Precise Wavelength Research Articles

Design and Analysis of Ridge and Sub-Wavelength Grating Waveguide Based Micro Ring-Resonator Sensor

The subwavelength grating microring resonator based filter shows great promise in optical sensing and communication. However, it spectrum nature makes it unsuitable for tracking or extracting a single wavelength from a broadband light source. In this paper, we used side-mode suppression, based on an angular grating- subwavelength microring resonator which offer high flexibility in wavelength design within the silicon-on-insulator (SOI) waveguide. By periodically arranging silicon waveguide pieces in three different widths, we can set the effective index along the inner sidewall of subwavelength microring resonator. thereby can achieve the precise wavelength selection. We examine the effects of various key parameters on the center wavelength, side-mode suppressed ratio, and quality factor of this filter.The proposed structure's isalso analysed for coupling strength between the bus and subwavelength grating ring resonator. The wavelength selection, compact size, compatibility with other similar nature waveguide-based devices and design flexibility highlight its significant potential in compact optical sensing and optical communication

GaSb-Si3N4 hybrid lasers with precise wavelength control and narrow spectral linewidth based on low-kappa Bragg gratings

GaSb-Si3N4 hybrid lasers with precise wavelength control and narrow spectral linewidth based on low-kappa Bragg gratings

Encapsulating Rhodamine 6G in Oxidized Sodium Alginate Polymeric Hydrogel for Photodynamically Inactivating Cancer Cells.

As cancer therapy progresses, challenges remain due to the inherent drawbacks of conventional treatments such as chemotherapy, gene therapy, radiation therapy, and surgical removal. Moreover, due to their associated side effects, conventional treatments affect both cancerous and normal cells, making photodynamic therapy (PDT) an attractive alternative. As a result of its minimal toxicity, exceptional specificity, and non-invasive characteristics, PDT represents an innovative and highly promising cancer treatment strategy using photosensitizers (PSs) and precise wavelength excitation light to introduce reactive oxygen species (ROS) in the vicinity of cancer cells. Poor aqueous solubility and decreased sensitivity of Rhodamine 6G (R6G) prevent its use as a photosensitizer in PDT, necessitating the development of oxidized sodium alginate (OSA) hydrogelated nanocarriers to enhance its bioavailability, targeted distribution, and ROS-quantum yield. The ROS quantum yield increased from 0.30 in an aqueous environment to 0.51 when using alginate-based formulations, and it was further enhanced to 0.81 in the case of OSA. Furthermore, the nanoformulations produced fluorescent signals suitable for use as cellular imaging agents, demonstrating contrast-enhancing capabilities in medical imaging and showing minimal toxicity.

Comparative Analysis of Two Different MIM Configurations of a Plasmonic Nanoantenna

AbstractTwo plasmonic nanoantenna configurations—nanodisk and nanostrip arrays—in a metal–insulator-metal (MIM) setup were proposed, optimized, and compared by simulating their optical properties in three-dimensional models using COMSOL Multiphysics software. The optical responses, including electric field enhancement, absorption, reflection, and transmission spectra, were systematically investigated. Optimized geometrical parameters led to a significant enhancement of the electric field within the gap layers and almost perfect light absorptance for both structures. The results showed that the enhancement of the electric field depends on the polarization of the incident light. For both polarizations, the periodic circular nanodisk array showed a stronger field enhancement with an electric field enhancement factor of 6.6 × 106 and TE polarization, and a larger absorptance of 98% at its dipole resonance wavelength, indicating the fundamental plasmonic mode. In addition, weaker resonant modes were observed in the absorptance and reflectance spectra of both nanostructures, with the nanostrips exhibiting sharper and stronger higher-order modes, making them suitable for applications requiring precise wavelength selectivity and narrow-band responses. Despite their different geometric shapes, both structures exhibited similar optimized metal film thickness and nanoparticle height, comparable modes in number and position, and identical optimized light incidence angles. Furthermore, increasing the dielectric gap layer thickness and optimizing it to a specific value revealed its ability to measure the refractive index, making it a promising candidate for sensing applications.

