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We present a method based on a model of a Brillouin gain spectrum shape for measuring the strain formed at the circumference of ring structures. The effectiveness of this method is confirmed through our simulations.

UltraNarrow RF bandpass filters with a high extinction of up to 45 dB have been demonstrated by shaping the Brillouin gain and through destructive signal interference at the tail of the Brillouin response.

We demonstrate a record high Brillouin gain in a silicon chip through hybrid integration. Negligible nonlinear losses lead to a net gain amplification of 18.5 dB in a compact (0.3 mm2) 5.7cm As2S3 spiral.

A model that counts for temperature gradients in the target plasma, which leads to higher ion acoustic noise and enhanced levels of stimulated Brillouin scattering (SBS) gain and SBS reflectivity, has been adopted. Enhanced Brillouin gain leading to higher SBS reflectivity levels has been computed for non-homogeneous, non-Maxwellian plasmas. SBS reflectivity levels obtained are higher than those predicted by linear convective gain theory by several orders of magnitude and coincide with the high values of experimental data known in literature, which could not be interpreted by the linear convective gain theory.

The shape of the Brillouin gain spectrum (BGS) that is produced in an optical fiber undergoing strain varying linearly with respect to time, which is a typical example of temporally non-uniform strain, is theoretically derived through an analysis similar to that by which the BGS under spatially non-uniform strain would be derived. The BGS shape that is theoretically derived agrees well with the shape experimentally observed. The characteristics of the BGS deformation and strain measurement error under the temporally linear strain are discussed based on their similarity to the BGS shape derived under spatially linear strain.

The effect of the gain dependency of the Brillouin linewidth on double-slope-assisted Brillouin optical domain, dynamic sensing techniques is studied. These double-slope methods are immune to pump-power related peak Brillouin gain variations, however, they are not immune to gain-dependent variations of the shape of the Brillouin gain spectrum. For a 15ns pump pulse, this gain-dependent shape of the normalized Brillouin gain is shown to lead to a 5.5 [%/dB] strain error when the double-slope sum-difference approach is used, compared with a 7 [%/dB] error when the double-slope ratio approach is used. Ways to compensate for these issues are discussed.

The in-service loss monitoring of branched fibers in passive optical networks (PONs) is demonstrated in the field for the first time. End-reflection assisted Brillouin analysis employing a frequency shift averaging technique compensated for the variation in the Brillouin gain profile of installed optical cables. Complete loss monitoring for individual branched fibers in deployed PONs was successfully achieved.

We propose a novel Brillouin-based loss-monitoring scheme for passive optical networks (PONs) that can compensate for Brillouin gain profile variations along cables. The highly sensitive measurement of a PON with mixed deployment of different fibre types was successfully demonstrated.

The experimental validation of a full frequency-domain fiber-optic Brillouin sensing technique for temperature/strain measurements is presented. An original formulation is employed which relates the frequency-domain measurements to the Brillouin gain profile along the sensing fiber, useful to both improve the signal-to-noise ratio and to cope with the non-local effects occurring when long measurement distances are involved. By this formulation, a reconstruction algorithm is derived which determines the temperature/strain profile that provides a best fit to the measured data. Preliminary experimental results confirm the validity of the proposed technique.

We characterize the Brillouin gain spectra (BGS) in perfluorinated graded-index polymer optical fibers (PFGI-POFs) at 1.32 μm and 1.55 μm. Three kinds of PFGI-POFs with the same core diameter, but which are fabricated by different manufacturers, are tested. For all the PFGI-POFs, the Stokes power measured at 1.32 μm is higher than that at 1.55 μm due to the lower propagation loss, but significant differences in Stokes power are observed among the three. Based on the measurement obtained by the optical time-domain reflectometry, we show that the actual propagation loss of the PFGI-POFs plays a crucial role in observing BGS.

Acoustic dissipation in silica is dominated by defects that act as saturable absorbers at cryogenic temperatures. Using stimulated Brillouin spectroscopy we demonstrate that this loss channel can be mitigated in fiber, enhancing Brillouin gain.

We derive analytic expressions for the Brillouin thresholds of square pulses in optical fibers. The equations are valid for pulse durations in the transient Brillouin scattering regime (less than 100 nsec), as well for longer pulses, and have been confirmed experimentally. Our analysis also gives a firm theoretical prediction that the Brillouin gain width increases dramatically for intense pulses, from tens of MHz to one GHz or more.

