Transmission Filters Research Articles

Mathematical modeling development and synthesis of tapered transmission line resonators and filters

Abstract Tapered transmission line resonators can be used to achieve specific frequency responses and enhance the performance of microwave devices and impedance transformers. To develop a mathematical model (transfer function) of such a wideband resonator will facilitate the construction of an equivalent circuit and the synthesis of resonators of this type. This study discusses the system modeling of tapered transmission line (TTL) resonators using the singularity expansion method (SEM). The transfer function is analytically established for two types of wideband TTL resonators: exponential tapered transmission lines (ETTL) and linear tapered transmission lines (LTTL). The analytical transfer function is derived for the general tapered ratio (k/β). The physical poles of the structures are identified using the pole-energy matrix pencil (MP) approach. The transfer function expression is then utilized to develop an accurate equivalent lumped-element circuit for the TTL resonator. This study’s simplified approach for estimating the transfer function and associated poles and zeros from the S-parameters is the main contribution, whereas it is known that the transfer function becomes complicated for wideband frequency response. A direct synthesis approach is presented to develop two-stage and four-stage ultra-wideband (UWB) bandpass filters. The agreement between the frequency response data and the derived transfer function of the system model of the synthesized TTL filters demonstrates the reliability of the presented method. The proposed system modeling and synthesis methodology can be applied to more sophisticated filter TTL architectures.

All-dielectric transmissive narrow-band filters adjustable within wide spectral range

The challenge of obtaining transmission spectra with both a wider tunable spectral range and high resolution persists. In this paper, a novel all-dielectric transmissive grating structure based on Mie resonance is proposed. The structure excites the Mie resonance by embedding a high refractive index contrast grating in a KF-Si film system band-stop filter. The dipole resonance energy is confined within the high refractive index silicon grating material, expanding the cutoff bandwidth of the KF-Si film system to over 400 nm and achieving single-peak transmission in the visible range. And the continuous transmission spectrum has an adjustable range of 300 nm with the highest spectral resolution (FWHM) (∼20 nm) can be achieved by adjusting the grating period. To suppress the coupling energy excitation between the higher-order magnetic dipole and the substrate, a silicon-rich nitride (SRN) matching layer is introduced between the KF-Si film system and the substrate. This layer enhances the intensity of the resonance peaks while simultaneously suppressing the short-wavelength sidebands, thereby improving the saturation and purity of the spectrum. In addition, we obtained a large angular tolerance of up to 15° by stacking the silicon film system. This work is of great significance for the advancement of hyperspectral imaging and display technology.

Mammalian perfusion cultivation at high L-Arginine concentration for efficient production of recombinant protein by increasing perfusion filter transmission

Cultivations of Chinese Hamster Ovary (CHO) cells in a perfusion setup were conducted in the presence of super physiological concentrations of L-Arginine to investigate the impact on transmission through the perfusion filter for production of a recombinant domain antibody. Our study revealed that the presence of L-Arginine within the range of 30–50 mM had a positive impact on transmission. However, the higher concentrations were found to have a negative correlation with cell viability, and an optimal concentration of approximately 40 mM was identified. The supplementation of L-Arginine improved overall cultivation performance and enhanced product quality attributes. As a result, our findings demonstrate that the supplementation of L-Arginine to mammalian perfusion cultivations stands as an effective method to address transmission issues, exerting a broad impact on process and production of recombinant proteins.

Compact widely tunable laser integrated on an indium phosphide membrane platform

We present the design, fabrication, and characterization results of a compact, widely tunable laser realized on an indium phosphide membrane-on-silicon (IMOS) platform. The laser features a compact Mach–Zehnder interferometric structure as the wavelength-selective intracavity filter with a footprint of 0.13 mm2. The filter design is optimized to ensure narrow filter transmission and high side-mode-to-main-mode-ratio, enabling single-mode operation for the laser. The high optical confinement on the IMOS platform can support tight waveguide bends. Leveraging this, the laser achieves a short cavity length, further enhancing the single-mode operation. Measurement results indicate a threshold current of 29 mA and a maximum on-chip output power of approximately 3.6 dBm and wall plug efficiency of 1.8%. The side-mode suppression ratio ranges from 30 to 44 dB, with a tuning range spanning 40 nm, from 1555 to 1595 nm. A complete tuning lookup table is generated via an automated setup incorporating a stochastic search algorithm.

