All fiber on-line Raman detection system with silver-coated hollow fiber

We proposed a portable online Raman detection system with all fiber components, by inserting two large-diameter optical fibers respectively into each end of the inner metal-coated capillary for Raman excitation and signal collection simultaneously. The all fiber structure not only could enhance the interaction length between the excitation beam and the detecting material, but also provide a very effective Raman signal collection mechanism. Furthermore, in our proposed setup, the output fiber is bent back to the input side and form a Sagnac loop. Both inserted fibers act as the input port as well as the output port for the transmission and reflection mode simultaneously. With the combination of both modes and both beam directions, the Raman signal could be roughly enhanced 4 times. The result of theoretical modelling and the experimental measurement confirm that this portable all fiber detection system is a very effective way for Raman excitation and signal detection, which could be widely used for liquid and gas online detection system.