Applied technique of focused ion beam milling based on microstructure of photonic bandgap fiber

In this paper, a precision micromachining technique for photonic bandgap fiber (PBGF) using focused ion beam (FIB) milling was reported. Types of PBGF have the honeycomb structure with a hollow core surrounded by microstructured cladding, and the widths of the thin silica struts are only 10∼100 nm. The shape of fiber section is the most important prerequisite for maintaining good output coupling efficiency and allowing gas diffusion. Therefore, a proper machining method can avoid microstructure collapse and is crucially important for the experimental investigations. The FIB milling process was discussed and realized to improve performance of PBGF gas cell in this study. The absorption spectra of acetylene (C₂H₂) gas and methane (CH ₄) gas have been investigated using the propose measurement system based on PBGF gas cell. The experimental results clearly indicated a high overlap between the propagating light and filled gas inside the PBGF. Therefore, these studies can contribute to highly sensitive gas sensing, higher accurate wavelength references, and other applications.