Guided modes in magneto-optical waveguides and the role in resonant transmission

Abstract

Magneto-optical (MO) effect can break the reciprocal propagation of an optical wave along a MO-metal interface. We show that this nonreciprocal property also influences the guided modes in metal-MO-metal waveguides. Especially, the field profiles of the guided modes are neither symmetric nor anti-symmetric, but asymmetric. We then study the resonant optical transmission through a thin metal film with subwavelength MO slits. Magnetic field changes the transmission spectra of the structure, and a MO-induced transparent window is open, where the MO medium becomes extremely anisotropic. The guided-mode mediated high transmission is associated with an asymmetric field distribution and a circling energy flux.

Nonreciprocal propagating electromagnetic modes without phase gradients

“…This implies that k-zero modes are nonreciprocal, a characteristic that is frequently associated with the MO effect [11][12][13][14][15][16]. As shown in Fig.…”

“…We show that k-zero modes are nonreciprocal and can be realized by utilizing the magneto-optic (MO) effect [11][12][13][14][15][16]. Furthermore, we emphasize that the existence of k-zero modes is closely related to the unique nonzero lateral displacement at normal incidence when reflected from a MO medium.…”

“…It requires that the MO material should be metal-like, i.e., n 2 e < 0. This can be satisfied by utilizing semiconductors with proper doping density [15,16], within which a MO response of ε r = 1 − ω 2 p /(ω 2 − ω 2 B + jω 2 ) and γ = ω B ω 2 p /ω(ω 2 − ω 2 B + jω 2 ) can be obtained, where ω p = (ne * 2 /m * ε 0 ) 1/2 is the bulk plasmon frequency, ω B = e * B 0 /m * is the cyclotron frequency, n is the carrier concentration, e * and m * are the effective charge and mass of carrier, and represents damping [15,16]. A negative ε r can be obtained in the quasi-Reststrahlen band between ω B and (ω 2 B + ω 2 p ) 0.5 .…”

“…Since the doping density and the external magnetic field B 0 are artificially tunable, the required conditions of k-zero modes could be easily met. For example, when m * = 0.014m e and e * = e [15,16] we can realize ω p = 2π × 40 GHz when a doping density n of 2.8 × 10 11 cm −3 is utilized. A moderate magnetic field B 0 of 0.002 T can render ω B = 0.10ω p .…”

Optical Propagation in Magneto-Optical Materials

“…The design of optical devices with MO materials is addressed in several works such as [2][3][4][5]. The challenges for the design of such devices are the development of MO materials with high-induced anisotropy and high transparency at the optical spectrum.…”