Plasmonic Filter Research Articles

Robust global optimization of plasmonic filter based on Q factor analysis using graded index

Abstract To reduce the impact of uncertainties in various manufacturing processes while maintaining satisfactory performance level, we propose a robust global optimization approach for plasmonic filters based on extraordinary optical transmission by use of Q factor analysis with reasonable computational cost. The gradient index is employed as a metric for robustness, and the multiobjective genetic algorithm is selected as a global optimization tool. The figures of merit and gradient index are chosen as two objective functions with the design variables being the slit width, slit height, and period of the slit array, respectively. The finite element method is employed to investigate a variety of optical properties rigorously. The numerical optimization results demonstrate that the proposed approach provides improved effectiveness and efficiency in designing plasmonic filters under fabrication uncertainties by using Q factor analysis. The method proposed in this study enables systematic robust optimization while accounting for manufacturing uncertainties, which would be infeasible under typical time constraints. Specifically, within the proposed optimization framework, Q factor analysis can be employed due to a 20.60-times reduction in computational time. To the best of our knowledge, this represents the first robust optimization design for enhanced filter performance based on Q factor analysis in EOT, necessitating comprehensive spectrum calculations alongside fabrication tolerance considerations.

Plasmonic filter paper substrates coated with antibacterial silver nanoparticles for the identification of trace Salmonella

Plasmonic filter paper substrates coated with antibacterial silver nanoparticles for the identification of trace Salmonella

Numerical analysis of an all-fiber plasmonic polarization filter using dual elliptical gold thin layers deposited photonic crystal fiber

In order to solve the problems of high performance and small size incompatibility, as well as limited bandwidth, of traditional polarization filters in optical communication systems, this work presents an all-fiber polarization filter using dual elliptical gold layer deposited photonic crystal fiber by the finite element tool. The gold layers are plated on the inside of the two elliptical holes to create surface plasmon resonance effect, which cause the signal intensity in x-polarized direction to be much greater than that in y-polarized direction. The simulation results illustrate that when hole-to-hole pitch Λ is 2.0 μm, cladding hole diameter d 1 is 2.0 μm, two inner-holes’ diameter d 2 is 0.3 μm, spacing between two inner-holes d s is 0.755 μm, the major axis length of elliptical holes a is 2.0 μm, the minor axis length of elliptical holes b is 0.97 μm, the gold thin layer t is 100 nm, the proposed PCF filter exhibits good filtering performance at the communication wavelength of 1.55 μm, where the confinement loss in x- and y-polarized direction are 303.91 dB cm−1 and 0.06 dB cm−1, respectively. The crosstalk and operating bandwidth improve with the increment of device’s length, the 800 μm-long PCF filter possesses the maximum crosstalk of −211.14 dB and the bandwidth of 600 nm. Finally, the experimental scheme is also discussed. We believe that this photonic filter can play a significant role in optical communication, optical sensing, spectral analysis, and other related fields.

Numerical simulation of an in-fiber broadband plasmonic polarization filter using photonic crystal fiber with dual elliptical gold layers

The demand for advanced and compact photonic filters is increasing in today's optical communication systems. This work introduces a new all-fiber broadband polarization filter using photonic crystal fiber with dual elliptical gold layers. The filtering performance is evaluated and analyzed by the finite element method. The simulation results demonstrate that the two elliptical gold layers can effectively induce a significant change in the energy of x-polarized light, leading to a great difference between the two polarized lights. By selecting reasonable structural parameters of the proposed PCF, the 1 mm-long in-fiber filter has a maximum extinction ratio of -108.90 dB, a low insertion loss of 0.64 dB around 1.31 µm and an ultra-broad bandwidth of 1020 nm, covering two common communication windows of 1.31 µm and 1.55 µm. Additionally, the filtering experimental scheme is discussed. This filter is expected to drive the advancement of optical integrated chips and all-optical communication networks.

