Distributed Raman Amplification Research Articles

On the Mitigation of RIN Transfer and Transmission Performance Improvement in Bidirectional Distributed Raman Amplifiers

We develop a novel broadband first-order Raman pump for use as a forward pump in transmission experiments. Our results show significant signal relative intensity noise (RIN) reduction, to a level comparable to backward only pumping. The corresponding optical signal to noise ratio can be improved in dual and first-order forward pumped 83.32 km bidirectional distributed Raman amplifiers by using the proposed broadband pump as a first-order pump. A detailed experimental characterization of RIN, signal power evolution and performance of a 10 × 120 Gb/s DP-QPSK coherent wavelength division multiplexing transmission system are presented. We report ∼10 dB RIN reduction and 0.7 dB Q factor improvement, which allows a 1250 km transmission distance increase compared with conventional low RIN and narrowband first-order pump sources. We also demonstrate that, bidirectional pumping with only broadband first-order forward pumping at 50 mW shows the lowest RIN transfer from pump to signal. This extends the transmission reach up to 8332 km with maximum distances increased by 1250 and 1667 km compared with conventional backward only and first-order semiconductor forward pumped bidirectional pumping, respectively.

63 km BOFDA for Temperature and Strain Monitoring.

We demonstrate (and are the first to do so) 63 km Brillouin Optical Frequency-Domain Analysis (BOFDA) for temperature and strain monitoring using a 100 km fiber loop. The use of BOFDA for long-range applications can be considered a novel approach, as previous investigations focused on the utilization of Brillouin Optical Time-Domain Reflectometry and Analysis (BOTDR and BOTDA, respectively). At 51.7 km, a 100 m hotspot (37 C) was detected without using distributed Raman amplification or image processing.

Hybrid cladding-pumped multicore EDFA/Raman amplification for space division multiplexing transmission systems.

We propose and demonstrate a hybrid cladding-pumped multicore erbium-doped fiber amplifier (EDFA) and distributed Raman amplification for space division multiplexing transmission systems. The cladding-pumped multicore EDFA is used to efficiently amplify signals in multiple cores simultaneously, while Raman pumping is used to control loss in each core individually. We construct an in-line amplified 7-core transmission line, and show that distributed Raman amplification can compensate loss variation between cores. Furthermore, we transmit 46 WDM PDM-16QAM signals over a long distance of greater than 1000 km and demonstrate good transmission performance.

Backward Supercontinuum Generation Excited By Random Lasing

Backward supercontinuum generation excited by random lasing is proposed and demonstrated for the first time. Unlike conventional supercontinuum generation, completely distributed random fiber laser is first used as an effective seeding laser to initiate supercontinuum emission in a composite configuration with TrueWave and dispersion compensated fibers. The two fibers provide both amplified random distributed feedback and nonlinear effect induced spectral broadening. Taking advantages of intrinsic characteristics of random distributed Rayleigh scattering and low-noise backward distributed Raman amplification of random lasing, backward supercontinuum is realized with much lower intensity fluctuation in time domain compared to the forward counterpart. The study of combined effects of random lasing and strong nonlinear mechanism not only enrich the research scope of supercontinuum and random fiber lasers, but also provide a practical way for the development of stable broadband light sources for various applications.

The Gaussian Noise Model in the Presence of Inter-Channel Stimulated Raman Scattering

A Gaussian noise (GN) model is presented that properly accounts for an arbitrary frequency dependent signal power profile along the link. This enables the evaluation of the impact of inter-channel stimulated Raman scattering (ISRS) on the optical Kerr nonlinearity. Additionally, the frequency dependent fiber attenuation can be taken into account and transmission systems that use hybrid amplification schemes can be modeled, where distributed Raman amplification is partly applied over the optical spectrum. To include the latter two cases, a set of coupled ordinary differential equations must be numerically solved in order to obtain the signal power profile yielding a semi-analytical model. However for lumped amplification and negligible variation in fiber attenuation, a less complex and fully analytical model is presented which is referred to as the ISRS GN model. The derived model is exact to first-order for Gaussian modulated signals and extensively validated by numerical split-step simulations. A maximum deviation of $0.1$~dB in nonlinear interference power between simulations and the ISRS GN model is found. The model is applied to a transmission system that occupies an optical bandwidth of $10$~THz, representing the entire C+L band. At optimum launch power, changes of up to $2$~dB in nonlinear interference power due to ISRS are reported. Furthermore, comparable models published in the literature are benchmarked against the ISRS GN model.

