Structural protein-based whispering gallery mode resonators

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. Here we report whispering-gallery-mode (WGM) microresonators fabricated entirely from semicrystalline structural proteins (i.e., squid ring teeth, SRT, from Loligo vulgaris and its recombinant) with quality factors as high as 10⁵. We first demonstrate versatility of protein-based devices via facile doping, engaging secondary structures. Then we investigate thermorefractivity and find that it increases with β-sheet crystallinity, which can be altered by methanol exposure and is higher in the selected recombinant SRT protein than its native counterpart. We present a set of photonic devices fabricated from SRT proteins such as add-drop filters and fibers. Protein-based microresonators demonstrated in this work are highly flexible and robust where quality factors and spectral position of resonances are unaffected from mechanical strain. We find that the thermo-optic coefficients of SRT proteins are nearly 100× larger than silica and more than 10× larger than polydimethylsiloxane. Finally, we demonstrate an optical switch utilizing the surprisingly large thermorefractivity of SRT proteins. Achieving 41 dB isolation at an input power of 1.44 μW, all-protein optical switch is 10× more energy efficient than a conventional (silica) thermo-optic switch.