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Stimulated Brillouin scattering (SBS) is the major factor that limits the maximum optical fiber output power in narrow linewidth applications, which include important fields such as passive optical networks (PONs), high-power fiber amplifiers, and lasers. Great efforts have been dedicated to suppressing the SBS effect and increasing the maximum optical fiber output power. This paper focuses on key fiber-based techniques to suppress SBS. These techniques take advantages of the properties of optical fibers. We present how these properties (electric modes, acoustic modes, and material properties) could be utilized to suppress SBS. The fiber-based techniques are divided into transverse optical fiber design, longitudinal variant fiber design, and external perturbations (strain and temperature) on optical fibers. Transverse optical fiber design focuses on the mechanism electro-acoustic interaction. Large effective area fiber design and acoustic tailoring techniques have been discussed. Longitudinal variant fiber design considers the nonlinear SBS interaction along propagation distance, and various techniques related have been presented. External perturbations (strain and temperature) on optical fibers emphasize on how external static perturbations could modify the SBS effect. [ABSTRACT FROM AUTHOR]

A multimode optical fiber supports excitation and propagation of a pure single optical mode, i.e., the field pattern that satisfies the boundary conditions and does not change along the fiber. When two counterpropagating pure optical modes are excited, they could interact through the stimulated Brillouin scattering (SBS) process. Here, we present a simple theoretical formalism describing SBS interaction between two individual optical modes selectively excited in an acoustically isotropic multimode optical fiber. Employing a weakly guiding step-index fiber approach, we have built an analytical expression for the spatial distribution of the sound field amplitude in the fiber core and explored the features of SBS gain spectra, describing the interaction between modes of different orders. In this way, we give a clear insight into the sound propagation effects accompanying SBS in multimode optical fibers, and demonstrate their specific contributions to the SBS gain spectrum. [ABSTRACT FROM AUTHOR]

A theoretical and experimental study on the stimulated Brillouin scattering (SBS) threshold for optical pulse in the presence of modulation instability (MI) in long optical fiber is presented. The effects of MI on the SBS gain and threshold are analyzed based on the coupled-wave equation. An analytic expression is obtained to calculate the SBS threshold in the presence of MI. Numerical simulation is conducted to study the effects of the repetition rate and amplified spontaneous emission (ASE) noise on the SBS threshold for optical pulses. An experiment is conducted, and the results agree well with the theoretical analysis. The results clearly reveal how MI affects the Brillouin gain and SBS threshold of optical pulses in long optical fiber. The SBS threshold is affected by the ASE noise level and the repetition rate of the optical pulse. The study is helpful for the power evaluation of interferometric fiber sensing systems and optical power transmission systems. [ABSTRACT FROM AUTHOR]

Distributed optical fiber sensing technology has been widely applied in the areas of infrastructure health monitoring, national defense security, etc. The long-range high-spatial-resolution Brillouin optical correlation domain analysis (BOCDA) has extensive development and application prospects. In this paper, long-range BOCDAs are introduced and summarized. Several creative methods underpinning measurement range enlargement, including the interval enhancement of the adjacent correlation peak (CP), improvements in the signal-to-noise ratio, and the concurrent interrogation of multiple CPs, are discussed and experimentally verified, respectively. The main drawbacks in the present BOCDA schemes and avenues for future research and development have also been prospected. [ABSTRACT FROM AUTHOR]

Optical carrier recovery provides a method to increase the carrier-to-signal power ratio at the receiver side of an optical communications system. Here, we propose to use optical carrier recovery based on stimulated Brillouin scattering to help overcome performance limits of Kramers-Kronig direct detection systems that arise due to the need for a high carrier-to-signal power ratio. By transmitting a low power pilot tone along with the signal, we simplify the stimulated Brillouin scattering based optical carrier recovery subsystem, toward better compatibility with the technology demands of short-reach systems. Experimental results show that after 80 km standard single mode fibre transmission, an 8.8 dB required optical signal-to-noise ratio improvement is achieved by the proposed optical carrier recovery subsystem, when compared with the standard Kramers-Kronig direct detection system. Moreover, we measure a receiver sensitivity enhancement of more than 2.8 dB in an optically pre-amplified receiver. These results indicate the potential of the proposed optical carrier recovery subsystem to improve reach or power requirements for Kramers-Kronig direct detection systems. [ABSTRACT FROM AUTHOR]

