Interference Filters Research Articles

Noise Reduction System Using Passive Bandpass Noise Filter on Podcast Microphone

The general properties of waves are refraction, reflection, bending (diffraction), interference and polarization. Sound is a form of wave and is in accordance with the law of wave refraction where waves coming from a less dense medium to a denser medium will be refracted closer to the normal line or vice versa. Sound waves easily experience diffraction because sound waves in air have wavelengths of around several centimeters to several meters. Then basically every room, whether you feel it or not, will always have sound. This is inversely proportional to light which has a wavelength of around 500 mm. Therefore, an interference reduction system using a passive bandpass interference filter on the podcast microphone is necessary to reduce interference. Test results carried out by filters used to reduce noise using Passive Band Pass. the waveform is still the original spectrum at 0 Hz – 120 Hz, the original sound conditions and does not cause interference, but interference occurs and filtering Category (Noise %) 10 – 40 low - 98 – 99 high.

Polyp segmentation with interference filtering and dynamic uncertainty mining.

Objective.Accurate polyp segmentation from colo-noscopy images plays a crucial role in the early diagnosis and treatment of colorectal cancer. However, existing polyp segmentation methods are inevitably affected by various image noises, such as reflections, motion blur, and feces, which significantly affect the performance and generalization of the model. In addition, coupled with ambiguous boundaries between polyps and surrounding tissue, i.e. small inter-class differences, accurate polyp segmentation remains a challenging problem.Approach.To address these issues, we propose a novel two-stage polyp segmentation method that leverages a preprocessing sub-network (Pre-Net) and a dynamic uncertainty mining network (DUMNet) to improve the accuracy of polyp segmentation. Pre-Net identifies and filters out interference regions before feeding the colonoscopy images to the polyp segmentation network DUMNet. Considering the confusing polyp boundaries, DUMNet employs the uncertainty mining module (UMM) to dynamically focus on foreground, background, and uncertain regions based on different pixel confidences. UMM helps to mine and enhance more detailed context, leading to coarse-to-fine polyp segmentation and precise localization of polyp regions.Main results.We conduct experiments on five popular polyp segmentation benchmarks: ETIS, CVC-ClinicDB, CVC-ColonDB, EndoScene, and Kvasir. Our method achieves state-of-the-art performance. Furthermore, the proposed Pre-Net has strong portability and can improve the accuracy of existing polyp segmentation models.Significance.The proposed method improves polyp segmentation performance by eliminating interference and mining uncertain regions. This aids doctors in making precise and reduces the risk of colorectal cancer. Our code will be released athttps://github.com/zyh5119232/DUMNet.

Solution Cathode Glow Discharge – Atomic Emission Spectrometry (SCGD-AES) With an Interference Filter for Spectral Discrimination for the Determination of Thallium in Surface Water

Solution cathode glow discharge atomic emission spectrometry (SCGD-AES) using wide-bandpass (10-nm) interference filters (IF) as a spectral discrimination device was used for the determination of thallium (Tl) in surface water. The use of wide-bandpass interference filters greatly reduces the cost of traditional detection instruments. The influence of solution flow rate, discharge current and pH on the detection limit was characterized. Moreover, matrix effect experiments were performed to study the effect of different concentrations of Na+, K+, Ca2+, and Mg2+ on the Tl signal intensity. Using a solution flow rate of 2.8 mL/min, a discharge current of 50 mA, and pH of 1.0 with HNO3 as the supporting electrolyte, SCGD coupled with an interference filter provided a detection limit of 7.76 μg/L for Tl in water samples, comparable to traditional SCGD-AES. Furthermore, the spiked recovery rate of Tl is quantitative in real water samples and comparable to the performance of inductive coupled plasma – optical emission spectrometry (ICP-OES).

