Q-SWITCHED OSCILLATOR SEED-SOURCE FOR MOPA LASER ILLUMINATOR METHOD AND APPARATUS

• US 20110122895A1
• Filed: 11/22/2010
• Published: 05/26/2011
• Est. Priority Date: 11/23/2009
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Savage-Leuchs, Matthias P., Dilley, Christian E., Lemaire, Charles A.
• Granted Patent: US 8,934,509 B2
• Time in Patent Office: Days
• US Class Current: 372/10
• CPC Class Codes: B60Q 1/0076 Switches therefor B60Q1/1446, B60Q1/343, B60Q1/40 take precedence
• CPC Class Codes: H01S 2301/03 Suppression of nonlinear conversion, e.g. specific design to suppress for example stimulated brillouin scattering [SBS], mainly in optical fibres in combination with multimode pumping
• CPC Class Codes: H01S 3/06704 Housings; Packages
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06716 Fibre compositions per se C03C13/04or doping with active elements lasing materials in general H01S3/14
• CPC Class Codes: H01S 3/0675 Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
• CPC Class Codes: H01S 3/06758 Tandem amplifiers
• CPC Class Codes: H01S 3/06791 Fibre ring lasers fibre laser gyrometers G01C19/72
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/094011 with bidirectional pumping, i.e. with injection of the pump light from both two ends of the fibre
• CPC Class Codes: H01S 3/094053 Fibre coupled pump, e.g. delivering pump light using a fibre or a fibre bundle
• CPC Class Codes: H01S 3/0941 of a laser diode
• CPC Class Codes: H01S 3/1022 by controlling the optical pumping
• CPC Class Codes: H01S 3/113 using intracavity saturable absorbers
• CPC Class Codes: H01S 3/115 using intracavity electro-optic devices
• CPC Class Codes: H01S 3/127 Plural Q-switches
• CPC Class Codes: H01S 3/2316 Cascaded amplifiers
• CPC Class Codes: H01S 5/146 using a fiber as external cavity

Abstract

An apparatus, method and system that uses a Q-switched laser or a Q-seed source for a seed pulse signal having a controlled high-dynamic-range amplitude that avoids and/or compensates for pulse steepening in high-gain optical-fiber and/or optical-rod amplification of optical pulses. Optionally, the optical output is used for LIDAR or illumination purposes (e.g., for image acquisition). In some embodiments, well-controlled pulse shapes are obtained having a wide dynamic range, long duration, and not-too-narrow linewidth. In some embodiments, upon the opening of a Q-switch in an optical cavity having a gain medium, the amplification builds relatively slowly, wherein each round trip through the gain medium increases the amplitude of the optical pulse. Other embodiments use quasi-Q-switch devices or a plurality of amplitude modulators to obtain Q-seed pulses. These configurations provide optical pulses having wide dynamic ranges that ameliorate problems of pulse steepening, non-linear spectral broadening and the like in very-high-power MOPA devices.

Claims

1. A method comprising:

generating a seed signal having a Q-switched-pulsed-laser temporal shape;

providing an optical gain fiber having a second optical pump source; and

amplifying the Q-switched pulsed-laser seed signal in the optical gain fiber to obtain an output beam having a power of at least one milliJoule (1 mJ).

2. The method of claim 1, further comprising:

providing a vehicle having an enclosure;

supplying electrical power;

using the electrical power, controlling and powering the pump source; and

controlling an output direction of the output beam in one of a plurality of different possible directions relative to the vehicle.

3. The method of claim 1, wherein the generating of the seed signal having the Q-switched-pulsed-laser temporal shape includes optically amplitude-modulating a signal inside a uni-directional ring cavity.

4. The method of claim 1, wherein the generating of the seed signal having the Q-switched-pulsed-laser temporal shape includes optically amplitude-modulating a signal inside cavity that is implemented in a single package having a volume of no more than 6 cm³.

5. The method of claim 1, wherein the generating of the seed signal having the Q-switched-pulsed-laser temporal shape includes generating an optical pulse having a full-width half-maximum (FWHM) duration of no more than 50 nanoseconds.

6. The method of claim 1, wherein amplifying of the Q-switched pulsed-laser seed signal includes outputting the output beam pulse with a power of at least 4 milliJoules (mJ).

7. The method of claim 1, wherein the seed signal has a linewidth of at least 1 terahertz (THz), in order to reduce SBS problems.

8. An apparatus comprising:

a Q-switched seed laser having a first pump source configured to output a Q-switched pulsed-laser seed signal; and

an optical gain fiber having a second optical pump source and operatively coupled to receive light from the Q-switched seed laser and operatively configured to amplify the Q-switched pulsed-laser seed signal in the optical gain fiber to obtain an output beam having a power of at least one milliJoule (1 mJ).

9. The apparatus of claim 8, further comprising:

a vehicle having an enclosure;

an electrical power supply attached to the vehicle;

a laser controller operatively coupled to receive electrical power from the electrical power supply and operably coupled to power and control the first pump source; and

a beam-direction controller operably coupled to receive the output beam from the optical gain fiber and operable to direct the output beam in one of a plurality of different possible directions relative to the vehicle.

