Extremely Sensitive Photonic Crystal Fiber–Based Cancer Cell Detector in the Terahertz Regime

A new photonic crystal fiber (PCF)–based, hollow-core, optical waveguide is proposed and numerically investigated to quickly identify numerous species of cancerous cells in the human body. Typical and cancerous cells have different refractive indices (RIs), and via this characteristic, the other important optical parameters are evaluated. The guiding properties of this proposed cancer cell sensor are analyzed in the COMSOL Multiphysics environment which used the finite element method as mathematical tool to solve differential equations. Furthermore, to ensure the highest simulation accuracy, extremely fine mesh elements are introduced. The simulation studies confirm that the proposed sensor, at 2.5 THz, achieves an extremely high relative sensitivity of almost 98% with negligible loss (< 0.025 dB/cm). Furthermore, a high numerical aperture (NA) and spot size, with low modal area, enhance the propagation characteristics of the sensor to a new height. The sensor’s physical structure is very simple so that it can be easily fabricated with modern fabrication technology. Thus, it seems that this sensor will open a new door in the field of detecting and diagnosing different cancer cells.

     

Theoretical Study of a Planar Structure Plasmonic Nanolaser in Visible Regime

The potential of a plasmonic nanolaser using semiconductor gain to compensate the metal loss was investigated theoretically in multilayer planar structure geometry. The propagation constant of surface plasmon (SP) mode, Purcell factor, and modal gain were calculated via transfer matrix method. Near SP resonance, the Purcell factor shows sensitive frequency dependence and exponential decay with distance. The huge Purcell factor leads to an impractical current density about several hundreds kiloampere/square centimeter (kA/cm²). When the spectra peak of optical gain in a semiconductor is shifted about 0.7 eV below SP resonance, the moderate Purcell factor shows a rather broadband enhancement. Net modal gain was achieved at an injected current density of 12.1 kA/cm², comparable to that of conventional photonic laser diodes. The structure is further optimized by inserting a (low permittivity) dielectric spacer between the semiconductor active region and metal.

     

Spectral Tunability and Selectivity Based on Multiple Resonance Modes in End-Coupled Sectorial-Ring Cavity Waveguide

A plasmonic nanodevice in end-coupled sectorial-ring cavity waveguide is reported, and the spectral characteristic of the novel system is studied. It is built with sectorial-ring cavity resonator end-coupled to plasmonic waveguide, and  this resonator is an oversize central angle (θ), alterable symmetry plane angle (ϕ), and fixed radius and gap, which has the advantages of forming split-ring-like, realizing asymmetrical cavity, and achieving spectral tunability and selectivity. The two-dimensional simulation indicates that the extra noninteger and traditional integer resonance modes are excited in the novel system, and the noninteger resonance modes are not achievable for the circular-ring cavity waveguide. It displays that these resonance modes of the novel system are drastically affected by changing the position of ϕ, which has different changes on maximum transmittances but is almost unchanged on resonance wavelengths. Importantly, the multiple resonance modes are highly sensitive to ϕ, and the proper modes are significantly enhanced, weakened, excited, or disappeared. It also displays that these resonance modes of the novel system are efficiently affected by changing the size of θ, which has similar and different influences on resonance wavelengths and maximum transmittances. This work shows that the method helps in designing accurately the transmission spectrum with prospective modes in nanophotonics, and the structure facilitates for realization of tunable and selective multichannel nanofilter or nanosensor in integration.

