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A polymer-based compact comb filter with flat top spectral characteristics is reported. A design equation has been derived from which the values of the device parameters can be optimized to render the desired performance characteristics of the filter. The polymer waveguide version of this filter has been fabricated and its experimental spectral characteristics agree very well with the theoretical one. This filter is compact with dimensions 26 × 8 mm2 because no cascade of unbalanced Mach-Zehnder interferometers is used. Its flat top extends to 50% of the channel width and channel isolation is 22 dB. The filter covers both the C-band and L-band wavelength range with channel spacing 1.6 nm.