Performance Enhancement of Nanoscale VO₂ Modulators Using Hybrid Plasmonics

Abstract

Vanadium dioxide (VO 2 ) is a phase change material (PCM) that exhibits a large change in complex refractive index on the order of unity upon switching from its dielectric to its metallic phase. Although this property is key for the design of ultra-compact optical modulators of only a few-microns in footprint, the high absorption of VO 2 leads to appreciable insertion loss (IL) that limits the modulator performance. In this work, through theory and numerical modeling, we report on a new paradigm, which demonstrates how the use of a hybrid plasmonic waveguide to construct a VO 2 based modulator can improve the performance by minimizing its IL while achieving high extinction ratio (ER) in comparison to a purely dielectric waveguide. The hybrid plasmonic waveguide that contains an additional metal layer with even higher loss than VO 2 enables unique approaches to engineer the electric field (E-field) intensity distribution within the cross-section of the modulator. The resulting Figure-of-Merit FoM = ER/IL is much higher than what is possible by simply incorporating VO 2 into a silicon wire waveguide. A practical modulator design using this new approach, which also includes input and output couplers yields ER = 3.8 dB/µm and IL = 1.4 dB/µm (FoM = 2.7), with a 3-dB optical bandwidth >500 nm, in a device length = 2 µm, and crosssectional dimensions = 200 nm × 450 nm. To our knowledge, this is one of the smallest modulator designs proposed to-date that also exhibits amongst the highest ER, FoM, and optical bandwidth, in comparison to existing designs. In addition to VO 2 , we investigate two other PCMs incorporated within the waveguide structure. The improvements obtained for VO 2 modulators do not extend to other PCMs.

On-Chip Integrated Photonic Devices Based on Phase Change Materials

“…In one such proposal, a layer of silver was added between the vanadium dioxide layer and the silicon layer. This unique hybrid plasmonic solution could reduce the insertion loss while maintaining a high extinction ratio [154]. One bottleneck in the performance of VO 2 modulators is that the transverse electric (TE) polarized mode interacts weakly with them compared to the transverse magnetic (TM) mode.…”

“…In one such proposal, a layer of silver was added between the vanadium dioxide layer and the silicon layer. This unique hybrid plasmonic solution could reduce the insertion loss while maintaining a high extinction ratio [154].…”

Nanoscale plasmonic slot waveguides for enhanced Raman spectroscopy

“…The flexibility of this WG structure is that it can be optimized for either minimum modal loss or maximum fraction of E-field intensity within the gap region, simply by tuning the width of the left Si 3 N 4 cladding while keeping all other WG dimensions constant. Hybrid plasmonic WGs with very similar structures as we study here have been demonstrated for several applications [79][80][81] ; in each case the optimal device was also obtained by tuning the thicknesses of the constituent layers. The details of the optimization of the hybrid plasmonic slot WG are shown in Fig.…”

Design of High Performance Hybrid Plasmonic Modulator Based on ITO and Graphene

“…Metal oxide semiconductor-based hybrid plasmonic waveguides are used to design compact, broadband silicon-based optical modulators. These waveguides use doped silicon, Indium Tin Oxide (ITO), vanadium dioxide, or graphene (Kim and Kim, 2016, Du et al, 2019, Babicheva et al, 2013, Liu et al, 2011a, Wong and Helmy, 2017. A fundamental characteristic of these materials is adjusting the density of carriers and injecting charge into the material by applying an electric eld (Lin and Helmy, 2015b, Koch et al, 2016, Shah et al, 2018, Jin et al, 2016, Wood et al, 2018.…”