Brillouin Amplification Research Articles

High-efficiency DBA-BOTDA with optimized SNR by multiple bandwidths pump modulation

For Brillouin optical time-domain analysis (BOTDA) based on distributed Brillouin amplification (DBA), constant Brillouin response achieved by the exponentially variable bandwidth/intensity pump modulation suffers from the much lower pumping efficiency for long-range sensing, which counterbalances the merit of DBA. In this Letter, pump modulation by multiple constant bandwidths was proposed and demonstrated. The ∼98.9 km sensing with ∼5 m spatial resolution and no use of optical pulse coding (OPC) was achieved by ∼8 dBm Brillouin pump, which is lower by ∼9 dB in theory by comparison with exponentially increased bandwidth modulation. Compared with traditional DBA-BOTDA, signal-to-noise ratio (SNR) enhancement with >4.6 dB was obtained. The flattened standard deviation (STD) of Brillouin frequency shift (BFS) (less than ∼2 MHz) along the whole fiber was demonstrated.

Low-noise and high-gain of stimulated Brillouin amplification via orbital angular momentum mode division filtering.

We demonstrate a Brillouin amplifier scheme by using orbital angular momentum mode division filtering, which is able to amplify the weak optical signals with low noise and high gain. The system retains the advantages of a conventional collinear Brillouin amplifier structure, and employs a liquid-crystal spatial light modulator to generate distinguishable degree-of-freedom of beams. As we all know, the noise mainly derives from the unwanted coupling in stimulated Brillouin scattering (SBS) processes, which severely limits the amplifier's performances. The efficient SBS noise-filtering method is discussed, which could improve the output beam quality effectively. The experimental results show the proposed amplifier scheme can overcome this obstacle, providing the magnification (or called signal gain) of 71dB for an input signal of 4.7×10-12 J. In addition, the amplified signal is recognized from the amplifier spontaneous-emission (ASE)-like noise with a signal-to-noise ratio of 6.7dB.

Demonstration of 2.5 J, 10 Hz, nanosecond laser beam combination system based on non-collinear Brillouin amplification.

We demonstrated a four-beam combined laser system based on Brillouin amplification with a nanosecond output of 2.5 J at a 10 Hz repetition rate. We used simulations and experiments to assess factors affecting the energy extraction efficiency of non-collinear Brillouin amplification. Our results indicate that higher efficiency can be achieved by adding pump beams to the Brillouin amplification process, which enhances optical field intensity and interaction strength. To the best of our knowledge, this is the first demonstration of a multi-beam combination system based on Brillouin amplification with an output of joule level energy, high peak power and nanosecond pulses in 10Hz repetitive operation.

Enhanced phase-sensitive OTDR system with pulse width modulation Brillouin amplification.

A pulse width modulation (PWM) Brillouin amplification has been proposed and demonstrated to improve the signal-to-noise ratio (SNR) and sensitivity of phase-sensitive optical time domain reflectometry (Ф-OTDR) especially for the far end of a sensing fiber. In the logarithmic unit, arbitrary gain distribution can be realized with the customizable PWM function. The gain distribution is adjustable by tuning the PWM parameters. To prove the concept, three typical gain distributions including up-ramp sawtooth, sine and triangle have been achieved with the corresponding driving functions. In experiments, a linear PWM pump light has been used to amplify the backscattering Rayleigh light. The signal at the leading end has been enhanced by about 11.5 dB. Meanwhile, 9 dB transmission attenuation (along 25 km SMF) has also been compensated excellently. To verify the effectiveness of attenuation compensation, two vibrations with a frequency of 100 Hz and 300 Hz have been recovered accurately at the trailing end. Besides, preamplifier and acoustic-optic modulator (AOM) was used to suppress the ASE noise and further improve the effective ER, respectively. With that, lower relative intensity noise (RIN) has been obtained in the proposed system compared to the conventional Brillouin amplification in Ф-OTDR. So the proposed PWM Brillouin amplification not only improves the SNR but also equalizes the sensitivity along whole sensing fiber. It avoids the complex calibration and suppresses the false alarm rate in field application. Foreseeably, this scheme is universal and can be adopted by other distributed fiber optic technique to enhance the system performance.

Design rules for optimizing unipolar coded Brillouin optical time-domain analyzers.

