Dual-wavelength System Research Articles

Dual-wavelength transmission based on liquid crystal tunable filter with high signal-to-noise ratio

Aiming at the problem of limited transmission energy of liquid crystal tunable filter (LCTF), a dual-wavelength transmission system with high signal-to-noise ratio (SNR) is proposed in this paper. The proposed transmission factor Qp is the main influence on the number and location of transmission wavelengths as well as the bandwidth of each transmission wavelength for dual-wavelength systems. Dual-wavelength LCTF can improve the effective transmission energy of the system by increasing the number of filtering channels, and the transmission energy can be increased by about 1.8 times and 70% at short and long wavelengths, respectively, which improves the signal-to-noise ratio (SNR) of the system. Moreover, the dual-wavelength LCTF system is even possible to increase the transmission energy by about 7% at a 33% increase in spectral resolution. Therefore, the dual-wavelength LCTF transmission method not only can improve the SNR of target detection with dual-wavelength response features, but also can effectively solve the problem of contradiction between spectral resolution and spectral transmission energy.

Towards non-invasive tissue hydration measurements with optical coherence tomography.

The attenuation coefficient ( ) measured by optical coherence tomography (OCT) has been used to determine tissue hydration. Previous dual-wavelength OCT systems could not attain the needed precision, which we attribute to the absence of wavelength-dependent scattering of tissue in the underlying model. Assuming that scattering can be described using two parameters, we propose a triple/quadrupole-OCT system to achieve clinically relevant precision in water volume fraction. In this study, we conduct a quantitative analysis to determine the necessary precision of measurements and compare it with numerical simulation. Our findings emphasize that achieving a clinically relevant assessment of a 2% water fraction requires determining the attenuation coefficient with a remarkable precision of 0.01 . This precision threshold is influenced by the chosen wavelength for attenuation measurement and can be enhanced through the inclusion of a fourth wavelength range.

High efficiency independent modulation at dual-wavelength based on Pancharatnam–Berry and propagation phases

Metasurfaces capable of controlling multiple wavelengths independently have attracted broad interests these years due to their significance in multi-channel information processing applications. Previous solving strategies include spatial multiplexing or extensive searching for appropriate structures, both of which have their own disadvantageous, such as low efficiency, large computer resource requirement, or time consumption. In this paper, by combining the Pancharatnam–Berry (PB) phase and propagation phase, we propose a strategy to simplify the design complexity in a dual-wavelength metasurface system, in which two simple rectangular-shaped dielectric pillars (T1 and T2) with different aspect ratios are chosen as basic structures and crossed at the geometric center to achieve manipulation. The larger pillar T2 controls the longer wavelength through the PB phase while the smaller T1 acts as a perturbation to T2. The crossed T1&T2 is studied as a whole to tune the short wavelength. The investigations by the multipole expansion method reveal that the polarization conversion ratio of the meta-atoms is dependent on the interference of the formed multipoles. To validate the proposed strategy, a dual-wavelength achromatic metalens and a wavelength-multiplexed holographic metasurface operating at the infrared thermal imaging band are designed. Our design strategy can find widespread applications in metasurfaces where multiple objectives are required to be realized.

Vein visualization enhancement by dual-wavelength phase-locked denoising technology

Visual near-infrared imaging equipment has broad applications in various fields such as venipuncture, facial injections, and safety verification due to its noncontact, compact, and portable design. Currently, most studies utilize near-infrared single-wavelength for image acquisition of veins. However, many substances in the skin, including water, protein, and melanin can create significant background noise, which hinders accurate detection. In this paper, we developed a dual-wavelength imaging system with phase-locked denoising technology to acquire vein image. The signals in the effective region are compared by using the absorption valley and peak of hemoglobin at 700[Formula: see text]nm and 940[Formula: see text]nm, respectively. The phase-locked denoising algorithm is applied to decrease the noise and interference of complex surroundings from the images. The imaging results of the vein are successfully extracted in complex noise environment. It is demonstrated that the denoising effect on hand veins imaging can be improved with 57.3% by using our dual-wavelength phase-locked denoising technology. Consequently, this work proposes a novel approach for venous imaging with dual-wavelengths and phase-locked denoising algorithm to extract venous imaging results in complex noisy environment better.

