Laser projector with reduced speckle
View Patent ↗A projector using coherent light as a light source includes: one or more coherent light sources emitting coherent light beams; a beam scanner which changes a direction of the coherent light beam; and a beam splitter which splits a beam into multiple segments and changes a phase of light of each split segment, the beam splitter being located in an optical path between the beam scanner and the coherent light source. This projector reduces speckle noises. The beam splitter includes a pair of transparent substrates; a plurality of parallel electrodes disposed on each surface of the pair of transparent substrates, the pair of the parallel electrodes being disposed in a perpendicular direction to each other. Voltages are applied to the respective electrodes at predetermined time intervals so as to produce different potentials in a liquid crystal sandwiched by the transparent substrates.
1. A projector for projecting a video including motions, using coherent light as a light source, the projector comprising:
one or more coherent light sources emitting a coherent light beam;
a beam scanning unit which changes a direction of the coherent light beam emitted from the one or more coherent light sources; and
a beam splitter which splits the coherent light beam into multiple segments and changes a phase of light of each split segment, the beam splitter being located in an optical path between the beam scanning unit and the one or more coherent light sources, wherein:
the beam splitter splits the coherent light beam two-dimensionally both in a scanning direction in which the coherent light beam is scanned by the beam scanning unit and in a direction perpendicular to the scanning direction,
the beam splitter comprises:
a pair of transparent substrates;
a plurality of first parallel electrodes disposed on one of the pair of transparent substrates and a plurality of second parallel electrodes disposed on the other one of the pair of transparent substrates, the first parallel electrodes being disposed in a direction perpendicular to the second parallel electrodes; and
a liquid crystal enclosed between the transparent substrates, wherein:
voltages are applied to the first and second parallel electrodes at each predetermined time intervals shorter than a frame time so as to produce different potentials in the liquid crystal enclosed between the transparent substrates,
the voltage applied to each electrode of the first parallel electrodes and the second parallel electrodes is randomly set at each of the predetermined time intervals, and
a phase of a voltage waveform when the voltage is applied is shifted for each electrode of the first parallel electrodes and the second parallel electrodes at a time period which is shorter than the predetermined time intervals.
2. The projector according to claim 1 , wherein for the voltages applied to the electrodes, multiple level voltage is applied.
3. The projector according to claim 1 , wherein:
the liquid crystal of the beam splitter is a ferroelectric liquid crystal.
4. The projector according to claim 1 , wherein: the liquid crystal of the beam splitter is a ferroelectric liquid crystal, and the phase of the voltage waveform has a timing difference shorter than a voltage application cycle.
5. The projector according to claim 1 , wherein voltages of square waveforms are applied to each of the first and second parallel electrodes.
6. The projector according to claim 5 , wherein voltages of square waves with a different timings are applied to each of the first and second parallel electrodes.
7. The projector according to claim 1 , wherein voltages of a sine waveform with different phases are applied to each of the first and second parallel electrodes.
8. The projector according to claim 1 , wherein the beam splitter linearly splits the coherent light beam in the direction perpendicular to the scanning direction in which the coherent light beam is scanned by the beam scanning unit.
9. The projector according to claim 1 , wherein the beam splitter linearly splits the coherent light beam in either the scanning direction in which the coherent light beam is scanned by the beam scanning unit or the direction perpendicular to the scanning direction.
10. A projector for projecting a video including motions, the projector comprising:
a red laser source emitting a red collimated light beam;
a blue laser light source emitting a blue collimated light beam;
a green laser source emitting a green collimated light beam;
a first dichroic prism which allows the light beam from the green laser source to pass therethrough and reflects the light beam from the red laser source;
a second dichroic prism which allows a light beam passed through the first dichroic prism to pass therethrough and reflects the light beam from the blue laser light source;
a beam splitter which splits a first light beam passed through the second dichroic prism into a plurality of light beams and performs phase modulation of the split light beams; and
a MEMS mirror which scans a light beam emitted from the beam splitter onto a screen, wherein:
the beam splitter splits the first light beam two-dimensionally both in a scanning direction in which the first light beam is scanned by the beam scanning unit and in a direction perpendicular to the scanning direction,
the beam splitter comprises:
a pair of transparent substrates;
a plurality of first parallel electrodes disposed on one of the pair of transparent substrates and a plurality of second parallel electrodes disposed on the other one of the pair of transparent substrates, the first parallel electrodes being disposed in a direction perpendicular to the second parallel electrodes; and
a liquid crystal enclosed between the transparent substrates, wherein:
voltages are applied to the first and second parallel electrodes at each predetermined time intervals shorter than a frame time so as to produce different potentials in the liquid crystal enclosed between the transparent substrates,
the voltage applied to each electrode of the first parallel electrodes and the second parallel electrodes is randomly set at each of the predetermined time intervals, and
a phase of a voltage waveform when the voltage is applied is shifted for each electrode of the first parallel electrodes and the second parallel electrodes at a time period which is shorter than the predetermined time intervals.