We demonstrate stimulated Brillouin amplification in a single-mode tellurite fiber. A Brillouin gain of 29 dB is achieved in a 100 m tellurite fiber with a pump power of 10 mW at 1550 nm. Stimulated Brillouin scattering (SBS) induced time delay per unit power and per unit length is also calculated using the measured data of Brillouin gain coefficients. A peak value of 0.09246 ns mW-1 m-1 and a time delay slope efficiency of 1.75 ns/dB are obtained for this tellurite fiber. Potential performance of a tellurite fiber for slow light generation is clarified on the base of Brillouin gain characteristic. Our results show that tellurite fiber is a potential candidate for Brillouin fiber amplifiers and slow light generation.

A new Brillouin fiber laser (BFL) configuration is demonstrated using similar components as a conventional BFL. The BFL is configured so that the single-mode fiber receives more Brillouin pump (BP) power to generate higher back-propagating Stokes power and Brillouin gain in the cavity. The proposed configuration shows an output peak power of -0.5 dBm, which is 5.7 dB higher when compared with the conventional configuration. However, the maximum output power was observed at 0.5 dBm with an output coupler of 20 to 80 ratio, whereby 20% of the light is allowed to oscillate in the cavity and 80% of the light is coupled out as output. The linewidth of the BFL (whose BP linewidth is about 200 MHz) is measured to be ∼30 kHz, using a heterodyne beat technique.

Coherent BOTDA with phase modulated probe light is proposed and demonstrated. Brillouin gain spectrum (BGS) information is amplitude modulated on the GHz frequencies to reduce baseband noise perturbations and increase the spatial resolution to 2-meter.

We demonstrate the combination of a tunable Brillouin microcavity laser and a second reference microcavity that together provide a compact 1550 nm laser source with fractional noise < 7.8E-14 1/√Hz at 10 Hz offset.

We experimentally show record 4.4 dB continuous-wave on-off Brillouin gain in a partially underetched silicon wire. Additional improvements in optical losses and mechanical confinement may enable clear net gain in this structure.

Numerical and experimental results on stimulated Brillouin scattering (SBS) in a graded-index multimode silica fiber are reported. The Brillouin Gain Spectrum (BGS) is shown to strongly depend on the pump and probe modal content. By use of a numerical model, the BGS at varying launching conditions of both pump and probe beams is computed. Numerical results show that intramodal and intermodal SBS contribute to the overall BGS. Experiments confirm the numerical predictions. (C) 2014 Optical Society of America

A novel end-reflection-assisted Brillouin analysis is proposed and demonstrated for discriminating branches of PON with similar lengths, employing correlation domain Brillouin gain analysis and correlation based branch discrimination technique.

In this work we report an experimental modal analysis of an aluminum rectangular plate, carried out by use of the balanced-detection DPP-BOTDA method based on double-pulse pump waveform, combined with the Slope-Assisted BOTDA technique. Compared to standard DPP-BOTDA, the balanced-detection DPP-BOTDA method allows to retrieve the differential Brillouin gain in real time, i.e. without the need of post-processing differentiation, therefore allowing its combination with the Slope-Assisted BOTDA technique. The experimental mode shape of the first resonance of the aluminum plate is compared to numerical results based on a finite-element analysis (FEA), demonstrating that the proposed technique is well suited to perform the modal analysis of a vibrating structure.

A number of transparent liquids have been evaluated for use in stimulated Brillouin scattering at 532 nm. Measurements were made of frequency shift, SBS threshold, reflectivity and optical breakdown properties. It was found that the alkanes, and in particular n-pentane, performed well and measurements were made of Brillouin gain coefficient and phonon lifetimes. It is suggested that these liquids are promising candidates for use in self-pumped phase conjugate mirrors, high gain Brillouin amplifiers and four-wave mixing mirrors.

Shape variation characteristics of the Brillouin gain spectrum caused by sinusoidal-like strain distribution, which is a typical non-uniform strain distribution produced in a ring structure, are clarified through numerical calculation and experiments.

Characterization of stimulated Brillouin scattering (SBS) in an elliptic-core two-mode fiber is experimentally demonstrated. The LP(01) or LP(11) mode is selectively launched to a fiber under test by a mode-selective coupler as a Brillouin pump, and the Brillouin gain spectra are analyzed for different mode pairs of the pump and probe waves. Intermodal SBS between counterpropagating LP(01) and LP(11) modes is observed, and the efficiency is measured to be about 58% of that of the SBS between the LP(01) modes.

We analytically investigate the case of the Brillouin interaction between probe waves propagating against two modulated pump waves. This investigation is motivated by the sweep-free BOTDA technique, where, to increase the BOTDR sensing speed, the Brillouin gain spectrum is simultaneously interrogated by many probe-pump pairs. It is shown both analytically and experimentally that the Brillouin interaction between a probe and its corresponding pump is negligibly affected by a neighboring pump only when the pump tones separation is much larger than the width of the Brillouin gain spectrum.

