Double Rayleigh Backscattering Research Articles

Studying the Double Rayleigh Backscattering Noise Effect on Fiber-Optic Radio Frequency Transfer

We report the effect of the double Rayleigh backscattering (DRB) noise, in which the interference of the signal light with the double Rayleigh backscattered light, on the fiber-optic radio-frequency (RF) transfer system. Here, we theoretically analyze and experimentally demonstrate that the DRB noise within the fiber link will become the dominative noise on the fiber-optic RF transfer system once narrow linewidth lasers are used. The strong DRB noise is experimentally confirmed through the measurement of the effect of the coherent interference term of the signal light and the double Rayleigh backscattered light on the 100 km RF transfer system. Our results provide evidence that the conventional RF transfer technique with the telecommunications-grade lasers, in which the chromatic dispersion effect in the single-mode fiber is compensated by dispersion compensation fibers (DCFs), could be the better choice for high-performance RF transfer.

Gain-forming effect on optical signal-to-noise ratio in Raman fiber amplifier

Abstract We have introduced the comprehensive optical-to-noise ratio (OSNR) to investigate simultaneously the effects of all three major linear noise sources in distributed Raman fiber amplifier (DRFA). The total noise power contains double Rayleigh backscattering (DRB) noise, amplified spontaneous emission (ASE) noise, and relative intensity noise (RIN). Also, we have introduced an approximated gain profile approach, which helps in evaluating the OSNR for higher-order pumping (HOP) configuration for backward, forward, and bidirectional DRFA schemes. Finally, by applying the dynamic and static full-numerical computations on a system of eight wavelength division multiplexing (WDM) channels (for amplifier lengths of 70, 140, and 210 km), we demonstrated that for RIN frequencies greater than 100 kHz, the higher-order bidirectional pumping scheme exceeds the backward schemes by 12 dB.

Performance analysis of distributed fiber Raman amplifiers employing higher order pumping schemes in optical transmission systems

Performance of fiber Raman amplifier is explored with special emphasis on higher order pumping configurations for wavelength division multiplexed optical transmission systems. The amplification analysis is done in terms of equivalent noise figure (ENF), optical signal-to-noise ratio (OSNR), and double Rayleigh backscattering (DRBS) noise powers. The investigations reveal that at 36 dB on--off gain, ENF improvement of 1 dB (using second order pumping) and of 2 dB (using third order pumping configuration) can be achieved. On similar lines, by varying input optical power and fiber length, OSNR and DRBS are reported for the higher order of pumping configurations. Overall, the work presents improvements of about 1 dB in ENF and 0.03 dB in OSNR. These investigations are produced at lower input signal powers.

Research on the [formula omitted]-OTDR fiber sensor sensitive for all of the distance

In this paper, a modified construction for the traditional ϕ-OTDR fiber sensor sensitive for all of distance is presented, the related numerical simulation and experiment analysis results show that this construction can reduce the gain imbalance for all of the distance along the fiber caused by the Rayleigh scattering loss of the fiber and the gain imbalance of Raman fiber amplifier in this fiber sensor system. In order to improve further the vibration sensitivity of this system, the possible methods to restrain the influences of modulation instability effect, Stimulated Brillouin effect, reduce the amplified spontaneous emission (ASE) noises of Raman laser (RL) and Erbium3+-doped fiber amplifiers (EDFA), double Rayleigh backscattering noise in this system are discussed, which will offer a great reference value for the science research and engineering application in the field of fiber sensor as we believe.

Characterization and Optimization of Unrepeatered Coherent Transmission Systems Using DRA and ROPA

We present a detailed investigation of the singe-channel 100G polarization-multiplexed quadrature-phase-shift-keying-based unrepeatered coherent transmissions using various order distributed Raman amplifiers (DRAs). The impact of main factors on the system performance is discussed including intrachannel nonlinearity, amplified spontaneous emission, double Rayleigh backscattering, and pump relative intensity noise (RIN)-induced impairments. After optimizing the pump power configuration, it is found that compared to a first- and a third-order DRA, a second-order DRA can provide the best performance owing to relative high optical signal-to-noise ratio (OSNR) and low pump RIN-induced penalty. By using the Giles model, the optimization of a remote optically pumped amplifier is performed in terms of the Erbium-doped fiber length and its farthest position, with given input signal's power and OSNR.

