Speckle noise reduction based on induced mode Hopping in a semiconductor laser diode by drive current modulation

• The drive current of a laser diode was modulated continuously.
• The speckle pattern was measured optically.
• The change in speckle noise was monitored.
• A reduction in speckle noise by drive current modulation is reported.
• A model based on induced mode hopping explains the speckle reduction.

We propose and demonstrate a speckle reduction technique in a laser diode projection system. By modulating the drive current of the laser diode continuously, we manage to generate independent longitudinal modes that arise from mode hopping. Since these modes have no fixed relationship between each other they act as independent sources which results in speckle reduction in the image. We experimentally demonstrate a speckle reduction factor of 2.17, which is in excellent agreement with our theoretical expectations. We conclude that mode hopping in laser systems can be used effectively to suppress speckle noise.