Composite Gratings Research Articles

A new method for designing highly efficient composite transmission gratings

A new method for designing highly efficient composite transmission gratings

Efficient second-harmonic generation of quasi-bound states in the continuum in lithium niobate thin film enhanced by Bloch surface waves

Abstract Nonlinear optics has generated a wide range of applications in the fields of optical communications, biomedicine, and materials science, with nonlinear conversion efficiency serving as a vital metric for its progress. However, the weak nonlinear response of materials, high optical loss, and inhomogeneous distribution of the light field hamper the improvement of the conversion efficiency. We present a composite grating waveguide structure integrated into a Bragg reflector platform. This design achieves high Q in the spectral range by exploiting the unique properties exhibited by the bound states in the Bloch surface wave-enhanced continuum, and efficient second-harmonic generation by close-field amplification with the optical field tightly localized in a nonlinear material. By manipulating the symmetry of the grating, a precise tune over the near field within a designated wavelength range can be achieved. Specifically, we select a photonic crystal configuration supporting surface waves, employing TE polarization conditions and an asymmetry factor of −0.1 between the composite gratings. This configuration resonates at a fundamental wavelength of 783.5 nm, exhibiting an impressive Q-factor of 106. Notably, at an incident light intensity of 1.33 GW/cm2, we achieve a normalized electric field strength of up to 940 at the fundamental frequency and a second-harmonic conversion efficiency of up to 6 × 10−3, significantly amplifying the second-harmonic response. The proposed configuration in this investigation has the potential to be integrated into the field of nonlinear optics for sensing frequency conversion applications.

Design of a highly sensitive terahertz temperature and refractive index composite sensor based on an InSb–Ag composite grating

This paper introduces an exceptionally highly sensitive sensor developed using InSb–Ag composite gratings for sensing temperature and refractive index in the terahertz region. The structural parameters of the sensor were optimized to produce two transmission spectra at frequencies of 2.016 THz and 10.428 THz, respectively, under T=290K with transverse magnetically polarized vertical incidence. The simulation results demonstrate that the temperature sensor displays a sensitivity of 25.27 GHz/K and 4.53 GHz/K; the respective refractive index sensor shows a sensitivity of 0.48 THz/RIU and 3.60 THz/RIU. The current paper analyzes the effects of incidence and polarization angles on the performance of the sensors. The findings indicate that polarization significantly correlates with the sensor. Regarding the incidence angle range of 0°–30°, the performance of the sensors is uncorrelated with the angle of incidence. Compared to other temperature and refractive index sensors, the composite grating sensor demonstrates superior sensing performance and holds great potential for developing high-performance dual-function sensors.

Exploring the structural color of micro-nano composite gratings with FDTD simulation and experimental validation.

The significance of micro-nano composite gratings (MNCGs) resides in their applications, including optical devices, sensors, and diffractive elements, which drive research interest in their diffraction characteristics. This study investigates both the diffraction characteristics of MNCGs and the factors that influence them by employing both Finite-Difference Time-Domain (FDTD) methods and experimental validation. The initial focus lies in deciphering the differences in diffraction characteristics between micro-gratings (MGs) and MNCGs by analyzing the coupling effects, diffraction order, color distribution, and intensity variation. Additionally, this research emphatically investigates five aspects to discover the influencing factors of MNCG's diffraction characteristics, such as the height, groove angle of MGs and the period, blaze angle, and height of nano-gratings (NGs). Results show that the structural coloration and saturation of MNCG surpass that of MG. NG plays the actual spectral role, and a reduction in the period of NG leads to enhanced splitting light capability of the white light. The optical detection tests validated the simulation results. The present study reveals the diffractive properties of MNCGs, providing technical insights for the design and processing of optically variable devices.