     

Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor

Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic samples with a wide range of possible sensor designs such as interferometers and resonators ^1,2. Most of the existing RI sensing applications focus on biological materials in aqueous solutions in visible and IR frequencies, such as DNA hybridization and genome sequencing. At terahertz frequencies, applications include quality control, monitoring of industrial processes and sensing and detection applications involving nonpolar materials.Several potential designs for refractive index sensors in the terahertz regime exist, including photonic crystal waveguides ³, asymmetric split-ring resonators ⁴, and photonic band gap structures integrated into parallel-plate waveguides ⁵. Many of these designs are based on optical resonators such as rings or cavities. The resonant frequencies of these structures are dependent on the refractive index of the material in or around the resonator. By monitoring the shifts in resonant frequency the refractive index of a sample can be accurately measured and this in turn can be used to identify a material, monitor contamination or dilution, etc.The sensor design we use here is based on a simple parallel-plate waveguide ^6,7. A rectangular groove machined into one face acts as a resonant cavity (Figures 1 and 2). When terahertz radiation is coupled into the waveguide and propagates in the lowest-order transverse-electric (TE₁) mode, the result is a single strong resonant feature with a tunable resonant frequency that is dependent on the geometry of the groove ^6,8. This groove can be filled with nonpolar liquid microfluidic samples which cause a shift in the observed resonant frequency that depends on the amount of liquid in the groove and its refractive index ⁹.Our technique has an advantage over other terahertz techniques in its simplicity, both in fabrication and implementation, since the procedure can be accomplished with standard laboratory equipment without the need for a clean room or any special fabrication or experimental techniques. It can also be easily expanded to multichannel operation by the incorporation of multiple grooves ¹⁰. In this video we will describe our complete experimental procedure, from the design of the sensor to the data analysis and determination of the sample refractive index.     

Alphabetic-Core Assisted Microstructure Fiber Based Plasmonic Biosensor

Light control capability of photonic crystal fiber (PCF) is a unique feature which can be applied to improve biosensing and plasmonic performance. Here, we reported alphabetic-core microstructure fiber-based plasmonic biosensor. Three different alphabetic R-, M-, and S-shaped cores of PCF-based plasmonic microstructures show controllable light propagation to enhance biosensor sensitivity and resolution. The light-guiding properties and sensing performance are investigated numerically using the finite element method (FEM). The proposed R-shaped core (RSC), M-shaped core (MSC), and S-shaped core (SSC) PCF-based plasmonic sensors show the maximum wavelength and amplitude sensitivities of 12,000, 11,000, 10,000 nm/RIU and 478, 533, and 933 RIU⁻¹, respectively, in the refractive index (RI) range of 1.33 to 1.40. The sensors also exhibit promising wavelength resolution of 8.33 × 10⁻⁶, 9.09 × 10⁻⁶, and 1.0 × 10⁻⁶ RIU, with figure of merit (FOM) of 108, 143, and 217 RIU⁻¹ for RSC, MSC, and SSC PCFs, respectively. The tunable sensing performance is also observed in design structures due to controllable light traveling path and their interaction with analytes. The proposed alphabetic-core PCF SPR sensors would be a promising candidate for the application of light controlling, trapping in microscale environment, and biosensing.

     

Tunable Plasmon-Induced Transparency Effect in MIM Side-Coupled Isosceles Trapezoid Cavities System

We propose a plasmonic structure based on the metal-insulator-metal waveguide with the side-coupled isosceles trapezoid cavities. Both of the structures based on the side-coupled trapezoid cavities separated or connected with waveguides can realize the plasmon-induced transparency (PIT). By adjusting the structure parameters, the off-to-on PIT response can be tunably achieved. The coupled mode theory (CMT) method is used to study the PIT phenomenon and explain the transmission characteristics. This work may provide a potential way for designing highly integrated photonic devices.

     

Multilayer Hybrid Plasmonic Nano Patch Antenna

This is the first report of a hybrid plasmonic nano patch antenna having metal insulator metal (HMIM) multilayer configuration. It is designed in a footprint area of 1.7 × 1.175 μm² to resonate at 1.55 μm wavelength. The proposed antenna is inset fed by an HMIM plasmonic waveguide for achieving proper impedance matching. It is observed, through electromagnetic numerical simulation, that the proposed plasmonic nano patch antenna emits a directional beam with a bandwidth, gain, and efficiency of 0.194 μm, 8.3 dB, and 96% respectively, which are significantly higher than previously reported designs. Since inset-fed antennas are suitable for developing high-gain antenna array, hence further, we examined antenna performance by designing antenna array. The proposed antenna is practically realizable and can be fabricated using standard semiconductor fabrication process. Moreover, it could be used for numerous chip scale applications such as wireless interconnects energy harvesting, photoemission, photo detection, scattering, heat transfer, spectroscopy, and optical sensing.

