Transmission Peak Research Articles

Research on Solid-state Optical Filtering Technology Using Faraday Anomalous Dispersion in Rare Earth-doped Crystals

This paper proposes a Faraday anomalous dispersion optical filter that uses rare earth-doped crystals to overcome the limitations of current atomic filtering technology, which include limited working wavelength and Doppler broadening. The paper analyses Er3+: LiYF4 1530 nm as an example filter. The results show that the proposed filter achieves high transmission while maintaining an ultra-narrow bandwidth transmission spectrum. The maximum transmission efficiency reaches 94.8% with a transmission bandwidth of hundred trillions HZ. The position of the transmission peak can be tuned by adjusting the size of the magnetic field, enabling the conversion of the transmission spectrum between the line center and the line wing.

An acoustic design project for final year engineering students using resonant arrays

This paper reviews the creation of a design course for mechanical engineering students at the University of Auckland. The primary objective of the course is to introduce students to the field of acoustics, teaching basic theoretical and experimental acoustics principles, together with product design and fabrication methods, in an engaging and educational manner. During the course, students were assigned the task of developing a noise reduction duct jacket that reduced sound propagation whilst allowing free airflow, all within specified dimensions. Students were required to create designs that attenuated a predefined sound spectrum, with both narrow-band and wide-band components. Over six weeks students developed their designs using mathematical modelling and fabricated their prototypes. The performance of their suppressors was assessed through sound pressure level and impedance tube transmission loss measurements. Students then modified their designs to maximise performance before final submission. Four-person teams produced a diverse range of implementations. The most successful designs achieved impressive performance with peak transmission loss up to 70dB, 2kHz bandwidths of 10 + dB transmission loss and a delta dBA reduction of 21.5 dB. Student feedback indicates a high level of satisfaction with the course, highlighting its effectiveness in imparting key knowledge and skills in acoustics engineering.

Quantum graphs and microwave networks as narrow-band filters for quantum and microwave devices.

We investigate properties of the transmission amplitude of quantum graphs and microwave networks composed of regular polygons such as triangles and squares. We show that for the graphs composed of regular polygons, with the edges of the length l, the transmission amplitude displays a band of transmission suppression with some narrow peaks of full transmission. The peaks are distributed symmetrically with respect to the symmetry axis kl=π, where k is the wave vector. For microwave networks the transmission peak amplitudes are reduced and their symmetry is broken due to the influence of internal absorption. We demonstrate that for the graphs composed of the same polygons but separated by the edges of length l^{'}<l, the transmission spectrum is generally not symmetric according to the axis kl^{'}=π. We also show that graphs composed of regular polygons of different size with the edges being irrational numbers are not fully chaotic and their level spacing distribution and the spectral rigidity are well described by the Berry-Robnik distributions. Moreover, the transmission spectrum of such a graph displays peaks which are very close to one. Furthermore, the microwave networks are investigated in the time-domain using short Gaussian pulses. In this case the delay-time distributions, though very sensitive to the internal structure of the networks, show the sequences of transmitted peaks with the amplitudes much smaller than the input one. The analyzed properties of the graphs and networks suggest that they can be effectively used to manipulate quantum and wave transport.

Cross-sectional Ct distributions from qPCR tests can provide an early warning signal for the spread of COVID-19 in communities.

