Grating Array Research Articles

Enhanced broadband quantum efficiency in LWIR T2SL detectors with guided-mode resonance structure

Type-II superlattice (T2SL) detectors are emerging as key technologies for next-generation long-wavelength infrared (LWIR) applications, particularly in the 8–14 µm range, offering advantages in space exploration, medical imaging, and defense. A major challenge in improving quantum efficiency (QE) lies in achieving sufficient light absorption without increasing the active layer (AL) thickness, which can elevate dark current and complicate manufacturing. Traditional methods, such as thickening the absorber, are limited by the short carrier lifetime in T2SLs, necessitating alternative solutions. In this study, we introduced a guided-mode resonance (GMR) structure into T2SL LWIR detectors to enhance QE while maintaining a thin AL for efficient carrier collection. The GMR structure was fabricated by introducing a grating array on the surface of the detector and an Au mirror beneath the absorber. This configuration enhanced light trapping, which introduced additional resonance modes. The optimized grating design, with a 5 µm period and a fill factor of 0.6, significantly increased absorption, as predicted by finite-difference time-domain (FDTD) simulations and confirmed experimentally. The GMR-enhanced T2SL detector demonstrated a 2.58-fold improvement in QE over conventional LWIR detectors and a 1.33-fold increase compared to Fabry-Pérot (FP) resonance-based detectors in the 6–11 µm range. Despite exhibiting an almost identical dark current density, the GMR LWIR detector demonstrated superior performance, featuring a broader cut-off wavelength of 9.3 µm and higher QE compared to FP LWIR detectors.

Settlement Monitoring of Ultra-Long GIS in Substations Based on Weak Fiber Bragg Grating Array

Settlement Monitoring of Ultra-Long GIS in Substations Based on Weak Fiber Bragg Grating Array

Fast and High-Precision Shape Sensing Based on Dual-Comb Fiber Bragg Grating Array Demodulation

Fast and High-Precision Shape Sensing Based on Dual-Comb Fiber Bragg Grating Array Demodulation

Bioinspired single-shot polarization photodetector based on four-directional grating arrays capped perovskite single-crystal thin film.

Polarization photodetectors (pol-PDs) have widespread applications in geological remote sensing, machine vision, biological medicine, and so on. However, commercial pol-PDs use bulky and complicated optical systems with lenses, polarizers, and mechanical spools, which are complex and cumbersome, and respond slowly. Inspired by the desert ants' compound eyes, we developed a single-shot pol-PD based on four-directional grating arrays capped perovskite single-crystal thin film without other standard polarization optics. Our pol-PD has a high detectivity, two orders of magnitude greater than that of commercial photodetectors, and exhibits high polarization sensitivity. The high performance of our pol-PD is due to the highly crystalline perovskite single-crystal thin film and regular nanograting structure, made by a nanoimprinting crystallization method. Our single-shot pol-PD is a compact on-chip optoelectronic device that demonstrates excellent performance in a wide range of applications including accurate bionic navigation, sharp image restoration in hazy scenes, stress visualization of polymers, and detection of cancerous areas in tissues without histological staining.

Real-Time Strain Field Measurement Based on Dense Fiber Bragg Gratings Array

Real-Time Strain Field Measurement Based on Dense Fiber Bragg Gratings Array

A small-sized fire detection method based on the combination of the SIC algorithm and 1-DCNN

The article proposes a method for detecting small-sized fires using an Ultra-Weak Fiber Bragg Grating (UWFBG) array fire monitoring system, addressing issues of slow response speed and insufficient spatial resolution in traditional fire monitoring systems. The system’s spatial resolution is improved by regional subsection monitoring and using the Spectral Intensity Change (SIC) algorithm combined with a one-dimensional convolutional neural network (1-DCNN) model for hot spot recognition. This approach can ignore the impact of noise on the reflected spectra to some extent, overcoming the limitations of traditional methods. Simulation results demonstrate that when the signal-to-noise ratio (SNR) is above 10 dB, the accuracy of hot spot recognition is significantly improved. At an SNR of 15 dB, the recognition accuracy reaches 98.5 %. Furthermore, addressing the spectral distortion issue in the sensor array, introducing the 1-DCNN model achieves a recognition accuracy of 98.6 %. The proposed method can identify small-sized fires of 10 cm, providing a safe and reliable solution for fire monitoring systems in subway tunnels.

