Incoherent pulse compression in laser range finder

Grodensky, Daniel; Kravitz, Daniel; Arbel, Nadav; Levanon, Nadav; Zadok, Avi

doi:10.1117/12.2050092

Cited by 3 publications

(2 citation statements)

References 8 publications

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“…Traditionally the method is based on the intensity modulation of a pump wave, enabling a natural incorporation of unipolar code sequences (containing 0's and 1's) into conventional distributed fiber sensors. This is the case of conventional optical time-domain reflectometers (OTDR) [21,22], Raman-based distributed sensors [23,24], Brillouin-OTDR sensors [25,26], hybrid schemes [27], and laser range finder [28], in which pulse coding has shown important improvement with respect to conventional schemes. In addition, unipolar coding has also been used in BOTDA sensing [9][10][11]; however, the Brillouin gain and loss processes can offer the unique possibility to implement another kind of coding scheme: the so-called bipolar coding [12] (i.e.…”

Section: Principle Of Bipolar Golay Coding and Impact Of Pump Depletimentioning

confidence: 99%

Increasing robustness of bipolar pulse coding in Brillouin distributed fiber sensors

2015

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Abstract:The robustness of bipolar pulse coding against pump depletion issues in Brillouin distributed fiber sensors is theoretically and experimentally investigated. The presented analysis points out that the effectiveness of bipolar coding in Brillouin sensing can be highly affected by the power unbalance between -1's and + 1's elements resulting from depletion and amplification of coded pump pulses. In order to increase robustness against those detrimental effects and to alleviate the probe power limitation imposed by pump depletion, a technique using a three-tone probe is proposed. Experimental results demonstrate that this method allows increasing the probe power by more than 12.5 dB when compared to the existing single-probe tone implementation. This huge power increment, together with the 13.5 dB signal-to-noise enhancement provided by 512-bit bipolar Golay codes, has led to low-uncertainty measurements (< 0.9 MHz) of the local Brillouin peak gain frequency over a real remoteness of 100 km, using a 200 km-long fiber-loop and 2 m spatial resolution. The method is evaluated with a record figure-of-merit of 380'000. Gonzalez-Herraez, and L. Thévenaz, "Extending the real remoteness of long-range Brillouin optical time-domain fiber analyzers," J. Lightwave Technol. 32(1), 152-162 (2014). 18. Y. Dong, L. Chen, and X. Bao, "Extending the sensing range of Brillouin optical time-domain analysis combining frequency-division multiplexing and in-line EDFAs," J.

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Section: Principle Of Bipolar Golay Coding and Impact Of Pump Depletimentioning

confidence: 99%

Increasing robustness of bipolar pulse coding in Brillouin distributed fiber sensors

2015

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“…Several types of codes could be used in amplitude modulation of the pump wave. For example, the incoherent compression of complementary Golay code pairs, using the same protocol of section 2.2, was successfully employed in laser range-finding experiments [45]. Note that the use of code pairs would require twice the number of scans that is necessary when using a single sequence.…”

Section: Summary and Discussionmentioning

confidence: 99%

High-resolution long-range distributed Brillouin analysis using dual-layer phase and amplitude coding

et al. 2014

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A new, hybrid time-domain and correlation-domain Brillouin analysis technique is proposed and demonstrated, providing a large number of high-resolution acquisition points. The method is based on dual-layer hierarchal encoding of both amplitude and phase. The pump and signal waves are co-modulated by a relatively short, high-rate binary phase sequence. The phase modulation introduces Brillouin interactions in a large number of discrete and localized correlation peaks along the fiber under test. In addition, the pump wave is also amplitude-modulated by a slower, carefully synthesized, long on-off-keying sequence. Brillouin interactions at the correlation peaks imprint weak replicas of the pump amplitude sequence on the intensity of the output signal wave. The Brillouin amplifications at individual correlation peaks are resolved by radar-like, matched-filter processing of the output signal, following a recently-proposed incoherent compression protocol. The method provides two significant advantages with respect to previous, pulse-gated correlation-domain analysis schemes, which involved a single pump pulse. First, compression of the extended pulse sequence enhances the measurement signal-to-noise ratio, which is equivalent to that of a large number of averages over repeating single-pulse acquisitions. The acquisition times are potentially much reduced, and the number of resolution points that may be practically interrogated increases accordingly. Second, the peak power level of the pump pulses may be lowered. Hence, the onset of phase pattern distortion due to self-phase modulation is deferred, and the measurement range can be increased. Using the proposed method, the acquisition of Brillouin gain spectra over a 2.2 km-long fiber with a spatial resolution of 2 cm is demonstrated experimentally. The entire set of 110,000 resolution points is interrogated using only 499 position scans per choice of frequency offset between pump and signal. A 5 cm-long hot-spot, located towards the output end of the pump wave, is properly recognized in the measurements.

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Adaptable Pulse Compression in ϕ-OTDR With Direct Digital Synthesis of Probe Waveforms and Rigorously Defined Nonlinear Chirping

et al. 2022

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Recent research in Phase-Sensitive Optical Time Doman Reflectometry (ϕ-OTDR) has been focused, among others, on performing spatially resolved measurements with various methods including the use of frequency modulated probes. However, conventional schemes either rely on phase-coded sequences, involve inflexible generation of the probe frequency modulation or mostly employ simple linear frequency modulated (LFM) pulses which suffer from elevated sidelobes introducing degradation in range resolution. In this contribution, we propose and experimentally demonstrate a novel ϕ-OTDR scheme which employs a readily adaptable Direct Digital Synthesis (DDS) of pulses with custom frequency modulation formats and demonstrate advanced optical pulse compression with a nonlinear frequency modulated (NLFM) waveform containing a complex, rigorously defined modulation law optimized for bandwidth-limited synthesis and sidelobe suppression. The proposed method offers high fidelity chirped waveforms, and when employed in resolving a 50-cm event at ∼1.13 km using a 1.2-µs probe pulse, matched filtering with the DDS-generated NLFM waveform results in a significant reduction in range ambiguity owing to autocorrelation sidelobe suppression of ∼20 dB with no averages and windowing functions, for an improvement of ∼16 dB compared to conventional linear chirping. Experimental results also show that the contribution of autocorrelation sidelobes to the power in the compressed backscattering responses around localized events is suppressed by up to ∼18 dB when advanced pulse compression with an optical NLFM pulse is employed.

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Incoherent pulse compression in laser range finder

Cited by 3 publications

References 8 publications

Increasing robustness of bipolar pulse coding in Brillouin distributed fiber sensors

Increasing robustness of bipolar pulse coding in Brillouin distributed fiber sensors

High-resolution long-range distributed Brillouin analysis using dual-layer phase and amplitude coding

Adaptable Pulse Compression in ϕ-OTDR With Direct Digital Synthesis of Probe Waveforms and Rigorously Defined Nonlinear Chirping

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