SARS-CoV-2 PCR testing data has been widely used for COVID-19 surveillance. Existing COVID-19 forecasting models mainly rely on case counts obtained from qPCR results, even though the binary PCR results provide a limited picture of the pandemic trajectory. Most forecasting models have failed to accurately predict the COVID-19 waves before they occur. Recently a model utilizing cross-sectional population cycle threshold (Ct-the number of cycles required for the fluorescent signal to cross the background threshold) values obtained from PCR tests (Ct-based model) was developed to overcome the limitations of using only binary PCR results. In this study, we aimed to improve on COVID-19 forecasting models using features derived from the Ct-based model, to detect epidemic waves earlier than case-based trajectories. PCR data was collected weekly at Northeastern University (NU) between August 2020 and January 2022. Campus and county epidemic trajectories were generated from case counts. A novel forecasting approach was developed by enhancing a recent deep learning model with Ct-based features and applied in Suffolk County and NU campus. For this, cross-sectional Ct values from PCR data were used to generate Ct-based epidemic trajectories, including effective reproductive rate (Rt) and incidence. The improvement in forecasting performance was compared using absolute errors and residual squared errors with respect to actual observed cases at the 7-day and 14-day forecasting horizons. The model was also tested prospectively over the period January 2022 to April 2022. Rt curves estimated from the Ct-based model indicated epidemic waves 12 to 14 days earlier than Rt curves from NU campus and Suffolk County cases, with a correlation of 0.57. Enhancing the forecasting models with Ct-based information significantly decreased absolute error (decrease of 49.4 and 221.5 for the 7 and 14-day forecasting horizons) and residual squared error (40.6 and 217.1 for the 7 and 14-day forecasting horizons) compared to the original model without Ct features. Ct-based epidemic trajectories can herald an earlier signal for impending epidemic waves in the community and forecast transmission peaks. Moreover, COVID-19 forecasting models can be enhanced using these Ct features to improve their forecasting accuracy. In this study, we make the case that public health agencies should publish Ct values along with the binary positive/negative PCR results. Early and accurate forecasting of epidemic waves can inform public health policies and countermeasures which can mitigate spread.

Epidemiological and genomic investigation of chikungunya virus in Rio de Janeiro state, Brazil, between 2015 and 2018.

Since 2014, Brazil has experienced an unprecedented epidemic caused by chikungunya virus (CHIKV), with several waves of East-Central-South-African (ECSA) lineage transmission reported across the country. In 2018, Rio de Janeiro state, the third most populous state in Brazil, reported 41% of all chikungunya cases in the country. Here we use evolutionary and epidemiological analysis to estimate the timescale of CHIKV-ECSA-American lineage and its epidemiological patterns in Rio de Janeiro. We show that the CHIKV-ECSA outbreak in Rio de Janeiro derived from two distinct clades introduced from the Northeast region in mid-2015 (clade RJ1, n = 63/67 genomes from Rio de Janeiro) and mid-2017 (clade RJ2, n = 4/67). We detected evidence for positive selection in non-structural proteins linked with viral replication in the RJ1 clade (clade-defining: nsP4-A481D) and the RJ2 clade (nsP1-D531G). Finally, we estimate the CHIKV-ECSA's basic reproduction number (R0) to be between 1.2 to 1.6 and show that its instantaneous reproduction number (Rt) displays a strong seasonal pattern with peaks in transmission coinciding with periods of high Aedes aegypti transmission potential. Our results highlight the need for continued genomic and epidemiological surveillance of CHIKV in Brazil, particularly during periods of high ecological suitability, and show that selective pressures underline the emergence and evolution of the large urban CHIKV-ECSA outbreak in Rio de Janeiro.

Pixelated Filter Array for On-Chip Polarized Spectral Detection.

On-chip multi-dimensional detection systems integrating pixelated polarization and spectral filter arrays are the latest trend in optical detection instruments, showing broad application potential for diagnostic medical imaging and remote sensing. However, thin-film or microstructure-based filter arrays typically have a trade-off between the detection dimension, optical efficiency, and spectral resolution. Here, we demonstrate novel on-chip integrated polarization spectral detection filter arrays consisting of metasurfaces and multilayer films. The metasurfaces with two nanopillars in one supercell are designed to modulate the Jones matrix for polarization selection. The angle of diffraction of the metasurfaces and the optical Fabry-Perot (FP) cavities determine the spectrum's center wavelength. The polarization spectral filter arrays are placed on top of the CMOS sensor; each array corresponds to one pixel, resulting in high spectral resolution and optical efficiency in the selected polarization state. To verify the methodology, we designed nine-channel polarized spectral filter arrays in a wavelength range of 1350 nm to 1550 nm for transverse electric (TE) linear polarization. The array has a 10 nm balanced spectral resolution and average peak transmission efficiency of over 75%, which is maintained by utilizing lossless dielectric material. The proposed array can be fabricated using overlay e-beam lithography, and the process is CMOS-compatible. The proposed array enables broader applications of in situ on-chip polarization spectral detection with high efficiency and spectral resolution, as well as in vivo imaging systems.

