Narrow Wavelength Bands Research Articles

Measurement of optical density in a narrow wavelength band: A method for correcting the results of indirect measurements

Measurement of optical density in a narrow wavelength band: A method for correcting the results of indirect measurements

Multifunctional integrated droplet lens based on microfluidics.

A multifunctional integrated droplet lens based on microfluidics is proposed. The lens consists of a microfluidic chip, four droplets with different properties, and transparent silicone oil. Visible-light, infrared, narrow wavelength band, and light-switching droplets can be used for imaging in the VIS-NIR (visible to near-infrared), narrow wavelength band, and blocking light, respectively. The optical focal power of the proposed lens is -134.6 D ∼ -91.62 D with visible-light droplet and -21.1 D ∼ -12.9 D with infrared droplet. When the droplet lens is used as an optical switch, the maximum optical attenuation is 251:1. It is measured that the transmitted power can be adjusted from 0.015 mW to 0.096 mW when the initial incident power is 0.776 mW. The proposed lens integrates the functions of zoom and optical attenuation. It offers important advantages in providing lightweight, high integration and shows a wide range of potential applications in microscopy systems, microfluidic systems, and variable optical attenuators.

Vegetation monitoring in mining area using canopy reflectance and landsat8 oli image

The aim of this study is to find out the vegetation monitoring in mining areas which is of great significance in grasping the ecological environment status of mining areas. As the first target of spectral reflection, the vegetation canopy directly affects the results of spectral reception. Leaf Angle Distribution (LAD) is a key canopy structural parameter, which directly determines the amount of solar radiation intercepted by the canopy. Taking the relationship between the effect of leaf inclination angle on vegetation canopy reflectance and NDVI as an entry point, the study monitored and analyzed the vegetation in Dexing mining area, China, from 2013 to 2018 by NDVI, based on which the Copper Stress Vegetation Index (CSVI), which is applicable to the narrow wavelength band of remote sensing imagery, was evaluated whether it could be applied to the wide wavelength band. The results show that the NDVI value of the horizontal distribution is significantly higher than that of other leaf inclination distributions, and the NDVI in the direction of the horizontal distribution is 0.82, while the NDVI in the direction of the hi-straight distribution is 0.75; the NDVI of the mining area decreases gradually with the increase of the area of the mining area, and the correlation coefficients of the two groups of CSVI based on the wide and narrow bands are not large, which is not suitable for the vegetation monitoring by using the Landsat8 OLI imagery. Wide band is less applicable for vegetation monitoring. Bangladesh J. Bot. 53(3): 835-847, 2024 (September) Special

Measurement of optical density in a narrow wavelength band: a method for correcting the results of indirect measurements

The issues of correspondence of the results of direct and indirect measurements of optical density in a narrow wavelength band are considered. The optical density in a narrow wavelength band was measured by filtering the luminous flux according to the international standard ISO 5-3:2009 “Photography and graphic technology – Density measurements. Part 3: Spectral conditions” (direct measurement) and spectral method (indirect measurement). In order to ensure the uniformity of optical density measurements in a narrow wavelength band and establish the traceability of measurement results to the State Primary Standard of optical density units GET 206-2016, the degree of conformity of the results obtained by two methods was investigated. The techniques of measuring optical density in a narrow wavelength band for each method are described. The method of fi ltering the luminous flux was implemented using GET 206-2016, namely using a complex for measuring diffuse optical transmittance density. The Cary 7000 spectrophotometer (Agilent, USA) was used to implement the spectral method. Data on measuring the optical density of glass light fi lters by two methods are presented. A method for correcting the results of spectral measurements has been developed and a correction to the results of spectral measurements has been determined. The developed method and the correction make it possible to establish the correspondence of the results of spectral measurements to the results of measurements by fi ltering the luminous fl ux. Also, the described method for correcting the results of spectral measurements makes it possible to establish the traceability of the results of optical density measurements by the spectral method to the measurement results using GET 206-2016.

