Optical Properties of Silicone Thin Films

Silicone-based materials possess a set of optical properties most appropriate for waveguide applications and optical sensing with polymer-supported indicator dyes. These properties include  

As expected, the introduction of different groups will have an influence on the absorption. Methyl siloxanes do not show any characteristic absorption in the UV or visible regions, while methylphenyl copolymers display characteristic absorption bands at 270, 264 and 250 nm (Table 22.3). 

The high transparency of silicones allows the development of optical chemical sensors that work in a broad spectral range that spans from the UV [28] and visible (see next section), to the near infrared [21, 22, 26]. Moreover, this transparency is not reduced upon exposure to water vapor, heat or UV, leading to durable robust optical sensors [76], 

Concerning the refractive index, sihcones may have an extremely wide range that goes from 1.38 to 1.60. Polydimethylsiloxane has a refractive index of 1.40 at 25 °C (598 nm). Substitution of trifluoropropyl groups for the methyl groups reduces the refractive index to 1.38, while the 

Silicone polymer or copolymer Loss at specific wavelength dB/cm  

---