Solution‐Processed Disordered Plasmonic Surfaces as Optics for Infrared Imaging

AbstractIn recent years, thermal imaging and sensing technologies have seen dramatic increases in usage for a range of applications. However, the material cost and manufacturing complexity of infrared optics remain a major barrier toward their democratization. Here, a solution‐processed plasmonic reflective filter (PRF) is presented as a scalable, disordered, and low‐cost thermal infrared (TIR) optic. The PRF selectively absorbs sunlight and specularly reflects TIR wavelengths, with a performance comparable to state‐of‐the‐art infrared optics made of materials like Germanium. Unlike the latter, however, the PRF is fabricated using low‐cost materials and a “dip‐and‐dry” chemical synthesis technique, which enables orders of magnitude lower manufacturing costs. The PRF's optical functionality and integration into infrared imaging systems are experimentally demonstrated. The chemical synthesis technique also affords exceptional spectral tuneability and material compatibility compared to traditional fabrication methods. The PRF's tuneable and broadband TIR yield can be augmented by inexpensive dielectric or polymeric filters to yield novel capabilities such as wide‐area ambient temperature surveys. Practically, the PRF represents a significant advance toward democratizing the benefits of thermal imaging and sensing. Scientifically, it represents a previously unexplored optical functionality of disordered materials, and a new direction for versatile chemical synthesis in designing optical components.

Eco-friendly and biocompatible gelatin plasmonic filters for UV-vis-NIR light

The quest for environmentally sustainable materials spans many fields and applications including optical materials. Here, we present the development of light filters using a gelatin-based nanocomposite. Owing to the plasmonic properties of metallic nanoparticles (NPs), strong light-matter interactions, these filters can be customized across the UV-Visible-NIR spectrum. The filters are designed for modular use, allowing for the addition or removal of desired spectral ranges. Moreover, the nanocomposites are composed of biodegradable and biocompatible materials which highlight the intersection of chemistry and ecological awareness for the exploration of new eco-friendly alternatives. These plasmonic gelatin-based filters block light due to the Localized Surface Plasmon Resonance (LSPR) of the NPs and can be tailored to meet various requirements, akin to a diner selecting options from a menu. This approach is inspired by culinary techniques, and we anticipate it will stimulate further exploration of biomaterials for applications in optics, materials science or electronics.

Design and simulation of a compact plasmonic photonic crystal fiber filter with wide band and high extinction ratio

In order to realize the performance optimization and function expansion of modern all-optical systems, this work presents a compact plasmonic photonic crystal fiber (PCF) filter, using finite element tool. The deposited gold and graphene layers within the elliptical pores interact with the transmitted light, creating surface plasmon resonance (SPR) effect that amplifies the energy difference between x- and y-polarized light greatly. The simulation results indicate that the structural parameters are configured with the cladding holes' diameter of 0.6 μm, the large-holes’ diameter of 1.2 μm, the inner small-holes’ diameter of 0.2 μm, the lattice constant of 2.0 μm, the elliptical holes' minor axis length of 0.45 μm, the elliptical holes' major axis length of 1.30 μm, the gold layer thickness of 50 nm, and the graphene layer thickness of 20 nm, the central wavelength of the proposed PCF filter is 1.56 μm. When the length of this PCF filter is 1 mm, a maximum extinction ratio (ER) of 133 dB, an operating bandwidth exceeding 800 nm, covering two common communication windows of 1.31 μm and 1.55 μm, as well as a low insertion loss (IL) of 0.59 dB can be achieved. What's more, the feasibility of fabricating the device is also examined. This filter with compactness, broadband and high-extinction demonstrates promising applications in optical communication, optical sensing, optical computing, and various other fields.

