Polarization dependent devices realized by using asymmetrical hole array on a metallic film Shaoyun Yin, Chongxi Zhou, Xiaochun Dong, Chunlei Du* State Key Laboratory of Optical Technologies for Microfabrication, Institute of Optics and Electronics, Chinese Academy of Sciences, P.O.Box 350, Chengdu 610209, China *corresponding author
[email protected]
A method is brought forward for realizing polarization dependent devices by employing sub-wavelength asymmetrical hole array on a metallic film. Based on the fundamental mode approximation, the phase retardations of rectangular hole for two orthogonal polarization incident waves are analyzed and calculated. Using rectangular hole array, a bifocal-polarization lens for the infrared radiation with 10.6µm wavelength is designed. Its focal lengths for x- and y- polarized incident wave are examined by the finite difference time domain (FDTD) method and the Rayleigh-Sommerfeld diffraction integrals and the obtained results agree well with the designed values. © 2008 Optical Society of America OCIS codes: (260.3910) metals, optics; (260.5430) Polarization; (310.0310) thin film; (260.3060) Infrared; (050.1970) Diffractive optics;
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(C) 2009 OSA
Received 11 Nov 2008; revised 15 Dec 2008; accepted 20 Dec 2008; published 7 Jan 2009
19 January 2009 / Vol. 17, No. 2 / OPTICS EXPRESS 598
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1. Introduction Polarization technology is an important branch of optical technology. Polarization dependent devices such as polarizer, beam splitter and phase retarder are widely used in the fields of optical detecting [1], beam shaping [2] and information reading-writing [3]. However, traditional polarization dependent devices have several deficiencies. First of all, the devices employing the double refraction effect of birefringent crystals are usually big and relatively heavy [4]. Secondly, in region of the infrared radiation, it is difficult to find suitable birefringent crystal. Except a kind of line grid polarizer has been used extensively for a long time [5], other polarization dependent devices are rarely reported. In our previous work, a structure lens based on sub-wavelength square hole array on metallic film had been developed [6, 7]. This structure lens has the virtues of light weight and high compactness; it also has the potential for realizing large numerical aperture. However, due to the symmetry of the square hole, the structure lens is independent of the incident polarization. If the holes are unsymmetrical, the phase retardations of the transmitted electromagnetic waves for different polarizations will be different. In this paper, the phase retardations of a rectangular hole are analyzed and calculated. Based on the rectangular holes array, a method is proposed to realize a type of phase modulation devices which modulate the phases independently for two eigen polarizations. The devices manufactured by this method are of light weight and high compactness which are also suitable for the use in region of infrared radiation. 2. Design method The polarization characters of a rectangular hole can be determined by solving the Helmholtz equation. Considering a rectangular hole with sides ax and ay perforated on the metallic film with thickness h, if h>λo, and λo/2
