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Most recently, electrochromic (EC) oxides, such as WO3, have transcended far beyond their traditional scope of transmission modulation in smart windows. The ionically facilitated EC effect, leads to an extraordinary increase in excess charge carriers in the host oxide, effectively doping WO3 up to 1022 cm-3 electrons. With the protonation doping, the dielectric properties of the given oxide can be altered dynamically and locally. Hence, WO3 changes its refractive index from n = 1.9 to 2.3, and its extinction by Δ𝑘 = 0.5 in the near infrared (NIR). Here, we introduce a plasmonic, EC (‘plasmochromic’) nanowaveguide modulator, for ultrahigh modulation depth. WO3 is integrated into a plasmonic metalinsulator- metal (MIM) waveguide structure with a dual-function waveguide core containing amorphous LiNbO3 (LN). In this novel architecture, LN provides sufficient ionic conduction for EC switching, while simultaneously supporting optical mode propagation. By decoupling the ionic pathway and the direction of plasmon propagation, the EC waveguide achieves unprecedented modulation speed and depth when compared to traditional EC devices. FDTD simulations predict a maximum modulation depth of 80 dB for 20 μm waveguide length, while measured values show up to 2.5 dB/μm modulation with switching times of a few seconds. The waveguide platform further provides great retention (> 20 h) of the switching state, while allowing very low operating voltages with a figure of merit of 8 dB/V. We envision EC oxide to provide pathways to dynamic photonic devices under low voltage settings, where high modulation is necessary.
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