Enhanced Transmission Performance Using Backward-Propagated Broadband ASE Pump

We propose a novel first order incoherent broadband amplified spontaneous emission (ASE) pump which can be used as a seed pump in dual order backward-pumped distributed Raman amplification. Using this broadband ASE pump mitigates the relative intensity noise (RIN) transfer from the backward-propagated second order pump to the signal, and extends the reach of $10\times120$ Gb/s DP-QPSK WDM transmission to 7915 km, giving a minimum of 12% (833 km) increase, compared with using low RIN semiconductor laser diode and random distributed feedback fiber laser.

SPM and XPM crosstalk in WDM systems with DRA: Channel spacing and attenuation effects

This paper presents a theoretical analysis of a closed formula for nonlinear crosstalk due to self-phase modulation (SPM) and cross phase modulation (XPM) in wavelength division multiplexing (WDM) systems. The influence of channel spacing and attenuation on the system behavior is modeled and investigated. The system under consideration is a standard single-mode fiber (SSMF) with a single-span distributed Raman amplifier (DRA) and is operating at 100 Gbps.

Raman amplification by employing data modulated pump signals for bi‐directional communication

AbstractWe propose a symmetric 10 × 10 Gb/s bidirectional wavelength division multiplexed passive optical link having a length of 80‐km supported only by Raman amplification through pre‐amplified data modulated uplink channels. The conventionally ignored wavelength region of E‐band has been utilized for employing pre‐amplified data modulated Raman pumps. The proposed network allows the use of single low‐cost and low‐power amplifier for distributed Raman amplification instead of multiple high‐cost Raman laser pump modules.

RIN Mitigation and Transmission Performance Enhancement With Forward Broadband Pump

We demonstrate that using a broadband, first order, and coherent pump laser enables effective and efficient forward-pumped distributed Raman amplification for long-haul transmission systems, thanks to the simultaneous suppression of ASE noise and RIN-related penalty. We show in both experiments and simulation that this scheme extends the reach of 10 × 120 Gb/s DP-QPSK WDM transmission by a minimum of 50%, compared with low RIN Bi-doped fibre laser and other commercially available pump lasers. Moreover, it requires very low forward pump power, and maintains uniform/symmetric signal power distribution which allows effective nonlinearity compensation.

A Distributed Raman Amplifier Based on the Backward-Pumped Random Fiber Laser

For the first time, a backward-pumped random distributed feedback fiber laser is applied to the conventional distributed Raman amplification (DRA). A new asymmetric DRA scheme for improving the signal power variation (SPV) performance was achieved. The scheme was studied numerically and was shown to effectively reduce the SPV of all signals to less than 1.2 dB, whilst maintaining a flat ON–OFF gain over 40 nm bandwidth for a 61.5 km fiber span. Moreover, the nonlinear Fourier transform technique, which is utilized to deal with the nonlinear noise, could be realized on the proposed scheme with such a low SPV.

Investigation on the pre-compensation and post-?compensation cascaded multi-channel-chirped fiber Bragg gratings for a repeaterless transmission system

We experimentally designed dispersion-managed repeaterless transmission systems with a pre-compensation and post-compensation technique using multi-channel-chirped fiber Bragg gratings. The repeaterless transmission link supports a single channel (1548.51 nm) with a 10 Gbps repeaterless transmission system over 300 km standard single-mode fiber (SSMF). In the system design, two distributed Raman amplifiers (DRAs) were used to improve the signal level propagated along the 300 km SSMF. The co-propagating DRA provided 15 dB on–off gain and the counter-propagating produced 32 dB on–off gain at the signal wavelength. The experiment results show that the post-compensation configuration achieves an optimal performance with a bit error rate at 1×10−9.

Noise and transmission performance improvement of broadband distributed Raman amplifier using bidirectional Raman pumping with dual order co-pumps.

We demonstrate a low noise bidirectional broadband distributed Raman pumping scheme combining dual order co-propagated pumps without increasing the signal RIN level. The noise performance improvement is compared experimentally and numerically with conventional counter-pumping only and bidirectional pumping with only a 2nd order co-pump for a 70nm bandwidth and 61.5km distributed Raman amplifier. The proposed broadband pumping scheme shows 1.2dB maximum noise figure improvement and extends the long-haul transmission reach up to 6150km with a Q-factor improvement of ~0.7dB compared with counter-pumping only scheme.