Theoretical study of a Janus layered photonic structures based on improved particle swarm algorithm for detection of serum creatinine and glucose concentration

An improved particle swarm optimization (IPSO) algorithm is proposed to perform parameter optimization of the sensor which is realized by Janus layered photonic structures (LPS) based on the optical Tamm state (OTS) and defect layer, which can be used to detect serum creatinine (SCR) solution concentration (CSCR ) and glucose solution concentration (CG ) by adjusting the thickness and refractive index (RI) of the medium in the structure to control the peak and frequency changes of the transmission and absorption peaks. Due to the characteristic of Janus, the light incident from different directions can produce different effects. The OTS based on metal properties has sensitive and narrow absorption peaks when the light comes in forward propagation, its absorption characteristics allowing accurate measurement of CSCR with a high sensitivity (S) of 172 THz/RIU and a relevant quality factor (Q) of 651 and a lower detection limit (DL) of 2.3163 × 10−4. It has a significant Q of 4.5 × 104, DL of 4.825 × 10−5, and S of 11.7857 THz/RIU with its transmission characteristics which can be used to detect CG when the light comes in backward propagation. It can be said that the IPSO has a certain application prospect for the design of optical sensing.

Uni-and bidirectional soliton rains in a NALM mode-locked Tm-doped fiber laser

We report the generation of different drifting patterns of soliton rains in a Tm-doped fiber laser mode locked by the technique of nonlinear amplifying loop mirror. The directional control of drifting soliton rain has been achieved by varying pump power and polarization. At a stable pumping level, a kind of bidirectional soliton rain is observed from a unidirectional one for the first time. In the bidirectional case, the forward and backward solitons, leaving from the two sides of the condensed phase, appear in the spectrum as two typical soliton peaks on a wide pedestal, 2 nm in separation. The spectral result implies that the secondary drifting solitons are formed by developing one strong sideband of the primary soliton rain, induced by a shift of the transmission peak.

A novel approach for constructing the calibration curve applied in determining the thickness of different types of materials

A solution using a gamma-ray beam to measure the thickness of materials with different elemental composition is necessary as this issue has not been previously addressed. Traditionally, a linear calibration curve is only utilized to determine the thickness of a specific material. This means that multiple separate calibration curves must be used when measuring the thickness of different types of materials, which results in increased time and cost. This study proposes a novel aproach for constructing calibration curves that can be applied to measure the thickness of materials with different elemental composition. The methodology and mathematical formalism are described. For each material type, the linear calibration curve (LCC) of lnR (R represents the ratio of areas under the transmission peak for measurements with and without a sample) versus thickness of material plate has been constructed. The slope of this linear calibration curve, depending on the linear attenuation coefficient (LAC) of the material, enables easy determination of material thicknesses. To assess accuracy, we conducted thickness measurements on reference material plates including aluminum, steel, copper, and graphite. The obtained results indicate that relative deviations between measured and reference thicknesses are below 2.39%, confirming the usefulness and reliability of the proposed approach in measuring thickness for different types of materials.

Tunable slow light device based on a graphene metasurface.

Slow light devices have significant applications in memory, switching, and quantum optics. However, the design and fabrication of slow light devices with large tunable group delay are still challenging. Here, a graphene-based slow light device that can electrically modulate the group delay of terahertz (THz) waves is proposed and experimentally demonstrated. The unit cell of the device consists of a U-shaped metal resonator and an Ω-shaped metal resonator, with three graphene ribbons embedded between the two resonators. Under electrical stimuli, a relatively high amplitude modulation depth of 74% is achieved and the maximum transmission amplitude is as high as 0.7 at the transmission peak of 0.6 THz. Most importantly, the maximum group delay variation reaches 5 ps at 0.76 THz and the maximum group delay amplitude is as high as 8.8 ps. The experiment shows good agreement with simulation. This study paves a new way for developing novel switchable nanophotonic devices and slow light devices.