     

Design and Optimization of Open-cladded Plasmonic Waveguides for CMOS Integration on Si3N4 Platform

Herein, we present a design analysis and optimization of open-cladded plasmonic waveguides on a Si₃N₄ photonic waveguide platform targeting CMOS-compatible manufacturing. For this purpose, two design approaches have been followed aiming to efficiently transfer light from the hosting photonic platform to the plasmonic waveguide and vice versa: (i) an in-plane, end-fire coupling configuration based on a thin-film plasmonic structure and (ii) an out-of-plane directional coupling scheme based on a hybrid slot waveguide. A comprehensive numerical study has been conducted, initially deploying gold as the reference metal material for validating the numerical models with already published experimental results, and then aluminum and copper have been investigated for CMOS manufacturing revealing similar performance. To further enhance coupling efficiency from the photonic to the plasmonic part, implementation of plasmonic tapering schemes was examined. After thorough investigation, plasmo-photonic structures with coupling losses per single interface in the order of 1 dB or even in the sub-dB level are proposed, which additionally exhibit increased tolerance to deviations of critical geometrical parameters and enable CMOS-compatible manufacturing.

     

Novel Dielectric-Loaded Plasmonic Waveguide for Tight-Confined Hybrid Plasmon Mode

In this paper, a novel metal-dielectric waveguide structure is proposed to support hybrid long range surface plasmon polaritons (LRSPPs) with a highly confined mode field. The simulation results showed that our proposed structure has better mode confinement and propagation length compared to that of conventional dielectric-loaded surface plasmon polaritons (DLSPPs) waveguides. This structure offers greater flexibility for the design of surface plasmon polaritons (SPPs) waveguides by altering the trade-off between mode confinement and propagation length. The proposed structure has significant potential for application in highly integrated photonic circuits.     

Reconfigurable Plasmonic Logic Gates

Reconfigurable one-, two-, and three-bit plasmonic logic gate configurations have been proposed, which work by covering a straight slot waveguide with materials with tunable dielectric constants, such as graphene. By encoding the logic states in the values of dielectric constants as opposed to different waveguides, the plasmon excitation problems are minimized and the simplified logic gate configurations could be easily implemented.

     

Direct Coupling Strategy in Plasmonic Nanocircuits for Low Loss and Easy Fabrication

Plasmonic nanocircuits can deliver light in subwavelength scale, however, require state-of-the-art fabrication process due to the ultra-small footprints. Here, we introduce direct coupling strategy based on metal-insulator-metal (MIM) waveguide systems to reduce the system loss as well as the fabrication difficulty and increase the structural stability. Following this strategy, the coupling between the input waveguide and square ring resonator (SRR) can be realized via an aperture, and for the coupling between SRRs, the metal gap can be removed. The numerical results show that such direct coupling can produce similar effects with conventional indirect coupling in MIM waveguide systems, and the physics mechanism behind as well as influences of geometric parameters on transmission spectrum is also investigated. This work provides a simpler approach to realize on-chip plasmonic nanodevices, such as filters, sensors, and optical delay lines, in practice.

     

Graphene Hybrid Surface Plasmon Waveguide with Low Loss Transmission

In this paper, a novel graphene hybrid surface plasmon waveguide structure is designed. Based on the finite element method, the mode characteristics, the quality factor, and the gain threshold of the waveguide structure are analyzed. The results show that the optical field constraint of the designed waveguide can reach a better level of deep sub-wavelength under the optimal parameters of 1550-nm working wavelength. The structure is applied to a laser, and the high quality factor, the low energy loss, the low threshold limit, and the ultra-small effective mode field area are obtained by adjusting waveguide design parameters. Compared with the common waveguide structure, this structure has stronger optical field limiting ability and microcavity binding ability. It provides theoretical and technical support for the development of new high-efficiency nano-laser devices and is expected to be applied to fields such as on-chip interconnects, photonic integrated circuits, optical storage, and optical signal processing.

