Characteristics Of Gratings Research Articles

Numerical study of dispersion characteristics of cylindrical spiral lines and periodic gratings based on them

Numerical studies of the dispersion characteristics of cylindrical spiral lines have been carried out. One-dimensional and two-dimensional periodic lattices formed by such lines are also considered. The eigenvalue method was used in combination with periodic boundary conditions. The dispersion characteristics are calculated in the range of parameters for which the conditions of applicability of the known approximate numerical-analytical methods for analyzing spiral lines are not met. The dispersion characteristics of the first two eigen-waves in one-dimensional and two-dimensional periodic lattices of spirals are obtained for different values of phase shifts between lattice periods. It is shown that the main type of wave in them is a wave slowed down relative to the axes of the lines with the direction of rotation of the field vector determined by the direction of winding of the spiral.

Development of an Imaging Spectrometer with a High Signal-to-Noise Ratio Based on High Energy Transmission Efficiency for Soil Organic Matter Detection.

Hyperspectral detection of the change rate of organic matter content in agricultural remote sensing requires a high signal-to-noise ratio (SNR). However, due to the large number and efficiency limitation of the components, it is difficult to improve the SNR. This study uses high-efficiency convex grating with a diffraction efficiency exceeding 50% across the 360-850 nm range, a back-illuminated Complementary Metal Oxide Semiconductor (CMOS) detector with a 95% efficiency in peak wavelength, and silver-coated mirrors to develop an imaging spectrometer for detecting soil organic matter (SOM). The designed system meets the spectral resolution of 10 nm in the 360-850 nm range and achieves a swath of 100 km and a spatial resolution of 100 m at an orbital height of 648.2 km. This study also uses the basic structure of Offner with fewer components in the design and sets the mirrors of the Offner structure to have the same sphere, which can achieve the rapid adjustment of the co-standard. This study performs a theoretical analysis of the developed Offner imaging spectrometer based on the classical Rowland circular structure, with a 21.8 mm slit length; simulates its capacity for suppressing the +2nd-order diffraction stray light with the filter; and analyzes the imaging quality after meeting the tolerance requirements, which is combined with the surface shape characteristics of the high-efficiency grating. After this test, the grating has a diffraction efficiency above 50%, and the silver-coated mirrors have a reflection value above 95% on average. Finally, the laboratory tests show that the SNR over the waveband exceeds 300 and reaches 800 at 550 nm, which is higher than some current instruments in orbit for soil observation. The proposed imaging spectrometer has a spectral resolution of 10 nm, and its modulation transfer function (MTF) is greater than 0.23 at the Nyquist frequency, making it suitable for remote sensing observation of SOM change rate. The manufacture of such a high-efficiency broadband grating and the development of the proposed instrument with high energy transmission efficiency can provide a feasible technical solution for observing faint targets with a high SNR.

Liquid crystal waveguide film and its application to smart glasses

Liquid crystal waveguide film that we can control through wide visible wavelength has been proposed. Recently, small optical system is needed for various industrial application. Among the application, liquid crystal is the material for controlling optical ray. The application includes optical switch and display by controlling birefringence. These applications include AR/VR display, for manufacturing, inspection, and so on. In this study, we have investigated liquid crystal (LC) waveguide film that light is emitted from the waveguide film on glasses toward the eye when the power is turned on. The cut-off of waveguide film is based on liquid crystal switch using refractive index anisotropy. We select smart glasses as one of the applications for AR/VR display. The potential of LC waveguide films is demonstrated by simulating the propagation characteristics of waveguides film, LC reorientations, and diffraction gratings in the field of RGB wavelength range. By using the waveguide structure, the film thickness can be configured to be less than 1 mm. We can expect the liquid crystal waveguide has much application to optical integrated circuit as other application except for smart glasses.

Refractive index sensing characteristics of long-period gratings in linearly arranged three-core fiber

We demonstrate the refractive index (RI) sensing characteristics of long-period gratings (LPGs) in linearly arranged three-core fiber (TCF), which are fabricated using arc discharge technique. Due to the asymmetric index modulation during fabrication, the RI sensitivity of TCF-LPGs in the 0° grating inscription direction is greater than that in the 90° grating inscription direction. The spectral and RI sensing characteristics of TCF-LPGs in the 0° grating inscription direction with different grating periods have been investigated experimentally. In the RI range from 1.4538 to 1.4589, the resonance at 1533.3 nm for TCF-LPGs with grating period of 465 μm could achieve the RI sensitivity of 15943.3 nm/RIU, which could be optimized to 18160.7 nm/RIU at 1676.3 nm as the TCF-LPGs with grating period of 600 μm. Moreover, the proposed TCF-LPGs exhibit notably greater RI sensitivity compared to arc-discharged LPGs in conventional single-mode fibre, presenting substantial advantage in RI sensing. And, changing the polarization state of the incident light enhances the RI sensitivity of TCF-LPGs.Additionally, the influence of bending or temperature interference on the RI sensitivity of TCF-LPGs is minimal, ensuring that interference with RI measurements can be neglected. The proposed sensor boasts cost-effectiveness, simplicity in structure, and high sensitivity to RI, showing substantial potential for applications in chemical and biological sensing.

