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Tunable side-polished fiber comb filters based on the thermooptic effect of a polymer layer inserted between a side-polished fiber and an overlay waveguide are presented. The thermal electrodes formed on a polymer layer control the refractive index of one and its index variation induces the shift in coupling wavelength by the phase change of an evanescent field at the overlay waveguide boundaries. The tuning rate as a -0.017 nm/mW and the response time with a 50 ms/nm have been achieved. The authors have also demonstrated that this comb filter makes it possible for the tunable erbium-doped fiber ring laser to be used as a lasing-wavelength selective element. The tunable range of this laser is obtained about 17 nm (1545-1562 nm).