Optical transmission of a subwavelength aperture: size and fiber parameter dependence of near-field resolution Lydia Alvarez a , Angel Sauceda a , Mufei Xiao b, * a Instituto de Ingenier  ıa Universidad Aut onoma de Baja California, CP 21280 Mexicali, Baja California, M exico b Centro de Ciencias de la Materia Condensada, Universidad Nacional Aut onoma de M exico, Apartado Postal 2681, CP 22800 Ensenada, Baja California, M exico Received 20 November 2002; received in revised form 14 February 2003; accepted 24 February 2003 Abstract We present a theoretical calculation of the optical transmission of a subwavelength circular aperture in a thick and perfectlyconductingscreencoateduponanopticalfiber.Thetheoryisemployedtostudyresolutionofscanningnear- field optical microscopy. In particular, we have studied the resolution dependence on the aperture size and the pa- rameters of the fiber that is used to form the probe. Ó 2003 Elsevier Science B.V. All rights reserved. PACS: 42.25.Bs; 42.50.Wm; 73.40.Gk Keywords: Near field; Aperture 1. Introduction A long standing problem in electromagnetic theoryistostudytheopticaltransmissionthrough a circular aperture whose diameter is comparable to or smaller than the light wavelength. General and accurate solutions do not exist for the prob- lem. However, in some special cases the problem canbesolvedaccurately.Theopticaldiffractionby subwavelength circular apertures in an infinitely thin and perfectly conducting screen was solved with a sufficient accuracy a long time ago [1–3]. A recently developed subfield in optics is the scanning near-field optical microscopy (SNOM) [4].Theprimaryreasonofdoingnear-fieldopticsis to overcome the diffraction resolution limit in the far field [5]. An important part of a SNOM is the probethatpicksupthenearfield.Inearliertimes, the near-field probe was a subwavelength circular aperture in a metallic screen. What was measured was the diffracted field in the other side of the screen. Since the size of the aperture was compa- rable to the screen thickness, it was expected that the finite screen thickness would be crucial for de- termining the diffraction distributions at various Optics Communications 219 (2003) 9–14 www.elsevier.com/locate/optcom * Corresponding author. Mailing address. CCMC-UNAM, P.O. Box 439036 San Ysidro, CA 92143, USA. Tel.: +52-646- 174-4602; fax: +52-646-174-4603. E-mail address: mufei@ccmc.unam.mx (M. Xiao). 0030-4018/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0030-4018(03)01277-X