Wavelength tuning of VCSELs via controlled strain.

Besides major advantages for telecommunication applications, vertical-cavity surface-emitting lasers (VCSELs) have attracted interest for their potential for neuro-inspired computing, frequency comb generation, or high-frequency spin oscillations. In the meantime, strain applied to the laser structure has been shown to have a significant impact on the laser emission properties such as the polarization dynamics or birefringence. In this work, we further explore the influence of strain on VCSELs and how this effect could be used to fine-tune the laser wavelength. Through a comprehensive investigation, we demonstrate a consistent wavelength shift up to 1 nm and report a sensitivity between 0.12 and 0.18 nm/millistrain. We also record birefringence values up to 292 GHz. Our results show that a controlled strain level could be considered for fine wavelength tuning and possibly alleviate the selection of VCSEL for precise wavelength requirements.

Comment on Yu et al. Land Surface Temperature Retrieval from Landsat 8 TIRS—Comparison between Radiative Transfer Equation-Based Method, Split Window Algorithm and Single Channel Method. Remote Sens. 2014, 6, 9829–9852

Accurate land surface temperature (LST) retrieval from satellite data is pivotal in environmental monitoring and scientific research. This study addresses the impact of variability in the effective wavelengths used for LST retrieval from the Thermal Infrared Sensor (TIRS) data of Landsat 8. We conduct a detailed analysis comparing the effective wavelengths reported by Yu et al. (2014) and those derived from data provided by the USGS. Our analysis reveals significant variability in the effective wavelengths for bands 10 and 11 of Landsat 8. By applying Planck’s Law and utilizing the K1 and K2 coefficients available in the metadata of Landsat 8 products, we derive the effective wavelengths for bands 10 and 11. We also rederive the effective wavelength by integrating the spectral response function of the TIRS1 sensor. Our findings indicate that the effective wavelength for band 10 is 10.814 μm, aligning with the USGS data, while the effective wavelength for band 11 is 12.013 μm. We discuss the implications of these corrected effective wavelengths on the accuracy of LST retrieval algorithms, particularly the single channel algorithm (SC) and the radiative transfer equation (RT) employed by Yu et al. The importance of using precise effective wavelengths in satellite-based temperature retrieval is emphasized, to ensure the reliability and consistency of results. This analysis underscores the critical role of accurate spectral calibration parameters in remote sensing studies and provides valuable insights in the field of land surface temperature retrieval from Landsat 8 TIRS data.

Hydrogen sulfide and metal-enriched atmosphere for a Jupiter-mass exoplanet.

As the closest transiting hot Jupiter to Earth, HD 189733b has been the benchmark planet for atmospheric characterization1-3. It has also been the anchor point for much of our theoretical understanding of exoplanet atmospheres from composition4, chemistry5,6, aerosols7 to atmospheric dynamics8, escape9 and modelling techniques10,11. Previous studies of HD 189733b have detected carbon and oxygen-bearing molecules H2O and CO (refs. 12,13) in the atmosphere. The presence of CO2 and CH4 has been claimed14,15 but later disputed12,16,17. The inferred metallicity based on these measurements, a key parameter in tracing planet formation locations18, varies from depletion19,20 to enhancement21,22, hindered by limited wavelength coverage and precision of the observations. Here we report detections of H2O (13.4σ), CO2 (11.2σ), CO (5σ) and H2S (4.5σ) in the transmission spectrum (2.4-5.0 μm) of HD 189733b. With an equilibrium temperature of about 1,200 K, H2O, CO and H2S are the main reservoirs for oxygen, carbon and sulfur. Based on the measured abundances of these three main volatile elements, we infer an atmospheric metallicity of three to five times stellar. The upper limit on the methane abundance at 5σ is 0.1 ppm, which indicates a low carbon-to-oxygen ratio (<0.2), suggesting formation through the accretion of water-rich icy planetesimals. The low oxygen-to-sulfur and carbon-to-sulfur ratios also support the planetesimal accretion formation pathway23.

