Dual-pump Raman amplification with increased flatness using modulation instability

The application of modulation instability-initiated nonlinear broadening of two CW pumps at different wavelengths, in order to achieve superior gain ripple performance in broadband Raman amplifiers, is demonstrated for the first time experimentally. A particular example using Truewave and LEAF fibers is offered, in which the 0.1 dB gain ripple band is extended from 5 nm to 19 nm. Experimental results are in a good agreement with numerical modeling. Guidelines for optimal broadening are discussed. © 2005 Optical Society of America.

Quasi-lossless data transmission with ultra-long Raman fibre laser based amplification

The project consists of an experimental and numerical modelling study of the applications of ultra-long Raman fibre laser (URFL) based amplification techniques for high-speed multi-wavelength optical communications systems. The research is focused in telecommunications C-band 40 Gb/s transmission data rates with direct and coherent detection. The optical transmission performance of URFL based systems in terms of optical noise, gain bandwidth and gain flatness for different system configurations is evaluated. Systems with different overall span lengths, transmission fibre types and data modulation formats are investigated. Performance is compared with conventional Erbium doped fibre amplifier based system to evaluate system configurations where URFL based amplification provide performance or commercial advantages.

Raman amplifiers:distributed raman amplification speeds comunication

A key technology for future long-distance, high-capacity terrestrial optical communication links, distributed Raman amplification can increase system performance and expand the range of operating wavelengths.

Optimal span length in high-speed transmission systems with hybrid Raman-erbium-doped fiber amplification

We show, using nonlinearity management, that the optimal performance in high-bit-rate dispersion-managed fiber systems with hybrid amplification is achieved for a specific amplifier spacing that is different from the asymptotically vanishing length corresponding to ideally distributed amplification [Opt. Lett. 15, 1064 (1990)]. In particular, we prove the existence of a nontrivial optimal span length for 40-Gbit/s wavelength-division transmission systems with Raman-erbium-doped fiber amplification. Optimal amplifier lengths are obtained for several dispersion maps based on commonly used transmission fibers. © 2005 Optical Society of America.

Impact of the fiber type and dispersion management on the performance of a NRZ 16 x 40 Gb/s DWDM transmission system

We examine the impact of the fiber type and dispersion management on the performance of a 16 × 40 Gb/s dense wavelength-division-multiplexing nonreturn-to-zero transmission system. The transmission line is composed of G.652 or G.655 fiber with periodic dispersion compensation and hybrid Raman erbium-doped fiber amplifier amplification.

Unrepeatered DPSK transmission over 360 km SMF-28 fibre using URFL based amplification

Unrepeatered 42.7 Gb/s per channel RZ-DPSK transmission over standard SMF-28 fibre with novel URFL based amplification using fibre Bragg gratings is investigated. OSNR and gain performance are studied experimentally and through simulations. Error free transmission for 16 channels across the full C-band with direct detection was experimentally demonstrated for 280 km span length, as well as 6-channel transmission at 340 km and single-channel transmission up to 360 km (75 dB) without employing ROPA or specialty fibres.©2013 Optical Society of America.

Impact of the fiber type and nonlinear management over the performance of a 16x40 Gb/s DWDM transmission system

We examine impact of the fiber type and nonlinear management over the performance of a 16x40Gb/s DWDM NRZ transmission system. The line is constituted of 3x100km of G.652 or G.655 fiber with hybrid Raman-EDFA amplification.

Improved WDM performance of a fibre optical parametric amplifier using Raman-assisted pumping

We experimentally demonstrate a Raman-Assisted Fibre Optical Parametric Amplifier (RA-FOPA) with 20dB net gain using wavelength division multiplexed signals. We report amplification of 10×58Gb/s 100GHz-spaced QPSK signals and show that by appropriate tuning of the parametric pump power and frequency, gain improvement of up to 5dB can be achieved for the RA-FOPA compared with combined individual contributions from the parametric and Raman pumps. We compare the RAFOPA with an equivalent-gain conventional FOPA and find that four-wave mixing crosstalk is substantially reduced by up to 5.8 ± 0.4dB using the RA-FOPA. Worst-case performance penalty of the RA-FOPA is found to be only 1.0 ± 0.2dB over all measured OSNRs, frequencies and input powers, making it an attractive proposal for future communications systems.

