Based on the thermo-optic tuning of a polymer waveguide Bragg reflector, we demonstrated a cost-effective tunable wavelength laser for WDM optical communications. The excellent thermo-optic effect of the polymer waveguide enabled direct tuning of the Bragg reflection wavelength by controlling the electrical power on a micro-heater. Wavelength tuning for 32 channels with 0.8 nm wavelength spacing was demonstrated as well as a continuous tuning with wavelength steps of 0.1 nm. To be qualified as a tunable laser for WDM-PON applications, wavelength stability within 0.15 nm was confirmed for an operating temperature range from -10 to 70 degrees C.