Lossless propagation in active channel plasmon polariton waveguides K. Sheikhi, N. Granpayeh n Center of Excellence in Electromagnetics, Faculty of Electrical Engineering, K. N. Toosi University of Technology, Tehran 1631714191, Iran article info Article history: Received 29 November 2013 Received in revised form 25 January 2014 Accepted 6 February 2014 Available online 15 February 2014 Keywords: Lossless plasmonic waveguides Channel plasmon polariton waveguide (CPPW) Plasmonic V-groove Plasmonic trench waveguide abstract In this paper, we have analyzed and simulated the propagation of lightwave in three different types of active channel plasmon polariton waveguides (CPPWs), V-groove, trench and step-trench at 1550 nm wavelength based on a kind of available semiconductor as the active gain medium. By using the finite- difference frequency-domain method, strong plasmon modes confinement is observed in these waveguides and the required gains for achieving lossless propagations are derived. Due to the strong optical confinement, strong nonlinearity effects can be acquired in CPPWs. The dependence of the required gains on the geometrical parameters of the structures and wavelength changes for acquiring lossless propagation are analyzed and discussed in all three waveguides. The simulation results show that the calculated gain values are achievable by the existing semiconductor technology. Results show that the required gains for lossless propagation in nanoscale plasmonic devices can be well controlled by adjusting their geometrical parameters. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Surface plasmonic waveguides (SPWs) which guide surface plasmon polaritons (SPPs) have been nowadays a subject of num- erous researches in nanotechnologies [1,2]. In these waveguides electromagnetic excitations, called SPPs, are confined to the metal–dielectric interface [3]. These structures, known as one of the most promising approaches to overcome the diffraction limit of light are capable to fulfill the further integration of optical devices and components [4]. After first proposition of thin metal films as SPWs [5], various metallic geometries such as rod with square cross section [6], gap [7], wedge [8], slot [9], trench [10], and mixed SPWs [11] have been proposed and the propagation and subwavelength confinement of the SPP modes have been investigated in them. Plasmon polariton waveguides with step- trench structure have been used in the semiconductor area to realize high power superluminescent diodes at the wavelength of 1550 nm [12–14]. Due to the close vicinity of the guided modes to the metal layers in SPWs, absorption losses are high and conse- quently the propagation length is limited [15]. One proposal to overcome this loss is the application of a gain medium to indemnify the loss in plasmonic waveguides [16–19]. In this paper, channel plasmon polariton waveguides (CPPWs) surrounded with semiconductor as the active gain media are numerically investigated. The wavelength is assumed to be 1.55 mm. Three plasmonic waveguide structures of V-groove, trench, and step-trench are numerically studied. Using the finite- difference frequency-domain (FDFD) method, strong mode con- finement is observed in all the waveguides. Therefore, strong nonlinearity effects can be achieved in CPPWs. By changing the waveguides' parameters, the required gain values for attaining lossless propagation are calculated. In the CPPWs, the spatial overlap between the guided mode and the gain region plays a crucial role in the required gain for lossless propagation. Our results demonstrate that any changes in the waveguide geome- trical parameters can modify the required gain value for lossless propagation in the CPPW structures. Being consistent with the material gain of the quantum dot and multi-quantum well (MQW) active media, the required gain values can be acquired with the assistance of the InAs/GaAs quantum dot and InGaAsP–InGaAlAs MQW active regions at the wavelength of 1550 nm [20,21]. The paper is organized as follows. In Section 2, the analysis algorithm is described. In Section 3, an active MIM waveguide and three different CPPWs are analyzed. The paper is concluded in Section 4. 2. FDFD algorithm for analysis of SPWs Due to the complex frequency relation behavior of dielectric function of metals, frequency domain methods, such as the finite- difference frequency-domain (FDFD) and the finite-element methods Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/optcom Optics Communications http://dx.doi.org/10.1016/j.optcom.2014.02.027 0030-4018 & 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ98 21 84062311; fax: þ98 21 884 620 66. E-mail address: granpayeh@eetd.kntu.ac.ir (N. Granpayeh). Optics Communications 322 (2014) 73–77