The PAU survey: photometric calibration of narrow band images

ABSTRACT The physics of the accelerating Universe (PAU) camera is an optical narrow band and broad band imaging instrument mounted at the prime focus of the William Herschel Telescope. We describe the image calibration procedure of the PAU survey data. We rely on an external photometric catalogue to calibrate our narrow band data using stars that have been observed by both data sets. We fit stellar templates to the stellar broad-band photometry of the Sloan Digital Sky Survey and synthesize narrow band photometry that we compare to the PAUS narrow band data to determine their calibration. Consequently, the PAUS data are in the AB system as inherited from its reference calibrator. We do several tests to check the performance of the calibration. We find it self-consistent when comparing repeated observations of the same objects, with a good overall accuracy to the AB system which we estimate to be at the 2 per cent precision level and no significant trends as a function of narrow band filter or wavelength. Repeated observations allow us to build a spatial map of the illumination pattern of the system. We also check the wavelength dependence of the calibration comparing to stellar spectra. We find that using only blue stars reduces the effects of variations in the stellar template fitting to broad-band colours, improving the overall precision of the calibration to around 1 per cent and its wavelength uniformity. The photometric redshift performance obtained with the PAUS data attests to the validity of our calibration to reach the PAUS science goals.

Single-layer waveguide with compound metasurfaces for highly efficient and chromatic-aberration-free augmented reality near-eye displays

Augmented reality (AR) near-eye displays seamlessly integrate virtual information with real world, in which the optical waveguide is the key component functioned as a coupler. Due to strong chromatic aberration, independent waveguides are always indispensable to separate the three primary colors that inevitably brings larger and thicker appearance. To address this, this paper proposes a new chromatic-aberration-free single-layer waveguide for AR displays by integrating a double-layer grating metasurface (MS) and the covered cylindrical MSs. The double-layer grating MS breaks through the limitations on a narrow wavelength band, enabling high diffraction efficiency for incident light deflection across the entire visible spectrum. Further, the cylindrical MSs provide accurate control over incident angles, not only overcoming the challenge of total reflection but also effectively eliminating chromatic aberration. Design results show that the proposed structure achieves an impressive diffraction efficiency of over 80 % for blue and green light and over 90 % for red light with an outstanding diffraction angular difference lower than 2.5 deg. Real-time ray tracing simulation demonstrates the capability of the designed AR engine to achieve high-resolution full-color imaging. The compound MSs enable precise light and color control for a single-layer waveguide coupler with exceptional diffraction efficiency and minimal chromatic aberration, which show great potential for cutting-edge AR applications.

Planar 16-band metasurface-enhanced spectral filter for integrated image sensing

We study theoretically and demonstrate experimentally a 16-band narrow band wavelength selective filter in the near-infrared range. The combination of a pair of distributed Bragg reflectors with a sub-wavelength grating metasurface embedded in the intra-cavity provides a narrow response which can be tuned by adjusting the geometry of the sub-wavelength grating metasurface. The key advantage of this approach is its ease of fabrication, where the spectral response is tuned by merely changing the grating period, resulting in a perfectly planar geometry that can be easily integrated with a broad variety of photodetectors, thus enabling attractive applications such as bio-imaging, time-of-flight sensors and LiDAR. The experimental results are supported by numerical simulations and effective medium theory that unveil the mechanisms that lead to the optical response of the device. It is also shown how the polarization dependence of the structure can be used to determine very accurately the polarization of incoming light.

Detecting colorectal lesions with image-enhanced endoscopy: an updated review from clinical trials.

