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An ultra-broadband optical filter based on stepchirped multimode waveguide Bragg grating (SCMWBG) with low insertion loss, high sidelobe suppression ratio (SLSR), compact size and relaxed fabrication accuracy is demonstrated on SOI platform. The grating length of SCMWBG is divided into grating segments with constant periods, and the period of each segment increases in a fixed step length of 1 nm. Each grating segment of the proposed SCMWBG is designed according to the phase-matching condition. The device is fabricated by a 193 nm DUV lithography, and employs complementary lateralmisalignment apodization to suppress the sidelobes. The measured insertion loss, SLSR and 3-dB bandwidth of fabricated SCMWBG are 1.2 dB, 17 dB and 72 nm, respectively.