Narrow-band Filters Research Articles

Research on Through-Flame Imaging Using Mid-Wave Infrared Camera Based on Flame Filter.

High-temperature furnaces and coal-fired boilers are widely employed in the petrochemical and metal-smelting sectors. Over time, the deterioration, corrosion, and wear of pipelines can lead to equipment malfunctions and safety incidents. Nevertheless, effective real-time monitoring of equipment conditions remains insufficient, primarily due to the interference caused by flames generated from fuel combustion. To address this issue, in this study, a through-flame infrared imager is developed based on the mid-wave infrared (MWIR) radiation characteristics of the flame. The imager incorporates a narrowband filter that operates within the wavelength range of 3.80 μm to 4.05 μm, which is integrated into conventional thermal imagers to perform flame filtering. This configuration enables the radiation from the background to pass through the flame and reach the detector, thereby allowing the infrared imager to visualize objects obscured by the flame and measure their temperatures directly. Our experimental findings indicate that the imager is capable of through-flame imaging; specifically, when the temperature of the target exceeds 50 °C, the imager can effectively penetrate the outer flame of an alcohol lamp and distinctly capture the target's outline. Importantly, as the temperature of the target increases, the clarity of the target's contour in the images improves. The MWIR through-flame imager presents considerable potential for the real-time monitoring and preventive maintenance of high-temperature furnaces and similar equipment, such as detecting the degradation of refractory materials and damage to pipelines.

High-Q coupled topological edge state in 1D photonic crystal mirror heterostructure for ultrasensitive thermal sensing

This work explores a novel 1D topological photonic crystal (PC) mirror heterostructure for high-performance thermal sensing. The design leverages a unique coupled topological edge state mode (CTES) exhibiting exceptional light confinement at the interface, characterized by a record-high quality (Q) factor. The study investigates the effects of nematic liquid crystal (NLC) integration and temperature variations to enhance functionality. Two NLC defect configurations are explored: complete replacement of silica layers and localized replacement within one topological PC. In both scenarios, the CTES mode exhibits tunability in frequency and Q factor due to the thermo-optic properties of the NLC. This dynamic control offers advantages for various applications beyond thermal sensing, including filtering and switching. The first NLC configuration achieves an outstanding Q factor of 107, surpassing the intrinsic value. Additionally, it demonstrates exceptional thermal sensitivity (−0.12317 nm/°C) and a remarkable figure of merit (1002.48 °C−1). These superior sensing characteristics are attributed to the strong light localization at the interface and the intensified light-matter interaction facilitated by the NLC. The second configuration offers a trade-off between sensitivity and tunability, exhibiting a Q factor in the 106 range, a sensitivity of −0.05853 nm/°C, and a figure of merit of 86.53 °C−1. This study presents a groundbreaking design for 1D topological PC mirror heterostructures with integrated NLC. This platform holds immense promise for developing high-performance, tunable narrowband filters and ultrasensitive thermal sensors, paving the way for advancements in diverse photonic applications.

Noise control in ducts using Herschel-Quincke acoustic metamaterial array

Acoustic resonators, like Helmholtz, side branch tubes, expansion chambers, Herschel-Quincke, and so on, are usually used to control duct noise in acoustic systems. Noise attenuation in local resonators occurs due to impedance mismatch of incident, transmitted, and reflected waves induced by the addition of resonators. The frequency band and the attenuation level generated by the resonator depend on its geometry and behave as a narrow-band filter. However, a much larger frequency band, called bandgap, is obtained if they are appropriately distributed (periodically or not) along the duct length. This paper investigates acoustic noise attenuation for an acoustic metamaterial using a Herschel-Quincke (HQ) resonator. It is modeled by the transfer matrix method and the finite element method. Also, a study about the arrangements of the HQ resonators (serial and parallel) is conducted to verify their accuracy and efficiency related to bandwidth enlargement and sound transmission loss. Simulated results are obtained for different examples and compared to those from the literature.