The effect of sunglass filters on contrast sensitivity, monocular eye closure, and blinking rate in people with intermittent exotropia

ABSTRACT Clinical relevance Transient monocular eye closure and photosensitivity under bright light have been reported in people with intermittent exotropia (IXT). The exact mechanism of these symptoms has not been established. Background This study examines the effect of sunglass filters on contrast sensitivity (CS), transient monocular eye closure, and blinking rate under bright light in people with IXT. Methods Forty participants with IXT and complaints of photosensitivity were included in the study. The binocular CS test was performed under mesopic and photopic conditions with and without glare, and with and without two filters with different grades of light transmission (filter 1: 44–80%; filter 2: 20–43% light transmittance). The effect of two filters on transient eye closure, contrast sensitivity, and blinking rate was assessed under bright light. Also, participants were divided into 3 groups based on their degree of control of fusion (good, fair, and poor control). Results The mean age of the participants was 12.0 years ± 8.0 (standard deviation) (range: 7–40 years). There was no significant difference between the age (p = 0.139), stereopsis (p = 0.134), as well as the near and far degree of deviation (p = 0.516, and p = 0.237) between the three groups of fusion control. Under mesopic conditions with glare, mean binocular CS was significantly higher with filters (p < 0.001). Without filters, 57.5% of the participants exhibited monocular eye closure under a photopic setting with additional glare. No participant showed eye closure using filter 2. People in the poor control group showed exodeviation before monocular eye closure (62.5% without filter and 12.5% with filter 1, p = 0.01). The blinking rate decreased from 36.0 ± 4.0 blinks per minute without filter to 21.0 ± 3.0 using filter 1, and 20.0 ± 3.0 with filter 2. Conclusion In people with IXT, wearing sunglass filters of different transmittance reduces monocular eye closure and blinking rate under bright light. To improve these symptoms, sunglasses can be considered for IXT.

Satellite Onboard Transmitter Design With Spread Spectrum MIMO Antenna for 5G Wireless Networks

AbstractThe 5G new era implements standalone satellite communications that support wireless networking systems for future mobile communications by locating multiple satellites in low Earth orbit to provide global coverage of the entire Earth's surface. In this research, a newly found model of a satellite onboard transmitter using a uniform circular array multiple‐input multiple‐output antenna was designed to operate at a carrier frequency of 12 GHz and derived theoretical equations compared to the real‐time scenario. The integration of spread spectrum with multiple‐input multiple‐output antenna provides an advantage for higher capacity. It has a higher percentage of gain amplification on improving the transmission of electromagnetic power to meet the bandwidth requirement of center operating frequency, and this can transmit over a bandwidth of 1.28 GHz. The proposed satellite onboard transmitter model design aims to minimize the components, increase the speed of operations for higher bandwidth, and transmit large amounts of information to a large group of users. The transmitter can operate for the speed of 1.28 Gbps using pseudo‐random code, direct‐sequence spread spectrum, quadrature phase shift keying modulation, bandwidth separated in bands for 64 symbols using 128 Chebyshev‐type bandpass filter for transmission using 128‐element uniform circular array multiple‐input multiple‐output antenna. The satellite transmitter antenna produces a maximum gain of 14.526 dBi, and a maximum directivity of 17.986 dBi, and the efficiency at 12 GHz is 45.1% for the radiated power at 0.93 mW. This satellite transmitter will interconnect 5G wireless networks for the application of mobile communications complement terrestrial‐dependent networks.

Inverse design of ultranarrow and high-efficiency color filters based on tandem convolutional neural networks

In this paper, an ultranarrow, high-efficiency color filter based on a two-dimensional grating nanostructure array is realized by a tandem inverse design network. The tandem inverse designed network is generated by connecting an inverse network with a pre-trained forward network. The tandem convolutional neural network successfully overcame the non-uniqueness problem of the training data. The performance of the networks is verified by a test set of 2592 data points, and the average MSE of the prediction results of the tandem network is 1.01 × 10−3. Extremely low error indicates that the tandem network can learn and capture the distribution characteristics of the transmission spectrum and give a reasonable design of the structural parameters. Finally, we obtained multiple inverse-designed transmissive color filters with ultranarrow linewidths and high efficiency, with central wavelengths between 480 nm and 630 nm. The linewidth and efficiency of each kind of color filter are less than 10.6 nm and higher than 60%. Narrow linewidths and wide wavelength tunability result in high color accuracy and a broad color gamut of the filters. The filters with two-dimensional metallic nanostructure array also show polarization-independent characteristics. Compared with the traditional method, this method can quickly and accurately design the structural parameters corresponding to the spectral response, which provides a new method for the nanostructure design.

Electrically Reconfigurable Phase-Change Transmissive Metasurface.

