Stimulated Brillouin Scattering Suppression Research Articles

SBS Suppressed Fiber With Hole-Assisted Structure

This paper describes a fiber design that incorporates a hole-assisted structure for suppressing stimulated Brillouin scattering (SBS). The proposed hole-assisted fibers (HAFs) have a simple structure with a low relative index difference and/or a small core radius. We suppress the SBS by extending the optical field into the cladding region, which reduces the overlap between a lightwave and an acoustic wave both in the fundamental mode. The bending loss remains low because of the optical field confinement provided by the air holes. We discuss the impact of the core profile on the SBS gain spectrum and show numerically a 13.5 dB improvement in the SBS threshold with both a low SBS gain and a large effective area. Moreover, we show that we can realize SBS suppressed HAF with a low bending loss and almost the same mode field diameter as SSMF by designing the air hole structure. Finally, we experimentally confirm the SBS suppression effect by using the fabricated HAF.

SBS threshold measurements and acoustic beam propagation modeling in guiding and anti-guiding single mode optical fibers

A 4.3 dB stimulated Brillouin scattering (SBS) threshold suppression is measured in a passive Al-doped acoustically anti-guiding single mode optical fiber relative to that of a Ge-doped acoustically guiding single mode optical fiber. Stimulated scattering is generated by the electrostrictive acoustic wave generated in the fiber core. This acoustic excitation has a decay length L(d) related to the sound absorption decay length L(abs) and the acoustic waveguide decay length L(wg) by: L(d)(-1)= L(abs)(-1)+ L(wg)(-1). The acoustic waveguide decay length L(wg) is associated with the diffraction, refraction and reflection of the acoustic wave in the elastically inhomogeneous optical fiber cores. The SBS gain is proportional to the net acoustic decay length L(d) and the relative SBS suppression is proportional to the ratio of the net decay lengths of the Al and Ge doped cores (L(Al)/ L(Ge)). An acoustic beam propagation model is used to calculate the evolution of the complex acoustic excitations in the optical cores and determine the acoustic wave decay lengths L(wg). Model predictions for the relative SBS suppression for the two fibers are in good agreement with experimental values obtained from Stokes power and optical heterodyne linewidth measurements.

Optical Fibers With Tailored Acoustic Speed Profiles for Suppressing Stimulated Brillouin Scattering in High-Power, Single-Frequency Sources

In this paper, we discuss the design of optical fibers with tailored acoustic speed profiles to suppress stimulated Brillouin scattering in high-power, single-frequency sources. We demonstrate the ability of these fibers to achieve single-mode output powers of greater than 500 W and discuss the potential to achieve powers beyond 1 kW.

光纤中基于多频相位调制的受激布里渊散射抑制

The method of generating equal-amplitude spectral lines by multi-frequency phase modulation is used in stimulated Brillouin scattering (SBS) suppression. The spectra of three, five, seven, and eleven equal-amplitude spectral lines are obtained in experiment with flatnesses less than 0.3 dB. Theoretical research on SBS suppression shows that the threshold power after modulation is in reverse proportion to the maximum square of amplitude moduli of fundamental frequency and the nth harmonic wave. The threshold powers of three, five, seven, and eleven equal-amplitude spectral lines are improved by 5.21, 8.36, 9.39, and 10.76 dB, respectively.

基于四波混频效应的差分相移键控信号波长转换的数值分析

We numerically investigate the main constrains for high efficiency wavelength conversion of differential phase-shift keying (DPSK) signals based on four-wave mixing (FWM) in highly nonlinear fiber (HNLF). Using multi-tone pump phase modulation techniques, high efficiency wavelength conversion of DPSK signals is achieved with the stimulated Brillouin scattering (SBS) effects effectively suppressed. Our analysis shows that there is a compromise between conversion efficiency and converted idler degradation. By optimizing the pump phase modulation configuration, the converted DPSK idler's degradation can be dramatically decreased through balancing SBS suppression and pump phase modulation degradation. Our simulation results also show that these multi-tone pump phase modulation techniques are more appropriate for the future high bit rate systems.

Suppression of stimulated Brillouin scattering in high-power single-frequency multicore fiber amplifiers

To describe the interplay between the first-order Stokes, pump, and signal in the multicore fiber amplifier, a set of differential equations is presented. The model takes into account the dependence of the stimulated Brillouin scattering (SBS) on the pump-induced temperature distribution along the fiber. The influence of pump schemes, pump powers, convective coefficient, density of the rare earth dopant ( N) and fiber length on suppression of the SBS is studied. The backward pump scheme has advantage over forward pump scheme in suppression of SBS. For the SBS gain spectrum, reducing convective coefficient can decrease the maximum SBS gain and increase the frequency detuning corresponding to the maximum SBS gain. Increasing N can lead to higher slope efficiency and shorter optimal fiber length, which can further suppress SBS. The SBS gain ( G) and maximum operating temperature are compared between the single core fiber amplifier and multicore fiber amplifier with the same optimal fiber length. Compared to the single core fiber amplifier, the multicore fiber amplifier has lower maximum operating temperatures, which provide more space for further increasing output power.