Multifunctional Device Design Based on Composite Gratings and Gradient Supersurfaces

Multifunctional Device Design Based on Composite Gratings and Gradient Supersurfaces

Simultaneous Measurement of Curvature Vector and Temperature Based on Composite Gratings Inscribed on D-Shaped Fiber

A novel two-parameter fiber sensor has been demonstrated, consisting of D-shaped composite fiber gratings (DCFG) which includes long period fiber grating (LPFG) and fiber Bragg grating (FBG) inscribed on D-shaped fiber. LPFG is inscribed on the side of D-shaped fiber by a high-frequency CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser. On account of the asymmetry of the structure in 90° and 270° and refractive index modulation (RIM) in 0° and 180°, the sensor can recognize the bending directions. In the theory, it is proved that by adjusting the thickness of D-shaped fiber, the bending sensitivity can be enhanced in 90° and 270° directions. In the experiments, the fiber sensor achieves the sensitivity of curvature up to 13.70 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , which is nearly two times as the similar structure without D-shaped fiber. The curvature and temperature sensitivities of LPFG and FBG are different in DCFG, so the proposed sensor can realize simultaneously measurement of curvature vector and temperature.

Terahertz multi-frequency splitter and spoof SPPs switch

In this paper, a spoof surface plasmon polaritons (SPPs)-based multi-frequency splitter in the terahertz (THz) band is realized by designing different grating heights. The structure is composed of an incident aperture waveguide and a composite gratings structure placed on both sides of the incident aperture waveguide. The composite grating structure has different grating heights, which is used to transmit and guide THz waves of different frequencies in different directions. Simulation results show that a mixed incident light consisting of three frequencies, of 0.5 THz, 0.7 THz and 1 THz, can be effectively separated by this splitter. Furthermore, the function of the spoof SPPs switch can be realized by increasing the number of incident aperture waveguides. The simple structure and small size, means that this multi-frequency splitter and switch can be conveniently integrated into THz sensing or THz communication systems.

Bi-layered composite gratings with high diffraction efficiency enabled by near-field coupling.

In this paper, we present a design method for bi-layered composite gratings to achieve high diffraction efficiency. These composite gratings feature strong near-field coupling between their constituent dielectric subwavelength gratings, thus enabling high-efficiency first-order diffraction in the far-field. An intuitive explanation based on a wavevector matching condition for such high diffraction efficiency composite gratings is provided. According to theoretical analysis, a design strategy for the proposed composite gratings is developed and verified by numerical simulations with gratings working in both TE and TM modes. The proposed strategy could open door to develop bi-layered composite gratings for manipulating diffracted waves with high efficiency, thus may potentially enable new applications in photonic systems.

Fabrication of X-ray absorption grating by thermal composite method

In this paper, we propose a new method to prepare X-ray absorption gratings. The thermal composite absorption gratings with periods of 80 μm and 140 μm are successfully fabricated by using the difference in X-ray absorption between aluminum and silver film. The production process and the use of equipment are simple and easy to implement. A number of absorption gratings can be produced in one production, which greatly reduces the cost of gratings. Finally, the X-ray single absorption grating imaging experiment is used to verify the effectiveness of the thermal composite absorption grating.

Bending Analysis of Molded Composite Grating Panels: Theoretical and Experimental Investigations

Proposing a theoretical procedure, the lattice structure of a composite grating is replaced with an equivalent orthotropic homogenous plate. Accordingly, the bending analysis of molded grating panels is facilitated using plate-bending theory as a manual calculation. The homogenization method establishes the required analytical relations for estimating effective material properties and effective thickness of the equivalent solid panel. The bending tests are performed on manufactured molded composite gratings under concentrated and distributed loadings. The performed test is also numerically simulated using finite element method. The results of developed theoretical modeling and finite element analysis are compared with experimental observations. A very good agreement is observed between the conducted experiments and estimated results through either numerical or theoretical modeling. Moreover, the performance of the theoretical modeling is also examined for other types of loadings and constraints and the outputs of the developed modeling are compared with available experimental data in open literature. The promising ability of proposed modeling procedure in replacing grating panels with equivalent solid plate is demonstrated for different meshes. This capability enables the engineers to perform bending analysis of grating panels with different meshes very easily and rapidly.

Fabrication of nanodiamond-dispersed composite holographic gratings and their light and slow-neutron diffraction properties

We demonstrate the use of nanodiamond in constructing holographic nanoparticle-polymer composite transmission gratings with large saturated refractive index modulation amplitudes at both optical and slow-neutron wavelengths, resulting in efficient control of light and slow-neutron beams. Nanodiamond possesses a high refractive index at optical wavelengths and large coherent and small incoherent scattering cross sections with low absorption at slow-neutron wavelengths. We describe the synthesis of nanodiamond, the preparation of photopolymerizable nanodiamond-polymer composite films, the construction of transmission gratings in nanodiamond-polymer composite films and light optical diffraction experiments. Results of slow-neutron diffraction from such gratings are also presented.

