High‐performance Brillouin distributed temperature sensor using Fourier wavelet regularised deconvolution algorithm

Recently, high power narrow linewidth fiber lasers are interested in wavelength beam combining. In narrow linewidth fiber laser, Stimulated Brillouin Scattering is the main power limiting factor. A Stimulated Brillouin Scattering suppressing method by modulating frequency distribution was proposed and examined both experimentally and theoretically. The Stimulated Brillouin Scattering threshold power increased a lot by increasing the frequency number and spacing. Finally, the linewidth of 8 GHz, power of 1kW and central wavelength of 1064.14nm, are achieved respectively in fiber laser. We analyzed the above results: the increasing of frequency number, controlling of frequency spacing all reduce power spectrum density. With the cascaded phase modulation technology, the Stimulated Brillouin Scattering threshold is increased, while the output power of fiber laser is increased a lot.Recently, high power narrow linewidth fiber lasers are interested in wavelength beam combining. In narrow linewidth fiber laser, Stimulated Brillouin Scattering is the main power limiting factor. A Stimulated Brillouin Scattering suppressing method by modulating frequency distribution was proposed and examined both experimentally and theoretically. The Stimulated Brillouin Scattering threshold power increased a lot by increasing the frequency number and spacing. Finally, the linewidth of 8 GHz, power of 1kW and central wavelength of 1064.14nm, are achieved respectively in fiber laser. We analyzed the above results: the increasing of frequency number, controlling of frequency spacing all reduce power spectrum density. With the cascaded phase modulation technology, the Stimulated Brillouin Scattering threshold is increased, while the output power of fiber laser is increased a lot.

We report a theoretical and experimental study on stimulated Brillouin scattering (SBS) suppression in a monolithic fiber amplifier with filtered and amplified pseudo-random binary sequence (PRBS) phase modulation. Theoretically, we use a time-dependent three-wave coupled nonlinear system considering both active fiber and passive fiber to describe the acoustic phonon, laser, and Stokes characteristics in a fiber amplifier. The SBS threshold power after filtered PRBS phase modulation is numerically evaluated to obtain the optimal parameters, and the time-averaged distributions of the counter-pump power, laser power, and Stokes power at different positions along the fiber length of the fiber system are simulated. Also, we established a four-stage fiber amplifier system to verify our theory. The configuration of the fiber amplifier system includes a filtered and amplified PRBS phase-modulated single-frequency fiber laser, a three-stage pre-amplifier, and a counter-pumping main stage, subsequently. 2.5 kW output power with an FWHM linewidth of 9.63 GHz is accomplished by a domestic ytterbium-doped double-clad fiber with core/cladding diameters of 20.2/400 µm. The reflectivity of the main stage is 0.049‰ at the maximum output power, which indicates the proposed architecture is under the SBS threshold. The experiments verify the accuracy of the theoretical model, which provides a reliable reference for evaluating the SBS suppression capability of the high-power narrow-linewidth fiber amplifier phase modulated by the filtered and amplified PRBS signal.

A theoretical analysis of stimulated Brillouin scattering (SBS) in linear cavity Yb3+ doped dual-clad fiber lasers is presented by solving the steady-state rate equations with SBS included. Solutions to suppress the detrimental effect in the fiber laser are discussed. It is shown that the first-order Stokes initiated by forward and backward pump light changes exponentially along the fiber, and laser power reduces greatly in the presence of SBS under bidirectional end pump. Furthermore, it is found that the SBS threshold power can be improved effectively by using large mode area fiber and shortening the cavity length.

Structured light with multiple degrees of freedom has inspired many advanced applications, and its nonlinear control plays an important role in the interactions between light and matter. Stimulated Brillouin scattering (SBS) based on light–sound coupling can be used to realize wavefront‐reversal nonlinear reflection of ordinary light; consequently, it is used to correct wavefront aberrations in high‐power laser systems. However, high‐fidelity wavefront reversal of structured light with orbital angular momentum and high‐reflectivity single‐end SBS of weak incident waves remain challenging. Here, the authors propose a cross‐pump focused SBS scheme that enables wavefront reversal with high fidelity, low threshold, and high reflectivity for arbitrary structured light . The authors demonstrate the capability of this approach to perform conformal and enhanced SBS reflections with a fidelity of >95% and reflectivity of >100%. Compared with the conventional focused SBS configuration, the SBS threshold is reduced by more than ten times, and wavefront reversal of weakly structured light is realized. This proof‐of‐principle study provides a high‐performance SBS platform with potential implications for high‐power structured lasers, high signal‐to‐noise‐ratio microscopy imaging, and the development of nonlinear optics with structured light.