Nonlinear inverse synthesis technique for optical links with lumped amplification

The nonlinear inverse synthesis (NIS) method, in which information is encoded directly onto the continuous part of the nonlinear signal spectrum, has been proposed recently as a promising digital signal processing technique for combating fiber nonlinearity impairments. However, because the NIS method is based on the integrability property of the lossless nonlinear Schrödinger equation, the original approach can only be applied directly to optical links with ideal distributed Raman amplification. In this paper, we propose and assess a modified scheme of the NIS method, which can be used effectively in standard optical links with lumped amplifiers, such as, erbium-doped fiber amplifiers (EDFAs). The proposed scheme takes into account the average effect of the fiber loss to obtain an integrable model (lossless path-averaged model) to which the NIS technique is applicable. We found that the error between lossless pathaveraged and lossy models increases linearly with transmission distance and input power (measured in dB). We numerically demonstrate the feasibility of the proposed NIS scheme in a burst mode with orthogonal frequency division multiplexing (OFDM) transmission scheme with advanced modulation formats (e.g., QPSK, 16QAM, and 64QAM), showing a performance improvement up to 3.5 dB; these results are comparable to those achievable with multi-step per span digital backpropagation.

All-optical OFDM and distributed Raman amplification:challenges to enable high capacities and extend reach

We review recent advances in all-optical OFDM technologies and discuss the performance of a field trial of a 2 Tbit/s Coherent WDM over 124 km with distributed Raman amplification. The results indicate that careful optimisation of the Raman pumps is essential. We also consider how all-optical OFDM systems perform favourably against energy consumption when compared with alternative coherent detection schemes. We argue that, in an energy constrained high-capacity transmission system, direct detected all-optical OFDM with `ideal' Raman amplification is an attractive candidate for metro area datacentre interconnects with ~100 km fibre spans, with an overall energy requirement at least three times lower than coherent detection techniques.

Performance comparison of 40 Gb/s ULH transmissions using CSRZ-ASK or CSRZ-DPSK modulation formats on Ultra Wave™ fiber

In this work we present extensive comparisons between numerical modelling and experimental measurements of the transmission performance of either CSRZ-ASK or CSRZ-DPSK modulation formats for 40-Gb/s WDM ULH systems on UltraWave™ fiber spans with all-Raman amplification. We numerically optimised the amplification and the signal format parameters for both CSRZ-DPSK and CSRZ-ASK formats. Numerical and experimental results show that, in a properly optimized transmission link, the DPSK format permits to double the transmission distance (for a given BER level) with respect to the ASK format, while keeping a substantial OSNR margin (on ASK modulation) after the propagation in the fiber line. Our comparison between numerical and experimental results permits to identify what is the most suitable BER estimator in assessing the transmission performance when using the DPSK format. © 2007 Optical Society of America.

Characterization of distributed Raman amplification-induced amplitude and phase impairments on unrepeated coherent transmission links

We experimentally characterize the distributed Raman amplification induced amplitude and phase impairments and evaluate the performance dependence of unrepeated 28 Gbaud 16QAM coherent transmissions over standard single mode fiber.

The impact of parametric noise amplification on long haul transmission throughput

Advanced signal processing, such as multi-channel digital back propagation and mid span optical phase conjugation, can compensate for inter channel nonlinear effects in point to point links. However, once such are effects are compensated, the interaction between the signal and noise fields becomes dominant. We will show that this interaction has a direct impact on the signal to noise ratio improvement, observing that ideal optical phase conjugation offers 1.5 dB more performance benefit than DSP based compensation.

Modified nonlinear inverse synthesis for optical links with distributed Raman amplification

We propose a modification of the nonlinear digital signal processing technique based on the nonlinear inverse synthesis for the systems with distributed Raman amplification. The proposed path-average approach offers 3 dB performance gain, regardless of the signal power profile.

Amplification schemes and multi-channel DBP for unrepeatered transmission

The performance of unrepeatered transmission of a seven Nyquist-spaced 10 GBd PDM-16QAM superchannel using full signal band coherent detection and multi-channel digital back propagation (MC-DBP) to mitigate nonlinear effects is analysed. For the first time in unrepeatered transmission, the performance of two amplification systems is investigated and directly compared in terms of achievable information rates (AIRs): 1) erbium-doped fibre amplifier (EDFA) and 2) second-order bidirectional Raman pumped amplification. The experiment is performed over different span lengths, demonstrating that, for an AIR of 6.8 bit/s/Hz, the Raman system enables an increase of 93 km (36 %) in span length. Further, at these distances, MC-DBP gives an improvement in AIR of 1 bit/s/Hz (to 7.8 bit/s/Hz) for both amplification schemes. The theoretical AIR gains for Raman and MC-DBP are shown to be preserved when considering low-density parity-check codes. Additionally, MC-DBP algorithms for both amplification schemes are compared in terms of performance and computational complexity. It is shown that to achieve the maximum MC-DBP gain, the Raman system requires approximately four times the computational complexity due to the distributed impact of fibre nonlinearity.