     

Coated Drop-Shaped Nanowires for Guiding THz Surface Plasmon Polaritons with Nanoscale Confinement and Ultra-Long Propagation Distances

Focusing far beyond the diffraction limit is very important for terahertz (THz) wave applications due to its much longer wavelength compared with optical wave. Surface plasmon polaritons (SPPs) on metal wires are frequently used to attain this focusing. However, when the mode width is reduced down to the nanometer scale, the mode loss is very high. Here, a coated drop-shaped nanowire (CDSN) is proposed for guiding THz SPPs with both ultra-strong mode confinement (10 nm) and extreme-long propagation length (1~15 mm), which result from the distinctive mode fields around the top and bottom arcs, respectively, of the metal wire. The fantastic mode properties make the waveguide very useful in nanophotonics, bio-photonics, and highly integrated photonic circuits.     

Photonic crystal nanostructures for optical biosensing applications

We present the design, fabrication and optical investigation of photonic crystal (PhC) nanocavity drop filters for use as optical biosensors. The resonant cavity mode wavelength and Q-factor are studied as a function of the ambient refractive index and as a function of adsorbed proteins (bovine serum albumin) on the sensor surface. Experiments were performed by evanescent excitation of the cavity mode via a PhC waveguide. This in turn is coupled to a ridge waveguide that allows the introduction of a fluid flow cell on a chip. A response of ∂λ/∂c=(4.54±0.66)×10⁵ nm/M is measured leading to a measured detection limit as good as  fg or  pg/mm²in the sensitive area.     

Highly Absorptive Chiral L-Shape MDM Plasmonic Metasurface as Multifunction Device: Design and Computational Studies

A multifunction plasmonic metasurface made of metal-dielectric-metal (MDM) layers is designed, and its chiral, absorption, and refractive index sensing properties are studied numerically using finite difference time domain (FDTD) computation. Top layer of the proposed novel metasurface consists of four L-shape gold strips arranged in a specific orientational sequence into a square unit cell whose period (along X direction and Y direction) is varied from 800 to 1400 nm in a step of 200 nm. The proposed super-structure shows highly chiral behaviour with multi bands circular dichroism (CD) between ~ 600 and 1200 nm with highest CD value of about 0.4. The CD spectral response is seen to be tunable with the structural parameters such as periods and appropriate L-strip length. True chiral nature of the proposed structure is cross-checked by computing its enantiomer that shows a mirror reflection of CD response of the original structure. Multi-work functionalities are investigated by studying perfect absorption and refractive index sensing properties of the metasurface. The study shows polarization independent multi-resonance spectral absorption that reaches to ~ 100% in some cases. On the other hand, refractive index sensing study shows high sensitivity (S) of 700–750 nm/RIU (per refractive index unit) with figure of merit (FOM) of 5–10. Owing to its exotic optical properties, the novel metasurface may be considered for chip level integration for multi-purpose work functionalities.

     

Tunable Spoof Surface Plasmons Bulleye Antenna

A tunable spoof surface plasmons antenna using sinusoidally modulated corrugated reactance surface based on a bulleye structure is proposed in this paper. The designed antenna is made of concentric metallic grooves etched on a metal plate, the depth of which is of sinusoidal periodic variation in the radial direction. This makes it possible that highly confined spoof surface plasmons along corrugated surface can be converted to radiation modes. The proposed bulleye antenna can work from 25.8 to 33 GHz and a bandwidth of 7.2 GHz and its main lobe can be directed at 30^∘ from the vertical direction at 30 GHz. This antenna has a maximum gain of 15 dB and its main lobe can scan from 14^∘ to 58^∘ by tuning the frequency from 28 to 32 GHz.