Ultra-compact narrow-band band-stop filter based on inverse design

Ultra-compact narrow-band band-stop filter based on inverse design

ODIN: Improved Narrowband Lyα Emitter Selection Techniques for z = 2.4, 3.1, and 4.5

Lyman-alpha-emitting galaxies (LAEs) are typically young, low-mass, star-forming galaxies with little extinction from interstellar dust. Their low dust attenuation allows their Lyα emission to shine brightly in spectroscopic and photometric observations, providing an observational window into the high-redshift Universe. Narrowband surveys reveal large, uniform samples of LAEs at specific redshifts that probe large-scale structure and the temporal evolution of galaxy properties. The One-hundred-deg2 DECam Imaging in Narrowbands (ODIN) utilizes three custom-made narrowband filters on the Dark Energy Camera (DECam) to discover LAEs at three equally spaced periods in cosmological history. In this paper, we introduce the hybrid-weighted double-broadband continuum estimation technique, which yields improved estimation of Lyα equivalent widths. Using this method, we discover 6032, 5691, and 4066 LAE candidates at z = 2.4, 3.1, and 4.5 in the extended COSMOS field (∼9 deg2). We find that [O ii] emitters are a minimal contaminant in our LAE samples, but that interloping Green Pea–like [O iii] emitters are important for our redshift 4.5 sample. We introduce an innovative method for identifying [O ii] and [O iii] emitters via a combination of narrowband excess and galaxy colors, enabling their study as separate classes of objects. We present scaled median stacked spectral energy distributions for each galaxy sample, revealing the overall success of our selection methods. We also calculate rest-frame Lyα equivalent widths for our LAE samples and find that the EW distributions are best fit by exponential functions with scale lengths of w 0 = 53 ± 1, 65 ± 1, and 59 ± 1 Å, respectively.

The PAU Survey: The quasar and UV luminosity functions at 2.7<z<5.3

We present the Lyman-alpha ( and ultraviolet (UV) luminosity function (LF) in bins of redshift for quasars selected in the Physics of the Accelerating Universe Survey (PAUS). A sample of 915 objects was selected at $2.7<z<5.3$ within an effective area of $ 36$ deg$^2$ observed in 40 narrow-band (NB) filters (FWHM $ We cover the intermediate--bright luminosity regime of the LF erg\,s $; $-29<M_ UV <-24$). The continuous wavelength coverage of the PAUS NB set allows very efficient target identification and precise redshift measurements. We show that our method is able to retrieve a relatively complete ($C 85<!PCT!>$) and pure ($P 90<!PCT!>$) sample of quasars for $ $. In order to obtain corrections for the LF estimation, and assess the accuracy of our selection method, we produced mock catalogs of $0<z<4.3$ quasars and galaxies that mimic our target population and their main contaminants. Our results show a clear evolution of the and UV LFs, with a declining tendency in the number density of quasars toward increasing redshifts. In addition, the faint-end power-law slope of the LF becomes steeper with redshift, suggesting that the number density of quasars declines faster than that of fainter emitters. By integrating the LF, we find that the total emitted by bright quasars per unit volume rapidly declines with increasing redshift, being subdominant to that of star-forming galaxies by several orders of magnitude by $z 4$. Finally, we stack the NB pseudo-spectra of a visually selected ``golden sample'' of 591 quasars to obtain photometric composite SEDs in bins of redshift, enabling us to measure the mean intergalactic medium absorption using the Lyman-alpha forest as a function of redshift, yielding results consistent with previous spectroscopic determinations.

Dez River Araphid/Bi-raphid diatoms for nano-optic applications

Micro and nano-silica structure technology is sumptuous and has empirical intricacies, so employing natural nanostructures can be inexpensive and more environmentally friendly. This green capacity can be the starting point of engineering and nanotechnology studies. Diatoms are good candidates for these structures, abundant in water and soil. They are types of algae with silicate frustules that may have periodic structures. Diatoms have a high potential to be used as sensors. They are very similar to photonic crystals.In this article, for the first time, some Araphid and Bi-raphid diatoms of the Dez River have been reported, and some of their optical characteristics have been investigated. The studied Dez-river Bi-raphid diatom shows no photonic band gap. Its periodic structure shows a maximum reflectance at λ=600nm, which seems to be an appropriate wavelength for the effective refractive index guiding mechanism through a siliceous defect. The studied Araphid diatoms show that the PBG waveguiding mechanism is achieved at the wavelength of about λ=690nm, too. This structure can be used as a narrow-band filter with a more than %95 efficiency for the mentioned wavelength. So the extraordinary structure of the Dez River Araphid and Bi-raphid diatoms can overtake the boundaries of the most advanced lithography techniques without spending time and money.

