Polymer fiber waveguides for terahertz radiation

Terahertz radiation offers many exciting applications noticeably in spectroscopy and it is showing promising results in imaging, mainly for security applications. In this project the study of using structured polymer fibers for THz waveguiding is presented. The inspiration for the THz fiber is taken from microstructured polymer optical fibers (mPOFs) used at optical wavelengths for sensing and communication.

The fibers investigated can be divided into two groups, the solid core fibers and the hollow core fibers. The solid core fibers offer the broadest bandwidth with the best dispersion profile, while the hollow core fibers hold the promise for lowest loss but at the cost of lower bandwidth. In both cases the fabrication and characterization of the fibers is presented.

The fibers are also investigated numerically and the numerical results are held up against the experimental results. The polymer material with lowest loss is Topas and all the solid core fibers are manufactured using this material. The polymer PMMA however has higher refractive index along with higher loss, and this higher refractive index is utilized to achieve a large bandwidth hollow core fiber with a low air-fill fraction.

Finally, an example of an application is presented in the form of a broadband 3-dB directional fiber coupler. The device is numerically investigated and designed in such a way that it is manufacturable.