Design of Plasmonic Comb-Like Filters Using Loop-Based Resonators

A subwavelength plasmonic comb-like filter is proposed by using dual symmetric slot cavities which are placed between two parallel metal–insulator–metal (MIM) structure waveguides. The structure can be considered as a resonance loop which consists of slot cavity resonators and MIM waveguide resonators. The reflective wavelength range and channel spacing are determined by the lengths of slot cavities and MIM waveguides, respectively. Three, four, and five reflective channels with high reflection are achieved in a small wavelength range. Higher channel count can be available by increasing the length or the real part of effective index of MIM waveguides. Such a device can find applications in various optical systems such as wavelength demultiplexing components.     

A Compact Nanoplasmonics Filter and Intersection Structure Based on Utilizing a Slot Cavity and a Fabry–Perot Resonator

By combining a Fabry–Perot (FP) cavity with a slot cavity, a compact filter structure is proposed. The peak resonance wavelength is determined by applying the FP resonance condition of the FP cavity. The relationship between filtering wavelength and cavity parameters is investigated. The results show that the filtering wavelength can be manipulated by changing the nanocavities' parameters. By using the finite difference time domain method, the theoretical predictions are confirmed. An intersection structure for nanoplasmonic waveguides is proposed and designed by utilizing two perpendicular filters. In addition to having compact dimensions, the proposed arrangement provides higher throughput and low cross talk. The proposed structure can be useful for designing compact integrated nanoplasmonic circuits.     

Reconfigurable SiC Embedded Photonic Structures with Self Optical Bias Control

Multilayered heterostructures based on embedded a-Si:H and a-SiC:H p-i-n filters are analyzed from differential voltage design perspective using short- and long-pass filters. The transfer functions characteristics are presented. A numerical simulation is presented to explain the filtering properties of the photonic devices. Several monochromatic pulsed lights, separately (input channels) or in a polychromatic mixture (multiplexed signal) at different bit rates, illuminated the device. Steady-state optical bias is superimposed from the front and the back side. Results show that depending on the wavelength of the external background and impinging side, the device acts either as a short- or a long-pass band filter or as a band-stop filter. Particular attention is given to the amplification coefficient weights, which allow to take into account the wavelength background effects when a band or frequency needs to be filtered or the gate switch, in which optical active filter gates are used to select and filter input signals to specific output ports in wavelength division multiplexing (WDM) communication systems. This nonlinearity provides the possibility for selective removal or addition of wavelengths. A truth table of an encoder that performs 8-to-1 MUX function exemplifies the optoelectronic conversion.     

Design of Full-Adder and Full-Subtractor Using Metal-Insulator-Metal Plasmonic Waveguides

The metal-insulator-metal (MIM) waveguides are considered best among all plasmonic waveguides for propagation of optical signal to deep sub-wavelength scale. In this paper, MIM plasmonic waveguides based Mach-Zehnder interferometer (MZI) is developed. It possesses nonlinear Kerr material in one of its linear arm for controlling of optical signal with light intensity. Self phase modulation (SPM) and cross phase modulation (XPM) processes inside nonlinear MZI are used to design novel and compact full-adder and full-subtractor. Analysis and verification of proposed devices are carried out using FDTD and MATLAB simulations.     

Numerical Investigation on Elliptic Cylindrical Nanowire Hybrid Plasmonic Waveguide–Based Polarization Beam Splitter

A novel design of elliptic cylindrical nanowire hybrid plasmonic waveguide (ECNHPW)–based polarization beam splitter (PBS) is proposed. In the proposed design, the ECNHPW arm acts as an input port and a bar port; on the other hand, a regular silicon wire (RSW) arm acts as a cross port. By selecting the physical parameters of the proposed PBS accurately, the transverse electric (TE) mode is merely satisfied with the phase-matching condition. In contrast, the transverse magnetic (TM) mode does not propagate to the RSW arm. Consequently, the TM input mode goes directly to the ECNHPW arm, while the TE input mode in ECNHPW is coupled with RSW arm. As a result, the two different polarization modes are meritoriously separated, and they pass through two different arms. For the proposed PBS, the insertion loss (IL) of both polarizations lies below 1 dB. For TE input, the value of the polarization extinction ratio (PER) is 27.2 dB, and for TM input, it is 23.9 dB at 1550 nm operating wavelength. Further optimization is implemented by varying the wavelength, thickness of SiO₂, and the gap between the waveguides using the finite element method (FEM). The proposed PBS is designed with 150 nm bandwidth, high PER, and low IL, which can be suitable for photonic integrated circuits (PICs).

