Design and 3D nanoprinting of fan-out diffractive elements for single-core to multicore fiber connections

Student thesis: Master's Thesis


Spatial division multiplexing in optical fiber technology is the latest addition to the multiplexing techniques in order to follow the ever-increasing demand for bandwidth. To make use of spatial division multiplexing one can utilize multicore fibers. Such fibers have been fabricated with low loss and low cross-talk establishing the need for practical connectors which bridge the gap between single-core and multicore fibers. This thesis aims to design a diffractive optical element that will be printed on the tip of a single-mode fiber and fans out the power in such a way that it projects as much optical power as possible on the cores. First a set of proof-of-concept diffractive optical elements is designed for a visible light laser source in VirtualLab. These are then imported into the software of the three-dimensional printer that utilizes two-photon polymerization direct
laser writing. In this thesis, the conventional direct laser writing method is used for the fabrication of the aforementioned diffractive optical elements on a borosilicate substrate.

The printed diffractive optical elements are optically inspected with a conventional optical microscope and then characterized by making use of a three-dimensional optical microscope which applies white light interferometry to generate the three-dimensional image. After inspection, the outputs of the different diffractive optical elements are measured and the theory is compared with practice. Finally, with the acquired knowledge and experience with the proof-of-concept, the diffractive optical element along with other parameters was downscaled by two orders of magnitude. In this new design space, a fan-out diffractive optical element is designed which can be fabricated on the tip of a single-mode fiber. After several iterations, it was found that thermally expanded core fibers can provide a solution for the problems found during the search for a design space.
This thesis is concluded with a design proposal which should theoretically work on a fiber tip at 1550 nm and several proposals for future work.
Date of Award28 Jun 2019
Original languageEnglish
Awarding Institution
  • Vrije Universiteit Brussel
SupervisorGebirie Yizengaw Belay (Advisor) & Koen Vanmol (Advisor)

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