The performance of unipolar unicolor coded Brillouin optical time-domain analysis (BOTDA) is evaluated based on both Simplex and Golay codes. Four major detrimental factors that limit the system performance, including decoded-gain trace distortion, coding pulse power non-uniformity, polarization pulling and higher-order non-local effects, are thoroughly investigated. Through theoretical analysis and an experimental validations, solutions and optimal design conditions for unipolar unicolor coded BOTDA are clearly established. First, a logarithmic normalization approach is proposed to resolve the linear accumulated Brillouin amplification without distortion. Then it is found out that Simplex codes are more robust to pulse power non-uniformity compared to Golay codes; whilst the use of a polarization scrambler must be preferred in comparison to a polarization switch to mitigate uncompensated fading induced by polarization pulling in the decoded traces. These optimal conditions enables the sensing performance only limited by higher-order non-local effects. To secure systematic errors below 1.3 MHz on the Brillouin frequency estimation, while simultaneously reaching the maximum signal-to-noise ratio (SNR), a mathematical model is established to trade-off the key parameters in the design, i.e., the single-pulse Brillouin amplification, code length and probe power. It turns out that the optimal SNR performance depends in inverse proportion on the value of maximum single-pulse Brillouin amplification, which is ultimately determined by the spatial resolution. The analysis here presented is expected to serve as a quantitative guideline to design a distortion-free coded BOTDA system operating at maximum SNR.

Multiwavelength Coherent Brillouin Random Fiber Laser With Ultrahigh Optical Signal-to-Noise Ratio

A narrow-linewidth multiwavelength Brillouin random fiber laser (MW-BRFL) was experimentally demonstrated and characterized, which was achieved by mutually combining Brillouin amplification with randomly distributed Rayleigh feedback in optical fibers. By cascading process through a sub-fiber loop, up to six orders Stokes emissions simultaneously resonate in a coherent lasing fashion under the acoustic coupling of stimulated Brillouin scattering in the presence of coherent Rayleigh scattered random feedback, which acts as an optical filter with the high reflection coefficient for lowest order longitudinal mode of each Stokes line to ensure single longitudinal mode operation. Consequently, random laser output with an unprecedented ultra-high optical signal-to-noise ratio of ∼47 dB and an optimal peak power discrepancy of 1.8 dB were obtained. Furthermore, each Stokes random lasing emission with narrow linewidth of ∼1 kHz was achieved thanks to coherent random lasing. Relative intensity noise transfer was observed in sequence from the first-to sixth-order Stokes emission. In this MW-BRFL, a wide tunable range over 30 nm of the operating wavelength was validated by shifting the central wavelength of the input pump from 1530 to 1560 nm. Meanwhile, the statistical properties of the MW-BRFL and the performance optimization were also experimentally investigated.

Phase-sensitive QPSK channel phase quantization by amplifying the fourth-harmonic idler using counter-propagating Brillouin amplification

We experimentally demonstrate all-optical phase-sensitive quantization of a 10–20 Gbaud quadrature phase-shift keying (QPSK) signal’s phase without an active phase-locked loop (PLL) by utilizing Brillouin amplification (BA) to amplify the fourth-harmonic idler without path separation, allowing the pump, signal, third-harmonic idler and amplified fourth-harmonic idler to remain synchronized in the phase. We observe up to 65% reduction in phase noise and 4.6 dB gain at a bit-error rate (BER) of 10−4 over 36 min of continues operation.

Ultra-Long-Distance Hybrid BOTDA/Ф-OTDR

In the distributed optical fiber sensing (DOFS) domain, simultaneous measurement of vibration and temperature/strain based on Rayleigh scattering and Brillouin scattering in fiber could have wide applications. However, there are certain challenges for the case of ultra-long sensing range, including the interplay of different scattering mechanisms, the interaction of two types of sensing signals, and the competition of pump power. In this paper, a hybrid DOFS system, which can simultaneously measure temperature/strain and vibration over 150 km, is elaborately designed via integrating the Brillouin optical time-domain analyzer (BOTDA) and phase-sensitive optical time-domain reflectometry (Ф-OTDR). Distributed Raman and Brillouin amplifications, frequency division multiplexing (FDM), wavelength division multiplexing (WDM), and time division multiplexing (TDM) are delicately fused to accommodate ultra-long-distance BOTDA and Ф-OTDR. Consequently, the sensing range of the hybrid system is 150.62 km, and the spatial resolution of BOTDA and Ф-OTDR are 9 m and 30 m, respectively. The measurement uncertainty of the BOTDA is ± 0.82 MHz. To the best of our knowledge, this is the first time that such hybrid DOFS is realized with a hundred-kilometer length scale.

Active frequency matching in stimulated Brillouin amplification for production of a 2.4 J, 200 ps laser pulse.

A frequency matching Brillouin amplification in high-power solid-state laser systems is proposed. The energy extraction efficiency could be maintained at a high level in a non-collinear Brillouin amplification structure using an exact Stokes frequency shift. Laser pulses having a width of 200 ps and energy of 2.4 J were produced. This method can be used to transfer energy from a long pulse to a short pulse through a high-power solid-state laser system.