Colonoscopy plays an important role in reducing the incidence and mortality of colorectal cancer by detecting adenomas and other precancerous lesions. Image-enhanced endoscopy (IEE) increases lesion visibility by enhancing the microstructure, blood vessels, and mucosal surface color, resulting in the detection of colorectal lesions. In recent years, various IEE techniques have been used in clinical practice, each with its unique characteristics. Numerous studies have reported the effectiveness of IEE in the detection of colorectal lesions. IEEs can be divided into two broad categories according to the nature of the image: images constructed using narrowband wavelength light, such as narrowband imaging and blue laser imaging/blue light imaging, or color images based on white light, such as linked color imaging, texture and color enhancement imaging, and i-scan. Conversely, artificial intelligence (AI) systems, such as computer-aided diagnosis systems, have recently been developed to assist endoscopists in detecting colorectal lesions during colonoscopy. To better understand the features of each IEE, this review presents the effectiveness of each type of IEE and their combination with AI for colorectal lesion detection by referencing the latest research data.

Improving hyperspectral image classification through spectral-spatial feature reduction with a hybrid approach and deep learning

ABSTRACT The Hyperspectral Image (HSI) is a great source of information for observing the earth’s elements due to its numerous narrow and continuous spectral wavelength bands. There are some key difficulties, such as the fact that the image bands are spectrally and spatially highly correlated, and the ‘curse of dimensionality’ in using the original HSI for classification. Band (dimensionality/feature) reduction is necessary to improve classification performance through feature extraction and selection. As such, this paper proposes a hybrid HSI classification paradigm, termed Hybrid-2DNET. Specifically, our proposed Hybrid-2DNET incorporates factor analysis-based feature extraction along the Minimum-Redundancy-Maximum-Relevance (mRMR)-based feature selection criterion and a 2D-wavelet Convolutional Neural Network (CNN) to reduce both spectral and spatial dimensionalities. The experimental analyses performed on three remote sensings HSI datasets, namely Indian Pines, University of Pavia, and Salinas Scene, manifest that our proposed Hybrid-2DNET outperforms the handcrafted and deep learning methods.

Wavelength‐Selective, Narrowband Graphene Transistor with a Plasmon‐Enhanced Pyroelectric Gate

Herein, a wavelength‐selective pyroelectric sensor based on a graphene field‐effect transistor (gFET) with a plasmon‐enhanced pyroelectric gate (PG) is reported. The PG gFET (PG‐gFET) uses a poly(vinylidene fluoride‐co‐trifluoroethylene) or PVDF‐TrFE membrane doped with plasmonic nanoparticles as the gate. Gold nanorods (AuNRs) or silver nanoparticles (AgNPs) are incorporated into the PVDF‐TrFE membrane to enhance the photothermal conversion efficiency of PVDF‐TrFE in a specific narrowband wavelength range. The wavelength‐selective photothermal effect can optically modulate the gate potential of the PG‐gFET; this, in turn, leads to a change in current through the graphene film of the transistor. The PG‐gFET with AuNRs exhibits a maximum responsivity of 0.79 μA mW−1 at the wavelength of 660 nm. Replacing AuNRs with AgNPs in the PVDF‐TrFE membrane results in tuning the plasmonic response of the transistor to 488 nm with a maximum responsivity of 0.68 μA mW−1. When plasmonic nanoparticles are absent from the PVDF‐TrFE membrane, the maximum response wavelength of the transistor is shifted to a midinfrared regime at 3125 nm, which is associated with the CC absorption of PVDF‐TrFE. The ability of the PG‐gFET to selectively respond to different light wavelengths will benefit many fields, including pyroelectric sensors, spectroscopy, and imaging.

Mitigation of nonlinearities in long-haul DWDM soliton-based communication system

Abstract The ongoing challenge of research and development is focusing on increasing the overall capacity of the transmission medium, achieving a high bit rate, and designing long-haul optical communication systems. The main requirement of the transmission system in supporting high bit rates in optical communication systems is their tolerance to nonlinear fiber impairments. Optical soliton pulses that preserve their shape over long distances are the straightforward solution to this problem. In this paper, DWDM soliton-based optical communication system is designed to mitigate the nonlinear effects at a data rate of 10 Gbps with channel spacing of 100 GHZ by using a microring resonator (MRR) device which acts as an add/drop filter that generates a filter narrowband wavelength from a wider optical spectrum. The transmission link of the optical fiber has a total length of 180 km and MRR is inserted at the end of the loop which provides the required bandwidth. The high bit rate signals can be transmitted through this MRR system to get the filtered signal which is less affected by the nonlinearities. This filtered signal is observed at a total transmission distance of 54,000 km. Also, by using dispersion compensation techniques, the impact of four-wave mixing (FWM) is mitigated. The performance of the designed system is evaluated based on the quality factor (Q-factor) along with the bit error rate (BER) obtained.