We propose and implement a microwave frequency measurement (MFM) scheme based on stimulated Brillouin scattering (SBS) and an apodized fiber Bragg grating (AFBG), achieving high accuracy in a wide range of measurement with a highly simplified configuration. By sweeping a reference frequency during SBS process, a frequency-to-power mapping between the reference frequency and the monitored output optical power of the MFM system is established. Unknown frequencies can be identified through a specific numerical relationship among the unknown frequency, reference frequency, and Brillouin frequency shift (BFS). The transmission and reflection properties of the AFBG are exploited to offer pump light and probe light simultaneously for SBS process, thereby reducing complexity of the MFM system. It can be derived theoretically that all frequencies larger than one BFS can be measured except for 3/2 BFS. This measurement blind spot can be eliminated by utilizing two segments of single-mode fibers with different BFSs. A measurement error of less than ±1 MHz within 10.68 GHz to 20 GHz is achieved in a proof-of-concept experiment of the proposed MFM approach. This method has also been proved to be applied to dual microwave frequency measurements. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate that multiple tapers in optical fibers allow for quasi-distributed refractive index sensing via a high spatial resolution Brillouin Optical Frequency-Domain Analysis (BOFDA) configuration. We first characterize, theoretically and experimentally, the variation of the Brillouin frequency shift (BFS) with the diameter of the tapered fiber. Then, we characterize the dependence of the BFS from the outer refractive index in an optical fiber taper with a waist diameter of 10 µm. Finally, we show that more tapers can be realized along the same fiber, in order to provide multi-point refractive index sensing. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a distributed liquid level sensor based on high-resolution Brillouin Optical Frequency-Domain Analysis and an actively heated cobalt-doped optical fiber. The liquid level position is determined by localizing the abrupt temperature change occurring along the active fiber at the liquid/air interface, through distributed temperature sensing. Differently from previous works based on the use of optically heated fibers, in the proposed configuration no separate laser source was employed to heat the fiber. In practice, a single laser source was adopted for both optical heating and distributed temperature sensing. The experiments report the measurement of the liquid level position with 5 mm level resolution along a 9-cm long heated fiber. The paper also discusses the limitations of the proposed method. In particular, the negative impact of spontaneous Brillouin scattering, in terms of measurement noise, is revealed by the measurements. We show that the spontaneous Brillouin scattering induces spurious components in the frequency-domain, affecting the accuracy of temperature measurements. [ABSTRACT FROM AUTHOR]

Forward stimulated Brillouin scattering in standard single‐mode fibers draws increasing interest toward sensing and signal processing applications. The process takes place through two classes of guided acoustic modes: purely radial ones and torsional‐radial modes with twofold azimuthal symmetry. The latter case cannot be described in terms of scalar models alone. In this work, the polarization attributes of forward stimulated Brillouin scattering in single‐mode fibers are investigated in analysis and experiment. Torsional‐radial acoustic modes are stimulated by orthogonally polarized pump tones, a first such report in standard single‐mode fibers. The scattering of optical probe waves by torsional‐radial modes may take up the form of phase modulation, cross‐polarization coupling, or a combination of both, depending on polarization. Lastly, this analysis predicts that circular and orthogonal pump tones may stimulate acoustic vortex beams: torsional‐radial modes that are rotating. The rotation represents the transfer of angular momentum between the polarization degree of freedom of the light field and the acoustic wave. [ABSTRACT FROM AUTHOR]

The monitoring of ionizing radiation is critical for the safe operation of nuclear and other high-power plants. Fiber-optic sensing of radiation has been pursued for over 45 years. Most protocols rely on radiation effects on the optical properties of the fiber. Here we propose a new concept, in which the opto-mechanics of standard fibers coated by thin layers of fluoroacrylate polymer are observed instead. The time-of-flight of radial acoustic waves through the coating is evaluated by forward stimulated Brillouin scattering measurements. The time-of-flight is seen to decrease monotonically with the overall dosage of gamma radiation from a cobalt source. Variations reach 15% of the initial value for 180 Mrad dose and remain stable for at least several weeks following exposure. The faster times-of-flight are consistent with a radiation-induced increase in the coating stiffness, observed in offline analysis. The effects on the coating are independent of possible changes in the optical parameters of the fiber. The combination of opto-mechanical analysis together with established fiber sensing protocols may help disambiguate the evaluation of multiple radiation metrics and reduce environmental cross-sensitivities. The technique is suitable for online monitoring and may be extended to spatially distributed measurements. [ABSTRACT FROM AUTHOR]

A dual-adaptive denoising algorithm based on complementary ensemble empirical mode decomposition (CEEMD) and particle swarm optimization (PSO) is proposed to improve the signal-to-noise ratio (SNR) of Brillouin optical time domain analysis (BOTDA) sensor. Here, CEEMD is employed to decompose the measurement signal into a series of intrinsic mode functions (IMFs) adaptively and accurately. The spectrum centroid method is applied to quantify objectively the range of denoising. Then PSO threshold algorithm is dedicatedly designed to search for the optimal/sub-optimal denoising threshold for noised IMFs, which can adjust the threshold size adaptively according to the noise level of input signal. The results show that the SNR can be improved by more than 14 dB and the Brillouin frequency shift (BFS) accuracy is optimized by 1.12 MHz in 22.5 km sensing fiber. This algorithm does not need any condition prediction in the process of denoising, which offers an adaptation and high SNR demodulation scheme for BOTDA sensor with only modifying the software. [ABSTRACT FROM AUTHOR]