Indocyanine Green-Loaded Liposomes-Assisted Photoacoustic Computed Tomography for Evaluating In Vivo Tumor Penetration of Liposomal Nanocarriers.

Liposomes possess the potential to enhance drug solubility, prolong the duration of circulation, and augment drug accumulation at the tumor site through passive and active targeting strategies. However, there is a lack of studies examining the in vivo tumor penetration capabilities of liposomes of varying sizes, which hampers the development of drug delivery systems utilizing liposomal nanocarriers. Here, we present an indocyanine green (ICG)-loaded liposomes-assisted photoacoustic computed tomography (PACT) for directly evaluating the tumor penetration ability of liposomal nanocarriers in vivo. Through the utilization of microfluidic mixing combined with extrusion techniques, we successfully prepare liposomes encapsulating ICG in both large (192.6 ± 8.0 nm) and small (61.9 ± 0.6 nm) sizes. Subsequently, we designed a dual-wavelength PACT system to directly monitor the in vivo tumor penetration of large- and small-size ICG-encapsulated liposomes. In vivo PACT experiments indicate that ICG-loaded liposomes of smaller size exhibit enhanced penetration capability within tumor tissues. Our work presents a valuable approach to directly assess the penetration ability of liposomal nanocarriers in vivo, thereby facilitating the advancement of drug delivery systems with enhanced tumor penetration and therapeutic efficacy.

Q-switched erbium-doped fiber lasers with ITO thin film saturable absorbers: A comprehensive cavity configuration study

This study presents the utilization of an indium tin oxide (ITO) thin film as a saturable absorber (SA) in various cavity configurations to illustrate a Q-switched erbium-doped fiber laser (EDFL). The system is designed in three distinct configurations, including linear, single-ring, and Figure-8 cavities, by integrating ITO in the setup, which has a modulation depth of 48.04 %. The research findings highlight that the single-ring cavity design has better performance over linear and Figure-8 designs in terms of Q-switched EDFL performance. The advantage of the single-ring cavity design is demonstrated by the higher values of the repetition rate and signal-to-noise ratio, which are 37.60 kHz and 57.45 dB, respectively. Subsequently, this single-ring cavity can be employed in applications of tunable, switchable dual-wavelength systems and optical fiber sensing.

An Innovative Dual-Wavelength Laser Technique for Atrophic Acne Scar Management: A Pilot Study.

Background and Objectives: Acne scars are one of the most disturbing and long-term symptoms of acne vulgaris, having a negative impact on a person's physical, emotional, and social well-being. Aim: the purpose of the study was to evaluate the efficacy and post-treatment outcomes of a dual-wavelength system combining the irradiation of two wavelengths at 10,600 nm and 1540 nm in the management of facial atrophic acne scars. Materials and Methods: Four healthy adult volunteers aged 24-53 years were enrolled. The areas treated were the full face (two patients), cheeks (one patient), and forehead (one patient). A dual-wavelength system (1540 nm and 10,600 nm) was used for this study. Patients underwent 2-4 treatment sessions, and the treatments were performed once every 45-90 days. All possible side effects such as burning sensation, dyschromia, mild to moderate post-treatment erythema, bleeding, itching, edema, and crusting were checked. The index to assess edema and erythema was based on a four-point scale (none, mild, moderate, and severe) and was applied before and at 3-month follow-up (3 MFU) after the last treatment session. In addition, a patient assessment was conducted before treatment and at 3 MFU after the last treatment session. Results: For all patients examined, the edema index was mild, while for the erythema index, 3/4 patients experienced moderate and 1/4 patients experienced mild symptoms. The mean patient downtime was 5.8 ± 0.5 days. Concerning the patient assessment, 2/4 subjects showed excellent improvement, 1/4 patients showed good improvement, and 1/4 patients showed slight improvement. As shown by the photographic assessment, a noticeable improvement in skin texture and a substantial reduction in acne scars were observed at the end of treatment. Conclusions: This dual-wavelength laser technology has the potential to be an interesting and safe approach for acne scar treatment, with a low risk of scarring/hypopigmentation and a shorter healing time.