Respiratory frequency and activity monitoring using Fibre Bragg Grating arrays

Respiratory frequency and activity monitoring using Fibre Bragg Grating arrays

Quasi-distributed acoustic sensing based on optical path difference demodulation for high-frequency and large-amplitude using an optical fiber interferometer array.

The phase-sensitive optical time domain reflectometry scheme has attracted great research interest in distributed acoustic sensing (DAS) but suffers from a trade-off between the dynamic range and signal frequency. In this paper, an optical path difference (OPD) demodulation method is applied to an interferometer array composed of an ultra-weak fiber Bragg grating (UWFBG) array and an imbalanced Michelson interferometer to solve this problem. As far as we know, this is the first time that OPD demodulation has been applied to DAS. The UWFBG array is interrogated by a frequency-modulated pulse, and the acoustic signal sensed by the fiber between any two adjacent UWFBGs can be retrieved by demodulating the variation of residual OPD of the interferometer formed by them. The proposed method is analyzed theoretically and validated experimentally; compared with the phase demodulation method, a 100-times boost in bandwidth is achieved for a signal with an amplitude of 0.4 µε. Results also show that the proposed method offers increasing signal-to-noise ratios as the frequency increases.

Enhancing the performance of DAS using a dual-wavelength UWFBG array with alternating arrangement

We propose a novel distributed acoustic sensor (DAS) based on a dual-wavelength ultra-weak fiber Bragg grating (UWFBG) array. The UWFBGs in the array have two wavelengths that are arranged alternately. Two double-pulses with different wavelengths and staggered launching times are used for sensing in the UWFBG array. This approach successfully overcomes the trade-off between spatial resolution and sensing distance in the traditional UWFBG-based DAS and effectively doubles the maximum achievable sampling rate constrained by the sensing distance. The crosstalk of different wavelengths is avoided by time division multiplexing. Comprehensive analyses and simulations are conducted to validate the performance enhancements, compared to the traditional method. In our proof-of-concept experiments, employing a 2 km alternating arranged dual-wavelength UWFBG array, we achieve a spatial resolution enhancement from 10 m to 5 m, expand the dynamic strain measurement range from 34.2 rad to 68.2 rad, and increase the frequency response from 9 kHz to 19 kHz.

Research on satellite structural health monitoring based on ultrashort femtosecond grating array and artificial neural network

The safety of spacecraft and satellite in orbit is very important, and structural health monitoring is needed. At present, the existing technology is limited by load and difficult to realize. In this paper, we propose a feasible method to detect and locate the damage of satellite by combining ultrashort femtosecond grating array inscribed on oxide-doped fiber with multilayer artificial neural network. An oxide-doped fiber with high robustness is designed, and ultrashort grating arrays are fabricated on the fiber by femtosecond laser point-by-point writing technology. The effects of impactor velocity and angle on impact response was investigated by numerical simulations and physical experiments. Subsequently, repeated impact experiments were conducted on the satellite to obtain the training dataset and testing dataset for two-dimensional convolutional neural network. The network with symmetric convention kernels has an 88.12% localization accuracy and a better performance in boundary region, and the network architecture with asymmetric convention kernels has a 90.31% accuracy and a better performance in middle region.

Experimental research on strain distribution measurement of PC beams based on weak grating array sensing technology.

The strain and deformation of bridges are important parameters to reflect the state of bridge structures. The traditional measurement methods are to obtain the partial strain of a bridge by point strain sensor or to obtain the deformation of some special bridge positions by static level and other methods. These methods can not realize the continuous distributed measurement of bridge stress state. The grating array is a new sensing technology with the characteristics of large capacity, long distance, distribution, and high precision. In this paper, the grating array strain optical cable is installed on PC (pre-stressed concrete) beams to conduct loading and unloading experiments under various working conditions compared with other measurement methods. The experimental results show that the grating array strain sensing technology can realize the distributed measurement of bridge strain, and offer a what we believe is a novel approach to bridge health monitoring.

Scalable free-space photonic antennas in foundry SOI silicon photonic platforms.

We present a flexible, scalable, and low-noise design scheme for coupling free-space light into a silicon-on-insulator (SOI) electronic-photonic integrated circuit. The proposed scheme utilizes arrays of grating couplers with compact, inverse-designed power combining networks to couple a distributed optical collection area to a single output waveguide, forming a photonic antenna. Fabrication density compliance is maintained regardless of the antenna size, and the collection area can be scaled while maintaining a fixed noise floor. Using experimental grating array antennas fabricated in the GF45CLO platform, we demonstrate up to a 6.7× increase in the signal-to-noise ratio (SNR) of a lens-less monolithic free-space photonic receiver using a 4×4 grating array.

