Synthesis of nonuniform long-period optical gratings with a continuous refractive index profile

O.V. Kolokoltsev, V.A. Sv, r. , d. , I.F. Llamas, C.L. Ordóñez Romero

Abstract


In this work we present a new method for such a non-trivial problem as the synthesis of optical filters based on non-uniform Long-Period Fiber Gratings (LPGs). The method is based on a real-coded genetic algorithm (GA) with a new quasi-analytical procedure for solving the Zakharov-Shabat Inverse Problem. The method possesses an improved computational stability compared to classic numerical algorithms. The main peculiarity of the non-uniform LPG transmission gratings, compared to the Bragg gratings, is that their optical fields oscillate rapidly. However, the quasi-analytical approach proposed allows one to reduce to a minimum the number of sampling points, without, at the same time, losing accuracy in the solution, i.e. the method possesses an improved efficiency. The algorithm convergence was also improved by using the relations of the law of conservation of energy between the interacting waves. It has been shown that the algorithm works adequately even for the case of strongly over-coupled co-propagating lightwave modes, as we demonstrate in several examples of the synthesis of ultra-wide pass-band optical filters (FWHM of 100-200 nm).

Keywords


Long-period fiber gratings; synthesis; optical filters; genetic algorithm

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REVISTA MEXICANA DE FÍSICA, year 67, issue 2, March-April 2021. Bimonthly Journal published by Sociedad Mexicana de Física, A. C. Departamento de Física, 2º Piso, Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad Universitaria, Alcaldía Coyacán, C.P. 04510 , Ciudad de México. Apartado Postal 70-348. Tel. (+52)55-5622-4946, https://rmf.smf.mx/ojs/rmf, e-mail: rmf@ciencias.unam.mx. Chief Editor: José Alejandro Ayala Mercado. INDAUTOR Certificate of Reserve: 04-2019-080216404400-203, ISSN: 2683-2224 (on line), 0035-001X (print), both granted by Instituto Nacional del Derecho de Autor. Responsible for the last update of this issue, Technical Staff of Sociedad Mexicana de Física, A. C., Fís. Efraín Garrido Román, 2º. Piso, Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad Universitaria, Alcaldía Coyacán, C.P. 04510 , Ciudad de México. Date of last modification, March 1st., 2021.

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