Coherent laser radar apparatus and radar/optical communication system

• US 6,580,497 B1
• Filed: 05/26/2000
• Issued: 06/17/2003
• Est. Priority Date: 05/28/1999
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Hirano, Yoshihito, Asaka, Kimio, Wadaka, Shusou
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): Hughes, Deandra M.
• Application Number:
  US09/579,462
• Time in Patent Office: 1,117 Days
• Field of Search: 356/4.07, 356/5.1, 356/5.15, 356/5.09, 356/28.05, 356/5.01, 359/341.5, 375/140
• US Class Current: 356/28.5
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/50 Systems of measurement based on relative movement of target
• CPC Class Codes: G01S 17/95 for meteorological use
• CPC Class Codes: G01S 7/481 Constructional features, e.g. arrangements of optical elements
• CPC Class Codes: G01S 7/4917 superposing optical signals in a photodetector, e.g. optical heterodyne detection
• CPC Class Codes: G01S 7/493 Extracting wanted echo signals
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

In a coherent CW laser radar apparatus, a soft target such as rain, fog, and air turbulence can be detected by using a CW laser. The coherent CW laser radar apparatus is arbandd by comprising: as an optical component, a CW laser oscillating a laser radiation having a single wavelength; a dividing means for dividing laser radiation derived from the CW laser; an optical modulator for modulating one of the laser radiation divided by the dividing means; an optical antenna for projecting the modulated laser radiation as transmitted radiation toward a target, and also for receiving scattered radiation from the target as received radiation; combining means for combining the other of the laser radiation divided by the dividing means as local radiation with the received radiation received from the optical antenna; and a photodetector for optical-heterodyne-detecting the combined radiation. Also, this coherent CW laser radar apparatus is further arbandd by employing: as an electric component, a pseudo-random modulation signal generator for supplying a pseudo-random modulation signal to the optical modulator; a variable delay device for time-delaying a portion of the pseudo-random modulation signal generated from the pseudo-random modulation signal generator; a correlating device for multiplying the output signal of the photodetector by the pseudo-random modulation signal time-delayed by the variable delay device; and signal processing means for acquiring physical information such as a distance of the target and a velocity of the target based upon a intensity and a frequency of the output signal from the correlating device, and also the delay time set by the variable delay device. In this radar apparatus, an optical path between the optical components is constituted by an optical fiber.

Claims

1. A coherent laser radar apparatus comprising:

as an optical component,

a CW laser oscillating a laser radiation having a single wavelength;

a dividing means for dividing laser radiation derived from said CW laser;

an optical modulator for modulating one of said laser radiation divided by said dividing means;

an optical antenna for projecting said modulated laser radiation as transmitted radiation toward a target, and also for receiving scattered radiation from the target as received radiation;

combining means for combining the other of said laser radiation divided by said dividing means as local radiation with said received radiation; and

a photodetector for optical-heterodyne-detecting said combined radiation and outputting a beat signal between said received radiation and said local radiation; and

also comprising;

as an electric component,

a pseudo-random modulation signal generator for supplying a pseudo-random modulation signal to said optical modulator;

a variable delay device for time-delaying a portion of the pseudo-random modulation signal generated from said pseudo-random modulation signal generator;

a correlating device for multiplying the output signal of said photodetector by the pseudo-random modulation signal, time-delayed by said variable delay device; and

signal processing means for acquiring physical information such as a distance of said target and a velocity of said target based upon a intensity and a frequency of the output signal from said correlating device, and also the delay time set by said variable delay device;

wherein;

an optical path between said optical components is constituted by an optical fiber.

2. A coherent laser radar apparatus as claimed in claim 1 wherein:

an optical fiber amplifier having a gain in the vicinity of a wavelength of the modulated laser radiation is further provided in the optical path between said optical modulator and said optical antenna.

3. A coherent laser radar apparatus as claimed in claim 2 wherein:

said CW laser corresponds to a CW laser oscillating a laser radiation having a single wavelength, the oscillation wavelength of which is a 1.5 μ

m band, whereas

said optical fiber amplifier corresponds to an optical fiber amplifier with employment of an Er³⁺ ion-doped optical fiber having a gain in the 1.5 μ

m band.

4. A coherent laser radar apparatus as claimed in claim 2 wherein:

said CW laser corresponds to a CW laser oscillating a laser radiation having a single wavelength, the oscillation wavelength of which is any one of a 1.06 μ

m band, a 0.98 μ

m band, and a 1.3 μ

m band, whereas

said optical fiber amplifier is an optical fiber amplifier with employment of an Nd³⁺ ion-doped optical fiber having a gain in any one of the 1.06 μ

m band, 0.98 μ

m band, and 1.3 μ

m band.