     

Tuning Plasmonic Near-Perfect Absorber for Selective Absorption Applications

In this study, we present a high-performance tunable plasmonic absorber based on metal-insulator-metal nanostructures. High absorption is supported over a wide range of wavelengths, which is retained well at a very wide range of incident angles too. The coupling process occurs with high absorption efficiency of ∼ 99% by tuning the thickness of the dielectric layer. In addition, a complex trapezoidal nanostructure based on simple metal-insulator-metal structures by stacking different widths of Cu strip-nanostructures in the vertical direction has been put forward to enhance light absorption based on selective absorption. A trapezoidal sample has been designed with a solar absorption as high as 95% at wavelengths ranging from 300 nm to 2000 nm for different operating temperatures. Furthermore, the optical absorber has a very simple geometric structure and is easy to integrate into complex photonic devices. Perfect absorption and easy fabrication of the metal-insulator-metal structure make it an attractive device in numerous photonic applications.

     

Hi-Bi Photonic Crystal Fiber for Broadband Filter Realization Using Copper Microwires

This paper presents a highly birefringence (Hi-Bi) photonic crystal fiber (PCF)-based single-polarization filter, which consists of copper microwires. Copper is chemically stable and the use of microwires is benefit to fabricate than any metal-coated PCF. The filter characteristics are inspected by the full-vector finite element method (FEM). The proposed filter can filter out y-polarized mode, while the x-polarized mode can be guided. The confinement loss of the y-polarized mode at the wavelength of 1.31 μm is achieved of 696.79 dB/cm, while the x-polarized loss is only 4.34 dB/cm. According to numerical results, 20 dB bandwidth of the proposed filter with a maximum value of crosstalk of 601.37 dB is achieved of 650 nm that range from 1.1 to 1.75 μm. Furthermore, the insertion loss of the guided mode (x-polarization) is as low as 0.142 dB for 1 mm of fiber length. Moreover, by optimizing the structural parameters, it has shown that the proposed filter can be effective at any wavelength at the optical communication window.

     

Ultra-stable D-shaped Optical Fiber Refractive Index Sensor with Graphene-Gold Deposited Platform

In this paper, we demonstrate a high sensitivity refractive index (RI) sensor with D-shaped structure covered with gold and graphene film. Specifically, the effect of structural parameters on the stability of fiber sensor is analyzed. In our research, it have been found that the sensor we proposed is not very sensitive to the change of structure parameters on the premise of ensuring the sensing precision. This advantage means that the requirements for machining errors are reduced. Further probing shows that the proposed sensor shows a maximum wavelength interrogation sensitivity of 4391nm/RIU with the dynamic refractive index range from 1.33 to 1.39 and a maximum amplitude sensitivity of 1139RIU^− 1 with the analyte RI = 1.38 in the visible region. The corresponding resolution are 2.28 × 10^− 5 and 8.78 × 10^− 6 based on the methods of wavelength interrogation and amplitude-(or phase-) based method. These characteristics of compact sensing architectures, simple to fabricate, and high sensitivity open the possibility of using this type of sensor in biological applications.

     

Electromagnetic Field Propagation in the One-Dimensional Silver Nanoparticle Dimer Chains: Hotspots and Energy Transport

Strong local electromagnetic (EM) fields and efficient EM energy transport in metallic nanostructures are two important issues in their applications in quantum computations/communications. We investigate the propagation characteristics of the hotspots in one-dimensional silver nanoparticle dimer chains, which combine the functions of the gap field enhancement and the waveguide. The near field and the far field induced interplay among the local field enhancement, the radiative interaction, and the dissipation affects significantly the EM field transport efficiency. Moreover, the correlation between local structure and global structure leads to the structure-dependent excitation. With the help of the combined effects of the structure-dependent excitation, the field confinement and the propagation, the efficient EM field excitation, and long-range propagation can be obtained by tuning the structure of our systems. With suitable geometric parameters (dimer orientations, dimer gap sizes) of our system, the electric field intensity at the position 5000 nm away from the starting point (exciting point) is about 50 times of the corresponding field intensity in a silver nanoparticle chain.