Radiated emission from DC bus loop of AC induction motor inverter FEM based and experimental evaluation

The paper describes practical method how to analyze locally radiated magnetic field to improve the geometry of printed circuit board (PCB) or busbar structure, select better control method and design electromagnetic interference (EMI) filter. Experimental prototype of three-phase induction motor variable frequency drive has been created and controlled by microcontroller with sinusoidal, namely pulse with modulation (PWM) method. Three-dimensional finite element model simulation of DC bus structure has been created and results has been obtained. Electromagnetic field was measured, practically and results compared with simulation-based ones. Simulation based and experimental results matches thus allowing to conclude method usefulness for cost effective way to test different geometries of DC bus, different modulation methods, EMI filters for variable frequency drive, and other power electronics converters.

A dual-wavelength erbium-doped fiber laser for high resolution strain sensing with compound filter of a Sagnac loop and a long period fiber grating

A dual-wavelength erbium-doped fiber laser (EDFL) strain sensing system composed of compound filter of a long period fiber grating (LPFG) and a Sagnac loop is proposed. Polarization maintaining fiber (PMF) in Sagnac loop acts both an interference filter and a strain sensing probe with high sensitivity, low cost, and low loss. LPFG is used to modulate the transmission wavelength and bandwidth of EDFL through adjusting its bending curvature. Flexible laser output with single wavelength and dual-wavelength tunable wavelength band of 10 nm is achieved in EDFL. The measurement sensitivity of strain reaches 8.33 pm/με, while the 3 dB linewidth is less than 2 nm and the signal-to-noise ratio (SNR) exceed 36 dB. This sensor has a high resolution (R) of 0.11 nm and a high quality factor (Q) of 38.13. The experimental results suggest that the system is suitable for precise strain measurement and has significant potential in fields like biomedicine, environmental monitoring, health monitoring, and aerospace.

Multicolor fluorescence microscopy for surgical guidance using a chip-scale imager with a low-NA fiber optic plate and a multi-bandpass interference filter.

In curative-intent cancer surgery, intraoperative fluorescence imaging of both diseased and healthy tissue can help to ensure the successful removal of all gross and microscopic diseases with minimal damage to neighboring critical structures, such as nerves. Current fluorescence-guided surgery (FGS) systems, however, rely on bulky and rigid optics that incur performance-limiting trade-offs between sensitivity and maneuverability. Moreover, many FGS systems are incapable of multiplexed imaging. As a result, clinical FGS is currently limited to millimeter-scale detection of a single fluorescent target. Here, we present a scalable, lens-less fluorescence imaging chip, VISION, capable of sensitive and multiplexed detection within a compact form factor. Central to VISION is a novel optical frontend design combining a low-numerical-aperture fiber optic plate (LNA-FOP) and a multi-bandpass interference filter, which is affixed to a custom CMOS image sensor. The LNA-FOP acts as a planar collimator to improve resolution and compensate for the angle-sensitivity of the interference filter, enabling high-resolution and multiplexed fluorescence imaging without lenses. We show VISION is capable of detecting tumor foci of less than 100 cells at near video framerates and, as proof of principle, can simultaneously visualize both tumors and nerves in ex vivo prostate tissue.

Effect of junction critical current disorder in superconducting quantum interference filter arrays

Effect of junction critical current disorder in superconducting quantum interference filter arrays

Derivation of depolarization ratios of aerosol fluorescence and water vapor Raman backscatters from lidar measurements