10. The apparatus of claim 8, wherein the Q-switched seed laser includes an optical amplitude-modulator operatively configured to amplitude modulate a signal inside a uni-directional ring cavity.

11. The apparatus of claim 8, wherein the Q-switched seed laser is implemented in a single package having a volume of no more than six (6) cm³.

12. The apparatus of claim 8, wherein the Q-switched seed laser generates an optical pulse having an FWHM duration of no more than 50 nanoseconds.

13. The apparatus of claim 8, wherein the output beam pulse has a power of at least 4 milliJoules (mJ).

14. The apparatus of claim 11, wherein the seed signal has a linewidth of at least 1 terahertz (THz), in order to reduce SBS problems.

15. An apparatus comprising:

a pulsed Q-seed source having a light source configured to output a Q-seed signal pulse having a temporal shape that, for at least the leading edge of the Q-seed signal pulse, substantially matches a temporal shape of a leading edge of a Q-switched laser pulse; and

an optical gain fiber having a first pump source and operatively coupled to the pulsed Q-seed source and configured to amplify the Q-seed signal pulse in the optical gain fiber to obtain an output beam having an energy of at least one milliJoule (1 mJ).

16. The apparatus of claim 15, further comprising:

a vehicle having an enclosure;

an electrical power supply attached to the vehicle;

a laser controller operatively coupled to receive electrical power from the electrical power supply and operably coupled to power and control the first pump source; and

a beam-direction controller operably coupled to receive the output beam from the optical gain fiber and operable to direct the output beam in one of a plurality of different possible directions relative to the vehicle.

17. The apparatus of claim 15, wherein the pulsed seed source includes a semiconductor diode laser that is driven by an electrical pulse that causes the semiconductor diode laser to emit a pulse having the leading edge of the seed pulse that substantially matches the temporal shape of the leading edge of a Q-switched laser pulse.

18. The apparatus of claim 15, wherein the pulsed seed source includes a semiconductor diode laser that outputs a continuous-wave (CW) laser signal that is coupled through an electro-optical modulator (EOM) that is driven by an electrical pulse that causes the electro-optical modulator to emit an amplitude-modulated pulse from the CW laser signal, the amplitude-modulated pulse having the leading edge of the seed pulse that substantially matches the temporal shape of the leading edge of a Q-switched laser pulse.

19. The apparatus of claim 15, wherein the pulsed seed source includes a semiconductor diode laser that outputs a CW laser signal that is coupled through an acousto-optical modulator (AOM) that is driven by an electrical pulse that causes the acousto-optical modulator to emit an amplitude-modulated pulse from the CW laser signal, the amplitude-modulated pulse having the leading edge of the seed pulse that substantially matches the temporal shape of the leading edge of a Q-switched laser pulse.

20. The apparatus of claim 15, wherein the seed signal has a linewidth of at least 1 terahertz (THz), in order to reduce SBS problems.

21. The apparatus of claim 15, wherein the pulsed Q-seed source includes a Q-switched laser that includes a gain medium within a lasing cavity, an optical pump source, and a 1×

N electrically controlled optical switch as a Q-switch in the cavity, wherein the optical switch includes a first state that optically couples light from the optical pump source to the gain medium while blocking signal lasing in the cavity and a second state that permits signal lasing in the cavity.

22. An apparatus comprising:

a Q-switched laser that includes a gain medium within a lasing cavity, an optical pump source, and a 1×

N electrically controlled optical switch as a Q-switch in the cavity, wherein the optical switch has a plurality of states including a first state that optically couples light from the optical pump source to the gain medium while blocking signal lasing in the cavity and a second state that permits signal lasing in the cavity.

23. The apparatus of claim 22, wherein the 1×

N optical switch is a 1×

2 electrically controlled optical switch.

24. The apparatus of claim 22, wherein the 1×

N optical switch is a 1×

3 electrically controlled optical switch.

25. An apparatus comprising:

an optical gain fiber having a second optical pump source;

means for generating a seed signal having a Q-switched-pulsed-laser temporal shape; and

means for amplifying the Q-switched pulsed-laser seed signal in the optical gain fiber to obtain an output beam having a power of at least one milliJoule (1 mJ).

26. The apparatus of claim 25, further comprising:

a vehicle having an enclosure;

means for controlling and powering the pump source; and

means for controlling an output direction of the output beam in one of a plurality of different possible directions relative to the vehicle.

27. The apparatus of claim 25, wherein the means for generating the seed signal includes means for optically amplitude-modulating a signal inside a uni-directional ring cavity.

28. The apparatus of claim 25, wherein the means for generating the seed signal includes means for optically amplitude-modulating a signal inside cavity that is implemented in a single package having a volume of no more than six (6) cm³.

29. The apparatus of claim 25, wherein the means for generating the seed signal includes means for generating an optical pulse having a full-width half-maximum (FWHM) duration of no more than 50 nanoseconds.

30. The apparatus of claim 25, wherein the means for amplifying the Q-switched pulsed-laser seed signal includes means for outputting the output beam pulse with a power of at least 4 mJ.

31. The apparatus of claim 25, wherein the means for generating the seed signal generates the seed signal with a linewidth of at least 1 terahertz (THz), in order to reduce SBS problems.