Graphene-assisted metamaterial absorber for refractive index sensor at lower optical frequencies

Numerical studies on a graphene-assisted metamaterial absorber operating at lower optical frequencies are presented. The metamaterial absorber comprises one-dimensional gold grating with a gold disk array in grooves on a monolayer graphene supported by a glass substrate. Numerical simulations are conducted using Computer Simulation Technology Microwave Studio to investigate the underlying absorption mechanisms in the system. The absorber shows a very sharp absorption band with almost unity absorptance and nearly 20 nm full width at half maximum at a wavelength of 766 nm. The simulated absorption spectrum of the absorber is theoretically validated using coupled mode theory, showing close agreement with the theoretical predictions. The absorption occurs due to the simultaneous excitation of localized and propagating surface plasmons under the transverse electric mode (where the electric field is aligned parallel to the length of the grating ridge) excitation in the system. The sensing performance of the absorber has been evaluated, demonstrating a sensitivity as high as 667 nm/RIU. Due to the robustness of the design, this absorber can be used to sense biological, chemical, gaseous, and even acidic samples since it is not comprised of any photoresist. The absorber holds potential for diverse applications, including graphene-based devices, narrowband filters, thermal emitters, solar cells, imaging apparatus, etc.

Light-injection attack against practical continuous-variable measurement-device-independent quantum key distribution systems

Continuous-variable measurement-device-independent quantum key distribution (CV-MDI QKD) can defend all detection-side attacks effectively. Therefore, the source side is the final battlefield for performing quantum hacking attacks. This paper investigates the practical security of a CV-MDI QKD system under a light-injection attack. Here, we first describe two different light-injection attacks, i.e., the induced-photorefractive attack and the strong-power injection attack. Then, we consider three attack cases where Eve only attacks one of the parties or both parties of the CV-MDI QKD system. Based on the analysis of the parameter estimation, we find that the legitimate communication parties will overestimate the secret key rate of the system under the effect of a light-injection attack. This opens a security loophole for Eve to successfully obtain secret key information in a practical CV-MDI QKD system. In particular, compared to the laser-damage attack, the above attacks use a lower power of injected light and have a more serious effect on the security of the system. To eliminate the above effects, we can enhance the practical security of the system by doping the lithium niobate material with various impurities or by using protective devices, such as optical isolators, circulators, optical power limiters, and narrow-band filters. Apart from these, we can also use an intensity monitor or a photodetector to detect the light-injection attack.

A lack of Lyman α emitters within 5 Mpc of a luminous quasar in an overdensity at z = 6.9: Potential evidence of negative quasar feedback at protocluster scales

High-redshift quasars are thought to live in the densest regions of space, which should be made evident by an overdensity of galaxies around them. However, campaigns to identify these overdensities by searching for Lyman-break galaxies (LBGs) and Lyman α emitters (LAEs) have had mixed results. These may be explained by either the small field of view of some of the experiments, the broad redshift ranges targeted by LBG searches, and the inherently high uncertainty of quasar redshifts estimated from ultraviolet emission lines, which makes it difficult to place the Ly-α emission line within a narrowband filter. Here, we present a 3 square degree search (∼1000 pMpc2) for LAEs around the z = 6.9 quasar VIK J2348–3054 using the Dark Energy CAMera (DECam) housed on the 4m Blanco telescope, finding 38 LAEs. The systemic redshift of VIK J2348–3054 is known from ALMA [CII] observations and places the Ly-α emission line of companions within the NB964 narrowband of DECam. This is the largest field-of-view LAE search around a z > 6 quasar conducted to date. We find that this field is ∼ten times more overdense than Chandra Deep-Field South, observed previously with the same instrumental setup as well as several combined blank fields. This is strong evidence that VIK J2348–3054 resides in an overdensity of LAEs over several Mpc. Surprisingly, we find a lack of LAEs within 5 physical Mpc of the quasar and take this to most likely be evidence of quasar-suppressing star formation in its immediate vicinity. This result highlights the importance of performing overdensity searches over large areas to properly assess the density of those regions of the Universe.

A novel narrowband MEMS filter with extensional mode resonators

This work proposes a novel electrostatic mechanically coupled narrowband filter based on width extensional mode (WEM) resonators. Rectangle plate WEM resonators have the potential for high quality factor (Q) and low motional resistance. The rectangle plate was slotted to reduce thermoelastic loss and optimize mode shape coefficient of WEMs. The Q values of coupled WEM resonators exceed 80,000, enabling a narrow bandwidth filter. A 3λ/4-length coupling beam filter (CBF) was demonstrated. The 3λ/4 coupling beam filter has a center frequency of 79.79 MHz and a bandwidth of 0.024 %. The CBF exhibits an impressive 26.39 dB stopband rejection and 6.97 dB insertion loss with 5.13 dB passband ripple. The MEMS filters presented in this work hold significant potential for applications in wireless communication systems.