Abstract. Polarization properties of the fluorescence induced by polarized laser radiation are widely considered in laboratory studies. In lidar observations, however, only the total backscattered power of fluorescence is analyzed. In this paper we present results obtained with a modified Mie–Raman–fluorescence lidar operated at the ATOLL observatory, Laboratoire d'Optique Atmosphérique, University of Lille, France, allowing us to measure depolarization ratios of fluorescence at 466 nm (δF) and of water vapor Raman backscatter. Measurements were performed in May–June 2023 during the Alberta forest fires season when smoke plumes were almost continuously transported over the Atlantic Ocean towards Europe. During the same period, smoke plumes from the same sources were also detected and analyzed in Moscow, at the General Physics Institute (GPI), with a five-channel fluorescence lidar able to measure fluorescence backscattering at 438, 472, 513, 560 and 614 nm. Results demonstrate that, inside the planetary boundary layer (PBL), the urban aerosol fluorescence is maximal at 438 nm, and then it gradually decreases with the increase in wavelength. The smoke layers observed within 4–6 km height present a maximum fluorescence at 513 nm, while in the upper troposphere, fluorescence maximum shifts to 560 nm. Regarding the fluorescence depolarization ratio, for smoke its value typically varies within the 45 %–55 % range. The depolarization ratio of the water vapor Raman backscattering at 408 nm is shown to be quite low (2±0.5 %) in the absence of fluorescence because the narrowband interference filter (0.3 nm) in the water vapor channel selects only the strongest vibrational lines of the Raman spectrum. As a result, the depolarization ratio at the water vapor Raman channel is sensitive to the presence of strongly depolarized fluorescence backscattering and can be used for the evaluation of the aerosol fluorescence contribution to measured water vapor mixing ratio.

Online Testing Method for the Fine Spectral Characteristics of Narrow-Band Interference Filters Based on a Narrow-Linewidth Tunable Laser.

The transmission spectrum of a narrow-band interference filter is crucial and highly influenced by factors such as the temperature and angle, thus requiring precise and online measurements. The traditional method of measuring the transmission spectrum of an interference filter involves the use of a spectrometer, but the accuracy of this method is limited. Moreover, placing a narrow-band interference filter inside a spectrometer hinders real-time online measurements. To address this issue, there is demand for high-precision online spectral testing methods. In response to this demand, we propose and experimentally validate a fine spectral characterization method for narrow-band interference filters. This method uses a narrow-linewidth tunable laser, achieving a spectral resolution in the MHz range for online testing. Two types of narrow-band interference filters were tested using the constructed laser spectroscopy experimental system, obtaining a transmission spectrum with a spectral resolution of 318 MHz. In comparison to spectrometer-based methods, our proposed method demonstrates higher spectral accuracy, enables online measurements, and provides more accurate measurements for special spectral interference filters. This approach has significant application value and promising development prospects.

Measurements of particle extinction coefficients at 1064 nm with lidar: temperature dependence of rotational Raman channels.

Aerosol intensive optical properties, including lidar ratio and particle depolarization ratio, are of vital importance for aerosol typing. However, aerosol intensive optical properties at near-infrared wavelength are less exploited by atmospheric lidar measurements, because of the comparably small backscatter cross section of Raman-scattering and a low efficiency of signal detection compared to what is commonly available at 355 nm and 532 nm. To obtain accurate optical properties of aerosols at near-infrared wavelength, we considered three factors: Raman-spectra selection, detector selection, and interference-filter optimization. Rotational Raman scattering has been chosen for Raman signal detection, because of the higher cross-section compared to vibrational Raman scattering. The optimization of the properties of the interference filter are based on a comprehensive consideration of both signal-to-noise ratio and temperature dependence of the simulated lidar signals. The interference filter that has eventually been chosen uses the central wavelength at 1056 nm and a filter bandwidth (full-width-at-half-maximum) of 6 nm. We built a 3-channel 1064-nm rotational Raman lidar. In this paper two methods are proposed to test the temperature dependence of the signal-detection unit and to evaluate the quality of the Raman signals. We performed two measurements to test the quality of the detection channel: cirrus clouds in the free troposphere and aerosols in the planetary boundary layer. Our analysis of the measured Raman signals shows a negligible temperature dependence of the Raman signals in our system. For cirrus measurements, the Raman signal profile did not show crosstalk even for the case of strong elastic backscatter from clouds, which was about 100 times larger than Rayleigh scattering in the case considered here. The cirrus-mean extinction-to-backscatter ratio (lidar ratio) was 27.8 ± 10.0 sr (1064 nm) at a height of 10.5-11.5 km above ground. For the aerosols in the planetary boundary layer, we found the mean lidar ratio of 38.9 ± 7.0 sr at a height of 1.0-3.0 km above ground.

Spectral origami: an angle-variable, wavelength-selective concept with a highly efficient filter-based sensing.