Switchable emissions of an Erbium-doped fiber laser using cascaded MZIs based on CHCF

In this work, a single and dual-wavelength erbium-doped fiber laser (EDFL) based on two Mach-Zehnder interferometers (MZIs) in cascade structure was experimentally validated. MZIs were assembled by joining a capillary hollow-core fiber (CHCF) piece between two multimode fibers (MMFs) sections. The switchable operation is reached by moving the spectrum of one MZI when the temperature is increased. The maximum measured signal noise to ratio (SNR) was more than 50 dB for the single and dual-wavelength laser lines. Besides, stable output is shown since no power and wavelength variations were noticed. It is important to mention that emissions are obtained at precise wavelength positions and not arbitrarily as described by other investigations. This EDFL can be used in applications of optical fiber communications systems and fiber sensing.

Innovative Stacked Yellow and Blue Mini-LED Chip for White Lamp Applications.

This study introduces a novel approach for fabricating vertically stacked mini-LED arrays, integrating InGaN yellow and blue epitaxial layers with a stress buffer layer to enhance optoelectronic characteristics and structural stability. This method significantly simplifies the LED design by reducing the need for RGB configurations, thus lowering costs and system complexity. Employing vertical stacking integration technology, the design achieves high-density, efficient white light production suitable for multifunctional applications, including automotive lighting and outdoor signage. Experimental results demonstrate the exceptional performance of the stacked yellow and blue mini-LEDs in terms of luminous efficiency, wavelength precision, and thermal stability. The study also explores the performance of these LEDs under varying temperature conditions and their long-term reliability, indicating that InGaN-based yellow LEDs offer superior performance over traditional AlGaInP yellow LEDs, particularly in high-temperature environments. This technology promises significant advancements in the design and application of lighting systems, with potential implications for both automotive and general illumination markets.

Research on Automatic Wavelength Calibration of Passive DOAS Observations Based on Sequence Matching Method

Passive differential optical absorption spectroscopy (DOAS) is widely used to monitor the three-dimensional distribution of atmospheric pollutants. However, the observational and retrieval accuracy of this technique is significantly influenced by the precise wavelength calibration of solar spectra. Current calibration methods face challenges in automation when dealing with complex remote-sensing conditions. We introduce a novel automatic wavelength calibration algorithm for passive DOAS based on sequence-matching technology to estimate the spectral parameters of the spectrometer channels, integrating advanced processing measures such as feature structure enhancement and sub-pixel interpolation. These measures significantly reduce the dependency on reference spectrum resolution and accurately correct even minor spectral shifts. We perform sensitivity experiments using synthetic spectra to determine optimal retrieval configurations, followed by field tests at four cities on the Yangtze River Delta, China, to calibrate and compare passive DOAS instruments of various resolutions. Comparative verification in these field studies demonstrated that our algorithm was suitable for rapid spectral calibration within a wider resolution range of 0.03 nm to 0.1 nm with a wavelength inversion error &lt; 0.01 nm. This highlights the applicability and calibration precision of our algorithm.

Quickly tunable ultra-narrow filter via a metal film waveguide.

The development of fast, efficient, and cost-effective tunable optical filters is a tireless pursuit of the goal in the field of optical signal processing and communications. However, the traditional filters have been limited by their complex structures, slow tuning speed, and high cost. To address this challenge, we present a tunable ultra-narrow bandpass filter, which is fabricated by a metal layer cladded in a high-parallelism and high-precision piezoelectric ceramic for an interlayer. Experimental results show a remarkable full width at half maximum of 51 pm and a fast response time of 800 ns. In addition, by cascading double filters, the wavelength of the output light has been fine-tuned from a Vernier effect. Moreover, we realize a tunable filter to select and output several ultra-narrow single peaks with 56% efficiency in the 2 nm range. Furthermore, it offers a wide tunable range, exceptional narrowband filtering performance, and fast piezoelectric response times. Hence, it is particularly well suited to applications requiring precise wavelength selection and control, opening new possibilities in the field of tunable optical filters.

