Stimulated Brillouin Scattering Effect Research Articles

Preliminary theoretical analysis of multi-wavelengthlaser active coherent beam combination

In active coherent beam combination (CBC), a single-frequency seed laser is often considered to be indispensable for improving the spatial coherence property and obtaining high brightness in the far field. Nevertheless, the single-frequency radiation restricts the output power of coherently combined fiber amplifiers, owing to low stimulated Brillouin scattering (SBS) threshold. The seed laser oscillating at different frequencies proves to have the potential in mitigating SBS effects in fiber amplifiers, and therefore it is able to increase the emission power of CBC greatly. In this study, the basic mathematical model is founded on the basis of the fundamentals of CBC, and the multi-wavelength two-channel CBC estimation formula is proposed on the calculation of some two-channel examples. The optical path difference is the key factor in multi-wavelength CBC. We propose the concepts of "controllable area" and "uncontrollable area" for the optical path difference. If and only if the optical path difference falls into the controllable area, desirable combination effects can be obtained by the active control. In the case of getting the value of optical path difference randomly, excellent combination effects can still be gained and the probability has a close correlation with the spectrum profile, which is inversely proportional to the number of wavelengths approximatively. The multiple control method is competent for the multi-wavelength CBC. In this method, the optical path difference is adjusted into the controllable area by large optical path controllers and then the phase of each channel is locked by precise optical path controllers.

Analysis of bottlenecks in DWDM fiber optic communication system

This paper deals with the limiting factors like Stimulated Brillouin Scattering (SBS), Stimulated Raman Scattering (SRS) and Four Wave Mixing (FWM) in DWDM Fiber Optic Communication. The variation of SBS threshold power level for the spectral width of the source is analyzed and it is found that addition of spectral width in the source lowers the SBS effect. By reducing the SBS effect, we could transmit more optical power in a single channel and maintain high OSNR. Similarly the effect of phase mismatching (dispersion) and wavelength spacing on both FWM and SRS are analyzed. This work aims at finding the optimal value of spectral width, dispersion and channel spacing, thereby exploring the possibilities of increasing the overall capacity of the fiber optic trunk line.

The Effect of Stimulated Brillouin Scattering on WDM-PON

The existing TDM-PON (Time-Division Multiplexing Passive Optical Network) technologies like EPON (Ethernet PON) or GPON (Gigabit PON) have limitations of bandwidth due to the concept of time division .The bit rate can only be enlarged increasing the speed of the common channel (10G EPON). Another way of achieving the bandwidth growth is the use of WDM (Wavelength Division Multiplexing) technology .The main problem of the WDM-PON is the ability to use the existing cable plant with high losses due to power splitters. Hybrid TDM/WDM-PON conception is the only way of upgrading of the existing technologies. However, there is a lack of power budget to enlarge a number of wavelengths and the splitting ratio. The easiest way of enlarging the power margin is the increase of inserted power. The main limitation is SBS (Stimulated Brillouin Scattering), which scatters all the power after the threshold. The paper contains: SBS threshold measurement and comparison with theoretical data, the evaluation On-Off Keying effect on SBS threshold, calculation of maximum power budget and channel (client) number limited by SBS for 16-channel TDM/WDM-PON system based on SBS threshold measurement data.

High performance laser linewidth broadening for stimulated Brillouin suppression with zero parasitic amplitude modulation

To enable optimum network transmission, the ideal is to launch as high laser power as possible into the optical fiber, to overcome the effects of fiber attenuation and maintain an acceptable signal to noise ratio. Launching high powers into a fiber however, results in unwanted nonlinear effects. Stimulated Brillouin scattering (SBS) is one of the nonlinear effects which reflects a significant proportion of the transmitted optical power back to the transmitter, degrading the system severely. This paper reports the development of a digitally selected supermode distributed Bragg reflector monolithic laser chip which can provide significant linewidth broadening using a pure frequency modulation technique by application of a dither current. By modifying a small segment of the laser chip material refractive index, it produces a modulation of the longitudinal mode and hence laser frequency; the monolithic laser chip has reduced the effects of SBS significantly with very little parasitic amplitude modulation.

Effects of Nonlinear Stimulated Brillouin Scattering on Performance Analysis of an Optical CDMA Transmission System

We conducted a computer simulation study to assess the effects of Stimulated Brillouin Scattering (SBS) on performance analysis of optical CDMA based on Enhanced Double Weight (EDW) code. It has been observed that SBS causes backward scattering of transmit signal and this in turn causes a reduction of received power and limitation improvement for the bit error rate. The maximum transmission distance is evaluated for optical CDMA based on BER equal to 10 -9 and transmitted power into fiber below SBS threshold power. Also in this paper, we demonstrate how the speed of data transfer, directly modulated technique and effective core area of optical fiber transmission influence the Brillouin threshold power in optical CDMA system.