Stimulated Brillouin scattering (SBS) in plastic optical fibers (POFs) is observed, for the first time to the best of our knowledge, using pump-probe technique without lock-in detection, and the dependences of the Brillouin gain spectrum on POF length, pump power, and probe power are fully investigated. An optimal POF length exists for SBS observation, because POFs have relatively high propagation loss of 250 dB/km at 1.55 μm; it is found to be 3.8 m when 21.1-dBm pump and 22.2-dBm probe waves are used. As the probe and pump powers grow higher, the Stokes power is also increased but nonlinearly, which indicates that the Brillouin signal observed with this technique can be directly applied to the implementation of POF-based Brillouin optical time-domain analysis systems.

Numerical and experimental investigations of stimulated Brillouin scattering signal amplification in standard single-mode fibers under pump depletion show that while gains are reduced, the same orthogonal input states of polarization that provide maximum and minimum gain in the undepleted case practically continue to do so in the depleted regime. Using a scaled Brillouin gain coefficient, the power distribution of these max/min polarizations along the fiber can be deduced from a scalar formulation.

We have investigated experimentally the performance of an SBS suppression fiber with a nonuniform dopant concentration along its length fabricated by the VAD method. We have achieved an SBS threshold of 15 dBm against a continuous wave at 1.55 /spl mu/m. This is 7 dB larger than that of conventional fiber. We have confirmed experimentally that the increase in the SBS threshold can be estimated from the ratio of the Brillouin frequency shift change over the effective interaction length to the intrinsic Brillouin gain bandwidth. Moreover, we have confirmed that there is no BER degradation after a transmission of 138 km through a 2.5 Gb/s intensity modulation direct detection system when the SBS suppression fiber is used with an input power of 16 dBm.

We exploit the strong Brillouin gain of chalcogenide glasses to generate frequency combs in a centimeter scale fiber devices. These can be applied to generation of ultra-high frequency picosecond pulse trains or complex reflection filters.

We report an ultrahigh resolution, tunable RF photonic notch filter with > 55 dB of suppression, achieved with less than 1 dB of SBS gain in a 6.5-cm chalcogenide photonic chip.

Described herein is a set of optical fibers that possess intrinsically low Brillouin gain. Proper compositional tailoring of the material comprising the fiber, whether crystalline or glassy, can substantially suppress, or even remove, Brillouin scattering.

Detection of cracks while at their early stages of evolution is important in health monitoring of civil structures. Review of technical literature reveals that single or sparsely distributed multiple cracks can be detected by Brillouin-scattering-based optical fiber sensor systems. In a recent study, a pre-pump-pulse Brillouin optical time-domain analysis (PPP-BOTDA) system was employed for detection of a single microcrack. Specific characteristics of the Brillouin gain spectrum, such as Brillouin frequency shift, and Brillouin gain spectrum width, were utilized in order to detect the formation and growth of microcracks with crack opening displacements as small as 25 μm. In most situations, formations of neighboring microcracks are not detected due to inherent limitations of Brillouin-based systems. In the study reported here, the capability of PPP-BOTDA for detection of two neighboring microcracks was investigated in terms of the proximity of the microcracks with respect to each other, i.e., crack spacing distance, crack opening displacement, and the spatial resolution of the PPP-BOTDA. The extent of the study pertained both to theoretical as well as experimental investigations. The concept of shape index is introduced in order to establish an analytical method for gauging the influence of the neighboring microcracks in detection and microcrack differentiation capabilities of Brillouin-based optical fiber sensor systems.

The complicated competition relationships between stimulated Brillouin scattering (SBS), modulation instability (MI) and stimulated Raman scattering (SRS) are observed, by injecting rectangular optical pulses with duration of 200 ns into 50 km single mode fiber. Under certain conditions, SBS suppresses MI by converting the transmission power to the backscattering power. MI also can suppress SBS by broadening the spectrum of the transmission light and decreasing the Brillouin gain. When SRS occurs, MI and SBS are suppressed simultaneously because a large amount of transmission power is consumed by converting to the Raman Stokes light.

We present two recently developed new methods for fast and distributed strain/temperature sensing in optical fibers, based on Brillouin optical time domain analysis (BOTDA). Both methods make use of very fast (

In this paper, we perform a theoretical study of processes that demonstrates additional time delay obtained by remodeling Brillouin gain spectrum, and we also study the main influence factors on pulse time delay and broadening, as well as analyze the ways which increases the delay, and further suppresses pulse broadening. The results show that by remodeling Brillouin gain spectrum, one obtains 25% delay improvement over the single intrinsic Brillouin gain spectrum; by deriving the expression of broadening factor, one finds that the increase of intrinsic SBS resonance linewidth leads to the decrease of the broadening quantity which corresponds to the maximum delay. Moreover, the increase of the peak power of absorption spectrum further leads to an increase of pulse delay. When the normalized frequency shift is below a certain value, probe pulse can be compressed; When the second-order gain is positive, pulse will be compressed; when the second-order gain is negative, pulse will become broad. DOI: http://dx.doi.org/10.11591/telkomnika.v10i6.1543 Full Text: PDF

We have proposed and experimentally demonstrated a novel frequency-doubling optoelectronic oscillator (OEO) using carrier suppression and Brillouin-gain-assisted carrier recovery. In the experiment, two frequency-doubled microwave signals at 20.062 and 9.976 GHz are shown to demonstrate the effectiveness of the proposed frequency-doubling OEO.