Analytical approach of Brillouin amplification over threshold.

We report on an accurate closed-form analytical model for the gain of a Brillouin fiber amplifier that accounts for material loss in the depleted pump regime. We determined the operational model limits with respect to its relevant parameters and pump regimes through both numerical and experimental validation. As such, our results enable accurate performance prediction of Brillouin fiber amplifiers operating in the weak-pump, high-gain, and saturation regimes alike.

Strongly coupled stimulated Brillouin amplification in pump-ionizing plasma

Laser amplification based on strongly coupled stimulated Brillouin scattering in plasma is investigated. The pump and seed are at the same wavelength of 800 nm and the same duration of 3.5 ps, but with a different intensity. The plasma is produced by the front part of the pump via tunnel ionization from hydrogen. The hydrogen is fully ionized to eliminate small-scale density fluctuations in the plasma, so the transmission level of the seed is enhanced to 22%, and a relative amplification factor of 6 is obtained.

Giant enhancement of stimulated Brillouin scattering with engineered phoxonic crystal waveguides.

Stimulated Brillouin scattering (SBS) is a third-order nonlinear process that involves the interaction of two light fields and an acoustic wave in a medium. It has been exploited for applications of optical communication, sensing, and signal processing. This effect, originally demonstrated in long optical fibers, has recently been realized in silicon waveguides on a chip-scale integrated platform. However, due to the weak per-unit-length SBS gain, the length of the silicon waveguides is usually several centimeters, which prevents device miniaturization for high-density integration. Here, we engineer a phoxonic crystal waveguide structure to achieve significantly enhanced SBS gain in the entire C band, by taking advantage of its simultaneous confinement of slow propagating optical and acoustic waves. The resulting SBS gain coefficient is greater than 3 × 104 W-1 m-1 in the wavelength range of 1520-1565 nm with the highest value beyond 106 W-1 m-1, which is at least an order of magnitude higher than the existing demonstrations. This giant enhancement of SBS gain enables ultracompact and high-performance SBS-based integrated optoelectronic devices such as Brillouin lasers, amplifiers, and signal processors.

Comparative study on reduced impacts of Brillouin pump depletion and nonlinear amplification in coded DBA-BOTDA

The impacts of Brillouin pump depletion and nonlinear amplification in coded long-range Brillouin optical time-domain analysis (BOTDA) based on distributed Brillouin amplification (DBA) were studied. The error of Brillouin frequency shift (BFS) due to Brillouin pump depletion was compared for DBA-BOTDA using non-cyclic and cyclic coding. For non-cyclic coding, significant over- and under-shoots of BFS were found in the range with larger BFS variation, such as hot spot. The impact of Brillouin pump depletion can be reduced considerably by cyclic coding. Furthermore, to compensate the BFS error due to nonlinear amplification, a simple and effective log linearization was proposed and demonstrated.

Forward Raman scattering of the seed pulse in strongly coupled stimulated Brillouin amplification in plasma

Short laser pulse can be amplified and compressed via strongly coupled stimulated Brillouin scattering (sc-SBS) in plasma. But the sc-SBS amplification is subject to various deleterious instabilities. Here, we present specific analyses on the forward Raman scattering (FRS) of the seed pulse. FRS grows from noises and depletes the seed energy. It causes strong seed modulations and decoherence, which terminate the amplification. The theoretical model of sc-SBS coupled with FRS is investigated. Then, we examine the suppression effects of the density gradient and density random inhomogeneities on FRS. These effects are described well by the numerical simulations and particle-in-cell simulations.

Weak laser pulse signal amplification based on a fiber Brillouin amplifier

We propose a high-gain and frequency-selective amplifier for a weak optical signal based on stimulated Brillouin scattering in a single mode fiber. To be able to satisfy the needs of high gain and high signal-to-noise ratio laser pulse amplification, different fiber lengths and core diameters are used to fulfill this experiment. In the experiment, a 430 nW (peak power) pulsed signal is amplified by 70 dB with a signal-to-noise ratio of 14 dB. The small size, high gain, low cost, and low noise of the fiber Brillouin amplifier make it a promising weak signal amplification method for practical applications such as lidar.

Detuned Brillouin amplification of OTDR signals with an enhanced signal-to-noise ratio.

The technique known as external Brillouin amplification of Rayleigh scattering is characterized in the detuning regime. When employed as an amplifier of OTDR signals, it is shown that the signal-to-noise ratio is significantly improved for optimum pump Stokes detuning, leading to enhanced nanostrain sensitivity. This effect is due to the Brillouin bandwidth dependence on the Stokes power.

