Surface roughness effect on optical loss in waveguide using isotropically induced crosslink network of siloxane–polyimide copolymer

Abstract

AbstractOptical properties of two‐fluorinated polysiloxane‐co‐polyimide (PI‐PDMS and 3‐(aminopropyl)triethoxysilane [PI‐APTES]) were investigated based on their molecular structure and compared with the pure PI at 1,550 nm radiation. The refractive indexes and birefringence of the copolymers were reduced which is attributable to the chain flexibility as substantiated from the differential scanning calorimetry result. They are highly transparent at near infrared (NIR) region with light transmittance above 90% at visible region while displaying excellent thermal stability up to 456°C. Asymmetry planar waveguides was fabricated which recorded a respectable low optical loss 0.020 dB/cm for pure PI, 0.042 dB/cm for PI‐PDMS, and 0.066 dB/cm for PI‐APTES, respectively. Despite proving low NIR absorption and low birefringence, extrinsic factor namely surface roughness was accounted as affecting the higher optical loss in polyimide siloxane copolymer compared to pure PI. The excellent thermal and optical properties displayed by these series of material established their viable application as waveguide material at 1,550 nm wavelength.