78 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 26, NO. 1, JANUARY 1, 2014 Optical Fiber Microcavity Strain Sensors Produced by the Catastrophic Fuse Effect Paulo F. C. Antunes, M. Fátima F. Domingues, Nélia J. Alberto, and P. S. André, Senior Member, IEEE Abstract— We present an innovative and cost effective approach to produced sensors based on optical fiber microcavi- ties. The proposed microcavities were manufactured by splicing a standard optical fiber with recycled optical fibers destroyed by the catastrophic fuse effect, yielding strain sensors with sensitivity up to 2.56 pm·με -1 . The feasibility of this solution employing recycled optical fibers was demonstrated, presenting an economical solution for sensing purposes, when compared with cavities produced using complex methods. We also show, for the first time, that the sensitivity of these microcavities Fabry-Perot interferometers sensors depends on the cavity volume. Index Terms—Fiber optic, fiber fuse effect, fiber optic sensors, Fabry-Perot interferometer. I. I NTRODUCTION O N the last decades, due to the considerable research investments worldwide, optical fiber sensors become one of the most promising sensing technologies. This result from the advantages over traditional electronic sensing, namely, the reduced weight and volume, the immunity to electromagnetic interference, the electrical isolation and reduced production cost [1]. Nowadays, optical fiber sensors are widely used for several applications, such as biometrics or structural health monitoring, among many others [2]–[4]. Within all the optical fiber sensing technologies, the ones based on Fiber Bragg grat- ings (FBG) or Fabry-Perot Interferometer (FPI) microcavities have become the most attractive due to the miniature size, linear response and higher sensitivity [1]–[6]. However, the sensors production based on these technolo- gies requires a significant economical investment for the implementation of the manufacturing equipment. Namely, for the FPI microcavities production, which are usually manu- factured with a femtosecond pulsed laser, requiring complex Manuscript received June 15, 2013; revised September 10, 2013; accepted October 23, 2013. Date of publication November 5, 2013; date of current version December 17, 2013. This work was supported in part by Fundação para a Ciência e Tecnologia through the Ph.D. Fellowship under Grant SFRH/BD/69097/2010, and in part by the Post-Doctoral Fellowship under Grants SFRH/BPD/78141/2011 and SFRH/BPD/76735/2011. P. F. C. Antunes and M. F. F. Domingues are with the Instituto de Telecomunicações and Departamento de Física, University of Aveiro, Aveiro 3810-193, Portugal (e-mail: pantunes@av.it.pt; fdomingues@av.it.pt). N. J. Alberto is with the Instituto de Telecomunicações and the TEMA- NRD, Mechanical Engineering Department and Aveiro Institute of Nanotech- nology, Aveiro University, Campus Universitário Santiago, Aveiro 3810-193, Portugal (e-mail: nelia@av.it.pt). P. S. André is with the Instituto de Telecomunicações and Department of Electrical and Computer Engineering, Instituto Superior Técnico, University of Lisbon, Lisboa 1049-001, Portugal (e-mail: paulo.andre@lx.it.pt). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LPT.2013.2288930 Fig. 1. Images of an optical fiber damaged by the catastrophic fuse effect: left) Fiber cross section SEM and right) optical microscopy, revealing the voids along the fiber core. The last produced void is visible in the left side. alignment and positioning systems. The relevance of the FPI based sensors is observed in several recently works involving the production, application and characterization of microcav- ities, see references [7], [8] and references herein. In this letter we propose a novel and cost effective solution to obtain optical fibers FPI sensors, based on microcavi- ties produced by the recycling of optical fibers destroyed through the catastrophic fuse effect. This technique consid- erably reduces the process manufacturing costs, making the manufacturing apparatus affordable and with smaller experi- mental complexity. II. SENSOR DESCRIPTION AND MANUFACTURE METHOD The catastrophic fiber fuse effect phenomenon, first observed in 1987, is characterized by the continuous self- destruction of the optical fiber, induced by high intensity optical signal [9]. The process can be initiated by a local heating point, a damaged or unclean connector or in a fiber tight bend [10], creating a fuse zone, that vaporizes the optical fiber core and moves towards the optical signal source, with a typical propagation velocity of 0.5 m · s -1 [11]. This phenomenon was initially ignored, due to the high power required to ignite the process. However, nowadays, the fiber fuse effect is considered a back draw for the propagation of high intensity signals in the optical fiber infrastructures. The fibers destroyed by this effect reveals the presence of periodic hollow voids in the core, whose dimensions and spatial period are in the order of a few micrometers [12]. These voids are in fact microcavities, as observed by scanning electronic microscopy (SEM) of the fiber cross section, Fig. 1 (left). After the interruption of the fuse zone propagation, the last produced void is characterized by a larger dimension, when compared with the remaining voids, as visible in the microscope image, Fig. 1 (right). 1041-1135 © 2013 IEEE