5. A coherent laser radar apparatus as claimed in claim 2 wherein:

said CW laser corresponds to a CW laser oscillating a laser radiation having a single wavelength, the oscillation wavelength of which is a 1.3 μ

m band, whereas

said optical fiber amplifier corresponds to an optical fiber amplifier with employment of a Pr³⁺ ion-doped optical fiber having a gain in the 1.3 μ

m band.

6. A coherent laser radar apparatus as claimed in claim 2 wherein:

said CW laser corresponds to a CW laser oscillating a laser radiation having a single wavelength, the oscillation wavelength of which is a 1 μ

m band, whereas

said optical fiber amplifier corresponds to an optical fiber amplifier with employment of a Yb³⁺ ion-doped optical fiber having a gain in the 1 μ

m band.

7. A coherent laser radar apparatus as claimed in claim 2 wherein:

said CW laser corresponds to a CW laser oscillating a laser radiation having a single wavelength, the oscillation wavelength of which is a 2.1 μ

m band, whereas

said optical fiber amplifier corresponds to an optical fiber amplifier with employment of an Ho³⁺ ion-doped optical fiber having a gain in the 2.1 μ

m band.

8. A coherent laser radar apparatus as claimed in claim 2 wherein:

said CW laser corresponds to a CW laser oscillating a laser radiation having a single wavelength, the oscillation wavelength of which is a 2.0 μ

m band, whereas

said optical fiber amplifier corresponds to an optical fiber amplifier with employment of an Tm³⁺ ion-doped optical fiber having a gain in the 2.0 μ

m band.

9. A coherent laser radar apparatus as claimed in claim 1 wherein:

said CW laser corresponds to a CW laser radiation source having a high spectrum purity, in which a line width of oscillated laser radiation is made narrower than a width of a frequency dispersion which is applied to said received radiation and is caused by the target.

10. A coherent laser radar apparatus as claimed in claim 9 wherein:

said CW laser radiation source having the high spectrum purity includes;

a solid-state laser module oscillated having a single wavelength, which contains a means for fine-controlling all, or any one of a temperature, a resonator length, and pumping intensity; and

phase noise compensating means for detecting phase noise of output radiation from said solid-state laser module by using a portion of said output radiation thereof, and for supplying a feedback signal used to fine-control all, or any one of said temperature, said resonator length, and said pumping intensity from the phase noise detection output to said solid-state laser module.

11. A coherent laser radar apparatus as claimed in claim 1, further comprising:

means for detecting a time change in a difference between a summation of an optical path length of the transmitted radiation from the CW laser in the apparatus to the optical antenna and an optical path length of the received radiation from the optical antenna to the optical detector; and

means for controlling the optical path length of any one of said transmitted radiation, said received radiation, and said local radiation based upon the output signal derived from said means for detecting the time change in the difference of said optical path lengths.

12. A coherent laser radar apparatus as claimed in claim 11, wherein:

said means for detecting the time change in the difference of the optical path lengths is arranged by;

a fixed delay device for applying a constant time delay to a portion of the pseudo-random modulation signal generated from said pseudo-random modulation signal generator;

a correlating device for multiplying the output signal of said photodetector by the time-delayed modulation signal derived from said fixed delay device;

a microwave reference oscillator having a high spectrum purity; and

means for detecting a phase difference between the output signal of said correlating device and the output signal of said microwave reference oscillator.

13. A coherent laser radar apparatus as claimed in claim 11, wherein:

said means for controlling the optical path length is arranged by;

an electro-optical crystal element positioned in an optical path; and

means for applying an electric field to said electro-optical crystal element.

14. A coherent laser radar apparatus as claimed in claim 1 wherein:

the respective structural elements of said coherent laser radar apparatus are set on a mobile object such as an aircraft, a satellite, and a vehicle.

15. A coherent laser radar apparatus as claimed in claim 14 wherein:

said pseudo-random signal generator generates a pseudo-random signal as a modulation signal in such a manner that a time width “

τ

”

of the pseudo-random signal per 1 bit is set to (τ

>

1/f_L) in the case that a minimum frequency of a measuring frequency band to be measured is selected to be “

f_L.”

16. A coherent laser radar apparatus as claimed in claim 14 wherein:

said coherent laser radar apparatus includes at least one set of such a combination between a fixed delay device and a correlating device, instead of both said variable delay device and said correlating device;

said fixed delay device applies a constant time delay to a portion of the pseudo-random modulation signal of said pseudo-random modulation signal generator; and

said correlating device multiples the output signal derived from said photodetector by the output signal derived from said fixed delay device.

