Laser communication device

• US 5,999,299 A
• Filed: 05/14/1998
• Issued: 12/07/1999
• Est. Priority Date: 08/27/1992
• Status: Expired due to Fees

• Current Assignee: Thermotrex Corporation (Thermo Fisher Scientific Incorporated)
• Original Assignee: Thermotrex Corporation (Thermo Fisher Scientific Incorporated)
• Inventors: Chan, Victor, Bloom, Scott, Menders, James, Rivers, Michael
• Primary Examiner(s): BACARES, RAFAEL D
• Application Number:
  US09/079,377
• Time in Patent Office: 572 Days
• Field of Search: 359/172, 359/152, 359/159, 359/154, 359/498, 359/187, 359/181
• US Class Current: 398/130
• CPC Class Codes: H04B 10/11 Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
• CPC Class Codes: H04B 10/1143 Bidirectional transmission
• CPC Class Codes: H04B 10/118 specially adapted for satellite communication

Abstract

A laser communication device for transmitting and receiving information imposed on laser beams. A transmitting unit and a receiving unit are implemented based on atomic line filters. The transmitting unit includes a compact tunable laser locked to a selected atomic transition line. Information may be imposed on a laser beam by modulating the frequency thereof while maintaining its output power substantially unchanged.

Claims

1. A laser communication device, comprising:

a transmitting module configured to have at least one laser that produces a signal beam and a first atomic optical filter based on an atomic medium that is disposed relative to said laser to receive at least a portion of said signal beam, wherein said first atomic optical filter produces an optical feedback signal based on an interaction of said portion of said signal beam with said atomic medium at or near an atomic transition line and said laser is locked in frequency domain with respect to said atomic transition line; and

a receiving module disposed relative to said transmitting module and configured to have a second atomic optical filter based on said atomic medium wherein said second atomic optical filter is configured to transmit light at or near said atomic transition line and to substantially block light at other frequencies.

2. A device as in claim 1, wherein said transmitting module further comprises a laser controller operable to control at least the frequency of said laser with respect to said atomic transition line according to said optical feedback signal from said first atomic optical filter.

3. A device as in claim 2, wherein said laser controller is operable to perform a frequency modulation on said laser relative to said atomic transition line of said first atomic optical filter according to a temporal modulation criterion to imprint communication data on said signal beam for transmission.

4. A device as in claim 3, wherein said transmitting module is configured to produce an intensity modulation on said signal beam in response to said frequency modulation on said laser, said intensity modulation representing said communication data.

5. A device as in claim 3, wherein said transmitting module is configured to represent said communication data by said frequency modulation on said laser while maintaining an intensity of said signal beam substantially constant and continuous.

6. A device as in claim 1, further comprising a beam-splitting element in the path of said signal beam to split said signal beam into a diagnostic signal beam and an output signal beam, wherein said first atomic optical filter is positioned so as not to intercept said signal beam and said output signal beam and wherein said beam-splitting element directs said diagnostic signal beam to pass through said first atomic optical filter which generates said optical feedback signal.

7. A device as in claim 1, wherein said first atomic optical filter is positioned in the optical path of said signal beam so that a transmitted beam of said signal beam through said first atomic optical filter is used to communicate said communication data to said receiving module.

8. A device as in claim 1, wherein said first and second atomic optical filters are Voigt and Faraday filters, respectively.

9. A device as in claim 1, wherein each of said first and second atomic optical filters is either a Voigt filter or a Faraday filter.

10. A device as in claim 1, wherein said atomic medium includes an alkali element.

11. A device as in claim 10, wherein said alkali element is cesium.

12. A device as in claim 3, wherein said laser is a diode laser and further comprising a partially reflecting element disposed relative to said diode laser and said first atomic optical filter, said reflecting element operating to partially reflect said portion of said signal beam received by said first atomic optical filter back to said diode laser so that the frequency of said diode laser is locked with respect said atomic transition line.

13. A method as in claim 1, wherein said second atomic optical filter has a second transmission bandwidth that is greater than a first transmission bandwidth of said first atomic optical filter.

14. A method for communicating data by laser beams, comprising:

controlling a frequency of a laser beam of a laser with respect to an atomic transition line of an atomic medium by using a first atomic optical filter based on said atomic medium to receive at least a portion of said laser beam;

producing an optical feedback signal based on an interaction of said portion of said laser beam with said atomic medium at or near said atomic transition for locking said laser in frequency domain with respect to said atomic transition line;

modulating the frequency of said laser with respect to said atomic transition line to imprint first data onto said laser beam to produce a first signal beam;

receiving a second signal beam by using a second atomic optical filter based on said atomic medium wherein said second atomic optical filter is configured to transmit light at or near said atomic transition line and to substantially block light at other frequencies; and

detecting and extracting second data from said received second signal beam.

15. A method as in claim 14, wherein said step of modulating the frequency of said laser produces an intensity modulation in said first signal beam to represent said first data.

16. A method as in claim 14, wherein said step of modulating the frequency of said laser produces a frequency modulation on said first signal beam to represent said first data while maintaining an intensity of said first signal beam substantially constant and continuous.

17. A method as in claim 14, wherein said laser is locked at or near 852.11 nm by using said first atomic optical filter.

18. A method as in claim 14, wherein said second atomic optical filter has a second transmission bandwidth that is greater than a first transmission bandwidth of said first atomic optical filter.

19. A method for communicating information between one laser transceiver and another similar laser transceiver via laser beams, comprising:

producing a signal laser beam of a selected range of wavelengths by using a laser in said one laser transceiver;

modulating said signal laser beam to impose a digital communication signal thereon by using a signal modulator disposed relative to said laser in said one laser transceiver;

using a telescopic viewing device to locate said another laser transceiver and to facilitate pointing said laser transceiver in a direction of said another laser transceiver;

receiving a laser beam having a selected range of wavelengths from said another laser transceiver;

filtering said laser beam from said another laser transceiver by using an optical filter closely matched to at least one wavelength of said received laser beam;

detecting communication signals that are transmitted by said another laser transceiver through said optical filter; and

using a laser ranging unit, a GPS unit and an electronic compass to determine positioning of said one laser transceiver and said another laser transceiver.

20. A method as in claim 19, wherein said telescopic viewing device comprises a binocular.

21. A method as in claim 19, further comprising using a tilt gage to determine positioning of said one laser transceiver and said another laser transceiver.

22. A method as in claim 19, further comprising using a microphone and earphones in communicating information.

23. A method as in claim 19, further comprising using a video camera and an electronic view finder in communicating information.

24. A method as in claim 19, further comprising using a speaker in communicating said data.

25. A method as in claim 19, wherein said step of receiving said laser beam having said selected range of wavelengths from said another laser transceiver is performed by using a photo diode, a preamplifier, a frequency to voltage converter and a data converter.

26. A method as in claim 19, wherein said optical filter in the step of filtering is an atomic line filter configured to provide a noise equivalent bandwidth of less than 0.1 nm and to have a transmission band closely matched to at least one wavelength of said received laser beam.

27. A method as in claim 26 where said atomic line filter is a Faraday filter or a Voigt filter.