Subwavelength film sensing based on terahertz anti-resonant reflecting hollow waveguides

Institute of Electro-Optical Science and Engineering and Advanced Optoelectronic Technology Center, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan, R.O.C.
Optics Express (Impact Factor: 3.49). 08/2010; 18(18):19353-60. DOI: 10.1364/OE.18.019353
Source: PubMed


A simple dielectric hollow-tube has been experimentally demonstrated at terahertz range for bio-molecular layer sensing based on the anti-resonant reflecting wave-guidance mechanism. We experimentally study the dependence of thin-film detection sensitivity on the optical geometrical parameters of tubes, different thicknesses and tube wall refractive indices, and on different resonant frequencies. A polypropylene hollow-tube with optimized sensitivity of 0.003 mm/μm is used to sense a subwavelength-thick (λ/225) carboxypolymethylene molecular overlayer on the tube's inner surface, and the minimum detectable quantity of molecules could be down to 1.22 picomole/mm(2). A double-layered Fabry-Pérot model is proposed for calculating the overlayer thicknesses, which agrees well with the experimental results.

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