A nonlinear-optic waveguide device has a thin-wire optical waveguide including a core having a cross-sectional area of at most 1 .mu.m.sup.2 and a cladding, the core and the cladding having a refractive index difference of at least 1. A light pulse introduced into the core has a peak power of at least several hundreds W and a pulse duration of at most 10 ps. The thin-wire optical waveguide has a length of about 1 cm. The nonlinear optical device, a mode-locked semiconductor laser, and tunable optical filter are combined into a white pulse light source.