Vitor M. Schneider

Analysis of strategies to improve the directionality of square lattice band-edge photonic crystal structures

Recently, photonic crystal band-edge structures have been analyzed in the literature. However, most devices that have been presented so far emit light in different directions. We present a modal analysis (no gain included) of a few schemes to improve the directionality of these devices, i.e., in such a way that light that exits from them will travel mainly in a certain direction, eventually coupling its energy to a wide waveguide.

Cantor set fiber Bragg grating

The theory of fractals has already been applied to many fields in science, such as physics, biology, and chemistry. One of the most commonly used fractals in these applications is the Cantor set. Novel fiber Bragg gratings are proposed that combine the present technology of fiber Bragg gratings with the theory of Cantor sets. The principal goal of this work is to analyze how Cantor sets, applied to gratings, can alter their reflectivity spectra. Specifically, it is observed that, as the order of the Cantor set increases, the bandpass reflectivity spectra of these gratings broaden and evolve into more-complex patterns. Also, self-similarity properties can be observed in the spectra of these gratings. Numerical examples demonstrate variations in the spectra of these structures as the fractal order increases.

High-tolerance power splitting in symmetric triple-mode evolution couplers

This paper describes the analytic behavior of super-mode propagation in a symmetric triple-mode evolution coupler. Numerical simulations of this new design based on window filter functions are performed. Fabrication tolerances are assessed and checked for several design parameters, which resulted in a higher insensitivity to small design variations when compared to other standard coupler designs, reducing the necessity of individual trimming for applications when accuracy is critical. The use of different power splitting ratios is also demonstrated by means of static and dynamic changes in the design, opening a wide range of possible applications.

Wavelength insensitive asymmetric triple mode evolution couplers

This article describes the analytic behavior of an asymmetric triple mode evolution coupler. This new design, based on window filter functions, is analyzed by the coupled mode theory, and its performance verified by the method of lines. The validity of the formulation based on mode coupling is determined, where fabrication tolerances are assessed and checked for several design parameters. Wavelength independence is observed leading to highly insensitive optical couplers for applications in wavelength division multiplexing systems.

Analysis of distributed-feedback lasers with fractionally organized gratings

We analyze the performance of distributed-feedback lasers with special grating structures. These grating structures consist of subgratings with different lengths (that are integer multiples of a reference length) and/or different phase shifts (that are also integer multiples of a reference phase shift). These grating structures can provide transmission peaks with high quality factors, which may be useful for distributed-feedback lasers. To assess the usefulness of these devices, threshold and steady-state analysis are performed for a few selected examples. A given design example is shown to provide a low threshold without major variations in photon density along the device.

Photonic Crystal Micro-Cavity Based Radiation Filter

In this paper, a band-stop radiation filter based upon a planar photonic crystal single-defect micro-cavity is studied. The micro-cavity is located within a photonic crystal region and fed by a ridge waveguide. Because the micro-cavity structure is bounded on one side by a limited number of crystal rows, there is strong radiation, at resonance, into the surrounding 2D slab (i.e., the region that is free from the photonic crystal). The antenna radiation pattern of this micro-cavity can be substantially directional and is strongly dependent upon the cavity resonant wavelength, giving the possibility for this device to act as a directional radiation filter.The theoretical analysis of this device is performed by using 2D Finite-Difference Time-Domain (FDTD) methods, while the device is fabricated in an InP epi-layered structure. Initial characterization results are also presented for this single-defect radiation filter.

Dispersion characteristics of segmented optical fibers

A direct scalar two-dimensional routine based on the method of lines is implemented to analyze the dispersion characteristics of segmented fibers. In this kind of structure, dispersion control in a simple profile is achieved by variations in the filling ratio of the coaxiallike structure.

A high nonlinearity elliptical fiber for applications in Raman and Brillouin sensors

Raman and Brillouin effects have found special applications in distributed sensing for smart materials and structures. In these sensors, the fiber acts as a distributed sensor, sensing strain and temperature over a range of tens of kilometers and, at the same time, carries this information to the installation that will process them. In order to optimize the fiber to operate under the Brillouin and Raman regimes, a special elliptical fiber with small effective area has been designed, which will allow these sensors to cover longer distances and/or employ lower power lasers.

Geometrical optics analysis of multi-layer GRIN tapers

Several gradient-index (GRIN) tapers have been analyzed in the literature, whether with a transverse parabolic index distribution or with a hyperbolic secant index profile. In this work, a new class of GRIN tapers, formed by grouping together several sections of transverse parabolic index devices is analyzed, focusing the attention on some of its limitations and advantages over ordinary tapers. Numerical simulations based upon geometric optics are conducted to analyze the behavior of these tapers.

On the design of integrated optical adiabatic tapers made by the sol-gel deposition technique

This paper discusses the different techniques available for fabricating tapered structures based on the sol-gel deposition process. Experimental difficulties are examined and conclusions drawn leading to the best approach for a future device.