Design of miniaturized wide band-pass plasmonic filters in MIM waveguides with tailored spectral filtering

This paper reports the design and numerical results of three new extremely compact and efficient flat-top band-pass plasmonic filters operating in the near-infrared region. The proposed structures are realized in metal–insulator-metal plasmonic waveguides based on stub, tilted T-junction and right-angle trapezoid configurations. A built-in parameterized genetic algorithm is applied to maximize the transmission efficiency, while at the same time contributing to shrinking down the size of the device structures. It is shown that the tunability of the optical filters can be realized by modulating their structural parameters to gain control over the band-pass filtering wavelengths. Numerical calculations are conducted based on the finite element method of CST Microwave Studio and demonstrate that the suggested ultra-compact plasmonic waveguide filters offer wide bandwidths of more than 270 nm, 424 nm, and 289 nm, with transmission efficiencies of higher than 80%, 74.2%, and 74.3%, respectively. The sizes of the proposed wavelength filters are 490 nm × 575 nm, 350 nm × 180 nm, and 420 nm × 150 nm, respectively, which make them attractive candidates for applications in high density photonic integrated circuits (PICs). As a result, because of the promising characteristics of the proposed topologies such as their high efficiency, compact size, tunability, and simple structure they may find applications in on-chip integration, laser technology, and multi-photon fluorescence.

Optimization of plasmonic nanofluid filters for spectral splitting photovoltaic/thermal systems

There remains a scarcity of studies on the utilization and optimization of core–shell plasmonic nanofluid filter although it shows potential in solar energy exploitation. To fill this research gap, this paper introduces an optimization methodology founded on merit function (MF) to optimize the Au@SiO2-based nanofluid filters for enhancing the photovoltaic/photothermal (PV/T) system performance. Initially, the MF model of the nanofluid filtered-PV/T system was constructed based on a reliable optical model and validated by referenced experimental results. Using these models, the effect of nanofluid parameters on the system performance and the mechanism of optimization procedure were investigated. Results indicated that modifying SiO2 shell thickness is a cost-effective means of tailoring the transmittance of the nanofluids compared to adjusting the Au core diameter. The optimization mechanism can be summarized as enhancing electrical efficiency or improving thermal efficiency to offset electricity losses. Furthermore, the MF of the Au@SiO2/EG nanofluid increased from 1.3737 to 1.3844 with optical thickness decreasing from 44 mm to 40 mm by mixing with Ag@SiO2 nanoparticles, indicating the cost-effectivity of blended nanofluid. The MF of the optimized blended nanofluids are 0.007–0.084 higher than those of the referenced nanofluids. This work offers a feasible pathway toward achieving high-performance nanofluid optical filters.

High-performance plasmonic mid-infrared bandpass filters by inverse design.

Plasmonic spectral filters composed of periodic nanostructured metal films offer novel opportunities for the development of multispectral imaging technologies in the mid-infrared region. However, traditional plasmonic filters, which typically feature simplistic structures such as nanoholes or nanorings, are constrained by a narrow bandpass and significant crosstalk, leading to limited practical performance. Filters designed using inverse techniques allow a substantial degree of freedom in creating intricate structures that align with desired spectral characteristics, including a quasi-square spectral profile, high transmission, wide full width at half maximum, and reduced crosstalk. In this study, we have utilized an inverse design algorithm to engineer high-performance bandpass filters for the mid-infrared range, achieving an average transmittance exceeding 80% within the bandpass window and below 10% in the stop band, which is comparable to that of commercial multilayer Bragg filters. Nanofabrication processes were employed to transfer the designed pattern into the gold film on ZnS substrate that is transparent in the mid-infrared range. The resulting filters exhibit spectral performance analogous to that of the inversely designed models, making them suitable for direct integration with mid-infrared photodetector arrays in multispectral imaging systems.

