Laser video projection system and method with anti-piracy feature
A pulsed laser device and a laser display system using the pulsed laser device are disclosed that thwart recording of displayed video images with electronic imaging devices. The pulsed laser device is Q-switched, whereby the Q-switch trigger pulses have a temporal pattern that includes a blanking period of a duration that is longer than a repetition time between consecutive trigger pulses and shorter than a time period perceived by the human eye. The output beam of the Q-switched pulse laser is frequency-converted by non-linear optical frequency conversion into an imaging beam, for example, a three-color RBG beam, that can be modulated for displaying color images. The blanking period renders the displayed images practically unsuitable for off-screen recording with electronic image recording devices, such as CCD movie cameras.
1. A pulsed laser device comprising:
an optical cavity;
an optically pumped laser medium and a Q-switch disposed in the optical cavity; and
a trigger generator producing trigger pulses to trigger the Q-switch, said trigger pulses having a temporal pattern which includes a blanking period;
wherein a duration of the blanking period is selected to be longer than a repetition time between consecutive trigger pulses and shorter than a time period perceived by the human eye.
2. The laser device of claim 1 , wherein the repetition time between the consecutive trigger pulses corresponds to a pulse repetition rate of between approximately 10 and 100 kHz.
3. The laser device of claim 1 , wherein the repetition time between the consecutive trigger pulses corresponds to a pulse repetition rate of approximately 50 kHz.
4. The laser device of claim 1 , wherein the duration of the blanking period is between approximately 1 and 10 milliseconds.
5. The laser device of claim 1 , wherein the duration of the blanking period is between approximately 1 and 2 milliseconds.
6. The laser device of claim 1 , wherein the trigger pulses have a pulse width of between approximately 1 and 20 nanoseconds.
7. The laser device of claim 1 , wherein the trigger pulses have a pulse width of approximately 10 nanoseconds.
8. The laser device of claim 1 , wherein the laser medium comprises Nd:YVO 4 .
9. A laser display system comprising:
a pulsed laser device with
an optical cavity;
an optically pumped laser medium and a Q-switch disposed in the optical cavity;
a trigger generator producing trigger pulses to trigger the Q-switch, said trigger pulses having a temporal pattern which includes a blanking period, said pulsed laser device emitting a pulsed pump beam;
non-linear optical conversion means receiving the pulsed pump beam and frequency-converting the pulsed pump beam into an imaging beam; and
a spatial light modulator receiving image information and modulating the imaging beam according to the received image information to produce a displayed image,
wherein a duration of the blanking period is selected to be longer than a repetition time between consecutive trigger pulses and shorter than a time period perceived by the human eye.
10. The laser projection system of claim 9 , wherein the non-linear optical conversion means comprise a plurality of non-linear optical frequency converters to produce separate RGB imaging beams.
11. The laser projection system of claim 10 , wherein the separate RGB imaging beams are modulated and combined to form a color image.
12. The laser device of claim 9 , wherein the repetition time between the consecutive trigger pulses corresponds to a pulse repetition rate of between approximately 10 and 100 kHz.
13. The laser device of claim 9 , wherein the repetition time between the consecutive trigger pulses corresponds to a pulse repetition rate of approximately 50 kHz.
14. The laser device of claim 9 , wherein the duration of the blanking period is between approximately 1 and 10 milliseconds.
15. The laser device of claim 9 , wherein the duration of the blanking period is between approximately 1 and 2 milliseconds.
16. The laser device of claim 9 , wherein the trigger pulses have a pulse width of between approximately 1 and 20 nanoseconds.
17. The laser device of claim 9 , wherein the trigger pulses have a pulse width of approximately 10 nanoseconds.
18. The laser device of claim 9 , wherein the laser medium comprises Nd:YVO 4 .
19. A method of displaying an image with anti-piracy protection, comprising:
producing a Q-switched pulsed laser output beam, said Q-switched beam being switched by trigger pulses having a temporal pattern that includes a blanking period;
converting said pulsed laser output beam by non-linear optical frequency conversion to an imaging beam;
modulating said imaging beam with image information; and
displaying an image formed from said imaging beam containing said image information,
wherein a duration of the blanking period is selected to be longer than a repetition time between consecutive trigger pulses and shorter than a time period perceived by the human eye.
20. The method of claim 19 , wherein the non-linear optical frequency conversion produces separate RGB imaging beams, and said displayed image is a full color image.