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Article first published online: 11 SEP 2014
DOI: 10.1002/adom.201400228
Fabrication and characterization in the THz frequency range of silk foams and silk foam-based waveguides using lyophilisation and casting techniques are reported. The lack of biocompatible and biofriendly waveguides for low-loss, low-dispersion guidance of THz waves motivates the work for applications in remote and stand-off sensing in biomedical and agro-alimentary industries. Silk foams produced are 94% porous. Optical characterization is carried out using THz time-domain spectroscopy. The cutback measurements of foam samples show that the foam refractive index is close to that of air (
). Silk foam losses scale quadratically with frequency (
), being one order of magnitude smaller than those of solid silk. As an example of a basic guided wave device, fabrication and optical characterization of 10 cm-long, 5 mm-diameter step-index THz fibers having silk foam in the core and air in the cladding is demonstrated. Cutback measurements confirm that in the mid-THz spectral range, step-index fibers operate effectively in a single mode regime. Effective refractive index and propagation loss at frequencies higher that 0.2 THz are close to that of a silk foam from which the fiber core is made. At the same time, at these frequencies, modal group velocity dispersion is smaller than 
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