Photonic crystal fiber microtaper supporting two selective higher-order modes with high sensitivity to gas molecules

A photonic crystal fiber consisting of three rings of air holes was tapered down to 3-5 mu m. The voids of the fiber were collapsed so a solid microtaper was formed. In this microtaper two selective higher-order modes propagate and interfere. This makes the transmission of the taper to exhibit a sinusoidal pattern with subnanometric width fringes. It was found that the device was highly sensitive to gas molecules. The latter is attributed to surface refractive index changes, number of molecules enveloping the taper, and high sensitivity of the modes participating in the interference. (C) 2008 American Institute of Physics.