Micro-void arrays in an optical fiber machined by a femtosecond laser for obtaining bending direction sensitive sensors

Abstract

Novel devices can be produced by means of femto-second laser processing. A new function of the optical fiber sensors has successfully achieved by a femto-second laser to detect directional bending which has been impossible for conventional fiber sensors. The proposed sensor has an internal structure which is consisted of micro-voids array configured along the optical fiber axis in a non-axially asymmetric configuration. The bending direction can be detected sensitively with the sensor to intensity changes of light through the fiber core because of the non-axial form of produced voids array. A laser processing system has been constructed to accomplish the fine control of laser beam for precisely creating micro structures in a very thin optical fiber core region with a monitoring camera by which the micro structures made can be viewed. Optimum irradiation conditions were set so as to fabricate sensor elements with different sensing lengths. Based on the directional detection principle proposed in this work, various sensor performances has been obtained in terms of the possibility and repeatability for directional bending detection by observing transmitted light intensity through the optical fiber core.