Photonic Sensing: Principles and Applications for Safety and Security Monitoring

Chapter 5

Photonic Liquid Crystal Fiber Sensors for Safety and Security Monitoring

Tomasz Wolinski

Warsaw University of Technology, Faculty of Physics, Warszawa Poland

5.1 Introduction

In the past decade, photonic crystal fibers (PCFs) [1–3] have attracted an increasing scientific interest owing to a great number of potential applications, including that for fabrication of new class of in-fiber devices. PCFs are manufactured as an array of silica tubes and rods, which are then heated to around 2000°C and drawn down to the fiber. Their core is usually made by a defect in the periodical structure of the PCF cross section (missed or additional rod/tube). In this way, either a hollow-core PCF or a solid core PCF can be manufactured. Optical wave guiding in a PCF is governed by one of the two principal mechanisms responsible for light trapping within the core. While the first one is a classical propagation effect based on the modified total internal reflection (mTIR or index guiding) phenomenon, which is well known and similar to the wave guiding effect within a conventional fiber, the second, referred to as the photonic band gap (PBG) effect, occurs if the refractive index of the core is lower than the mean reflective index of the cladding region.

Infiltrating the air holes with different materials allows for creation of a special class of infused PCFs with enhanced optical properties. In this context, the application of liquid crystals (LCs) has gained particular attention, resulting ...