High-Precision Ultralong Distance Time Transfer Using Single-Fiber Bidirectional-Transmission Unidirectional Optical Amplifiers

This paper demonstrates a fiber-optic time transfer over a 6000 km noncalibrated fiber link using proposed single-fiber bidirectional-transmission unidirectional optical amplifiers (SFBT-UOAs). The proposed SFBT-UOA employs a 2 × 2 optical switch to enable the time-division-multiplexed time signals for both directions to pass through the same UOA in different time slots. The bidirectional delay symmetry is guaranteed to the maximum extent by allowing the time signals to be transmitted back and forth using the same wavelength over a single fiber. Meanwhile, the noises suffered in the systems employing single fiber bidirectional optical amplifiers (SF-BOAs), such as double Rayleigh backscattering, are effectively suppressed. Consequently, high-precision fiber-optic time transfer can be implemented over ultralong distance by adopting the proposed SFBT-UOAs. Moreover, the SFBT-UOA can support the conventional network services via wavelength division multiplexings (WDMs) and, therefore, offers the potential to perform high-precision time transfer over long-haul commercial fiber links. Over 6000 km, the measured time deviations of fiber-optic time transfer in the laboratory are less than 190 ps/s and 61 ps/105 s, respectively. The calculated combined uncertainty is not beyond 70 ps, which agrees well with the experimental verification over the noncalibrated fiber link.

Algebraic cancellation of polarisation noise in fibre interferometers.

This experiment uses digital interferometry to reduce polarisation noise from a fiber interferometer to the level of double Rayleigh backscatter making precision fiber metrology systems robust for remote field applications. This is achieved with a measurement of the Jones matrix with interferometric sensitivity in real time, limited only by fibre length and processing bandwidth. This new approach leads to potentially new metrology applications and the ability to do ellipsometry without polarisation elements in the output field.

Noise induced in optical fibers by double Rayleigh scattering of a laser with a 1/f^ν frequency noise

We study, theoretically and experimentally, intensity noise induced by double Rayleigh scattering in long optical fibers. The results of the theoretical model are compared to experimental results performed with a high-coherence-length laser with a frequency noise spectrum that is dominated by 1/fν noise. Excellent quantitative agreement between theoretical and experimental RF spectra were obtained for frequencies as low as 10 Hz and for fiber lengths between 4 and 45 km. Strong low-frequency intensity noise that is induced by 1/fν frequency noise of the laser may limit the performance of interferometric fiber optic sensors that require high-coherence-length lasers. The intensity noise due to double Rayleigh backscattering can be suppressed by reducing the coherence length of the laser. Therefore, the intensity noise has a complex and non-monotonic dependence on the 1/fν frequency noise amplitude of the laser. Stimulated Brillouin scattering will add a significant noise for input powers greater than about 7 mW for a 30 km length fiber.

Suppressing Rayleigh backscatter and code noise from all-fiber digital interferometers

We configure an all-fiber digital interferometer to eliminate both code noise and Rayleigh backscatter noise from bidirectional measurements. We utilize a sawtooth phase ramp to upconvert code noise beyond our signal bandwidth, demonstrating an in-band noise reduction of approximately two orders of magnitude. In addition, we demonstrate, for the first time to our knowledge, the use of relative code delays within a digital-interferometer system to eliminate Rayleigh-backscatter noise, resulting in a noise reduction of a factor of 50. Finally, we identify double Rayleigh-backscatter noise as our limiting noise source and suggest two methods to minimize this noise source.

