Arnan Mitchell

Reduced Cost Photonic Instantaneous Frequency Measurement System

A wideband photonic instantaneous frequency measurement system is proposed and practically demonstrated. This system employs only a low-frequency inexpensive photodetector and thus the system cost is reduced.

Efficiency and Scalability of Dielectric Resonator Antennas at Optical Frequencies

Dielectric resonators have been foreseen as a pathway for the realization of highly efficient nanoantennas and metamaterials at optical frequencies. In this paper, we study the resonant behavior of dielectric nanocylinders located on a metal plane, which in combination create dielectric resonator antennas operating in reflection mode. By implementing appropriate resonator models, the field distributions, the scaling behavior, and the efficiency of dielectric resonator antennas are studied across the spectrum from the microwave toward visible frequency bands. Numerical results confirm that a radiation efficiency above 80% can be retained up to the near-infrared with metal-backed dielectric resonators. This paper establishes fundamental knowledge toward development of high efficiency dielectric resonator antennas and reflection metasurfaces at optical frequencies. These dielectric resonators can be incorporated as basic elements in emerging applications, e.g., flat optical components, quantum dot emitters, and subwavelength sensors.

Search for high-performance probe-fed stacked patches using optimization

High-performance circular probe-fed stacked patch antenna designs are explored through the use of numerical optimization. New trends are sought to aid understanding and to suggest novel solutions. We describe the optimization technique, present a new design trend relating efficiency and bandwidth to the choice of substrate dielectric, and propose and demonstrate a novel, optimized antenna achieving 33% bandwidth whilst maintaining greater than 80% surface wave efficiency.

Investigation of resonantly enhanced Modulators on LiNbO/sub 3/ using FEM and numerical optimization technique

Highly efficient resonantly enhanced modulators on X-cut LiNbO/sub 3/ are investigated through the use of numerical optimization. We describe the optimization technique and present a new design trend relating the link-gain efficiency of optical radio systems that employ external modulation to the choice of modulator electrode geometric dimensions, especially the electrode gap. Using this optimization technique, resonant-type modulators with link gain enhancement up to 6 dB are achievable while maintaining excellent return loss at a resonant frequency of 1.8 GHz. The characteristics of both the optical waveguide and the coplanar electrode are characterized by finite-element simulation.

Photonic Instantaneous Frequency Measurement: Parallel Simultaneous Implementations in a Single Highly Nonlinear Fiber

A microwave photonic system that simultaneously implements multiple parallel instantaneous frequency measurement systems within a single highly nonlinear optical fiber is proposed and practically demonstrated. Three optical carriers of different wavelengths are modulated by the same radio-frequency (RF) signal and then delayed differentially. All three carriers are then mixed within a highly nonlinear optical fiber. The mixing products are separated, and the optical power of each is used to deduce input RF frequency. We demonstrate simultaneous acquisition of two distinct frequency measurement responses over the range from 1 to 40 GHz. This system is all-optical and requires no high-speed electronic components. Avenues for further increasing the number of simultaneous channels are identified.

Improvement to the PML boundary condition in the FEM using mesh compression

Numerical errors encountered when using the perfectly matched layer (PML) absorbing boundary condition with the finite-element method are investigated to discover more efficient implementation schemes. Closed-form expressions for the numerical reflection at an interface between two general biaxial materials are applied to the special case of a PML boundary. Expressions for an anisotropically compressed mesh are then derived, revealing that reflections can be greatly reduced through increasing mesh density only where it is required. Significant improvements over previously reported PML boundaries are demonstrated.

Closed-form expressions for the numerical dispersion and reflection in FEM simulations involving biaxial materials

Closed-form expressions for the numerical errors caused by finite-element discretization of problems involving materials of biaxial permittivity and permeability tensors are developed. In particular, we derive expressions for the numerical dispersion and reflection in both first-order node and edge basis function finite-element formulations in an equilateral triangular mesh. Results using these closed-form expressions are compared to practical numerical simulations. The application of these expressions to the analysis of the performance of the perfectly matched layer boundary is suggested.

Integrated optic RF phase shifter for continuous beam steering at 1-1200 MHz

A novel integrated optical RF phase shifter comprising a variable directional coupler and integrated feedback loop is demonstrated. RF phase shifts in the range 37/spl deg/-91/spl deg/ at 1.2 GHz can be continuously selected via a DC bias. The phase shifter scales linearly with frequency and thus may be applied to broadband antenna array phasing.

An anisotropic PML for use with biaxial media

This paper presents the conditions required for an anisotropic perfectly matched layer for material exhibiting a biaxial permittivity tensor. Such materials are common in optical devices. This derivation does not treat arbitrary orientations, but should be general enough for many common situations. The effectiveness of this absorbing boundary condition is considered using the finite-element method.

Wide-band variable transversal phase-shifter

We present a novel broadband phase-shifter based on a transversal filter configuration. This approach allows flexible control of the amplitude response while providing continuous variation of a linear phase slope. Numerical examples, both ideal and using practical RF components are presented and practical challenges in realising the phase-shifter are identified.