Spectral Analysis of Pink Mealy Bug Damaged Mulberry Plants Using Hyperspectral Radiometry

Mulberry (Morus spp.) foliage forms a sole food to silkworms, Bombyx mori L. Its quality plays a pivotal role in superior silk fiber production. Like any other plants, mulberry is susceptible to detrimental diseases and infested by insect pests. Many sucking pests cause damage to mulberry among which, pink mealybug causes severe damage leading to significant loss in mulberry leaf yield (12-25 %). Conventional approaches to assess and manage damage caused by pink mealybugs demand substantial manpower and expertise, resulting in time-consuming and inefficient processes. However, leveraging modern tools and technologies like remote sensing has emerged as a remarkably effective strategy for crop protection and management.Specifically, hyperspectral remote sensing proves invaluable by furnishing insights into the biophysical and biochemical traits of crops. This is achieved through the recording of narrow wave bands that reflect specific plant characteristics. The main objectives were to understand the spectral reflectance characteristics of healthy and pink mealy bug damaged mulberry crops, to identify the optimal spectral bands and vegetative indices for detecting pink mealy bug damage in mulberry and to explore the feasibility of estimating pest damage levels based on the spectral properties of mulberry crops. Top of FormAt the mulberry garden of the Department of Sericulture, Tamil Nadu Agricultural University (TNAU), Coimbatore, studies were conducted on spectral analysis of pink mealy bug damaged mulberry plants using hyperspectral radiometry during 2018. In this trial, at 15-day intervals during the active damage stage, the percentage damage was observed in plots infested with pink mealy bugs and those that were healthy. Measurements of spectral reflectance across various wavelengths and vegetation indices (VIs) were taken using a hyperspectral radiometer. The analysis included evaluating the sensitivity of different spectral bands and VIs to pink mealybug damage, along with employing correlation and regression analyses between the extent of pest damage and the VIs. The findings revealed distinct differences in the spectral reflectance profiles of mulberry plants compared to their healthy counterparts. Typically, affected plants exhibited increased reflectance in the red (620–680 nm) and green (520–590 nm) bands and reduced near-infrared (NIR) reflectance (770–860 nm). The average values of the Normalized Difference Vegetation Index (NDVI), Green Red Vegetation Index (GRVI), and Ratio Vegetation Index (RVI) were significantly lower in the pink mealybug-damaged plants across all measurements. Notably, red reflectance demonstrated the greatest sensitivity to pink mealybug-induced damage. The study highlighted the Simple Ratio (SR) index as particularly effective for identifying pest damage. Damage estimation by pink mealybugs was refined using linear regression models based on spectral indices, specifically NDVI, RVI, and GRVI. The correlation intensity analysis pinpointed the green region at 516.73 nm as showing the most significant negative correlation (r = -0.02), whereas the highest positive correlation with pink mealybug damage was observed in the NIR region (r = 0.77), underscoring the precise wavelengths and indices most indicative of pest impact. Thus, using hyperspectral radiometry identification of damage caused by pink mealy bug possible, through analysis of spectral bands and indices.

Highly precise FBG wavelength demodulation method with strong multiplexing ability and positioning function based on time-domain detection.

Based on the theory of the microwave photonic filter (MPF), to our knowledge, a novel fiber Bragg grating (FBG) wavelength demodulation method based on time-domain detection is proposed. The method uses VNA (vector network analyzer) to measure the S21 parameter of the sensor system, and converts them to the time-domain through inverse discrete Fourier transform (IDFT), The wavelength demodulation and positioning of FBG can be realized by measuring the amplitude and position of the time-domain peak. In order to improve the number of FBG multiplexes, a method is proposed to eliminate the effect of spectrum overlap by normalization in the case of two FBGs and three FBGs. The experimental results show that the temperature sensitivity is 0.00503 RAC/°C, the positioning resolution of the system is 1.25 cm, and the limit of the wavelength difference between two FBGs allowed by the system is 0.25 nm. This method has the advantages of high demodulation precision, strong multiplexing ability and high precision positioning, and has broad application prospects.