On-chip Brillouin purification for frequency comb-based coherent optical communications.

In this Letter, for the first time, to the best of our knowledge, we harness on-chip Brillouin scattering for narrowband amplification and spectral purification of frequency comb lines for coherent optical communications. A parametrically generated optical frequency comb with a low carrier-to-noise power ratio was filtered through narrowband Brillouin amplification utilizing the same comb as the optical pump. This was achieved on a photonic chip to enable successful transmission of an advanced modulation format signal: 64-level quadrature amplitude modulation. 96Gb/s data were modulated on two polarizations on multiple comb lines across 1532.9-1557.5nm, demonstrating the scalability of this concept for operation in wavelength division multiplexing applications. The small form factor of the photonic chip reduces the polarization drifts when compared to optical fibers and paves the way for photonic integration.

Stimulated Brillouin scattering materials, experimental design and applications: A review

Stimulated Brillouin scattering (SBS), as one type of third-order nonlinear optics effect, is extensively exploited and rapidly developed in the field of lasers and optoelectronics. A large number of theoretical and experimental studies on SBS have been carried out in the past decades. Especially, the exploration of new SBS materials and new types of SBS modulation methods have been engaged simultaneously, as the properties of different materials have great influence on the SBS performance such as generation threshold, Brillouin amplification efficiency, frequency shift, breakdown threshold, etc. This article provides a comprehensive review of the characteristics of different types of SBS materials, SBS applications, experimental design methods, as well as the parameter optimization method, which is expected to provide reference and guidance to SBS related experiments.

Mitigating the effects of the gain-dependence of the Brillouin line-shape on dynamic BOTDA sensing methods.

It has been recently shown that in stimulated Brillouin amplification (pulsed pump & CW probe) the line-shape of the normalized logarithmic Brillouin Gain Spectrum (BGS) broadens with increasing gain. Most pronounced for short pump pulses, a linewidth increase of ~3 MHz (~1.5 MHz) per dB of additional gain was observed for a pump pulse width of 15 ns (30 ns), respectively. This gain-dependency of the shape of the BGS compromises the accuracy of the otherwise attractive, highly dynamic and distributed slope-assisted BOTDA techniques, where measurand-induced gain variations of a single probe, are converted to strain/temperature values through a calibration factor that depends on the line-shape of the BGS. A previously developed technique with built-in compensation for Brillouin gain variations, namely: the Ratio Double Slope-Assisted BOTDA (RDSA-BOTDA) method, where both slopes of the BGS are interrogated, fails to meet this new challenge of the gain-induced shape dependence of the BGS, resulting, for instance, in significant measurement errors of ~5% per dB of gain change for a 15 ns pump pulse. Here, we propose and demonstrate an extension of the RDSA-BOTDA method, which now offers immunity also to Brillouin gain-dependent line-shape variations. Requiring a prior characterization of the gain-induced line-shape dependency of the fiber and pump-pulse-width in use, this mitigation technique takes advantage of the fact that the sum of the measured logarithmic gains at judiciously chosen two fixed frequency points of the BGS can be used to determine the local peak gain, via a pre-established calibration curve. Based on the deduced correct peak gain, its associated BGS shape can now be used in the application of the previously introduced RDSA-BOTDA technique to obtain error-free results, independent of the gain dependence of the line-shape. The proposed technique has been successfully put to test in an experiment, involving a RDSA-BOTDA measurement of a fiber segment, vibrating at 50 Hz with a constant, peak-to-peak amplitude of 640 microstrain. As the Brillouin gain was manually varied from 1 to 3.5 dB, classical data processing, based on a single gain value, predicted amplitudes which varied by as much as 90 microstrain, while the proposed mitigation technique produced the correct constant amplitude, regardless of the gain changes. This restored accuracy of the RDSA-BOTDA technique is of importance, especially for monitoring real-world dynamic scenarios, where high Brillouin gains, which often locally vary due to dynamically introduced losses, can successfully achieve fast gain-independent double-slope-assisted Brillouin measurements (many kHz's of sampling rates over hundreds of meters), with enhanced spatial resolution and signal to noise ratio.

X-ray amplification by stimulated Brillouin scattering

Plasma-based parametric amplification using stimulated Brillouin scattering offers a route to coherent x-ray pulses orders of magnitude more intense than those of the brightest available sources. Brillouin amplification permits amplification of shorter wavelengths with lower pump intensities than Raman amplification, which Landau and collisional damping limit in the x-ray regime. Analytic predictions, numerical solutions of the three-wave-coupling equations, and particle-in-cell simulations suggest that Brillouin amplification in solid-density plasmas will allow compression of current x-ray free-electron laser pulses to subfemtosecond durations and unprecedented intensities.