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Addressing Factors Affecting Fluorescent Signal Collection of a Multimode Photonic Crystal Fiber Fluorometer

A multimode photonic crystal fiber (PCF) fluorometer interrogated by a spectrometer is investigated. By adding a glass tip at the end of the PCF, we found that this fluorometer significantly enhances the fluorescent light collection efficiency (CE). Factors associated with the CE and stray light rejection are addressed. The experimental study verifies the proposed PCF probe based on the consideration of solely meridian rays. However, our further study in this paper shows the significance of skew rays under total internal reflection (TIR), which in fact carry 53% of the total guidable fluorescent signal power and are blocked in our experiment. We highlight that this missing power is strongly associated with the numerical aperture (NA) of each optical component in the system and suggest further improvement on the components in the system. The proposed PCF fluorometer is particularly efficient and cost effective for an immersion medium with a high attenuation.