Research Of Laser Direct Writing Using Micro-and Nanofibers

We firstly reports a novel direct writing technique using micro-and nanofiber worldwide, which adopts the micro touch model during the exposure. The experiment results show that the writing resolution can be up to 350 nm. In the condition of inadequate exposure, the 100-nm-lines are achieved, which is lower than one quarter of exposure wavelength (442 nm).Direct writing techniques allow maskless definition of surface micro-and nanostructures, and it is necessary to develop the simpler, more cost-effective and higher resolution direct writing technique. Optical micro-and nanofibers have attracted much attention due to their advantages, such as tight optical confinement, low optical loss, high fraction of evanescent fields, strong field enhancement. All these attractive properties make the micro-and nanofiber suitable for maskless lithography. First, tight optical confinement can provide high exposure resolution. Second, low optical loss and strong field enhancement ensure exposure power. Third, high fraction of evanescent fields can be easily coupled into photoresist layer. Based on these properties, this dissertation presents a novel direct writing technique utilizing the micro-and nanofibers. Herein, the fiber probes are similar to an inked pen, transferring a laser "ink" from the probe tip to a photoresist layer through direct micro touch. However, there are some differences between the direct writing fiber probes and the usual micro-and nanofibers. The usual micro-and nanofibers are used to fabricate a variety of micro-and nanophotonic components or devices, such as fiber gratings, Mach-Zehnder interferometers, filters, ring resonators, knot lasers, etc, where they act as waveguides. Contrary to the above-mentioned uninterrupted micro-and nanofibers, the micro-and nanofiber probes are interrupted and serve as submicron-dimension point sources. They are also different from usual fiber tapers, which have some applications, such as sensors, filters, optical tweezers, etc. The fiber probes for direct writing gradually change its diameter to a submicron tip, so their cone angles are much smaller than those of usual fiber tapers.In this dissertation, the direct writing technique using micro-and nanofibers is described in detail. The micro-and nanofiber serves as a tightly confined point source and it adopts micro touch mode in the process of writing. Firstly, the propagation and endface pattern of micro-and nanofiber are theoretically shown. The energy distribution of direct writing model is analyzed by Three-Dimension Finite-Difference Time-Domain method. Secondly, the system and operation of laser direct writing using micro-and nanofiber are carefully established. Thirdly, the exposure model is caculated and the experimental results are presented. Experimental results demonstrate that micro-and nanofiber direct writing has some advantages:simple process, high resolution, large writing area, and controllable width of lines. In addition, by altering writing direction of lines, complex submicron patterns can be fabricated. In the end of this dissertation, the surface plasmons technique is introduced to this direct writing approach, and the simulation shows that the writing resolution is further improved via the excitation of surface plasmons.