Stimulated Brillouin Scattering Amplification Research Articles

Demonstration of standing cavity Brillouin random fiber lasers using double fiber Bragg grating arrays

Bidirectional feedback by fiber Bragg grating arrays (FBGAs) reduced the loss of the cavity and increased stimulated Brillouin scattering (SBS) gain by bi-directional Stokes wave through FBGA associated Rayleigh feedback of the pump wave. As a result, the Q value of the Brillouin random fiber laser (BRFL) increased significantly, which leads to narrow linewidth. This is different from the ring configuration with unidirectional SBS gain versus dual SBS gain of the same fiber length. Highly efficient use of the SBS gain fiber for coherent SBS amplification suppressed thermal noise associated Stokes wave. Such an efficient SBS laser is realized by a standing cavity BRFL based on double FBGAs. Multiple scattering of light traveling in strong scattering FBGAs enables light localization and the generation of high-Q reflection peaks. Coherent SBS amplification with high Q help to reduce laser relative intensity noise (RIN) and laser linewidth. Experimental results demonstrate that the BRFL supports localized modes by increasing the scattering strength of the FBGA random feedback, resulting in long lifetime and single-frequency emission with 20 dB noise floor reduction. The BRFL with a 1 km Brillouin gain fiber exhibits lower RIN and narrower linewidth than that with a 10 km Brillouin gain fiber due to the stronger gain competition of more modes in the longer cavity length. The optimized standing caivty BRFL with 1 km gain fiber leads to 3.5 kHz linewidth versus 40 kHz from the pump laser. These findings provide experimental evidence that double FBGAs offer a unique setting to control mode dynamics, realizing low-noise single-frequency lasing.

Modeling stimulated Brillouin backscatter from outer-cone quads across multiple inertial confinement fusion hohlraum designs

Stimulated Brillouin scattering (SBS) is a potential risk for laser damage in the experiments carried out at the National Ignition Facility (NIF), and by altering the energy deposition pattern in hohlraums, it affects the symmetry of indirect-drive inertial confinement fusion implosions. We have surveyed backward SBS on outer-cone quads across NIF integrated hohlraums of various platforms numerically, using three-dimensional (3D) simulations with the backscatter code pF3D [Berger et al. Phys. Plasmas 5, 4337 (1998)] and ray-based gain calculations. Simulated reflected powers and energies, as well as the spectrum of reflected light all compare favorably with measurements. Ray-based calculations of exponential SBS amplification (“gain”), which assume a strongly damped plasma wave and steady-state response, are performed using a novel method that includes the 3D speckled field of the laser that drives SBS. This approach is useful for understanding qualitative differences between hohlraum designs and identifying regions susceptible to SBS within hohlraums. Quantitatively, gains are not found to correlate with SBS reflectivities in 3D, necessitating fully wave-based calculations that naturally include diffraction and various temporal dependencies.

Dual-frequency pulse laser based on acousto-optic modulation.

Non-collinear stimulated Brillouin scattering (SBS) amplification can obtain high peak power Stokes output while ensuring the stability, but the frequency mismatch reduces the energy conversion efficiency of the system. In this paper, a dual-frequency pulse laser based on acousto-optic crystal modulation is designed. The output pulse pair can be used as pump and Stokes light, respectively, which realizes the active frequency matching of the gain medium Brillouin frequency shift during the SBS amplification process and helps to maintain ideal energy conversion efficiency. The dual-frequency laser finally produced a laser pulse pair with a pulse width adjustment range of 100 ps-50 ns, a frequency shift range of 0 GHz-2 GHz, and the polarization extinction ratio (PER) reaches 20.82dB.

Wideband tunable optoelectronic oscillator based on the deamplification of stimulated Brillouin scattering.

