ABSTRACT
A novel tunable terahertz notch filter is demonstrated using antiresonant reflecting hollow waveguides with movable metal layers outside dielectric claddings. Based on the Fabry-Pérot resonance of the dielectric cladding, multiple deep notches are observed in a broad THz transmission spectrum. Continuous shift of notch frequencies is for the first time experimentally observed by lateral translation of metal layers from dielectric claddings. The measured maximum frequency-tuning-range approached 60GHz, equaling to 50% of the bandwidth of every passband, and a 20dB rejection notch-depth with a linewidth as narrow as 6GHz at frequency of around 0.2THz was also achieved. Numerical simulations match the measurements and verify the spectral-tuning mechanism.
ABSTRACT
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.