This study demonstrates the concept of an angle-variable compact spectral module. As a key feature, the filter-based module enables highly efficient wavelength-selective light detection by applying the reflective beam path according to the origami example. It was accomplished through inclined mirrors, which allow for different incident angles on the wavelength separating interference filters used in a robust assembly with no moving parts. To experimentally verify the concept, a wavelength range between 550 and 700 nm was detected by 11 spectral channels. These initial results showed the potential to develop easily scalable and application-tailored sensors, which can overcome conventional filter-based sensor approaches that use upright or fixed-angle illumination.

Dynamics of the plasma induced by laser on a cryogenically cooled aluminum target for application in space propulsion

In this work, we investigate the properties of the plasma induced by focusing a high-power laser beam on an aluminum target that was cooled by a helium refrigerator from room temperature down to 20 K. Fast, streak photographs of the plasma were taken at different temperatures and laser energies. From the images obtained, position-vs-time plots were made for each experiment, and from them, the speed was calculated. Additionally, narrowband interference filters were employed to image the dynamics of ions and neutrals separately. It was found that the plasma plume has two distinct speeds: that of its center and that of the outer edge. For unfiltered images, the former has values within the interval 6.2 to 9.1 km/s, while the latter can reach speeds of the order of hundreds of km/s. It was found that the plume of a target cooled to 20 K has a length that is 8%–12% less than the corresponding size at room temperature. Chilling the target did not seem to affect significantly either the plume's speed of expansion or the size of the crater produced. Lower bounds were estimated for the momentum imparted to the ejecta and the specific impulse. The latter can reach a 920-s level, nearly twice as much the amount obtained with chemical rocket fuel.

On the issue of capacitively coupled circuits using to explain the mutual influence of wires

The wire, as a separate element, is practically never sanctified in the literature. There is no radio-electronic device without a wire. It is the frequency characteristics of the wire impedance that limit the frequency characteristics of the inductor impedance, i.e. limit the frequency range of the radio interference filter. Therefore, it is important to understand the physics of the processes occurring in the wire. In addition, it is important to understand how the wire “parasitic” parameters affect the other elements “parasitic” parameters. An explanation for the presence of capacitance in a wire equivalent circuit through the skin effect phenomenon is proposed in this article. The using of the concept of capacitively coupled circuits as a dual analogue of inductively coupled circuits is proposed. It is shown that the duality of inductively coupled circuits and capacitively coupled circuits is possible only due to the duality of the alternating vortex magnetic field and the alternating vortex electric field. The viability of using the concept of capacitively coupled circuits is shown using the example of the measured impedance of two wires in various variants of parallel connection.

(Invited) Detection of Wavelength Information by Filter-Free Wavelength Sensor and Its Applications

