Implementation of a Current Drive Modulator for Effective Speckle Suppression in a Laser Projection System

We report on the implementation of a current drive modulation circuitry that is effective in suppressing speckle noise for laser diodes. The drive circuit allows for operating the laser diode current at constant dc or modulating the current with square or triangular wave signals. We theoretically investigate the speckle reduction factors that correspond to the different modes of operation. The theory predicts that triangular wave modulation gives the highest speckle reduction ratio. This means that when used as a projector, the laser should be fed with triangular modulated current for the most effective speckle suppression. We then verified the theoretical results by experimental measurements. We demonstrated effective speckle noise suppression by implementing a drive current modulator.