Effective speckle reduction in laser projection displays

Two alternative methods for effectively reducing the speckle noise in laser based rear and front projection displays are studied and demonstrated. Firstly, widening of the laser emission spectrum to nearly 4nm by tailoring the structures of 640nm band AlGaInP/GaInP based edge emitting broad-area red laser diode arrays, realized a reduction of speckle contrast from 20% to an acceptable level of 5%. Designing the power/wavelength distribution of the multiple emitters to achieve a flat top profile for the total spectrum plays an important role in maximizing the speckle reduction effect. This approach could easily be adapted to laser diodes arrays of other materials or wavelengths. Secondly, relative oscillation movement within the screen layers can also reduce the speckle contrast to the acceptable level of 5%. The moving layer material and the oscillation period has been studied and optimized to maximize the reduction level for both rear and front projection configurations. The two speckle reduction techniques were evaluated on a front projector utilizing a red laser assisted UHP lamp hybrid light source, and showed significant enhancement in view ability by the suppression of speckle. Combining the two techniques lead to further reduction in speckle and scintillation noise to a supreme level of 2%, enabling a practical solution for wide color gamut and high efficiency laser projection displays.