A Lightweight Remote Sensing Payload for Wildfire Detection and Fire Radiative Power Measurements

Small uncrewed aerial systems (sUASs) have the potential to serve as ideal platforms for high spatial and temporal resolution wildfire measurements to complement aircraft and satellite observations, but typically have very limited payload capacity. Recognizing the need for improved data from wildfire management and smoke forecasting communities and the potential advantages of sUAS platforms, the Nighttime Fire Observations eXperiment (NightFOX) project was funded by the US National Oceanic and Atmospheric Administration (NOAA) to develop a suite of miniaturized, relatively low-cost scientific instruments for wildfire-related measurements that would satisfy the size, weight and power constraints of a sUAS payload. Here we report on a remote sensing system developed under the NightFOX project that consists of three optical instruments with five individual sensors for wildfire mapping and fire radiative power measurement and a GPS-aided inertial navigation system module for aircraft position and attitude determination. The first instrument consists of two scanning telescopes with infrared (IR) channels using narrow wavelength bands near 1.6 and 4 µm to make fire radiative power measurements with a blackbody equivalent temperature range of 320-1500 °C. The second instrument is a broadband shortwave (0.95-1.7 µm) IR imager for high spatial resolution fire mapping. Both instruments are custom built. The third instrument is a commercial off-the-shelf visible/thermal IR dual camera. The entire system weighs about 1500 g and consumes approximately 15 W of power. The system has been successfully operated for fire observations using a Black Swift Technologies S2 small, fixed-wing UAS for flights over a prescribed grassland burn in Colorado and onboard an NOAA Twin Otter crewed aircraft over several western US wildfires during the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field mission.

Mutual Information-Driven Feature Reduction for Hyperspectral Image Classification

A hyperspectral image (HSI), which contains a number of contiguous and narrow spectral wavelength bands, is a valuable source of data for ground cover examinations. Classification using the entire original HSI suffers from the "curse of dimensionality" problem because (i) the image bands are highly correlated both spectrally and spatially, (ii) not every band can carry equal information, (iii) there is a lack of enough training samples for some classes, and (iv) the overall computational cost is high. Therefore, effective feature (band) reduction is necessary through feature extraction (FE) and/or feature selection (FS) for improving the classification in a cost-effective manner. Principal component analysis (PCA) is a frequently adopted unsupervised FE method in HSI classification. Nevertheless, its performance worsens when the dataset is noisy, and the computational cost becomes high. Consequently, this study first proposed an efficient FE approach using a normalized mutual information (NMI)-based band grouping strategy, where the classical PCA was applied to each band subgroup for intrinsic FE. Finally, the subspace of the most effective features was generated by the NMI-based minimum redundancy and maximum relevance (mRMR) FS criteria. The subspace of features was then classified using the kernel support vector machine. Two real HSIs collected by the AVIRIS and HYDICE sensors were used in an experiment. The experimental results demonstrated that the proposed feature reduction approach significantly improved the classification performance. It achieved the highest overall classification accuracy of 94.93% for the AVIRIS dataset and 99.026% for the HYDICE dataset. Moreover, the proposed approach reduced the computational cost compared with the studied methods.

Improvement of on-cell metrology using spectral imaging with TCAD modeling

On-cell metrology based on spectral imaging (SI) with TCAD modeling is developed for measuring advanced logic devices. Spectral imaging has been adopted because it can directly measure a cell-block of logic device, which could not be achieved with the conventional methodology. One of conventional methodology, optical critical dimension (OCD), assumes that the cell-block is infinitely periodic, so that relatively large metrological site is needed. However, SI has also disadvantages, it use only one spectrum type and narrow wavelength band. To overcome such limitations, we adopt TCAD modeling by providing realizable sets of spectrum and structure. TCAD model acts as a data augmentation of structural parameter and corresponding simulation spectrum. From sufficient learning data, their correlation was successfully obtained through machine learning. With the proposed method, we could obtain both wafer-to-wafer distribution and in-wafer distribution with a good tendency in logic devices.

