Research On Micro-/Nanofiber Bragg Gratings And Their Applications

As one of the typical micro/nanoscale optical waveguides, micro-/nanofibers (MNFs) offer a number of advantages including high compactness, large surface-to-volume ratio, large fractional evanescent fields, high mechanical strength and low optical loss. In recent years, MNFs and MNF-based microphotonic devices have been attracting increasing attentions and have become a hot topic in the area of fiber optics and micro/nanophotonics.This work started from the taper-drawing fabrication of MNFs. Based on the existing techniques, we proposed a novel approach to fabricate ultra-long microfibers (MFs) with diameters of several micrometers and lengths up to tens of meters. Employed an auto-termination mechanism in laser-heated fiber tapering, we optimized the heating power from a CO2 laser, speed of a DC motor for taper drawing, and a step motor for winding the as-drawn MF, and fabricated ultra-long MFs reproductively.The second part of the work focused on the fabrication and optical characterization of MF Bragg gratings (MFBGs). Using focused ion beam milling technique, Bragg gratings are written on the MFs with diameters less than 2μm. Evident grating features with transmission dip up to 15 dB are obtained. Benefited from the high-index contrast of the grating structure, the length of the MFBG can be reduced to 500μm. Additionally, the grating-length-dependent behavior of the MFBG is also investigated.Finally, we investigated the possibility of using MFBGs for sensing applications. We use a 1.8-μm-diameter MFBG for measuring the concentration of a glycerin solution. Based on the spectral shift of Bragg wavelength, we determined the surrounding refractive index (RI), and consequently the concentration of the glycerin solution, with a RI sensitivity up to 660 nm/RIU at a RI of 1.39.Benefitted from their small footprints, fiber-optic compatibility, high strengths and high sensitivity to environment, MFBGs may find applications in miniaturized fiber-optic filters, resonators and lasers, and represent a new type of functional structures integrating fiber optics and nanotechnology.