David Hernandez Pinilla1,Ngo Duc Thien1,2,Ørjan Handegård1,2,Toan Tran1,2,Naoki Furuhata1,Tadaaki Nagao1,2
National Institute for Materials Science1,Hokkaido University2
David Hernandez Pinilla1,Ngo Duc Thien1,2,Ørjan Handegård1,2,Toan Tran1,2,Naoki Furuhata1,Tadaaki Nagao1,2
National Institute for Materials Science1,Hokkaido University2
Spectrally selective devices in the infrared spectral region are key components for the development of modern spectroscopic applications such as infrared sensors, thermal emitters, biomedical analysis or thermophotovoltaic devices among others [1,2]. Nowadays, the technological demands of some of these applications require narrowband devices with a very well-defined spectral resolution. In order to ensure the accurate performance of these devices, an intense research was carried out on tunability mechanisms to control their optical response, leading to mechanical, electrical, optical and thermal tunability approaches. Among these, thermo-optical phase-change materials such as the widely investigated VO<sub>2 </sub>or Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> (GST) [3,4], are promising candidates for the development of spectrally selective tunable devices due to the distinctive optical properties they exhibit in their different thermodynamic phases. However, the lossy character that these thermochromic materials display in the infrared spectral region hinder the high spectral resolution of final devices. In this context, alternative low-loss adaptive thermo-optical materials are expected to improve the spectral resolution and outperform devices based on VO<sub>2</sub> and GST. As an example, here we show how the application of specific thermal treatments to narrowband photonic structures based on a material as ubiquitous as Si can lead to the development of highly-accurate spectrally-selective tunable devices with narrow bandwidth operation.<br/>In this work, we fabricated photonic structures that rely on interference effects arising from multiple reflected beams on planar resonant cavities loaded with distributed Bragg reflectors (DBR) [5]. The architecture can be summarized as (Si-SiO<sub>2</sub>)-DBR/SiO<sub>2</sub>-cavity/LaB<sub>6</sub>. By using low-loss materials such as Si and SiO<sub>2</sub> for the DBR, the electromagnetic dissipation losses in the structure can be reduced, thus ensuring devices with narrow spectral bandwidths. Additionally, since the optical properties of the materials play crucial roles in DBR-based structures, by monitoring the thermal-induced changes of phase from amorphous to polycrystalline Si, a continuous modification of the optical properties of the DBR structure can be achieved, resulting in the fine tuning of the resonant wavelength of the final device. This strategy can be applied to many other amorphous materials as an alternative to lossy thermochromic materials. This way, by using low-loss temperature-responsive materials, it is possible to simultaneously achieve both improved spectral resolution and fine spectral tunability for the development of spectrally selective devices capable of answering the highly-demanding spectral requirements of modern spectroscopic applications.<br/><b>REFERENCES</b><br/>[1] T. Yokoyama et al, <i>Adv. Opt. Mater.</i> <b>4</b>, 1987 (2016).<br/>[2] T. D. Dao et al, <i>Adv. Sci.</i> <b>6</b>, 1900579 (2019).<br/>[3] K. K. Du et al, <i>Light Sci. Appl.</i> <b>6</b>, e16194 (2017).<br/>[4] S. J. Kim et al, <i>Nanophotonics</i> <b>10</b>, 713 (2021).<br/>[5] A. T. Doan et al, <i>Opt. Express</i> <b>27</b>, A725 (2019).