A wideband tunable optoelectronic oscillator (OEO) based on the deamplification of stimulated Brillouin scattering (SBS) is proposed and experimentally demonstrated. A tunable single passband microwave photonic filter (MPF) utilizing phase modulation and SBS deamplification is used to realize the tunability of the OEO. Theoretical analysis of the MPF and phase noise performance of the OEO are presented. The frequency response of the MPF is determined by the + 1st sideband attenuation due to SBS deamplification and phase shift difference between the two sidebands due to chromatic dispersion and SBS. The close-in (< 1 MHz) phase noise of the proposed OEO is shown to be dominated by the laser frequency noise via phase shift of SBS. The conversion of the laser frequency noise to the close-in phase noise of the proposed OEO is effectively reduced compared with the OEO based on amplification by SBS. Tunable 7 to 40 GHz signals are experimentally obtained. The single-sideband (SSB) phase noise at 10 kHz offset is -128 dBc/Hz for 10.30 GHz signal. Compared with the OEO based on SBS amplification, the proposed OEO can achieve a phase noise performance improvement beyond 20 dB at 10 kHz offset. The maximum frequency and power drifts at 10.69 GHz are within 1 ppm and 1.4 dB during 1000 seconds, respectively. To achieve better close-in phase noise performance, lower frequency noise laser and higher pump power are preferred. The experimental results agree well with the theoretical models.

Stimulated Brillouin scattering in integrated ring resonators

We investigate stimulated Brillouin scattering (SBS) in ring resonators that exhibit linear and nonlinear losses. We present both analytic and numerical tools that can be used to compute the amplification and lasing threshold for the SBS-induced Stokes line. We show that, for both linear and nonlinear losses, there is a maximum achievable SBS amplification, and we show how this depends on the parameters of the ring and on the material parameters. We also study the relation between the critical coupling and input pump power to achieve amplification in various situations. We present simplified models that can be used to accurately predict the nonlinear behavior of the ring and consequently estimate the pump power required to achieve the optimum gain in a range of technologically important situations.

Widely tunable microwave photonic filter based on self-adaptive optical carrier regeneration

In this paper, we have designed and proofed a widely tunable microwave photonic filter (MPF) on the basis of self-adaptive optical carrier regeneration method through stimulated Brillouin scattering (SBS) amplification. The MPF system features with a single microwave passband as the result of the processed signal sideband beating with the regenerated optical carrier. Since the Brillouin-laser optical carrier and the SBS amplification are generated from one laser source, the optical carrier regeneration process of the proposed MPF is self-adaptive and carrier-frequency independent. Moreover, by simply varying the wavelength spacing between the optical carrier and the optical filter, the central passband of the MPF can be continuously tuned from 6 to 32 GHz, which is limited by the bandwidth of the modulator and the photodetector. The 3 dB bandwidth and the out-of-band suppression ratio of the MPF can reach 640 MHz and 21 dB, respectively.

Effect of pump mode structure on reflectance of SBS mirrors

In this paper, we have studied a two pass amplifier with a single and two-cell stimulated Brillouin scattering (SBS) phase conjugating mirrors. The role of longitudinal mode structure on the energy reflectivity of the SBS process and temporal behavior of the reflected pulse has been investigated experimentally. The results for different mode structures including single, double and multi-mode pump pulse for SBS mirrors with single and two cells are compared to each other. Our results show that the two cell SBS mirror has some new advantages over the single cell configuration when the laser oscillator operates in multi-mode regime. We found higher reflectivity at high entrance energy for backwardly amplified Stokes pulse. The mode beating become considerably smaller and fluctuations of Stokes pulse are smoothed in the SBS amplifier.

Secure optical communication using stimulated Brillouin scattering in optical fiber

We propose to encrypt/decrypt high-speed optical signal using stimulated Brillouin scattering (SBS) effect in optical fiber for the first time. The broadened SBS gain or loss distorts the amplitude and phase of the optical signal so as to realize all-optical encryption. The corresponding SBS loss or gain with the same bandwidth and amplitude recovers the distorted signal to implement optical decryption. The encryption/decryption keys could be the SBS gain amplitude, bandwidth, central wavelength and the spectral shape, which are configurable and can be flexibly controlled by the users. The operation principle of the SBS based encryption and decryption is explained in detail. Complete encryption and error-free decryption for a 10.86-Gb/s on-off-keying signal has been experimentally demonstrated using broadband SBS amplification and absorption. The immunity of the proposed encryption method to the eavesdropper's attack is also analyzed. The SBS based secure optical communication is compatible with the current optical communication systems.

