Method and apparatus for nondestructive determination of core size of hollow-core photonic bandgap fiber using Fabry-Perot interference

摘要

The nondestructive determination of core size of a hollow-core photonic bandgap fiber (HC-PBF) using Fabry-Perot (FP) interference is performed with an apparatus including a tunable laser source (TLS), a 1×2 single-mode (SM) coupler, an SM collimator, a six-axis translation stage, an optical detector, and an oscilloscope. The light from the TLS passes through the 1×2 SM coupler and the SM collimator to perpendicularly enter two parallel air-SiO₂ interfaces of the core of the fiber and is reflected, while the TLS is tuned from one wavelength to another. Then the reflected spectrum is guided to the optical detector, where its interference intensity is converted into voltage intensity to be displayed at the oscillator and fitted with a least-squares method to obtain the distance between the two air-SiO₂ interfaces. The core size of the fiber can be obtained by rotating the fiber and repeating the procedure at multiple angular positions.