# 04 - Photonic crystal fibers with disordered claddings - a new path towards improved light guidance in defect cores

**Source**: https://www.cs.tum.de/spp1839/projects/1st-period-2015-2018/04.html
**Parent**: https://www.cs.tum.de/spp1839/projects.html

Photonic crystal fibers (PCFs) represent a
special type of optical fiber including sophisticated internal
microstructure and having led to applications in various areas such as
biophotonics or nonlinear optics. One particular PCF geometry contains
regular arrays of longitudinal dielectric strands with refractive
indices higher than the host material and extending through the entire
length of the fiber. Such an array acts as a photonic band gap (PBG)
medium and light guidance along the fiber is achieved by omitting one
or more holes within the array, i.e. doping the lattice. Due to the PBG
effect, these fibers guide light within particular spectral intervals -
so-called transmission bands - with the bandwidth predefined by the
strand and/or array properties. Another type of band gap fiber are
hollow-core (HC) PBG fibers, including air hole arrays with a central
HC. These fibers have recently gained significant attention due to
promising applications in e.g. particle acceleration or in nonlinear
ultraviolet generation. Both PBG designs include regular arrays of
strands and, as a result, reveal particular undesired properties such
as limited transmission bandwidths, showing that regular hole arrays
are not favorable for all possible applications. In the proposed
project we plan to investigate and understand the influence of
different types of disorder on the optical properties of PCFs and
develop new types of disordered fiber claddings with the overall idea
of going beyond the state-of-the-art of currently used PBG-PCFs.

The main objective of the project is to evaluate if
disorder within the PCF-cladding can lead to improved guidance
properties in terms of phase and group velocity dispersion, model
attenuation, robustness against bending and transmission window
bandwidth. The disorder is introduced either by material variation or by
diameter or shape modifications. The first benchmark geometry are
all-solid fibers with disordered claddings allowing studying all
relevant cladding properties related to disorder in a controlled manner.
In a second step, the project will be focused on PBG fibers with
liquid-filled HCs. These fibers have an entirely solid cladding
consisting of disordered arrays of HI strands in a low index matrix with
a central liquid core, which typically has a lower index than the
matrix itself. The project comprises on the one hand in-depth
theoretical investigation and design studies (Weiss group) and, on the
other hand, the experimental implementation and precise characterization
of such novel kind of fiber (Schmidt group). The project will define a
new class of microstructured fibers with engineered properties and
applications in highly-relevant areas such as biophotonics or nonlinear
optics.

## Contributors

- [Prof. Markus A. Schmidt](http://www.acp.uni-jena.de/schmidt.html)
- [Prof. Thomas Weiss](http://www.pi4.uni-stuttgart.de/home/institute/junior_research_groups/physical_optics)

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