Pristine spider silk fibers as waveguiding microstructure in free space and in an integrated photonic chip

• Published in: 2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC p. 1
• Main Authors: Huby, N., Renault, A., Beaufils, S., Vié, V., Lefevre, T., Paquet-Mercier, F., Pézolet, M., Bêche, B.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.05.2013
• Subjects: Microstructure; Optical coupling; Optical fiber devices; Optical fibers; Photonics; Polymers
• DOI: 10.1109/CLEOE-IQEC.2013.6800954

Summary form only given. Silk fibers produced by nature are among the most interesting materials. Besides their high degree of biocompatibility, they are bioresorbable, ecologically friendly, and offer excellent mechanical properties. In particular, silks of spider and worm have aroused a huge interest as seen by the large literature on their structural organization [1, 2]. Thanks to material engineering possibility [3, 4], regenerated worm silk has been intensively studied and used in different fields such as electronics and photonics [5, 6]. On the other hand, native silks fibers are utilized in textile applications and in surgery procedures but have not yet deserved attention for photonic applications. However, the exceptional mechanical properties of natural silk mainly originate from an elaborated hierarchical organization which has not yet been reproduced in regenerated silk.We demonstrate the promising optical fiber behavior of pristine dragline silk from the spider Nephila clavipes, as well as its integration in a photonic chip made of synthetic polymer microstructures patterned by UV-lithography. The spinning process of the native fiber leads to a diameter of 5 microns, homogeneous over long distances. Since silk manipulation is straightforward, optical propagation in straight and loop configurations has been validated. In free space, attenuation coefficient (propagation losses) and coupling losses were estimated by the cut-back method on straight fiber at 10.5 dB/cm and 10 dB, respectively.In addition, the integration of the pristine silk fiber on a photonic chip and working optical hybrid devices based on synthetic polymer and natural silk fibers were demonstrated. Fig. 1a) is a scanning electron microscope of a chip composed of native spider silk embedded in SU8 microstructures (disk-reservoirs MD1 and MD2) designed by UV-lithography7. During light injection in a SU8 waveguide connected to MD1, light propagates to MD1 where light is confined at the edges of the disk. Fig. 1b is a micro-beam profile of the chip during light injection and shows that light is confined along the silk fiber and at the edges of MD2. This confirms the optical coupling between synthetic polymer microstructures and silk fiber. These results highlight the potential role of this unique material for biophotonic applications either in free space or in integrated chip for which light propagation and/or sensing in biocompatible media is needed.