A Sensitive Fluorescence Analysis Method of Pathogenic Microorganisms Based on Silicon Photomultiplier.

The monitoring of pathogenic microorganisms in water is important for public health and disease outbreaks prediction. Recently, optical detection techniques have drawn much attention due to the advantages of rapid response, security and high sensitivity. In this paper, a fluorescence spectrometer based on 375nm exciting laser and the microchannel liquid sample flow technology is proposed. The 4 × 4 narrowband filter array was coupled to a Silicon Photomultiplier (SiPM) array with single-photon sensitivity. B500 fluorescent microspheres and Escherichia coli were used for performance evaluation of the spectrometer. As a result, it is feasible to use random particle counting method to detect the bacteria concentration level in water even low to several CFU/mL. In addition, based on Python tools and neural network algorithm models, the fluorescence spectra of different kinds of substances (biotic and abiotic) can be classified with an accuracy of more than 97%. The method was successfully applied to tap water samples. The results suggest that the proposed method is applicable for on-site bacteria detection.

Theoretical study of a tunable optical device on the base of magnetoactive cholesteric liquid crystals

We investigated the light reflection from half-space of cholesteric liquid crystal (CLC) being in external static magnetic field directed along the helix axis at normal light incidence. In this case there appear three photonic band gaps (PBGs) and these bands can be tuned in large intervals. We found the eigenpolarizations (EPs) at reflection of light from half-space and investigated their peculiarities. We have shown that in the absence both of absorption and of external magnetic field and at minimal influence of dielectric boundary (when the dielectric permittivity of isotropic half-space which borders with CLC half-space is equal to the CLC's mean dielectric permittivity) these polarizations are orthogonal. While, in the presence of external magnetic field they become quasi-orthogonal everywhere outside the main PBG (which exist also at the absence of external magnetic field), and they are significantly non-orthogonal within the main PBG. At some values of helix pitch they become significantly non-orthogonal practically everywhere. Moreover, in this case there exist some special points where the EPs degenerate. This system can apply as tunable narrow-band or broad-band filter and mirror, a highly tunable broad/narrow-band optical diode, and other devices.

Waveguide-Based Split-Ring Resonators for Narrow-Band Filters Near 380 GHz

This work addresses the design of sub-terahertz narrow-band resonators for high performance and low-cost manufacturability. The intended application for these resonators is to realize narrow-band filters for passive millimeter-wave sounding of upper atmospheric humidity using the 380 GHz water vapor absorption line. Various narrow-band resonator designs and manufacturing processes were considered for this application. A design based on a waveguide split-ring resonator topology was selected to be developed and manufactured using laser machining. Experimental results are presented and compared with results from simulations for ten narrow-band resonators fabricated with a design center frequency in the WR-2.2 (325–500 GHz) waveguide band.

Measurement Error Analysis of Seawater Refractive Index: A Measurement Sensor Based on a Position-Sensitive Detector.

The seawater refractive index is an essential parameter in ocean observation, making its high-precision measurement necessary. This can be effectively achieved using a position-sensitive detector-based measurement system. However, in the actual measurement process, the impact of the jitter signal measurement error on the results cannot be ignored. In this study, we theoretically analysed the causes of long jitter signals during seawater refractive index measurements and quantified the influencing factors. Through this analysis, it can be seen that the angle between the two windows in the seawater refractive index measurement area caused a large error in the results, which could be effectively reduced by controlling the angle to within 2.06°. At the same time, the factors affecting the position-sensitive detector's measurement accuracy were analysed, with changes to the background light, the photosensitive surface's size, and the working environment's temperature leading to its reduction. To address the above factors, we first added a 0.9 nm bandwidth, narrow-band filter in front of the detector's photosensitive surface during system construction to filter out any light other than that from the signal light source. To ensure the seawater refractive index's measuring range, a position-sensitive detector with a photosensitive surface size of 4 mm × 4 mm was selected; whereas, to reduce the working environment's temperature variation, we partitioned the measurement system. To validate the testing error range of the optimised test system, standard seawater samples were measured under the same conditions, showing a reduction in the measurement system's jitter signal from 0.0022 mm to 0.0011 mm, before and after optimisation, respectively, as well as a reduction in the refractive index's deviation. The experimental results show that the refractive index of seawater was effectively reduced by adjusting the measurement system's optical path and structure.

