A planar optical waveguide is provided. The planar optical waveguide includes a polymer substrate having a coefficient of thermal expansion, a first cladding disposed on the substrate, and a core disposed on at least a portion of the first cladding. The core is a halogenated polymer having an absorptive optical loss of less than approximately 2.5.times.10.sup.-4 dB/cm in the range from about 1250 to 1700 nm. The core has a thermo-optic coefficient and a refractive index, a product of the thermo-optic coefficient and the reciprocal of the refractive index being approximately equal to the negative of the coefficient of thermal expansion.