We present the design and modeling of novel electro-optic modulators and switches that have large extinction ratios, such that these electro-optic modulators and switches operate at the optical communication wavelength range (around 1550 nm). Firstly, we describe the design of an electro-optic modulator based on a tunable slotted ring resonator, having two pairs of partially overlapping graphene layers above and below of the slotted ring (in some portion of the circumference). We demonstrate that the transmission of light through the through port can be modulated by the application of voltage across the graphene layers. Secondly, we discuss the design of electro-optic switches using phase change materials either in a micro disk resonator or in a photonic crystal slab waveguide. These devices are based on the shift in the resonant frequency of a micro disk resonator and on the shift in the photonic bandgap of the photonic crystal slab waveguide, respectively, when its refractive index changes upon the application of voltage across the phase change material. A three dimensional finite-difference time-domain modeling software (Lumerical FDTD) was used for optical modeling and a commercial device modeling software (Lumerical DEVICE) was for the electrical modeling. The proposed electro-optic modulators and electro-optic switches can be used in optoelectronics, as well in the telecom wavelength range.
In this paper, we describe the design and modeling of novel long-range hybrid plasmonic waveguides that consist of both plasmonic thin films and nano-scale structures of a high refractive index material (such as silicon), with a material of low refractive index (such as silicon di-oxide) lying in the region between the nano-scale structures and the plasmonic thin film. We have employed complex geometry of silicon nanostructures in the vicinity of a plasmonic thin film. The effective refractive index and the corresponding propagation length obtained for these plasmonic waveguides and hybrid plasmonic waveguides were obtained using a full-vector finite difference eigen mode solver. In our simulations, different structural parameters of the the hybrid plasmonic waveguides were varied, and the effect of these parameters ⎯ on the propagation length and effective mode area ⎯ was analyzed. We describe the design of novel hybrid plasmonic waveguides that have a propagation length greater than 1 mm and also have a low effective mode area. The waveguides being proposed by us can be fabricated with relative ease using the standard lithography processes.
This paper presents hybrid plasmonic substrates fabricated by a combination of bottom-up and top-down process of fabrication which can be employed as efficient Surface enhanced Raman scattering (SERS) substrates for chemical sensing. The hybrid approach leads to a cost-efficient fabrication with smaller fabrication times than the pure top-down approach and higher degree of control than the pure bottom-up approach. We demonstrate the achievement of sub-20 nm gaps on a large area with this hybrid methodology. These small gaps lead to the formation of electromagnetic hotspots, i.e., regions of high electromagnetic enhancement. The electromagnetic behavior of these substrates is analyzed theoretically using Finite Difference Time Domain modeling. The sub-20 nm gaps lead to the electromagnetic SERS enhancements of the order of ∼108, and a change in the gap size can tune the plasmon resonance wavelength from the visible to the near-IR region of the spectrum. It is thus shown that these SERS substrates offer high SERS enhancement along with a capability of passive tunability of the plasmon resonance wavelength by changing the geometrical parameters in these substrates.
A highly sensitive and easy-to-fabricate hydrogen sensor based on a plasmonic ‘gold nanowire array on a palladium layer deposited on a metallic substrate' is proposed. Plasmonic waveguide modes are excited in the gaps between the nanowires in this ‘gold nanowire array on a palladium spacer layer deposited on a metallic substrate' system. As incident light is coupled into the plasmonic modes, a dip in the reflectance spectra is observed at the resonant wavelength, i.e., the wavelength at which the incident light is coupled into plasmonic modes. On exposure to hydrogen, the palladium spacer layer transforms to palladium hydride (PdHx), where x, the atomic ratio of H:Pd, increases as the hydrogen concentration increases. This transformation changes the optical properties of the Pd layer, and hence the position of the resonance wavelengths (λres), i.e., the position of the reflection dips in the reflectance spectra of the Au-Pd-Au system, for various concentrations of hydrogen. The difference between the positions of the resonant wavelengths of PdHx and Pd, (λres(PdHx)−λres(Pd)), is used as a measure of the sensitivity of the proposed hydrogen sensor. Analysis of this shift in the plasmon resonance wavelength is done numerically, using Rigorous Coupled Wave Analysis (RCWA) for various values of d, the side length of the nanowires; t, the thickness of the Pd spacer; g, the gap between the adjacent nanowires and θ, the angle of the incident radiation. It is found that, in the presence of hydrogen, the maximum shift in the resonance wavelength for the proposed sensor is ~41 nm as compared to the case when hydrogen is absent. This shift in the resonance wavelength is higher than many currently employed plasmonic Pd-based hydrogen sensors. Thus, the proposed ‘gold nanowire array on a palladium spacer layer deposited on a metallic substrate' is an easy-to-fabricate, selective and sensitive hydrogen sensor.
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