Investigation of transmission and reflection of antiresonance in a SMF-capillary-SMF structure

The antiresonance spectral characteristics based on a silica capillary sandwiched between two single-mode fibers are investigated on the aspects of both transmission and reflection. Basic theory of the antiresonance reflecting optical waveguide model is presented and analyzed for this structure. During the fabrication, suitable parameters are adopted in in the manual welding process to keep the cross section of the capillary fiber away from the discharge electrode, which ensures the smoothness between the welding surfaces. Subsequently, three experimental samples are fabricated with the same inner diameter and various lengths of 650 μm, 837 μm, and 1070 μm, respectively. It can be observed that devices with different lengths have the same resonance wavelength in the wavelength range of 1500-1700 nm. However, the transmission depth at the resonance wavelength increases with the increase of the capillary length. We also discuss the relationship between inner diameter and transmission spectra through three samples with inner diameters of 25 μm, 50 μm, and 75 μm. The experimental results show that the free spectral range is 22.9 nm, 29.8 nm, and 44.1 nm, respectively. It also exists antiresonance in the reflection, which shows a novel mechanism for possible sensing applications.