The Prevalence of Human Plasmodium Species during Peak Transmission Seasons from 2016 to 2021 in the Rural Commune of Ntjiba, Mali.

Up-to-date knowledge of key epidemiological aspects of each Plasmodium species is necessary for making informed decisions on targeted interventions and control strategies to eliminate each of them. This study aims to describe the epidemiology of plasmodial species in Mali, where malaria is hyperendemic and seasonal. Data reports collected during high-transmission season over six consecutive years were analyzed to summarize malaria epidemiology. Malaria species and density were from blood smear microscopy. Data from 6870 symptomatic and 1740 asymptomatic participants were analyzed. The median age of participants was 12 years, and the sex ratio (male/female) was 0.81. Malaria prevalence from all Plasmodium species was 65.20% (95% CI: 60.10-69.89%) and 22.41% (CI: 16.60-28.79%) for passive and active screening, respectively. P. falciparum was the most prevalent species encountered in active and passive screening (59.33%, 19.31%). This prevalence was followed by P. malariae (1.50%, 1.15%) and P. ovale (0.32%, 0.06%). Regarding frequency, P. falciparum was more frequent in symptomatic individuals (96.77% vs. 93.24%, p = 0.014). In contrast, P. malariae was more frequent in asymptomatic individuals (5.64% vs. 2.45%, p < 0.001). P. ovale remained the least frequent species (less than 1%), and no P. vivax was detected. The most frequent coinfections were P. falciparum and P. malariae (0.56%). Children aged 5-9 presented the highest frequency of P. falciparum infections (41.91%). Non-falciparum species were primarily detected in adolescents (10-14 years) with frequencies above 50%. Only P. falciparum infections had parasitemias greater than 100,000 parasites per µL of blood. P. falciparum gametocytes were found with variable prevalence across age groups. Our data highlight that P. falciparum represented the first burden, but other non-falciparum species were also important. Increasing attention to P. malariae and P. ovale is essential if malaria elimination is to be achieved.

Quantum resonant optical bistability with a narrow atomic transition: bistability phase diagram in the bad cavity regime

We report on the observation of a novel manifestation of saturation-induced optical bistability in a resonantly pumped optical ring cavity interacting strongly with a cloud of atoms via a narrow atomic transition. The bistability emerges, above a critical pump rate, as an additional peak in the cavity’s normal mode spectrum close to atomic resonance. This third transmission peak is usually suppressed due to strong resonant absorption, but in our experiment it is visible because of the linewidth of the atomic transition being much smaller than that of the cavity, which sets the experiment into the bad-cavity regime. Relying on complete saturation of the transition, this bistability has a quantum origin and cannot be mimicked by a classical material presenting a nonlinear refraction index. The appearance of the central peak in addition to the normal modes is predicted by a semi-classical model derived from the Tavis–Cummings Hamiltonian from which we derive a bistability phase diagram that connects our observations with former work on optical bistability in the good cavity regime. The phase diagram reveals several so far unexplored bistable phases.

An accurate measurement method of gear transmission error based on a double-angle measurement device

In this paper, a geometric model of a grating and reading head was established, where the relationship between the angle deviation, which was compensated for by double reading heads, and the actual angle is deduced. A new measurement method was proposed by applying the clock pulse counting method to the measurement of the transmission error of the gear pair input-and-output angle encoder while taking into account the gear pair’s transmission error. To demonstrate the feasibility of this measurement method, a transmission error test bench of involute gear pairs was built. Based on the output gear, the counted pulses were divided into integer pulses and non-integer pulses, and a transmission error curve was obtained by processing the pulses. The transmission errors of a helical gear with untrimmed angles and a gear pair with trimmed angles were also measured. Compared with the untrimmed gear pair, the first-order amplitude of the trimmed gear pair was reduced by 25.25%, 0.79%, and 16.9%, but other whole-order full-harmonic amplitudes were excited. However, the peak value of the single tooth surface of the trimmed gear pair was generally less than that of the untrimmed gear pair. The peak transmission error and the amplitude of the tooth harmonic frequency had good repeatability, within 16%, which verified the feasibility of the transmission error test method. The measurement precision reached 1 arcsecond in the tooth frequency.