Analysis of Possibilities of Increasing the Spanned Distance Using EDFA and DRA in DWDM System

The aim of this article is a comparison of the EDFA (Erbium Doped Fibre Amplifier) and the DRA (Distributed Raman Amplifier) in a fully optical communication system, working on a specific wavelength. The amplifiers are compared based on their position in the optical loop and are evaluated according to the Q-factor and bit error rate (BER). In the case of the DRA, the accomplished distance was smaller, while changing the optical power in CW (Continuous Wave) to attain better BER. In the application of the EDFA a similar optical loop was created, as well, while the basic parameter for comparison was a bit speed. For the EDFA the bit speed was changed from 10 to 15 Gbps. For the DRA the change was in the power from 1 to 3 mW with the bit speed kept at 10 Gbps. This publication also focuses on the need for such application of a transfer system in a software environment. It would enable examination and research and consequently a minimising of the influence of non-linear effects impacting the particular WDM (Wavelength Division Multiplex) system.

A simple strategy to design broadband low power consumption distributed Raman amplifier

In this work, a simple strategy to design wideband low power consumption Raman amplifiers is demonstrated for a three-pump configuration using a low water peak optical fiber. The approach is based on the introduction of a novel numerical measure, which quantifies and isolates pump-pump interaction contribution to gain profile and analyzes its correlation to amplifier minimum ripple. The method tailors the amplifier gain spectrum over 80nm bandwidth with a ripple smaller than 1dB, a gain on the order of 4dB for up to 75km fiber length, and a total pump power consumption smaller than 300mW

Enhanced Coherent BOTDA System Without Trace Averaging

We propose and experimentally demonstrate a scheme of a coherent Brillouin time domain analysis (BOTDA) system without any trace averaging. Assisted by a commercial integrated coherent receiver with a local oscillator generated through single sideband modulation from the same laser source, the Brillouin signals carried on a stable intermediate frequency (IF) are extracted by electrical/digital filters and then recovered to baseband by digital signal processing. This increases the signal-to-noise ratio and avoids the need of trace averaging and enables real-time signal acquisition. To eliminate the Brillouin gain fluctuation, two adjacent Brillouin time-domain traces stimulated by two sequential orthogonal pump pulses are recovered after the IF signals are detected in a real-time manner. Based on this configuration, a spatial resolution of 4 m and Brillouin frequency shift uncertainty of 1.473 MHz are realized in distributed temperature sensing over 40.63 km range. With the nonlocal means algorithm and distributed Raman amplification integrated into the system, the BFS uncertainty is enhanced to 0.843 MHz and better spatial resolution of 2 m over the same sensing fiber is achieved.

DBPSK and DQPSK crosstalk in single-span WDM systems using DRA.

A closed-loop formula is derived for the nonlinear crosstalk degradation due to self-phase modulation and cross-phase modulation in a wavelength-division multiplexing system. The crosstalk is investigated in differential binary phase-shift keying (DBPSK) and differential quadrature phase-shift keying (DQPSK) schemes. The system under consideration is standard single-mode fiber with a single-span distributed Raman amplifier. The backward DBPSK shows a better performance with minimum crosstalk performance of 71%, as compared to backward DQPSK.

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.

Co-Propagating Dual-Order Distributed Raman Amplifier Utilizing Incoherent Pumping

We propose a distributed Raman amplifier available for dual-order co-propagating configuration with low-relative intensity noise (RIN) transfer. The first-order and second-order pumps are composed of incoherent and coherent light sources, respectively. By using the incoherent light source as a first-order pump, RIN transfer can be reduced. A semiconductor optical amplifier-based first-order incoherent light source for the configuration has been developed. The results of the RIN measurement and 22.5-Gbaud polarization-division multiplexing 16 quadrature amplitude modulation (PDM-16QAM) transmission experiment over 2720 km in a re-circulating loop show that the proposed configuration will be effective for a practical low-noise co-propagating Raman amplifier.

Experimental Evaluation of Impairments in Unrepeatered DP-16QAM Link with Distributed Raman Amplification

The transmission impairments of a Raman amplified link using dual-polarization 16-quadrature amplitude modulation (DP-16QAM) are experimentally characterized. The impact of amplitude and phase nois ...

Digital back-propagation for nonlinearity mitigation in distributed Raman amplified links.

The performance of digital back-propagation (DBP) for distributed Raman amplified optical communication systems is evaluated through analytical models and numerical simulations, and is compared with conventional lumped amplifier solutions, such as EDFA. The complexity of the DBP algorithm including the characteristic signal power profile of distributed Raman amplifiers is assessed. The use of full-field DBP in distributed Raman amplified systems leads to 1.3 dB additional gain with respect to systems employing lumped amplification, at the cost of only a 25% increase in complexity.