Recent progress in research on photonic crystal fiber devices

Recent progress in research on photonic crystal fiber (PCF) devices that are fabricated by air hole state control with CO₂ laser irradiation is reviewed. Fabrications of polarization-maintaining PCF couplers (PM-PCFCs) and their coupling characteristics depending on states of air holes are described. The states of air holes in the tapered regions of couplers could be controlled by adjustment of the laser power density in the fusion and the elongation processes. It was demonstrated that the air hole remaining PM-PCFC exhibited polarization-splitting characteristics and that the air hole collapsed PM-PCFC had polarization insensitive coupling characteristics. Fabrications of polarization-maintaining PCF (PM-PCF) optical attenuators by air hole diameter control are also presented. The air hole diameter ratio to pitch of the PM-PCF could be controlled by the laser power adjustment. The desired attenuation could be obtained by the laser power adjustment because the attenuation depended on the air hole ratio.