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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A variable birefringence effect has been observed with 1D PMMA surface gratings on a gold film substrate. By changing the operation wavelength on the Au film, the birefringence value Δn(eff) changes from positive to negative. The result verified that this uniaxial crystal-like plasmonic surface gratings showed good superlensing effect at 515 nm when PMMA width:Air width=1:1 where the absolute value of Δn(eff) is relatively large.