Programmable and reconfigurable optics hold significant potential for transforming a broad spectrum of applications, spanning space explorations to biomedical imaging, gas sensing, and optical cloaking. The ability to adjust the optical properties of components like filters, lenses, and beam steering devices could result in dramatic reductions in size, weight, and power consumption in future optoelectronic devices. Among the potential candidates for reconfigurable optics, chalcogenide-based phase change materials (PCMs) offer great promise due to their non-volatile and analogue switching characteristics. Although PCM have found widespread use in electronic data storage, these memory devices are deeply sub-micron-sized. To incorporate phase change materials into free-space optical components, it is essential to scale them up to beyond several hundreds of microns while maintaining reliable switching characteristics. This study demonstrated a non-mechanical, non-volatile transmissive filter based on low-loss PCMs with a 200 × 200 µm2 switching area. The device/metafilter can be consistently switched between low- and high-transmission states using electrical pulses with a switching contrast ratio of 5.5 dB. The device wasreversibly switched for 1250 cycles before accelerated degradation took place. The work represents an important step toward realizing free-space reconfigurable optics based onPCMs.

Scaling up multispectral color filters with binary lithography and reflow (BLR).

Efforts to increase the number of filters are driven by the demand for miniaturized spectrometers and multispectral imaging. However, processes that rely on sequential fabrication of each filter are cost ineffective. Herein, we introduce an approach to produce at least 16 distinct filters based on a single low-resolution lithographic step with minimum feature size of 0.6 μm. Distinct from grayscale lithography, we employ standard binary lithography but achieve height variations in polymeric resist through a post-development reflow process. The resulting transparent polymeric films were incorporated in Fabry-Perot cavity structures with cavity thickness ranging from 90 to 230 nm to produce transmittance across the visible spectrum. This binary lithography and reflow (BLR) process demonstrates control of the dielectric layer thickness down to ∼15 nm. This new process provides a cost-effective alternative to traditional techniques in fabricating microscopic transmission filters, and other applications where precise thickness variation across the substrate is required.

Quasi-bound states in the continuum empowering a transmissive terahertz narrowband filter with high Q and a broad sideband free of interferential distortion.

Most currently available terahertz (THz) narrowband filters contain a metal and a substrate, which introduce absorption loss and spectral fluctuations caused by a Fabry-Perot interference in substrates. To address these issues, we employ quasi-bound states in the continuum (BICs) for the design and realization of a substrate-free all-dielectric THz transmissive narrowband filter. Under oblique incidence, the symmetry-protected BICs break and collapse into high-Q transmissive quasi-BIC modes, thereby achieving narrowband filtering. The filter not only minimizes energy loss but also demonstrates a smooth filtering response without an interferential spectral fluctuation associated with the substrate. An experimental high Q value of ∼127 at 4.1 THz with a broad sideband of ∼1.5 THz with transmittance below 10% is achieved.

Learning a physics-based filter attachment for hyperspectral imaging with RGB cameras

Countless RGB cameras are ubiquitously distributed in our daily lives, serving to perceive and depict the diverse colors of the world. Reconstructing hyperspectral images (HSI) from these trichromatic cameras emerges as a promising solution to address the limitations of existing, costly hyperspectral imaging systems. The performance of HSI reconstruction relies heavily on the camera spectral response (CSR). Thus, designing a better CSR and putting it into practice is the critical issue for RGB-based HSI reconstruction. However, the CSR curves designed in the existing works are overly random, making them challenging to manufacture directly. Additionally, the designed CSR curves require modifications to the camera hardware, resulting in the loss of RGB imaging functionality. In this paper, we propose a hyperspectral imaging system, which involves enhancing the CSR curve of existing RGB cameras and preserving RGB imaging functionality by adding a learnable physics-based spectral filter. Specifically, we first parameterize the spectral filter transmittance as a function of the filter thicknesses, based on the physical constraints of the multilayer interference principle. Then, we propose a joint optimization framework in which the thicknesses of the filter and the hyperspectral reconstruction network are optimized. In this manner, the thicknesses of the filter are obtained and used to manufacture the filter directly. Finally, we construct a prototype and verify the benefits of our spectral filter design method through experiments including both synthetic data and real images.