Improving thermal efficiency of solar stills: Bioactive nano-PCM and Cramer’s rule analysis

Green-sourced Petroselinum crispum leaf (P) was carefully harvested and underwent extraction processes. This material was then combined with TiO2 nanoparticles (T) into paraffin wax (P) to create the PTP nanocomposite, using an economically viable and environmentally friendly approach, with P serving as a consistent, reducing, and stabilizing element. The synthesized PTP was thoroughly analyzed using Spectrophotometer, Fourier-transform-IR spectroscopy, X-Ray diffraction, DSC, TGA, and SEM for characterization. The PTP samples were applied in constructing a Single Slope Wick Solar Still (SWS), aiming to induce surface plasmon resonance around 450 nm across the absorber plate. The excitation of PTP at SPR led to the release of significant heat, contributing to temperature increments of the aqueous medium by varying percentages (10 %, 20 %, 30 %, and 40 %) under different ratios upon exposure to solar radiation at the precise plasmon resonance wavelength. This study introduced the first-time application of Cramer's rule (determinant technique) in solving energy balance equations for temperature components. Evaluation revealed that incorporating 30 % PTP notably enhanced SWS efficiency, achieving an optimal distillate output of 8.70 l/m2day, including 1.95 l/m2 at night, resulting in an efficiency of 42.74 %.

Impact of Hybrid Plasmonic and Temperature in Random Laser Tuning

This research explores the interaction between silver films and dispersed silver nanowires (Ag NWs) in the context of generating random laser emission. To achieve random lasing, we use a mixture of Rhoda mine B (RhB) dye and a polyvinyl alcohol (PVA) matrix as the gain medium. The combination of silver components plays a crucial role in trapping and controlling light. The surface characteristics of the film, including its roughness and the interplay between localized and extended surface plasmons significantly affect the performance of the random laser (RL). The laser’s threshold is closely linked to the thickness of the film, which is influenced by its surface roughness. Additionally, variations in film thickness lead to wavelength modulation, ranging from 597 nm to 606 nm, primarily due to the reabsorption of RhB. Moreover, this research demonstrates the intriguing capability to tune emission wavelengths in response to temperature changes, promising precise wavelength control for plasmonic devices and potential applications.

A comparative study on the degradation of carbamazepine by UV laser/chlorine and UV laser/PS processes: Performance and mechanisms

Residual carbamazepine (CBZ) in water is difficult to remove through conventional treatment processes, threatening the safety of drinking water. Ultraviolet-based advanced oxidation processes (UV-AOPs) have shown promise in removing refractory organic pollutants, while the low energy and efficiency of traditional mercury lamps hinder their practical applications. In this study, the performance and mechanism of an intensive-energy light source, UV laser, were systematically explored in UV-AOPs (laser/chlorine, laser/persulfate (PS)). It was found that UV laser exhibited a significantly activating ability for chlorine and PS due to its precise wavelength and high pulse energy. When exposed to UV laser (266 nm, 4.2 mW/cm2) combined with 200 μM chlorine and PS, the kinetic rate constants for the degradation of 10 μM CBZ were determined to be 3.160 × 10-3 and 1.227 × 10-3 s−1, respectively. The degradation of CBZ was dominated by hydroxyl radicals (60.98 %) and sulfate radicals (23.15 %) in laser/PS system, while in laser/chlorine system, hydroxyl radicals (54.90 %), chlorine radicals (27.43 %), and chlorine oxide radicals (13.81 %) were primary reactive species. Furthermore, both the laser/chlorine and laser/PS systems demonstrated compatibility with a wide pH range of 5.0–9.0 and high resistance to anionic interference. Moreover, the electrophilic and nucleophilic sites of CBZ and energy barrier of the initial reaction were calculated based on the density functional theory (DFT). Additionally, the degradation pathways of CBZ and the toxicity of transformation products in laser/chlorine and laser/PS processes were proposed and evaluated. These results demonstrated that the UV laser-based processes exhibited promising prospects in eliminating refractory organic pollutants in water treatment.