     

Multiple Surface Plasmon Resonances in a Metal–Insulator–Metal Structure Assembled Via Silver–Copper Nanoparticle Arrays

The Ag–Cu nanoparticle arrays, prepared using the electrochemical deposition method, were assembled into the metal–insulator–metal (MIM) structure with polyvinyl alcohol acting as insulating layer, the transmission spectrum of the MIM structure was observed to support the multiple surface plasmon resonances in the wavelength range 1,000 to 2,600 nm. The multiple peaks were formed due to the superposition and coupling of the surface plasmon resonance of nanoparticles with various sizes in the metal layers. The newly found MIM structure in which multiple resonances exist has a potential application in multiband-pass filters and optical magnetic metamaterials at the resonance wavelength.     

Plasmonic Wavelength Demultiplexer with Mode Conversion Capabilities

An efficient wavelength demultiplexer with its input as a metal-insulator-metal (MIM) waveguide mode and output an out of plane free-space mode is proposed. The proposed demultiplexer design is integrated on a MIM waveguide such that power is evanescently coupled into an array of appropriately designed cavity-groove combination. The demultiplexer design permits control of phase of the dropped wavelength to achieve a desired wavefront. We demonstrate this through generation of circular and plane wavefront. By controlling the evanescently coupled power into the cavity-groove combinations, it is possible to dramatically improve the efficiency of the proposed demultiplexer. Results are simulated using FEM technique.     

Enhancement of Second Harmonic Generation in Metal-Insulator-Metal Plasmonic Waveguides

Nonlinear effects such as second harmonic generation (SHG) are important for applications such as switching and wavelength conversion. In this study, the generation of second harmonic in metal-insulator-metal (MIM) plasmonic waveguides was investigated for both symmetric and asymmetric structures. This study considered two different structures as plasmonic waveguides for the generation of second harmonic, and analysis was performed using the finite-difference time-domain method. Besides, the structure has grating on both sides for more coupling between photons and plasmons. The wavelength duration of grating per unit length (number of grooves) was optimized to reach the highest second harmonic generation. To perform this optimization, the wavelength of operation (λ = 458 nm) was considered. It was shown that field enhancement in symmetric MIM waveguides can result in the enhancement of SHG magnitude when compared to literature values. Also, asymmetric devices result in more than two orders of magnitude enhancement in SHG, as compared to the symmetric structure. It has been shown that the electric field of the second harmonic depends on the thickness of the crystal (insulator). Hence, its thickness was optimized to achieve the highest electric field.     

Optical Transmission Through Multilayered Ultra-Thin Metal Gratings

Optical transmission properties of multilayered ultra-thin metal gratings are numerically studied. The transmission spectrum has a broad stop-band with extremely low transmittance compared to that of a single-layer one for TM polarization. The stop-band is shown to be formed by multiple-interference tunneling and various plasmon resonance processes in ultra-thin-metal and dielectric multilayers. That is on the transmission background of non-apertured metal/dielectric multilayer structures that have low transmission in the long-wavelength range due to destructive multiple-interference tunneling, the transmission is further suppressed in the stop-band by plasmon resonances in the top metal/dielectric layers, e.g., the anti-symmetric bound surface plasmon mode in the ultra-thin metal layer and the gap surface plasmon mode in the metal-sandwiched dielectric layer. High transmission beyond the stop-band is due to coupled gap surface plasmon mode in the entire multilayer structures. Applications of the optical properties of the multilayered ultra-thin metal gratings are suggested for optical filtering (wavelength or polarization selective).     

Highly Compact Circulators in Square-Lattice Photonic Crystal Waveguides

We propose, demonstrate and investigate highly compact circulators with ultra-low insertion loss in square-lattice- square-rod-photonic-crystal waveguides. Only a single magneto- optical square rod is required to be inserted into the cross center of waveguides, making the structure very compact and ultra efficient. The square rods around the center defect rod are replaced by several right-angled-triangle rods, reducing the insertion loss further and promoting the isolations as well. By choosing a linear-dispersion region and considering the mode patterns in the square magneto-optical rod, the operating mechanism of the circulator is analyzed. By applying the finite-element method together with the Nelder-Mead optimization method, an extremely low insertion loss of 0.02 dB for the transmitted wave and ultra high isolation of 46 dB∼48 dB for the isolated port are obtained. The idea presented can be applied to build circulators in different wavebands, e.g., microwave or Tera-Hertz.     