Transmission of vertical vibration through a seat cushion at the seat pan: Effect of foam physical properties during different excitation magnitudes

The vibration characteristics of car seats directly influence the ride comfort. Polyurethane foam is the key part of a seat, and its physical parameters have an important impact on the seat. In this study, the influence of the foam thickness and foam hardness on the vibration characteristics of seat cushion with different excitation magnitudes was investigated by using transmissibility and seat effective amplitude transmissibility (SEAT) value. First, vibration tests were carried out at a vertical vibration simulator with width-limited white noise vibration frequencies from 0.5 to 20 Hz with root-mean-square (r.m.s.) values of 0.4, 0.8, and 1.2 m/s2, the acceleration at the platform and the body-foam interfaces were measured to calculate the transmissibility, and the influence of the foam physical properties on the transmissibility was analyzed. Then, the SEAT value was introduced to assess the vibration isolation efficiency of the foam cushion, and the influence of the foam physical properties of the foam cushion on the vibration isolation efficiency was analyzed. With increasing thickness of the foam and decreasing hardness of the foam at the seat pan, the peak transmissibility increased and the resonance frequency decreased. The SEAT values show that increasing the foam thickness is beneficial to the improvement of the vibration isolation efficiency of the seat, but there is a diminishing return; the combination of physical parameters of low hardness and high thickness could make the vibration isolation performance of the seat better. In addition, the nonlinearity of human-seat system during different vibration magnitude was found.

Performance of finite-size metal-dielectric nanoslits metasurface optical filters.

In this work, we analyze the performance of finite-size metal-dielectric nanoslits guided mode resonance metasurface optical filters by using finite-difference time-domain simulations and spatial Fourier transform analysis. It is shown that in the direction of the nanoslits period, the critical size required to maintain the performance of the corresponding infinite size filter is the product of the nanoslits period and the quality factor of the infinite size filter. Size reduction in this dimension below the critical dimension reduces the peak transmittance and broadens the spectral linewidth of the filter. In the dimension orthogonal to the nanoslits period direction, the critical dimension size required is not related to the quality factor of the corresponding infinite size filter. Our analysis shows that the critical size is 12 times the filter peak wavelength in the orthogonal dimension for maintaining the filter performance. The 12 times filter wavelength requirement corresponds to the second zero of the Fourier transform of the aperture function.

Programmable nanophotonic planar resonator filter-absorber based on phase-change InSbTe

Reconfigurable plasmonic-photonic electromagnetic devices have been incessantly investigated for their great ability to optically modulate through external stimuli to meet today's emerging needs, with chalcogenide phase-change materials being promising candidates due to their remarkably unique electrical and optics, enabling new perspectives in recent photonic applications. In this work, we propose a reconfigurable resonator using planar layers of stacked ultrathin films based on Metal-dielectric-PCM, which we designed and analyzed numerically by the Finite Element Method (FEM). The structure is based on thin films of Gold (Au), aluminum oxide (Al2O3), and PCM (In3SbTe2) used as substrate. The modulation between the PCM phases (amorphous and crystalline) allows the alternation from the filter to the absorber structure in the infrared (IR) spectrum (1000–2500 nm), with an efficiency greater than 70% in both cases. The influence of the thickness of the material is also analyzed to verify tolerances for manufacturing errors and dynamically control the efficiency of transmittance and absorptance peaks. The physical mechanisms of field coupling and transmitted/absorbed power density are investigated. We also analyzed the effects on polarization angles for Transversal Electric (TE) and Transversal Magnetic (TM) polarized waves for both cases.

