Optical Detection Devices Research Articles

Low-cost optical techniques for detecting and imaging different objects underwater

The camera has been commonly used in underwater image acquisition experiments, but the image noise is high, and the distance is limited because of the underwater scattering effect. In this paper, the optical detection device of underwater objects, 520 nm continuous laser modulation by PWM pulse modulation (10 Hz, 60% space ratio), was used to scan and detect two completely different objects (such as advanced resin and green leaves). The photodetectors were used to replace cameras, collect and process the received laser echo signals, and image and display the data. The detected objects images can be visually displayed in the form of grayscale images (resolution of 143 x 62), and the corresponding effects have been discussed. In the experiment, we used a 70 cm long ultra-white glass cylinder and detected a distance of 45 cm, and the results were very consistent with the actual situation.

Wear-Resistant Blazed Gratings Fabricated by Etching-Assisted Femtosecond Laser Lithography

Blazed gratings are widely used in optical detection devices with the unique property of concentration of light energy to a desired diffraction order. However, traditional substrates for fabricating blazed gratings are easily damaged with the wear and tear in long-term usage under harsh conditions. Here, we propose the fabrication of blazed gratings on sapphire with high mechanical stability by femtosecond laser lithography combined with subsequent reactive ion etching (RIE). Various sapphire blazed gratings with periods from 2 μm to 10 μm and heights from 260 nm to 2 μm were realized to concentrate light energy (wavelengths of 405 nm, 532 nm and 633 nm) to different diffraction orders (1st, 2nd, and 3rd). The results provide great insights for the construction of micro-optical devices that have potential applications under harsh conditions.

Basic principles of information security monitoring in physical channels of optical access networks

The article presents theoretical information about the methods of information retrieval from optical fibers. The simplest analyzed method is the bending of the optical fiber when violating the conditions of total internal reflection. The functional dependence of the losses and the level of radiated power on the parameters and bending geometry of the optical fiber are given. In this case, the introduced losses are monitored in the monitoring system for detecting fiber bends. The structure, principles of operation, and trends in the development of monitoring systems are presented. The main technical characteristics of optical radiation detection devices are demonstrated.

Differences in optical properties of fruit tissues between stone fruits and citrus fruits

Stone fruits have a single-core, and the core volume is large, located in the center of the fruit. In the process of transmission and reflection spectroscopic detection, the influence of fruit core on light cannot be ignored when light passes through flesh. Analyzing the difference in optical characteristics between stone fruits and citrus fruits tissues can provide a theoretical basis for the design of a reasonable optical detection device. It is of great significance for the optical detection of fruit quality. In this paper, a self-developed near-infrared diffuse reflection optical fibre probe with multi-point emission and multi-point reception is used to collect the diffuse reflection spectra of peach and navel orange, and compare the spectral characteristics of the two fruits. The spectral energy of peach is about twice as strong as the spectral energy of navel orange between 600 nm and 900 nm. Preprocess the spectral data with preprocessing methods to reduce the influence of noise and stray light. Compare the partial least squares (PLS) regression models of peach and navel orange. Experiments show that the results of using the baseline correction preprocessing method are all the best. The prediction correlation coefficient (Rp) of the peach is better than that of the navel orange and the root mean square error of the prediction (RMSEP) is also lower. The Rp of peach reached 0.92, and RMSEP was 0.32°Brix. It turned out that after light enters the fruit tissues, part of the light will be reflected out of the fruit when it encounters the core of the fruit. Therefore, in the diffuse reflection detection mode, stone fruits can receive more light and the spectral energy will be stronger than that of citrus fruits.

Optical Characteristics of the Nano-Apertures on the Pyramid

Recently there have been tremendous interests for developing the single molecule analysis device. We have previously reported the fabrication of the nanopores and nano-slit pores on the various nanostructures such as the Au-coated pyramid and the flat membrane for optical detection detection device. In this report, we address the fabrication of the various nano-aperture optical platform, and optical characterization of the fabricated devices. For aperture opening less than 50 nm, the strong spp-mediated intraband transmission peak at 500 nm is presented, while for the aperture size greater than 200 nm, the surface plasmonic coupling peaks among the nano-apertures are observed. As an example, we present the optical intensities measured from the various size of the nanopores on pyramid as in figure. The fabricated spp-mediated optical intensites from the optical platform device can be utilized for the next generation optical detection device. Figure 1

A comparison of different optical instruments and machine learning techniques to identify sprouting activity in potatoes during storage