Suppression of Stimulated Brillouin Scattering by Increased Landau Damping in Multiple-Ion-Species Hohlraum Plasmas

We demonstrate that multiple-ion-species plasmas greatly reduce stimulated Brillouin scattering (SBS) in high-electron temperature inertial confinement fusion hohlraums. Landau damping is increased by adding hydrogen to a CO(2) gas filled hohlraum. We find that the SBS reflectivity decreases monotonically with increasing hydrogen fraction from 18% to 3% with a simultaneous increase of laser beam transmission. Detailed simulations with a 3D laser-plasma interaction code are in agreement with the experimentally observed reduction in backscattered light.

Suppressing stimulated Brillouin scattering in fiber amplifiers using nonuniform fiber and temperature gradient

A nonuniform large mode area fiber having an larger core at most locations to reduce power intensity and having a relatively smaller core at certain locations to reduce bending sensitivity is proposed for suppression of stimulated Brillouin scattering (SBS) in a high power fiber amplifier. A comprehensive model taking into account fiber nonuniformity, profile and temperature gradient shows that the fiber can achieve kilowatt output at a temperature gradient of >250 degrees C. Compared with a conventional large mode area fiber, a total of 7 dB SBS suppression can be achieved using this unique fiber.

Suppression of stimulated Brillouin scattering in high-power single-frequency fiber amplifiers

The effect of temperature variation along a high-power fiber amplifier on the stimulated Brillouin scattering (SBS) threshold is considered theoretically. We show that for an end-pumped rare-earth-doped double-clad fiber the inhomogeneous distribution of temperature, which is caused by the absorption of pump radiation, may result in total suppression of SBS even for output powers well above 200 W.

Bismuth nonlinear fibre-based optical phase conjugator without SBS-induced efficiency limitation and its application to dispersion compensation in transmission link

The implementation of a stimulated Brillouin scattering (SBS) free, optical fibre phase conjugator by use of only 1 m length of fabricated bismuth oxide-based nonlinear fibre (Bi-NLF), has been experimentally demonstrated. A high OSNR phase-conjugated signal was readily achieved owing to the unique properties of the Bi-NLF such as an ultra-high χ(3) nonlinearity and a high SBS threshold although no SBS suppression scheme was employed. Using the phase conjugator, error-free transmission of the signal is readily achieved over a 150 km SMF link.

Linearly-polarized single-transverse-mode high-energy multi-ten nanosecond fiber amplifier with 50W average power

A linearly polarized single-transverse-mode Yb-doped double clad polarization-maintaining fiber amplifier at 1064nm is reported, which delivers 53.1W average power at 40kHz repetition rate, with pulse energy >1mJ, duration 30ns, polarization extinction ratio 13dB, and M(2)1.2. Stimulated Brillouin scattering (SBS) phenomenon during amplification is discussed, and a new SBS suppression approach using linewidth broadening induced by self-phase modulation (SPM) is demonstrated.

Stimulated Brillouin scattering suppression using cross-phase modulation induced by an optical supervisory channel in WDM links

A stimulated Brillouin scattering (SBS) suppression method is proposed for wavelength-division-multiplexed (WDM) links, based on the cross-phase modulation (XPM) effect induced by an optical supervisory (SV) channel. Since the XPM on each signal channel is induced by the 52-Mb/s optical SV channel, the SBS suppression is nearly insensitive to WDM signal channels. We experimentally demonstrate that the proposed method can increase the SBS threshold and reduce the error floors irrespective of the bit rate, channel power, channel wavelength, and channel spacing of the WDM channels.

Increase of the SBS threshold in a short highly nonlinear fiber by applying a temperature distribution

We evaluate numerically and experimentally the stimulated Brillouin scattering (SBS) threshold increase for a short, highly nonlinear GeO/sub 2/-doped fiber by applying different temperature distributions along the fiber. The temperature coefficient for the Brillouin frequency downshift is measured to 1.2 MHz//spl deg/C. A threefold SBS threshold increase is obtained for a 100-m long highly nonlinear fiber with a 140/spl deg/C temperature gradient. The proposed scheme is implemented in a wavelength converter based on fiber optical four-wave mixing (FWM). The SBS suppression scheme shows negligible influence on the FWM efficiency as well as the wavelength conversion bandwidth. The temperature coefficient for the zero dispersion wavelength is measured to 0.062 nm//spl deg/C.

