Wavelength blending with reduced speckle and improved color for laser projection

•A theoretical model which can calculate the speckle contrast ratio(SCR) of a wavelength blended light source has been presented.•The model has been verified by wavelength blending using a semiconductor green LD and a DPSS green laser. And the model can also predict the optimal power ratio between multiple lasers when using wavelength blending to reduce speckle.•A practical speckle reduction system combined with wavelength blending has been proposed and demonstrated. The system can provide less speckle and more accurate color (according to Rec.2020) compared to LD.•Based on presented paper, it has been predicted that a laser light source for projection systems with an low SCR (4%) and accurate color can be generated.

In this paper, a theoretical model was established to study speckle reduction using the wavelength blending technique with multiple lasers for the first time. An optimized power ratio of two lasers was then obtained using the theoretical model. A diode pumped solid state (DPSS) laser at 532 nm and a semiconductor laser diode (LD) at 520 nm were used to verify the simulated results. A speckle reduction system which utilizes wavelength blending was also proposed and demonstrated. Using wavelength blending, this system has a lower speckle as compared with one in which only one wavelength is used, and an improved green primary color (with respect to the Rec. 2020 standard) as compared with the one that only semiconductor LD is employed.