Enhancing the locality of optical interrogation with photonic-crystal fibers

Small-core photonic-crystal fibers (PCFs) are shown to enhance the locality of optical interrogation in fiber-probe-based imaging. We demonstrate that, in a typical fluorescence imaging experiment, the longitudinal dimension of the interrogated region closely follows the amtan−1θd scaling with the effective mode radius am and the beam-divergence angle θd. The confinement of optical interrogation provided by small-core, high-index-step PCF probes is high enough to enable interrogation of individual neurons in a typical brain imaging experiment.