Abstract

The performance of a frequency-modulated continuous-wave (FMCW) semiconductor laser radar has been examined. Frequency modulation (linear chirp) has been studied experimentally in detail. To create a linear frequency sweep, we modified the modulating function according to the measured frequency response of the laser, using an arbitrary function generator. The measurements indicate the possibility of achieving a spectral width of the signal peak that is transform limited rather than limited by the frequency modulation response of the laser, which permits the use of a narrow detection bandwidth. The narrow width results in a relatively high signal-to-noise ratio for low output power and thus also in relatively long-range and high-range accuracy. We have performed measurements of a diffuse target to determine the performance of a test laser radar system. The maximum range, range accuracy, and speed accuracy for a semiconductor laser with an output power of 10 mW and a linewidth of 400 kHz are presented. The influence of the laser’s output power and coherence length on the performance of a semiconductor-laser-based FMCW laser radar is discussed.

© 1999 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” in Proc. IEEE 84, 205–226 (1996); R. M. Huffaker, R. M. Hardesty, “Remote sensing of atmospheric wind velocities using solid-state and CO2 coherent laser systems,” Proc. IEEE 84, 181–204 (1996).
    [CrossRef]
  2. R. Passy, N. Gisin, J. P. von der Weid, H. H. Gilgen, “Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources,” J. Lightwave Technol. 12, 1622–1630 (1994).
    [CrossRef]
  3. L.-T. Wang, K. Iiyama, F. Tsukada, N. Yoshida, K.-I. Hayashi, “Loss measurement in optical waveguide devices by coherent frequency-modulated continuous-wave reflectometry,” Opt. Lett. 18, 1095–1097 (1993).
    [CrossRef] [PubMed]
  4. M. Harris, G. N. Pearson, J. M. Vaughnan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45, 1567–1581 (1998).
    [CrossRef]
  5. M. P. van Exter, S. J. M. Kuppens, J. P. Woerdman, “Excess phase noise in self-heterodyne detection,” IEEE J. Quantum Electron. 28, 580–584 (1992).
    [CrossRef]
  6. L. E. Richter, H. I. Mandelberg, M. S. Kruger, P. A. McGrath, “Linewidth determination from self-heterodyne measurements with subcoherence delay times,” IEEE J. Quantum Electron. QE-22, 2070–2074 (1986).
    [CrossRef]
  7. S. Nilsson, T. Kjellberg, T. Klinga, R. Schatz, J. Wallin, K. Streubel, “Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts,” J. Lightwave Technol. 13, 434–441 (1995).
    [CrossRef]
  8. C. Karlsson, D. Letalick, G. Pearson, M. Harris, “Frequency modulation of a DFB laser diode for CLR applications,” in Proceedings of the Ninth Conference on Coherent Laser Radar (Swedish Defence Research Establishment, Linköping, Sweden, 1997).
  9. See, e.g., M. I. Skolnik, Introduction to Radar Systems (McGraw-Hill, New York, 1981).
  10. See, e.g., D. Letalick, I. Renhorn, O. Steinvall, “Measured signal amplitude distributions for a coherent FM-cw CO2 laser radar,” Appl. Opt. 25, 3927–3938 (1986).
  11. S. Kobayashi, Y. Yamamoto, M. Ito, T. Kimura, “Direct frequency modulation in AlGaAs semiconductor lasers,” IEEE J. Quantum Electron. QE-18, 582–595 (1982).
    [CrossRef]
  12. E. Goobar, M. Schiess, “Characterization of modulation and noise properties of a three-electrode DFB laser,” IEEE Photon. Technol. Lett. 4, 414–416 (1992).
    [CrossRef]
  13. Kap10 product from Radians Innova AB, Gothenburg, Sweden.
  14. D. Letalick, “Coherent CO2 laser radar in active imaging systems,” dissertation 216 (Chalmers University of Technology, Gothenburg, Sweden, 1991).
  15. G. W. Kamerman, “Laser radar” in Active Electro-Optical Systems, C. S. Fox, ed., Vol. 6 of The Infrared & Electro-Optical Systems Handbook (SPIE Press, Bellingham, Wash., 1993).
  16. J. P. von der Weid, R. Passy, G. Mussi, N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15, 1131–1141 (1997).
    [CrossRef]
  17. R. G. Frehlich, M. J. Kavaya, “Coherent laser radar performance for general atmospheric refractive turbulence,” Appl. Opt. 30, 5325–5352 (1991).
    [CrossRef] [PubMed]

1998 (1)

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

1997 (1)

J. P. von der Weid, R. Passy, G. Mussi, N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15, 1131–1141 (1997).
[CrossRef]

1996 (1)

J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” in Proc. IEEE 84, 205–226 (1996); R. M. Huffaker, R. M. Hardesty, “Remote sensing of atmospheric wind velocities using solid-state and CO2 coherent laser systems,” Proc. IEEE 84, 181–204 (1996).
[CrossRef]

1995 (1)

S. Nilsson, T. Kjellberg, T. Klinga, R. Schatz, J. Wallin, K. Streubel, “Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts,” J. Lightwave Technol. 13, 434–441 (1995).
[CrossRef]

1994 (1)

R. Passy, N. Gisin, J. P. von der Weid, H. H. Gilgen, “Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources,” J. Lightwave Technol. 12, 1622–1630 (1994).
[CrossRef]

1993 (1)

1992 (2)

M. P. van Exter, S. J. M. Kuppens, J. P. Woerdman, “Excess phase noise in self-heterodyne detection,” IEEE J. Quantum Electron. 28, 580–584 (1992).
[CrossRef]

E. Goobar, M. Schiess, “Characterization of modulation and noise properties of a three-electrode DFB laser,” IEEE Photon. Technol. Lett. 4, 414–416 (1992).
[CrossRef]

1991 (1)

1986 (2)

See, e.g., D. Letalick, I. Renhorn, O. Steinvall, “Measured signal amplitude distributions for a coherent FM-cw CO2 laser radar,” Appl. Opt. 25, 3927–3938 (1986).

L. E. Richter, H. I. Mandelberg, M. S. Kruger, P. A. McGrath, “Linewidth determination from self-heterodyne measurements with subcoherence delay times,” IEEE J. Quantum Electron. QE-22, 2070–2074 (1986).
[CrossRef]

1982 (1)

S. Kobayashi, Y. Yamamoto, M. Ito, T. Kimura, “Direct frequency modulation in AlGaAs semiconductor lasers,” IEEE J. Quantum Electron. QE-18, 582–595 (1982).
[CrossRef]

Flamant, P. H.

J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” in Proc. IEEE 84, 205–226 (1996); R. M. Huffaker, R. M. Hardesty, “Remote sensing of atmospheric wind velocities using solid-state and CO2 coherent laser systems,” Proc. IEEE 84, 181–204 (1996).
[CrossRef]

Frehlich, R. G.

Gilgen, H. H.

R. Passy, N. Gisin, J. P. von der Weid, H. H. Gilgen, “Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources,” J. Lightwave Technol. 12, 1622–1630 (1994).
[CrossRef]

Gisin, N.

J. P. von der Weid, R. Passy, G. Mussi, N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15, 1131–1141 (1997).
[CrossRef]

R. Passy, N. Gisin, J. P. von der Weid, H. H. Gilgen, “Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources,” J. Lightwave Technol. 12, 1622–1630 (1994).
[CrossRef]

Goobar, E.

E. Goobar, M. Schiess, “Characterization of modulation and noise properties of a three-electrode DFB laser,” IEEE Photon. Technol. Lett. 4, 414–416 (1992).
[CrossRef]

Harris, M.

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

C. Karlsson, D. Letalick, G. Pearson, M. Harris, “Frequency modulation of a DFB laser diode for CLR applications,” in Proceedings of the Ninth Conference on Coherent Laser Radar (Swedish Defence Research Establishment, Linköping, Sweden, 1997).

Hayashi, K.-I.

Iiyama, K.

Ito, M.

S. Kobayashi, Y. Yamamoto, M. Ito, T. Kimura, “Direct frequency modulation in AlGaAs semiconductor lasers,” IEEE J. Quantum Electron. QE-18, 582–595 (1982).
[CrossRef]

Kamerman, G. W.

G. W. Kamerman, “Laser radar” in Active Electro-Optical Systems, C. S. Fox, ed., Vol. 6 of The Infrared & Electro-Optical Systems Handbook (SPIE Press, Bellingham, Wash., 1993).

Karlsson, C.

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

C. Karlsson, D. Letalick, G. Pearson, M. Harris, “Frequency modulation of a DFB laser diode for CLR applications,” in Proceedings of the Ninth Conference on Coherent Laser Radar (Swedish Defence Research Establishment, Linköping, Sweden, 1997).

Kavaya, M. J.

Kimura, T.

S. Kobayashi, Y. Yamamoto, M. Ito, T. Kimura, “Direct frequency modulation in AlGaAs semiconductor lasers,” IEEE J. Quantum Electron. QE-18, 582–595 (1982).
[CrossRef]

Kjellberg, T.

S. Nilsson, T. Kjellberg, T. Klinga, R. Schatz, J. Wallin, K. Streubel, “Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts,” J. Lightwave Technol. 13, 434–441 (1995).
[CrossRef]

Klinga, T.

S. Nilsson, T. Kjellberg, T. Klinga, R. Schatz, J. Wallin, K. Streubel, “Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts,” J. Lightwave Technol. 13, 434–441 (1995).
[CrossRef]

Kobayashi, S.

S. Kobayashi, Y. Yamamoto, M. Ito, T. Kimura, “Direct frequency modulation in AlGaAs semiconductor lasers,” IEEE J. Quantum Electron. QE-18, 582–595 (1982).
[CrossRef]

Kruger, M. S.

L. E. Richter, H. I. Mandelberg, M. S. Kruger, P. A. McGrath, “Linewidth determination from self-heterodyne measurements with subcoherence delay times,” IEEE J. Quantum Electron. QE-22, 2070–2074 (1986).
[CrossRef]

Kuppens, S. J. M.

M. P. van Exter, S. J. M. Kuppens, J. P. Woerdman, “Excess phase noise in self-heterodyne detection,” IEEE J. Quantum Electron. 28, 580–584 (1992).
[CrossRef]

Letalick, D.

M. Harris, G. N. Pearson, J. M. Vaughnan, 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, e.g., D. Letalick, I. Renhorn, O. Steinvall, “Measured signal amplitude distributions for a coherent FM-cw CO2 laser radar,” Appl. Opt. 25, 3927–3938 (1986).

D. Letalick, “Coherent CO2 laser radar in active imaging systems,” dissertation 216 (Chalmers University of Technology, Gothenburg, Sweden, 1991).

C. Karlsson, D. Letalick, G. Pearson, M. Harris, “Frequency modulation of a DFB laser diode for CLR applications,” in Proceedings of the Ninth Conference on Coherent Laser Radar (Swedish Defence Research Establishment, Linköping, Sweden, 1997).

Mandelberg, H. I.

L. E. Richter, H. I. Mandelberg, M. S. Kruger, P. A. McGrath, “Linewidth determination from self-heterodyne measurements with subcoherence delay times,” IEEE J. Quantum Electron. QE-22, 2070–2074 (1986).
[CrossRef]

McGrath, P. A.

L. E. Richter, H. I. Mandelberg, M. S. Kruger, P. A. McGrath, “Linewidth determination from self-heterodyne measurements with subcoherence delay times,” IEEE J. Quantum Electron. QE-22, 2070–2074 (1986).
[CrossRef]

Mussi, G.

J. P. von der Weid, R. Passy, G. Mussi, N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15, 1131–1141 (1997).
[CrossRef]

Nilsson, S.

S. Nilsson, T. Kjellberg, T. Klinga, R. Schatz, J. Wallin, K. Streubel, “Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts,” J. Lightwave Technol. 13, 434–441 (1995).
[CrossRef]

Passy, R.

J. P. von der Weid, R. Passy, G. Mussi, N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15, 1131–1141 (1997).
[CrossRef]

R. Passy, N. Gisin, J. P. von der Weid, H. H. Gilgen, “Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources,” J. Lightwave Technol. 12, 1622–1630 (1994).
[CrossRef]

Pearson, G.

C. Karlsson, D. Letalick, G. Pearson, M. Harris, “Frequency modulation of a DFB laser diode for CLR applications,” in Proceedings of the Ninth Conference on Coherent Laser Radar (Swedish Defence Research Establishment, Linköping, Sweden, 1997).

Pearson, G. N.

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

Renhorn, I.

Richter, L. E.

L. E. Richter, H. I. Mandelberg, M. S. Kruger, P. A. McGrath, “Linewidth determination from self-heterodyne measurements with subcoherence delay times,” IEEE J. Quantum Electron. QE-22, 2070–2074 (1986).
[CrossRef]

Schatz, R.

S. Nilsson, T. Kjellberg, T. Klinga, R. Schatz, J. Wallin, K. Streubel, “Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts,” J. Lightwave Technol. 13, 434–441 (1995).
[CrossRef]

Schiess, M.

E. Goobar, M. Schiess, “Characterization of modulation and noise properties of a three-electrode DFB laser,” IEEE Photon. Technol. Lett. 4, 414–416 (1992).
[CrossRef]

Skolnik, M. I.

See, e.g., M. I. Skolnik, Introduction to Radar Systems (McGraw-Hill, New York, 1981).

Steinvall, K. O.

J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” in Proc. IEEE 84, 205–226 (1996); R. M. Huffaker, R. M. Hardesty, “Remote sensing of atmospheric wind velocities using solid-state and CO2 coherent laser systems,” Proc. IEEE 84, 181–204 (1996).
[CrossRef]

Steinvall, O.

Streubel, K.

S. Nilsson, T. Kjellberg, T. Klinga, R. Schatz, J. Wallin, K. Streubel, “Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts,” J. Lightwave Technol. 13, 434–441 (1995).
[CrossRef]

Tsukada, F.

van Exter, M. P.

M. P. van Exter, S. J. M. Kuppens, J. P. Woerdman, “Excess phase noise in self-heterodyne detection,” IEEE J. Quantum Electron. 28, 580–584 (1992).
[CrossRef]

Vaughan, J. M.

J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” in Proc. IEEE 84, 205–226 (1996); R. M. Huffaker, R. M. Hardesty, “Remote sensing of atmospheric wind velocities using solid-state and CO2 coherent laser systems,” Proc. IEEE 84, 181–204 (1996).
[CrossRef]

Vaughnan, J. M.

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

von der Weid, J. P.

J. P. von der Weid, R. Passy, G. Mussi, N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15, 1131–1141 (1997).
[CrossRef]

R. Passy, N. Gisin, J. P. von der Weid, H. H. Gilgen, “Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources,” J. Lightwave Technol. 12, 1622–1630 (1994).
[CrossRef]

Wallin, J.

S. Nilsson, T. Kjellberg, T. Klinga, R. Schatz, J. Wallin, K. Streubel, “Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts,” J. Lightwave Technol. 13, 434–441 (1995).
[CrossRef]

Wang, L.-T.

Werner, C.

J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” in Proc. IEEE 84, 205–226 (1996); R. M. Huffaker, R. M. Hardesty, “Remote sensing of atmospheric wind velocities using solid-state and CO2 coherent laser systems,” Proc. IEEE 84, 181–204 (1996).
[CrossRef]

Woerdman, J. P.

M. P. van Exter, S. J. M. Kuppens, J. P. Woerdman, “Excess phase noise in self-heterodyne detection,” IEEE J. Quantum Electron. 28, 580–584 (1992).
[CrossRef]

Yamamoto, Y.

S. Kobayashi, Y. Yamamoto, M. Ito, T. Kimura, “Direct frequency modulation in AlGaAs semiconductor lasers,” IEEE J. Quantum Electron. QE-18, 582–595 (1982).
[CrossRef]

Yoshida, N.

Appl. Opt. (2)

IEEE J. Quantum Electron. (3)

S. Kobayashi, Y. Yamamoto, M. Ito, T. Kimura, “Direct frequency modulation in AlGaAs semiconductor lasers,” IEEE J. Quantum Electron. QE-18, 582–595 (1982).
[CrossRef]

M. P. van Exter, S. J. M. Kuppens, J. P. Woerdman, “Excess phase noise in self-heterodyne detection,” IEEE J. Quantum Electron. 28, 580–584 (1992).
[CrossRef]

L. E. Richter, H. I. Mandelberg, M. S. Kruger, P. A. McGrath, “Linewidth determination from self-heterodyne measurements with subcoherence delay times,” IEEE J. Quantum Electron. QE-22, 2070–2074 (1986).
[CrossRef]

IEEE Photon. Technol. Lett. (1)

E. Goobar, M. Schiess, “Characterization of modulation and noise properties of a three-electrode DFB laser,” IEEE Photon. Technol. Lett. 4, 414–416 (1992).
[CrossRef]

J. Lightwave Technol. (3)

J. P. von der Weid, R. Passy, G. Mussi, N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15, 1131–1141 (1997).
[CrossRef]

S. Nilsson, T. Kjellberg, T. Klinga, R. Schatz, J. Wallin, K. Streubel, “Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts,” J. Lightwave Technol. 13, 434–441 (1995).
[CrossRef]

R. Passy, N. Gisin, J. P. von der Weid, H. H. Gilgen, “Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources,” J. Lightwave Technol. 12, 1622–1630 (1994).
[CrossRef]

J. Mod. Opt. (1)

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

Opt. Lett. (1)

Proc. IEEE (1)

J. M. Vaughan, K. O. Steinvall, C. Werner, P. H. Flamant, “Coherent laser radar in Europe,” in Proc. IEEE 84, 205–226 (1996); R. M. Huffaker, R. M. Hardesty, “Remote sensing of atmospheric wind velocities using solid-state and CO2 coherent laser systems,” Proc. IEEE 84, 181–204 (1996).
[CrossRef]

Other (5)

C. Karlsson, D. Letalick, G. Pearson, M. Harris, “Frequency modulation of a DFB laser diode for CLR applications,” in Proceedings of the Ninth Conference on Coherent Laser Radar (Swedish Defence Research Establishment, Linköping, Sweden, 1997).

See, e.g., M. I. Skolnik, Introduction to Radar Systems (McGraw-Hill, New York, 1981).

Kap10 product from Radians Innova AB, Gothenburg, Sweden.

D. Letalick, “Coherent CO2 laser radar in active imaging systems,” dissertation 216 (Chalmers University of Technology, Gothenburg, Sweden, 1991).

G. W. Kamerman, “Laser radar” in Active Electro-Optical Systems, C. S. Fox, ed., Vol. 6 of The Infrared & Electro-Optical Systems Handbook (SPIE Press, Bellingham, Wash., 1993).

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (12)

Fig. 1
Fig. 1

Power spectral density for delay times of (a) τ d c = 0.1, (b) τ d c = 1, and (c) τ d c → ∞. The spectra were calculated with a linewidth of 800 kHz, which corresponds to a coherence time of 0.20 µs.

Fig. 2
Fig. 2

FM with a triangular modulation function. The target has a radial speed, which gives rise to a Doppler shift. Note that the upper and lower curves are not drawn to scale.

Fig. 3
Fig. 3

Experimental arrangement. The detected signal was analyzed with a sweeping spectrum analyzer or sampled with a digital oscilloscope and subsequently FFT analyzed; f1 and f2 are low-pass filters; see text.

Fig. 4
Fig. 4

Modulation with a sinusoid. Example of the spectrum used to estimate the frequency excursion; f mod,s = 30 Hz and τ d , corresponding to 8-m fiber.

Fig. 5
Fig. 5

Examples of time traces used to estimate the FM phase. The lower curve is the interferometer signal; the upper curve is the modulating signal.

Fig. 6
Fig. 6

Part of the measured FM response for a modulation current of 4.7 mA (peak to peak). The modulation was applied to the center section of the three-section laser diode.

Fig. 7
Fig. 7

Signal spectra recorded by the sweeping spectrum analyzer (linear scale). For the amplitude compensated spectra, the phases of all harmonics were zero; for the phase compensated spectra the amplitudes of the different harmonics were those of a perfect triangular function. The modulation parameters were f mod = 1 kHz and Δf = 1.4 GHz, and the length difference between the two interferometer arms was 10 m. The spectra demonstrate the effect of compensating for the modulation current. Fifteen overtones were compensated for.

Fig. 8
Fig. 8

Spectra obtained with the digital oscilloscope and subsequent FFT analysis. The spectra are offset to each other; 1+15 and 1+31 indicate the response of the fundamental and the number of harmonics that were measured and compensated for. The two upper spectra originate from signals with a measurement time of twice the modulation period; the lowest spectrum correspond to a measurement time of a fifth of a modulation period. R = 20 m (in fiber), Δf = 1.4 GHz, and f mod = 1 kHz.

Fig. 9
Fig. 9

Digital scope and FFT. Delay corresponding to 10-m fiber. Modulation parameters were f mod = 30 Hz and Δf = 2.4 GHz. FFT resolution was 10 Hz. Fifteen harmonics were compensated for.

Fig. 10
Fig. 10

Calculated SNR as a function of range for various output powers, linewidths, and bandwidths. Bold curves correspond to the laser radar measurements discussed below. Values for other parameters are stated in Appendix B. The system is assumed to be focused for all ranges.

Fig. 11
Fig. 11

Laser radar measurement setup. All fibers were terminated by FC/APC connectors, except the end at the telescope, which was terminated by an FC/PC connector. This fiber end reflects radiation that serves as the LO. One advantage of this setup is its insensitivity to changes in light polarization within the fibers. The setup results in a 6-dB loss of the SNR compared with that of an ideal lossless system if the measurements are shot-noise limited; the loss is 0 dB if the measurements are phase-noise limited (by the interference between the LO and target reflection).

Fig. 12
Fig. 12

Measured frequency and range accuracy for f mod = 1000 Hz and Δf = 1.4 GHz. Other parameters are defined in Section 4 and Appendix B. We varied the SNR by changing the distance to the target or defocusing the beam.

Equations (11)

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

Sω, τd=2I1I2 exp-τd/τcδω-ωm+2I1I2τcπ1+τc2ω-ωm2×1-exp-τd/τccosω-ωmτd+sinω-ωmτdω-ωmτc.
R=cfh4Δffmod=cf2+f18Δffmod,
fh,maxΔf2sin2πfmod,sτ,
Δθ=2πfmod,sth,0-tm,0-π/2.
imod=i012-4π2k=1,3,NΔf1Δfk1k2cosk2πf1t+Δθk.
fDR<4RΔffmodc.
SNR=ηtotPrecRexp2R/cτchνB+ηtotRηlinPrecRτcπ1-exp2R/cτc1+2RcτcB,
ΔR=c/2nΔf,
σR=cσfh4Δffmod,
f¯=i Sfifii Sfi.
SNR=ηtotPrecRhνB, ηtot=ηhomηdetηcohRηlinR, Prec=PlasρπArecR2 Tatm2TtraTrec, ηcohR=11+w0ρ02+πw02λR21-RF2, ρ0R=Hk20R Cn2r1-rR5/3dr-3/5, TatmR=exp-αR,  α=2×10-3V.

Metrics