A photonic-assisted multiple microwave frequency measurement approach based on stimulated Brillouin scattering (SBS) and frequency-to-time mapping with high accuracy and a wide frequency measurement range is reported. A frequency sweeping signal is modulated on an optical carrier that is shifted by the Brillouin frequency shift as a frequency sweeping optical probe wave. The unknown microwave frequencies are modulated on the original optical carrier to pump a length of single-mode fiber. Thanks to the SBS effect, the Brillouin gain spectrum is detected by the frequency sweeping optical probe wave. After the optical signal from the probe branch is detected at a photodetector, the amplitude of the direct-current component will be much increased at the exact time when the SBS gain generated by the unknown signal overlaps with a specific optical wavelength of the frequency sweeping optical signal. Therefore, the unknown microwave frequencies are mapped to the time domain. More importantly, by introducing a two-step accuracy improvement, including the reference calibration and the curve smoothing, the measurement accuracy of the proposed approach is greatly improved compared with most of the available approaches. An experiment is performed. Microwave frequency measurement from 6 to 18 GHz is demonstrated with a measurement error of less than ±1 MHz. [ABSTRACT FROM AUTHOR]

A nonlinear method to generate and control both the type and magnitude of the birefringence, as well as differential group delay (DGD) in optical fibers is studied. Experiments show that both parameters of birefringence can be dynamically changed with only a slight variation of the SBS-induced gain of the system. The method is based on exploiting polarization dependence of stimulated Brillouin scattering in optical fibers. The generation of controlled DGD and DGD dispersion (DGDD) is also demonstrated. Proof-of-concept experiments are provided showing the feasibility of dynamically inducing linear, circular and elliptical birefringence, as well as DGD and DGDD. [ABSTRACT FROM AUTHOR]

This paper reviews the recent advances on the high-performance distributed Brillouin optical fiber sensing, which include the conventional distributed Brillouin optical fiber sensing based on backward stimulated Brillouin scattering and two other novel distributed sensing mechanisms based on Brillouin dynamic grating and forward stimulated Brillouin scattering, respectively. As for the conventional distributed Brillouin optical fiber sensing, the spatial resolution has been improved from meter to centimeter in the time-domain scheme and to millimeter in the correlation-domain scheme, respectively; the measurement time has been reduced from minute to millisecond and even to microsecond; the sensing range has reached more than 100 km. Brillouin dynamic grating can be used to measure the birefringence of a polarization-maintaining fiber, which has been explored to realize distributed measurement of temperature, strain, salinity, static pressure, and transverse pressure. More recently, forward stimulated Brillouin scattering has gained considerable interest because of its capacity to detect mechanical features of materials surrounding the optical fiber, and remarkable works using ingenious schemes have managed to realize distributed measurement, which opens a brand-new way to achieve position-resolved substance identification. [ABSTRACT FROM AUTHOR]

A novel method of stimulated Brillouin scattering (SBS) gain suppression in passive single-mode optical fibers is proposed and experimentally verified. The effect is achieved due to special propagation conditions created for a number of the core-bounded acoustic modes effectively involved in the SBS, such that its gain becomes approximately evenly distributed over a wide spectral range, thereby proportionally reducing its maximum. To verify and investigate this method in depth, single-mode large-mode-area (LMA) fibers with correspondingly optimized acoustic index profiles are fabricated, experimentally tested, and analyzed. Uneven complex doping of the core with two additives, P2O5 and F, forms a high-contrast gradient acoustic index profile while maintaining a quasi-uniform optical refractive index profile. With a contrast of P2O5 of more than 6 mol.%, we achieved 8 dB of SBS suppression over conventional uniformly doped LMA fibers. Moreover, it is shown that more than 10 dB of SBS gain suppression can be achieved if the optimal dopant distribution is realized. [ABSTRACT FROM AUTHOR]

We investigate the inter-mode forward stimulated Brillouin scattering (FSBS) in nanofibers in this article. An extraordinary high Brillouin peak value is predicted for the interaction between the HE11 and the high-order optical mode (TE01). The corresponding excited acoustic mode (R11) has the characteristics of the relatively uniform large normalized displacements and the phase velocity less than the shear acoustic velocity of silica, which completely differs from the transverse acoustic mode in the intra-mode FSBS process of the HE11. The Brillouin peak value by the contribution of R11 can reach 260.5 W−1m−1 at a frequency of 0.1905 GHz, which is at least an order of magnitude higher than the maximum peak value in the intra-mode forward Brillouin gain spectrum (BGS). Moreover, for a nanofiber radius of 0.57 to 1 μm, the contribution of R11 is always the most prominent to the BGS. This work provides further insight into phonon-photon coupling in nanofibers. [ABSTRACT FROM AUTHOR]

