Thermo-opticCoefficientofPolyisobutyleneUltrathinFilmsMeasured with Integrated Photonic Devices

The optical properties of polymeric materials, such as transmission loss and the thermo-optic coefficient, determine their utilityinnumerousapplications,rangingfromnanotechnologytothe automotive and aerospace industries. However, because of the wide variation in the physical properties of polymers, many are unsuited for characterization using conventional techniques; consequently, their optical properties are unknown. One such polymer is poly- isobutylene, which is viscous at room temperature and therefore is not compatible with conventional transmission loss and the thermo- optic coefficient characterization techniques because they rely on contact measurements. To overcome this, we have developed an integrated, microscale optical sensor that relies on an evanescent wave to study the material's optical behavior. Using this device, we successfully determined the refractive index, the transmission loss,andthethermo-opticcoefficientofultrathin filmsofpolyisobutylene.The filmsaredepositedonthesensor'ssilicasurfaceusing either spin coating or surface-initiated cationic polymerization, demonstrating the flexibility of this approach.