Silicon photonic thermal photodetectors for mid-infrared sensing

中红外（mid-IR）吸收光谱是一种众所周知的、通用的分析技术，通过测量分析物吸收的中红外光的波长来独特地识别和测量气体、化学品和生物分子的浓度。然而，现有的中红外吸收传感器要么体积庞大且价格昂贵（例如台式光谱仪），要么灵敏度和特异性较差（例如基于LED的传感器）。这种传感器的小型化可能对各种医疗、工业和环境传感场景产生革命性的影响。利用硅芯片上的中红外光学电路，可以制造出高性能、低成本、小型的光谱传感器。这些芯片将理想地结合传感器所需的所有光学功能（即光源、光路由波导、光与分析物之间的相互作用以及光检测），并且可以以低成本大批量制造，这要归功于现有的用于电子和近红外光通信的硅制造基础设施。在过去的几年里，我们看到了创建这些传感器系统所需的许多组件的快速发展：可以在几乎任何中红外波长以低损耗传输光的硅光子波导已经被开发出来，而在中红外波长发射高功率的激光器现在已经很容易获得，并且已经成功地与硅波导集成在一起。然而，实用的光电探测器技术仍然严重缺乏；那些已经集成在硅芯片上的光学电路要么制造成本昂贵，要么不切实际，因为它们必须冷却到低温，要么不能在所有要求的波长下工作。该项目将开发新型波导集成热光电探测器，其工作原理是将入射光转换为可通过电子电路测量的温度变化。它们将能够在室温下在任何中红外波长下工作，并且将使用低成本技术制造。该项目还将证明，采用这些光电探测器的传感器可以达到临床和工业用途所需的灵敏度，通过使用它们来测量软饮料中低浓度的人造甜味剂——这是工业上重要的应用实例。这些探测器有可能将中红外传感器系统从学术界的好奇转变为商业上可行的技术。

Mid-infrared (mid-IR) absorption spectroscopy is a well-known and versatile analytical technique for uniquely identifying and measuring the concentrations of gases, chemicals, and biological molecules by measuring which wavelengths of mid-IR light an analyte absorbs. Existing mid-IR absorption sensors are however either bulky and expensive (e.g. benchtop spectrometers), or have poor sensitivity and specificity (e.g. LED based sensors). Miniaturising such sensors could be transformative for diverse medical, industrial, and environmental sensing scenarios.High performance, low cost, and small spectroscopic sensors could be created using mid-IR optical circuits on silicon chips. These chips would ideally combine all of the required optical functions of the sensor (i.e. light source, waveguides for routing light, interaction between the light and the analyte, and light detection), and could be fabricated at low cost in high volumes, thanks to existing silicon manufacturing infrastructure that has been developed for electronics and for near-infrared optical communications.The last few years have seen rapid development of many of the components that are needed to create these sensor systems: silicon photonic waveguides that can transmit light with low loss at almost any mid-IR wavelength have been developed, while lasers emitting high powers in the mid-IR are now readily available and have been successfully integrated with silicon waveguides.However, there remains a crippling lack of practical photodetector technologies; those that have already been integrated wilth optical circuits on silicon chips are either expensive to manufacture, are impractical because they have to be cooled to cryogenic temperatures, or do not work at all required wavelengths. This project will develop new waveguide integrated thermal photodetectors, which work by converting the incoming light into a temperature change that can be measured with an electronic circuit. They will be able to operate at room temperature at any mid-IR wavelength, and will be manufactured using low cost techniques. This project will also demonstrate that sensors employing these photodetectors can reach the sensitivities required for clinical and industrial uses, by using them to measure low concentrations of artificial sweeteners in soft drinks - an industrially important example application. These detectors will potentially transform mid-infrared sensor systems from an academic curiosity into a commercially viable technology.