Investigation of Nonlinear Effects in Multitone-Driven Narrow-Linewidth High-Power Amplifiers

In this paper, we investigate two approaches to multitone seeding of high-power ytterbium-doped amplifiers using a symbolic and numerical code that solves a two-point boundary problem. Optimization of amplifier action through wavelength separation and/or seed power ratios is considered in relation to the two most dominant nonlinear effects: stimulated Brillouin scattering (SBS) and four-wave mixing. One approach uses a large wavelength separation among the input signals, while the other approach entails that the wavelength separation is set to twice the Brillouin shift. Both techniques are shown to mitigate SBS effects, although for the latter case, four-wave mixing sidebands can carry a substantial amount of power.

包层抽运掺镱光纤激光器中受激拉曼散射和受激布里渊散射效应

包层抽运掺镱光纤激光器中受激拉曼散射和受激布里渊散射效应

Translation of Gbps Phase-Modulated Optical Signal From Near-Infrared to Visible Band

Phase-coded optical signal was spectrally translated from the conventional near-infrared communication band to the visible band. Spectrally narrow 780-nm pump was combined with phase-modulated 1575-nm signal in a small core photonic crystal fiber (PCF), to generate 518-nm idler through parametric process. The phase-modulated idler carrying 1-Gbps information was received in an error-free manner. The onset of the stimulated Brillouin scattering (SBS) was found to be a major limitation for conversion efficiency and noise performance. The SBS effect and the birefringence properties of the small core PCF were studied at both 780 and 1550 nm and their impact on the parametric process was analyzed.

Performance of WDM fiber-radio network using distributed Raman amplifier

We investigate the impairment induced by stimulated Brillouin scattering (SBS) effect and noise characteristics of wavelength-division-multiplexing fiber-radio network assisted by distributed Raman amplifier (DRA) or erbium-doped fiber amplifier. Experimental results indicate that forward-pumping DRA can increase the link optical output power limited by SBS effect in downstream transmission and backward-pumping DRA can improve signal-to-noise ratio in upstream transmission, which is verified by binary phase-shift keying transmission experiments. Moreover, our experimental results show that DRA does not introduce additional impairment from interchannel crosstalk due to cross-phase modulation and degradation in spur-free dynamic range.

Experimental validation of double-pass discrete Raman amplifier limitation for large signals

In this letter, we present a report on the experimental validation of double-pass discrete Raman amplifier (DRA) limitation for large signals. It has been proven that the limitation of double-pass Raman amplifier for large signals is due to stimulated Brillouin scattering (SBS) even though with a modulated signal at 10-Gb/s data. The multichannel amplification shows that this limitation can be relaxed due to energy distribution among the channels, the SBS threshold is enhanced. An average gain of 19.2 dB is obtained in four-channel amplification without any significant SBS effects. The double-pass DRA is found suitable for large signals to be deployed in wavelength division multiplexing systems

Non-linear transmission effects in duobinary and dicode optical systems

This paper presents optical duobinary and dicode signalling, as alternatives to the binary format, in order to improve the transmission performance in the presense of non-linear effects in a dense wavelength division multiplex (WDM) optical system. Duobinary signalling is applied to an optical system to explore the reduction of stimulated Brillouin scattering (SBS) effects. Duobinary signalling suppresses the SBS effects, and an eye-opening improvement of 0.25 to 1.2 dB is achieved relative to binary transmission over a range of input power levels. An experimental study demonstrates that duobinary modulation suppresses the four wave mixing (FWM) products of a dense WDM system by a maximum of 3 dB. The suppression is maintained over a range of channel spacings. An investigation of the impact of fibre dispersion on FWM products under binary, duobinary and dicode modulation in a dense WDM system is then performed, with interchannel spacing and optical power variation. This leads to the development of a set of guidelines for the application areas, in which it is appropriate to use duobinary or dicode modulation in WDM systems as a means of mitigating the impact of FWM.

Investigation of stimulated Brillouin scattering effects in radio-over-fiber distribution systems

Stimulated Brillouin scattering (SBS) imposes a limitation on the transmitted power in radio-over-fiber (RoF) distribution systems. By employing an optical filter at the transmitter that converts the optical microwave signal to single sideband format (in order to overcome dispersive fading), it is also possible to reduce the effect of SBS on system performance. In this paper the authors compare the cases of filtering the optical microwave signal at the transmitter or the remote site of a RoF system, in terms of the effect of SBS on system performance. The authors also investigate and demonstrate how the modulation depth of the optical-microwave data signal influences the Brillouin threshold in RoF distribution systems.

