Michael Cada

As the limitations of integrated electronics start to appear, it becomes important to look for potential alternatives. Silicon photonics holds a lot of promise in this regard. It cannot only provide superior performance to traditional integrated electronics in many aspects, but also co-exist in harmony with it through the realization of electro-optic devices. The focus of this paper is on Photonic Integrated Circuits (PICs) only. A theoretical understanding of Mach-Zehnder Interferometer (MZI) circuits has been developed. Computational design tools have been employed to model photonic waveguides. The design of optical waveguides has been numerically investigated in MATLAB through the Effective Index Method (EIM). The material properties of silicon and silicon dioxide, used in the simulations, have been presented. The properties include the refractive indices, group refractive indices and effective indices. Waveguide geometrical parameters have been explored and a 500 nm x 220 nm silicon waveguide structure has been finalized for experimental work. The schematics for four MZI optical circuits have been prepared in KLayout. Interoperability of KLayout and Ansys Lumerical Interconnect allows for spectral response to be obtained through simulations. The circuits consist of grating couplers, Y-branch splitters and bidirectional couplers. The input signal is split into two waveguide paths. Both waveguide paths culminate into grating couplers connected to photodetectors. The signals from both the channels have been recorded. The fabrication of the chip has been carried out at Applied Nanotools Inc. through Electron Beam Lithography (EBL). The characterization of the devices has been done at 25oC. A decent conformity can be observed between simulation and experimental results.

In this paper, the ‘terahertz gap’ has been addressed by designing a novel THz metasurface for potential use in biosensing applications. The metasurface sensor employs Surface Plasmon Resonance (SPR). It operates in the 0 - 1 THz band. Two sharp reflection dips are provided by the sensor, which serve as indicators of analyte refractive index variations. Geometrical as well as compositional parameters of the biosensor design have been studied to optimize the performance in the targeted frequency band. The sensor design shows compatibility with different metals. The performance of the metasurface with gold, copper and aluminum has been investigated. The metasurface geometry is decently resilient to fabrication tolerances. The sensor maintains its resonance conditions when the angle of incidence is changed with minor deviations in the spectral response, but the polarization state of the incident terahertz beam clearly disturbs the absorption peak. Therefore, the sensing performance is restricted to a maximum allowable incidence angle of 20 degrees and circularly polarized terahertz beams. The resonance conditions for the metasurface appear around 0.4 and 0.7 THz. Both resonances have been investigated with respect to changes in the analyte refractive index. The chosen refractive index range is 1 to 1.5. The sensor response is calibrated by plotting the resonance frequency versus the refractive index. Least squares regression technique has been used to extract a data model for sensor response. Comparison of the proposed design with contemporary works has been incorporated into the paper. The sensor provides sensitivities of 0.1614 THz/ RIU and 0.23 THz/ RIU. The electromagnetic simulations have been carried out through the Finite Element Method (FEM).

This paper proposes an optical sensor based on nanoscale metamaterial structures. The design of the sensor has been explored with respect to biosensing applications through numerical modeling and analysis. The sensor comprises silica substrate and diamond nanostructures, both of which represent dielectrics. The sensing principle is based on the detection of ambient refractive index change. As the analyte properties change, the refractive index changes, as well. The refractive index change has been detected by striking electromagnetic waves onto the structure and noting the spectral response. Ultraviolet waves have been utilized for recording spectral responses and evaluating sensor performance. The sensor displays multiple sharp resonance peaks in the reflected beam. By altering the refractive index of the analyte present around the sensor, the peaks can be seen choosing different wavelengths. The resonance peaks have been investigated to observe electric and magnetic field dipoles in the sensor structure. The spectrum peaks have also been studied to understand fabrication tolerances. The sensor displays a linear response, along with a large Quality (Q) factor. The maximum value of the achieved Quality (Q) factor for the proposed sensor is 1229 while operating across the refractive index range of 1.4–1.45. The claim has been supported by comparison with contemporary works on similar platforms. A range of other sensing parameters have also been calculated and benchmarked. Metamaterial-based optical sensors can provide smaller device sizes, faster response times and label-free detection.

