We study a novel fabrication method of micro/nano optical fiber by mechano-electrospinning (MES) direct-written technology. MES process is able to precisely manipulate the position and diameter of the electro-spun micro/nano fiber by adjusting the mechanical drawing force, which through changing the speed of motion stage (substrate). By adjusting the substrate speed, the nozzle-to-substrate distance and the applied voltage, the poly(methyl methacrylate) (PMMA) micro/nano optical fibers (MNOF) with controlled diameter are obtained and the tapered MNOF are fabricated by continuously changing the substrate speed. The transmission characteristics of PMMA micro/nano fiber is experimentally demonstrated, and a PMMA micro/nano fiber based refractive index sensor is designed. Our works shows the new fabrication method of MNOF by MES has the potential in the field of light mode conversion, optical waveguide coupling, refractive index detection and new micro/nano optical fiber components.
Tilted fiber Bragg gratings (TFBGs) have been demonstrated to be accurate refractometers as they couple light from the fiber core to the cladding. In our experiment, we changed the physical structure of the TFBGs to improve the refractive index sensing ability. One way is to stretch the grating section 5 mm longer. The result showed that not only the number of the cladding mode of the TFBG decreases but also the full width half-maximum (FWHM) of the cladding modes and core mode changes. The FWHM of the cladding mode of the tapered TFBG is more than twice than that of the original. However, the refractive index sensitivity of the tapered TFBG has no obvious improvement. Another way is to etch the grating section with 20% hydrofluoric acid solution. We find that the smaller the clad diameter, the higher the refractive index sensitivity of the TFBG.
Wavelength division multiplex technology can enhance the sensing capacity by detecting various samples simultaneously. Whisper-Gallery-Mode (WGM) can be selected simulated in the micro-bubble by a directional coupler made by Si3N4 grating. Some grating parameters, including period, width, and refractive index modulation are numerically simulated by FDTD solution software to find their impacts on the WGM selected process. Grating with a particular period can simulated a WGM in micro-resonator on purpose. The interference of different bubble resonators is also discussed in this paper.
Microbubble resonators combine the unique properties of whispering gallery mode resonators with the capability of integrated microfluidics. The microbubble resonator is fabricated by heating the tapered tip of a pressurized glass capillary with oxyhydrogen flame. Firstly, a microtube with a diameter of 250um is stretched under heating of oxyhydrogen flame, the heating zone length is set to be 20mm and the length of stretch is set to be 7000um.Then nitrogen will be pumped in to the tapered microtube with the pressure of 0.1Mpa, the tapered tip will be heated by the oxyhydrogen flame continuously until a microbubble forms. An optical fiber taper with a diameter of 2 um, fabricated by stretching a single-mode optical fiber under flame was brought in contact with the microbubble to couple the light from a 1550nm tunable diode laser into the whispering gallery mode. The microbubble resonator has a Q factors up to 1.5 × 10<sup>7</sup> around 1550nm. Different concentrations of ethanol solution (from 5% to 30%) are filled into it in order to test the refractive index sensing capabilities of such resonator, which shows a sensitivity of 82nm/RIU.