Design and Fabrication of a Five-Order Narrow-Band Coaxial Filter based on Cross-Coupling and Non-Cross-Coupling Methods

In this paper, the design, analysis, and fabrication of a novel coaxial filter based on folded topology are presented. First, two structures of cross-coupling and non-cross-coupling were proposed to achieve the best performance of the coaxial cavity. Second, to reach the smallest dimensions, a folded topology was chosen. Third, phase relationship and also matrix coupling are introduced for determining suitable phase shifts. The proposed method is verified by fabricating a five-order narrow-band coaxial cavity filter for a transverse electromagnetic (TEM) mode at 4 GHz. Finally, the simulation and measurement results of the coaxial cavity filter are presented. Good agreement between simulation and fabrication confirms the validity of the proposed methodology.

Low temperature coefficient of frequency AlN Lamb wave resonator using groove structure between interdigital transducers

The lithographically tunable and small size features of Lamb wave resonators (LWRs) take a bright future for their use in high frequency narrow band filters. Resonant frequency drift due to temperature variation has a large impact on the narrower passband and a temperature coefficient of frequency (TCF) closer to 0 can broaden the stable temperature range of the resonator. This paper proposes a method of etching grooves in the area of the piezoelectric layer not covered by the Interdigital transducer (IDT) electrodes to improve the temperature stability of the Lamb resonator. Through the finite element method and theoretical analysis, the phase velocity, group velocity, and TCF dispersion curve of different modes of the resonator with groove structure were determined. The reason for the change of TCF under different normalized thicknesses of AlN was explained through the conversion of the LWR from a contour mode resonator (CMR) to a Cross-Sectional Lamé Mode Resonator. Simulation and test have shown that etching grooves have the effect of reducing TCF by adjusting the electromechanical coupling coefficient. The test shows that 205 nm-depth grooves can lower the TCF of the S0 mode IDT-Open LWR from −13.3 to −5.1 ppm/°C and S1 mode from −36.8 to −9.0 ppm/°C, respectively. The TCF of S0 and S1 mode LWRs decreased by 61.7% and 75.5%, respectively, after 205 nm groove etching. The groove etching method greatly raises the temperature stability of the LWR, enabling Lamb wave filters to operate stably over a wider temperature range.

Miniaturized spectrometers based on graded photonic crystal films

Miniaturized spectrometers have become increasingly important in modern analytical and diagnostic applications due to their compact size, portability, and versatility. Despite the surge in innovative designs for miniaturized spectrometers, significant challenges persist, particularly concerning manufacturing cost and efficiency when devices become smaller. Here we introduce an ultracompact spectrometer design that is both cost-effective and highly efficient. The core dispersion element of this new design is a graded photonic crystal film, which is engineered by applying gradient stress during its fabrication. The film shows bandstop transmission spectral profiles, akin to a notch filter, enhancing light throughput compared to conventional narrowband filters. The spectral analysis, with a resolution of 5 nm and operating within the wavelength range of 450-650 nm, is conducted by reconstructing the spectrum from a series of such notch transmission profiles along the graded photonic crystal film, utilizing a sophisticated algorithm. This approach not only reduces manufacturing costs but also significantly improves the sensitivity (with a light throughput efficiency of 71.05%) and overall performance of the limitations of current technology, opening up new avenues for applications in diverse fields.

Exploring the efficacy of subwavelength gratings as short-wavelength infrared filters

Advancements in nanofabrication technology have greatly facilitated research on nanostructures and their associated properties. Among these structures, subwavelength components have emerged as promising candidates for ultra-compact optical elements, can potentially supplant conventional optical components and enable the realization of compact and efficient optical devices. Spectral analysis within the infrared spectrum offers a wealth of information for monitoring crop health, industrial processes, and target identification. However, conventional spectrometers are typically bulky and expensive, driving an increasing demand for cost-effective spectral sensors. Here we investigate three distinct subwavelength grating structures designed to function as narrowband filters within the short-wavelength infrared (SWIR) range. Through simple adjustments to the period of grating strips, these filters selectively transmit light across a wide wavelength range from 1100 to 1700 nm with transmission exceeding 70% and full width at half maximum (FWHM) down to 6 nm. Based on a simple design, the results present great potential of subwavelength grating filters for multiband integration and developing ultra-compact spectral sensors.

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.