DIABETIC RETINOPATHY LESION DETECTION FROM MULTISPECTRAL RETINAL IMAGES THROUGH NEURAL NETWORK

Diabetic Retinopathy (DR) is one of the fastest growing dysfunctions of human retina. Significant research has been conducted using RGB fundus imaging for automatic detection of retinal lesions affected by DR. However, due to only three imaging bands, the accuracy from RGB fundus images is unlikely to improve any further. In contrast to RGB imaging, multispectral imaging has the key advantage of multiple narrow wavelength bands that can be used as spectral features to improve the detection accuracy. Nevertheless, the inter and intra-retinal variation of color, contrast, and illumination is a challenge to process the multispectral images. In this study, a complete framework is proposed to develop and evaluate methods for automatic detection of DR lesions. A multispectral retinal image database, DIARETSPECDB1, is investigated in order to detect the most common DRs such as Microaneurysms (MA), Hard Exudates (HE) and Hemorrhages (HEM). The reflectance values of the spectral bands are used as features of a three-layer basic neural network (NN) to determine the baseline performance of multispectral data instead of any advanced model. According to the results, the model outperforms existing technique producing overall accuracy 94.5%, and the obtained specificity/sensitivity is 0.95/0.89, 0.97/0.89, and 0.88/0.84 for MAs, HEs and HEMs, respectively.

Polymer-Based High Diffraction Efficiency and High Resolution Volume Holographic Transmission Gratings

We report on the optical characterization of very high-efficiency and high-resolution holographic volume phase transmission gratings. The gratings are recorded in a new photo-polymerizable mixture made by epoxy-resin and multi-acrylate. The epoxy-resin used is known to make tenacious acrylate-based films. The holographic mixture contains two photo-initiators, the synergic effect of which enables a reliable photo-polymerization process in the visible region of the electromagnetic spectrum. The recorded holograms are mechanically stable, show long-term temporal stability and very high values of diffraction efficiency, coupled with good angular selectivity due to a relatively narrow band of wavelengths. We measured the intensity of the transmitted beam and calculated the intensity of the diffracted beam at different wavelengths, deriving the refractive index modulation and the grating pitch by fitting the experimental data with a slightly modified theoretical approach. These kind of mixtures can be used in several fields of application, such as chemical or bio-sensors, high resolution optical sensors, high-density optical data storage, encryption and security.

Vis-NIR Hyperspectral Imaging for Online Quality Evaluation during Food Processing: A Case Study of Hot Air Drying of Purple-Speckled Cocoyam (Colocasia esculenta (L.) Schott)

In this study, hyperspectral imaging (HSI) and chemometrics were implemented to develop prediction models for moisture, colour, chemical and structural attributes of purple-speckled cocoyam slices subjected to hot-air drying. Since HSI systems are costly and computationally demanding, the selection of a narrow band of wavelengths can enable the utilisation of simpler multispectral systems. In this study, 19 optimal wavelengths in the spectral range 400–1700 nm were selected using PLS-BETA and PLS-VIP feature selection methods. Prediction models for the studied quality attributes were developed from the 19 wavelengths. Excellent prediction performance (RMSEP < 2.0, r2P > 0.90, RPDP > 3.5) was obtained for MC, RR, VS and aw. Good prediction performance (RMSEP < 8.0, r2P = 0.70–0.90, RPDP > 2.0) was obtained for PC, BI, CIELAB b*, chroma, TFC, TAA and hue angle. Additionally, PPA and WI were also predicted successfully. An assessment of the agreement between predictions from the non-invasive hyperspectral imaging technique and experimental results from the routine laboratory methods established the potential of the HSI technique to replace or be used interchangeably with laboratory measurements. Additionally, a comparison of full-spectrum model results and the reduced models demonstrated the potential replacement of HSI with simpler imaging systems.

