Automated technique to inscribe reproducible long-period gratings using a CO_2 laser splicer

Abstract

We propose a technique to inscribe long period gratings (LPGs) in standard single-mode fibers (SSMFs). The proposed method uses a commercial CO₂ splicer that allows for the rotation of the fiber during laser irradiation, enabling a uniform exposure around the fiber. LPGs inscribed in SSMFs with different periods are presented. Gratings can be reproduced with a maximum difference between resonant wavelength values of less than 1 nm. Furthermore, it is possible to inscribe gratings with attenuation dips of -25 dB while at the same time obtaining polarization-dependent losses as low as 2 dB.

Analysis of Long Period Gratings Inscribed by CO2 Laser Irradiation and Estimation of the Refractive Index Modulation

“…The LPGs were inscribed using the technique proposed in [ 13 ], which uses a commercial CO 2 laser fiber processing system (LZM-100 LAZERMaster from AFL Fujikura, Chessington, Surrey, UK). This point-by-point technique allows for constant rotation of the fiber during irradiation, leading to a uniform exposure around the fiber that results in a circularly symmetric refractive index change.…”

“…Segments of the fiber are periodically exposed to 10.6 µm wavelength radiation from a CO 2 laser, producing a localized fiber heating and a consequent refractive index change [ 11 ]. Several CO 2 laser irradiation techniques to inscribe LPGs with antisymmetric and symmetric irradiation have been demonstrated and improved [ 2 , 11 , 12 , 13 ]. At the same time, studies on the physical mechanism involved in the refractive index change have been performed.…”

“…Here, we report a detailed theoretical model, based on coupled mode theory, for CO 2 laser symmetrically irradiated LPGs in SMFs that permit the estimation of the refractive index change from the LPG transmission spectrum. We use an automated LPG inscribing technique recently proposed in [ 13 ] that has the advantage of producing highly reproducible LPGs with a circularly symmetric refractive index change. The theoretical model takes into consideration the specifications of this inscription technique.…”

UV Inscription and Pressure Induced Long-Period Gratings through 3D Printed Amplitude Masks

“…[5]. LPGs have been fabricated with a variety of techniques, such as irradiation through: UV laser [1], CO 2 laser [6], and femtosecond laser [7]; electric arc discharge [8,9]; mechanically induced by pressing a periodically grooved plate on a fiber [10][11][12] using machined metallic or silica plates [10], v-grooves on a tube [13]; coil spring [14], and recently, pilling of blades [15], and 3D printing of amplitude masks [11,12]; ion implantation [16]; and periodical etching of the fiber cladding to produce a corrugated structure [17]. Among those, the CO 2 and the UV laser inscription have been one of the most used.…”

“…However, deep UV lasers (e.g., krypton fluoride (KrF) at 248 nm wavelength and the argon fluoride laser (ArF) at 193 nm wavelength), are wide spread due to their wide use in optical lithography. Furthermore, through the UV inscription, it is possible to modulate the core refractive index homogeneously, contrary to side irradiation through CO 2 laser, where additional methodologies such as fiber rotation, use of mirrors, etc., are needed [6,[18][19][20]. Additionally, the widespread use of Bragg grating inscription systems using UV lasers makes its use an opportunity for the fabrication of LPGs, even considering the requirement of photosensitive fibers [5].…”