Multilayered periodic reflector and Bragg waveguide for integrated optics.

Abstract

With computed data, comparison and discussion of some important characteristics such as reflectivity and selectivity of a double triple, quadruple and quintuple layered periodic reflector are extensively analyzed.

The electromagnetic wave propagation in the multilayered Bragg waveguide is considered. A generalized closed form expression for the reflectivity of a multilayered periodic Bragg reflector is presented. This expression is valid for any arientation of a polarization and any values of a layer thickness, index of refraction, wavelength, and an angle of incidence.

Among several structures investigated, a symmetric triple basic period exhibits unique property such as long wavelength or short wavelength pass characteristics. In addition to above aspects, the calculated reflectivity would place this triple structure in a range that would make it more superior to the double structure Bragg waveguide. It was observed that (('n(, 1))(, )('n(, 2))(, )('n(, 1))) basic structure has largest stopband among other symmetric structures for a given indices of refraction.

Addition of a number of layer in basic period have no significant effect on the magnitude of reflectance, while adjusting and controlling refractive index and thickness in each layer build up complexities in practical fabrication process. But with regard to bandwidth, the selectivity is drastically improved as the number of (lamda)(, o)/4 layer in basic period increases.

Finally, Bragg waveguides composed a triple layered periodic reflector have been studied thoroughly with regard to mode characteristics, field profiles in each layers, optical confinement and loss due to wave leaking into substrate. The attenuation constant becomes minimum at the optimum thickness corresponding to the center of the allowed range of guiding layer thickness and decreases exponentially with number of period. Arbitrary low loss waveguide is achieved with 5 periods of a triple layer.