Low loss, low dispersion T-ray transmission in Microwires S. Afshar a , S. Atakaramians b , B. M. Fischer b , H. Ebendorff-Heidepriem a ,T. Monro a , and D. Abbott b a Centre of Expertise in Photonics, School of Chemistry and Physics, The University of Adelaide, Adelaide, SA 5005, Australia b Centre for Biomedical Engineering and School of Electrical & Electronic Engineering, The University of Adelaide, Adelaide, SA 5005, Australiam Email: Shahraam.afshar@adelaide.edu.au Abstract: We present low loss, < 0.01 1/cm, and dispersion, < 10 ps/(km.nm), properties of microwires for terahertz transmission. These wires have diameters smaller than the operating wavelength, resulting in the propagation of enhanced evanescent fields. ©2007 Optical Society of America OCIS codes: (260.3090) physical optics, infrared far; (060.2430) Fibers, single mode 1. Introduction Terahertz (THz) spectroscopic techniques have attracted a lot of interest due to their applications in detection of biological and chemical materials over the last decade[1]. Low loss and dispersion THz transmission is one of the key main issues of these techniques. Chen et al. have recently reported [2] loss values less than 0.01cm −1 near 0.3 THz in plastic fibers. The concept of THz guided propagation in these fibers is similar to nanowire optical fibers[3], i.e., the diameter of the fibers are smaller than the operating wavelength (THz) and hence we coin the term microwires for these fibers. Due to large wavelength-to-fiber-core ratio, the fractional power delivered inside the lossy core of microwires is reduced, thus reducing the overall loss. Based on measurements of the refractive indices of four glasses (F2, SF6, SF57 and Bismuth) and a polymer (PMMA) in terahertz spectrum region, and an analytical model of vectorial form of Maxwell’s equations for a simple rod geometry, we have investigated the loss and dispersion properties of microwires with different core diam rs and glasses. ete 2. Experiment and results To measure the refractive indices and losses of the glasses and the polymer, we use a commercially available THz time-domain spectrometer (Picometrix T-Ray 2000). The samples are well polished on both sides with cross section of 2 cm x 2 cm and 0.5 mm thickness. The results of the measurements of the refractive indices are show in Fig1., which indicates higher refractive indices of the glasses in comparison with PMMA. Based on experimental results and solution of vectorial form of Maxwell’s equations, we have calculated the power fraction, PF; the fraction of total power of a guided mode existing outside the waveguide, as shown in Fig 2. Figure 1. Refractive indices of the bulk materials Figure 2. Power fraction outside the microwires measured with a THz time domain spectrometer. versus the diameter at f = 0.5 THz (λ = 600 µm). Figure 2 clearly indicates that for microwires with diameter below the wavelength (λ=600 μm), PF approaches unity. However the slop and the value of the PF depend on rod-air refractive index contrast. Defining the effective loss of a microwire as the material loss (rod and air) averaged with respect to the field distribution in the transverse directions, we have calculated the effective loss of microwires with different diameters and glass/polymer compositions at the wavelength λ = 600 μm, as shown in Fig. 3. For microwires with diameters above the wavelength, the effective loss approaches the loss values of the initial bulk materials. However, in the a2468_1.pdf JWA105.pdf