Collimated microfiber spectroscopy for optical characterization of disordered porous anodic alumina

A novel collimated microfiber spectroscopy technique using an optical fiber probe with microball lens was developed to observe the photonic crystalline characteristics of porous anodized alumina (PAA) slabs with disordered arrays of holes. Transmittance spectra of the PAA slab observed by the microfiber probe with ball lens showed a broad valley at ~410 nm; conversely, no significant valley was observed by an ordinary microfiber spectroscope without ball lens. The broad valley was comparable with that observed in a spectrum simulated for a model based on a scanning electron microscopy image of the PAA slab by using the finite-difference time-domain method.