Grating Bio-Microelectromechanical Platform Architecture for Multiple Biomarker Detection.

A label-free biosensor based on a tunable MEMS metamaterial structure is proposed in this paper. The adopted structure is a one-dimensional array of metamaterial gratings with movable and fixed fingers. The moving unit of the optical detection system is a component of the MEMS structure, driven by the surface stress effect. Thus, these suspended optical nanoribbons can be moved and change the grating pattern by the biological bonds that happened on the modified cantilever surface. Such structural variations lead to significant changes in the optical response of the metamaterial system under illuminating angled light and subsequently shift its resonance wavelength spectrum. As a result, the proposed biosensor shows appropriate analytical characteristics, including the mechanical sensitivity of Sm = 11.55 μm/Nm-1, the optical sensitivity of So = Δλ/Δd = 0.7 translated to So = Δλ/Δσ = 8.08 μm/Nm-1, and the quality factor of Q = 102.7. Also, considering the importance of multi-biomarker detection, a specific design of the proposed topology has been introduced as an array for identifying different biomolecules. Based on the conducted modeling and analyses, the presented device poses the capability of detecting multiple biomarkers of disease at very low concentrations with proper precision in fluidic environments, offering a suitable bio-platform for lab-on-chip structures.

One-step fabrication of multifunctional superhydrophobic copper surfaces via laser-assisted ablation PDMS solution

The super-hydrophobic surfaces have been greatly restricted in multi-functional applications because of the poor surface durability and multi-step processes such as preparing rough structures and low surface energy modification. In this work, a multifunctional wear-resistant super-hydrophobic surface (SHS) was primarily developed by one step laser etching polydimethylsiloxane (PDMS) i.e. the uncured PDMS layer was laser-ablated just after it was coated on the surface of copper. The wettability, morphology and chemical composition of the surfaces were characterized by a contact Angle measuring instrument, scanning electron microscope (SEM) and Fourier transform infrared spectrometer (FTIR). The results show that the developed SHS has the high contact angle (WCA) of 156.8° and low sliding angle (WSA) of 4.6°; which presents a regular linear grating array and a large number of coral-like rough structures, and the developed SHS can withstand at least 120 tape stripping tests, 40 sandpaper friction abrasion tests, 60 h of high temperature treatment (100 °C∼300 °C) or 240 h of ultraviolet light exposure tests, respectively. The self-cleaning rate and anti-fouling rate of the SHS were 94.2 % and 91.8 %, respectively, and the freezing time of droplets on the SHS is 162 s longer than that on the original copper surface, and almost 3 times longer than that on the smooth surface. In all, the non-polluting wear-resistant multifunctional SHS was primarily developed by laser ablation of metals and polymers, which has strong potential usage in the fields of anti-fouling of industrial pipeline systems and anti-icing of outdoor power transmission systems.

Efficient generation of octave-separating orbital angular momentum beams via forked grating array in lithium niobite crystal.

The concept of orbital angular momentum (OAM) of light has not only advanced fundamental physics research but also yielded a plethora of practical applications, benefitting from the abundant methods for OAM generation based on linear, nonlinear and combined schemes. The combined scheme could generate octave-separating OAM beams, potentially increasing the channels for optical communication and data storage. However, this scheme faces a challenge in achieving high conversion efficiency. In this work, we have demonstrated the generation of multiple OAM beams at both fundamental frequency and second harmonic (SH) wavelengths using a three-dimensional forked grating array with both spatial χ (1) and χ (2) distributions in a lithium niobate nonlinear photonic crystal platform. The enhancements of the fundamental and SH OAM beams have been achieved by employing linear Bragg diffraction and nonlinear Bragg diffraction, respectively, i.e., quasi-phase matching. The experimental results show that OAM beams with variable topological charges can be enhanced at different diffraction orders via wavelength or angle tuning, achieving conversion efficiencies of 60.45 % for the linear OAM beams and 1.08 × 10-4 W -1 for the nonlinear ones. This work provides a promising approach for parallel detection of OAM states in optical communications, and extends beyond OAM towards the control of structured light via cascaded linear and nonlinear processes.

Flexible Arc-Shaped Micro-Fiber Bragg Grating Array Three-Dimensional Tactile Sensor for Fingertip Signals Detection and Human Pulse Monitoring.