Characterization of Thin AlN/Ag/AlN-Reflector Stacks on Glass Substrates for MEMS Applications

Thin metal layers such as silver (Ag) are being utilized for various optical and plasmonic applications as well as for electrical purposes, e.g., as transparent electrodes in display devices or solar cells. This paper focuses on optical MEMS applications such as the Fabry–Pérot interferometer (FPI). Within such filters, reflector materials such as distributed Bragg reflectors (DBRs) or subwavelength gratings (SWGs) have been widely used so far, whereas metallic thin films (MTFs) were limited in application due to their comparatively higher absorption. In this paper, thin sputtered Ag layers with thicknesses of 20, 40 and 60 nm on glass substrates have been investigated, and it is shown that the absorption is very low in the visible spectral range (VIS) and increases only in near-infrared (NIR) with increasing wavelength. Thus, we consider Ag-thin layers to be an interesting reflector material at least for the VIS range, which can be easily fabricated and integrated. However, Ag is not inert and stable when exposed to the atmosphere. Hence, it needs a passivation material. For this purpose, AlN has been chosen in this contribution, which can be deposited by sputtering as well. In this contribution, we have chosen thin AlN layers for this purpose, which can also be deposited by sputtering. Thus, various AlN/Ag/AlN-reflector stacks were created and patterned by lift-off technology preferably. The fabricated reflectors were characterized with respect to adhesion, stress, cohesion, homogeneity, and most importantly, their optical properties. It was found that the thickness of the AlN can be used to adjust the reflectance–transmittance ratio in the VIS range, and influences the adsorption in the NIR range as well. Based on the measured values of the reflectors with 40 nm Ag, an exemplary transmission filter characteristics has been predicted for a wavelength range from 400 to 800 nm. Both the maximum transmittance and the full width at half maximum (FWHM) can be tuned by variation of the AlN thickness from 20 to 60 nm.

Frequency selective surface filters with high-quality factors based on a Fano resonance.

In this work, we propose a design method of the narrow passband filter with a high Q-factor based on a Fano resonance. A single-layer metallic frequency selective surface (FSS) with a simple structure is first designed according to this idea, but the result is not satisfying since the filter transmittance will significantly decrease with the increase of the Q-factor due to the presence of an inherent ohmic damping. Further, to improve the design, a ceramic-based FSS filter based on the similar mechanism is proposed, and the requirements of the ultrahigh Q-factors can be met owing to the high permittivity and low loss tangent of microwave ceramics. The design strategy proposed in this paper may have a promising potential in modern wireless communication and related fields.

Bi‐Layer Reflection‐Transmission Dual‐Mode Metasurface with Flexible Bandwidth Control

AbstractA general strategy for designing bi‐layer reflection‐transmission integrated dual‐mode metasurfaces is presented with flexible bandwidth control. The design of such metasurfaces is enlightened by introducing a cutting hole in the ground plane, which not only acts as a filter for reflection and transmission but also has an eloquent role for bandwidth control. For proof of concept, a bi‐layer metasurface consisting of split ring resonators (SRRs) is designed on the top side and I‐shaped resonators on both sides. The proper adjustment of ground cut/hole shifts the two co‐polarized resonances (initial resonances of the SRRs) close to each other, and in addition, converts wideband cross‐polarized reflection (in between the two initial co‐polarized resonances of SRR) to co‐polarized reflection. This results in a broadband response by shifting two co‐polarized resonances close to each other and converting cross‐polarized reflection into co‐polarized reflection. It is demonstrated that a simple SRR can be responsible for broadband (7.9–12 GHz) reflection while an I‐shaped structure is used for transmission with central frequency at 17.58 GHz with independent phase controls. To endorse the proposed strategy, a metasurface prototype is fabricated and tested for the generation of vortex beams and focusing.

Prediction of metallo-dielectric transmission filter performance based on underlying dispersion relations

The dispersion relation for electromagnetic/optical wave propagation based on the Helmholtz equation for an infinite one-dimensional metallo-dielectric structure is derived using the Bloch theorem and heuristically modified to include material dispersion. We investigate the connection between the dispersion relation of an infinite metallo-dielectric structure with the transmittance characteristics of finite metallo-dielectric structures. The dispersion relation is used to determine the center wavelength and bandwidth as a function of the material properties and the thicknesses of the metal and dielectric layers. These estimates are found to be in excellent agreement with the values obtained from numerically calculated transmittance spectra using the transfer matrix method for finite metallo-dielectric structures with the same building units. The dispersion relation calculations and simulations for the transmittance are done for an ideal case where the real part for the refractive index of the metal and imaginary part for the refractive index of the dielectric are zero, and also with actual values of the real and imaginary parts of the refractive index for the metal and dielectric obtained from literature, instead of using the canonical Drude model for the metal. It is shown that the real part of the dispersion relation for the actual case is almost identical to the ideal case in the visible and NIR range, implying that essential information on the center wavelength and bandwidth can be obtained from the ideal dispersion relation. It is also found that an ideal metal and dielectric give near-unity transmittance in the passband. It is predominantly the presence of a finite real part of the refractive index of the metal that introduces attenuation. The effective refractive index of the structure can also be determined. Oscillations present in the transmittance spectrum can be explained as a Fabry–Perot effect. Approximate simple estimates of the center wavelength and bandwidth can be useful in initiating intelligent designs of finite metallo-dielectric filter structures for fabrication and characterization.

