Transmission Properties of Subwavelength Planar Fractals for THz Wavelengths Zhang J.*(1), Ade P.A.R.(2), Tucker C.(2), Savini G.(3), Zhao G.Z.(4) (1) Computing and Technology Department, Anglia Ruskin University. East Rd, Cambridge CB1 1PT. UK. Jin.zhang@anglia.ac.uk (2) School of Physics and Astronomy, Cardiff University. The Parade, CF24 3AA Cardiff, Wales, UK (3) Optical Science Laboratory, Physics and Astronomy Department, University College London, Gower Street, London WC1E 6BT, UK (4)Department of Physics, Capital Normal University, Lab of THz Spectroscopy and Imaging, Beijing, China 100037 ABSTRACT We investigate the transmission properties of planar H- fractal structures in THz range. 3D EM simulations using HFSS are used to design the parameters of the fractals and to evaluate the optical properties. We observe the transmission spectra with pass bands and stop bands, which show the subwavelength transmission through the non-metallic gaps. This unique transmission property through subwavelength apertures makes it potentially useful frequency selective components in THz region. We experimentally demonstrate its behavior by designing and fabricating four prototype planar fractals in the range of 0-1.5THz and characterize using a polarizing Fourier transform spectrometer. We find good agreement between the models and measurements. INTRODUCTION The electromagnetic transmission properties through subwavelength apertures have attracted increasing attention due to the potential applications as frequency- selective components (FSS) in the development of terahertz optoelectronics. Extensive experimental and theoretical work has been carried out to analyse the physical details of the transmission process. The phenomenon of enhanced transmission through the metallic film with periodic arrays of subwavelength holes was first reported by Ebbesen in 1998 [1]. Later Qu presented the experimental result of the transmission magnitude and phase change of terahertz pulses through thin metallic films patterned with subwavelength hole arrays on silicon wafers [2]. In 2002 Wen presented by both experiment and theory that a specific class of planar conducting fractals can exhibit multiple stop and pass bands over a broad microwave frequency range, with the desired property that the fractal patterns can be significantly subwavelength in dimensions [3]. More recently optical transmission properties of subwavelength planar fractals in terahertz frequency region were studied experimentally by means of time-domain spectroscopy (THz-TDS) [4, 5, 6]. It showed that the frequency gaps corresponding to wavelengths can be significantly larger than the size of the sample; this makes planar fractals a possible potentially useful frequency-selective material. Zhao attributed the detected transmittance from subwavelength fractals to localized resonances. Followed the experimental work done by Zhao [4, 5], in this paper, we investigate the performance of the planar fractals as a potential band pass/stop filter. In Section 2 we present a theoretical analysis to obtain a physical insight into the behavior and to show how the geometrical parameters relate to its performance. We also present the design parameters of four patterns and expected performance in the 0-1.5THz region. The modeling uses a commercial finite-element analysis package, the high frequency structure simulator (HFSS) [7]. In Section 3 we describe the device manufacture, the measurement and the discussion of the results. The components were fabricated at Cardiff using photolithographic process to produce the patterns in a thin copper layer on a thin dielectric membrane support. Spectral measurements were made using a polarizing Fourier transform spectrometer (pFTS) which enabled the polarisation properties of the structures to be investigated. The measured results are compared with predictions from HFSS. We find good agreement between the models and measurements. THEORY AND MODELING Essential