Numerical design of a high-performance polarization beam splitter assisted by composite subwavelength gratings.

We report a compact polarization beam splitter (PBS) consisting of slotted waveguides assisted by composite subwavelength gratings (CSWGs) on a silicon-on-insulator platform. By tailoring the material anisotropy of the CSWGs, coupling strengths of transverse-electric (TE) and transverse-magnetic (TM) polarization coupling strengths are respectively suppressed and enhanced significantly, achieving concurrent improvements in polarization extinction ratio (PER), device footprint, and working bandwidth (BW) compared with purely slotted waveguides. Differing in construction from mono-material SWGs, the CSWGs comprise silicon strips covered with a silicon dioxide (SiO2) layer of the same thickness as the slot layer of the slotted waveguides, simplifying the fabrication process and further reducing device length. Numerical simulations show significant improvement in PERTM from about 15 dB for the purely slotted waveguides to 28 dB for the proposed design, with a 40% reduction in device length at a wavelength of λ = 1550 nm. Within a BW of ∼60 nm, the proposed PBS achieves PERTM ∼25 dB, PERTE >15 dB, and insertion loss (ILs) <0.1 dB for TE and TM modes. Fabrication tolerance investigations are also described and discussed. The proposed idea paves the way for simultaneous improvements in PER, footprint, and working BW for PBSs comprising a variety of coupled-waveguide systems.

Dual-microcavity resonance and plasmon-cavity polaritons enhanced the broadband absorption of polymer-based organic solar cells by employing micro-nano composite gratings

Abstract A broadband-absorption enhancement in two kinds of polymer-based organic solar cells (OSCs) is demonstrated in this work by employing micro-nano composite gratings (MNCGs). The structure of MNCGs is nano-grating covering on the surface of micro-grating. By embedding the MNCGs at the interface of the active layer/Ag cathode, the multi-absorption-enhancement mechanisms, such as dual-microcavity resonance, plasmon-cavity polaritons and light-scattering effects, are excited and result in a broadband-absorption enhancement. The light absorption of active layer in the MNCG-based OSC is numerically calculated. As a result, comparing to the planar OSCs, the absorption intensity is increased by 50.41% and 20.43% in these two kinds of polymer-based OSCs, respectively. Meanwhile, the MNCGs can also be universally used in all kinds of polymer-based OSCs to increase the light absorption of the active layer.

Quantitative Characterization of Optical Coupling in Nanoporous ZnO–WO3 and ZnO–PEDOT Composite Electrodeposited Gratings Using Electrodiffraction Measurements

To quantitatively characterize the optical coupling between ZnO (a high refractive index but nonabsorptive material) and an electrochromic material (either tungsten oxide (WO3) or poly(3,4-ethylenedioxythiophene) (PEDOT)), electrodiffractive and electrochromic properties were investigated from a novel two-component composite nanostructured electrodeposited grating that incorporated both ZnO and either WO3 or PEDOT. The sequential electrodeposition of these two materials through a photopatterned photoresist layer onto a fluorine-doped tin oxide (FTO)-coated glass substrate created a grating structure that exhibited optical diffraction that could be modulated electrochemically. SEM images of the electrochromic gratings revealed that the ZnO electrodeposition created a high surface area nanostructured thin film. The nanostructured ZnO is nonabsorbing, but its high refractive index and large surface area redirect light into the electrochromic grating and create a 4-fold enhancement in the grating’s electrodif...