Characteristics of Helical Long-Period Gratings Inscribed in Seven-Core Fibers by CO2 Laser

Characteristics of Helical Long-Period Gratings Inscribed in Seven-Core Fibers by CO₂ Laser

A Study on Length Traceability and Diffraction Efficiency of Chromium Gratings

Measurement traceability is a prerequisite for achieving accurate and reliable results as well as technical standardization. The period of Chromium (Cr) gratings fabricated by atomic lithography can be directly traced back to natural constants. Applying the Cr grating to grating interferometry can achieve nanometer measurement traceability. This research aims to analyze the diffraction efficiency characteristics of self-traceable Cr gratings to provide a theoretical basis for the fabrication and application of Cr gratings. In this regard, we establish the theoretical model of the laser beam incident angle and grating diffraction efficiency using the rigorous coupled-wave method. Then, we analyze the influence of the laser beam incident angle on grating diffraction efficiency by simulation, verify the accuracy of the theoretical model, and finally build a measurement system for grating diffraction efficiency. Through experiments, we find that the diffraction efficiency of the grating shows a rapid increase to reach a stable maximum value followed by a decrease, when a laser beam with a wavelength of 405 nm is incident on the surface of a self-traceable grating in Transverse Magnetic (TM) polarization and the incident angle changes within an effective range. The experimental results are consistent with the trend of theoretical calculation results.

Enhancement of punching shear behavior of reinforced concrete flat slabs using GFRP grating

The literature review showed insufficient relevant research on the application of Glass-Fiber-Reinforced-Polymers (GFRP) gratings in the structural elements, while GFRP bars, laminate, sheets, and strips, have been extensively explored. This research aims to present a proposal for a new reinforcing system using GFRP gratings to improve the punching shear resistance of RC flat slabs. Results of seven specimens tested experimentally under vertical static loading are displayed, taking into account the influence of the gratings variables. Test results revealed an improvement in the ultimate load ranging between 9.03% and 27.67% for the specimens strengthened by the proposed GFRP grating system. A Nonlinear Finite Element Analysis (NLFEA) was carried out using the ANSYS program with correlational evaluation using load-deflection response and cracking pattern, which resulted in a good convergence of numerical simulations and experimental performance results ranging from 1.0% to 8.0%. Key parameters, namely the concrete compressive strength, steel reinforcement yield strength, main steel reinforcement ratio, secondary steel reinforcement ratio, column dimensions, slab thickness, concrete cover, and GFRP gratings characteristics, were investigated through a parametric study adopting NLFEA by the ANSYS program, where the output results were compared to the recent code provisions.

Perceived Structure and Search Efficiency: Investigating the Role of Plaid Composition and Grating Characteristics

Perceived Structure and Search Efficiency: Investigating the Role of Plaid Composition and Grating Characteristics

Directional Magnetic Field Sensing Characteristics of Polarization Insensitive Long-period Grating

Directional Magnetic Field Sensing Characteristics of Polarization Insensitive Long-period Grating

Solid-state electrochemical oxidation with polyelectrolyte membrane stamps for micro-/nanoscale pattern formation on Au surfaces.

Nanoscale-patterned Au surfaces are promising for a wide range of applications from bio/chemical sensors to high-performance electrodes. However, pattern formation using conventional resist-based methods is complex, expensive, and environmentally unfriendly. Herein, we report a novel approach for pattern formation on Au surfaces using solid-state electrochemical treatment with polymer electrolyte membrane (PEM) stamps. During electrolysis, the patterned structure of the PEM stamp was transferred onto the Au surface to form micro- and nanoscale oxide patterns. X-ray analysis of the treated surface confirmed the formation of an oxide film on the Au surface, which was subsequently reduced to metallic Au after air exposure for several weeks. Although the pattern height decreased with air exposure, a patterned structure with a height of several hundred nanometers was maintained following oxide reduction. Reflectance spectroscopy revealed that the patterned Au surface exhibited sharp reflectance peaks, the intensities and positions of which strongly depended on the measurement angle, which are key characteristics of diffraction gratings. This fast and facile electrochemical treatment process is promising for the preparation of patterned Au surfaces that can be applied in optical gratings and localized surface plasmon resonance sensors.