In this Letter, we propose a novel method based on the inhomogeneous Brillouin gain saturation to reduce the gain bandwidth significantly below its natural value. Based on our first experiments, we report a decrease of the bandwidth in a standard single mode fiber down to 3 MHz.

A single frequency distributed feedback Brillouin fiber laser exhibiting a threshold of 30 mW, and pump-to-Stokes conversion efficiency of 27% is shown. The Brillouin laser operates over a pump frequency detuning range exceeding 1 GHz.

We present a novel fault location technique for PONs that employs Brillouin gain analysis. We describe the measurement of 4-branched optical fibers in a PON with a spatial resolution of 10 m.

We study the Brillouin gain depletion as the probe frequency is tuned across the gain spectrum. A broadening of the Brillouin gain spectrum is observed as the probe is tuned to the edges of the spectrum.

We experimentally investigated the influence of amplified spontaneous emission within the Brillouin gain bandwidth on the Brillouin scattered part of a single-frequency signal. A significant influence could be seen in a passive fiber.

The influence of material doping profile and geometrical structure on Brillouin gain characteristics has been investigated. Based on a FEM modeling, importance of internal residual stress induced by fiber drawing conditions is also pointed out.

Stimulated Brillouin scattering (SBS) in a perfluorinated graded-index polymer optical fiber (POF) with 120 μm core diameter was experimentally observed for the first time, to the best of our knowledge, at 1.55 μm wavelength with the pump-probe technique. Compared to spontaneous Brillouin scattering previously reported, the Brillouin gain spectrum (BGS) was detected with an extremely high signal-to-noise ratio, even with a short POF (1 m) and scrambled polarization state. We also investigated the BGS dependences on probe power and temperature, which indicate that SBS in a POF measured with this technique can be utilized to develop high-accuracy temperature sensing systems.

Characterization of acoustic modes is important in the study of Brillouin gain spectrum. In this paper, acoustic modes of a suspended core fiber are numerically calculated by finite element method. Due to high contrast between mechanical coefficient of silica and air, full vectorial finite element method is used. Since core of SCF is surrounded by large air holes, the solutions are compared with those for a bare cylindrical silica rod in air.

Finite-element calculations of the Brillouin gain spectrum in photonic crystal fibers (PCFs) with cores incorporating random arrangements of regions with discrete acoustic velocities are presented. The peak Brillouin gain coefficient for PCFs with cores with an acoustic domain size of approximately 0.26 microm(2) and an acoustic velocity variation of 3% was calculated to be 3.3 x 10(-12) m/W with a Brillouin gain spectrum FWHM of 280 MHz. This corresponds to a decrease in the peak Brillouin gain coefficient of 7.4 dB relative to a PCF with an acoustically homogeneous core.

The design of Brillouin scattering suppressed optical fibers is described, including optimization of the acoustic index profile, designs for acoustic anti-guidance, and materials considerations for both design implementation and further reductions in Brillouin gain.

Brillouin scattering properties in a perfluorinated graded-index polymer optical fiber (POF) with 120 μm core diameter were experimentally investigated using a laser with an operating wavelength of 1.55 μm. The Brillouin frequency shift and the Brillouin bandwidth were 2.83 GHz and 105 MHz, respectively. The calculated Brillouin gain coefficient of 3.09×10−11 m/W was comparable to that of fused silica fibers. The Brillouin threshold power of the 100 m POF was estimated to be 24 W, which we believe can be reduced by employing POFs with smaller cores.

Finite element calculations of inter-modal Brillouin gain between LP(0n) modes in acoustically-inhomogeneous higher order mode (HOM) fibers are presented. When the pump beam is launched in the LP(08) mode, the LP(01) mode of the Stokes beam experiences the highest gain, approximately 6.7 dB higher than the peak LP(08)-LP(08) gain. An LP(01) Stokes beam experiences successively more Brillouin gain when pumped by higher-order LP(0n) modes.

We demonstrate a white-light-cavity (WLC) using a fiber resonator, pumped by two frequencies for two Brillouin gain peaks. Such a WLC is suitable for trap-door data buffering with a high delay-bandwidth product and negligible distortion