A flexible arc-shaped micro-Fiber Bragg Grating (mFBG) array three-dimensional tactile sensor for fingertip signal detection and human pulse monitoring is presented. It is based on a three mFBGs array which is embedded in an arc-shaped poly (dimethylsiloxane) (PDMS) elastomer, which can effectively discriminate the normal force, left force, and right force by monitoring the reflected intensity variation of the three mFBGs. Different from the traditional FBG sensors, this sensor measures force by detecting changes in light intensity, effectively avoiding the wavelength cross-sensitivity impact of temperature variations on the sensor performance. This design strategy simplifies the sensor structure, reduces the system complexity and signal interrogation cost, and enhances reliability and practicality. Through systematic experiments, we successfully validated the sensor's superior performance, achieving a minimum detection force of 0.01 N and providing robust data support for practical applications. In addition, the sensor has been used to monitor human pulse accurately. The successful fabrication and experimental validation of this sensor lay a foundation for its widespread application in fields such as robot perception and human vital signal detection.

Length-extended 3D shape sensor using wavelength/space-division multiplexing grating arrays in a multicore fiber.

Limited by the multiplexing number of fiber Bragg grating (FBG), further improvement in the length of 3D shape sensing based on FBG technology is challenging. In this Letter, a wavelength-division and space-division multiplexing multicore fiber grating method is proposed, which extends the sensing length. Employing the femtosecond-laser point-by-point technology, we inscribed WDM grating arrays in six outer cores of a seven-core fiber, respectively. Three cores were utilized as a segment for shape sensing, and two such segments were offset by a specific length and combined to form a shape sensor. Utilizing an FBG interrogator, the proposed shape sensor achieved 2D and 3D shape sensing at a length of 967 mm and effectively mitigated the effects of temperature variations. In experiments, maximum shape reconstruction errors per unit lengths are 1.89%, 2.72%, and 1.47% for 2D shape, 3D shape, and an arbitrary shape under variable temperature conditions, respectively. The proposed method holds promise for further extending the shape sensing length by utilizing multicore fibers or fiber clusters containing more cores.

Linear dispersion (GDD) design using grating group

Precise control of dispersion output holds paramount significance across domains such as optical fiber communication, time stretching, and spectral interferometric ranging. In comparison to other dispersion elements, like prisms, gratings are widely applied in the field of dispersion control due to their advantages of broad spectral range, tunability, and high resolution. Moreover, linear dispersion is the most desired characteristic by designers in most cases. Here, we develop a dispersion model for grating groups to determine the optimal structural parameters for achieving linear dispersion in high-order grating arrays. Based on our model, we provide corresponding parameter selection methods that allow for quantitative design of the size and slope of output dispersion by adjusting input parameters such as angle, distance, and parallelism. Additionally, we experimentally establish a dispersion interferometry structure based on the grating ensemble that validates our proposed approach's capability for linear dispersion output (linearity better than 0.9998). We believe that our approach is universally significant and contributes to enhancing the performance of dispersion interferometric measurement systems, chirp amplification systems, and other related systems.

A Real-Time In Situ Wafer Temperature Measurement System Based on Fiber Bragg Grating Array

A Real-Time In Situ Wafer Temperature Measurement System Based on Fiber Bragg Grating Array

Design of an enhanced spatial resolution indoor plantar strain and gait analysis setup for biomedical applications

In the recent years, measurement of plantar strain and gait analysis has gained huge attention and plays a pivotal role in monitoring posture related ailments or Diabetic Foot Ulcer (DFU). Fibre Bragg Grating Arrays (closely spaced FBGs), another category of optical sensors, are employed in this study to understand the strain and gait of human foot. These arrays offer critical advantages such as enhanced sensitivity, data acquisition, multiplexing abilities, and sensor location effect compensation. For experimentation, five arrays were distributed among different regions (Upper, Medial, and Heel) of foot and their strain patterns for six volunteers (three male and three female) were recorded for eighty seconds. The data was analysed in two ways, Combined (data of array sensors were averaged to target the whole area) and Individual (for independent analysis of each sensor in array). Incoherent transitions and strain patterns of FBGs within the same arrays observed in individual analysis, explains enhanced resolution capabilities of the arrays. Strain mapping of sensor behaviour also confirmed the identification of various forms of gait i.e., Heel Strike, Flat Foot, Heel Off, and Zero Contact. The average standard deviation values for the arrays was reported below 0.16.