Abstract

A coherent laser radar has been built by use of a master-oscillator power-amplifier arrangement in which the master oscillator is an external-cavity semiconductor laser and the power amplifier is an erbium-doped fiber amplifier with ∼1-W output at a wavelength of 1.55 µm. The beams are routed within single-mode optical fiber, allowing modular construction of the optical layout with standard components. The system employs separate transmit and receive optics (a bistatic configuration) and has sufficient sensitivity for reliable Doppler wind-speed detection in moderate scattering conditions at short range (to as much as ∼200 m). The bistatic arrangement leads to a well-defined probe volume formed by the intersection of the transmitted laser beam with the virtual backpropagated local-oscillator beam. This could be advantageous for applications in which the precise localization of wind speed is required (e.g., wind tunnel studies) or in which smoke, low cloud, or solid objects can lead to spurious signals. The confinement of the probe volume also leads to a reduction in the signal power. A theoretical study has been carried out on the reduction in wind signal strength compared with the monostatic arrangement, and the results are compared with experimental observation.

© 2001 Optical Society of America

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References

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  1. See, for example, J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” Proc. IEEE 84, 205–226 (1996).
  2. C. M. Sonnenschein, F. A. Horrigan, “Signal-to-noise relationships for coaxial systems that heterodyne backscatter from the atmosphere,” Appl. Opt. 10, 1600–1604 (1971).
    [CrossRef] [PubMed]
  3. C. Werner, F. Köpp, R. Schwiesow, “Influence of clouds and fog on LDA wind measurements,” Appl. Opt. 23, 2482–2484 (1984).
    [CrossRef] [PubMed]
  4. F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser Doppler Anemometry (Academic, London, 1976).
  5. T. Okoshi, K. Kikuchi, A. Nakayama, “Novel method for high-resolution measurement of laser output spectrum,” Electron. Lett. 16, 630–631 (1980).
    [CrossRef]
  6. M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45, 1567–1581 (1998).
    [CrossRef]
  7. C. Karlsson, F. Olsson, D. Letalick, M. Harris, “All-fiber multifunction continuous-wave coherent laser radar at 1.55 µm for range, speed, vibration, and wind measurements,” Appl. Opt. 39, 3716–3726 (2000).
    [CrossRef]
  8. R. G. Frehlich, M. J. Yadlowsky, “Performance of mean-frequency estimators for Doppler radar and lidar,” J. Atmos. Ocean. Technol. 11, 1217–1230 (1994).
    [CrossRef]
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    [CrossRef] [PubMed]
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    [CrossRef]
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    [CrossRef] [PubMed]
  12. R. L. McGann, “Flight test results from a low-power Doppler optical air data sensor,” in Air Traffic Control Technologies, R. G. Otto, J. Lenz, eds., Proc. SPIE2464, 116–124 (1994).
    [CrossRef]
  13. M. Harris, G. N. Pearson, K. D. Ridley, C. Karlsson, F. Olsson, D. Letalick, “Single-particle laser Doppler anemometry at 1.55 µm,” Appl. Opt. 40, 969–973 (2001).
    [CrossRef]
  14. V. Srivastava, M. A. Jarzembski, D. A. Bowdle, “Comparison of calculated aerosol backscatter at 9.1- and 2.1-µm wavelengths,” Appl. Opt. 31, 1904–1906 (1992).
    [CrossRef] [PubMed]

2001

2000

1998

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45, 1567–1581 (1998).
[CrossRef]

1996

See, for example, J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” Proc. IEEE 84, 205–226 (1996).

1994

M. Harris, G. N. Pearson, C. A. Hill, J. M. Vaughan, “Higher moments of scattered light fields by heterodyne analysis,” Appl. Opt. 33, 7226–7230 (1994).
[CrossRef] [PubMed]

R. G. Frehlich, M. J. Yadlowsky, “Performance of mean-frequency estimators for Doppler radar and lidar,” J. Atmos. Ocean. Technol. 11, 1217–1230 (1994).
[CrossRef]

1992

1984

1981

B. J. Rye, “Refractive-turbulence contribution to incoherent backscatter heterodyne lidar returns,” J. Opt. Soc. Am 71, 687–691 (1981).
[CrossRef]

1980

T. Okoshi, K. Kikuchi, A. Nakayama, “Novel method for high-resolution measurement of laser output spectrum,” Electron. Lett. 16, 630–631 (1980).
[CrossRef]

1971

1966

Bowdle, D. A.

Durst, F.

F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser Doppler Anemometry (Academic, London, 1976).

Flamant, P. H.

See, for example, J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” Proc. IEEE 84, 205–226 (1996).

Frehlich, R. G.

R. G. Frehlich, M. J. Yadlowsky, “Performance of mean-frequency estimators for Doppler radar and lidar,” J. Atmos. Ocean. Technol. 11, 1217–1230 (1994).
[CrossRef]

Harris, M.

Hill, C. A.

Horrigan, F. A.

Jarzembski, M. A.

Karlsson, C.

Kikuchi, K.

T. Okoshi, K. Kikuchi, A. Nakayama, “Novel method for high-resolution measurement of laser output spectrum,” Electron. Lett. 16, 630–631 (1980).
[CrossRef]

Köpp, F.

Letalick, D.

McGann, R. L.

R. L. McGann, “Flight test results from a low-power Doppler optical air data sensor,” in Air Traffic Control Technologies, R. G. Otto, J. Lenz, eds., Proc. SPIE2464, 116–124 (1994).
[CrossRef]

Melling, A.

F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser Doppler Anemometry (Academic, London, 1976).

Nakayama, A.

