Reversibly Programmable Photonics via Responsive Polyelectrolyte Multilayer Cladding

Reversibly programmable photonic integrated circuits (PICs) that can facilitate multifunctionality have been long sought after to deliver user‐level design flexibility. Issues like complicated control, continuous power consumption, and high optical losses hinder their large‐scale adaptation. In this work, a novel approach toward programmable photonics using a responsive polyelectrolyte multilayer (PEM) cladding is presented. Reversible (de)swelling of PEMs by consecutive exposure to acidic and neutral pH solutions yields highly contrasting refractive index changes in the dry film. Utilizing this effect, an easily applied technique for programming photonic integrated devices with two different approaches, complete and area‐selective deposition, for several reversible cycles is demonstrated. These devices operate at two distinct states that are virtually lossless and nonvolatile. This proof‐of‐concept demonstration is suitable for various photonic integration platforms to facilitate reconfigurable photonic processors, static memories, and fine‐tuning of fabrication related limitations. Therefore, these results are the first step toward PEM‐assisted reversibly programmable multipurpose PICs for low‐cost mass production. Reversible programming of photonic devices is achieved by cladding them with responsive polyelectrolyte multilayers. Upon exposure to solutions of specific acidity, the cladding reversibly (de)swells, producing a large refractive index difference, affecting the light‐guiding material underneath. A shift of half the free spectral range is obtained by switching the polymeric coating, realizing reversible programming of the cladded photonic devices.