Multiple ultra-narrow band-stop filters based on MIM plasmonic waveguide with nanoring cavities

In this work, multiple ultra-narrow band-stop filters based on metal–insulator–metal (MIM) plasmonic waveguide filters with high efficiency are designed and analyzed numerically. The relationship between incident radiation and transmission spectra is investigated between 0.45 μm and 1.5 μm in the electromagnetic spectrum by finite-difference time-domain (FDTD) method. The designed structures have a bus waveguide coupled with nanoring cavity resonators of different sizes. Minimum transmission is 1.3% at 622 nm. The full width at half maximum (FWHM) is 8.64 nm and the quality factor is obtained as 72.33 in this wavelength. The highest quality factor is 185.48 and the lowest FWHM is 4.2 nm at 779 nm. The designed waveguide-based filters can be used for integrated optical devices from visible to near-infrared regimes.

SERS-based immunoassay on a plasmonic syringe filter for improved sampling and labeling efficiency of biomarkers.

Rapid, sensitive, and quantitative detection of biomarkers is needed for early diagnosis of disease and surveillance of infectious outbreaks. Here, we exploit a plasmonic syringe filter and surface-enhanced Raman spectroscopy (SERS) in the development of a rapid detection system, using human IgG as a model diagnostic biomarker. The novel assay design facilitates multiple passages of the sample and labeling solution through the detection zone enabling us to investigate and maximize sampling efficiency to the capture substrate. The vertical flow immunoassay process in this study involves the utilization of filter paper embedded with gold nanoparticles (AuNPs) to form a plasmonic substrate. Capture antibody (anti-human IgG) is then immobilized onto the prepared plasmonic paper and inserted into a vertical flow device (syringe filter holder). Sample solution is passed through the filter paper and the target antigen (human IgG) is selectively captured by the immobilized antibody to form an antibody-antigen complex. Next, functionalized AuNPs as extrinsic Raman labels (ERLs) are passed through the filter paper to label the captured biomarker molecules forming a layered structure. This sandwiched geometry enhances plasmonic coupling and SERS signal to provide highly sensitive detection of biomolecules. Systematic studies to investigate the impact of multiple infuse/withdraw cycles of the sample and labeling solutions reveal that antigen and ERL binding are maximized with 10 and 20 cycles, respectively. The optimized assay achieves a detection limit of ∼0.2 ng mL-1 for human IgG with a total assay time of less than 5 minutes, meeting the demands for rapid point of care diagnostics. Additionally, the optimized platform was implemented in the quantitative analysis of the SARS-CoV-2 nucleocapsid protein, the typical target in commercial, FDA-approved rapid antigen tests for COVID-19.

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

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

Tailored Fabrication of Plasmonic Film Light Filters for Enhanced Microalgal Growth and Biomass Composition.

Through plasmon resonance, silver and gold nanoparticles can selectively backscatter light within different regions of the visible electromagnetic spectrum. We engineered a plasmonic film technology that utilizes gold and silver nanoparticles to enhance light at the necessary wavelengths for microalgal photosynthetic activities. Nanoparticles were embedded in a polymeric matrix to fabricate millimeter-thin plasmonic films that can be used as light filters in microalgal photobioreactors. Experiments conducted with microalga Chlamydomonas reinhardtii proved that microalgal growth and photosynthetic pigment production can be increased by up to 50% and 78%, respectively, by using these plasmonic film light filters. This work provides a scalable strategy for the efficient production of specialty chemicals and biofuels from microalgae through irradiation control with plasmonic nanoparticles.

Plasmonic filter paper for preconcentration, separation and SERS detection harmful chemicals in chili product by fluid flow

We proposed a triple functional SERS substrate by immobilized Ag nanoparticles on the surface of filter paper. The high dense Ag nanoparticles were distributed on the SERS substrate via in-situ growth process. By optimizing the parameter in preparation process, the optimal filter paper SERS substrate was fabricated by using 30 mM of AgNO3 with 20 S growth time. Due to capillary-effect wicking of cellulose fiber, the paper SERS substrate provide simple, fast and pump-free function for transferring analyte onto sharp tip through development of fluid. The fluid flow also brings target concentrate effect within the tip area. Furthermore, the separation feasibility was obtained during the development process of fluid. The preconcentrated effects not only enhanced the SERS signal of analyte, but also improve the fluorescence visible effect. The filter paper SERS substrate was successfully used for separating, concentrating and detecting Sudan dye from chili product, the detection limit could achieve 10−6 M. This study developed a portable, cost-effective and eco-friendly SERS substrate for separating and detecting trace chemical in food.

