Reduction of speckle and interference patterns for laser projectors

An apparatus for reducing laser speckle and interference fringes, comprising:

• a continuous wave laser having a laser output defining an optical path to be split into multiple optical paths;
• a spatial light modulator (SLM) optically coupled to the continuous wave laser, wherein the SLM has a defined pixel rate;
• a beam combiner positioned optically down field from the continuous wave laser for recombining the multiple optical paths;
• a first half wave plate placed in an optical path incident to the laser output and configured to polarize the laser output to be s-polarized with respect to the beam combiner;
• a first polarization-independent beam splitter optically positioned and configured to divide the laser output of the continuous wave laser into a first laser beam and a second laser beam;
• a phase modulator optically positioned and configured to oscillate a phase of the second laser beam with an amplitude sufficient to create a phase delay of an odd integer multiple of approximately half a wavelength of the laser output and at a frequency at least twice that of the pixel rate of the SLM;
• a second polarization-independent beam splitter optically positioned and configured to reflect approximately half of the first laser beam and half of a phase modulated second laser beam and to transmit approximately half of the first laser beam and half of the phase modulated second laser beam to produce third and fourth laser beams, each of the third and fourth laser beams comprising approximately half of the first laser beam and approximately half of the phase modulated second laser beam;
• a second half wave plate optically positioned and configured to polarize the fourth laser beam to be p-polarized with respect to the beam combiner;
• the beam combiner configured to combine an s-polarized third laser beam and a p-polarized fourth laser beam into a fifth laser beam;
• a quarter wave plate optically positioned and configured to substantially linearly polarize the fifth laser beam;
• and
• a polarization rotator optically positioned and configured to rotate a polarization of the substantially linearly polarized fifth laser beam.

A method for reducing laser speckle and interference patterns in a laser projector display, when using a laser projector having a spatial light modulator (SLM) with a defined pixel rate, comprising:

• polarizing a laser output of a continuous wave laser such that the laser output is s-polarized with respect to a beam combiner;
• dividing the s-polarized laser output into a first laser beam and a second laser beam;
• modulating a phase of the second laser beam with an amplitude sufficient to create a phase delay of approximately half a wavelength of the laser output and at a frequency at least twice that of the SLM's pixel rate;
• mixing the first and second laser beams to create third and fourth laser beams, each of the third and fourth laser beams comprising approximately half of the first laser beam and approximately half of a phase modulated second laser beam;
• polarizing the fourth laser beam to be approximately p-polarized with respect to the beam combiner;
• and
• combining the third and fourth laser beams with the beam combiner to create a fifth laser beam.

A means for reducing laser speckle and interference patterns in a laser projector display, when using a laser projector having a spatial light modulator (SLM) with a defined pixel rate, comprising:

• a means for polarizing a laser output of a continuous wave laser such that the laser output is s-polarized with respect to a beam combiner;
• a means for dividing the s-polarized laser output into a first laser beam and a second laser beam;
• a means for modulating a phase of the second laser beam with an amplitude sufficient to create a phase delay of approximately half a wavelength of the laser output and at a frequency at least twice that of the SLM's pixel rate;
• a means for mixing the first and second laser beams to create third and fourth laser beams, each of the third and fourth laser beams comprising approximately half of the first laser beam and approximately half of a phase modulated second laser beam;
• a means for polarizing the fourth laser beam to be approximately p-polarized with respect to the beam combiner;
• and
• a means for combining the third and fourth laser beams with the beam combiner to create a fifth laser beam.