Fabrication of photonic crystal fiber optical attenuators with air hole diameter control using CO2 laser irradiation technique

•Photonic crystal fiber attenuators were fabricated using CO2 laser irradiation.•The air hole diameter ratio to pitch could be controlled by laser power adjustment.•The attenuation could be controlled by adjustment of the air hole ratio.•The attenuators exhibited good wavelength independent characteristics.•The attenuation phenomena in the attenuators were theoretically discussed.

Photonic crystal fiber (PCF) optical attenuators with air hole diameter control were fabricated by PCF fusion using CO2 laser irradiation technique. The diameters of air holes in the PCF cross-section were equally decreased by laser irradiation with a PCF rotation. We demonstrated that the air hole diameter or the air hole diameter ratio to pitch could be adjusted by the irradiated laser power. It was clarified that the larger attenuation could be obtained for the smaller air hole diameter ratio to pitch. The attenuation was controlled from 5 dB to 20 dB at 1550 nm-wavelength for the air hole diameter ratio to pitch from 0.35 to 0.225, where the length of air hole diameter controlled region was 10 mm. It was also clarified that the fabricated PCF optical attenuators exhibited good wavelength independent characteristics for 980 nm-, 1310 nm-, and 1550 nm-wavelengths.