Combined Effect of ASE and DRBS on Noise in Pulse-Pumped Fiber Raman Amplifiers

Amplified spontaneous emission (ASE) and double Rayleigh backscattering (DRBS) degrade the effective noise figure (ENF) and ultimately limit the performance of fiber Raman amplifiers (FRAs). This limitation is especially severe when a time-division-multiplexed (TDM) pumping scheme is employed. In this paper, we theoretically study the joint impact of ASE and DRBS on ENF in pulse-pumped FRAs. We demonstrate that the ASE is the major source of noise for small pump duty cycles, whereas DRBS dominates when a typical FRA operates in the continuous-wave regime. If the pump power is gradually increased, ENF improves until the gain reaches an optimal value. We show the increase of the optimal gain with pump duty cycle and with decreasing fiber scattering efficiency. Our study reveals the importance of taking into account the effects of both ASE and DRBS for an accurate estimation of ENF penalty in pulse-pumped FRAs, especially operating at high gains when pump duty cycle is small.

Performance of DRA with different pumping schemes based on coupling equation

After the coupling equations of co-pumping, counter-pumping and bidirectional-pumping distributed Raman amplifiers (DRAs) are theoretically analyzed, the power distributions of these three DRAs are acquired with numerical analysis. The performance factors, such as net gain (NG), amplified spontaneous emissions (ASE) noise, double Rayleigh backscattering (DRB) noise, noise figure (NF) and optical signal noise ratio (OSNR), are discussed in depth. It can be found that the NGs of the three DRAs are almost equal. The counter-pumping scheme will induce higher ASE. And the co-pumping DRA has greater DRB noise, but its NF and OSNR are both better than the others’. Furthermore, the relations between signal power and NG, NF, OSNR are also investigated. It is shown that the NF and OSNR of the co-pumping scheme are superior to those of the other two schemes at small input signal power. The above conclusions can play a very important role in guiding the optimum design of DRA.

Influence of double Rayleigh backscatter in CATV systems with Raman amplifiers

The double Rayleigh backscatter (DRB) effect in long distance CATV systems using fiber Raman amplifiers (FRAs) is investigated theoretically in the paper. As a comparison, performance of a system with erbium doped fiber amplifier (EDFA) is also evaluated. According to the simulation results, it is found that, in case of FRA, the increase of carrier-to-noise ratio (CNR) due to the DRB effect will not impair the performance more than that using EDFA.

Analytical Design, Analysis, and Optimization of Raman Fiber Amplifiers With TDM Pumps

In this paper, we analyze Raman amplifiers (RAs) with time division multiplexed (TDM) pumps via an analytical approach. First of all, a detailed analytical solution for the forward and backward propagating waves in the TDM-pumped RAs is presented. Then, the gain of the TDM-pumped RAs is treated analytically. After revealing the nature of resonant gain enhancement, a relatively simple formula of the optimal input pump power configuration is derived via the least squares method. Afterwards, enhanced double Rayleigh backscattering noise and amplified spontaneous emission noise are analyzed and explicit analytical formulas derived. Thereafter, a simple formula to evaluate the impact of the pump modulation is proposed for the design, analysis, and optimization. The analysis of the TDM-pumped RAs highlights the optimization of the parameters of the TDM pumps, such as the pump wavelengths, pump power, and pump modulation frequency as well as the pumping order.

Detailed investigation on gain-clamping characteristics of ultralong fiber Raman laser using FBGs

A comprehensive theoretical model to explore the gain-clamping characteristics of ultralong fiber Raman lasers (UL-FRL) based on fiber Bragg gratings (FBGs) in which the amplified spontaneous emission (ASE), double Rayleigh backscattering (DRB), and modulation-instability- (MI-) induced spectral broadening effect are considered to be self-consistent. The experimental results are used to validate the theoretical model. The influences of pump configuration and fiber length on dynamic range, noise performance, and nonlinear impairment are discussed in detail. The result shows that an ultralong transmission of up to ~155 km by using a total of 1.38 W Raman pump power accompanied by gain clamping can be achieved; a backward pump is helpful to obtain a wider dynamic range and to avoid nonlinear impairment, but it is harmful to noise performance; and shorter fiber length is helpful to obtain both optimized gain clamping and weakened nonlinear impairment. Such an UL-FRL has considerable potential to realize both ultralong signal transmission and gain clamping to overcome signal distortion and interchannel cross talk in dense wavelength division multiplexing (DWDM) networks.

