Palm Kevin J, Krayer Lisa J, Munday Jeremy N
Opt Express. 2022 Jun 6;30(12):21977-21989. doi: 10.1364/OE.450724.
Optical switchability is an important functionality for photonic devices, which allows them to accommodate a wide range of applications. One way to achieve this switchability is to utilize the reversible and tunable optical changes of metal hydrides. When exposed to H gas, certain metals go through dramatic changes in optical properties as hydrogen atoms expand the lattice spacing. In this paper, we propose a switchable absorption device consisting of a Pd-capped Mg thin film deposited onto a near-zero-index substrate. By utilizing Mg's extreme optical changes upon hydrogenation and combining it with the high optical contrast of the near-zero-index substrate, we can create a device that is fully switchable from a highly reflective state to a broadband absorbing state. When modeling the substrate as a Drude material with a plasma wavelength of 600 nm, we calculate an absorption change of > 70% from 650-1230 nm, with a peak total absorption of 78% at 905 nm. We experimentally demonstrate this effect using 25 nm of Mg with a 3 nm Pd capping layer deposited onto an ITO-coated glass substrate. This device achieves an absorption change of 76% at 1335 nm illumination, with a maximum absorption of 93% in the hydride state, utilizing ITO's near-zero-index region in the near-infrared. By tuning the near-zero-index region of the substrate, this effect can be extended from the visible through the infrared.
光学可切换性是光子器件的一项重要功能，这使其能够适应广泛的应用。实现这种可切换性的一种方法是利用金属氢化物的可逆和可调光学变化。当暴露于氢气时，某些金属会随着氢原子扩大晶格间距而发生显著的光学性质变化。在本文中，我们提出了一种可切换吸收器件，它由沉积在近零折射率衬底上的钯包覆镁薄膜组成。通过利用镁氢化时的极端光学变化，并将其与近零折射率衬底的高光学对比度相结合，我们可以制造出一种能够从高反射状态完全切换到宽带吸收状态的器件。当将衬底建模为等离子体波长为600 nm的德鲁德材料时，我们计算出在650 - 1230 nm范围内吸收变化大于70%，在905 nm处的总吸收峰值为78%。我们通过在涂有ITO的玻璃衬底上沉积25 nm厚的镁和3 nm厚的钯包覆层，对这一效应进行了实验验证。该器件在1335 nm光照下实现了76%的吸收变化，在氢化物状态下最大吸收为93%，利用了ITO在近红外区域的近零折射率特性。通过调整衬底的近零折射率区域，这种效应可以从可见光扩展到红外光。
