Three-Dimensional Photonic Circuits in Rigid and Soft Polymers Tunable by Light

Polymeric matrices offer a wide and powerful platform for integrated photonics, complementary to the wellestablished silicon photonics technology. The possibility to integrate, on the same chip, different customized materials allows for many functionalities, like the ability to dynamically control the spectral properties of single optical components. Within this context, this Article reports on the fabrication and optical characterization of integrated photonic circuits for the telecom Cband, made of a combination of both rigid and tunable elastic polymers. By using a 3D photolithographic technique (direct laser writing), in a single-step process, every building block of the polymeric circuit is fabricated: straight and bent waveguides, grating couplers, and single and vertically coupled whispering gallery mode resonators designed in planar and vertical geometries. Using this platform, a new type of operation was introduced through true three-dimensional integration of tunable photonic components, made by liquid crystalline networks that can be actuated and controlled by a remote and non-invasive light stimulus. Depending on the architecture, it is possible to integrate them as elastic actuators or as constituents of the photonic cavity itself. The two strategies then exploit the optical induced deformation and variation of its refractive index, inducing a net red or blue shift of the cavity resonances, respectively. This work paves the way for light-tunable optical networks that combine different photonic components, made by glassy or shape-changing materials, in order to implement further photonic circuit requirements.