Low-Noise Fiber Raman Amplifiers Based on a Raman Ring Fiber Oscillator

We propose two discrete fiber Raman amplifier schemes using Raman ring fiber oscillator, a two-stage scheme, and a forward pumping scheme, to reduce double Rayleigh backscattering noise at high gains over 20 dB. Both schemes have low noise characteristics compared to a previous scheme. Bit-error-rate measurements at 10 Gb/s show power penalty free operation for the two-stage scheme at a gain of 25 dB.

Bit-Error-Rate Evaluation of the Distributed Raman Amplified Transmission Systems in the Presence of Double Rayleigh Backscattering Noise

A new exact bit-error-rate evaluation method for distributed Raman amplification transmission systems in the presence of both amplified spontaneous emission and double Rayleigh backscattering (DRB) is developed based on a study of statistical characterization of DRB

Full characterization of modern transmission fibers for Raman amplified-based communication systems

Telecommunication carriers have to estimate the Raman parameters of the fibers installed on their optical transport networks in order to facilitate the design of the next generation of high bit-rate Raman amplified-based transmission systems. This paper reports a very complete characterization of the most popular modern transmission fibers in terms of Raman efficiency, noise figure and double Rayleigh backscattering crosstalk. Our experiment is based on an averaged power analysis, applied to a counter-pumped long-haul distributed fiber Raman amplifier. We evaluate as well at 40 Gb/s for these different fiber types the double Rayleigh backscattering impact in terms of Q-factor penalty for various Raman gains and RZ modulation formats with different duty cycles.

Raman amplification characteristics at 850 nm in a silica-based photonic crystal fiber

We achieve a 2.5-dB improvement in the power penalty in a 10-Gb/s-based distributed Raman amplification transmission at 850 nm using a silica-based low-loss photonic crystal fiber (PCF). The experimental results agree well with a signal-to-noise ratio improvement model. The model indicates the negligible influence of double Rayleigh backscattering in the fabricated PCF

Optimal design of distributed Raman amplifiers employed in long-haul optical transmission systems

The optimization of pumping schemes of distributed Raman amplifiers employed in long-haul optical transmission systems is investigated in detail. Considering the received optical signal to noise ratio (OSNR) as well as nonlinear distortion and the optimal signal power distribution, i.e. uniform distribution, is achieved by using variational method. But the analytical optimal distribution does not exist when taking double Rayleigh backscattering (DRB) into account. Comparison between three Raman amplification schemes, i.e. bidirectional dual-order, first-order pumping and Raman-plus-Erbium doped fiber amplifier hybrid amplification, is carried out at identical nonlinear phase shifts. The results show that symmetric bidirectional dual-order pumping can achieve the best OSNR performance through appropriate choice of the second-order pump wavelength and second-to-first-order pump power ratio in most cases for both short- and long-span applications. However, hybrid amplification will be a better choice when the DRnoise is dominant. These results will be helpful for designing long-haul transmission systems.

Design and analysis of a broadband dispersion compensating photonic crystal fiber Raman amplifier operating in S-band

This paper presents an optimized design of a dispersion compensating photonic crystal fiber (PCF) to achieve gain-flattened Raman performances over S-band using a single pump. Genetic algorithm interfaced with an efficient full-vectorial finite element modal solver based on curvilinear edge/nodal elements is used as an optimization tool for an accurate determination of PCF design parameters. The designed PCF shows high negative dispersion coefficient (-264 ps/nm/km to -1410 ps/nm/km) and negative dispersion slope, providing coarse dispersion compensation over the entire S-band. The module comprised of 1.45-km long optimized PCF exhibits +/-0.46 dB gain ripples over 50 nm wide bandwidth and shows a very low double Rayleigh backscattering value (-59.8 dB). The proposed module can compensate for the dispersion accumulated in one span (80-km) of standard single mode fiber with a residual dispersion of +/-700 ps/nm, ensuring its applicability for 10 Gb/s WDM networks. Additionally, the designed PCF remains single mode over the range of operating wavelengths.