Modification of a photonic crystal fiber by selective collapse of the microstructure holes

In this paper, an optical fiber post-processing rig is described, as well as its use for collapsing selected holes in the microstructure of a photonic crystal fiber. As a result, discrete devices can be designed and fabricated. A PCF with the ring of holes nearest to the core locally collapsed is shown to operate as a modal Mach-Zehnder interferometer with a 35-nm spectral period and an 8-dB modulation depth. We also demonstrate the capability of producing complex structures, with the letter “M” inscribed in a PCF through the collapse of the selected holes.