The quality of potato tubers is dependent on several attributes been maintained at appropriate levels during storage. One of these attributes is sprouting activity that is initiated from meristematic regions of the tubers (eyes). Sprouting activity is a major problem that contributes to reduced shelf life and elevated sugar content, which affects the marketability of seed tubers as well as fried products. This study compared the capabilities of three different optical systems (1: visible/near-infrared (Vis/NIR) interactance spectroscopy, 2: Vis/NIR hyperspectral imaging, 3: NIR transmittance) and machine learning methods to detect sprouting activity in potatoes based on the primordial leaf count (LC). The study was conducted on Frito Lay 1879 and Russet Norkotah cultivars stored at different temperatures and classification models were developed that considered both cultivars combined and classified the tubers as having either high or low sprouting activity. Measurements were performed on whole tubers and sliced samples to see the effect this would have on identifying sprouting activity. Sequential forward selection was applied for wavelength selection and the classification was carried out using K-nearest neighbor, partial least squares discriminant analysis, and soft independent modeling class analogy. The highest classification accuracy values obtained by the hyperspectral imaging system and was 87.5% and 90% for sliced and whole samples, respectively. Data fusion did not show classification improvement for whole tubers, whereas a 7.5% classification accuracy increase was illustrated for sliced samples. By investigating different optical techniques and machine learning methods, this study provides a first step toward developing a handheld optical device for early detection of sprouting activity, enabling advanced aid potato storage management.

Strong coupling of optical interface modes in a 1D topological photonic crystal heterostructure/Ag hybrid system.

We theoretically investigate the strong coupling of a topological photonic state (TPS) and Tamm plasmon polaritons (TPPs) in a graphene embedded one-dimensional topological photonic crystal (TPC)/Ag structure in visible range. It is shown that the strong interaction of a TPS at the TPC heterointerface and TPP at the Ag surface enables a large Rabi splitting up to 96.8meV with a dual-narrow-band perfect absorption. A spectral linewidth of the hybrid mode can be 0.3nm with a Q factor of 1078. The numerical results also reveal that mode coupling can be either tuned by adjusting the geometric parameters or actively controlled by the incident angle, offering a remarkable polarization-independent strong light-matter interaction. The coupled mode theory is employed to explain the strong TPS-TPP coupling. The polarization-independent and controllable strong mode coupling with a dual-narrow-band perfect absorption in this simple lamellar geometry offers new possibilities for developing various on-chip optical detection, sensing, filtering, and light-emitting devices.

Optical characteristics of porous silicon photonic crystals prepared on the back surface of silicon wafers

Surface-enhanced Raman scattering sensors and optical detection devices often incorporate rough surfaces or porous Si photonic crystals to enhance optical absorption and localized surface plasmon resonances. This study reports a porous Si photonic crystal structure fabricated on the backside of a crystalline Si substrate by room-temperature electrochemical etching. Scanning electron microscopy showed that the rough surface did not affect the vertical etching rate, but influenced the porosity and pore size distribution. X-ray diffraction analysis showed broader and lower-intensity peaks from the sample prepared on the back side, indicating that the backside porous Si had strong light-scattering effects and lattice contraction, which led to greater oxidation because of its higher porosity. A reflectance of ∼1% was obtained over a broad wavelength range (400–700 nm) and the optical reflectance suppression mechanism was analyzed. These optical characteristics showed backside porous Si photonic crystals have significant potential utility in photovoltaic and photonics applications.

A Remote Subgrade Settlement Monitoring System Based on Optical Method

Monitoring of subgrade settlement in railway and highway helps to maintain traffic safety and reduce infrastructure losses. When an excess subgrade settlement is detected, maintenances of the unqualified subgrade will be processed in time, and early warning of constructions will be processed to prevent the occurrence of safety accident. In this article, a noncontact, real-time, and unattended system based on optical method is introduced to monitor the subgrade settlement remotely. Several high-power infrared LED targets are mounted on the subgrade and they will move as the subgrade subsides. The movements of the LED targets are detected by an optical detection device based on the principle of optical imaging. The displacement data is remotely transmitted to a server for analysis via GPRS. The remote monitoring system has been applied to the monitoring of subgrade settlement of Zhensheng highway in Guizhou province of China in 2014. This technology helped to detect the subgrade settlement that was caused by the construction of Beiyinpo railway tunnel. Four test points on road surface were monitored at a sampling rate every 20 minutes. The effectiveness of the system has been verified by the practical application.

