Refractive Index Contrast Polymers: Photoresponsive Systems with Spatial Modulation of Refractive Index for Photonics

Abstract: The development of an intriguing concept using optical polymers for photonics is reported to enable modulation of refractive index (RI) in solution cast thin films with precise spatial control. While extensive efforts in polymer science have focused on methods to prepare optically transparent polymers with high RI, the creation of photoresponsive polymer systems to spatially adjust the refractive index upon irradiation is a distinct technical challenge requiring development of materials amenable to this process. The ability to create refractive index contrast (i.e., a difference in RI between two domains) is a critical capability required in photonics for the fabrication of integrated photonics devices, such as, polymer waveguides. In this report, we detail the synthesis of optical polymers tailored to this application, termed Refractive Index Contrast (RIC) polymers, in which the RI of the material can be photopatterned where UV exposure in the presence of a photoacid generator resulted in a permanent increase of RI in the exposed regions thus creating regions of high RIC. This process creates the high RI core of waveguides in a single step and lends itself to rapid fabrication of photonic devices via direct laser writing. Waveguides made from RIC polymers were found to have propagation losses of ∼2 dB/cm at 1550 nm.