An Airborne Visible Light Lidar’s Methodology for Clear Air Turbulence Detection Based on Weak Optical Signal

A clear air turbulence (CAT) detection method using a 532 nm visible light airborne laser radar (LiDAR) system is proposed to address the urgent challenge in the aviation safety field. This method is based on the indirect detection technique of atmospheric molecular density for CAT and utilizes the strong aerosol scattering absorption characteristics of the iodine molecular 1109 absorption line to eliminate the interference of aerosol scattering and extinction on the weak molecular backscattering signal caused by CAT. This enables CAT detection under conditions where traditional ultraviolet LiDAR systems fail to function properly due to aerosol presence. The influence of axial wind speed and atmospheric temperature variations on the molecular backscattering spectrum in the aircraft flight path is studied, and a formula for vertical wind speed inversion in the CAT field is derived. The 532 nm airborne LiDAR CAT detection theoretical model and system architecture are presented. Through simulation analysis, the CAT detection range of the visible light LiDAR system is evaluated under different aircraft cruising altitudes and turbulence intensities. The results indicate that, with the proposed LiDAR system, the aerosol scattering influence can be effectively suppressed, and CAT can be detected up to 7 km for light-to-moderate turbulence and 10 km for moderate turbulence ahead of the aircraft when traditional ultraviolet LiDAR systems fail as the backscattering coefficient ratio between aerosol and molecule reaches the 10−1 condition. Based on this finding, a suggestion is made to construct a dual-wavelength (ultraviolet-visible) LiDAR system for CAT detection, aiming to solve the full coverage problem of CAT detection under various aerosol conditions. This study has a reference value for promoting the early resolution of CAT detection in the aviation field.

Multispectral LiDAR-based underwater ore classification using a tunable laser source

Light Detection and Ranging (LiDAR) technology has been extensively used to collect precise geometric information. However, conventional LiDAR sensors are restricted to single-wavelength operation, limiting their ability to capture valuable spectral information. Multispectral LiDAR (MSL) systems, on the other hand, have emerged as a promising solution by facilitating the active acquisition of spatial and spectral data. These advanced systems exhibit tremendous potential in facilitating advanced analysis and classification of seafloor sediments. In this study, the first demonstration of an MSL system optimized for investigating the feasibility of underwater ore classification using a tunable laser source is described. The MSL prototype features a spectral resolution of 10 nm, and 11 spectral channels, covering the range from 460 to 560 nm. Laboratory-based experiments were conducted to evaluate the accuracy of range measurements and the classification performance of the system. The spectral profiles of eight distinct ore samples acquired by the MSL were utilized for classification using four classification methods: naive Bayes (NB), k Nearest Neighbor (KNN), support vector machine (SVM), and random forest (RF). Furthermore, comparative analyses were conducted to investigate the classification enhancements realized by leveraging the MSL system with multiple spectral channels as opposed to single-wavelength and dual-wavelength systems.

Improved topography measurement with a high dynamic range using phase difference sensing technology.

Phase difference sensing technology (PDST) is employed for topography measurement, and two interference structures are proposed to achieve upper-limit adjustment and high resolution in the measurement range: a dual-wavelength system with a single Fabry-Perot (FP) cavity and a single-wavelength system with dual FP cavities. The phase difference between the two interference signals is determined by an elliptic fitting algorithm (EFA), and this change in phase difference is utilized to characterize the step height. Experimental results indicate that the measurement upper-limit can be adjusted to either 410 µm, 187 µm, or 108 µm by varying the wavelength difference in the dual-wavelength system, which gives a measurement error of 2.96%. In contrast, while offering a measurement resolution of 3.47 nm, the single-wavelength system exhibits a measurement error of 5.38%. The proposed method is capable of satisfying the measurement requirements during micro-electromechanical system (MEMS) processing with proficiency.

