A nonlinear optical device is provided. More specifically, a wavelength conversion device package with less optical loss stabilizes optical alignment under an external environmental change, for example, in a temperature variation by providing a temperature regulating block and a temperature sensor to an optical oscillator and a wavelength modulator and fixing a flexible optical transmitter to the optical oscillator and the wavelength modulator.The wavelength conversion device package includes an optical oscillator comprising a light source for emitting a light; a flexible optical transmitter for transferring the light emitted from the optical oscillator to a wavelength modulator; and the wavelength modulator for receiving the light from the optical transmitter and radiating a wavelength-modulated light.