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An ultrashort polarization splitter based on the zero-gap directional coupler is proposed and realized. Its interference section is 8.8 mum long. It is also shown that the length of the interference section can be reduced to about 2.1 mum. The crosstalk for both transverse-electric (TE) and transverse-magnetic (TM) polarizations is 16 dB at a wavelength of 1.55 mum. The extinction ratios of TE and TM polarizations are 18.2 and 13.7 dB, respectively. The device has 3-dB bandwidth of 43 nm in TE polarization and 50 nm in TM polarization with the center wavelength at 1.55 mu m.