Preparation and sensing characteristics of long-period fiber gratings based on periodic microchannels

Preparation and sensing characteristics of long-period fiber gratings based on periodic microchannels

Preparation and Sensing Characteristics of Long-Period Fiber Gratings Based on Periodic Microchannels

Preparation and Sensing Characteristics of Long-Period Fiber Gratings Based on Periodic Microchannels

Optimization and fabrication of chromium grating in self-traceable interferometer

Metrological methods rooted in natural constants present a robust strategy for ensuring traceability in nanometric measurements. A Chromium (Cr) grating, meticulously constructed through atom lithography and possessing a pitch of d = 212.7705 ± 0.0049 nm intrinsically traceable to the Cr transition frequency 7S3→7P40, exhibits promising potential as a self-traceable length standard in nano-length metrology via a grating interferometer. The objective of this research is to elucidate and optimize the diffraction characteristics that augment the Cr grating's functionality as a self-traceable length standard within the length traceability chain predicated on the Cr transition frequency. To this end, we explore the geometric morphology and diffraction characteristics of the Cr grating. This investigation also dissects the influence of the grating's polarization-sensitive traits on the Littrow configuration grating interferometer and establishes the criteria for Cr grating fabrication. Empirically, we fabricate an enlarged Cr grating through scanning atom lithography, delineate its diffraction performance, and perform an initial verification of length measurement in a self-traceable grating interferometer. This investigation aligns with the global progression towards a more streamlined metrology development, offering a valuable benchmark for propelling future advancements in metrological technologies within the new traceability chain.

Вплив тонких плівок Se на ефективність збудження поверхневих плазмон-поляритонів в срібних та алюмінієвих голографічних решітках

In this paper, we study the effect of thin selenium layers up to 3 nm thick on the efficiency of excitation of surface plasmon polaritons (SPPs). The Se layers were deposited by thermal evaporation in vacuum on the surface of silver and aluminum gratings. Gratings with a groove profile close to sinusoidal and a period equal to а = 694 nm were formed on chalcogenide photoresist films using interference lithography. Then they were coated with layers of the above metals with a thickness of 80–85 nm using thermal evaporation. Registration of SPP excitation on the gratings was carried out by measuring the angular dependences of the intensity of specularly reflected or diffracted p-polarized He-Ne laser radiation on a stand mounted on the basis of a G5M goniometer and a Fedorov table. An atomic force microscope was used to determine the shape of the groove profile and the depth of the grating relief. It has been found that for silver gratings with a relief modulation depth h/a less than the optimal value (which ensures maximum plasmon absorption, i.e., the maximum efficiency of SPP excitation), selenium deposition causes significant degradation of the plasmon resonance: a decrease in the depth of the minimum of the total reflection Rpt (i.e., a decrease in the efficiency of plasmon absorption), a shift of the Rpt minimum towards larger angles, and its widering. For silver gratings with h/a greater than the optimal value, a similar shift and widering of the plasmon resonance is also observed. However, at the same time, a significant deepening of the Rpt minimum is recorded, that is, an increase in the efficiency of SPP excitation. Such changes in the plasmon characteristics also appear on aluminum gratings, however, in this case the effect of the selenium layers is weaker by an order of magnitude. The obtained results allow us to propose a method of correcting the plasmonic characteristics of silver gratings in which the value of h/a is higher than optimal.

Real-Time Imaging of Plasmonic Concentric Circular Gratings Fabricated by Lens-Axicon Laser Interference Lithography.

Concentric circular gratings are diffractive optical elements useful for polarization-independent applications in photonics and plasmonics. They are usually fabricated using a low-throughput and expensive electron beam lithography technique. In this paper, concentric circular gratings with selectable pitch values were successfully manufactured on thin films of azobenzene molecular glass using a novel laser interference lithography technique utilizing Bessel beams generated by a combined lens-axicon configuration. This innovative approach offers enhanced scalability and a simplified manufacturing process on larger surface areas compared to the previously reported techniques. Furthermore, the plasmonic characteristics of these concentric circular gratings were investigated using conventional spectrometric techniques after transferring the nanostructured patterns from azobenzene to transparent gold/epoxy thin films. In addition, the real-time imaging of surface plasmon resonance colors transmitted from the concentric circular gratings was obtained using a 45-megapixel digital camera. The results demonstrated a strong correlation between the real-time photographic technique and the spectroscopy measurements, validating the efficacy and accuracy of this approach for the colorimetric studying of surface plasmon resonance responses in thin film photonics.

Sensing characteristics of structural microfiber long-period gratings.

