Multiple-wavelength synthetic green laser source for speckle reduction

We demonstrate a frequency-converted green laser source simultaneously emitting three spectral lines with nearly equal intensity and ~ 0.5 nm separation, enabling a factor of √3 reduction of speckle contrast in pico-projector applications. The source consists of an external cavity 1060 nm diode laser pump with dual-wavelength reflection provided by a volume Bragg grating and a quasi-periodically poled MgO-doped lithium niobate waveguide engineered to phase-match multiple-wavelength frequency conversion. 62 mW output power and 33% conversion efficiency are demonstrated.