Inexpensive Alizarin Red S-based optical device for the simultaneous detection of Fe(III) and Al(III)

This work presents a simple, fast, disposable and low-cost colorimetric sensor for the simultaneous detection of Fe(III) and Al(III). It is obtained by fixing a classical dye, Alizarin Red S, on an inert solid support, i.e., a product of the washing powder market known as “Colour Catcher®” (here named under the acronym CC) generally used in the washing machine to prevent colour run problems. The device so obtained is called Aliz-CC@. Fe(III) and Al(III) interaction with the Alizarin Red S-based sensor, generates a change in the adsorption spectra of the fixed dye, allowing to highlight a naked-eye colour change. The relationship between the Fe(III) and Al(III) content and the colour change profiles of the sensor, is provided by using Partial Least Squares regression (PLS).

A new low-cost portable multispectral optical device for precise plant status assessment

Plant stress monitoring is of crucial importance to understand the plant response to environmental conditions, and has been widely applied in various fields including biology, agronomy, botany, and horticulture. A number of methods and instruments for plant stress monitoring have been proposed, most of which show significant disadvantages such as high cost, poor accuracy or complex operation that limit the use of such devices. In this paper, we propose a low cost, portable active multispectral optical device for precise plant stress detection and field mapping named Plant-O-Meter. The device has an integrated multispectral source that comprises light sources of the four most indicative wavelengths (850, 630, 535 and 465 nm), and enables simultaneous illumination of the whole plant. Sequential illumination and detection provide rapid reflectance measurements, which are wirelessly transmitted to android operated devices for processing and data storing. The device was tested in laboratory conditions comparing the Plant-O-Meter measurements with the image results from a SPECIM hyperspectral camera and a GreenSeeker handheld device and under field conditions with the GreenSeeker. The comparison revealed comparable performance, showing strong correlation with both the hyperspectral (R2 = 0.997) and the GreenSeeker handheld (R2 = 0.954 from the laboratory measurements and R2 = 0.886 from the field experiments), indicating that the device exhibits strong potential for accurate plant stress measurements. Moreover, owing to the very simple operating principle, the device represents a compact, cost-effective, and easy-to-operate solution.

Design of Hybrid Electrospun Nanofibers Comprising a Xerogel Functionalized with a Fluorescent Dye for Application as Optical Detection Device

The electrospinning technique allows the production of micro- and nanofibers, which can be used to obtain membranes with high surface area and high porosity. These properties are of importance with...

A Portable Biosensor for 2,4-Dinitrotoluene Vapors.

Buried explosive material, e.g., landmines, represent a severe issue for human safety all over the world. Most explosives consist of environmentally hazardous chemicals like 2,4,6-trinitrotoluene (TNT), carcinogenic 2,4-dinitrotoluene (2,4-DNT) and related compounds. Vapors leaking from buried landmines offer a detection marker for landmines, presenting an option to detect landmines without relying on metal detection. 2,4-Dinitrotoluene (DNT), an impurity and byproduct of common TNT synthesis, is a feasible detection marker since it is extremely volatile. We report on the construction of a wireless, handy and cost effective 2,4-dinitrotoluene biosensor combining recombinant bioluminescent bacterial cells and a compact, portable optical detection device. This biosensor could serve as a potential alternative to the current detection technique. The influence of temperature, oxygen and different immobilization procedures on bioluminescence were tested. Oxygen penetration depth in agarose gels was investigated, and showed that aeration with molecular oxygen is necessary to maintain bioluminescence activity at higher cell densities. Bioluminescence was low even at high cell densities and 2,4-DNT concentrations, hence optimization of different prototypes was carried out regarding radiation surface of the gels used for immobilization. These findings were applied to sensor construction, and 50 ppb gaseous 2,4-DNT was successfully detected.

Evaluation of a Combined Reflectance Confocal Microscopy–Optical Coherence Tomography Device for Detection and Depth Assessment of Basal Cell Carcinoma