We present a novel and simple scheme for all-optical microwave photonic frequency converter, free of electrical components, based on stimulated Brillouin scattering (SBS) effect. An SBS-based frequency shifter is incorporated to generate Stokes wave whose frequency is down-shifted by vb, where vb is defined as the Brillouin frequency shift. With a tunable optical passband filter, the up/down frequency conversion can be realized through the same structure. In the proof-of-concept experiment, the microwave signal at 1 to 15 GHz can be up-converted while the microwave signal at 11 to 29 GHz can be down-converted by the microwave photonic frequency converter. Moreover, the frequency and power stability of the generated signals are also investigated in three hours. To vindicate flexibility, low cost and easy implementation of the proposed all-optical setup, an experiment is carried out, and it turns out that only the frequency-to-be-converted signal source is needed while providing the ultra-wideband up/down conversion. [ABSTRACT FROM AUTHOR]

In this paper, we propose the use of a dual wavelength scheme for active distributed temperature sensing based on Co2+-doped fibers. A Brillouin Optical Frequency-Domain Analysis (BOFDA) set-up, operating at 850 nm, is used to detect the temperature changes along Co2+-doped optical fibers with various absorption coefficients, while optical heating is performed through a 1550-nm optical pump. A simple model describing optical heating along the Co2+-doped fiber is introduced and experimentally validated. As a proof of concept, we demonstrate that the sensor is capable to distinguish a 1-m portion of fiber immersed into water, from a section of equal length surrounded by air. [ABSTRACT FROM AUTHOR]

We propose a linearly configured Brillouin optical correlation domain analysis system incorporated with time domain data processing, where a fiber under test (FUT) is accessed from single end and multiple sensing points are simultaneously interrogated to extend the measurement range. In our scheme, correlation peaks (CPs) are sequentially generated by the interaction between a pump pulse outgoing from the system and a probe wave reflected from the end of an FUT, where the time-domain data processing is applied to obtain the Brillouin gain spectrum of each CP. In experiments, we demonstrate simultaneous acquisition of Brillouin gain spectra at 982 CPs with a spatial resolution of less than 5 cm and a sensing range extended from 10.3 m to 10.15 km. We also show that the amplitude of frequency modulation (Δf), which has been limited to the Brillouin frequency of an FUT in linear-configured BOCDA systems, can be enlarged without definite limitation by the time-domain data processing. In the experimental confirmation Δf of 15.6 GHz, about 1.5 times of the Brillouin frequency of FUT, is successfully applied to simultaneous analysis of 98 CPs by the time-domain data processing. [ABSTRACT FROM AUTHOR]

A Brillouin phase spectra (BPS) demodulation approach in Brillouin optical time-domain analysis (BOTDA) based on phase to intensity conversion is proposed and demonstrated. By utilizing the cascaded modulation of the probe light and coherent detection in a symmetric double-sidebands BOTDA, the Brillouin phase shift is transferred into the signal intensity so that it can be recovered with a simple envelope detection. Moreover, the measurement accuracy is significantly improved by the reduction of phase noise caused by the fiber transmission. A 2-m spatial resolution over 39.1-km fiber and 0.7 °C temperature accuracy at the end of the fiber are achieved using the BPS measurement. Compared with the conventional IQ demodulation without phase noise elimination, the precision is improved ∼6.3 dB and the maximum variation of the Brillouin frequency shift (BFS) is reduced from 13 MHz down to 2 MHz. Meanwhile, the comparison experiment with the Brillouin gain spectrum (BGS) detection is also implemented. The proposed method achieves smaller BFS uncertainty in comparison with the conventional BGS detection. At the end of the fiber, uncertainty is reduced from 1 MHz down to 0.7 MHz. [ABSTRACT FROM AUTHOR]