Phase compensation algorithm based on image segmentation in dual-wavelength holographic microscopy.

In order to solve the problem of phase compensation errors in the traditional 2π phase compensation method caused by a rough surface and complex structure of objects in dual-wavelength digital holographic microscopy, a phase compensation algorithm based on image segmentation was proposed. First, the phase less than zero in the phase obtained by an equivalent wavelength is compensated for by adding 2π initially. Then the phase after the initial compensation is binarized, and the small connected areas in the binarized graph are removed, so as to obtain a new binarized graph. Finally, according to the two binarized graphs, the phase of the object after the initial 2π phase compensation is recompensated for in different regions, so as to obtain the continuous phase distribution of the object. Based on the dual-wavelength digital holographic microscopy experimental system with an adjustable equivalent wavelength, the proposed algorithm is used to perform three-dimensional imaging of the channel of the microfluidic chip. The experimental results show that the proposed method can effectively obtain the continuous real phase of the object when the structure of the object is known, so as to obtain a more accurate and reliable three-dimensional topography of the object. The above results provide a new idea for the high-quality three-dimensional imaging of the microfluidic system.

Removal of diclofenac by UV-B and UV-C light-emitting diodes (LEDs) driven advanced oxidation processes (AOPs): Wavelength dependence, kinetic modelling and energy consumption

In this study, the degradation of diclofenac (DCF), a frequently detected non-steroidal pharmaceutical, was evaluated by using UV-B and UV-C (265, 285, and 310 nm) light-emitting diodes (LEDs) alone and in combination with hydrogen peroxide (UV/H2O2) and free chlorine (UV/FC). The degradation of DCF followed a pseudo first-order kinetic, and their trend reflected the pattern of the molar absorption coefficients of the DCF and the oxidants. A positive synergistic factor was found for the UV-LED driven advanced oxidation processes in almost all cases, but despite the higher degradation rates, the overall electricity demand is similar to UV alone due to the oxidants’ energy cost. The rigorous kinetic degradation mechanisms at different wavelengths were proposed for the two processes, UV/H2O2 and UV/FC, where the predicted values were respectively kHO = 9.12 · 109 M−1 s−1 and kCl = 1.30 · 1010 M−1 s−1. No significant synergy (p > 0.05) was found for the dual-wavelength system (265 + 285 nm), and the time-based constants in all cases changed linearly with lamp intensity. Finally, dissolved organic carbon and phytotoxicity analysis revealed low mineralisation (around 20–30%) associated with the formation of stable dimers and a decrease in toxicity towards tomato and radish seeds. In the main, this work shows the great potential of implementing wavelength-specific LEDs in water treatments and effectively designing the reactor playing with adjustable intensities and kinetic degradation rates.

The Vertical Distributions of Aerosol Optical Characteristics Based on Lidar in Nanyang City from 2021 to 2022

To investigate the vertical distribution of aerosol optical characteristics in Nanyang City, a ground-based dual-wavelength (532 nm and 355 nm) lidar system was developed for aerosol observation at the Nanyang Normal University Station (NYNU) from November 2021 to December 2022. Spatio-temporal dynamics information on vertical distributions of aerosol optical properties during polluted and non-polluted days was obtained. Aerosols were characterized by low altitudes (up to 2 km), thinner layers, and high-altitude (up to 4 km) thick layers during non-polluted and polluted days, with extinction coefficient values of ~0.03 km−1 and ~0.2 km−1, respectively. The mean values of the extinction coefficient at different altitudes (0~5 km) were all about ten-times higher on polluted days (0.04~0.19 km−1) than on non-polluted days (0.004~0.02 km−1). These results indicate that aerosol loadings and variations at different altitudes (0~5 km) were much higher and more prominent on polluted days than non-polluted days. The results show ten-times larger aerosol optical depth (AOD) values (0.4~0.6) on polluted days than on non-polluted days (0.05~0.08). At the same time, AOD values on both polluted and non-polluted days slightly decreased from 19:00 to 05:00, possibly due to dry depositions at nighttime. For the first time, this study established a ground-based lidar remote sensing system to investigate the vertical distribution of atmospheric aerosol optical characteristics in Henan Province. The experimental results can provide scientific dataset support for the local government to prevent and control air pollution.

