Submitted to: Proceedings of SPIE
Publication Type: Proceedings
Publication Acceptance Date: 10/19/2004
Publication Date: 11/30/2004
Citation: Chen, G. 2004. Profile optimization of tapered waveguide sensors by luminescence imaging. Proceedings of SPIE.
Technical Abstract: Fiber-optic evanescent field sensors provide unique analytical features. For a single-fiber configuration, the sensing zone geometry plays an important role in coupling excitation energy to the evanescent field and reciprocally collecting the fluorescence signal. A linear tapered fiber geometry was demonstrated to outperform cylindrical geometry in both aspects by V-number conversion within the taper zone. Besides the intrinsic limitation of extremely small penetration depth in evanescent field, the spectroscopic throughput of the fiber tapered sensor is further restricted by the small fiber diameter. Up to now, studies on taper profile optimization are restricted due to limited techniques to create fiber tapers and the fragile nature of the finished sensors. To improve spectroscopic throughput, we scaled up waveguides to a 6 mm diameter. The tapered waveguides were fabricated from quartz rods by traditional torch drawing technique. Exponential-linear tapers provided the best spectroscopic performance among other geometries. Their profile was further optimized based on fluorescence imaging, a technique that visually revealed the location and intensity of light leaking from the core to the cladding. The finished taper sensors were used in time-resolved luminescence (TRL) measurements using tetracycline as a model analyte. A linear response was observed in 0-1 ppm range with r2 = 0.9999, and a 1.34 ppb limit of detection (LOD) was achieved.