Femtosecond laser enabled selective micro-holes drilling on the multicore-fiber facet for displacement sensor...

We experimentally demonstrate a femtosecond laser enabled selective micro-holes drilling technique on the multicore-fiber facet. The precise position of individual cores at the seven-core fiber facet is initially locked by the image processing algorithm, and then six micro-holes are successfully fabricated after the pulse energy of femtosecond laser is optimized. Meanwhile, the use of fabricated seven-core fiber for the application of reflective intensity-modulated fiber optics displacement sensor (RIM-FODS) is comprehensively investigated. By using the beam propagation method (BPM), we theoretically investigate the effect of micro-hole depth on the RIM-FODS performance, in terms of both dead zone and measurement range. We identify that, with the increase of micro-hole depth, the dead zone range can be substantially reduced at the expense of measurement range reduction. However, multiple micro-holes with a successive depth difference can overcome such problem. When the micro-holes with depths of 5, 10, 15, 20, 25, 30 μm are fabricated on the seven-core fiber facet, and the dead zone range can be substantially reduced from 150 μm to 20 μm, together with an extension of measurement range from 250 μm to 400 μm.