Realization of a single-mode plasmonic bandpass filter based on a ring-shaped resonator and silver nanorods

Realization of a single-mode plasmonic bandpass filter based on a ring-shaped resonator and silver nanorods

High-sensitivity computational miniaturized terahertz spectrometer using a plasmonic filter array and a modified multilayer residual CNN

Abstract Spectrometer miniaturization is desired for handheld and portable applications, yet nearly no miniaturized spectrometer is reported operating within terahertz (THz) waveband. Computational strategy, which can acquire incident spectral information through encoding and decoding it using optical devices and reconstruction algorithms, respectively, is widely employed in spectrometer miniaturization as artificial intelligence emerges. We demonstrate a computational miniaturized THz spectrometer, where a plasmonic filter array tailors the spectral response of a blocked-impurity-band detector. Besides, an adaptive deep-learning algorithm is proposed for spectral reconstructions with curbing the negative impact from the optical property of the filter array. Our spectrometer achieves modest spectral resolution (2.3 cm−1) compared with visible and infrared miniaturized spectrometers, outstanding sensitivity (e.g., signal-to-noise ratio, 6.4E6: 1) superior to common benchtop THz spectrometers. The combination of THz optical devices and reconstruction algorithms provides a route toward THz spectrometer miniaturization, and further extends the applicable sphere of the THz spectroscopy technique.

Plasmonic band-gap filter by using tapered waveguide

Plasmonic band-gap filter by using tapered waveguide

High-performance plasmonic graphene-based multiplexer/demultiplexer

This paper proposes the use of two innovative single-mode plasmonic resonator-based filters to design a two-channel multiplexer/demultiplexer that demonstrates high transmission efficiencies and small sizes below 0.042 μm2. The proposed filters utilize slits in the center of rectangular and square-shaped resonators which results in a single-mode filtering effect. The study employs numerical and theoretical analyses, specifically the finite difference time domain method and coupled-mode theory, to evaluate the designed structures. The simulation results indicate that the rectangular-based demultiplexer has a cross-talk of −34 dB, a maximum transmission efficiency of 0.93, and an amplitude modulation of 0.44 dB, while the square-shaped resonator-based demultiplexer has a maximum transmission efficiency of 0.83, an amplitude modulation of 0.1 dB, and a cross-talk of −39.5 dB. These findings suggest that the proposed structures hold potential for application in optical communication systems.

Investigation of perfect narrow-band absorber in silicon nano hole array

In this paper, we proposed a triple layer structure consisting of the bottom silver layer, thin silicon oxide space layer, and ultrathin semiconductor silicon film with nano hole array achieving three absorption peaks with narrow band. The absorption spectrum can be easily controlled by adjusting the structural parameters including the radius and period of the nano hole array, and the maximal absorption can reach 99.0% and the narrowest full width of half maximum can reach about 6.5 nm in theory. We also clarified the physical mechanism of the proposed structure in details by finite-difference time-domain simulation, in which the three narrow band perfect adsorption peaks can be attributed to electric dipole resonance, magnetic dipole resonance and plasmonic resonance respectively. At the same time, we used a low-cost nanosphere lithography method to fabricate the proposed nano hole array in large area. In experiment, the absorption peak of the proposed triple layer structure can reach up to 98.3% and the narrowest full width of half maximum can reach up to about 10.1 nm. The highest quality factor Q can reach up to 98.4. This work can open a new avenue for high-quality factor narrow band perfect absorption using ultrathin semiconductor film and benefit for many fields such as infrared sensors, plasmonic filters, and hyperspectral imaging.