Danilo H. Spadoti

Efficient and short-range light coupling to index-matched liquid-filled hole in a solid-core photonic crystal fiber

A photonic crystal fiber (PCF) with a section of one of the holes next to the solid core filled with an index-matched liquid is studied. Liquid filling alters the core geometry, which locally comprises the original silica core, the liquid channel and the silica around it. It is demonstrated that when light reaches the filled section, it periodically and efficiently couples to the liquid, via the excitation of a number of modes of the composite core, with coupling lengths ranging from tens to hundreds of microns. The resulting modal-interference-modulated spectrum shows temperature sensitivity as high as 5.35 nm/°C. The proposed waveguide geometry presents itself as an interesting way to pump and/or to probe liquid media within the fiber, combining advantages usually found separately in liquid-filled hollow-core PCFs (high light-liquid overlap) and in solid-core PCFs (low insertion losses). Therefore, pumping and luminescence guiding with a PCF filled with a Rhodamine solution is also demonstrated.

Anisotropy minimization via least squares method for transformation optics

In this work the least squares method is used to reduce anisotropy in transformation optics technique. To apply the least squares method a power series is added on the coordinate transformation functions. The series coefficients were calculated to reduce the deviations in Cauchy-Riemann equations, which, when satisfied, result in both conformal transformations and isotropic media. We also present a mathematical treatment for the special case of transformation optics to design waveguides. To demonstrate the proposed technique a waveguide with a 30° of bend and with a 50% of increase in its output width was designed. The results show that our technique is simultaneously straightforward to be implement and effective in reducing the anisotropy of the transformation for an extremely low value close to zero.

Three-dimensional quasi-conformal transformation optics through numerical optimization.

In this paper we demonstrate the possibility to achieve 3-dimensional quasi-conformal transformation optics through parametrization and numerical optimization without using sliding boundary conditions. The proposed technique, which uses a quasi-Newton method, is validated in two cylindrical waveguide bends as design examples. Our results indicate an arbitrarily small average anisotropy can be achieved in 3D transformation optics as the number of degrees of freedom provided by the parametrization was increased. The waveguide simulations confirm modal preservation when the residual anisotropy is neglected.

Comparison of Anisotropy Reduction Strategies for Transformation Optics Designs

In this paper, we present new strategies to reduce anisotropy in transformation optics designs and compare them to other techniques. Perturbation functions are used to modify the original transformation to achieve a quasi-conformal map, resulting in a medium with isotropic properties. All strategies investigated have no effect on the original boundary conditions of the transformation, such that neither the initial design is affected nor are reflections at the boundaries introduced. The results show that there exists a clear compromise between the residual anisotropy and the required refractive index contrast in the optimized transformation, but the former can be made as small as desired when the degree of freedom provided by perturbation functions is increased, although it is never exactly zero.

Reflectionless quasiconformal carpet cloak via parameterization strategy

In this work the possibility of using both the parameterization function and the least squares method to achieve a quasiconformal carpet cloak via a transformation optical design is demonstrated. The parameterization strategy allows us to obtain a continuous interface around the media, and, therefore, the resulting structure is reflectionless. Polynomial series are added to the coordinate transformation functions, providing a number of degrees of freedom (DoF) without modifying the device boundary conditions. The anisotropy reduction effects over the coordinate transformation are analyzed for different numbers of DoF in the parameterization function. The method’s connection with the Riemann mapping theorem is also studied. Our results indicate that anisotropy can be reduced to very close to zero with increasing DoF without incurring edge reflections around the carpet cloak.

Waveguide-Based Antenna Arrays for 5G Networks

This work reports the development of two high-performance waveguide-based antenna arrays for 5G cellular networks, operating in the underutilized millimetre wave (mm-wave) frequency spectrum. Two different scenarios of mm-wave communications are proposed for illustrating the applicability of the proposed arrays, which provide specific radiation patterns, namely, 12 dBi gain omnidirectional coverage in the 28 GHz band and dual-band sectorial coverage using the 28 and 38 GHz bands with gain up to 15.6 dBi. Numerical and experimental results of the array reflection coefficient, radiation pattern, and gain have been shown in an excellent agreement.

Full three-dimensional isotropic carpet cloak designed by quasi-conformal transformation optics

A fully three-dimensional carpet cloak presenting invisibility in all viewing angles is theoretically demonstrated. The design is developed using transformation optics and three-dimensional quasi-conformal mapping. Parametrization strategy and numerical optimization of the coordinate transformation deploying a quasi-Newton method is applied. A discussion about the minimum achievable anisotropy in the 3D transformation optics is presented. The method allows to reduce the anisotropy in the cloak and an isotropic medium could be considered. Numerical simulations confirm the strategy employed enabling the design of an isotropic reflectionless broadband carpet cloak independently of the incident light direction and polarization.

Photonic downconversion and optically controlled reconfigurable antennas in mm-waves wireless networks

We report on optically controlled antennas and photonic downconversion for mm-wave wireless communication applications. Experimental results demonstrate a transmission of 1.25 Gb/s using 28 and 38GHz frequency bands.

Dual-use system combining simultaneous active radar & communication, based on a single photonics-assisted transceiver

This paper report on the development and field trial of a dual-band and dual-use system based on a single photonics-based transceiver and a single radiating element, able to simultaneously carry out radar and communication functionalities. The coexistence of the two operations does not introduce any penalty on the system performance. The innovative sharing of both transceiver and antenna element allows for a reduction in terms of cost and Size Weight and Power consumption. The dual-use radar-communication system has been demonstrated in a outdoor field trial combining a radar experiment in S-band and C-band OFDM (Orthogonal Frequency Division Multiplexing) communication.

A liquid-filled W-type optical fiber temperature sensor

This paper describes the theoretical analysis and design of a temperature sensor based on a hollow core W-type optical fiber. The core region is filled with a proper mixture of solvents to achieve design goals. Results have shown that high sensitivity devices can be build using this structure.