Typical applications of integrated photonics in the mid-infrared (MIR) are different from near-infrared (telecom) range and, in many instances, they involve chemical sensing through MIR spectroscopy. Such applications necessitate tailored designs of optical waveguides. Both cross-sectional designs and processing methods of MIR waveguides have been a subject of extensive research, where material transparency and substrate leakage of guided modes have been the most common challenges. Both these challenges can be solved simultaneously with air-suspended waveguides. In this paper, tantalum pentoxide (Ta₂O₅, tantala) thin films deposited on silicon were tested for two different dry under-etching procedures, XeF₂ and SF₆ plasma, with both of them facilitating selective removal of silicon. We analyze the advantages and limitations of these two methods and optimize the processing for fabricating membranes with arbitrary length and cross-sectional aspect ratio over 300. The performance of these high-aspect-ratio membranes as a framework for single-mode waveguides is rigorously analyzed at 2566 nm wavelength. With tantala being transparent up to 10 µm wavelength, such waveguides are particularly well suited for gas sensing in MIR.

中文翻译：

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用于中红外气体传感的独立式五氧化二钽波导

中红外 (MIR) 集成光子学的典型应用不同于近红外 (电信) 范围，在许多情况下，它们涉及通过中红外光谱进行化学传感。此类应用需要对光波导进行定制设计。中红外波导的横截面设计和加工方法一直是广泛研究的主题，其中材料透明度和导模的衬底泄漏是最常见的挑战。这两个挑战都可以通过空气悬浮波导同时解决。在本文中，对沉积在硅上的五氧化_二钽（Ta ₂ O ₅，钽）薄膜进行了两种不同的干蚀刻工艺测试，XeF ₂和 SF ₆等离子体，它们都有助于选择性去除硅。我们分析了这两种方法的优点和局限性，并优化了制造任意长度和横截面纵横比超过 300 的膜的工艺。严格分析了这些高纵横比膜作为单模波导框架的性能波长为 2566 nm。由于 tantala 的透明波长可达 10 µm，因此此类波导特别适用于 MIR 中的气体传感。