A key property that differentiates optical polymers from more conventional optical materials such as glass, is the rapid variation of the refractive index with temperature. This large difference in dn/dT can be leveraged to produce efficient thermo-optically active optical components. An advanced polymeric waveguide technology was developed for affordable thermo-optically active integrated optical devices that address the needs of the telecom industry. We engineered high-performance organic polymers that can be readily made into single-mode waveguide structures of controlled geometries and of modal profiles that closely match standard telecom glass fibers. These materials are formed from highly-crosslinked halogenated acrylate monomers with specific linkages that determined properties such as flexibility, toughness, optical loss, thermal stability, and humidity resistance. These monomers are intermiscible, providing for precise continuous adjustment of the refractive index over a wide range. In polymer form, they exhibit state-of-the-art loss values, suppressed polarization effects, and exceptional environmental stability. The devices we describe include thermally tunable Bragg-grating-based wavelength filters, thermally tunable arrayed-waveguide gratings, and digital optical switches.