Transverse coupling to the core of a photonic crystal fiber: the photo-inscription of gratings.

The effect of the microstructure on transversely coupled laser light into the core of a photonic crystal fiber is investigated. Computational two-dimensional modeling and direct experimental measurements indicate that there exist angles and positions of the fiber microstructure, relative to a transversely launched laser beam, that preferentially couple laser light into the fiber core. The implications of these observations on long period and fiber-Bragg grating fabrication in photonic crystal fibers are discussed.