an optical wavelength conversion device is composed of a nonlinear optical material , and a first cladding layer having a refractive index lower than the refractive index of the nonlinear optical material and covering the nonlinear optical material , thereby to convert a fundamental wave entering the optical wavelength conversion device to a second harmonic , to guide the second harmonic through the first cladding layer , and to radiate the second harmonic . a second cladding layer formed of a material having a refractive index lower than the refractive index of the first cladding layer is provided outside of the first cladding layer , thereby to protect the first cladding layer .