Stimulated Brillouin Scattering(SBS) is one of important nonlinear optical effects in optical fiber transmission system, it limits the optical power that can be transmitted through fiber. If input optical power is over SBS threshold, part of power will be changed to backward Stokes wave, this process exacerbates the system transmission characteristic very much. In this paper, SBS effect was systemically studied by experiments. Firstly, backward Stokes wave was observed, we investigated its spectrum and frequency shift to pumping signal wave. Then, the relationship of SBS threshold characteristic with linewidth of light source and modulation formats was discussed, and approved by experiments. The impact on bite error rate characteristic of system due to SBS was also investigated experimentally.

Using 2.4-nsec pulses at 350 nm, we have observed transverse stimulated Brillouin scattering (SBS) in fused-silica optical components. Transverse SBS sets in when the product of laser fluence and growth time for the scattered optical wave exceeds ∼2.3 J nsec/cm2. An increase in laser bandwidth to 8.3 GHz suppresses SBS losses up to approximately twice the SBS threshold. We review the theory of transverse, broadband SBS and its scaling with experimental parameters.

Based on pump-probe technique (PPT), we observed stimulated Brillouin scattering (SBS) in a 100-m-long silica graded-index multimode optical fiber with the same core diameter as that of a perfluorinated graded-index polymer optical fiber (PFGI-POF) (= 50 μm). The SBS threshold was measured to be -50 mW, which was much lower than 5.08 W, the SBS threshold obtained for the same fiber without PPT. This result indicates that PPT is useful even under multimode conditions and that the difficulty in observing SBS in PFGI-POFs consists not in their physical problems but in their material problems (high propagation loss, etc.).

Stimulated Brillouin scattering (SBS) is one of important nonlinear effects in optical fiber communication systems. Due to its low threshold, it limits the optical power that couples into the fiber. In this paper, Stimulated Brillouin scattering and the effect of phonon loss to SBS in optical fiber communication systems are investigated. In experiments we measure first the power of backward Stokes wave and output light under various input powers of the systems with different lengths of fibers. Then for observing the effect of the phonon blocker to the SBS threshold, we repeat the same experiments but with a phonon blocker inserted at different locations of the fiber link. The experiments indicate that adding phonon blocker to the fiber is able to increase the SBS threshold, and the blocker at different locations makes different effects.

Nonlinear distortion for single-sideband (SSB) signals will significantly reduce the performance of Kramers–Kronig (KK) receiver-based optical transmission. In this work, we present a proof-of-concept study of stimulated Brillouin scattering (SBS)-induced nonlinear distortion for 10 Gbaud and 28 Gbaud SSB QAM16 transmission over 80 km standard single mode fiber (SSMF) based on a KK receiver. Significantly reduced bit error rate (BER) has been experimentally observed due to the SBS and the threshold of SBS at about 7 dBm is detected for such an 80 km SSMF link. With left sideband (LSB) modulation of SSB, together with optical filtering, reduced SBS nonlinear distortion has been achieved with ~2 dB power tolerance improvement. The results reveal an important issue of SBS-induced nonlinear distortion, which would be of great significance for KK receiver-based optical transmission applications.

Dynamic aspects of stimulated Brillouin scattering (SBS) and criteria for its occurrence in optical communications are studied numerically. SBS is shown to cause sharp amplitude modulations in phase-shift keying (PSK) modulated systems close to or above the SBS threshold. It is shown that the convolution method to high accuracy yields correct relative gains for different modulation sequences. The transient change of backscattered radiation caused by abrupt changes in the modulation format is studied and it is demonstrated that the transition can occur on different time scales. >

We introduce a new figure of merit (FOM) including the input pump power limit associated with stimulated Brillouin scattering (SBS) for evaluation of the Kerr nonlinearity efficiency of optical fibers. The new FOM is expressed as gammaL(eff)P(SBS) (gamma is a nonlinearity parameter, L(eff) is effective length, and P(SBS) is the SBS threshold), while the conventional FOM is given by gammaL(eff). Using the new FOM, we perform an efficiency comparison among four types of state-of-the-art nonlinear optical fiber: a Bi2O3-based nonlinear fiber, a silica-based holey fiber, a highly nonlinear dispersion-shifted fiber, and a conventional dispersion-shifted fiber. The Bi2O3-based nonlinear fiber is found to have the best Kerr nonlinearity efficiency owing to the superior nonlinear property of the Bi2O3 glass compared with that of the silica.