Mechanically Tunable Bilayer Composite Grating for Unique Light Manipulation and Information Storage

AbstractComposite gratings play important roles in modern information technology. However, such gratings are generally based on the same structural pattern with limited types, and their structural parameters are difficult to tune, which greatly limit their application. A mechanically tunable composite grating in bilayer film, which orthogonally couples a sinusoidal phase grating and a rectangular phase grating, is developed here. The structural parameters of the grating can be well tuned by mechanically stretching or releasing the grating in the uniaxial direction. Naturally, this property allows tunable light manipulation: that is, a single incident laser beam can be split into a 2D diffraction beams array, and the intensity and propagation angle of each diffraction beam can be precisely controlled via mechanical manipulation of the grating. A theoretical model based on scalar diffraction theory that can quantitatively describe and accurately predict this light manipulation is further established. In addition, after treatment with an electron beam, the tunable structures can be immobilized, which enables the storage of information in the bilayer film. This work may open up new pathways for composite grating fabrication and further extend the applications of composite gratings in diverse fields.

Efficiency enhancement in ultrathin crystalline silicon solar cells with composite surface gratings

We investigate the light absorption in an ultrathin crystalline silicon solar cell with composite grating structures using three dimensional rigorous coupled wave analysis. Comparing with conventional surface gratings, the composite grating which is a superposition of two subgratings with different length scales demonstrates efficient light trapping in thin film solar cells in a broad spectral range. The light absorption is found to be close to the Yablonovitch limit in both visual and infrared regions. The optimized structure yields an ideal photocurrent density of 33.9mA/cm2 at an equivalent thickness of 2µm. This is comparable to the performance of the recently proposed double-sided grating design (Wang et al., 2012 [19]). These results suggest that the composite grating structures promise efficiency enhancement in ultrathin solar cells with improved technology compatibility.

Multi‐wavelength L‐band gain‐clamped erbium‐doped fiber amplifier with high gain and flatness by using composite FBGS

ABSTRACTThe gain‐clamped erbium‐doped fiber amplifiers (EDFA) can efficiently stabilize the gain fluctuation of signals, but with the price of gain–loss and worsened flatness. In this paper, we theoretically study the relationships between clamping and loss and propose a novel linear‐cavity gain controller based on a pair of composite fiber Bragg gratings (FBGs) to balance gain and clamping, which consist of a uniform FBG with high‐reflectivity and a chirp‐FBG with low‐reflectivity. The comprehensive experiments and comparisons are then conducted in terms of gain, flatness and clamping capability. Under the optimized central wavelength and reflectivity of FBGs, the ±0.1 dB stability of multi‐wavelength signals is achieved in ∼30 dB dynamic range. Moreover, our designed amplifier simultaneously guarantees the high average gain (∼24 dB) and low un‐flatness (∼±0.8 dB) in the range of 1570–1610 nm. This is a very promising technology for practicality of L‐band gain‐clamped EDFAs due to its simple configuration and adjustment. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:691–695, 2017

Advancing data analysis for reflectivity measurements of holographic nanocomposite gratings

We discuss the analysis of neutron rocking curves measured with holographic nanoparticle-polymer composite gratings with SANS instruments and at very-cold neutron beamlines. In particular, the effects of broad incident wavelength-distributions and of nonuniformity of the refractive-index profile along the grating depth are assessed.

Wavefront sensing based on phase contrast theory and coherent optical processing

A novel wavefront sensing method based on phase contrast theory and coherent optical processing is proposed. The wavefront gradient field in the object plane is modulated into intensity distribution in a gang of patterns, making high-density detection available. By applying the method, we have also designed a wavefront sensor. It consists of a classical coherent optical processing system, a CCD detector array, two pieces of orthogonal composite sinusoidal gratings, and a mechanical structure that can perform real-time linear positioning. The simulation results prove and demonstrate the validity of the method and the sensor in high-precision measurement of the wavefront gradient field.

Nanoparticle-polymer composite volume holographic gratings dispersed with ultrahigh-refractive-index hyperbranched polymer as organic nanoparticles.

We report on volume holographic recording at a wavelength of 532 nm in photopolymerizable polymer nanocomposites that are incorporated with new hyperbranched polymers (HBPs) acting as transporting organic nanoparticles. Since HBPs possess an ultrahigh index of refraction of 1.82 due to the inclusion of triazine and aromatic ring units, high-contrast transmission volume holographic gratings with refractive index modulation amplitudes as large as 2.2×10(-2) are recorded. This value enables us to realize a 10 μm thick transmission volume grating with the diffraction efficiency near 100% in the green.