17. A coherent laser radar apparatus as claimed in claim 1 wherein:

said coherent laser radar apparatus is further comprised of an optical space communication apparatus including;

an optical switch provided in a reception optical path from said optical antenna, for switching the optical paths;

an optical receiver for receiving received radiation of an optical communication from said optical switch via an optical circulator;

an optical transmitter for outputting transmitted radiation for the optical communication via said optical circulator to said optical switch; and

a communication signal processing apparatus for demodulating the optical communication received radiation received from said optical receiver so as to extract communication information therefrom, and also for producing a modulation signal based upon communication information to be transmitted so as to output said produced modulation signal to said optical transmitter; and

wherein;

said optical antenna functions as an optical antenna for an optical communication purpose by switching the optical path by said optical switch, whereby a function of an optical space communication is additionally provided with said coherent laser radar apparatus.

18. A coherent laser radar apparatus as claimed in claim 1 wherein:

said coherent laser radar apparatus is further comprised of;

a communication signal processing apparatus for demodulating the received optical communication received radiation so as to extract communication information therefrom, and also for producing a modulation signal based upon communication information to be transmitted so as to output the produced modulation signal; and

wherein;

said optical modulator modulates transmitted radiation for an optical communication by the modulation signal outputted from said communication signal processing apparatus; and

a function of an optical space communication is added to said coherent laser radar apparatus by employing a function of an optical transmitter in which optical communication transmitted radiation is outputted by said CW laser and said optical modulator;

a function as an optical communication optical antenna to said optical antenna; and

a function as an optical receiver for receiving the optical communication received radiation to said photodetector.

19. A coherent laser radar apparatus comprising:

as an optical component,

a CW laser oscillating a laser radiation with a single wavelength;

a dividing means for dividing laser radiation derived from said CW laser;

an optical modulator for modulating one of said laser radiation divided by said dividing means;

an optical antenna for projecting said modulated laser radiation as transmitted radiation toward a target, and also for receiving scattered radiation from the target as received radiation;

combining means for combining the other of said laser radiation divided by said dividing means as local radiation with said received radiation; and

a photodector for optical-heterodyne-detecting said combined radiation and outputting a beat signal between said received radiation and said local radiation; and

also comprising;

as an electric component,

a pseudo-random modulation signal generator for supplying a pseudo-random modulation signal to said optical modulator;

a time delay device for time-delaying a portion of the pseudo-random modulation signal generated from said pseudo-random modulation signal generator;

a correlating device for multiplying the output signal of said photodetector by the pseudo-random modulation signal time-displayed by said time delay device; and

signal processing means for acquiring physical information such as a distance of said target and a velocity of said target based upon a intensity and a frequency of the output signal from said correlating device, and also the delay time set by said time delay device;

wherein;

said pseudo-random modulation signal generator employs as a pseudo-random modulation signal, such a pseudo-random sequence (PN code) that time required for one sequence length is sufficiently longer than time required for laser radiation which is reciprocated within a distance band where received radiation having sufficiently high intensity can be obtained by said optical antenna.

20. A coherent laser radar apparatus comprising:

as an optical component,

a CW laser oscillating a laser radiation having a single wavelength;

a dividing means for dividing laser radiation derived from said CW laser;

an optical modulator for modulating one of said laser radiation divided by said dividing means;

an optical antenna for projecting said modulated laser radiation as transmitted radiation toward a target, and also for receiving scattered radiation from the target as received radiation;

combining means for combining the other of said laser radiation divided by said dividing means as local radiation with said received radiation; and

a photodetector for optical-heterodyne-detecting said combined radiation and outputting a beat signal between said received radiation and said local radiation; and

also comprising;

as an electric component,

a pseudo-random modulation signal generator for supplying a pseudo-random modulation signal to said optical modulator;

a time delay device for time-delaying a portion of the pseudo-random modulation signal generated from said pseudo-random modulation signal generator;

a correlating device for multiplying the output signal of said photodetector by the pseudo-random modulation signal time-delayed by said time delay device; and

signal processing means for acquiring physical information such as a distance of said target and a velocity of said target based upon a intensity and a frequency of the output signal from said correlating device, and also the delay time set by said time delay device;

wherein;

said pseudo-random modulation signal generator owns a function capable of switching pseudo-random modulating signals produced based on a plurality of pseudo-random sequence (PN code) different from each other to thereby produce the switched pseudo-random modulating signal.