We present a detailed investigation into the sensing characteristics of a structural microfiber long-period grating (mLPG) sensor. By spirally winding a thinner microfiber to another thicker microfiber, periodic refractive index modulation is formed while the optical signal transmitted in the thicker microfiber is resonantly coupled out to the thinner microfiber, and then a 5-period four-port mLPG can be obtained with a device length of only ∼570 µm demonstrated a strong resonant dip of 25 dB. We studied the sensitivity characteristics of the four-port mLPG with surrounding strain, force, temperature and refractive index, and the obtained sensitivities were -6.4 pm/µɛ, -8418.6 nm/N, 7.62 pm/°C and 2122 nm/RIU, respectively. With the advantages of high refractive index sensitivity and wide wavelength tunable range, the four-port mLPG has great potential in applications such as tunable filters and biochemical sensor.

Accurate measurement and adjustment method for interference fringe direction in a scanning beam interference lithography system.

To improve the exposure contrast of the scanning beam interference lithography (SBIL) system, a mathematical model of scanning exposure that includes the direction error of the measurement mirror is established. The effect of the angle between the interference fringe direction and the X-axis measurement mirror direction on the exposure contrast is analyzed. An accurate method for interference fringe direction measurement based on the heterodyne interferometry measurement method of the metrology grating and phase shift interferometry is proposed. This method combines the diffraction characteristics of the metrology grating and the phase shift algorithm to calculate the angle between the interference fringe direction and the measurement mirror direction accurately and adjust it. Experiments show that this angle reaches 0.6777 µrad, which meets high-precision grating fabrication requirements. Exposure comparison experiments performed at various angles show that a smaller angle between the interference fringe direction and the measurement mirror direction leads to better grating groove production by scanning exposure, which is consistent with the theoretical analysis. The accuracy of the theoretical analysis and the feasibility of the interference fringe direction adjustment method are verified, laying a foundation for high-quality grating fabrication by the SBIL system.

Research on Application of Fiber Bragg Grating Seepage Pressure Sensor in Soil Test

Combined with the pressure sensitive characteristics of corrugated diaphragm and the strain sensing characteristics of fiber Bragg grating (FBG), a kind of FBG sensor is developed to measure the seepage pressure change of soil in a small range. By carrying out the soil seepage flow monitoring test and the laboratory slope model test, and comparing the theoretical and measured values of these tests, it can be found that: it is feasible to apply FBG seepage pressure sensor to the seepage pressure monitoring of soil mass. The sensor can guarantee the validity and reliability of data in the medium-term or long-term monitoring process, and shows superior performance compared with conventional seepage pressure sensor. The FBG seepage pressure sensor has the characteristics of high sensitivity, stable long-term performance, high precision and strong real-time performance. It provides a new measurement method for the seepage pressure monitoring of soil mass within the range of 0 to 100 kPa.

Long-period gratings for monitoring the resin transfer molding of fiber-reinforced polymer composites.

The spectral characteristics of long-period gratings (LPGs) have been researched over the last two decades, and many sensing applications of LPGs have been proposed due to their spectral sensitivity to many surrounding environmental parameters such as the temperature, pressure, and refractive index. However, this sensitivity to many parameters can also be a curse due to cross-sensitivity and the inability to distinguish which environmental parameter is responsible for the LPG's spectral behavior. For the application proposed here-monitoring the progress of a resin flow front, its velocity, and the permeability of the reinforcement mats during the infusion stage of resin transfer molding-the multi-sensitivity of LPGs is a distinct advantage, as it provides the ability to monitor the mold environment at various stages of manufacturing.

A reference-free dual-comb spectroscopy calibrated by passive devices

Dual-comb spectroscopy has enabled new approaches for optical precision measurements. Although Doppler-limited resolution can be achieved over long-time scales across a large bandwidth, the development of dual-comb spectroscopy is hindered by strict demands for light source stability. Typically, expensive and complex self-reference systems are required to lock the carrier-envelope offset frequency (fceo) of the laser. Additionally, simply locking the repetition frequency (frep) to a radio frequency reference source still results in residual relative timing jitter between light sources. Here we extracted the relative fceo fluctuation between the frep-locked lasers from the high-precision passive notch filtering characteristics of the phase-shifted fiber Bragg grating and then eliminated it through online phase calibration. By introducing a passive broadband Fabry–Perot cavity with excellent thermal wavelength stability, we subsequently corrected residual relative timing jitter with online wavelength calibration, and the standard deviation of the relative wavelength drift was reduced to less than 0.4 pm within the full operating range. The spectral profile can also be extracted and removed by the Fabry–Perot cavity through intensity calibration. By calibrating these three dimensions, we built a reference-free post-calibration dual-comb spectroscopy and used this powerful tool to measure the Fabry–Perot cavity resonance peaks, the notch filtering narrow band of phase-shifted fiber Bragg gratings, and the absorption characteristics of hydrogen cyanide gas. The system achieves a spectral resolution of 0.8 pm over a bandwidth of more than 100 nm. This low-cost and convenient scheme provides new ideas for the application of dual-comb spectroscopy systems.