In this work, buried-type single-mode benzocyclobutene (BCB) channel waveguides fabricated by 248nm krypton fluorine (KrF) excimer laser for a blue laser of wavelength 473nm are first demonstrated. The ultraviolet-induced refractive index changes, measured by prism coupler and spectroscopic ellipsometer, are dependent on the number of laser shots and the pulse repetition rate. By arranging the number of laser shots and the mask width, mode sizes with different aspect ratios can be obtained. Moreover, the proposed UV illumination method is much simpler and more flexible than the conventional dry etching method.