Polymer microstructured fibers for guiding of THz radiation: [invited]

Waveguides of various kinds for guided propagation and manipulation of light at terahertz (THz) frequencies are currently attracting considerable attention. There are several applications and perspectives which drive the development of techniques for waveguiding of broadband as well as narrowband THz radiation, including low-loss transport of THz signals [1] between high-speed devices, integrated components for manipulation of THz light [2], such as power splitters, polarization management, and frequency filters, and confinement of the electric field of a THz signal in a small volume, enabling spectroscopic investigations of minute sample quantities [3]. In this presentation we will describe our current efforts in the development, fabrication and characterization of a class of THz waveguides and components based on microstructured polymer optical fibers (mPOF’s) [4] designed for the THz frequency range [5]. Fabrication and characterization of tailored mPOF’s Similar to photonic crystal fibers for the near-infrared, we fabricate our mPOF structures in a fiber draw tower. Based on numerical simulations, a fiber cross section is first designed using standard and custom finite-element methods and FDTD methods, and based on the design, a preform is drilled in a low-loss polymer preform. This preform is heated to above the glass transition temperature of the polymer, and the preform is drawn to the desired dimensions in a single manufacturing step. Optical characterization of the fabricated fibers and components is carried out by THz time-domain spectroscopy, where the amplitude and phase of the transmitted signal through the sample is compared to a reference signal. In this manner we can characterize both loss and dispersion of the waveguide. In addition, near-field measurements across the facets of the fiber have allowed a direct visualization of the guided modes in the fiber [5]. We will discuss the optimal material choice for various kinds of polymer-based fibers, including solid-core and air-core photonic crystal fibers, and show examples of characterization of such components. We will also discuss the design of extremely broadband power splitters for the THz range with a uniform 3-dB splitting ratio of several hundred GHz.