Developing efficient techniques to bridge single-plasmon radiations to nanoscale plasmonic waveguides nowadays is still a critical consideration for on-chip integration of solid-state photonic circuits. Here, we propose and theoretically demonstrate the generation and routing of single plasmons in nanowire-based hybrid plasmonic coupling structures with nanodisk antenna resonators. Optimizations of key characteristic parameters illustrate that the structure not only offers an enhanced tradeoff between the propagation length (20m) and mode confinement (2/8450), but also exhibits outstanding plasmon generation and guiding properties, such as a Purcell factor of 2.14 106, a coupling efficiency from emissions to desired waveguides of 59%, and a Figure-of-Merit of 3 107 in the visible and infrared spectral range, which outperforms the previous plasmonic structures. The plasmon emission properties are also quite robust against possible emitter positioning imperfections. Our work may inspire new opportunities in helping design quantum-plasmonic platforms for future quantum information processing and related on-chip plasmonic devices

Phase-matched wavelength conversion is achieved in difference frequency generation (DFG) in a structure of gallium arsenide (GaAs) with periodic arrays of nanoholes. Linear properties (refractive indices) of the structure are determined from the S-parameters of the structure. Finite difference time domain (FDTD) simulation is used to calculate the S-parameters. The longest wavelength achieved is 16.2229 μm and the shortest is 3.2961 μm. The results of the FDTD simulation are compared with results obtained from the effective medium theory by using the Maxwell Garnett model. The comparison shows excellent agreement.

Graphene, a two-dimensional monatomic layer of carbon material, has demonstrated as a good candidate for applications of ultrafast photodetectors, transistors, transparent electrodes, and biosensing. Recently, many studies have shown that using metallic deep gratings could enhance the absorptance of graphene of 2.3% up to 80% in the near infrared region for applications in photon detection. This paper presents utilizing a nanograting structure, namely, a compound metallic grating could greatly enhance the absorptance of graphene to 100% and widen its spectral bandwidth to 600 nm, which are greater than those of previous work. The study also showed that the absorptance spectrum is insensitive to angles of incidence. Furthermore, the proposed graphene-covered compound grating might bring a lot of benefits for graphene designs-based optical and optoelectronic devices.

The dispersion equation for surface plasmons (SPs) at a dielectric/conductor interface has been studied extensively with respect to the design of plasmonic devices. A key design requirement is the reduction of damping in the propagating SP polariton wave. Satisfaction of this constraint requires that an “electron gas” in a conducting medium, such as a doped semiconductor, move along the interface at speeds that approximate the polariton wave speed. At these low relative speeds, the efficient exchange of energy between the drifting electrons and a traveling SP polariton may be enabled. The ill-conditioned, eighth-order, complex coefficients dispersion equation derived earlier is dependent upon six parameters that vary over many orders of magnitude. The dispersion equation is also found to be singular in regions of practical interest, and, taken together, these properties have hampered the success of numerical investigations. Therefore, the dispersion equation is analytically investigated here, and closed-form results are found for the parametric dependence of the surface polariton’s propagation constant on five dimensionless groups. These new solutions show how compensation of propagation losses without the use of structures can be achieved and provide avenues that guide device design. The closed-form results are used to initialize numerical optimization by providing sufficiently accurate starting points within the parameter space that avoid numerical ill-conditioning.

The lack of anisotropic properties in GaAs prevents the use of birefringence as a phase matching technique in three-wave mixing with GaAs as a nonlinear medium. When metallic nanowires are embedded in GaAs, the composite structure is characterized as a metamaterial with anisotropic properties, if the separation distance between the nanowires is less than the wavelengths of the mixed waves. The effective permittivity is used to investigate this metamaterial structure with its anisotropic properties theoretically in terms of phase matching for difference frequency generation. The resultant difference frequencies, which are in the mid-infrared region, are broadly tunable from 2.8 to 11 μm. This tuning is performed by varying the pump and the signal wavelengths in the range between 1 to 2 μm. The losses of the structure due to absorption are included using the transfer matrix method.

A robust fiber-optic interferometer, which is formed by introducing two bends (i.e. z shape) to the standard telecommunication single mode fiber, is designed and analyzed theoretically and experimentally for the refractive index (RI) sensing. The first (second) bend couples (re-couples) the core (cladding) mode to the cladding (core) modes. The RI-sensitive phase difference between the core and cladding modes gives rise to the modulation of the transmitted intensity. The experimental results show that the z-shaped interferometric sensor possesses an RI sensitivity as high as 196 nm/RIU and fit well with the theoretical predictions. An investigation of the effect of perturbations of bent angle reveals that the sensor possesses relative high sensitivities as the bent angle ranges from 13° to 17° with difference between the maximum and minimum sensitivities only 2.5% indicating the structure has a good fabrication tolerance to the inaccuracy of the bent angles. In addition, the sensor has advantages of low cost, simple structure and ease of fabrication, showing great potential in many sensing applications.

The theoretical background to calculate the effective index tuning using the ultrafast electro-optic Kerr effect and a design of slot waveguide geometry are presented. Analysis of the slot waveguide ring resonator with silicon nanocrystals as the active medium to implement the CMOS compatible electro-optic Kerr effect modulator indicates a modulation bandwidth of 51 GHz, therefore, allowing for 90 Gb/s data rate transmission, and a low energy consumption of 22.99 fJ/bit.