Slit beam shaping technique for femtosecond laser inscription of enhanced plane-by-plane FBGs

Roldán Varona, Pablo; Pallarés Aldeiturriaga, David; Rodríguez Cobo, Luis; López Higuera, José Miguel

doi:10.1109/JLT.2020.2992568

Ver/Abrir

SlitBeamShapingTechn ... (3.000Mb)

Identificadores

URI: http://hdl.handle.net/10902/20861

DOI: 10.1109/JLT.2020.2992568

ISSN: 0733-8724

ISSN: 1558-2213

Fecha

2020-08-15

Derechos

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Publicado en

Journal of Lightwave Technology, 2020, 38(16), 4526-4532

Editorial

Institute of Electrical and Electronics Engineers Inc.

Enlace a la publicación

https://doi.org/10.1109/JLT.2020.2992568

Palabras clave

Femtosecond laser

Fiber bragg grating

Optical fiber sensor

Plane-by-plane

Slit beam technique

Resumen/Abstract

In this work, the development of plane-by-plane (Plb-Pl) fiber Bragg gratings (FBGs) by using a single pulse is reported. A slit oriented along the longitudinal axis of the fiber is employed for this. The purpose is to shape the beam so that the focal volume is spatially wider in the transverse direction of the fiber. In this way, it is possible to make 2-D modifications of the refractive index whose width and height depends on the slit width and the pulse energy, respectively. Through an analytical mathematical modelling, the relationship between the diameter of the Gaussian laser beam (D ) and the slit width (s = D,) is determined in order to obtain a circular cross-section. In the experimental results carried out, it can be observed that D /D, = 3 ratio cause positive and uniform refractive index changes, compared to the negative and inhomogeneous refractive index changes corresponding to point-by-point (PbP) FBGs. Likewise, Pl-b-Pl FBGs, presenting a broader modification of the core cross-section, show significantly lower losses in transmission (0.3 dB), as well as better reflectivity and FWHM. It is observed that these three parameters (losses, reflectivity and FWHM) have a monotonous tendency according to the slit width. Polarization-dependence is also evaluated.