We report on a high peak power pulsed fiber laser emitting in the L band limited by stimulated Brillouin scattering (SBS). On-going developments target at building fiber lasers for CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensing from space such as ASCENDS emitting at 1572nm. Unfortunately the relevant CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> lines compatible with Erbium amplification are located in the L amplification band, where the cross sections are small. Consequently, those fiber sources have low non-linear threshold and low efficiency. The European Space Agency is funding a project dedicated to the design of a high power pulsed fiber laser for CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> DIAL monitoring with emission lines located closed to 1579 nm. The system requires 150 ns pulse duration at 4 kHz pulse repetition frequency (PRF). The high precision on the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentration measurement requires narrow linewidth and the laser is primarily limited by Stimulated Brillouin Scattering (SBS). SBS threshold can be improved by: reducing fiber length, reducing effective Brillouin gain or increasing effective area. Due to the small cross-sections of Erbium in L band, large doping concentration or large fiber length are required. Large mode area phosphate Erbium-Ytterbium codoped fibers have been used to generate 84 μJ for 1 μs pulses with 1% efficiency which corresponds to ~84 W peak power.

ABSTRACTStokes field demonstrated unusually narrow spectrum and non-Gaussian statistics for SBS in 300-rn single-mode opticalfiber with enhanced Rayleigh losses. We shown that SBS lasing takes place in the fiber. The effect is explained by dynamicdistributed feedback due to double Rayleigh scattering of the Stokes field. Results of numerical simulation of the cooperativeSBS-RS process in fiber are in good agreement with experimental results. 1. INTRODUCTION Stimulated Brillouin scattering (SBS) is the resonance interaction between pump wave backscattered optical Stokes wave,and hypersound wave induced in the medium. SBS is initiated by spontaneous scattering of the pump wave on occasionalhypersound waves caused by thermal noise. Being essentially nonlinear process, SBS in optical fibers demonstrates a complicateddynamic behavior'.The presence ofthe external feedback makes SBS dynamics even richer. Significant narrowing ofthe spectrumand decreasing ofthe SBS threshold are usually observed for SBS in fiber ring interferometers. Regularization ofthe Stokes fieldchaotic fluctuations and soliton mode generation are observed both in low fitness ring fiber resonators and in the long single-modeoptical fiber when small (—3%) parasitic reflections from the non-angled fiber ends creates low fitness Fabry-Perot interferometerin the fiber2._________________________________________________

A bidirectional full duplex radio over fiber (RoF) system is proposed for multi-band signal generation and transmission. A multi-band signal is generated at the central station (CS), which includes 10 GHz baseband, 40, and 70 GHz millimeter-wave (mm-wave) by optical frequency multiplication technique of radio frequency (RF) local oscillator (LO) with frequency of 15 GHz. The simultaneous transmission of the 16-QAM OFDM-based multi-band downlink signal and 4-QAM uplink signal over a single fiber is demonstrated. The carrier for uplink transmission is extracted from the unmodulated downlink signal with tunable FBG which is modulated by OFDM-based 4-QAM uplink data obtained from the user end via an antenna. The frequency reuse from the downlink signal makes the base station (BS) free from the laser source. At the user end, the multi-band signals for multi-serve application are obtained by heterodyne beating of multiple bands. An increase in launch power induces fiber dispersion and non-linearities like self-phase modulation (SPM) and cross phase modulation (XPM), which depends on the nonlinear refractive index of the fiber. Different industrial standard fibers with common specifications and modulation format along with co-shared components are deployed, and system performance is analyzed. The stimulated Brillouin scattering (SBS) can be mitigated by optimizing the launch power within the SBS threshold. The nonlinear effects are minimized at the system level without the requirement of additional digital signal processor (DSP) . The theoretical and simulation analysis shows that the designed bidirectional RoF link exhibits an improved system performance for bidirectional transmission with negligible power penalty.

The stimulated Brillouin scattering (SBS) effect in fiber amplifiers using white noise signal (WNS) phase modulated seed is simulated. The influences of cut-off frequencies of WNS and the output fiber structure on SBS threshold are discussed. Basing on simulation results, optimized phase modulation signal and output fiber structure are achieved to suppress SBS. A fiber laser is established according to the simulation results.