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This paper presents a detailed design, fabrication, and thermal tuning characteristics of a polarization independent tunable interleaver. Its operation principle is by using a double layer waveguide structure and vertically coupled polarization splitters to achieve a polarization diversity configuration so as to manipulate separately transverse electric (TE) and transverse magnetic (TM) polarization light signals. The fabricated interleaver is with two types of tuning manner. First, its center wavelength can be adjusted by changing the substrate temperature, which can be used to align the International Telecommunication Union grid for the TM polarization modes. Second, the center wavelength in the TE output spectra can be tuned to meet the ones in the TM output spectra by using thermo-optic effect to fine tune the mode index of the upper channel waveguide. The fabricated device was 18 mm × 9 mm and exhibited complete polarization independences with respect to center wavelength and channel spacing with very little tuning power consumption of ~0.6 mW over the entire C band. The tuning range of the center wavelength was about 1.4 nm.