Single-sensor filter-intensified fiber optic 4D tomographic CH* chemiluminesence flame measurements.

Chemiluminesence is one of the most common reacting flow visualization techniques, in which a narrowband wavelength associated with species radicals is captured on an image sensor. This technique can provide key insights into flame physics, particularly when a full 3D field can be extracted. Tomographic imaging can capture 3D instantaneous information, but becomes impractical to use when the technique is extended to larger, heavier high-speed imaging equipment. This has resulted in many researchers using fiber-based endoscopes (FBE) to capture multiple views on a single image sensor. However, the introduction of the fiber bundle and corresponding equipment to image specific combustion radicals results in a low SNR imaging environment when captured at high repetition rates. Additionally, when varying equivalence ratios, the signal can become further diminished because the combustion radicals signal weakens at fuel rich and fuel lean conditions. Therefore, this work determines the efficacy of using a filter-intensified FBE approach to capture the CH* radical of a hydrocarbon flame under varying equivalence ratio conditions by comparing the resulting reconstructions to previous quantitative flame measurements.

Preliminary Analysis on Environmental and Intrinsic Factors on FBG-Based Vibration Sensors

In recent years, optical-based sensors have sparked interest for the many advantages over traditional, electrical-based sensors, such as EMI insensitivity, ease of multiplexing on a single line, resilience to hostile environment and very compact size and global weight saving due to signal cables reduction. Considering said properties, optical sensors offer a compelling alternative to traditional sensing elements. One type of optical sensor is the Fiber Braggs Gratings sensors (FBG), which is a type of sensor that reflects a very narrow band of wavelengths, called Bragg wavelength, while being transparent for others; this behavior is achieved by local variations of the core refractive index. The Bragg wavelength can be easily correlated with physical changes in the sensor itself, due to either physical strain or temperature variation. It should be noted that the achievable measurement accuracy is thus comparable to the Bragg wavelength. However, for any practical application, FBGs need to be bonded to a support or surface; in this case, there is a lack of understanding of the effects of temperature and humidity variations on the combined sensor-glue system. In this work, a setup, intended to characterize the sensitivity of the fiber-glue combination to humidity and temperature will be presented.

Smartphone-Based Microscopy with Silicone Lens Embedding Nanostructured Photonic Components

In this work [1], the moldless preparation of a silicone (i.e., poly(dimethylsiloxane), PDMS) lens embedding nanostructured porous silicon (PSi) optical components is discussed, along with its application to smartphone-based microscopy in biology and medicine.A nanostructured PSi surface is used to redirect a droplet of uncured silicone into a lightweight, high-magnifying lens (10 mg mass and 4.7 mm focal length). Geometrical and optical properties of the lens are easily controllable by tuning of the nanostructure features (i.e., thickness and porosity of PSi). Design of the PSi layer as an optical component (e.g., distributed Bragg reflector, rugate filter, resonant cavity) further enables to embed nanostructured optical elements in the lens, so as to select the light transmitted through the lens itself. The fabrication process of the lens has high reliability (yield >95%), low-cost (0.01 $).As proof of concept applications, using a single monolithic lens/filter element self-adhered to a commercial smartphone camera we will discuss: fluorescence imaging and counting of live/dead isolated human cancer cells with high magnification and rejection of the excitation light; selection of a narrow wavelength band from the emission spectrum of a fluorescent dye; changing of the color of a white light emitting diode (from red to blue) through shaping of the diode emission spectrum.[1] Mariani, V. Robbiano, R. Iglio, A. A. La Mattina, P. Nadimi, J. Wang, B. Kim, T. Kumeria, M. J Sailor, G. Barillaro, Moldless Printing of Silicone Lenses with Embedded Nanostructured Optical Filters, Adv. Funct. Mater., 1906836 (2019).