Degradation of modulation and noise characteristics of semiconductor lasers after propagation in optical fiber due to a phase shift induced by stimulated Brillouin scattering

Here we demonstrate theoretically that stimulated Brillouin scattering (SBS) can induce a phase shift of the optical carrier relative to its sidebands due to the waveguiding effect of the optical fiber on the acoustic wave. This causes conversion of frequency modulation to intensity modulation, which results in an increase in the relative intensity noise and degradation of the modulation response of directly modulated lasers after propagation in an optical fiber, in agreement with our experimental observations. Suppression of SBS can be achieved at low frequencies and high modulation powers due to the laser adiabatic chirp.

SBS Suppression Using a Multichannel Tunable Laser with Data-Encoding Capability

We demonstrate stimulated Brillouin scattering (SBS) using a new laser transmitter. The device uses an integrated FM modulator for both SBS suppression and channel tuning, and an integrated AM modulator for data encoding. We measure thresholds of 25 dBm on four separate wavelength division multiplexing channels. The required modulation signal is very small, 95 mVpp, and the residual AM is only 1 %.

New SBS suppression fiber with uniform chromatic dispersion to enhance four-wave mixing

A new type of stimulated Brillouin scattering (SBS) suppression fiber has been developed whose dopant concentration and core radius are nonuniform along its length. The chromatic dispersion distribution is kept uniform along its length by varying the core radius in accordance with the /spl Delta/ value to enhance four-wave mixing (FWM) intentionally. The output power of the FWM signal with this fiber was about 15 dB higher than that with a conventional disperion-shifted fiber when the input power was 15 dBm, which is just above the SBS threshold power.

SBS and MPI suppression in analogue systems with integrated electroabsorption modulator/DFB laser transmitters

The performance of analogue CATV systems using narrow linewidth sources and low-chirp modulation is limited by low power-thresholds for stimulated Brillouin scattering (SBS) and excess noise from multipath interference (MPI). Using a low-chirp linearised integrated DFB laser/electroabsorption modulator as a transmitter, the authors have increased the SBS threshold by 5 dB to +13.6 dBm fibre launch power and suppressed MPI by dithering the laser bias current at 1.7 GHz.

Fundamental investigation of stimulated brillouin scattering suppression by fiber cabling

AbstractOne of the main factors preventing the increase of the input power of optical fibers is the saturation of the input power by stimulated Brillouin scattering (SBS). In this paper, theoretical and experimental investigations are performed of three methods for suppressing SBS. the first method is to enlarge the optical fiber Brillouin gain bandwidth by applying a periodic strain distribution in the longitudinal direction of an optical fiber using the structure of the optical fiber cables. the second method is to shift the frequency of the Brillouin gain spectrum by connecting fibers with different core dopant concentrations. the third method is the combination of the two methods described above.In the cable described in this paper, a sinusoidal strain distribution was induced in the fibers with a maximum strain amplitude of 0.4 percent and a pitch of 600 mm by using a double‐stranded structure. By doing so, the Brillouin gain bandwidth could be enlarged up to 400 MHz. Also, a frequency difference of 580 MHz is induced by connecting fibers with a dopant difference of a maximum of 4.4 percent between each fiber. It is shown that the SBS can be suppressed upto a CW optical input power of +17.4 dBm by widening the bandwidth and connecting optical fibers with shifted bandwidths. There fore, it is concluded that the proposed method is effective and practical for SBS suppression.

Maximum repeaterless transmission of lightwave systems imposed by stimulated Brillouin scattering in fibres

To aid in designing high-speed optical networks, the fundamental limitations of lightwave transmission systems are investigated from the viewpoint of fibre nonlinearities, particularly of stimulated Brillouin scattering (SBS). When SBS occurs, the fibre launch power is usually restricted; thus, SBS is detrimental to lightwave systems. The effects of SBS on signals transmitted in fibres are clarified for several modulation schemes, especially coherent modulation schemes. A generalized model based on the maximum power spectrum density in the signals is proposed to estimate the degree of SBS generation. The maximum repeaterless transmissions for various bit rates, laser diode linewidths, and Brillouin gains of optical fibres are presented. The degradation of transmission due to SBS is clarified experimentally, focusing on the bit error rate, fibre input power, and spectra of signals transmitted in fibres. In addition, various techniques for suppressing the SBS effects are proposed. A repeaterless transmission experiment conducted over 364.3 km using optical booster amplifiers is presented to verify the effectiveness of the SBS suppression technique.

Suppression of stimulated Brillouin scattering in a fibre by changing the core radius

Stimulated Brillouin scattering (SBS) in a fibre is suppressed by making the core radius nonuniform along its length to utilise the core-radius dependence of the longitudinal acoustic frequency. The effective Brillouin gain of an SBS suppression fibre prepared by the VAD method was reduced by 3.5 dB compared with conventional fibres.