A detector is provided for sampling and identifying a material, such as a medium in which the detector is disposed. The detector includes an annular photonic crystal fiber, first and second electrodes, an electrical power supply, an illumination source and an analyzer. The fiber has opposite longitudinal ends, surrounds a center core tube and includes fused capillary tubes. The electrodes are disposed between the fiber's longitudinal ends. The electrical power supply connects between the electrodes. The illumination source emits light into the core tube from one of the opposite ends. The analyzer for compares an emission pattern from light transverse to the fiber against an established pattern, and indicates match in response to correspondence between the patterns. The annular structure has a two-dimensional optical photonic band-gap. The analyzer monitors the emission pattern by optical frequency domain reflectometry or optical time domain reflectometry.