As matter of course traditional silica optical fibers have been widely utilized in slow-light generation promoted by an inelastic scattering process designated as stimulated Brillouin scattering (SBS). We intend to explore two different configurations of the solid-core Er-doped and undoped tellurite glass triangular lattice microstructured optical fibers (T-MOFs) by using a theoretical model, for investigating the optical characteristics of slow-light generation assisted by SBS, such as effective mode area, minimum and maximum pump powers, Brillouin gain and the time delay. Also, we studied the effect of cladding parameters on effective index of the mode, and the spectral response of group velocity as well as dispersion coefficient for both geometries of the MOFs. Comparisons have been made with those numerically simulated results as available in the literature, and the relative errors are also evaluated. • Theoretical model is used to explore two configurations of tellurite glass microstructured optical fibres (MOFs). • Optical performance of slow-light in Er-doped and undoped tellurite high-index core MOFs are investigated. • Tellurite MOF doped with erbium enhances the maximum allowable pump power. • Comparable time delay can be tuned with reduced length by tailoring the cladding parameters of the MOFs. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a millimeter-level-spatial-resolution Brillouin optical correlation-domain analysis system based on a broadband chaotic laser, where the spatial resolution only depends on chaotic signal bandwidth. By adjusting the bandwidth of chaos, the single correlation peak has been compressed to be extremely narrow. The Brillouin gain spectrum was obtained by replacing a previous optical power meter with a lock-in amplifier. Thus, the signal-to-noise ratio improved and the data acquisition time reduced effectively. This experiment is the first in that the distributed tensile strain was observed via a chaotic Brillouin optical correlation-domain analysis system with a 3.5-mm spatial resolution over 165-m measurement range. The standard deviation in the reconstructed Brillouin frequency shift was ±2 MHz. To the best of our knowledge, the proposed system is a broadband-source optical sensing system with the highest reported spatial resolution. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a high-speed single-end-access Brillouin optical correlation-domain sensor based on a lock-in-amplifier (LIA)-free detection scheme. In the system, the pump and the probe are injected into the same end of a polarization-maintaining fiber with orthogonal polarization states, and a state-of-polarization-selective reflection configuration installed at the other end of the PMF is used to reflect the probe but block the pump. Therefore, the forward pump interacts with the backward probe, and this situation is similar to the process in the conventional double-end-access Brillouin optical correlation domain analysis system. In order to implement high-speed measurement, a voltage-controlled oscillator, rather than a microwave synthesizer, is used to sweep the pump-probe frequency interval rapidly. By using an LIA-free detection scheme, an ultrahigh sampling rate of up to 200  kS/s at an arbitrary position is first achieved. As a proof of concept, dynamic strains with frequencies up to 10 000 Hz are measured at an arbitrary position with a centimeter-level spatial resolution. When distributed measurements are performed with 400 points, a repetition rate of 250 Hz with a measurement accuracy of 1.5 MHz (the sampling rate is set to be 100 kS/s) is verified by measuring dynamic strains with frequencies up to 40 Hz in a fully distributed manner. [ABSTRACT FROM AUTHOR]

The non-linear interaction between a Rayleigh-backscattered wave and a forward-traveling optical pump pulse is explored using sources separated by approximately one Brillouin shift. It is shown that the pump pulse modulates the Rayleigh backscatter at those locations where the frequencies of the counter-propagating waves differ by a Brillouin shift. As a result, a new Brillouin optical time-domain analysis technique is demonstrated that measures the spatial distribution of the Brillouin gain spectrum from one end only of the sensing fiber. In our experiments, spectra were acquired at a rate of 40 spectra per second over a sensing range of order 1 km with a spatial resolution of 3 m. The experimental arrangement and data analysis are described and a dataset is processed to extract the real part of the Brillouin gain spectrum and determine the peak of the gain spectrum as a function of location along the fiber. We also show that the new technique detects local changes in the phase due to the Brillouin interaction. The potential and limitations of the new technique are also discussed. [ABSTRACT FROM AUTHOR]

Microwave signals with high frequency, flexible tunability, and low phase noise are highly desired in signal processing and radar systems. In this letter, an optical injection-locking scheme using the high-order phase modulation sideband is introduced to realize a stable Brillouin optoelectronic oscillator (OEO). Pure microwave signals up to 40 GHz with low phase noise are obtained using an electrical drive signal below 5 GHz. A flexible frequency tuning with high resolution of 8 MHz is maintained by controlling the electrical drive signal and the slave laser, and the side mode suppression ratio is higher than 60 dB. The phase noise of the OEO-generated microwave signals under different master lasers is measured and compared to verify the significance of the master lasers with ultralow frequency noise. The maximum frequency drift of a 10.79-GHz signal is 1.4 kHz within 600 s, showing the stability of the proposed Brillouin OEO. [ABSTRACT FROM AUTHOR]

This paper demonstrates the generation of the Brillouin fiber laser (BFL) with 0.5 m long hafnium bismuth erbium doped fiber (HBEDF) as a hybrid gain medium. As the gain medium is pumped by a 980 nm laser diode at the power of 170 mW, a stable Stokes is observed at the output power of −2.96 dBm with Brillouin pump (BP) power of 3 dBm. The laser operates at wavelength shifted by 0.09 nm from the BP. To the best of the authors' knowledge, this is the first report of a compact BFL without employing any lengthy SMF, which features a simple cavity configuration. [ABSTRACT FROM AUTHOR]

Brillouin light scattering describes the diffraction of light waves by acoustic phonons, originating from random thermal fluctuations inside a transparent body, or by coherent acoustic waves, generated by a transducer or from the interference of two frequency-detuned optical waves. In experiments with optical fibers, it is generally found that the spontaneous Brillouin spectrum has the same frequency dependence as the coherent Brillouin gain. We examine the origin of this similarity between apparently different physical situations. We specifically solve the elastodynamic equation, giving displacements inside the body, under a stochastic Langevin excitation and in response to a coherent optical force. It is emphasized that phase matching is responsible for temporal and spatial frequency-domain filtering of the excitation, leading in either case to the excitation of a Lorentzian frequency response solely determined by elastic loss. [ABSTRACT FROM AUTHOR]

