A liquid crystal microlens array for a low speckle laser projector

A design for a liquid crystal microlens array (LC-MLA) for a laser projector system capable of simultaneously achieving a uniform flat-top beam profile and low speckle is proposed. The Gaussian profile of a laser beam can be homogenized to obtain different flat-top intensities by controlling its focal length of the LC-MLA. Changing the focal length of the LC-MLA changes the angles of the rays in the output beam for the same incident light, which in turn gives rise to a series of independent speckle patterns within the integration time, while the speckle contrast is reduced by superposing the speckle patterns. Overdrive and dual-frequency driving techniques are applied to speed up the response time to produce more independent speckle patterns within the integration time. The experimental results for this projector show that the speckle contrast can be greatly reduced by as much as 52 %.