  Nature provides a set of solutions for photonic structures that are finely
tuned, organically diverse and optically efficient. Exquisite knowledge of
structure-property relationships in proteins aids in the design of materials
with desired properties for building devices with novel functionalities, which
are difficult to achieve or previously unattainable. Recent bio-inspired
photonic platforms made from proteinaceous materials lay the groundwork for
many functional device applications, such as electroluminescence in peptide
nucleic acids, multiphoton absorption in amyloid fibers and silk waveguides and
inverse opals. Here we report whispering-gallery-mode (WGM) microresonators
fabricated entirely from semi-crystalline structural proteins (i.e., squid ring
teeth, SRT, from Loligo vulgaris and its recombinant) with unconventional
thermo-optic response. We demonstrated waveguides, add-drop filters and
flexible resonators as first examples of energy-efficient, highly flexible,
biocompatible and biodegradable protein-based photonic devices. Optical
switching efficiency in these devices is over thousand times greater than the
values reported for Silica WGM resonators. This work opens the way for
designing energy efficient functional photonic devices using structure-
property relationships of proteins.