Development of Visible Multi−Bandpass Filter Based on F−P Structure

In order to reduce the noise interference of smart wearable devices, spectral filtering technology is used to suppress noise. This technology prevents interference signals from entering the detector from the source, thereby achieving high−precision noise reduction processing. According to the system requirements, a multi−bandpass filter with a wavelength range of 400~1000 nm was designed and prepared on a BK7 substrate. Ta2O5 and SiO2 were selected as the high− and low−refractive−index materials, respectively. By analyzing the −Fabry–Perot narrowband theory, the bandwidth matching coefficient was computed, and the interference order was calculated using the interval of the transmission peak wavelengths. Multiple F−P coating systems were connected through the matching layer to adjust the position of the transmission peak and broaden the bandwidth range. The design was optimized using Macloed film system design software, resulting in the design of a wide half−wave and cutoff multi−bandpass filter. The appropriate preparation process was chosen based on changes in refractive index, surface roughness, and the temperature gradient of the materials. The filter was then produced using Leybold SYRUSpro1110. Sensitivity, filter roughness, and the weak absorption of the film system were tested, and the results met the system requirements.

Active control of resonant asymmetric transmission based on topological edge states in paired photonic crystals with a Ge2Sb2Te5 film.

For many high-precision applications such as filtering, sensing, and photodetection, active control of resonant responses of metasurfaces is crucial. Herein, we demonstrate that active control of resonant asymmetric transmission can be realized based on the topological edge state (TES) of an ultra-thin G e 2 S b 2 T e 5 (GST) film in a photonic crystal grating (PCG). The PCG is composed of two pairs of one-dimensional photonic crystals (PCs) separated by a GST film. The phase change of the GST film re-distributes the field distributions of the PCG; thus active control of narrowband asymmetric transmission can be achieved due to the switch of the on-off state of the TES. According to multipole decompositions, the appearance and disappearance of the synergistically reduced dipole modes are responsible for the high-contrast asymmetric transmission of the PCG. In addition, the asymmetric transmission performances are robust to the variation of structural parameters, and good unidirectional transmission performances with a high peak transmission and high contrast ratio can be balanced, as the layer number of the two PCs is set as four. By changing the crystallization fraction of GST, the peak transmission and peak contrast ratio of asymmetric transmission can be flexibly tuned with the resonance locations kept almost the same.

Exploring Photonic Crystals: Band Structure and Topological Interface States

The physical mechanisms supporting the existence of topological interface modes in photonic structures, formed with the concatenation of two finite, N-period, one-dimensional photonic crystals, are investigated. It is shown that these mechanisms originate from a specific configuration of bands and bandgaps of topological origin in the band structure of the concatenated structure. Our analysis reveals that the characteristics of such a configuration depend on the structural parameters, including the number, N, of unit cells, and determine the properties of the corresponding resonant transmission peak. It was shown that the width and maximum value of the transmission peaks decrease with N. These results not only provide new physical insight into the origin and nature of such modes, but also can be used to control and manipulate the transmission peak properties, such as peak values, full width at half maximum (FWHM), and Q-factor, which are of special interest in the fields of optical sensing, filters, etc.

Plasmon Hybridizations in Compound Nanorod-Nanohole Arrays.

This study shows that a hybridized plasmonic mode, represented by an additional transmission peak, in a compound structure consisting of a nanorod embedded in a nanohole can be effectively described as a quasi-dipole oscillator. When two nanorods are introduced into a nanohole, these two quasi-dipoles can couple and hybridize, giving rise to two additional transmission peaks in the enhanced optical transmission spectrum. The relative intensities of these peaks can be controlled by adjusting the incident polarization, while their separations can be tuned by modifying the length of the nanorods. The concept of quasi-dipoles in compound nanohole structures can be further extended to predict the coupling behavior of even more complex compound configurations, such as multiple nanorods within nanoholes, resulting in the generation of multiple hybridization states. Consequently, the shape and response of the transmission peaks can be precisely engineered. This strategy could be used to design nanohole-based metasurfaces for applications such as ultra-thin optical filters, waveplates, polarizers, etc.