Non-contact oxygen saturation monitoring for wound healing process using dual-wavelength simultaneous acquisition imaging system.

Here we report the fabrication of a noncontact pulse oximeter system based on a dual-wavelength imaging system and its oxygen saturation monitoring performance during wound healing. The dual-wavelength imaging system consists of 660nm and 940nm light-emitting diodes and a multi-spectral camera that simultaneously accepts visible and near-infrared images. Using the proposed system, images were acquired at 30 fps at both wavelengths, and photoplethysmography signals were extracted by specifying a specific region in the images. We removed the signals caused by small movements and smoothed them using the discrete wavelet transform and moving average filter. To confirm the feasibility of the proposed noncontact oxygen saturation system, a wound model was created using a hairless mouse and oxygen saturation was measured during wound healing. The measured values were compared and analyzed using a reflective animal pulse oximeter. Through a comparative analysis of these two devices, the error of the proposed system was evaluated and the possibility of its clinical application and wound healing monitoring through oxygen saturation measurement confirmed.

Polarization phase unwrapping by a dual-wavelength Mueller matrix imaging system.

In this Letter, we report a dual-wavelength Mueller matrix imaging system for polarization phase unwrapping, allowing simultaneous acquisition of the polarization images at 633 nm and 870 nm. After phase unwrapping, the relative error of linear retardance is controlled to be 3% and the absolute error of birefringence orientation is about 6°. We first show that polarization phase wrapping occurs when the samples are thick or present obvious birefringence effects, and further analyze the effect of phase wrapping on anisotropy parameters via Monte Carlo simulations. Then, experiments on porous alumina with different thicknesses and multilayer tapes are performed to verify the feasibility of phase unwrapping by a dual-wavelength Mueller matrix system. Finally, by comparing the temporal characteristics of linear retardance during tissue dehydration before and after phase unwrapping, we emphasize the significance of the dual-wavelength Mueller matrix imaging system not only for anisotropy analysis in static samples, but also for determining the trend in polarization properties of dynamic samples.

Measurement of liquid refractive index by quantitative phase reconstruction of single frame dual-wavelength digital hologram

A measurement method of liquid’s refractive index by means of single-shot dual-wavelength off-axis digital holographic microscopy system and a microfluidic chip is presented. The refractive index of liquid filled in the microchannel of a microfluidic chip can be calculated directly with the unwrapped phase map obtained at the synthetized wavelength, without requirement of knowing another liquid’s refractive index as a measurement reference. Moreover, it also avoids the influence of the accuracy of the known refractive index on the refractive index to be measured. The refractive indices of salt solutions and sucrose solutions in the several concentrations are achieved in the experiments, which verifies that the measurement of liquid’s refractive index is accurate and reliable. With the merit of accurate measurement of liquid’s refractive index based on the one-frame dual-wavelength hologram, it is expected that this approach will be employed to detect in real-time the fluid’s parameters related to its refractive index.

Evaluation of a New Lightweight UAV-Borne Topo-Bathymetric LiDAR for Shallow Water Bathymetry and Object Detection.

