J Comput Electron DOI 10.1007/s10825-015-0689-x Binary optimization of gold nano-rods for designing an optical modulator Farzin Emami 1 · Majid Akhlaghi 1 · Najmeh Nozhat 1 © Springer Science+Business Media New York 2015 Abstract An optical modulator with ultra small plasmonic nano rods that can filter the coherent optical frequency is developed. The performance of optical modulator based on dimmer metal nano rods on the top of silicon waveguides as coherent perfect absorber (CPA) is studied. In the proposed model, the optical modulator is excited by two monochro- matic incident plan waves with the same frequencies and two polar angles “θ = 0” and “θ = /2”. When the signal with θ = 0 is applied to the modulator separately, the incident wave transmits from the first path and suppresses for the sec- ond one, while when both signals are applied to the modulator simultaneously, the CPA occurs for the first path and the ligth- wave transmits from the second one. Therefore for two paths there are two states. “on” state when ligthwave transmitted from each path and “off” state when ligthwave suppressed. In this case two paths consist of different array of nano rods locations. Since the CPA efficiency depends strongly on the number of plasmonic nano rods and the nano rods location, a new efficient binary optimization method based the teaching– learning-based optimization (TLBO) algorithm is proposed to design an optimized array of the plasmonic nano-rods in order to achieve the maximum absorption coefficient in the ‘off’ state and the minimum absorption coefficient in the ‘on’ state. In Binary TLBO, a group of learner consists a matrix with binary entries, control the presence (‘1’) or the absence (‘0’) of nano rods in the array. B Majid Akhlaghi m.akhlaghi@sutech.ac.ir 1 Department of Opto Electronic, Shiraz University of Technology, Shiraz, Iran 1 Introduction There has been a considerable interest in the picoseconds range plasmonic devices, since they are well known for their ability to localize light beyond the diffraction limits. To provide the basic nanophotonic circuitry functionalities, elementary plasmonic devices such as waveguides, modu- lators, sources, amplifiers, and photodetectors are required. Vuckovic et al. reported the SP enhanced LED analyzing by both theoretically and experimentally [1]. Thus, great atten- tion has been focused on SP enhanced emission. Hobson et al. reported the SP enhanced organic LEDs [2]. For InGaN QWs, Gontijo et al. reported the coupling of the spontaneous emission from QW into the SP on silver thin firm [3] and showed increased absorption of light at the SP frequency. Okamoto et al. reported for the first time large photolumines- cence (PL) increases from InGaN/GaN QW material coated with metal layers [4]. Homeyer et al. demonstrate that an extraction enhancement by a factor of 2.8 can be obtained for a GaN quantum well structure using metallic nanostruc- tures, compared to a flat semiconductor [5]. Many theoretical and experimental researches have demonstrated that, for the dielectric-based photonics, large portion of electromagnetic waves spread over the space and cannot be confined in a small region due to the diffraction limit of light. This limits its ability of reducing optical modal volume to cubic half wavelength scale. In contrast, surface plasmon polaritons (SPPs), the electromagnetic waves propagating on the inter- face between metal and dielectrics, have allowed the modal confinement below the diffraction limit [6, 7]. This allows low power operation and integration on a chip in a variety of applications such as nanolasers [8–11], modulators [12], and splitters [13]. Micro ring based devices have attracted spe- cial attention in recent years. The silicon-based microring demodulators, modulators, switches and filters, fabricated in 123