Photothermal heaters are important devices for optical switches and memories based on the thermo-optic/magneto-optic effect and phase change materials. We demonstrated photothermal heating in Si plasmonic waveguides loaded with Co thin films by measuring the resistance change upon inputting transverse-magnetic (TM) mode light. Temperature rise is proportional to the light intensity with clear polarization dependence. The photothermal conversion efficiency was estimated at 36 K/mW and maximum temperature rise was estimated at 221 K at steady state upon the inputting 6.3 mW TM mode light for the 400 nm-wide, 8 µm-long and 189 nm-thick Co film deposited on the Si wire waveguide with 129 nm-thick SiO2 buffer layer. The method to increase the efficiency is discussed based on the experimental and simulation results considering the thickness of the SiO2 buffer layer, Co layer and Si core layer, waveguide width, and wavelength. Local photothermal heaters in this study can be applied to a variety of fields including optical switches/memories without electrical control signals in photonic integrated circuits, on-chip optical sensors, and a lab-on-a-chip in biology, chemistry, and medicine.

We report the design and fabrication of Si plasmonic waveguide local heaters with ring resonators. Quantification of the local temperature rise is reported through analysis based on the thermo-optic(TO) effect, and the heaters can be miniaturized by introducing a stronger interaction between the propagating light and matter. The resonance wavelength in the waveguide heater was shifted toward a longer wavelength by injecting transverse magnetic mode light, and the shift was proportional to the light intensity. The local temperature rise was 288 K upon inputting 6.3 mW light, and the photothermal conversion efficiency was as high as 46.1 K/mW in a Si plasmonic waveguide loaded with 30 nm-thick and 1 μm-long Co thin films, showing improved characteristics compared with previous devices. Investigation toward achieving a higher efficiency is discussed based on simulation and experimental results, for realizing photothermal waveguide heaters with smaller size, and lower input power for various applications.

Zinc oxide (ZnO) is a promising material for combining with magneto-optic (MO) materials because it can propagate stable exciton-polaritons, with velocities considerably lower than that of photons in a vacuum. This study investigated the influence of sputtered ZnO and Al:ZnO top layers on MO responses of a bismuth-substituted yttrium iron garnet (Bi:YIG) film. The ZnO top layer modulated the Faraday rotation and magnetic circular dichroism (MCD) of the Bi:YIG around the exciton resonance wavelength of ZnO at 369 nm. Furthermore, Al-substituted ZnO, which is a conductive ZnO, also changed the MO effects around the exciton resonance wavelength. These results imply that the exciton-polaritons in ZnO affect the MO interaction, because of their considerably low group velocity. The results suggest potential for controlling the MO response via excitons.

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