Fabrication of a side aligned optical fibre interferometer by focused ion beam machining

Abstract

Focused ion beam (FIB) machining is a promising technique for the fabrication of micro-optical components with high quality surface finishes. In this work, a prototype of a side aligned optical fibre interferometer was successfully fabricated by the three-dimensional deterministic FIB machining technique. A highly accurate 45• reflective mirror with surface roughness (Ra) of 10 nm has been successfully fabricated at the centre of the fibre to direct the core guided light to the side of the fibre. A surface topography simulation method was developed to simulate the ion beam polishing process. According to the simulation result, a 0.5• offset on the ion beam polishing direction is necessary to maintain the machining accuracy. In the fabrication process, it was also found that for structures requiring a high aspect ratio the existence of an open edge can mitigate against the material redeposition on the sidewalls and therefore increase the overall material removal rate. The fibre has been tested optically and the interference signals have been successfully observed, demonstrating the alignment accuracy of the fabrication method.

Optical Fiber Probe Microcantilever Sensor Based on Fabry–Perot Interferometer

“…Except for the literature mentioned above, Sun et al [ 90 ] proposed a prototype of a fiber-side microcantilever fabricated by a three-dimensional deterministic FIB machining technique. As shown in Figure 11 , a deep groove was machined in the top of a single-mode fiber, which formed a Fabry–Perot cavity.…”

“…Different from ref. [ 90 ], Li employed a ps-laser to produce the deep groove with high-speed material removal, while the microcantilever surface and the 45° reflective mirror was still machined by FIB milling to obtain a smooth optical surface. The performance test indicated that the side-microcantilever accelerator has an acceleration measurement range from 0 g to 6 g with a resolution of 0.01 g.…”

A review of focused ion beam applications in optical fibers

“…It has also been effectively used to cleave and polish the fiber endfacet [131][132][133][134][135][136][137]. In addition, FIB machining has been employed for fabricating lab-aroundfiber and lab-in-fiber devices such as microgratings [138][139][140][141][142][143][144][145][146][147][148][149][150], microcavities [151][152][153][154][155][156][157][158][159][160], as well as access holes and channels [161][162][163][164][165][166][167][168][169]. It is worth mentioning that the beam shaping structures fabricated on the fiber tip predominate in FIB applications in optical fibers (figure 7).…”

“…Furthermore, a side aligned optical fiber interferometer was experimentally demonstrated by Sun et al using FIB milling [159]. A high beam current of 50 nA at 30 kV was used to remove huge volume of the fiber material to create a high aspect-ratio (∼20:1) cavity for sensing.…”