Three-layered single mode fibers with a GeO2 and F co-doped inner core are proposed. Stimulated Brillouin scattering properties in the fibers are investigated for the discriminative sensing of strain and temperature. The optical properties of the proposed fibers are designed to be well compatible with those of the widely used standard single mode fibers. The acoustic properties, including effective acoustic velocity, Brillouin frequency shifts, and peak Brillouin gain efficiencies of the first three acoustic modes, are numerically calculated and elaborately analyzed under different structural and doping parameters. The co-doped fibers with three different structural and doping parameters are chosen for simultaneous sensing of temperature and strain because of their capability of supporting two comparable peaks, which can be easily identified and distinguished in the Brillouin gain spectrum. The sensing properties of the fibers are estimated and discussed. The temperature and strain sensitivities as well as the temperature and strain errors are calculated to be comparable to those of the few mode fibers and multimode fibers. [ABSTRACT FROM PUBLISHER]

We propose a novel M-shaped single mode fiber (M-SMF) sensor based on stimulated Brillouin scattering of higher-order acoustic modes for simultaneous temperature and strain measurement. Numerical investigation of longitudinal acoustic modes in the M-SMF shows that multi-peak Brillouin spectrum in M-SMF is contributed by the couplings between the LP01 optical mode and multiple acoustic modes. The Brillouin characteristics in the M-SMF are compared with those of standard single mode fiber. Utilizing the multi-peak feature of Brillouin gain spectrum, sensing characteristics of the M-SMF under different temperature and strain conditions were studied. Thanks to the widely spaced L01 and L02 acoustic mode peaks in the Brillouin spectrum of M-SMF, the proposed fiber enables discriminative sensing of temperature and strain at an accuracy of 0.47 °C and 12.3 με, respectively. [ABSTRACT FROM PUBLISHER]

In this paper, a multiwavelength two-mode Brillouin fibre laser generated by two-mode optical fibre (TMOF) is proposed and demonstrated experimentally. The system comprises a 500 m long TMOF. A tunable laser source amplified by a high power erbium doped fibre amplifier acts as the Brillouin pump (BP) followed by a single mode fibre Bragg grating as a reflector in the cavity with a centre wavelength of 1544 nm. The BP is observed in the superposition ofandmodes in the few-mode fibre. The set-up is capable of generating a maximum of 12 clearly defined Stokes lines at the pump power of 28.6 dBm, spanning from 1543.88 to 1544.92 nm. [ABSTRACT FROM PUBLISHER]

A novel optoelectronic oscillator (OEO) using a phase modulator is proposed and experimentally demonstrated. A carrier phase shift technique based on Brillouin-induced slow light effect is used to realize a conversion from phase modulation to intensity modulation. Two kinds of pump structures for producing large nonlinear phase shifts, a single-pump structure and a dual-pump structure, are investigated. As a comparison, the single-sideband phase noises of the single-pump and dual-pump OEOs are measured, respectively. The experimental results indicate that the single-pump OEO exhibits better phase noise performance near carrier than the dual-pump OEO. The maximum fractional frequency deviation of both types of OEOs is about ±0.85 ppm over 5000 s. The proposed scheme can be widely used in stable microwave or millimeter wave generation. [ABSTRACT FROM PUBLISHER]

The optical and acoustic fields of stimulated Brillouin scattering (SBS) and the interaction between them are investigated in the As 2 S 3 chalcogenide suspended-core microstructured optical fibers (MOFs) by the finite-element method (FEM). The optical and acoustic fundamental modes are analyzed at 1550 nm. The core diameters of the MOFs vary from 1.0 to 6.0 μm. For each case, the holes of the MOFs are filled with different materials such as trichlormethane (CHCL 3 ), alcohol and water. When the core diameter is 6.0, 4.5, 3.0, 2.0 and 1.0 μm, the ratios of difference for optical fields are ∼0.66%, 0.97%, 1.48%, 1.94% and 3.55%, respectively, while the ratios of difference for acoustic fields are ∼0.13%, 0.24%, 0.34%, 0.74% and 29.13%, respectively. The overlap factors between optical and acoustic fields are calculated, which change with the core diameter and the filled material. The results will be helpful to strengthen or suppress the SBS effect in practical applications. [ABSTRACT FROM AUTHOR]

The distributed Brillouin analysis of an 8.8-km-long fiber with a spatial resolution of 2 cm is presented. All 440 000 potential resolution points are addressed in the measurement. A 7-cm-long hot-spot, located toward the output end of the pump wave, is properly identified in the experiment. The experimental error in the estimate of the local values of the Brillouin frequency shift is ±3.5 MHz. The analysis is based on the simultaneous generation and analysis of Brillouin interaction in more than 2000 correlation peaks, induced by periodic phase modulation of the pump and signal waves. The Brillouin amplifications at individual peaks are resolved using radar-like coding of pump wave magnitude by a 10000 bit-long aperiodic sequence, and postdetection compression at the receiver end. Extensive numerical simulations of the Brillouin interactions over kilometers of fiber with centimeter resolution are reported as well. The results are at the state of the art for high-resolution distributed Brillouin sensors. [ABSTRACT FROM PUBLISHER]

