A tunable channel selector operating over both the C and L bands of wavelength-division-multiplexing optical network is proposed based on a thermo-optic tunable Bragg grating device in a polymer waveguide. A tilted Bragg grating cascaded with an asymmetric Y-branch waveguide effectively implements a small Bragg-reflection wavelength filter that does not require an external circulator. To increase the operating wavelength span of the channel selector, two Bragg gratings with different periods are fabricated on a single substrate for covering C and L bands, respectively. A wide tuning range over 80 nm along with a narrow bandwidth is demonstrated. Moreover, the polarization dependence of the reflection spectrum is observed to be less than 0.1 nm.