This paper introduces the wavelength and light intensity detection method using the filter-free wavelength sensor without optical filters. Optical detection methods are widely used in medical, environmental, chemical, biofield, and agricultural analyses. In the biofield, the optical detection method makes it possible to predict, diagnose, and analyze diseases by detecting the wavelength information and light intensity, such as absorption, fluorescence, and spectral shift.In order to measure a specific wavelength and intensity of light, mainly used a detection method such as a filter cube of a fluorescence microscope or a monochromator of a spectrometer system. Even if this system has high sensitivity and selectivity, it is not easy to apply to POCTs that require portability due to the high price and increased system volume due to the integration of optical filters and other parts. Therefore, various studies have reported using semiconductor processes to detect the wavelength and light intensity with a high-performance and miniaturized system.An on-chip photodetection device has been reported, such as a fluorescence detection sensor to integrate interference or absorption filters on CMOS image sensors with high selectivity and sensitivity. Since the specific wavelength of light intensity detection is possible, it can apply to biofields such as fluorescence analysis. However, detecting different wavelength changes by fluorescent reagent is difficult because the optical filter is integrated into the CMOS image sensor. A method of multi-wavelength analysis with the single-pixel without an optical filter is reported using a CMOS-buried quad p-n junction photodetector. Since the light wavelength has a different absorption depth depending on the silicon absorption coefficient, it is possible to separate wavelength by measuring the current generated at each p-n junction. Therefore, it will provide a high-space-resolution image in the biofield. However, the possibility detection wavelength band is fixed according to the buried p-n junction numbers and depth.Previously, we reported a filter-free wavelength sensor with a photogate structure. Sensor can detect light intensity and wavelength without optical filters based on the dependence of the light absorption depth in silicon. The sensor fabricates using the 1-polysilicon, 2-metal process in the LSI facility of the Toyohashi University of Technology in Japan, as shown in Fig1(a). The sensor consists of a three-layer structure where deep n-well and p-well were formed on a p-type silicon substrate, as shown in Fig1(b). Applying a voltage to the photogate and n-well forms a potential peak W as a mountain shape below the sensing area. Therefore, the photocurrent generated by the incident light was divided into the surface side (I PG), and bottom side (I n-well) based on the potential peak W and wavelength identification is possible from the current ratio (I n-well/I PG). To detect the wavelength information of multi-peak light for applications in the biofield, compare the centroid wavelength and current ratio. We experimentally confirmed that the centroid wavelength was proportional to the current ratio by the light absorption depth of silicon. Since the light absorption depth depends on the light wavelength, the current ratio is constant even when the light intensity changes. Therefore, estimation of the light intensity is possible by the sum of each current.We proposed a wavelength, spectral shift, and absorbance measure method using a filter-free wavelength sensor to apply various fields. Figure 2(a) shows a schematic for detecting the fluorescence wavelength. Without using optical filters, fluorescence can be quantified by calculating the centroid wavelength of the light even when the excitation light is emitted simultaneously. In addition, it successfully identified fluorescence emitted from Legionella bacteria [1]. Figure 2(b) shows a schematic diagram that can identify the change in the spectrum using a sensor. Integrating an LSPR biosensor into a filter-free wavelength sensor makes it possible to measure the amount of spectrum changed by molecular binding. Therefore, miniaturization of the LSPR detection system becomes possible, and we succeeded in detecting and quantifying the S-protein of SARS-CoV-2 [2]. Figure 2(c) shows a schematic diagram of the absorbance measurements method for samples that absorb a specific wavelength range. By the proposed absorbance measurement method was possible to measure the ratio of chlorophyll content and chlorophyll a/b ratio contributing to plant photosynthesis [3].The filter-free wavelength sensor fabricated by the semiconductor process has been confirmed for its application as an optical detection system. In the future, we will continue research to develop an optical sensor system that is more compact, sensitive, and selective and can be applied to various fields.[1] Biosensors, vol.12, no.11, p.1033 (2022)[2] Applied Physics Express, vol.16, no.1, p.012012 (2023)[3] Jpn. J. Appl. Phys., vol.61, p.SD1041 (2022) Figure 1

Development of a 483 nm external cavity diode laser with cat-eye reflector

An external cavity diode laser, equipped with a cat-eye reflector setup, an interference filter, and a polarizing beam splitter, has been demonstrated to produce a laser wavelength of approximately 483 nm. This ECDL is based on the affordably priced commercial laser diode, GH04850B2G. Critical characteristics, such as fluctuations in optical power and output wavelength in response to injected current, were investigated. In anticipation of potential experiments involving rubidium Rydberg atoms, a simulation of the electromagnetically induced transparency spectrum was conducted using this laser setup in conjunction with a 780-nm laser.

