15 April 2000 Ž . Optics Communications 177 2000 79–84 www.elsevier.comrlocateroptcom Spectral-hole filter fabricated using sculptured thin-film technology Ian J. Hodgkinson a,1 , Qi hong Wu a,2 , Akhlesh Lakhtakia b,3 , Martin W. McCall c, ) a Department of Physics, UniÕersity of Otago, P.O. Box 56, Dunedin, New Zealand b ( ) Computational & Theoretical Materials Sciences Group CATMAS , Department of Engineering Science & Mechanics, PennsylÕania State UniÕersity, UniÕersity Park, PA 16802–1401, USA c Department of Physics, The Blackett Laboratory, Imperial College of Science, Technology and Medicine, Prince Consort Road, London SW7 2BW, UK Received 15 December 1999; accepted 29 February 2000 Abstract Ž . A Fabry–Perot description of the three-layer spectral-hole filter SHF fabricated using sculptured thin-film technology is presented. The identical outer layers are made of a thin-film helicoidal bianisotropic medium, and individually act as Bragg reflectors of one circular polarization. The middle layer, made of a homogeneous, isotropic, dielectric medium, functions as a quarter-wave spacer layer at the center-wavelength of the Bragg regime. The measured transmittance spectrums of the fabricated SHF are evaluated relative to exact theoretical results. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Sculptured thin films; Thin-film helicoidal bianisotropic medium; Linear birefringence; Spectral hole filter; Fabry–Perot filter 1. Introduction Last year, the concept of an all-film, ultranarrow- wx bandpass, circular-polarization filter 1 fabricated wx with sculptured thin film technology 2 was pro- posed. The optical filter comprises three layers: The first and the third layers are identical and are made of a thin-film helicoidal bianisotropic medium Ž . TFHBM , which possess a chiral micromorphology ) Corresponding author. E-mail: m.mccall@ic.ac.uk 1 E-mail: ijh@physics.otago.ac.nz 2 E-mail: qihong@physics.otago.ac.nz 3 E-mail: axl4@psu.edu and are periodically nonhomogeneous along, say, the x axis. The middle layer is made of an isotropic and homogeneous medium. All mediums are assumed to be linear dielectrics, and their magnetic as well as magnetoelectric constitutive properties are assumed wx to be negligible 3 . A schematic of the proposed device is shown in Fig. 1, and the x axis is implicitly normal to all interfaces in the filter. Suppose the TFHBM layers are structurally left- handed. Then each TFHBM layer of sufficient thick- ness and high transparency allows the passage of Ž . normally incident right-circularly polarized RCP light, but strongly reflects normally incident left-cir- Ž . cularly polarized LCP light, in the so-called Bragg w x wavelength-regime 4,5 . The middle layer, or the 0030-4018r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0030-4018 00 00603-9