Observation of pulse delaying and advancement in optical fibers using stimulated Brillouin scattering

We demonstrate experimentally that it is possible to control optically the group velocity of an optical pulse as it travels along an optical fiber. To achieve this control we use the effect of Stimulated Brillouin Scattering. In our experiments we have achieved changes in the group index of 10-3 in several kilometer-length fibers, thus leading to pulse delaying and advancement in the range of tens of nanoseconds. We believe that this is the first evidence of such optically-controlled strong delay changes in optical fibers. In this paper we derive the basic theory behind these group-delay changes and we demonstrate the effect in two kinds of fibers which are conventionally used.

STIMULATED BRILLOUIN SCATTERING IN THE MIDINFRARED REGION OF THE SPECTRUM

The behavior of optical‐medium parameters governing the efficiency of stimulated Brillouin scattering (SBS) with an increase in the pump‐radiation wavelength is studied, and the range of media promising for accomplishing the phase self‐conjugation in the course of SBS in the midinfrared region of the spectrum is determined. The SBS effect in the 10‐μm region is realized experimentally in a fiber waveguide made of KRS‐5. The result obtained is in good agreement with the calculated SBS gain (0.14 cm/MW) and decay time of sound (∽200 ns) in KRS‐5. It is noted that the attainment of fairly high efficiencies of SBS reflection and phase self‐conjugation for the above‐threshold intensities of excitation are controlled only by the level of technology for fabrication of fiber waveguides from infrared materials, the properties of which can still be much improved.

Thermally Induced Effects of Stimulated Brillouin Scattering via Phase-Conjugation Mirror for Repetitive Laser Pulse.

We designed and demonstrated two new schemes to improve the performance of stimulated Brillouin scattering (SBS) cells for a high average power laser. By introducing a lamellar flow cell, thermallyinducedefocusingand convection via laser light absorption were removed. By inserting a rotational wedge plate, the spot wasrotated in time and locate heat sources were diffused. As a result, the SBS reflectivity and fidelity wereimproved dramatically with acetone. Using the cell, the operational power can be improved by as much asseveral hundred times the closed-type. If a medium with a small absorption coefficient such asheavy fluorocarbonsis used, the phase conjugate performance enables the incident power to reach a kW level.

Dynamic stimulated Brillouin scattering analysis

We present a new simple analysis-including the effect of spontaneous emission-of the (dynamic) influence of stimulated Brillouin scattering (SBS) on the detected receiver eye diagram. It applies in principle for general types of modulation formats such as the digital formats of amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK). The analysis is formulated for a determination of the signal power depiction and intersymbol interference (ISI) caused by the combined effect of fiber dispersion, fiber attenuation and nonlinear fiber effects such as the effect of self-phase modulation (SPM) and SBS. The analysis allows a quantification of the dithering influence on the SBS threshold. Representative numerical examples are presented for two single-channel ON-OFF modulated 10-Gh/s systems utilizing Franz-Keldysh and Mach-Zehnder-type modulators.

Effect of dynamic stimulated Brillouin scattering on millimeter-wave fiber radio communication systems

The effect of dynamic stimulated Brillouin scattering (SBS) on millimeter-wave fiber radio communication systems has been studied and compared with results by steady-state analysis (SSA). More information is provided by the dynamic SBS analysis as the probability density functions (pdf's) of both SBS power and received signal can be calculated approximately. The worst-case power by SSA overestimates the effect of SBS greatly while the average power by SSA underestimates it. The dynamic SBS analysis, therefore, should be used for estimating the effect of SBS on millimeter-wave fiber radio communication systems, especially for low bit rate and short length ones.

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.

Overmodulation of intensity modulated signalsdue to stimulated Brillouin scattering

The authors give the first report of stimulated Brillouin scattering (SBS) in optical fibres causing waveform distortion in intensity modulated (IM) optical signals. The effect of SBS on an IM optical signal is experimentally verified. SBS was found to induce overmodulation of the optical signal. >

Transmission limitations of CPFSK coherent lightwave systems due to stimulated Brillouin scattering in optical fiber

Transmission limitations imposed by stimulated Brillouin scattering (SBS) are investigated for repeaterless coherent lightwave systems, particularly for continuous phase-shift keying (CPFSK). The effects of SBS on the modulated signals in optical fibers are studied for CPFSK, amplitude shift keying (ASK), and phase shift keying (PSK). A generalized model based on the maximum power spectrum density (PSD) in the modulated signals is proposed for SBS analysis. This model is useful to estimate the Brillouin gain and its threshold to determine the optical power limitation of the fiber for any modulated signal with non-negligible linewidth. It is clarified theoretically that the Brillouin gain with CPFSK approaches that with ASK and PSK at higher bit rates if the modulation index is 1 and 0.65, respectively. The dependency of Brillouin gain on bit rate and linewidth of a laser diode transmitter are evaluated. SBS induced by CPFSK modulated signals was measured to clarify the modulation condition dependences and to verify the model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>