Theoretical investigation leading to design of a single-mode As2Se3-chalcogenide photonic crystal fiber is reported for generation of a tunable slow light. Maximum allowable pump power for undistorted output pulse, Brillouin gain, and time-delay experienced by the pulse propagating in designed photonic crystal fibers are simulated. We have found that Brillouin gain upto ∼88 dB/m and time delay up to ∼137 ns can be obtained from 1-m-long photonic crystal fiber pumped with 100 mW. Simulated results indicate that the time delay experienced by the pulse can be tuned with the pump power and structural parameters of As2Se3 -chalcogenide photonic crystal fiber. [ABSTRACT FROM PUBLISHER]

Brillouin dynamic gratings (BDGs) in optical fibers have been developed for more than a decade and gained considerable interests in different photonics fields. Based on its features of flexibility and all-optical generation, BDG has been explored for many applications including distributed optical fiber sensing (temperature, strain, transverse pressure, hydrostatic pressure, and salinity), all-optical signal processing, all-optical delay, microwave photonic filter, and ultrahigh resolution optical spectrometry. Especially in recent years, besides the longitudinal BDG in the backward stimulated Brillouin scattering (SBS), the transverse BDG associated with the forward SBS has been proposed for substance identification and characterization of optical fiber diameter. In this paper, a systematically theoretical analysis of BDG in optical fibers is given and its recent advances in applications is summarized. [ABSTRACT FROM AUTHOR]

Tunable pulse broadening cancellation via doublet Brillouin gain lines in a silica fiber was theoretically investigated. Minimum broadening factor of 0.96 with time delay of 134.5 ps is achieved by optimizing doublet Brillouin lines for 200 ps Gaussian pulse with pulse distortion. Frequency separation between two gain lines and spectrum bandwidth of single gain line and peak gain values are optimized and considered in the present paper. [ABSTRACT FROM AUTHOR]

A tunable single passband microwave photonic filter with high selectivity and flexible tunability based on stimulated Brillouin scattering (SBS) is theoretically analyzed. The passband is generated due to phase to amplitude modulation conversion by mapping the Brillouin gain spectrum induced by SBS process. Typically the linewidth of Brillouin gain spectrum for a given fiber is a constant, which restricts the filtering performance in terms of selectivity. In order to alleviate this restriction, spectrum narrowing technique is applied to reduce filter bandwidth by superimposing the gain spectrum with two loss spectra. In addition, the technique based on gain-loss compensation is used to broaden the filter tunable range. In theory, near 60 % filter bandwidth reduction and maximum tuning range of $$2\nu _{B}$$ are achieved. [ABSTRACT FROM AUTHOR]

We demonstrate the effect of stimulated Brillouin scattering (SBS) on the conversion efficiency and the nature of noise transfer from the mixing frequencies to the generated frequencies during the wavelength conversion of 10 Gbps amplitude modulated signal using four-wave mixing in a highly nonlinear fiber. The impact of SBS is found to be different for the Stokes and anti-Stokes components. [ABSTRACT FROM AUTHOR]

Harnessing nonlinear optical effects in a photonic chip scale has been proven useful for a number of key applications in optical communications. Microwave photonics (MWP) can also benefit from the adoption of such a technology, creating a new concept of nonlinear integrated MWP. Here, we look at the potential of using nonlinear optical effects in a chip scale to enable RF signal processing with enhanced performance. We review a number of recent results in this field, with particular focus on the creation of frequency agile and high suppression microwave bandstop filters using on-chip stimulated Brillouin scattering. We also discuss the future prospect of nonlinear integrated MWP to enable a general purpose, programmable analog signal processor, as well as compact, high performance active microwave filters with enhanced energy efficiency. [ABSTRACT FROM PUBLISHER]

The manipulation of the group velocity of optical signals (slow and fast light) has many possible appli- cations in telecommunications, sensing, nonlinear optics, and so on. The exploitation of the effect of stimulated Brillouin scattering (SBS) is of special interest for the alteration of the group velocity in optical fibers, since it just requires standard telecom equipment and low-to-moderate optical power. However, each delay in one single, low-gain SBS-based slow-light system is accompanied by a pulse broadening. This is a result of the inherent Kramers-Kronig relations among the gain, the phase change, and the accompanied group velocity. For an ideal flat gain, the phase change is nonideal, and for an ideal phase change the gain curve leads to a broadening. Furthermore, if the gain bandwidth is adapted to the signal by broadening, the delay will be reduced. Thus the signal broadening can be reduced by several methods for one single low-gain slow-light system, but it cannot be zero. Here, we will show how a zero-broadening SBS-based slow light can be achieved with several methods. The basic idea is a reshaping of the original pulse in a second stage by saturation of the SBS system, or by the superposition of two gains. As will be shown, all of these systems show an almost ideal overall gain and phase function over the bandwidth of the pulses. Thus, SBS-based slow light with a delay bandwidth product of 1 bit and zero distortion is possible. [ABSTRACT FROM AUTHOR]

