ancient material has been introduced into biomedical fi eld as a promising biomaterial which opened a new era in the development of optical interfaces and sensors for biomedical applications. Silk material from worm cocoon can be processed into different forms, such as spheres, sponges, fi bers, [13][14][15] foams [ 16 ] and fi lms. [ 4,9,11,12 ] Among these various forms, silk fi lms attracted signifi cant attention for applications in optics and photonics, due to high transparency (>95%) and excellent surface fl atness of such fi lms. As a result, a great variety of optical devices has been fabricated using silk fi lms. For example, silk-based diffractive gratings have been fabricated by casting silk solution onto polydimethylsiloxane (PDMS) negative molds. Silk lenses, microlens arrays and 64-phase level 2D diffraction masks were realized using molding technique. [ 4,17 ] Doped fl uorescent silk-protein fi lms with a two-dimensional square lattice of air holes were proposed and demonstrated to achieve enhancement in fl uorescent emission. [ 18 ] Active optical optofl uidic pH sensor were realized by chemical modifi cation of the silk protein fi lms with 4-aminobenzoic and by combining the elastomer in a single microfl uidic device. [ 19 ] Although many silk-based optical devices have been demonstrated, most of them operate in the visible region. [ 4,5,11,[17][18][19] Recently, the growing demand for THz waveguides and sensors for non-destructive sensing in biomedicine and agriculture is motivating silk material research in THz region. In 2010, split ring resonator-based metamaterials using silk fi lms as a substrate were demonstrated. [ 20 ] The authors also showed that silk is semi-transparent in the 0.15-1.5 THz region, having a relatively high loss of ∼15 cm −1 at 0.3 THz. In 2012, the same group demonstrated conformal, adhesive, edible food sensors [ 21 ] based on the THz metamaterials on silk substrates. By monitoring the antenna resonant response that changes continuously during the food storage, the authors have demonstrated potential of this technology for monitoring changes in the food quality.To the best of our knowledge, up to date, there were no reports of using silk to fabricate THz waveguides. This, most probably, is related to the high absorption loss of silk in the THz spectral region. Indeed, bulk absorption loss of silk is almost hundred times larger than the bulk absorption loss of polyethylene (∼0.2 cm −1 at 0.3 THz), which is often used for fabrication of THz fi bers. [22][23][24] At the same time, low-loss, lowdispersion waveguides for delivery of THz light is an important