Plasmonic Directional Couplers Based on Multi-Slit Waveguides

We propose and investigate the performance of the plasmonic directional couplers based on two dimensional multi-slit plasmonic waveguides, employing the finite difference time domain simulation method. The idea behind the directional properties of the directional couplers is the interference of two wave components, in and out of phase, at the coupled and isolated ports, respectively. The coupler is also analyzed by an analytic method. The simulation results comply well with those of the analytic considerations. The effects of variations of the coupler structural parameters, crosstalk between the input and output ports, and the overall structure loss are also investigated.     

Utilizing the Metallic Nano-Rods in Hexagonal Configuration to Enhance Sensitivity of the Plasmonic Racetrack Resonator in Sensing Application

A high sensitive plasmonic refractive index sensor based on metal-insulator-metal (MIM) waveguides with embedding metallic nano-rods in racetrack resonator has been proposed. The refractive index changes of the dielectric material inside the resonator together with temperature changes can be acquired from the detection of the resonance wavelength, based on their linear relationship. With optimum design and considering a tradeoff among detected power, structure size, and sensitivity, the finite difference time domain simulations show that the refractive index and temperature sensitivity values can be obtained as high as 2610 nm per refractive index unit (RIU) and 1.03 nm/°C, respectively. In addition, resonance wavelengths of resonator are obtained experimentally by using the resonant conditions. The effects of nano-rods radius and refractive index of racetrack resonator are studied on the sensing spectra, as well. The proposed structure with such high sensitivity will be useful in optical communications that can provide a new possibility for designing compact and high-performance plasmonic devices.     

Systematic Theoretical Analysis of Selective-Mode Plasmonic Filter Based on Aperture-Side-Coupled Slot Cavity

By taking the aperture as a resonator, we propose an analytical model to describe the dynamic transmission in metal-dielectric-metal (MDM) waveguide aperture-side-coupled with slot cavity. The theoretical results and the finite-difference time-domain (FDTD) simulations agree well with each other, and both demonstrate the mode selectivity and filtering tunability of the plasmonic structure. By adjusting the phase shifts in slot cavity or resonance frequency determined by the aperture, one can realize the required transmission spectra and slow light effect. The theoretical analysis may open up avenues for the control of light in highly integrated optical circuits.     

Extraordinary Optical Transmission Performances of Nanosandwiched Grating for Wideband Multi-Function Integration

In this paper, we present a peculiar metal-dielectric-metal (MDM) nanosandwich grating structure that can achieve extraordinary optical transmission performances at normal incidence in the ultraviolet-visible-near infrared (UV-VIS-NIR) regions. The proposed structure shows three obvious spectrum characteristics: it can obtain high transmittance up to 80 % in NUV region and efficiently blocking visible wavelengths for transverse-magnetic (TM) polarized incidence; a broadband NIR polarizer can be inspired in the wavelength range from 950 to 1400 nm; more surprisingly, these performances do not deteriorated until 30° tilting angle. Compared to other grating structures with single metal overlayer, it shows wider band-stop characteristics and higher broadband transmission transmittance and extinction ratio (ER) in the investigated wavebands. We analyze the underlying physical mechanism by using numerical simulation, which is primarily attributed to metal ultraviolet transparency, surface plasmon polariton (SPP) at metal/dielectric interface, Fabry–Perot (FP)-like cavity mode within this dielectric grating, and optical magnetic resonance especially in the dielectric interlayer of the MDM sandwiched structure. This structure is very important for developing high-performance subwavelength multifunctional integrated optical devices.     

