arXiv subjects

Wakana Kubo

Publications and source records attributed to Wakana Kubo.

3 recordsLinked to original sources

arXiv2026

Robust Broadband Infrared Unidirectional Absorption Enabled by a Non-Hermitian Multilayer

Unidirectional electromagnetic absorption provides a powerful approach for controlling light and heat, yet broadband realization in the infrared spectral region remains experimentally unexplored. Here, we report a non-Hermitian multilayer structure that enables robust broadband infrared unidirectional absorption. By combining low- and high-loss materials and engineering their thicknesses using the transfer-matrix formulation, the structure exhibits nearly perfect absorption spectrally matched to the blackbody radiation at 373 K under forward illumination, while suppressing backward absorption below 30%. Spectral analysis indicates that the observed unidirectionality originates from non-Hermitian physics near an exceptional point. Notably, broadband unidirectional absorption is achieved even without strict exceptional-point condition. This indicates that the observed unidirectionality is governed by the combination effect of loss distribution and optical interference, rather than a singular condition, ensuring robustness against film thickness variations. Furthermore, thermal shielding experiments demonstrate that the structure enables unidirectional control of thermal radiation, resulting in a temperature difference of up to 21 0C between forward and backward configurations. These results establish a robust strategy for broadband directional control of infrared radiation, with potential applications in passive thermal management, including thermal smart windows and infrared heat-shielding devices.

physics.optics↗

arXiv2023

Metasurface absorber enhanced thermoelectric conversion

Metasurfaces are artificial thin materials that achieve optical thickness through thin geometrical structure. This feature of metasurfaces results in unprecedented benefits for enhancing the performance of optoelectronic devices. In this study, we report that this metasurface feature is also essential to drive photo-thermoelectric conversion, which requires the accumulation of thermal energy and effective heat conduction. For example, a metasurface-attached thermoelectric device placed in an environment with uniform thermal radiation generates an output voltage by gathering the thermal energies existing in the environment and creating an additional thermal gradient across the thermoelectric element. In contrast, when a 100-um-thick-carbon-black-coated electrode was used instead of the metasurface, the device showed low-er thermoelectric performance than that of the metasurface-attached device although carbon black exhibits higher infrared absorption than the metasurface. These results indicate that metasurface characteristics of optical thickness and thin geometrical structure for achieving the high thermal conductance are essential in enhancing the performance of photo-thermoelectric devices in terms of the effective collection of thermal energies and conduction of local heating.

physics.optics↗

arXiv2022

Metamaterial Thermoelectric Conversion

We propose a thermoelectric device that can produce a thermal gradient even in a uniform-temperature environment. We introduced a metamaterial absorber (MA), which comprised a transparent calcium fluoride layer sandwiched between a silver mirror layer and silver microdisk arrays, at one end of a thermoelectric device made of bismuth antimony telluride. The heating efficiencies of the MA and opposite electrodes of the device were unbalanced; consequently, the Seebeck effect was induced, resulting in electricity generation. We fabricated the MA on a copper electrode loaded on a thermoelectric device, and the device was placed in a uniform-temperature environment at 364 K. The thermal gradient across the device was experimentally measured and was found to be 0.14 K.

physics.optics↗