T. Okoshi, K. Kikuchi, A. Nakayama, “Novel method for high-resolution measurement of laser output spectrum,” Electron. Lett. 16, 630–631 (1980).
[CrossRef]

Okoshi, T.

T. Okoshi, K. Kikuchi, A. Nakayama, “Novel method for high-resolution measurement of laser output spectrum,” Electron. Lett. 16, 630–631 (1980).
[CrossRef]

Olsson, F.

Pearson, G. N.

Ridley, K. D.

Rye, B. J.

B. J. Rye, “Refractive-turbulence contribution to incoherent backscatter heterodyne lidar returns,” J. Opt. Soc. Am 71, 687–691 (1981).
[CrossRef]

Schwiesow, R.

Siegman, A. E.

Sonnenschein, C. M.

Srivastava, V.

Steinvall, K. O.

See, for example, J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” Proc. IEEE 84, 205–226 (1996).

Vaughan, J. M.

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45, 1567–1581 (1998).
[CrossRef]

See, for example, J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” Proc. IEEE 84, 205–226 (1996).

M. Harris, G. N. Pearson, C. A. Hill, J. M. Vaughan, “Higher moments of scattered light fields by heterodyne analysis,” Appl. Opt. 33, 7226–7230 (1994).
[CrossRef] [PubMed]

Werner, C.

See, for example, J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” Proc. IEEE 84, 205–226 (1996).

C. Werner, F. Köpp, R. Schwiesow, “Influence of clouds and fog on LDA wind measurements,” Appl. Opt. 23, 2482–2484 (1984).
[CrossRef] [PubMed]

Whitelaw, J. H.

F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser Doppler Anemometry (Academic, London, 1976).

Yadlowsky, M. J.

R. G. Frehlich, M. J. Yadlowsky, “Performance of mean-frequency estimators for Doppler radar and lidar,” J. Atmos. Ocean. Technol. 11, 1217–1230 (1994).
[CrossRef]

Appl. Opt.

Electron. Lett.

T. Okoshi, K. Kikuchi, A. Nakayama, “Novel method for high-resolution measurement of laser output spectrum,” Electron. Lett. 16, 630–631 (1980).
[CrossRef]

J. Atmos. Ocean. Technol.

R. G. Frehlich, M. J. Yadlowsky, “Performance of mean-frequency estimators for Doppler radar and lidar,” J. Atmos. Ocean. Technol. 11, 1217–1230 (1994).
[CrossRef]

J. Mod. Opt.

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45, 1567–1581 (1998).
[CrossRef]

J. Opt. Soc. Am

B. J. Rye, “Refractive-turbulence contribution to incoherent backscatter heterodyne lidar returns,” J. Opt. Soc. Am 71, 687–691 (1981).
[CrossRef]

Proc. IEEE

See, for example, J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” Proc. IEEE 84, 205–226 (1996).

Other

R. L. McGann, “Flight test results from a low-power Doppler optical air data sensor,” in Air Traffic Control Technologies, R. G. Otto, J. Lenz, eds., Proc. SPIE2464, 116–124 (1994).
[CrossRef]

F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser Doppler Anemometry (Academic, London, 1976).

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Figures (5)

Fig. 1
Fig. 1

System layout and experimental geometry, showing components connected by single-mode optical fiber, which permits great flexibility in component positioning: 1 × 2, 2 × 2, fiber couplers; OI, optical isolator; AOM, acousto-optic modulator (optional); EDFA, 1-W erbium-doped fiber amplifier; FPC, fiber polarization controller; T, transmitted beam; R, received signal photons (backscattered from atmospheric aerosols); BPLO, virtual backpropagated LO beam.

Fig. 2
Fig. 2

Measurement geometry showing the region of overlap for the transmit beam and virtual BPLO. The z axis is defined along the bisector, where z = 0 corresponds to the position of the beam waist radius w 0. For the tightly focused case considered here, the waist is displaced negligibly from the focus. The half-angle divergence θ d is assumed identical for the two beams, and they intersect at an angle 2θ in the xz plane.

Fig. 3
Fig. 3

Relative contribution to signal power as a function of distance along the beam z expressed in units of the Rayleigh range R R . The theoretical curves have been plotted for several values of the transmit–receive separation θ/θ d , including the value θ/θ d = 1.375 pertaining to this lidar. Experimental data, ●, obtained from a hard target is also plotted for comparison with the dashed curve (θ/θ d = 1.375).

Fig. 4
Fig. 4

Reduction in wind signal for a bistatic lidar compared with a monostatic system as a function of the transmit–receive separation θ/θ d . For any practical system a minimum limit of the order of θ/θ d ∼ 1.4 must apply to avoid substantial overlap of the beams.

Fig. 5
Fig. 5

Experimental measurements of wind velocity with the bistatic wind sensor: (a) strong signal in high-scattering conditions (low visibility, ∼1 km), 512 averages; (b), (c), weaker signals obtained at a visibility of 10–20 km, 1024 averages; (d) non-Gaussian signal showing evidence of single-particle scattering events (spikes) in turbulent conditions, 256 averages.

Equations (12)

Equations on this page are rendered with MathJax. Learn more.

NENS=ηIRτd2πhντc,
V=λδν cos θ/2,
CNRmono=ηPTβπλ2Bhνπ2+arctanπR2λf,
CNRmono=πηPTβπλ2Bhν,
PS=π/2PTβπλ.
S   ρπITIBPLOdxdy,
S  all space βπITIBPLOdxdydz,
ITIBPLO=w04wz4exp-4x2+y2+zθ2wz2,
wz=w01+λzπw0220.5,
Sz=w02wz2exp-2zθwz2,
ST  - Szdz
CNRbi=CNRmonoSTθSTθ=0,

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