A High Performance Plasmonic Sensor Based on Metal-Insulator-Metal Waveguide Coupled with a Double-Cavity Structure

A high performance plasmonic sensor based on a metal-insulator-metal (MIM) waveguide coupled with a double-cavity structure consisting of a side-coupled rectangular cavity and a disk cavity is proposed. The transmission characteristics of the rectangular cavity and disk cavity are analyzed theoretically and the improvements of performance for the double-cavity structure compared with a single cavity are studied. The influence of structural parameters on the transmission spectra and sensing performance are investigated in detail. A sensitivity of 1136 nm/RIU with a high figure of merit of 51,275 can be achieved at the resonant wavelength of 1148.5 nm. Due to the high performance and easy fabrication, the proposed structure may be applied in integrated optical circuits and on-chip nanosensors.     

Optical Channel Drop Filter Design Based on PCRR and Micro Cavity Resonator

Optical channel drop filter (OCDF) plays a key role in optical communication networks for filtering the individual wavelength among the group of channels in wavelength division multiplexing systems. There are several channel drop filters with different design mechanisms available in the literature, but those structure dimensions are not compact enough for the photonic integrated applications. Hence, in this paper, a compact and efficient OCDF is developed in the triangular lattice PC structure based on diamond-shaped photonic crystal ring resonator (PCRR) mechanism combined with micro cavity resonator (MCR). The developed OCDF is analysed for different operating wavelengths by considering the different positions of MCR around the main PCRR. Based upon the position of the MCR around PCRR, the three dropping wavelengths such as 1540 nm, 1550 nm, and 1570 nm are observed at the output waveguides with 100% dropping efficiency. Then the structural and performance parameter comparison is done between the proposed and existing structures in terms of device dimension, dropping efficiency, and quality factor. It is depicted through the results that the quality factor and the device dimension are better than that of the existing structures for 1550-nm wavelength.

     

Design and Analysis of Infrared Tunable All-Optical Filters Based on Plasmonic Hybrid Nanostructure Using Periodic Nanohole Arrays

A tunable high transmission optical bandpass filter based on a plasmonic hybrid nanostructure, composed of a periodic array of nanocircles and nanoholes combining two isolated waveguides is introduced in this paper. The presented design improves the coupling, which results in a higher transmission peak. To study the filtering operation, different topologies are investigated. The transmission properties and the resonance wavelengths are adjusted by sweeping various geometrical parameters. A multimode spectrum for each of the topologies is obtained. A tunable bandgap and bandwidth can be obtained by adjusting the refractive index of the periodic nanostructure. We have reached a maximum quality factor and a small full width at half-maximum bandwidth with the maximum transmission values greater than 80%. The advantages of the presented structures which include the benefits of both plasmonic and periodic nanostructures are tunability, high detection resolution, and integrability at the nanoscale for optical applications.

     

Structure of Multiple Fano Resonances in Double-baffle MDM Waveguide Coupled Cascaded Square Cavity for Application of High Throughput Detection

A structure of double-baffle metal-dielectric-metal (MDM) waveguide coupled cascaded square cavity is designed based on the transmission characteristics of the surface plasmon polaritons. Combined with coupled mode theory (CMT), the mechanism of multiple Fano resonances generated by this structure is analyzed qualitatively. The wide-band spectrum mode generated by the F-P resonant cavity and the four narrow-band spectrum modes produced by the cascaded square resonant cavities interfere with each other. Moreover, an new scheme of introducing a semiconductor material InGaAsP into this structure is designed for improving the transmittance of the Fano peaks. Analyze the influence of refractive indexes of the test objects on sensing performance by finite element method (FEM) quantitatively, which shows the improved structure can achieve the independent tuning of multiple Fano resonances. Combining with 96-well microplate technology, the structure can achieve the detection of multiple different samples with high-performance simultaneously. It is believed that the proposed structure has a strong reference significance for the design of optical micro-nanostructures for high throughput detection.

     

Numerical Investigation of a Branch-Shaped Filter Based on Metal-Insulator-Metal Waveguide

Using the finite difference time-domain method, we present a comprehensive numerical investigation of a branch-shaped filter based on the metal-insulator-metal (MIM) waveguide. The results show that several passbands and stopbands appear in the transmission spectra, which are resulted by the phase differences between the surface plasmon polaritons (SPPs) propagating along the straight waveguide and the SPPs resonating in the circuit formed by the branch and the straight waveguide. The effects of the structural parameters of the branch-shaped filters on their transmission properties are also studied. These results not only present an alternative plasmonic filter for the MIM waveguides but also help us to understand the transmission properties of the circuit-shaped structures.