Frequency quadrupled laser using thulium-doped fiber amplifier and method

Patent metadata

Field	Value
Publication number	US-9684077-B2
Application number	US-201514618879-A
Country	US
Kind code	B2
Filing date	Feb 10, 2015
Priority date	Mar 21, 2007
Publication date	Jun 20, 2017
Grant date	Jun 20, 2017

Abstract

An apparatus, method and associated fiber-laser architectures for high-power pulsed operation and pumping wavelength-conversion devices. Some embodiments generate blue laser light by frequency quadrupling infrared (IR) light from Tm-doped gain fiber using non-linear wavelength conversion. Some embodiments use a fiber MOPA configuration to amplify a seed signal from a semiconductor laser or ring fiber laser. Some embodiments use the frequency-quadrupled blue light for underwater communications, imaging, and/or object and anomaly detection. Some embodiments amplitude modulate the IR seed signal to encode communication data sent to or from a submarine once the modulated light has its wavelength quartered. Other embodiments transmit blue-light pulses in a scanned pattern and detect scattered light to measure distances to objects in a raster-scanned underwater volume, which in turn are used to generate a data structure representing a three-dimensional rendition of the underwater scene being imaged for viewing by a person or for other software analysis.

First claim

What is claimed is:

1. An apparatus comprising:
an infrared laser outputting a laser signal having a first wavelength between 1800 nm and 2000 nm as an intermediate optical signal output beam;
a frequency quadrupler operably coupled to receive the intermediate optical signal output beam and to output a frequency-quadrupled optical signal;
a beam polarizer configured to orient a polarization direction of the frequency-quadrupled optical signal in a direction that enhances transmission through an air-water interface;
a beam transmitter operably coupled to transmit the polarized frequency-quadrupled optical signal through water;
a light detector and processor configured to detect and process reflections from the transmitted frequency-quadrupled optical signal to generate image data, wherein the light detector includes a narrowband light filter configured to increase a signal-to-noise ratio of the detected reflections.

2. The apparatus of claim 1 , further comprising: a data encoder operably coupled to encode data on at least one of the intermediate optical signal output beam and the frequency-quadrupled optical signal such that the frequency-quadrupled optical signal has encoded data.

3. The apparatus of claim 1 , wherein the infrared laser includes a large-mode-area (LMA) fiber.

4. The apparatus of claim 1 , wherein the narrowband light filter includes a polarization beamsplitter configured to obtain a plurality of received signals from different polarizations obtained from the beamsplitter including a first polarization signal and a second polarization signal, wherein the processor is further configured to process the first polarization signal.

5. The apparatus of claim 4 , wherein the processor is further configured to subtract the second polarization signal from the first polarization signal to enhance a signal-to-noise ratio of the processed received signals.

6. An apparatus comprising:
a fiber gain medium;
means for optically pumping the fiber gain medium;
means for generating a laser seed signal;
means for optically coupling, into the fiber gain medium, the laser seed signal;
means for outputting, from the fiber gain medium, an amplified version of the laser seed signal as an intermediate optical signal output beam having a first wavelength between 1800 nm and 2000 nm;
means for frequency quadrupling the intermediate optical signal output beam to form a frequency-quadrupled optical signal;
means for orienting a polarization direction of the frequency-quadrupled optical signal in a direction that enhances transmission through an air-water interface;
means for transmitting the frequency-quadrupled optical signal through seawater; and
means for detecting, from water, a light signal caused by light interaction of the frequency-quadrupled signal; and means for processing the detected light signal to derive image information.

7. The apparatus of claim 6 , wherein the means for transmitting the frequency-quadrupled optical signal is arranged to communicate data between two ships, at least one of which is a submarine.

8. The apparatus of claim 6 , wherein the means for transmitting the frequency-quadrupled signal further includes means for scanning the transmitted frequency-quadrupled signal across a range of angles in order to detect three-dimensional (3D) image information.

9. The apparatus of claim 6 , wherein the means for frequency quadrupling the intermediate optical signal output beam further includes: means for frequency doubling the intermediate optical signal output beam to form a second optical signal output beam having a second wavelength that is one-half of the first wavelength of the intermediate optical signal output beam; and means for frequency doubling the second optical signal output beam to form the frequency-quadrupled optical signal having a third wavelength that is one-half of the second wavelength of the second optical signal output beam.

10. The apparatus of claim 6 , wherein the means for transmitting the frequency-quadrupled optical signal operates from a surface vehicle.

11. The apparatus of claim 6 , wherein the means for transmitting the frequency-quadrupled optical signal operates from an aircraft.

12. The apparatus of claim 6 , further comprising: means for illuminating underwater features using the frequency-quadrupled optical signal; and means for detecting and processing reflected light from the frequency-quadrupled optical signal to form an image.

13. A method comprising:
providing a fiber gain medium;
optically pumping the fiber gain medium;
generating a laser seed signal;
optically coupling, into the fiber gain medium, the laser seed signal;
outputting, from the fiber gain medium, an amplified version of the laser seed signal as an intermediate optical signal output beam having a first wavelength between 1800 nm and 2000 nm;
frequency quadrupling the intermediate optical signal output beam to form a frequency-quadrupled optical signal;
orienting a polarization direction of the frequency-quadrupled optical signal in a direction that enhances transmission through an air-water interface;
transmitting the frequency-quadrupled optical signal through water; and
detecting a light signal caused by light interaction of the frequency-quadrupled signal with an anomaly in the water; and processing the detected light signal to derive image information.

14. The method of claim 13 , further comprising: encoding the laser signal with data to be communicated through the water.

15. The method of claim 14 , wherein the transmitting of the signal is between two ships, at least one of which is a submarine.

16. The method of claim 13 , further comprising: detecting a light signal caused by light interaction of the frequency-quadrupled signal with a thermocline in the water; and processing the detected light signal to derive image information.

17. The method of claim 13 , wherein the transmitting of the frequency-quadrupled signal further includes scanning the transmitted frequency-quadrupled signal across a range of angles in order to detect three-dimensional (3D) image information.

18. The method of claim 13 , wherein the frequency quadrupling of the intermediate optical signal output beam further includes: frequency doubling the intermediate optical signal output beam to form a second optical signal output beam having a second wavelength that is one-half of the first wavelength of the intermediate optical signal output beam; and frequency doubling the second optical signal output beam to form the frequency-quadrupled optical signal beam having a third wavelength that is one-half of the second wavelength of the second optical signal output beam.

19. The method of claim 13 , wherein the transmitting of the frequency-quadrupled optical signal includes steering a majority of the frequency-quadrupled optical signal toward a desired target receiver.

20. The method of claim 13 , wherein the frequency-quadrupled optical signal has a wavelength that is set to a wavelength of Fraunhofer feature F.

Assignees

• Lockheed Corp

Inventors

• Mead Roy D
• Minelly John D
• Honea Eric C

Classifications

• H01S3/107

  using electro-optic devices, e.g. exhibiting Pockels or Kerr effect {(H01S3/1061, H01S3/1063, H01S3/1065 take precedence)} · CPC title

• H01S3/115

  using intracavity electro-optic devices · CPC title

• H01S3/0092

  Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity (nonlinear frequency conversion per se G02F1/35) · CPC title

• G01S7/4813

  Housing arrangements · CPC title

• G01S17/89 Primary

  for mapping or imaging · CPC title