Airborne LiDAR bathymetry (ALB) has proven to be an effective technology for shallow water mapping. To collect data with a high point density, a lightweight dual-wavelength LiDAR system mounted on unmanned aerial vehicles (UAVs) was developed. This study presents and evaluates the system using the field data acquired from a flight test in Dazhou Island, China. In the precision and accuracy assessment, the local fitted planes extracted from the water surface points and the multibeam echosounder data are used as a reference for water surface and bottom measurements, respectively. For the bathymetric performance comparison, the study area is also measured with an ALB system installed on the manned aerial platform. The object detection capability of the system is examined with placed small cubes. Results show that the fitting precision of the water surface is 0.1227 m, and the absolute accuracy of the water bottom is 0.1268 m, both of which reach a decimeter level. Compared to the manned ALB system, the UAV-borne system provides higher resolution data with an average point density of 42 points/m2 and maximum detectable depth of 1.7–1.9 Secchi depths. In the point cloud of the water bottom, the existence of a 1-m target cube and the rough shape of a 2-m target cube are clearly observed at a depth of 12 m. The system shows great potential for flexible shallow water mapping and underwater object detection with promising results.

Dual-wavelength multilevel diffractive lenses for near-infrared imaging

Optical imaging systems play an extremely important role for humans in exploring the world, but the existence of chromatic aberration greatly reduces the imaging ability. Conventional optical systems require the combination of multiple lenses to reduce chromatic aberration, but such a solution is not conducive to the miniaturization and weight reduction of the optical system. In this paper, we design dual-wavelength multilevel diffractive lenses that focus pairs of wavelengths on the same focal plane, using a modified direct-binary-search algorithm to maximize the focusing efficiency. The simulated focusing efficiencies are 72% (92%) and 79% (92%) at the wavelength of 1.064 μm and 1.55 μm, respectively, for the two-dimensional (one-dimensional) ones. Through this approach, the results presented here suggest good focusing performance at two wavelengths, providing a new opportunity for various applications in dual-wavelength imaging systems and lightweight collimators.

Numerical Analysis of 3.92 μm Dual-Wavelength Pumped Heavily-Holmium-Doped Fluoroindate Fiber Lasers

The 3.92 μm laser pumped by 888 and 962 nm sources in a high concentration holmium-doped InF3 fiber is predicted and verified by simulation for the first time. Most parameters involved in the numerical model are taken from published results about the fundamental properties of holmium in fluoroindate glasses. The remaining unknown parameters are estimated from published 888 nm single-wavelength pumping experimental data. Simulated results indicate that the dual-wavelength pumping system can give a more powerful output than the single-wavelength pumping system when the total launched power is at the same level. The laser output as a function of the power of each source, as well as several macro factors such as fiber length and output coupler reflectivity, are investigated to find the best condition for higher output. To evaluate the importance and influence of the known interionic energy transfer processes, we analyze the corresponding laser output and changes of population densities of laser upper and lower levels by isolating each process. This investigation gives a preliminary insight into the 3.92 μm laser performance and interionic dynamics of the dual-wavelength pumping system in holmium-doped InF3 fibers.

Flywheel-like diaphragm-based fiber-optic Fabry–Perot frequency tailored acoustic sensor

A novel design method for a fiber-optic Fabry–Perot (FP) acoustic sensor based on a flywheel-like diaphragm has been proposed and experimentally demonstrated. Through theory analysis and simulation, we have established a sensing model based on the flywheel-like diaphragm and illustrated the acoustic sensor’s resonant frequency regulation method. A flywheel-like diaphragm-based acoustic sensor has been fabricated and a dual-wavelength system is used to demodulate the phase fluctuation caused by the acoustic wave. Experimental results show that the proposed acoustic sensor has an acoustic pressure sensitivity of 1.3967 rad Pa−1 and noise-limited minimum detectable pressure of . The signal to noise ratio (SNR) of 1 kHz, 9 kHz, and 20 kHz are achieved to be 10.39 dB, 60.51 dB, and 37.14 dB, respectively. Over a fairly broad response range (1 kHz to 20 kHz), the average SNR is up to 45.57 dB. Moreover, our acoustic sensor’s directivity map approximates to a heart shape. Its excellent frequency response characteristics, sensitivity, and directivity pattern are believed to have bright application prospects.