TNT Vapor Detection Based on a Lab-on-a-Fiber: Achieving a Millimeter-Scale Sensing Element on Fiber

In this paper, we discuss in detail the lab-on-a-flber (LOF) concept that we proposed earlier (Ma et ah, Proc. 4th Eur. Workshop Opt. Fiber Sens., 2010, vol. 7653, PP. 76531E-76531E-4), and present a specific example of this platform intended for trace vapor TNT detection. We show how we arrive at the current LOF design by examining the performance, technical difficulties, and complexities of various possible architectures. In the design solution adopted in our example, the sensing section occupies a space measuring only 1.6 × 1.6 × 0.8 mm, but contains several optical and chemical components/functions including a transmission/reflection mirror and TNT sensory film coated on a segment of the side wall of the fiber core. The fiber itself thus serves as the film substrate and when coated with the film becomes an evanescent-wave form fluorescent emission power collector. Its tiny dimensions notwithstanding, the LOF performs several simultaneous functions, including power density tuning and stray excitation light blocking. In addition, this LOF platform features ease of system construction and polymer film application. We demonstrate its fast response to TNT vapor, in the form of a 29% signal drop after 10 s of exposure.