30-GHz millimeter-wave carrier generation with single sideband modulation based on stimulated Brillouin scattering

A new technique to generate a millimeter (mm)-wave carrier of 32.57 GHz (fLO = 10.85 GHz) with single sideband modulation (SSB) for radio-over-fiber (RoF) systems is experimentally demonstrated by using stimulated Brillouin scattering (SBS). The SSB is realized by directly amplifying the +3rd sideband of the modulated optical carrier in the process of SBS. The pump wave is provided through a double Brillouin scattering frequency shifting configuration. The use of the same laser source to generate the pump wave ensures the stability of the mm-wave generation system since the relative frequency shift between them can be eliminated. In addition, the mm-wave carrier obtains an RF power gain of 21 dB with the SBS amplification and a 3-dB bandwidth of 10 kHz.

Physical mechanism of “slow light” in stimulated Brillouin scattering

We show from analytical analysis of the basic stimulated Brillouin scattering (SBS) equations in the time domain that the SBS amplification process does not amplify an external Stokes pulse and therefore cannot induce group delay of the Stokes pulse as claimed in the literature. Rather, the delayed output Stokes pulse is the pump radiation reflected by the induced acoustic wave, the amplitude of which determines the rate of the amplification process and time delay of the pulse. The latter is predominantly a consequence of the SBS buildup process determined by the inertia of the acoustic wave excitation. Analytical solutions of the SBS equations in the frequency domain show that spectral broadening of the pump radiation leads to only negligible broadening of the SBS spectral bandwidth and so does not provide an effective means to achieve broadband pulse delay.

Large delay tunable slow-light based on high-gain stimulated-Brillouin-scattering amplification in optical fibers

Tunable stimulated-Brillouin-scattering (SBS)-based slow-light in optical fibers has potential applications in optical buffering in the future all-optical router commutation systems. However, due to the low SBS threshold and relatively high realistic signal power, the gain in the usual SBS systems is limited at ∼30 dB. This paper presents a high-gain SBS scheme to realize large delay slow-light, which benefits from avoiding the depletion of the pump power in a short fiber as SBS media. The experiment demonstrates that, up to 50 dB non-saturated gain has been observed in the single-stage 591.8 m fiber SBS amplification. The slow-light delay can be obtained 52 ns, and the fractional delay can exceed 1.

New progress of mm-wave radio-over-fiber system based on OFM

This paper presents an overview on new progresses of millimeter wave (mm-wave) radio-overfiber (RoF) system based on mm-wave generation by optical frequency multiplication (OFM), including generation of high-order optical side modes by optical modulation using dual-drive Mach-Zehnder modulator (DD-MZM) and enhancement of high-order optical side mode induced by selective amplification due to stimulated Brillouin scattering (SBS). The paper describes OFM by using DD-MZM in principle and verifies it in an experimental bidirectional 40 GHz RoF system. SBS amplification enhances the generated information-bearing mm-wave in downlink and also helps in producing a pure reference mm-wave for radio frequency-intermediate frequency (RF-IF) down-conversion in uplink. These efforts pushed the OFM technology of mm-RoF systems to achieve more and more feasibility and cost-effectiveness.

Vector analysis of stimulated Brillouin scattering amplification in standard single-mode fibers

The polarization properties of stimulated Brillouin scattering (SBS) amplification or attenuation in standard single-mode fibers are examined through vectorial analysis, simulation and experiment. Vector propagation equations for the signal wave, incorporating SBS and birefringence, are derived and analyzed in both the Jones and Stokes spaces. The analysis shows that in the undepleted pump regime, the fiber may be regarded as a polarization-dependent gain (or loss) medium, having two orthogonal input SOPs, and corresponding two orthogonal output SOPs, for the signal, which, respectively, provide the signal with maximum and minimum SBS amplification (or attenuation). Under high Brillouin gain conditions and excluding zero-probability cases, the output SOP of arbitrarily polarized input signals, would tend to converge towards that of maximum SBS gain. In the case of high SBS attenuation the output SOP of an arbitrarily polarized signal would approach the output SOP corresponding to minimum attenuation. It is found that for a wide range of practical pump powers ( < or = 100mW) and for sufficiently long fibers with typical SBS and birefringence parameters, the signal aligned for maximum SBS interaction will enter/emerge from the fiber with its electric field closely tracing the same ellipse in space as that of the pump at the corresponding side of the fiber, albeit with the opposite sense of rotation. The analytic predictions are experimentally demonstrated for both Stokes (amplification) and anti-Stokes (attenuation) signals.

