Advances in Optical Fiber Laser Micromachining for Sensors Development

Abstract

Additional information is available at the end of the chapter http://dx.doi.org/10.5772/52745. Introduction "oth lasers and optical fibers technology appeared in the s, being, from the start, close related. Even though the latter gained increased visibility in telecommunications, first experiments using optical fiber sensors are reported from early s. From then on, research in optical fiber sensors has increased taking advantage of their potential when comparing with traditional sensors. "lthough there are many well established techniques to manufacture optical fiber sensors, the use of laser technology as increased as their cost diminishes at least for older, well matured laser sources technology and new laser sources appeared. This new tool has the advantage of producing well controlled light beams.Nowadays, laser processing of optical fibers in the production of fiber-based sensors is an important research theme. In particular, the use of infrared radiation has directed attention as new applications were found and new short pulsed laser technology have been developed. In this chapter we will describe the main technology used and the physical principles involved. The key parameters in laser radiation interaction with the fiber materials will be described as well as the most common types of fiber-based sensors that can be produced. The application of ultraviolet UV , near-infrared NIR and mid-infrared MIR radiation in the fabrication of fiber grating FG sensors is analysed. The physical principles are described and a comparison between theoretical modelling and experimental results is presented for MIR radiation writing of long-period fiber sensors LPFG . Micromachining with nanosecond ns pulsed near-infrared laser radiation is presented and illustrate an ongoing research in the use of this type of laser to produce new cavity-based optical sensors. Experimental work is presented and its potential application is analysed. . Laser interaction with optical fiber materialsLaser interaction with the materials in general and optical fiber material in particular, depends on several parameters. These are related with the laser source its wavelength and emission regime, mainly and also on the characteristics of the material itself.Generally speaking, the common fibers used as sensors are made of glass materials. "lthough plastic and polymeric materials are also used, usually sensors are produced from fibers made of ultra pure chemicals like silicon tetrachloride SiCl , germanium tetrachloride GeCl and also phosphorus oxychloride POCl . The improvement of their optical properties is accomplished by doping with germanium, erbium and ytterbium among other rare earths. Nevertheless, in the purpose of this chapter, fused silica pure or doped will be considered as the typical bulk material for laser interaction regarding fiberbased optical sensors.The most common lasers emit either in the UV, visible or infrared IR . However, UV and IR lasers have been the major players in the field of processing optical fibers given that th...

Ultrashort Long-Period Fiber Grating Sensors Inscribed on a Single Mode Fiber Using CO2 Laser Radiation

“…This can be illustrated considering Figure 2, which shows the characteristic LPFG's phase matching curve, representing res versus Λ for a grating with 6 mm length, and considering a 2-layer model and an asymmetrical mode [46][47][48]. The plot shows a set of periods (Λ) complying with the phase matching condition (see (1)) for different resonance wavelengths. Each line represents a cladding mode, from the lowest-order mode ( = 1) to the highest-order mode ( = 7) (right to left).…”

“…Compared to other optical devices, LPFGs have a number of unique advantages: low insertion losses, high temperature sensitivity, and relatively simple fabrication. A further advantage of LPFG devices is their higher sensitivity to the environmental refractive index change without the need for access to the evanescent field, as in the case of the FBGs [1].…”

Recent Developments in Micro-Structured Fiber Optic Sensors

“…With the advancements of laser technology, new fabrication methods for micro-structured fiber-optic sensors have been employed [178]. In particular, femtosecond laser and excimer laser are good candidates due to their high instantaneous power and high single-photon energy, which is able to ablate the micro-structure with good quality [179,180].…”

3D Finite Element Model for Writing Long-Period Fiber Gratings by CO2 Laser Radiation

“…Within the family of thermal techniques, MIR from CO 2 lasers has guaranteed better predictability and repeatability [15]. …”

“…Since the first reports by Davis et al [13] and Akiyama et al [14] on the use of a 10.6 μm wavelength laser beam emitted by a CO 2 laser, different experimental methodologies have been used to write LPFGs [15]. The most common is, probably, using a static asymmetrical irradiation with a CW CO 2 laser and a cylindrical lens focusing a laser line on the fiber.…”