The limited tissue sampling of a biopsy can lead to an incomplete assessment of basal cell carcinoma (BCC) subtypes and depth. Reflectance confocal microscopy (RCM) combined with optical coherence tomography (OCT) imaging may enable real-time, noninvasive, comprehensive three-dimensional sampling in vivo, which may improve the diagnostic accuracy and margin assessment of BCCs. To determine the accuracy of a combined RCM-OCT device for BCC detection and deep margin assessment. This pilot study was carried out on 85 lesions from 55 patients referred for physician consultation or Mohs surgery at Memorial Sloan Kettering Skin Cancer Center in Hauppauge, New York. These patients were prospectively and consecutively enrolled in the study between January 1, 2017, and December 31, 2017. Patients underwent imaging, with the combined RCM-OCT probe, for previously biopsied, histopathologically confirmed BCCs and lesions clinically or dermoscopically suggestive of BCC. Only patients with available histopathologic examination after imaging were included. Improvements in sensitivity, specificity, and diagnostic accuracy for BCC using the combined RCM-OCT probe as well as the correlation between OCT-estimated depth and histopathologically measured depth were investigated. In total, 85 lesions from 55 patients (27 [49%] were female and 28 [51%] were male with a median [range] age of 59 [21-90] years) were imaged. Imaging was performed on 25 previously biopsied and histopathologically confirmed BCCs and 60 previously nonbiopsied but clinically or dermoscopically suspicious lesions. Normal skin and BCC features were correlated and validated with histopathologic examination. In previously biopsied lesions, residual tumors were detected in 12 of 25 (48%) lesions with 100% sensitivity (95% CI, 73.5%-100%) and 23.1% specificity (95% CI, 5.0%-53.8%) for combined RCM-OCT probe. In previously nonbiopsied and suspicious lesions, BCCs were diagnosed in 48 of 60 (80%) lesions with 100% sensitivity (95% CI, 92.6%-100%) and 75% specificity (95% CI, 42.8%-94.5%). Correlation was observed between depth estimated with OCT and depth measured with histopathologic examination: the coefficient of determination (R2) was 0.75 (R = 0.86; P < .001) for all lesions, 0.73 (R = 0.85; P < .001) for lesions less than 500 μm deep, and 0.65 (R = 0.43; P < .001) for lesions greater than 500 μm deep. Combined RCM-OCT imaging may be prospectively used to comprehensively diagnose lesions suggestive of BCC and triage for treatment. Further validation of this device must be performed on a larger cohort.

Broadband and wide angle near-unity absorption in graphene-insulator-metal thin film stacks

Broadband unity absorption in graphene-insulator-metal (GIM) structures is demonstrated in the visible (VIS) and near-infrared (NIR) spectra. The spectral characteristics possess broadband absorption peaks, by simply choosing a stack of GIM, while no nanofabrication steps and patterning are required, and thus can be easily fabricated to cover a large area. The electromagnetic (EM) waves can be entirely trapped and the absorption can be greatly enhanced are verified with the finite-difference time-domain (FDTD) and rigorous coupled wave analysis (RCWA) methods. The position and the number of the absorption peak can be totally controlled by adjusting the thickness of the insulator layer. The proposed absorber maintains high absorption (above 90%) for both transverse electric (TE) and transverse magnetic (TM) polarizations, and for angles of incidence up to 80°. This work opens up a promising approach to realize perfect absorption (PA) with ultra-thin film, which could implicate many potential applications in optical detection and optoelectronic devices.

A new method using Raman spectroscopy for in vivo targeted brain cancer tissue biopsy

Modern cancer diagnosis requires histological, molecular, and genomic tumor analyses. Tumor sampling is often achieved using a targeted needle biopsy approach. Targeting errors and cancer heterogeneity causing inaccurate sampling are important limitations of this blind technique leading to non-diagnostic or poor quality samples, and the need for repeated biopsies pose elevated patient risk. An optical technology that can analyze the molecular nature of the tissue prior to harvesting could improve cancer targeting and mitigate patient risk. Here we report on the design, development, and validation of an in situ intraoperative, label-free, cancer detection system based on high wavenumber Raman spectroscopy. This optical detection device was engineered into a commercially available biopsy system allowing tumor analysis prior to tissue harvesting without disrupting workflow. Using a dual validation approach we show that high wavenumber Raman spectroscopy can detect human dense cancer with >60% cancer cells in situ during surgery with a sensitivity and specificity of 80% and 90%, respectively. We also demonstrate for the first time the use of this system in a swine brain biopsy model. These studies set the stage for the clinical translation of this optical molecular imaging method for high yield and safe targeted biopsy.

Graphene plasmonics for surface enhancement near-infrared absorptivity.

Monolayer graphene has poor absorption in the near-infrared region. Its layer is only as thick as a single atom so it cannot have a high absorptivity. In this paper, in order to form a hybrid system, the absorption characteristics of monolayer graphene covering a metal/dielectric/metal substrate has been theoretically analyzed. The magnetic polaritons in the metal/dielectric couple with the plasmonic resonance in the graphene to dramatically enhance the graphene absorptivity. This study analyzes the factors that enhance the absorptivity, including the geometric parameters and the relative positions of the graphene. The local electromagnetic field and the power dissipation density are illustrated to explain the underlying mechanisms further. These numerical results can provide potential application in the field of optical detection and optoelectronic devices.

