JM3B.4.pdf Advanced Photonics for Communications © 2014 OSA Silicon Nanophotonic Waveguide Modulator with Graphene Active Medium Hongwei Zhao 1,* , Pietro Contu 1 and Jonathan Klamkin 1,2 1 Department of Electrical and Computer Engineering, Boston University, Boston, MA 02215, USA 2 Division of Materials Science and Engineering, Boston University, Boston, MA 02215, USA * Corresponding author: hwzhao@bu.edu Abstract: This work presents a nanophotonic modulator with a graphene active medium that is compatible with the silicon photonic platform. Using compact polarization rotators, the proposed device can be efficiently coupled with silicon nanowire waveguides. OCIS codes: (130. 3120) Integrated Optics Devices; (230. 4110) Modulators. 1. Introduction Silicon (Si) photonics has emerged as the premier photonics platform enabling the compact monolithic integration of active and passive components including optical modulators, photodetectors, low-loss waveguides, and polariza- tion control elements [1]. The Si nanophotonic modulator is one of the key components for on-chip optical inter- connects. However, Si does not exhibit a strong electro-optic effect, therefore it is challenging to realize compact power-efficient Si modulators [2]. The introduction of graphene as an active medium for nanophotonic modulators is promising because graphene demonstrates a gate-controllable broadband absorption and high mobility. Among the graphene modulator concepts that have been reported, the slot-waveguide based device is preferred as it enables high optical confinement for TM modes, thus exhibiting strong light-matter interaction [3–5]. In this work, a slot-waveguide nanophotonic modulator with a graphene active medium is proposed for the first time, that is compatible with conventional low-loss silicon nanowire waveguides. Polarization rotators and mode converters are incorporated at both the front and back ends of the device for efficient mode conversion from the TE mode of a Si nanowire waveguide to the TM mode of the slot-waveguide modulator. Additionally, the geometry of our modulator is optimized to achieve a low insertion loss of 0.38 dBμ m -1 and a high extinction ratio of 6.0 dBμ m -1 for a wavelength of 1.55 μ m. 2. Slot-waveguide modulator with single graphene layer Figure 1(a) shows the schematic of our proposed slot-waveguide modulator with a graphene active medium integrated with Si nanowire waveguides. At the front end, the fundamental TE mode (TE 0 ) is launched at the input Si nanowire (a) 0 5 10 15 20 25 30 35 0 0.5 1 Input Rotator: TE 0 --> TM 0 η 0 5 10 15 20 25 30 35 0 0.5 1 Output Rotator: TM 0 --> TE 0 L t (μm) η 99.5% at 9 μm 98.8% at 9 μm (b) Fig. 1: (a) 3-D schematic of the slot-waveguide graphene modulator integrated with Si nanowire waveguides, (b) conversion efficiency (η ) of the polorization rotators versus the taper length (L t ).