Issue 11, 2013

Chip-scale Mid-Infrared chemical sensors using air-clad pedestal silicon waveguides

Abstract

Towards a future lab-on-a-chip spectrometer, we demonstrate a compact chip-scale air-clad silicon pedestal waveguide as a Mid-Infrared (Mid-IR) sensor capable of in situ monitoring of organic solvents. The sensor is a planar crystalline silicon waveguide, which is highly transparent, between λ = 1.3 and 6.5 μm, so that its operational spectral range covers most characteristic chemical absorption bands due to bonds such as C–H, N–H, O–H, C–C, N–O, C[double bond, length as m-dash]O, and C[triple bond, length as m-dash]N, as opposed to conventional UV, Vis, Near-IR sensors, which use weaker overtones of these fundamental bands. To extend light transmission beyond λ = 3.7 μm, a spectral region where a typical silicon dioxide under-clad is absorbing, we fabricate a unique air-clad silicon pedestal waveguide. The sensing mechanism of our Mid-IR waveguide sensor is based on evanescent wave absorption by functional groups of the surrounding chemical molecules, which selectively absorb specific wavelengths in the mid-IR, depending on the nature of their chemical bonds. From a measurement of the waveguide mode intensities, we demonstrate in situ identification of chemical compositions and concentrations of organic solvents. For instance, we show that when testing at λ = 3.55 μm, the Mid-IR sensor can distinguish hexane from the rest of the tested analytes (methanol, toluene, carbon tetrachloride, ethanol and acetone), since hexane has a strong absorption from the aliphatic C–H stretch at λ = 3.55 μm. Analogously, applying the same technique at λ = 3.3 μm, the Mid-IR sensor is able to determine the concentration of toluene dissolved in carbon tetrachloride, because toluene has a strong absorption at λ = 3.3 μm from the aromatic C–H stretch. With our demonstration of an air-clad silicon pedestal waveguide sensor, we move closer towards the ultimate goal of an ultra-compact portable spectrometer-on-a-chip.

Graphical abstract: Chip-scale Mid-Infrared chemical sensors using air-clad pedestal silicon waveguides

Article information

Article type
Paper
Submitted
07 Feb 2013
Accepted
25 Mar 2013
First published
25 Mar 2013

Lab Chip, 2013,13, 2161-2166

Chip-scale Mid-Infrared chemical sensors using air-clad pedestal silicon waveguides

P. T. Lin, V. Singh, J. Hu, K. Richardson, J. D. Musgraves, I. Luzinov, J. Hensley, L. C. Kimerling and A. Agarwal, Lab Chip, 2013, 13, 2161 DOI: 10.1039/C3LC50177A

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements