Abstract

We report on an ultra-long range optical frequency domain reflectometry (OFDR) using a coherence-enhanced highly linear frequency-swept fiber laser source based on an optoelectronic phase-locked loop (OPLL). The frequency-swept fiber laser is locked to an all-fiber-based Mach-Zehnder interferometer (MZI) to suppress sweep nonlinearity and enhance the laser coherence, leading to a high coherence linear frequency sweep of 1 GHz in the duration time of 25 ms. This enables the OFDR to realize an ultra-long range measurement with a high spatial resolution. As a result, we obtain a 10 cm transform-limited spatial resolution at a 20 km fiber within 25 ms measurement time, and a 72 cm spatial resolution over an entire 200 km fiber link within 5 ms measurement time. The proposed reflectometry provides a high-performance solution with both high spatial resolution and ultra-long measurement range for field real-time fiber network monitoring and sensing applications.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction

Optical frequency-modulated continuous-wave (FMCW) reflectometry, because of its high spatial resolution and large dynamic range, is a promising candidate for many applications such as laser ranging (FMCW lidar), three-dimensional (3D) objects imaging, distributed fiber sensing, fiber-optic components characterization, swept-source optical coherent tomography (SS-OCT), etc [1–6]. Optical frequency-domain reflectometry (OFDR) is one of the most important systems utilizing FMCW reflectometry technology. OFDR has been principally used for analysis of local area networks and characterization of optical components over a relative short measurement range [7–11]. Recently, with the increasing requirement for distinguishing fault events in communication network and long-haul transmission network, long range OFDR is receiving growing interest from researchers [12–15].

Generally, conventional pulse based optical time-domain reflectometry (OTDR) is commonly used for diagnosis of long range optical fiber link, but it suffers from a trade-off between spatial resolution and dynamic range, and the spatial resolution is consequently greater than one meter. OFDR is a promising alternative for long range fiber measurement as it can provide both high spatial resolution and large dynamic range. It is of great significance to extend OFDR’s measurement range to a long distance, and many efforts [13–16] have been made. Nevertheless, to date the measurement range of an OFDR rivaling that of an OTDR is still highly desirable. Up to now, the longest measurement range of an OFDR ever reported is 170 km with a spatial resolution of 200 m [15].

Laser sources with high coherence and precise frequency sweep linearity are of vital importance for the long range coherent OFDR, as the maximum measurement range is limited by the laser coherence length and the spatial resolution is degraded because of the existence of sweep nonlinearity. Primarily, two classes of approaches are adopted aiming to realize such a light source [17]. One is mainly obtained using a narrow linewidth laser with an external single sideband (SSB) modulator modulated by an RF frequency-swept signal [13]. The other is obtained using a direct frequency modulated fiber laser whose frequency can be linearly tuned by a piezo-electric (PZT) component [12,18,19]. The advantage of the first approach is that it can realize relative high linear optical frequency tuning, as the tuning linearity is determined by the RF synthesizer. However, the sweeping range and repetition rate is limited by the RF electronic component and high frequency devices are usually expensive [17]. Besides, uniform performance of SSB modulation is hard to be achieved as the phase shift between I and Q branches of the SSB modulator is difficult to be precisely maintained during large frequency sweep [20]. For the latter, a major advantage over the former is that wideband frequency tuning can be obtained easily avoiding the problem of electronics bottleneck. However, inherent sweep nonlinearity always exists because of the non-uniform PZT tuning response [12,17] and, thus, the FMCW reflectometry performance is severely deteriorated. In addition, a most recent study shows for the first time that the external sources induced laser 1/f frequency noise greatly degrades the FMCW beat signal SNR compared to the generally concerned white frequency noise [21]. Active linearization techniques employing an optoelectronic phase-locked loop (OPLL) have shown their capabilities of greatly improving the laser spectral purity and the precision of frequency sweep. Besides, the detrimental effects due to 1/f frequency noise can be efficiently reduced by the OPLL as well [21]. In a previous work, an experiment based on servo-loop control method has been reported for nonlinear frequency error correction [22], but the sweep rate (600 MHz in 15 second) is very limited. While from the application point of view, real-time fiber measurement and field monitoring generally need a short measurement time at tens of milliseconds or less level, thus a much higher sweep rate is required [13,17].

In this paper, we present an ultra-long range OFDR system using a coherence-enhanced highly linear frequency-swept fiber laser source based on an OPLL. The frequency-swept fiber laser is firstly driven by an external pre-distorted PZT voltage to remove large sweep nonlinearity. Then it is locked to an all-fiber-based Mach–Zehnder interferometer (MZI) to suppress residual sweep nonlinearity and enhance the laser’s coherence. With these two techniques, a well-controlled high coherence linear sweep of 1 GHz in 25 ms time duration is achieved. We give a detailed analysis of frequency noise suppression under static and frequency-swept operation, respectively. Thanks to the improvement of the laser source, the reflectometry is able to realize an ultra-long range measurement with a sub-meter level high spatial resolution. Real-time measurement with a 10 cm transform-limited spatial resolution up to a 20 km fiber is achieved using the whole 25 ms sweep; and a 0.72 m spatial resolution is obtained over an entire 200 km fiber link using 5 ms measurement time.

2. Stabilization and analysis of the frequency-swept fiber laser source

2.1 Experimental setup and principle of the operation

The experimental setup is shown in Fig. 1. The frequency-swept laser used in the experiment is a commercially available single mode DFB fiber laser (~5 kHz measured linewidth at −3 dB, i.e. a coherence length of about 13 km) at the wavelength of 1550 nm, and frequency tuning is realized by piezo-electrical tuning with a modulation bandwidth of ~20 kHz. The output is firstly split into two parts; 90% portion of the output is used for FMCW ranging experiment. The 10% part is further split into two parts, one part is coupled into a reference MZI with an acousto-optic frequency shifter (AOFS) operating at 40 MHz in one arm; the reference MZI is used for active linearized OPLL control, and polarization maintaining fiber-optic components is used within the loop to avoid polarization issues. The other is coupled into an auxiliary MZI with an optical quadrature front end; the auxiliary MZI is used for pre-distortion of the PZT drive voltage and dynamic frequency noise spectrum measurement for the frequency-swept fiber laser. Both the reference and auxiliary MZI are placed in a sound-proof box, which is in addition set onto a passive vibration isolation platform, isolating it from potential acoustic perturbations and mechanical vibrations.

 figure: Fig. 1

Fig. 1 .Configuration of the OFDR system. The frequency-swept laser is a single mode DFB fiber laser, driven by a pre-distorted PZT voltage ramp. The reference interferometer, auxiliary interferometer, and measurement interferometer both are all-fiber-based MZI. The reference MZI is used for active linearized OPLL control; the auxiliary MZI is used for pre-distortion of the PZT drive voltage and dynamic frequency noise spectrum measurement; multiple reflection events of FUT are recorded by the measurement MZI and analyzed using the real-time spectrum analyzer. AWG, arbitrary wave generator; AOFS, acousto-optic frequency shifter for self-heterodyne detection; DPFD, digital phase frequency detector; PMC, polarization-maintaining coupler; PMF is 1 km polarization-maintaining delay fiber; BPD, balanced-photo detector; DAQ, data acquisition card; SMF, single mode fiber; PC, polarization controller.

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The reference MZI plays the role of optical frequency discriminator to transfer the laser frequency fluctuations to heterodyne signal phase fluctuations [11,23]. The transfer function is

δφ(f)/δυ(f)=(1ei2πfτ0)/if2πτ0rad/Hz,f1/τ0,
Where, τ0is the fiber delay time andfis the Fourier frequency. Assume the instantaneous optical frequency of the laser is expressed asv(t)=v0+rt+δv(t), wherev0is the initial optical frequency, r is the sweep rate, and δv(t) represents the frequency errors during the laser sweep. The beat note phase detected at the output of the interferometer can be expressed as [23]2πfbt+ϕ0+δφ(t), where,fb=rτ0+fAOFS, ϕ0is a constant term,δφ(t)=2πτ0δv(t). It contains the frequency errors during the laser sweep. The phase and frequency of the beat note are compared to a stable RF reference signal provided by a microwave generator (Keysight 8257D) at frequency fref=fbusing a low noise digital phase frequency detector. The resulting error signal is filtered and converted into an optical frequency correction signal which is fed back to piezoelectric transducer stretcher port to control the laser frequency. The loop filter consists of a proportional integrator with a cut-off frequency of about 0.8 kHz and a low-pass pole of about 30 kHz.

It is notable that the OPLL control is realized and valid on condition that the beat note phase changes due to the nonlinearity of the fiber laser frequency response is small. For a given fiber delayτ0, the fiber laser sweep nonlinearity should be limited. However, at higher sweep rates, the fiber laser frequency varies highly nonlinearly with the PZT drive voltage, and the OPLL can be thrown out of lock. To remove large sweep nonlinearity during the laser sweep, we first apply a simple pre-distortion scheme. This can be done iteratively, by starting with a simple linear PZT drive voltage ramp, measuring the deviation from a linear sweep by the auxiliary MZI [24], and adjusting the PZT drive voltage accordingly. Finally, a time-varying voltage ramp designed to produce a linear optical frequency sweep is applied to the PZT driver using an arbitrary waveform generator. The pre-distortion of the PZT drive voltage greatly reduces the sweep nonlinearity and enables phase-locking at high sweep rates. The delay of the reference MZI is chosen to be 5 us (i.e. a fiber length of 1 km); experimental results show that the time delay is adequate for sweep nonlinearity suppression and short term frequency stabilization.

2.2 Static laser frequency noise spectrum analysis

We first measured the intrinsic linewidth of the laser using a delayed self-heterodyne interferometer; the linewidth under open-loop operation is shown to be 5 kHz. Under closed-loop operation, we estimate the laser linewidth from its frequency noise PSD using power area method [25]. The phase noise of the beat note signal at the output of BPD1 is measured by a phase noise analyzer (Symmetricom 5125A), and then is converted to laser frequency noise as plotted in Fig. 2.

 figure: Fig. 2

Fig. 2 Measured static frequency noise PSD. Red line, free running laser; blue line, closed-loop operation. The frequency noise is suppressed more than 40 dB between 0.1 Hz and 100 Hz, the frequency noise PSD is about 0.5 Hz2/Hz at 1 Hz and well below 1 Hz2/Hz between 1 Hz and 1 kHz. Purple line: beta-line used in power area method to estimate laser linewidth, the estimated laser linewidth is 1.4 Hz for 2 s observing time.

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With the loop open, the free running laser exhibits a quasi-1/f type spectrum below ~5 kHz and frequency noise PSD is 56 dB Hz2/Hz at 1 Hz. When the loop is closed, the frequency noise is suppressed more than 40 dB between 0.1 Hz and 100 Hz, the frequency noise PSD is about 0.5 Hz2/Hz at 1 Hz and well below 1 Hz2/Hz between 1 Hz and 1 kHz. At higher frequencies, the frequency noise increases due to the limited gain and bandwidth of the OPLL. The bulge around 6 kHz is due to gain peaking around natural frequency of the optoelectronic feedback system transfer function and can be minimized at the expense of decreasing the noise suppression gain in a low Fourier frequency. The linewidth of the stabilized laser estimated by the power area method is shown to be 1.4 Hz for 2 s observing time, indicating a great coherence enhancement compared with the free running laser. Also, the linewidth of the free running laser calculated by the power area method is 4.5 kHz for the same observing time, which is basically consistent with the experimental result.

2.3 Frequency noise analysis of the frequency-swept fiber laser

As for frequency sweep, the sweep nonlinearity is measured by the auxiliary MZI, and a 96 V pre-distorted voltage ramp generates approximately 1.2 GHz laser frequency sweep during 30 ms period.

We first demonstrate a dynamic frequency noise measurement using the auxiliary MZI. The laser frequency is expressed asv(t)=v0+rt+δv(t), after delayed self-heterodyne and detected by BPD2 and BPD3 [24], the in-phase and quadrature beat note are expressed by

Ii(t)=Icos(2πfb1+φ1+δφ1(t))Iq(t)=Isin(2πfb1+φ1+δφ1(t)),
Where I is the beat note amplitude, τ1 = 5 us is the optical delay time, fb1=rτ1=200kHzis the beat frequency, φ1is a constant term, and δφ1(t)2πτ1δv(t)for typical frequency noise variation scale. The time domainδφ1(t)during the whole 30 ms period can be unambiguously extracted from Ii(t) andIq(t), and optical frequency noise spectrum can be restored utilizing the phase noise information. The phase noise δφ1(t)is then divided into numbers of equal-length time bands, and each spectrum is calculated by FFT transform in the corresponding time band. Here, the band length is chosen to be 1 ms, corresponding to a lower frequency of 1 kHz, and the total band number is 30. The dynamic frequency noise PSD during the sweep time is presented in Fig. 3, with two variables, i.e., Fourier frequency (1 kHz-100 kHz) and time (0-30 ms) as the x and y axis, respectively.

 figure: Fig. 3

Fig. 3 Dynamic frequency noise spectrum during 30 ms sweep time. In the beginning 5 ms of sweeping, the OPLL is losing lock, ascribing to the sudden change of sweep rate. After that, the loop gets into a stable state. Under locked state, the dynamic frequency noise PSD is efficiently suppressed within loop bandwidth. The frequency noise at 1 kHz is around 10 dB Hz2/Hz, while that before locked is 50 dB Hz2/Hz.

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As we can see, the dynamic frequency noise PSD spectra is degraded compared with that in static situation, which is believed to be inevitable to obtain fast frequency tuning. In the beginning 5 ms of sweeping, the OPLL experiences a process of getting into phase locked because of the sudden change of sweep rate, after that, the loop gets into a stable state. Under locked state, the dynamic frequency noise PSD is efficiently suppressed within loop bandwidth. The frequency noise at 1 kHz is around 10 dB Hz2/Hz, while that before locked is 50 dB Hz2/Hz. The result indicates that the frequency noise is suppressed 40 dB at 1 kHz and the low frequency noise suppression is of great significance to improve the coherence of the laser, as the laser coherence property is investigated to have a closer relation with the low frequency noise spectrum part [26,27]. The bulge around 25 kHz and the collapse around 34 kHz in the spectra are related to inherent piezo tuning response of the fiber laser [12].

To further characterize the laser frequency noise during the laser frequency sweep, the frequency-swept laser spectral purity is tested by spectra analysis of the heterodyne beat signal detected by the BPD1 using a real-time signal analyzer (Tektronix 5106B). As is shown in Fig. 3, the beginning 5 ms sweep is losing lock, so actually the useful part for FMCW measurement is the latter 1 GHz sweep in a 25 ms duration and only this segment is taken into spectra analysis. If the frequency sweep is perfectly linear, a Fourier transform-limited width of the beat signal is expected. The frequency of the beat note is shown to be around 40.2 MHz, corresponding to an optical frequency sweep rate of 40 GHz/s. The spectra of the detected heterodyne beat signal with and without stabilization are shown in Fig. 4 (relative to the beat frequency).

 figure: Fig. 4

Fig. 4 Beat note spectrum when the laser frequency is swept over 1 GHz in 25 ms. Green line, open-loop operation, the spectrum peak is blurred because of residual nonlinear sweep and phase noise. Red line, closed-loop operation, the broad noise component is efficiently suppressed within the loop bandwidth, and the beat signal spectrum characterizes a pure Fourier-transform-limited peak with a width of 40 Hz.

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When the loop is open, although large systematic nonlinearities are removed by the application of pre-distortion scheme, the spectrum peak is still blurred because of considerable residual nonlinear sweep and phase noise. In comparison, when the sweep rate is locked to the reference signal, the broad noise component caused by sweep nonlinearity and phase noise is efficiently suppressed within the loop bandwidth, and the beat signal spectrum characterizes a pure transform-limited single peak with a width of 40 Hz. The improved sweep spectral purity is of great significance to achieve a high signal-to-noise ratio and maintain spatial resolution in FMCW measurement applications.

3. Application with the OPLL controlled frequency-swept fiber laser source

The ranging performance of the OPLL controlled frequency-swept laser source is investigated using a real-time OFDR configuration shown in Fig. 1. The 90% part of the laser output is equally split into the reference and the measurement arm of an MZI. The beat signal of the reference and the measurement fields is detected by a BPD4and analyzed by the real-time signal analyzer. A trigger signal synchronized to the voltage ramp is used for data acquisition, and a Hanning type window is used to minimize the side lode effect. The laser frequency sweep time Ts is 30 ms. The repetition cycle Tr is 50 ms. And then multiple reflection events are recorded at a repetition rate of 20 Hz. The fiber under test (FUT) consists of five spools of standard single mode fiber under ordinary (not sound isolated) laboratory environment with lengths of about 20 km, 20 km, 40 km, 70 km, and 50 km, respectively. Angled physical contact (APC) connectors are used to connect the first four spools of fiber, and the last spool of fiber is connected by a physical contact (PC) fiber connector. The far end of the FUT is equipped with an open PC connector.

The measurement is firstly carried out with the whole 25 ms linear frequency sweep, corresponding to a 1 GHz sweep span, and theoretical spatial resolution is 10 cm. The measurement result is shown in Fig. 5 (a). Five peaks appear on the trace, corresponding to the fiber connectors within the FUT as well as the open far end. At the distance of 20 km, the spatial resolution (full width at half maximum) of the reflection peak is shown to be 14.4 cm (10 cm without a Hanning window), which is the transform-limited resolution of the 1 GHz tuning span. The measured spatial resolution at 40 km, 80 km, 150 km, and 200 km are 25 cm, 0.86 m, 1.17 m and 1.31 m, respectively. The dominant factor as regards to spatial resolution deterioration is believed to be phase noise caused by environmental acoustic perturbation. Previous study yielding similar results was performed in [28,29]. To decrease the ratio of these added phase noise which is accumulated with time, a short measurement time is desirable. As a faster sweep rate is limited by the laser piezo-electrical tuning response and the OPLL performance, a short measurement time is corresponding to a small tuning span. Here, 5 ms duration of the whole laser frequency sweep (10 ms-15 ms) is chosen, corresponding to a 200 MHz effective tuning span. The measurement result with the 5 ms laser frequency sweep is shown in Fig. 5(b), the measured spatial resolution is shown to maintain 0.72 m over the whole 200 km fiber link. It is notable that the transform-limited spatial resolution of a 200 MHz tuning span is 0.5 m, and the spatial resolution penalty is only caused by the Hanning type window used to minimize side lode. To the best of our knowledge, this is the longest measurement range ever reported for a coherent optical frequency domain reflectometry with a sub-meter level spatial resolution. This method provides a powerful solution for real-time ultra-long range optical fiber network monitoring and optical fiber sensing applications.

 figure: Fig. 5

Fig. 5 Measured Rayleigh backscattering and Fresnel reflections for a FUT length of 200 km fiber link, maximum measurement range for Rayleigh backscattering is 120 km. (a) Measurement using 25 ms sweep, the measured spatial resolution at 20 km, 40 km, 80 km, 150 km, and 200 km are 14.4 cm, 25 cm, 0.86 m, 1.17 m and 1.31 m, respectively. (b) Measurement using 5 ms sweep, the measured spatial resolution is 0.72 m over the whole 200 km fiber link.

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The measured spatial resolution of the five reflection events over the whole 200 km fiber link using 25 ms and 5 ms frequency sweep is presented in Fig. 6, the advantage of using a short measurement time for ultra-long range measurement is clear shown.

 figure: Fig. 6

Fig. 6 Measured spatial resolution of Fresnel reflection peaks over the FUT link. Blue trace, measurement using 25ms sweep. Red trace, measurement using 5ms sweep.

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The system precision is assessed with 10 successive measurements using 5 ms frequency sweep with the 200 km fiber far end PC, and the standard deviation of these measurements is 6 cm. The absolute accuracy and overall uncertainty of our measurements is related to several effects [30]. The first uncertainty is attributed to the length and refraction index variations of the fiber under test, which is easily affected by environmental perturbation, such as acoustic perturbations and mechanical vibrations. The next factor should be dominated by residual sweep errors and laser phase noise, due to the finite gain and bandwidth of the OPLL. Finally, although carefully isolated, the changes in the length and refractive index of the reference MZI due to temperature drift also make contribution to overall measurement uncertainty. As our measurement is carried out in the same media compared with the reference MZI (both are silica), and the sweep range is relative small. The chromatic dispersion mismatch effect, such as between the fiber interferometer (silica) and measurement path (air), is not observed in our measurement results [30,31].

4. Conclusion

In summary, we present an ultra-long range OFDR using a coherence-enhanced highly linear frequency-swept fiber laser source based on OPLL. The frequency-swept laser is successfully stabilized to an all-fiber-based MZI using optoelectronic phase-locked loop control with a pre-distortion scheme. A high coherence linear frequency sweep of 1 GHz in 25 ms is achieved. The sweep nonlinearity suppression and high coherence property of the frequency-swept laser source enables the FMCW reflectometry to realize an ultra-long range measurement with a high spatial resolution. The real-time measurement with a 10 cm transform-limited spatial resolution up to 20 km fiber is achieved using the whole 25 ms sweep and a 0.72 m spatial resolution is obtained over the 200 km fiber link using 5 ms measurement time to decrease the effect of accumulated acoustic phase noise caused by environmental perturbation. This is the longest measurement range with a sub-meter level spatial resolution ever reported to the best of our knowledge. The proposed reflectometry is believed to provide a high-performance solution with high spatial resolution, ultra-long measurement range, and short process time for practical long-haul fiber network monitoring and sensing applications.

Funding

National Natural Science Foundation of China (NSFC) (61690193)

References

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2. L. T. Wang, K. Iiyama, F. Tsukada, N. Yoshida, and K. Hayashi, “Loss measurement in optical waveguide devices by coherent frequency-modulated continuous-wave reflectometry,” Opt. Lett. 18(13), 1095–1097 (1993). [CrossRef]   [PubMed]  

3. P. C. Won, L. K. Seah, and A. K. Asundi, “FMCW reflectometric optical fiber strain sensor,” Proc. SPIE 4328, 54–62 (2001). [CrossRef]  

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5. H. Pan, X. Qu, and F. Zhang, “Micron-precision measurement using a combined frequency-modulated continuous wave ladar autofocusing system at 60 meters standoff distance,” Opt. Express 26(12), 15186–15198 (2018). [CrossRef]   [PubMed]  

6. T. DiLazaro and G. Nehmetallah, “Large-volume, low-cost, high-precision FMCW tomography using stitched DFBs,” Opt. Express 26(3), 2891–2904 (2018). [CrossRef]   [PubMed]  

7. J. P. von der Weid, R. Passy, and N. Gisin, “Mid-Range Coherent Optical Frequency Domain Reflectometry with a DFB Laser Diode Coupled to an External Cavity,” J. Lightwave Technol. 13(5), 954–960 (1995). [CrossRef]  

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References

  • View by:

  1. J. Zheng, “Optical frequency-modulated continuous-wave interferometers,” Appl. Opt. 45(12), 2723–2730 (2006).
    [Crossref] [PubMed]
  2. L. T. Wang, K. Iiyama, F. Tsukada, N. Yoshida, and K. Hayashi, “Loss measurement in optical waveguide devices by coherent frequency-modulated continuous-wave reflectometry,” Opt. Lett. 18(13), 1095–1097 (1993).
    [Crossref] [PubMed]
  3. P. C. Won, L. K. Seah, and A. K. Asundi, “FMCW reflectometric optical fiber strain sensor,” Proc. SPIE 4328, 54–62 (2001).
    [Crossref]
  4. J. Buck, A. Malm, A. Zakel, B. Krause, and B. Tiemann, “High-resolution 3D coherent laser radar imaging,” Proc. SPIE 6550, 655002 (2007).
    [Crossref]
  5. H. Pan, X. Qu, and F. Zhang, “Micron-precision measurement using a combined frequency-modulated continuous wave ladar autofocusing system at 60 meters standoff distance,” Opt. Express 26(12), 15186–15198 (2018).
    [Crossref] [PubMed]
  6. T. DiLazaro and G. Nehmetallah, “Large-volume, low-cost, high-precision FMCW tomography using stitched DFBs,” Opt. Express 26(3), 2891–2904 (2018).
    [Crossref] [PubMed]
  7. J. P. von der Weid, R. Passy, and N. Gisin, “Mid-Range Coherent Optical Frequency Domain Reflectometry with a DFB Laser Diode Coupled to an External Cavity,” J. Lightwave Technol. 13(5), 954–960 (1995).
    [Crossref]
  8. J. P. von der Weid, R. Passy, G. Mussi, and N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15(7), 1131–1141 (1997).
    [Crossref]
  9. B. Soller, D. Gifford, M. Wolfe, and M. Froggatt, “High resolution optical frequency domain reflectometry for characterization of components and assemblies,” Opt. Express 13(2), 666–674 (2005).
    [Crossref] [PubMed]
  10. K. Yuksel, M. Wuilpart, and P. Mégret, “Analysis and suppression of nonlinear frequency modulation in an optical frequency-domain reflectometer,” Opt. Express 17(7), 5845–5851 (2009).
    [Crossref] [PubMed]
  11. J. Qin, Q. Zhou, W. Xie, Y. Xu, S. Yu, Z. Liu, Yt. Tong, Y. Dong, and W. Hu, “Coherence enhancement of a chirped DFB laser for frequency-modulated continuous-wave reflectometry using a composite feedback loop,” Opt. Lett. 40(19), 4500–4503 (2015).
    [Crossref] [PubMed]
  12. J. H. Geng, C. Spiegelberg, and S. B. Jiang, “Narrow linewidth fiber laser for 100-km optical frequency domain reflectometry,” IEEE Photonics Technol. Lett. 17(9), 1827–1829 (2005).
    [Crossref]
  13. X. Fan, Y. Koshikiya, and F. Ito, “Centimeter-level spatial resolution over 40 km realized by bandwidth-division phase-noise-compensated OFDR,” Opt. Express 19(20), 19122–19128 (2011).
    [Crossref] [PubMed]
  14. Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, J. Jiang, Z. Meng, and H. Chen, “Compensation of laser frequency tuning nonlinearity of a long range OFDR using deskew filter,” Opt. Express 21(3), 3826–3834 (2013).
    [Crossref] [PubMed]
  15. Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
    [Crossref]
  16. Q. Liu, X. Fan, and Z. He, “Time-gated digital optical frequency domain reflectometry with 1.6-m spatial resolution over entire 110-km range,” Opt. Express 23(20), 25988–25995 (2015).
    [Crossref] [PubMed]
  17. E. Leviatan and A. Eyal, “High resolution DAS via sinusoidal frequency scan OFDR (SFS-OFDR),” Opt. Express 23(26), 33318–33334 (2015).
    [Crossref] [PubMed]
  18. P. Oberson, B. Huttner, O. Guinnard, L. Guinnard, G. Ribordy, and N. Gisin, “Optical frequency domain reflectometry with a narrow linewidth fiber laser,” IEEE Photonics Technol. Lett. 12(7), 867–869 (2000).
    [Crossref]
  19. C. Li, S. Xu, S. Mo, B. Zhan, W. Zhang, C. Yang, Z. Feng, and Z. Yang, “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Phys. Lett. 10(7), 075106 (2013).
    [Crossref]
  20. J. Li, J. Du, S. Wang, L. Li, L. Sun, X. Fan, Q. Liu, and Z. He, “Improving the spatial resolution of an OFDR based on recirculating frequency shifter,” IEEE Photonics J. 7(5), 6901310 (2015).
  21. T. DiLazaro and G. Nehmetallah, “Phase-noise model for actively linearized frequency-modulated continuous-wave ladar,” Appl. Opt. 57(21), 6260–6268 (2018).
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  22. H. Jiang, F. Kéfélian, P. Lemonde, A. Clairon, and G. Santarelli, “An agile laser with ultra-low frequency noise and high sweep linearity,” Opt. Express 18(4), 3284–3297 (2010).
    [Crossref] [PubMed]
  23. G. Gorju, A. Jucha, A. Jain, V. Crozatier, I. Lorgeré, J.-L. Le Gouët, F. Bretenaker, and M. Colice, “Active stabilization of a rapidly chirped laser by an optoelectronic digital servo-loop control,” Opt. Lett. 32(5), 484–486 (2007).
    [Crossref] [PubMed]
  24. Q. Zhou, J. Qin, W. Xie, Z. Liu, Y. Tong, Y. Dong, and W. Hu, “Dynamic frequency-noise spectrum measurement for a frequency-swept DFB laser with short-delayed self-heterodyne method,” Opt. Express 23(22), 29245–29257 (2015).
    [Crossref] [PubMed]
  25. Q. Zhou, J. Qin, W. Xie, Z. Liu, Y. Tong, Y. Dong, and W. Hu, “Power-area method to precisely estimate laser linewidth from its frequency-noise spectrum,” Appl. Opt. 54(28), 8282–8289 (2015).
    [Crossref] [PubMed]
  26. J.-F. Cliché, M. Allard, and M. Têtu, “High-power and ultranarrow DFB laser: the effect of linewidth reduction systems on coherence length and interferometer noise,” Proc. SPIE 6216, 62160C (2006).
    [Crossref]
  27. G. Di Domenico, S. Schilt, and P. Thomann, “Simple approach to the relation between laser frequency noise and laser line shape,” Appl. Opt. 49(25), 4801–4807 (2010).
    [Crossref] [PubMed]
  28. Y. Koshikiya, X. Fan, and F. Ito, “Influence of acoustic perturbation of fibers in phase-noise-compensated optical-frequency-domain reflectometry,” J. Lightwave Technol. 28(22), 3323–3328 (2010).
    [Crossref]
  29. O. Y. Sagiv, D. Arbel, and A. Eyal, “Correcting for spatial-resolution degradation mechanisms in OFDR via inline auxiliary points,” Opt. Express 20(25), 27465–27472 (2012).
    [Crossref] [PubMed]
  30. Z. W. Barber, W. R. Babbitt, B. Kaylor, R. R. Reibel, and P. A. Roos, “Accuracy of active chirp linearization for broadband frequency modulated continuous wave ladar,” Appl. Opt. 49(2), 213–219 (2010).
    [Crossref] [PubMed]
  31. T. DiLazaro and G. Nehmetallah, “Multi-terahertz frequency sweeps for high-resolution, frequency-modulated continuous wave ladar using a distributed feedback laser array,” Opt. Express 25(3), 2327–2340 (2017).
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2018 (3)

2017 (1)

2015 (6)

2013 (3)

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, J. Jiang, Z. Meng, and H. Chen, “Compensation of laser frequency tuning nonlinearity of a long range OFDR using deskew filter,” Opt. Express 21(3), 3826–3834 (2013).
[Crossref] [PubMed]

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
[Crossref]

C. Li, S. Xu, S. Mo, B. Zhan, W. Zhang, C. Yang, Z. Feng, and Z. Yang, “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Phys. Lett. 10(7), 075106 (2013).
[Crossref]

2012 (1)

2011 (1)

2010 (4)

2009 (1)

2007 (2)

2006 (2)

J.-F. Cliché, M. Allard, and M. Têtu, “High-power and ultranarrow DFB laser: the effect of linewidth reduction systems on coherence length and interferometer noise,” Proc. SPIE 6216, 62160C (2006).
[Crossref]

J. Zheng, “Optical frequency-modulated continuous-wave interferometers,” Appl. Opt. 45(12), 2723–2730 (2006).
[Crossref] [PubMed]

2005 (2)

B. Soller, D. Gifford, M. Wolfe, and M. Froggatt, “High resolution optical frequency domain reflectometry for characterization of components and assemblies,” Opt. Express 13(2), 666–674 (2005).
[Crossref] [PubMed]

J. H. Geng, C. Spiegelberg, and S. B. Jiang, “Narrow linewidth fiber laser for 100-km optical frequency domain reflectometry,” IEEE Photonics Technol. Lett. 17(9), 1827–1829 (2005).
[Crossref]

2001 (1)

P. C. Won, L. K. Seah, and A. K. Asundi, “FMCW reflectometric optical fiber strain sensor,” Proc. SPIE 4328, 54–62 (2001).
[Crossref]

2000 (1)

P. Oberson, B. Huttner, O. Guinnard, L. Guinnard, G. Ribordy, and N. Gisin, “Optical frequency domain reflectometry with a narrow linewidth fiber laser,” IEEE Photonics Technol. Lett. 12(7), 867–869 (2000).
[Crossref]

1997 (1)

J. P. von der Weid, R. Passy, G. Mussi, and N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15(7), 1131–1141 (1997).
[Crossref]

1995 (1)

J. P. von der Weid, R. Passy, and N. Gisin, “Mid-Range Coherent Optical Frequency Domain Reflectometry with a DFB Laser Diode Coupled to an External Cavity,” J. Lightwave Technol. 13(5), 954–960 (1995).
[Crossref]

1993 (1)

Allard, M.

J.-F. Cliché, M. Allard, and M. Têtu, “High-power and ultranarrow DFB laser: the effect of linewidth reduction systems on coherence length and interferometer noise,” Proc. SPIE 6216, 62160C (2006).
[Crossref]

Arbel, D.

Asundi, A. K.

P. C. Won, L. K. Seah, and A. K. Asundi, “FMCW reflectometric optical fiber strain sensor,” Proc. SPIE 4328, 54–62 (2001).
[Crossref]

Babbitt, W. R.

Barber, Z. W.

Bretenaker, F.

Buck, J.

J. Buck, A. Malm, A. Zakel, B. Krause, and B. Tiemann, “High-resolution 3D coherent laser radar imaging,” Proc. SPIE 6550, 655002 (2007).
[Crossref]

Chen, H.

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, J. Jiang, Z. Meng, and H. Chen, “Compensation of laser frequency tuning nonlinearity of a long range OFDR using deskew filter,” Opt. Express 21(3), 3826–3834 (2013).
[Crossref] [PubMed]

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
[Crossref]

Clairon, A.

Cliché, J.-F.

J.-F. Cliché, M. Allard, and M. Têtu, “High-power and ultranarrow DFB laser: the effect of linewidth reduction systems on coherence length and interferometer noise,” Proc. SPIE 6216, 62160C (2006).
[Crossref]

Colice, M.

Crozatier, V.

Di Domenico, G.

DiLazaro, T.

Ding, Z.

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
[Crossref]

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, J. Jiang, Z. Meng, and H. Chen, “Compensation of laser frequency tuning nonlinearity of a long range OFDR using deskew filter,” Opt. Express 21(3), 3826–3834 (2013).
[Crossref] [PubMed]

Dong, Y.

Du, J.

J. Li, J. Du, S. Wang, L. Li, L. Sun, X. Fan, Q. Liu, and Z. He, “Improving the spatial resolution of an OFDR based on recirculating frequency shifter,” IEEE Photonics J. 7(5), 6901310 (2015).

Du, Y.

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, J. Jiang, Z. Meng, and H. Chen, “Compensation of laser frequency tuning nonlinearity of a long range OFDR using deskew filter,” Opt. Express 21(3), 3826–3834 (2013).
[Crossref] [PubMed]

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
[Crossref]

Eyal, A.

Fan, X.

Feng, Z.

C. Li, S. Xu, S. Mo, B. Zhan, W. Zhang, C. Yang, Z. Feng, and Z. Yang, “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Phys. Lett. 10(7), 075106 (2013).
[Crossref]

Froggatt, M.

Geng, J. H.

J. H. Geng, C. Spiegelberg, and S. B. Jiang, “Narrow linewidth fiber laser for 100-km optical frequency domain reflectometry,” IEEE Photonics Technol. Lett. 17(9), 1827–1829 (2005).
[Crossref]

Gifford, D.

Gisin, N.

P. Oberson, B. Huttner, O. Guinnard, L. Guinnard, G. Ribordy, and N. Gisin, “Optical frequency domain reflectometry with a narrow linewidth fiber laser,” IEEE Photonics Technol. Lett. 12(7), 867–869 (2000).
[Crossref]

J. P. von der Weid, R. Passy, G. Mussi, and N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15(7), 1131–1141 (1997).
[Crossref]

J. P. von der Weid, R. Passy, and N. Gisin, “Mid-Range Coherent Optical Frequency Domain Reflectometry with a DFB Laser Diode Coupled to an External Cavity,” J. Lightwave Technol. 13(5), 954–960 (1995).
[Crossref]

Gorju, G.

Guinnard, L.

P. Oberson, B. Huttner, O. Guinnard, L. Guinnard, G. Ribordy, and N. Gisin, “Optical frequency domain reflectometry with a narrow linewidth fiber laser,” IEEE Photonics Technol. Lett. 12(7), 867–869 (2000).
[Crossref]

Guinnard, O.

P. Oberson, B. Huttner, O. Guinnard, L. Guinnard, G. Ribordy, and N. Gisin, “Optical frequency domain reflectometry with a narrow linewidth fiber laser,” IEEE Photonics Technol. Lett. 12(7), 867–869 (2000).
[Crossref]

Han, Q.

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
[Crossref]

Hayashi, K.

He, Z.

Q. Liu, X. Fan, and Z. He, “Time-gated digital optical frequency domain reflectometry with 1.6-m spatial resolution over entire 110-km range,” Opt. Express 23(20), 25988–25995 (2015).
[Crossref] [PubMed]

J. Li, J. Du, S. Wang, L. Li, L. Sun, X. Fan, Q. Liu, and Z. He, “Improving the spatial resolution of an OFDR based on recirculating frequency shifter,” IEEE Photonics J. 7(5), 6901310 (2015).

Hu, W.

Huttner, B.

P. Oberson, B. Huttner, O. Guinnard, L. Guinnard, G. Ribordy, and N. Gisin, “Optical frequency domain reflectometry with a narrow linewidth fiber laser,” IEEE Photonics Technol. Lett. 12(7), 867–869 (2000).
[Crossref]

Iiyama, K.

Ito, F.

Jain, A.

Jiang, H.

Jiang, J.

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
[Crossref]

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, J. Jiang, Z. Meng, and H. Chen, “Compensation of laser frequency tuning nonlinearity of a long range OFDR using deskew filter,” Opt. Express 21(3), 3826–3834 (2013).
[Crossref] [PubMed]

Jiang, S. B.

J. H. Geng, C. Spiegelberg, and S. B. Jiang, “Narrow linewidth fiber laser for 100-km optical frequency domain reflectometry,” IEEE Photonics Technol. Lett. 17(9), 1827–1829 (2005).
[Crossref]

Jucha, A.

Kaylor, B.

Kéfélian, F.

Koshikiya, Y.

Krause, B.

J. Buck, A. Malm, A. Zakel, B. Krause, and B. Tiemann, “High-resolution 3D coherent laser radar imaging,” Proc. SPIE 6550, 655002 (2007).
[Crossref]

Le Gouët, J.-L.

Lemonde, P.

Leviatan, E.

Li, C.

C. Li, S. Xu, S. Mo, B. Zhan, W. Zhang, C. Yang, Z. Feng, and Z. Yang, “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Phys. Lett. 10(7), 075106 (2013).
[Crossref]

Li, J.

J. Li, J. Du, S. Wang, L. Li, L. Sun, X. Fan, Q. Liu, and Z. He, “Improving the spatial resolution of an OFDR based on recirculating frequency shifter,” IEEE Photonics J. 7(5), 6901310 (2015).

Li, L.

J. Li, J. Du, S. Wang, L. Li, L. Sun, X. Fan, Q. Liu, and Z. He, “Improving the spatial resolution of an OFDR based on recirculating frequency shifter,” IEEE Photonics J. 7(5), 6901310 (2015).

Liu, K.

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
[Crossref]

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, J. Jiang, Z. Meng, and H. Chen, “Compensation of laser frequency tuning nonlinearity of a long range OFDR using deskew filter,” Opt. Express 21(3), 3826–3834 (2013).
[Crossref] [PubMed]

Liu, Q.

Q. Liu, X. Fan, and Z. He, “Time-gated digital optical frequency domain reflectometry with 1.6-m spatial resolution over entire 110-km range,” Opt. Express 23(20), 25988–25995 (2015).
[Crossref] [PubMed]

J. Li, J. Du, S. Wang, L. Li, L. Sun, X. Fan, Q. Liu, and Z. He, “Improving the spatial resolution of an OFDR based on recirculating frequency shifter,” IEEE Photonics J. 7(5), 6901310 (2015).

Liu, T.

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
[Crossref]

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, J. Jiang, Z. Meng, and H. Chen, “Compensation of laser frequency tuning nonlinearity of a long range OFDR using deskew filter,” Opt. Express 21(3), 3826–3834 (2013).
[Crossref] [PubMed]

Liu, Z.

Lorgeré, I.

Malm, A.

J. Buck, A. Malm, A. Zakel, B. Krause, and B. Tiemann, “High-resolution 3D coherent laser radar imaging,” Proc. SPIE 6550, 655002 (2007).
[Crossref]

Mégret, P.

Meng, Z.

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
[Crossref]

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, J. Jiang, Z. Meng, and H. Chen, “Compensation of laser frequency tuning nonlinearity of a long range OFDR using deskew filter,” Opt. Express 21(3), 3826–3834 (2013).
[Crossref] [PubMed]

Mo, S.

C. Li, S. Xu, S. Mo, B. Zhan, W. Zhang, C. Yang, Z. Feng, and Z. Yang, “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Phys. Lett. 10(7), 075106 (2013).
[Crossref]

Mussi, G.

J. P. von der Weid, R. Passy, G. Mussi, and N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15(7), 1131–1141 (1997).
[Crossref]

Nehmetallah, G.

Oberson, P.

P. Oberson, B. Huttner, O. Guinnard, L. Guinnard, G. Ribordy, and N. Gisin, “Optical frequency domain reflectometry with a narrow linewidth fiber laser,” IEEE Photonics Technol. Lett. 12(7), 867–869 (2000).
[Crossref]

Pan, H.

Passy, R.

J. P. von der Weid, R. Passy, G. Mussi, and N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15(7), 1131–1141 (1997).
[Crossref]

J. P. von der Weid, R. Passy, and N. Gisin, “Mid-Range Coherent Optical Frequency Domain Reflectometry with a DFB Laser Diode Coupled to an External Cavity,” J. Lightwave Technol. 13(5), 954–960 (1995).
[Crossref]

Qin, J.

Qu, X.

Reibel, R. R.

Ribordy, G.

P. Oberson, B. Huttner, O. Guinnard, L. Guinnard, G. Ribordy, and N. Gisin, “Optical frequency domain reflectometry with a narrow linewidth fiber laser,” IEEE Photonics Technol. Lett. 12(7), 867–869 (2000).
[Crossref]

Roos, P. A.

Sagiv, O. Y.

Santarelli, G.

Schilt, S.

Seah, L. K.

P. C. Won, L. K. Seah, and A. K. Asundi, “FMCW reflectometric optical fiber strain sensor,” Proc. SPIE 4328, 54–62 (2001).
[Crossref]

Soller, B.

Spiegelberg, C.

J. H. Geng, C. Spiegelberg, and S. B. Jiang, “Narrow linewidth fiber laser for 100-km optical frequency domain reflectometry,” IEEE Photonics Technol. Lett. 17(9), 1827–1829 (2005).
[Crossref]

Sun, L.

J. Li, J. Du, S. Wang, L. Li, L. Sun, X. Fan, Q. Liu, and Z. He, “Improving the spatial resolution of an OFDR based on recirculating frequency shifter,” IEEE Photonics J. 7(5), 6901310 (2015).

Têtu, M.

J.-F. Cliché, M. Allard, and M. Têtu, “High-power and ultranarrow DFB laser: the effect of linewidth reduction systems on coherence length and interferometer noise,” Proc. SPIE 6216, 62160C (2006).
[Crossref]

Thomann, P.

Tiemann, B.

J. Buck, A. Malm, A. Zakel, B. Krause, and B. Tiemann, “High-resolution 3D coherent laser radar imaging,” Proc. SPIE 6550, 655002 (2007).
[Crossref]

Tong, Y.

Tong, Yt.

Tsukada, F.

von der Weid, J. P.

J. P. von der Weid, R. Passy, G. Mussi, and N. Gisin, “On the characterization of optical fiber network components with optical frequency domain reflectometry,” J. Lightwave Technol. 15(7), 1131–1141 (1997).
[Crossref]

J. P. von der Weid, R. Passy, and N. Gisin, “Mid-Range Coherent Optical Frequency Domain Reflectometry with a DFB Laser Diode Coupled to an External Cavity,” J. Lightwave Technol. 13(5), 954–960 (1995).
[Crossref]

Wang, L. T.

Wang, S.

J. Li, J. Du, S. Wang, L. Li, L. Sun, X. Fan, Q. Liu, and Z. He, “Improving the spatial resolution of an OFDR based on recirculating frequency shifter,” IEEE Photonics J. 7(5), 6901310 (2015).

Wolfe, M.

Won, P. C.

P. C. Won, L. K. Seah, and A. K. Asundi, “FMCW reflectometric optical fiber strain sensor,” Proc. SPIE 4328, 54–62 (2001).
[Crossref]

Wuilpart, M.

Xie, W.

Xu, S.

C. Li, S. Xu, S. Mo, B. Zhan, W. Zhang, C. Yang, Z. Feng, and Z. Yang, “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Phys. Lett. 10(7), 075106 (2013).
[Crossref]

Xu, Y.

Yang, C.

C. Li, S. Xu, S. Mo, B. Zhan, W. Zhang, C. Yang, Z. Feng, and Z. Yang, “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Phys. Lett. 10(7), 075106 (2013).
[Crossref]

Yang, Z.

C. Li, S. Xu, S. Mo, B. Zhan, W. Zhang, C. Yang, Z. Feng, and Z. Yang, “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Phys. Lett. 10(7), 075106 (2013).
[Crossref]

Yao, X. S.

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, J. Jiang, Z. Meng, and H. Chen, “Compensation of laser frequency tuning nonlinearity of a long range OFDR using deskew filter,” Opt. Express 21(3), 3826–3834 (2013).
[Crossref] [PubMed]

Z. Ding, X. S. Yao, T. Liu, Y. Du, K. Liu, Q. Han, Z. Meng, J. Jiang, and H. Chen, “Long measurement range OFDR beyond laser coherence length,” IEEE Photonics Technol. Lett. 25(2), 202–205 (2013).
[Crossref]

Yoshida, N.

Yu, S.

Yuksel, K.

Zakel, A.

J. Buck, A. Malm, A. Zakel, B. Krause, and B. Tiemann, “High-resolution 3D coherent laser radar imaging,” Proc. SPIE 6550, 655002 (2007).
[Crossref]

Zhan, B.

C. Li, S. Xu, S. Mo, B. Zhan, W. Zhang, C. Yang, Z. Feng, and Z. Yang, “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Phys. Lett. 10(7), 075106 (2013).
[Crossref]

Zhang, F.

Zhang, W.

C. Li, S. Xu, S. Mo, B. Zhan, W. Zhang, C. Yang, Z. Feng, and Z. Yang, “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Phys. Lett. 10(7), 075106 (2013).
[Crossref]

Zheng, J.

Zhou, Q.

Appl. Opt. (5)

IEEE Photonics J. (1)

J. Li, J. Du, S. Wang, L. Li, L. Sun, X. Fan, Q. Liu, and Z. He, “Improving the spatial resolution of an OFDR based on recirculating frequency shifter,” IEEE Photonics J. 7(5), 6901310 (2015).

IEEE Photonics Technol. Lett. (3)

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Figures (6)

Fig. 1
Fig. 1 .Configuration of the OFDR system. The frequency-swept laser is a single mode DFB fiber laser, driven by a pre-distorted PZT voltage ramp. The reference interferometer, auxiliary interferometer, and measurement interferometer both are all-fiber-based MZI. The reference MZI is used for active linearized OPLL control; the auxiliary MZI is used for pre-distortion of the PZT drive voltage and dynamic frequency noise spectrum measurement; multiple reflection events of FUT are recorded by the measurement MZI and analyzed using the real-time spectrum analyzer. AWG, arbitrary wave generator; AOFS, acousto-optic frequency shifter for self-heterodyne detection; DPFD, digital phase frequency detector; PMC, polarization-maintaining coupler; PMF is 1 km polarization-maintaining delay fiber; BPD, balanced-photo detector; DAQ, data acquisition card; SMF, single mode fiber; PC, polarization controller.
Fig. 2
Fig. 2 Measured static frequency noise PSD. Red line, free running laser; blue line, closed-loop operation. The frequency noise is suppressed more than 40 dB between 0.1 Hz and 100 Hz, the frequency noise PSD is about 0.5 Hz2/Hz at 1 Hz and well below 1 Hz2/Hz between 1 Hz and 1 kHz. Purple line: beta-line used in power area method to estimate laser linewidth, the estimated laser linewidth is 1.4 Hz for 2 s observing time.
Fig. 3
Fig. 3 Dynamic frequency noise spectrum during 30 ms sweep time. In the beginning 5 ms of sweeping, the OPLL is losing lock, ascribing to the sudden change of sweep rate. After that, the loop gets into a stable state. Under locked state, the dynamic frequency noise PSD is efficiently suppressed within loop bandwidth. The frequency noise at 1 kHz is around 10 dB Hz2/Hz, while that before locked is 50 dB Hz2/Hz.
Fig. 4
Fig. 4 Beat note spectrum when the laser frequency is swept over 1 GHz in 25 ms. Green line, open-loop operation, the spectrum peak is blurred because of residual nonlinear sweep and phase noise. Red line, closed-loop operation, the broad noise component is efficiently suppressed within the loop bandwidth, and the beat signal spectrum characterizes a pure Fourier-transform-limited peak with a width of 40 Hz.
Fig. 5
Fig. 5 Measured Rayleigh backscattering and Fresnel reflections for a FUT length of 200 km fiber link, maximum measurement range for Rayleigh backscattering is 120 km. (a) Measurement using 25 ms sweep, the measured spatial resolution at 20 km, 40 km, 80 km, 150 km, and 200 km are 14.4 cm, 25 cm, 0.86 m, 1.17 m and 1.31 m, respectively. (b) Measurement using 5 ms sweep, the measured spatial resolution is 0.72 m over the whole 200 km fiber link.
Fig. 6
Fig. 6 Measured spatial resolution of Fresnel reflection peaks over the FUT link. Blue trace, measurement using 25ms sweep. Red trace, measurement using 5ms sweep.

Equations (2)

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δφ( f )/ δυ( f ) = ( 1 e i2πf τ 0 )/ if 2π τ 0 rad/ Hz , f1/ τ 0 ,
I i (t)=Icos(2π f b1 + φ 1 +δ φ 1 (t)) I q (t)=Isin(2π f b1 + φ 1 +δ φ 1 (t)),

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