Precise Wavelength Measurement of 543‐nm Frequency Stabilized He‑Ne Laser Using Optical Frequency Comb

Precise Wavelength Measurement of 543‐nm Frequency Stabilized He‑Ne Laser Using Optical Frequency Comb

Design and analysis of dual‐band plasmonic band pass filter using meandering step impedance resonator

AbstractIn this article, we demonstrated the minimum significant dielectric thickness of silicon dioxide (SiO2) below the diffraction limit for the confinement in the metal–insulator–metal (MIM) waveguide and utilizing this idea, we further exhibited the detail design analysis of dual‐band plasmonic meandering step impedance resonator (MSIR), which can achieve a high quality‐factor compared to a traditional step impedance resonator (SIR). MSIRs have sharper wavelength selectivity compared to SIRs, making them more suitable for applications that require precise wavelength tuning. The tunability of reflection and transmission characteristics with respect to design parameters has been reported. The designed MSIR has demonstrated a good passband response at wavelengths λ = 1414‐nm (E‐band) and 1577‐nm (L‐band) as well as turnability with design parameters. This filter achieved a large frequency spectral range of 139 nm and a high Q factor of ~3 × 104. This work enhances the capability of on‐chip filtering in the plasmonic platform.

Enhancing imaging capabilities with a high-sensitivity multichannel optical filter

This research introduces a high-sensitivity multichannel optical filter with combined filtering and imaging capabilities, enabling the separation of wavelengths from visible to near-infrared light into distinct colors. The device design comprises a metal-insulator-metal (MIM) straight waveguide coupled to six pairs of overlapping resonators. The transmittance properties and electromagnetic field distributions are analyzed by varying the geometrical sizes using the finite-element method. The designed structure effectively filters out four to fifteen color channels with a narrow full width at half maximum of approximately 2–6 nm. It provides precise multichannel transmittance wavelength selectivity with high color purity, spanning from visible to near-infrared. Additionally, this structure serves as a plasmonic refractive index sensor, demonstrating impressive sensitivity, figure of merit, quality factor, and dipping strength values of 1450 nm/RIU, 241.67 1/RIU, 259.11, and 81.89 %, respectively. These characteristics highlight the excellent sensing performance of the proposed structure, offering significantly higher resolution and smaller dimensions compared to conventional systems.

UV Spectrophotometric Method for Estimation of Voriconazole in Bulk Form

This study presents a validated UV spectrophotometric method for the precise estimation of voriconazole in bulk formulations. Voriconazole, an essential antifungal agent, demands accurate quantification for its pharmaceutical applications. The proposed method leverages the sensitivity of UV spectroscopy to determine voriconazole concentrations effectively.&#x0D; The method's validation adheres to regulatory guidelines, ensuring reliability and accuracy. Spectrophotometric analysis was performed within a specific wavelength range, demonstrating linearity, precision, accuracy, and robustness across different concentrations of voriconazole.&#x0D; Parameters such as specificity, sensitivity, and stability were evaluated to affirm the method's suitability for routine analysis.&#x0D; The results indicate the method's efficacy in quantifying voriconazole in bulk and semi-solid forms with high precision and sensitivity. This validated UV spectrophotometric method presents a valuable tool for pharmaceutical analysis, facilitating quality control and assurance in voriconazole formulations.&#x0D; Keywords: Voriconazole, UV spectrophotometry, Anti-fungal, semi-solid formulation, Beer’s Lambert’s law.