Interference filter based external-cavity diode laser with combined dual interference filters and largely adjustable feedback range

External-cavity diode lasers (ECDL) are widely used as light sources in laser spectroscopy, atomic physics, and quantum optics. This study demonstrated a home-made 852–nm ECDL with variable feedback, using the combined dual narrow-band interference filters (IFs) as the laser longitudinal mode selection element. The combination of narrow-band IFs, mainly for the current commercially available narrow-band IFs with the full width at half maximum (FWHM) of approximately 0.5 nm for 780-895 nm. We designed different narrow-band IFs combinations to achieve a narrower FWHM, and applied them in the ECDL. The combination of the dual narrow-band IFs further reduces the laser linewidth. We measured the laser linewidth using a high-finesse Fabry-Perot cavity with a linewidth of approximately 10 kHz. The laser linewidth is approximately 176 kHz for the Single-IF-ECDL and 96 kHz for the Dual-IF-ECDL with the same feedback. In addition, we have experimentally verified the results of narrower laser linewidth and larger tuning range with increase in the feedback. The developed Dual-IF-ECDL has the capability of narrow linewidth and wavelength tunability and can be applied to precision spectroscopy, cooling and trapping of neutral atoms.

Full-color optical combiner with good imaging quality and a wide angle of incident light acceptance.

This work demonstrates a full-color optical image combiner for augmented reality head-up displays. In this device, the angle of the incident light of the computer-generated image reflected by it can vary over a large range. It achieves improved performance by using a combination of polarization interference filters (PIFs), quarter-wave retarders (QWRs), and polarization volume holograms (PVHs). The details for an example design and its performance are presented.

Buildup of multiple spatiotemporal nonlinear dynamics in an all-fiber multimode laser

Ultrafast lasers based on multimode fibers have attracted extensive attention owing to the large mode-field area and nonlinear tolerance. The high spatial degree of freedom of multimode fibers is significant for spatiotemporal pulses locked both in transverse and longitudinal modes, where the energy of output pulses can be remarkably improved. Herein, the 1.5-μm all-fiber spatiotemporal mode-locked laser was realized based on carbon nanotubes as a saturable absorber. Moreover, by tuning the polarization controller and the pump power carefully, the output wavelengths can be ranged from 1529 to 1565 nm based on the multimode interference filter. In addition, Q-switched mode-locking and spatiotemporal mode-locked dual combs were also observed by further adjusting the polarization controller. Such a kind of an all-fiber multimode laser offers a crucial insight into the spatiotemporal nonlinear dynamics, which is of great significance in scientific research and practical applications.

Research Progress in Tunable Fiber Lasers Based on Multimode Interference Filters.

Tunable fiber lasers have the advantages of good beam quality, high integration, and adjustable output wavelength, and they are widely used in fields such as optical fiber communication and optical fiber sensing. The fiber filter is one of the key components of tunable fiber lasers. Among the various filters currently used, multimode interference filters have the advantages of simple structure, convenient implementation, flexible tuning methods, and convenient spectral range design. The structures of multimode interference filters based on multimode fibers, no-core fibers, multi-core fibers, tapered fibers, and other special fibers are introduced in this paper. The working principles and tuning methods are analyzed and the research progress of tunable fiber lasers based on these filters is summarized. Finally, the development trend of tunable fiber lasers based on multimode interference filters is discussed. The rapid development and applications of multimode interference filters can help improve the performance of continuous and pulse lasers as well as promote the practicality of tunable fiber lasers.

Interval Adjustable Dual-Wavelength Erbium-Doped Fiber Laser Based on Cascaded Two Mach-Zehnder Interferometers

An interference filter is designed by cascading two Mach-Zehnder interferometers (MZIs), which is then utilized in the construction of a wavelength interval adjustable dual-wavelength Erbium-doped fiber laser (EDFL). Each MZI consists of two 3 dB optical couplers (OCs) connected in series. The input light is split into two arms at the first OC and recombined at the second OC. The first MZI (MZI 1) has a smaller free spectral range (FSR) and is used for selecting the output wavelength of the laser. The second MZI (MZI 2) has a larger FSR and forms an envelope structure on the comb-like spectrum of MZI 1. By adjusting the optical path difference between the two arms of MZI 2, the FSR of the envelope can be changed, thereby altering the interval of the output wavelengths. The implemented filter is inserted into the EDFL to achieve stable dual-wavelength output. By stretching one arm of MZI 2, the interval of the dual-wavelength can be adjusted from 4.64 to 13.94 nm, with the side-mode suppression ratio of over 44 dB for all wavelengths.