Analysis and selection of optimum driving current combinations for tunable wavelength laser

Abstract

We present a demodulation technique to synthesise the physical parameters of an optical fibre Bragg grating (FBG) resonant cavity. The demodulation is achieved through a genetic algorithm (GA INTRODUCTIONIn the past, the all in-fibre resonators have been used for several different applications, from sensors to fibre laser resonators [1]. Recently, we have shown the possibility of realizing optical clock recovery recurring to ring lasers by using an intracavity gain clamped semiconductor optical amplifier and a resonant cavity based on Bragg gratings and on tuneable resonant cavities [2, 3].The correct extraction of parameters for a single fibre Bragg grating (FBG) or grating structures is of high relevance for device design and system simulation [4]. Several techniques have been proposed for the demodulation of FBG parameters [5 and references therein]. All of these require previous knowledge of the amplitude and phase spectrum. The experimental measurement of the latte is quite complex and has implicit an error when determined experimentally. These errors will propagate through the recovered parameters.Recently, Caucheteur et al. proposed a demodulation technique for fibre cavity resonators based uniquely on the adjustment of the amplitude spectrum [5]. However, for that propose a Nelder-Mead simplex algorithm was used, which has small robustness with respect to the initial parameters. Skaar et al. proposed the usage of a genetic algorithm for the reconstruction of FBG-based sensors [6].In this paper we propose, for the first time, utilization of a genetic algorithm (GA) to achieve the demodulation of a resonant cavity based on FBGs. RESONANT CAVITYThe resonant cavity was developed inscribing two low-reflectivity FBGs, approximately 1-cm apart, in a commercial high borongermanium co-doped optical fibre (Fibercore PS1250/1500). The fibre was placed on a motorized translation stage, thus allowing an , recurring to the phase-mask method. The experimental conditions were kept constant during the writing process, so it was expected that the parameters values for both gratings would be kept approximately constant. The cavity-reflection spectrum was measured using the phase-shift method, and a total of 311 data points were measured.The cavity complex reflection spectrum, for weak grating pairs, can be given bywhen r 1 () and t 1 () the reflection and transmission of the first grating, respectively. r 2 () is the reflection of the second grating, d represents the intragrating spacing, and n eff is the effective refraction index. The uniform grating reflection or transmission can be obtained analytically [7]. The objective is to find the cavity and FBG parameters coefficient that produce a reflection coefficient as close as possible to the target spectrum. To determine the correct parameters, we have implemented an algorithm which minimizes the errors between the measured spectrum and the analytical one, generated by Eq. (1), using a GA. The GA is an optimization method that requires only the information of the...

Analysis, Selection and Control of Optimal Driving Current Combinations in Wavelength Switching for DBR Lasers

“…Although it has many studies covering the methodologies of how to maintain wavelength stability in optic fiber communication system [2], it will be more effective by reducing the subsequent procedures in the wavelength stability operation if we can improve the output wavelength stability of the laser source; consequently we need a tunable laser with accurate and stable wavelength [3]. From technique point of view the Distributed Feed-back (DFB) Laser and Distributed Bragg Reflector (DBR) laser are the most matured laser fabrication processes [4][5][6][7]. It uses thermal modulation method to tune the laser bandwidth in DFB laser and because it has longer modulation time and shorter tunable bandwidth range; it usually makes DBR laser as the selected laser source for optic fiber communication system.…”