[Paper Review] A compact plasmonic MOS-based 2x2 electro-optic switch

Chenran Ye, Ke Liu+2 more|arXiv (Cornell University)|Jun 8, 2015

Photonic and Optical Devices26 references3 citations

TL;DR

This paper presents a compact 2x2 electro-optic switch based on a plasmonic metal-oxide-semiconductor (MOS) structure using indium-tin-oxide (ITO) as the active waveguide material. By applying a gating voltage to shift the plasma frequency in the ITO, the refractive index is modulated, enabling dynamic control of transverse magnetic (TM) polarized light between CROSS and BAR output ports with an extinction ratio of 18 dB (CROSS) and 7 dB (BAR), achieving ultrafast, low-energy fJ/bit operation suitable for silicon-on-insulator integration.

ABSTRACT

We report on a three-waveguide electro-optic switch for compact photonic integrated circuits and data routing applications. The device features a plasmonic metal-oxide-semiconductor (MOS) mode for enhanced light-matter-interactions. The switching mechanism originates from a capacitor-like design where the refractive index of the active medium, Indium-Tin-Oxide, is altered via shifting the plasma frequency due to carrier accumulation inside the waveguide-based MOS structure. This light manipulation mechanism controls the transmission direction of transverse magnetic polarized light into either a CROSS or BAR waveguide port. The extinction ratio of 18 dB (7) dB for the CROSS (BAR) state, respectively, is achieved via a gating voltage bias. The ultrafast broadband fJ/bit device allows for seamless integration with Siliconon- Insulator platforms to for low-cost manufacturing.

Motivation & Objective

• To develop a compact, low-energy electro-optic switch for photonic integrated circuits and data routing.
• To enhance light-matter interaction in a miniaturized waveguide structure using surface plasmon polaritons.
• To enable dynamic control of TM-polarized light via carrier-induced refractive index modulation in an ITO-based MOS structure.
• To achieve high extinction ratio and ultrafast switching with low energy consumption for compatibility with silicon-on-insulator platforms.
• To demonstrate seamless integration potential with existing CMOS-compatible photonic technologies.

Proposed method

• The device employs a three-waveguide configuration with a central ITO-based waveguide forming a capacitor-like MOS structure.
• A gating voltage is applied to accumulate carriers in the ITO, shifting its plasma frequency and altering the effective refractive index of the waveguide mode.
• The refractive index modulation enables dynamic control of the phase and power distribution between the two output ports (CROSS and BAR).
• The plasmonic mode confines light tightly at the ITO-silicon interface, enhancing light-matter interaction and enabling subwavelength device footprint.
• The switching mechanism relies on carrier accumulation in the ITO layer, which modifies the dielectric response and thus the propagation constant of the guided mode.
• The device is designed for compatibility with silicon-on-insulator (SOI) platforms, enabling low-cost, scalable fabrication.

Experimental results

Research questions

• RQ1 Can a plasmonic MOS structure in ITO achieve efficient and compact electro-optic switching for integrated photonic circuits?
• RQ2 To what extent can carrier-induced refractive index tuning in ITO enable high extinction ratio in a 2x2 switch?
• RQ3 What is the energy efficiency of the switching mechanism in terms of energy per bit (fJ/bit)?
• RQ4 How does the device performance scale with device size and operating wavelength in a CMOS-compatible platform?
• RQ5 Can the plasmonic MOS structure enable ultrafast switching with minimal crosstalk and low optical loss?

Key findings

• The device achieves an extinction ratio of 18 dB in the CROSS state and 7 dB in the BAR state, demonstrating effective switching performance.
• The switching mechanism operates at ultra-low energy consumption, achieving fJ/bit-level energy efficiency suitable for high-speed data communication.
• The plasmonic MOS structure enables strong light confinement and enhanced light-matter interaction, enabling subwavelength device dimensions.
• The device is compatible with silicon-on-insulator (SOI) platforms, enabling low-cost, scalable integration with existing CMOS fabrication processes.
• The switching is based on carrier accumulation in ITO, which modulates the plasma frequency and thus the refractive index of the active waveguide.
• The design supports dynamic control of TM-polarized light, with the output port selected via applied gating voltage.