Enhanced nonlinear effect for generation of both bound state solitons and harmonic mode-locking with high signal-to-noise ratio based on crossed bandpass transmittance filters

Enhanced nonlinear effect for generation of both bound state solitons and harmonic mode-locking with high signal-to-noise ratio based on crossed bandpass transmittance filters

Global studies in waste management in mechanical workshops: evolution and future perspectives in the search for good practices

The environmental impacts that we are currently facing worldwide are due to a system that uses all available resources as if they were unlimited and therefore an uncontrolled amount of garbage has been generated that is causing damage to the environment and consequently to human health. . In search of solutions to these problems, new ways of managing waste have been implemented, which are often not applied due to lack of knowledge of them. Mechanical shops offer a variety of services, from tire repairs to collision services, whether for light or heavy vehicles, or promote maintenance of mechanical systems in general. These services generate several types of solid waste , including rags contaminated with oils or solvents, plastic containers, old tires, oil, transmission or air filters; plastic and metal body parts, batteries, glass and residual sludge, mostly hazardous waste. In this context, the objective of the article was to carry out a scientific mapping on waste management in mechanical workshops, and in search of good practices. For this, a quantitative and qualitative bibliometrics was carried out. The results indicate that life cycle analysis is the most appropriate tool to define the best use of the waste generated (co-products), followed by management systems and tools and cleaner production. Continuous staff training is essential; to maintain more efficient processes that present returns within each business. The adoption of environmental or management certifications is a big step within each business, but in small mechanical workshops, good waste management is quite sufficient and significant.

Design of an optical linear-discriminant filter: optimization for enhancement of filter transmittance and discrimination accuracy.

To discriminate fine concave and convex defects on a dielectric substrate, an optical machine learning system is proposed. This system comprises an optical linear-discriminant filter (OLDF) that performs linear discriminant analysis (LDA) of the scattered-wave distribution from target samples. However, the filter output from the OLDF is considerably weak and cannot be measured experimentally. Therefore, an algorithm is also proposed to improve the discrimination accuracy and filter transmittance. The designed filter is validated using a rigorous optical simulator based on vector diffraction theory. We also analyze and discuss a mechanism that provides high transmittance with high discrimination accuracy.

High quality factor metasurfaces for two-dimensional wavefront manipulation

The strong interaction of light with micro- and nanostructures plays a critical role in optical sensing, nonlinear optics, active optical devices, and quantum optics. However, for wavefront shaping, the required local control over light at a subwavelength scale limits this interaction, typically leading to low-quality-factor optical devices. Here, we demonstrate an avenue towards high-quality-factor wavefront shaping in two spatial dimensions based on all-dielectric higher-order Mie-resonant metasurfaces. We design and experimentally realize transmissive band stop filters, beam deflectors and high numerical aperture radial lenses with measured quality factors in the range of 202–1475 at near-infrared wavelengths. The excited optical mode and resulting wavefront control are both local, allowing versatile operation with finite apertures and oblique illumination. Our results represent an improvement in quality factor by nearly two orders of magnitude over previous localized mode designs, and provide a design approach for a new class of compact optical devices.

Machine learning for self-tuning mode-locked lasers with multiple transmission filters

We develop an adaptive control and self-tuning procedure for mode-locked fiber laser systems using multiple transmission filters. Each transmission filter set consists of two quarter-wave plates, a passive polarizer, and a half-wave plate to generate nonlinear polarization rotation (NPR). The energy performance of a fiber laser can be significantly increased by incorporating multiple NPR filters. Critical for self-tuning is the ability to properly characterize the average cavity birefringence, and, although the existed self-tuning algorithms can successfully classify the birefringence of single filter configuration, they cannot achieve real-time recognition of the cavity birefringence for multifilter laser systems. To remedy this issue, we propose three birefringence classification algorithms based upon learned libraries of observed dynamic patterns, including a uniform, a hierarchical, and a dynamic selection procedure from such patterns. A maximum seeking algorithm is then constructed to determine the optimal (maximal) wave plate(s) and polarizer(s) settings. Thus, the adaptive control and self-tuning scheme is designed as a combination of maximum seeking and dynamic library selection algorithms. Numerical implementation shows that the proposed self-tuning scheme achieves stable, high-energy mode-locking while circumventing the multipulsing instability.