Integrated optical devices design by genetic algorithm

Abstract

In this work we use multiple scattering in conjunction with a genetic algorithm to reliably determine the optimized photonic-crystal-based structure able to perform a specific optical task. The genetic algorithm operates on a population of candidate structures to produce new candidates with better performance in an iterative process. The potential of this approach is illustrated by designing a spot size converter that has a very low F-number (F=0.47) and a conversion ratio of 11:1. Also, we have designed a coupler device that introduces the light from the optical fiber into a photoniccrystal-based waveguide with a coupling efficiency over 87% for a wavelength that can be tuned to 1.5 µm.42. 42.25.Fx;42.82.Bq; A new generation of optical devices is envisaged thanks to the properties of photonic crystals (PC's).1 Though the recent advances in three-dimensional PC's structures, in the last years much attention has been focused on systems based on two-dimensional (2D) PC's because of their easiness in the fabrication process. Thus, very compact optical devices and circuits can be designed by introducing point and/or line defects. In order to use such PC circuits in actual applications it is necessary to establish a connection with an optical fiber. However, the core of the optical fiber is about one order of magnitude larger than the PC-based waveguide. Therefore, the design of an efficient (low loss) spot size converter is a crucial goal in the field of PC; its solution will introduce the PCs devices in the market place. In this regard, several groups 2-7 have tackled this problem by using different approaches. Most of them proposed tapered waveguide structures 2-5 , or by using reflective structures to focus the light into the waveguide.6 A different approach consists of using the anisotropy of the PC's equifrequency surfaces. 7This letter introduces a method that is useful in determining the optimized configuration of a 2D-PC structure capable of performing a requested optical task with high efficiency . The method is illustrated by finding a spot size converter (lens) that has a conversion ratio 11:1. In addition, the designed PC structure that involves a spot-size converter in connection with a PC-based waveguide it is presented. The insertion loss predicted for this new structure is about 13%, which is of the lowest reported by numerical simulations based on different coupling mechanisms. 2-6Our method is based on a binary-coded genetic algorithm (GA), an optimization strategy inspired by Darwinian evolution 8 . This method has been applied to solve a wide variety of problems in different fields like, for example, molecular geometry optimization 9 , material design 10 , and artificial intelligence 11 . In the field of optics, the GA has been employed in the synthesis of Bragg gratings that conform to a particular spectrum, 12 , phase recovering from a fringe pattern 13 , and in designing irregular lateral tapering. 2Although our proposal is general and applicable to any dimensionality, here we analyze 2D-PCs f...

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