Faculty of Engineering, Department of Electrical and Computer Engineering, McMaster University, Hamilton, ON, L8S 4L8, Canada.
Department of Physics, School of Science and Engineering, The American University in Cairo, New Cairo, 11835, Egypt.
Sci Rep. 2022 Jun 4;12(1):9343. doi: 10.1038/s41598-022-13033-3.
In this work we propose a method for on-chip detection of the complex refractive index of the sensing medium at multiple wavelengths for selective sensing. For the optical sensor to be selective, i.e. able to determine the substance present in the medium, either surface functionalization or absorption spectroscopy is often used. Surface functionalization is a complex process and is mainly limited to biological media. On the other hand, absorption spectroscopy is not suitable for on-chip sensing with micrometer dimensions as this will result in poor sensitivity, especially when working far from the substance absorption peaks. Here, we detect the dispersion of both the real n and imaginary k parts of the refractive index which are unique for each substance. This is done using a single micro-ring resonator (MRR) that exhibits multiple resonances over the operating wavelength range. The real and imaginary parts of the medium refractive index are determined at each resonance using the resonance wavelength and the absorption coefficient, respectively. In addition, using this technique the concentration composition of a multi-element medium can be determined by solving a system of linear equations that corresponds to the different wavelengths (resonances). We designed a silicon-on-insulator (SOI) ring-resonator operating in the near-infrared region from λ = 1.46 µm to λ = 1.6 µm. The ring exhibits 11 resonances over the 140 nm operating wavelength range where the corresponding medium refractive index is obtained. This design can detect four different substances namely, methanol, ethanol, propanol, and water. An average error of less than 0.0047% and 1.65% in the detection of the real and imaginary parts, respectively were obtained. Finally, the concentration composition of different multi-element media were successfully determined using the least square method with 97.4% detection accuracy.
在这项工作中，我们提出了一种在多个波长下对传感介质的复折射率进行片上检测的方法，用于选择性传感。为了使光学传感器具有选择性，即能够确定介质中存在的物质，通常使用表面功能化或吸收光谱法。表面功能化是一个复杂的过程，主要限于生物介质。另一方面，吸收光谱法不适用于具有微米尺寸的片上传感，因为这将导致灵敏度差，特别是在远离物质吸收峰的情况下工作时。在这里，我们检测了折射率的实部 n 和虚部 k 的色散，这对于每种物质都是独特的。这是通过使用单个微环谐振器 (MRR) 来完成的，该谐振器在工作波长范围内表现出多个共振。使用共振波长和吸收系数分别在每个共振处确定介质折射率的实部和虚部。此外，通过使用该技术，可以通过求解与不同波长（共振）对应的线性方程组来确定多元素介质的浓度组成。我们设计了一种工作在近红外区域的硅绝缘体 (SOI) 环形谐振器，波长范围为 λ=1.46μm 至 λ=1.6μm。该环在 140nm 的工作波长范围内显示出 11 个共振，其中获得了相应的介质折射率。该设计可以检测四种不同的物质，即甲醇、乙醇、丙醇和水。在检测实部和虚部时，分别获得了小于 0.0047%和 1.65%的平均误差。最后，使用最小二乘法成功确定了不同多元素介质的浓度组成，检测准确率为 97.4%。
