st order diffraction efficiency. When the grating height is in the range of 155–185 nm with a grating period of 400 nm, the diffraction efficiency can reach up to 75 %–90 %, depending on the conditions of incidence. Then, with the aim of controlling the grating height, the nanograting structure fabrication processes are investigated under different revolving trajectory conditions by finite element analysis. The results show that the grating structures are formed mainly by extrusion caused by the moving tip, which results in the grating heights being affected by the undeformed chip thickness in each cycle and by the plastic deformation of the material. Under the optimal down-milling trajectory condition, nanograting structures with the expected height and good geometric consistency are obtained.

Dynamically tunable multi-band plasmon-induced absorption based on multi-layer borophene ribbon gratings.

In this paper, we propose a borophene-based grating structure (BBGS) to realize multi-band plasmon-induced absorption. The coupling of two resonance modes excited by upper borophene grating (UBG) and lower borophene grating (LBG) leads to plasmon-induced absorption. The coupled-mode theory (CMT) is utilized to fit the absorption spectrum. The simulated spectrum fits well with the calculated result. We found the absorption peaks exhibit a blue shift with an increase in the carrier density of borophene grating. Further, as the coupling distance D increases, the first absorption peak shows a blue shift, while the second absorption peak exhibits a red shift, leading to a smaller reflection window. Moreover, the enhancement absorption effect caused by the bottom PEC layer is also analyzed. On this basis, using a three-layer borophene grating structure, we designed a three-band perfect absorber with intensities of 99.83%, 99.45%, and 99.96% in the near-infrared region. The effect of polarization angle and relaxation time on the absorption spectra is studied in detail. Although several plasmon-induced absorption based on two-dimensional (2D) materials, such as graphene, black phosphorus, and transition metal dichalcogenides (TMDs), have been previously reported, this paper proposes a borophene-based metamaterial to achieve plasmon-induced perfect absorption since borophene has some advantages such as high surface-to-volume ratios, mechanical compliance, high carrier mobility, excellent flexibility, and long-term stability. Therefore, the proposed borophene-based metamaterial will be beneficial in the fields of multi-band perfect absorber in the near future.

Design, fabrication and characterization of a grating waveguide structure with embedded quantum wells based on the GaInP/AlGaInP platform

We propose a grating waveguide structure with embedded quantum wells that shows potential for improving the cooling scheme for red-emitting VECSELs. The reflectivity map, the internal field distribution and the transmission spectra of our recently fabricated structures are presented.

Highly Sensitive Refractive Index Sensor based on Silicon Nitride Strip Waveguide Directional Coupler

We propose a refractive index sensor, based on grating-assisted directional coupler, by comprising two coupled asymmetric strip waveguides with a top-loaded grating structure. We have studied variation of the sensitivity with the waveguide parameters to optimize the design of the sensor. The proposed sensor is an on-chip device with a high refractive index sensitivity of 104nm/RIU with $ \pm $ 140 nm fabrication tolerance, which is more than two times higher than the reported work, and the sensor can also achieve the ultrahigh sensitivity 105nm/RIU with the fabrication tolerance $ \pm $ 13nm. The sensor has large dynamic range from refractive index 1.0 to 1.55. We have also studied the propagation loss due to side wall roughness of the strip waveguide and found that it does not significantly affect sensor performance.

Polarization control of visible light based on composited multivariable nanowire gratings structure

Polarization control of visible light based on composited multivariable nanowire gratings structure

Sub-diffraction limited nanogroove fabrication of 30 nm features on diamond films using 800 nm femtosecond laser irradiation

By controlling the 800 nm fs laser energy and applying an isopropyl alcohol environment, controlled sub-diffraction limited lithography with a characteristic structure of approximately 30 nm was achieved on the surface of diamond films, and diamond gratings with a period of 200 nm were fabricated. The fabrication of single grooves with a feature size of 30 nm demonstrates the potential for patterning periodic or nonperiodic structures, and the fabrication of 200 nm periodic grating structures demonstrates the ability of the technique to withstand laser proximity effects. This enhances the technology of diamond film nanofabrication and broadens its potential applications in areas such as optoelectronics and biology.

Extend the bandwidth of terahertz polarization convertors further via all-dielectric grating structures

Extend the bandwidth of terahertz polarization convertors further via all-dielectric grating structures