Abstract

Index-guiding liquid-core photonic crystal fibers (PCFs) have received considerable attention lately due to their potential applications in sensing, spectroscopy, and nonlinear optics. These waveguides are generally obtained by selectively filling the central hole of a hollow-core PCF with the desired liquid. However, due to the micrometric dimensions of the core, the liquid may quickly evaporate, affecting guidance. In this paper we study evaporation as one of the possible mechanisms responsible for losses in index-guiding liquid-core PCFs. To this end, the evaporation rate of water is examined in capillaries with inner diameters that are similar to those of hollow-core PCFs. It was found that this rate initially decreases and then saturates at a constant value, which in general increased as the inner diameter decreased. The transmission loss of a water-core PCF was then measured over time at a wavelength of 633 nm. An exponential loss increase was detected, which is, indeed, expected if the evaporation rate is constant. The observed characteristic time of ~20 minutes is compatible with the expected evaporation rate. In summary, we find that evaporation is an important issue, which may limit the times over which experiments can be undertaken in liquid-core PCFs whose tips lie in air.

© 2008 AIP