Low cost optical device for detection of fluorescence from Ochratoxin A using a CMOS sensor

This manuscript describes a portable and low cost fluorescence set-up to quantify the concentrations of Ochratoxin A (OTA) in real samples using a developed system. The detection through the set up consist of an ultraviolet light at 365nm and a CMOS sensor controlled by an executable interface designed in MATLAB, with a time consumed from acquisition to processing to image display of 20seconds. It is reported that OTA is naturally fluorescent, so it allows the user to get a photograph of the OTA under excitation conditions and process the image in order to predict the concentrations of the sample. To capture and process the image, in an automatically manner, the system was completely based on the Red, Green and Blue (RGB) components. For each concentration of the OTA, the R, G, B coordinates were obtained and plotted to quantify the mycotoxin presented in the sample. The linearity for OTA was obtained in the concentrations range of 5–40μg/L. Immunoaffinity columns (IAC) and molecular imprinted polymer columns (MIP) were compared. The maximum recovery of 107.76% was recorded for 2μg/L of OTA using IAC in beer samples. The obtained results were cross validated using chromatographic method HPLC. The developed setup is easy to use, economical and portable.

Shack-Hartmann optimum threshold estimation for the point source

The Shack-Hartmann wavefront sensor (SHWFS) is an optical detection device based on the measurements of wavefront slopes. It is widely used in an adaptive optics system due to its simple structure and strong environment adaptability. The measuring accuracy of the SHWFS depends mainly on the accuracy of the spot image centroid in each sub-aperture. There are many centroid algorithms including the center of gravity algorithm, Gauss fitting algorithm, and correlation algorithm. As to the simplicity, robustness, high accuracy and stability, the center of gravity algorithm is more widely used. However, the accuracy of gravity algorithm is sensitive to the noise including discretization, aliasing, photon noise, readout noise, stray light, and direct current bias. To improve the accuracy of centroid, the output signals of SHWFS must be pre-processed to suppress the noise effect by using the method of thresholding in general. Many threshold methods have been presented to reduce the error of centroid and there theoretically exists an optimum threshold which causes the minimum error of centroid based on the characteristics of SHWFS and noise. However, it is difficult to separate the signals from the noises, and the optimum threshold cannot be estimated accurately in real time in the SHWFS systems. In this paper aiming at noises in SHWFS, which vary with time and space rapidly, a method based on the noise weighted function of the mean value of pixels and the local gradient direction of image signals in the moving windows is presented according to the characteristics of the Gaussian spot and noise distributions. Moreover, the theory and parameters determination of the method are analyzed. The method utilizes the probability that the pixels in the moving windows belong to the noise, and the probability is inversely proportional to the mean value of pixels and the local gradient direction of image signals, and so the monotonically reducing probability function of pixels is constructed. Finally, the standard deviation and mean value of noise can be obtained, and the estimation value of optimum threshold is equal to the mean value of noise plus three times the standard deviation of noise. To investigate the effects of the optimum threshold estimation with the different spot sizes, spot strengths and noise levels, the proposed algorithm is compared with traditional methods. The simulation and experimental results show that the proposed method could achieve higher accuracy, and the error between the threshold obtained by the method presented in this paper and theoretical optimum threshold is less than 10%, which is less than those from the traditional methods.

Polarimetric Multilongitudinal Mode Fiber Laser for Simultaneous Measurement of Strain and Temperature

A sensing system for simultaneously measuring strain and temperature is proposed by employing a polarimetric multilongitudinal mode fiber laser sensor and beat frequency demodulation device. The proposed fiber laser is built with two fiber Bragg gratings and a piece of Erbium-doped-fiber, which act as cavity reflector and gain medium, respectively. Owing to the intrinsic birefringence of fiber, two orthogonal polarization modes experience slight splitting, thus many longitudinal mode beat signals and polarization mode beat signals are generated in the laser cavity. Strain and temperature can be measured simultaneously by monitoring the frequency shift of longitudinal mode beat signal and polarization mode beat signal due to their different responses to strain and temperature. The selection of beat frequency signal pair for improving the laser sensitivity has also been analyzed and investigated experimentally. In addition, the repeatability and stability performances of the proposed laser were also investigated. The proposed sensing system just uses one polarimetric fiber laser sensor and one beat frequency demodulation equipment, and it shows distinctive advantages of simple structure, portability, high sensitivity, and low cost due to the avoidance of expensive optical detection device for wavelength monitoring.