Abstract: The coupled amplitude equations of stimulated Brillouin scattering in optical fibers are numerically solved with the fourth-order Runge–Kutta formula and the characteristics method; the influence of the shape, energy and duration of injected super-Gaussian shaped pulses on time delay and pulse broadening is investigated. The results indicate that time delay and pulse broadening depend on the shape, energy and duration of the injected pulses. Maximum time delay and less pulse broadening can be obtained by optimizing the shape of the super-Gaussian shaped pulses; the maximum time delay and corresponding gain increase with a decrease of injected energy, and larger relative delay can be obtained by a smaller duration pulse. These results provide a theory base for designing novel optical communication or sensing components. [Copyright &y& Elsevier]

An all-fiber passively Q-switched Yb-doped fiber laser with fiber saturable absorber (SA) based on a piece of Sm-doped fiber is presented. For the first time, we observe the fast stimulated Brillouin scattering Q-switched process in an Yb/Sm all-fiber laser and obtain 41 ns pulses and 1.7 kW maximum peak power. Compared with the reported traditional SA Q-switched process, the pulse energy and peak power are both improved an order of magnitude. Furthermore, a traditional SA Q-switched process with 450 ns pulsewidth and 7.5 W peak power is also obtained in the same structure by increasing the feedback of cavity's output end. [ABSTRACT FROM PUBLISHER]

Abstract: Chaotic stimulated Brillouin scattering (SBS) in optical fibers with weak external optical feedback has been investigated experimentally and theoretically. However, only the bifurcation route to chaos through period-one and quasi-periodic emission was discovered in the former work because the chaotic domain is very short in the general nonlinear system. In order to control the chaos process and observe finer periodic-orbit structures, a novel experiment was designed to extend the chaotic domain by using long optical fibers in the SBS system. In this experiment, the period-one, period-doubling, period-four and period-eight cycle routes to the chaos laser process as well as the more details of chaos, have been observed. [Copyright &y& Elsevier]

Optical fibers, the enablers of the Internet, are being used in an ever more diverse array of applications. Many of the rapidly growing deployments of fibers are in high-power and, particularly, high power-per-unit-bandwidth systems where well-known optical nonlinearities have historically not been especially consequential in limiting overall performance. Today, however, nominally weak effects, most notably stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) are among the principal phenomena restricting continued scaling to higher optical power levels. In order to address these limitations, the optical fiber community has focused dominantly on geometry-related solutions such as large mode area (LMA) designs. Since such scattering, and all other linear and nonlinear optical phenomena including higher order mode instability (HOMI), are fundamentally materials-based in origin, this paper unapologetically advocates material solutions to present and future performance limitations. As such, this paper represents a 'call to arms' for material scientists and engineers to engage in this opportunity to drive the future development of optical fibers that address many of the grand engineering challenges of our day. [ABSTRACT FROM AUTHOR]

In this paper, we investigate a nonlinear compensation technique with two different architectures using direct modulation (DM) and external modulation (EM) techniques, termed as DM based frequency dithering (DMFD) and EM based frequency dithering (EMFD). We show that DMFD and EMFD methods operate substantially different in radio-over-fiber (RoF) system by optimizing the dithering technique relative to the LTE technology. The proposed techniques is only applicable if the condition of fL <; fd <; fRF is met, where fL represents the dithering boundary limit of 14 MHz, fd is DMFD signal frequency and fRF is the RoF carrier frequency. Analysis of the optical launch power for DMFD and EMFD methods reveal that the stimulated Brillouin scattering threshold is above ~6 dBm for the LTE-RoF system. In addition, we also unveil that DMFD and EMFD methods do not introduce additional distortion for the linear and optimum optical launch power regions, which are frequency chirp driven regions. If the given condition is met, the proposed method improves the LTE-RoF system without any shortcoming. Finally, at 10 dBm launch power, DMFD and EMFD methods exhibits an average signal-to-noise ratio gain of ~5.95 and ~7.71 dB, respectively. [ABSTRACT FROM PUBLISHER]

Abstract: A concept of interaction length is proposed. Interaction length, which is dependent on pulse width, repetition rate and fiber length could be used to model and analyze the stimulated Brillouin scattering threshold (SBST) of nanosecond laser in optical fiber. The relationship of SBST of nanosecond fiber laser and interaction length was demonstrated. The validity of the concept is verified by detailed experiments. [Copyright &y& Elsevier]