Measurement of the SBS gain of radiation in glasses

A method for determining the specific gain under conditions of stimulated Brillouin scattering (SBS) is proposed, which is based on measuring the amplification of a Stokes beam with an inhomogeneous spatial intensity distribution in a sample used as an SBS amplifier. Under the same experimental conditions, the values of the SBS gain are obtained for the new phosphate glass KGSS 0180 (g = 1.9 cm/GW) and for the GLS 22 (g = 1.4 cm/GW), K8 (g = 1.3 cm/GW), and KU2 (g = 1.5 cm/GW) glasses, which are widely used in laser systems. The SBS frequency shift of radiation with a wavelength of 1.054 μm (14.57±0.02 GHz) and the hypersonic velocity (5030 m/s) have been determined for the KGSS 0180 glass by optical heterodyning. The relaxation time of hypersound in the noted media is estimated.

Experimental study of a broad-band XeCl double-pass amplifier with SBS mirror

An oscillator-amplifier XeCl laser system has been used to experimentally investigate the effectiveness of a liquid stimulated Brillouin scattering (SBS) mirror for correcting the spatial aberrations of broad-band laser radiation in a double-pass amplifier. It has been found that the SBS amplifier performance is strongly dependent on the intensity Ip exciting the Brillouin medium. A good beam reconstruction has been attained at Ip≤1GW/cm2, whereas highly aberrated output beams have been delivered by the SBS amplifier for Ip>1 GW/cm2. By comparing the broad-band SBS amplifier performance to that of the same amplifier with a dielectrically coated flat mirror at one end, it has been found that the use of a SBS mirror is advantageous to obtain lower divergence output beams only for low energy pump beams (<1 mJ).

Phase conjugation as a result of stimulated Brillouin scattering in an oscillator–amplifier system with a nonlinear filter

Methods of inducing a negative feedback by frequency doubling in a phase conjugation system comprising a stimulated Brillouin scattering (STBS) oscillator and an STBS amplifier were proposed and investigated experimentally.

Effect of laser mode structure on stimulated Brillouin scattering

The gain and reflectivity of the stimulated Brillouin scattering (SBS) process used as a Stokes-wave generator are shown theoretically to be independent of the mode structure of the pump laser provided that the pump-laser mode spacing exceeds the Brillouin linewidth and that the laser coherence length exceeds the characteristic gain length of the SBS process. Under the same set of conditions, the gain of an SBS amplifier is found to depend on the degree of correlation between the laser and Stokes fields. However, due to nonlinear coupling, these two fields become correlated within several characteristic gain lengths, and the subsequent propagation of the two fields is governed by the same set of equations that apply for the case of a single-mode pump laser. These theoretical predictions are tested experimentally for an SBS generator using acetone, carbon disulfide, and methanol as the Brillouin-active media, and the results are in full agreement with the theoretical predictions.

A review of stimulated Brillouin scattering excited with a broad-band pump laser

Stimulated Brillouin scattering (SBS) excited by a pump laser with a bandwidth large compared to the Brillouin linewidth is reviewed. SBS amplifier results show that either for low gain or for short pulses, the broad-band SBS gain is substantially lower than the steady-state gain. In the high gain limit, however, the fast phase fluctuations that are typical of a broad-band pump have a small effect on amplifier gain. Results for SBS that grows from noise show that fast pump phase fluctuations affect the gain only under two conditions. The first is when the coherence length of the pump is shorter than the gain length in the SBS medium. The second is when the pump is made up of two or more temporal modes separated by more than the SBS linewidth and aberrated with independent spatial profiles. In this case, the quality of wavefront inversion may be badly degraded as well. Areas for further work, including competing nonlinearities, are discussed.