Fluorescein filled photonic crystal fiber sensor for simultaneous ultraviolet light and temperature monitoring

• Using the fluorescein in combination with photonic crystal fiber.
• Unique properties of fluorescein investigated.
• Proposal and realization of the optical fiber sensor structure.
• The ultraviolet light and temperature sensitivity demonstrated.
• The potential of using as a tunable optical fiber are outlined.

We present a novel structure composed of a photonic crystal fiber filled with fluorescein dissolved in water spliced between two conventional multimode fibers. Based on unique features of the fluorescein luminescence it is possible to adjust its emission spectrum to required spectral region. With increasing value of the fluorescein solvent pH factor, the peak wavelength of the emission spectrum is shifting to longer wavelength values. Since the excitation spectrum of fluorescein is relatively wide, this optical fiber sensor could be used for an efficient ultraviolet light monitoring. The detection limit at the level 0.24 mW with 490 nm excitation wavelength is presented. Moreover the emission spectrum is temperature sensitive what provides possibility of simultaneous ultraviolet light and temperature monitoring. Also the temperature sensitivity of the structure based on intermodal interference investigation for a compensation purposes and structure usage as spectrum enlarger are outlined.