Performance Evaluation of Raman Amplifiers in Fibre Optic Communication Systems

This thesis presents an overview of Raman amplifiers in fibre optic transmission systems. Detailed analysis of the nonlinear accumulated noise and relative intensity noise (RIN) induced penalties are evaluated in discrete and distributed Raman amplifiers. In addition to these the thesis also includes different architectures of Raman amplifiers enabling multiband transmission. The parametric dependency of fibre chromatic dispersion (CD) on the accumulated nonlinear noise in discrete Raman amplifiers (DRAs) was studied both theoretically and experimentally. Analytical modelling was performed over different fibre types that are widely used as a gain medium in DRAs. It was found that systems using Raman gain fibres with a positive value of CD induce lower accumulated nonlinear noise in comparison to systems using Raman gain fibres with a negative value of CD. The results obtained from the analytical model were then validated experimentally over a long-haul transmission system with DRAs as an inline amplifier using a recirculation loop. RIN-induced penalties in distributed Raman amplifiers (DiRAs) were experimentally studied in two standard single-mode fibre (SSMF) G.654.E©TXF and G.652.D with different pumping schemes. Signal RIN for G.654.E© TXF was found to be lower in comparison to its counterpart G.652.D. The impact of RIN on the short-haul system was validated using both the test fibres pumped in a forward-pumped distributed Raman. Similarly, backward and bidirectional pumping was performed over a long-haul transmission system using a recirculation loop. It was experimentally observed that RIN-induced transmission penalties for G.654.E are lower in comparison to G.652.D making it a better choice of SSMF type for distributed amplification. Experiments on novel architectures such as cascaded dual-stage and dual-band designs were demonstrated over a coherent transmission system with S-, C- and L-band signals. It was observed that the dual-stage design requires a guard band of ~10 nm to prevent overlapping of the pumps and signal, reducing the overall transmission capacity. In contrast, for dual-band design, no such guard band was required, but this benefit comes at a cost of the additional pump requirement increasing the overall amplifier power consumption. The performances of novel multistage Raman amplifier structures were also evaluated over the E-, S-, C- and L-band. Experimental studies were performed independently using DRAs only, hybrid bismuth-DRA and hybrid distributed-DRA. The E- and S-band signals were seen to have higher performance penalties in comparison to C- and L-band signals in the case of DRAs only and hybrid bismuth-DRA. In contrast, for the hybrid distributed-discrete design, the E-band signals were seen to have a similar penalty as C- and L-band signals

Background subtraction using variable threshold RGB model

Background subtraction is an essential step in video processing since it extracts the region of interest from an arbitrary image. So, it reduces computational complexity. It also helps in proper implementation of algorithms for further processing as per requirement. This paper describes a simple method to extract the foreground. The algorithm used, works well for indoor operation

Ultra-wideband discrete Raman amplifier optimization for single-span S-C-L-band coherent transmission systems

We experimentally compare the performance of two key ultra-wideband discrete Raman amplifier structures, a cascaded dual-stage structure and an in-parallel dual-band structure, in fully loaded S-C-L band coherent transmission systems over 70 km of single-mode fiber. Our results show that dual-band discrete Raman amplifier with minimized backreflections can effectively avoid unstable random distributed feedback lasing, reduce the noise figure, and therefore improve the transmission performance for signals at shorter wavelengths, versus the cascaded dual-stage structure. The average noise figure for S-band signals is 6.8 dB and 7.2 dB for the dual-band structure and cascaded dual-stage structure, respectively, while the average S-band Q2 factor is similarly improved by 0.6 dB. Moreover, the cascaded dual-stage discrete Raman amplifier requires guard bands around the 1485-nm and 1508-nm pumps as the signal and pump wavelengths overlap, which results in a bandwidth loss of ∼10 nm and reduces the potential net data throughput to 28.6 Tb/s for 30-GBaud DP-16QAM signals. However, the dual-band structure can utilize the bandwidth more effectively, which leads to a higher estimated net data throughput of 31.2 Tb/s

Multi-band Transmission over E-, S-, C- and L-band with a Hybrid Raman Amplifier

Capacity enhancement by utilising the unused spectral bands of the low-loss optical window of standard single-mode fibre (SSMF) is a cost-effective solution for meeting the future demand of data traffic. The development of optical amplifiers that can operate in different spectral bands is expected to play an integral part in the establishment of multi-band networks. In this work, we perform experimental, analytical and numerical modelling of a multi-band transmission system using a hybrid distributed-discrete Raman amplifier enabling signal amplification from 1410-1605 nm. The developed amplifier was tested over 50km of SSMF using 200 Gbit/s channels, where successful transmission was achieved, well above the HD-FEC threshold of 8.5 dB. Further study on the multi-band transmission performance was carried out using a semi-analytical closed-form approximation and split-step Fourier method-based simulations for various related test cases. The analytical and numerical models are also compared with experimental results, showing reasonable agreement in terms of system performance estimation

30-GBaud DP 16-QAM transmission in the E-band enabled by bismuth-doped fiber amplifiers

We report the transmission of five 30-GBaud dual polarization 16-QAM signals over 160 km of standard single-mode fiber in the E-band (1410–1460 nm). The transmission line consists of two 80-km spans and three independent bismuth -doped fiber amplifiers. The developed amplifiers feature a maximum gain of 27.3 dB, 33.8 dB, and 28.3 dB with a minimum noise figure of 4.8 dB, 4.7 dB, and 5.3 dB, respectively. The maximum signal Q2 factor penalty is 4.5 dB, and the overall performance of the system is above the pre-forward-error-correction (FEC) threshold for a 10−15 post-FEC bit error rate. To the best of our knowledge, this is the record experimentally demonstrated transmission length for a coherent detection signal in the E-ban

RIN induced penalties in G.654.E and G.652.D based distributed Raman amplifiers for coherent transmission systems

Relative intensity noise (RIN) induced penalties were experimentally measured in distributed Raman amplifiers (DRAs) for G.654.E and G.652.D fibres with forward, backward and bidirectional pumping configurations. The measured signal RIN using the G.654.E fibre was ∼3.5 dB and ∼2 dB lower than the G.652.D fibre with forward (FW) pump configuration for PM-QPSK and PM-8QAM signals, with single span transmission showing a Q-factor improvement of ∼3 dB and ∼2.5 dB for G.654.E over G.652.D fibres. The performance penalty in a long haul coherent system was evaluated for 28 GBaud PM-QPSK signals using a recirculation loop for backward and bidirectional distributed Raman amplifiers. Our experimental results demonstrate an additional transmission distance of more than 1000 km for G.654.E over its counterpart G.652.D assuming a HD-FEC limit of 8.5 dB

Performance evaluation of discrete Raman amplifiers in coherent transmission systems

We evaluate the performance penalty due to discrete Raman amplifier (DRA) in a long haul WDM transmission system. The investigation was primarily performed to study the impact of the accumulated nonlinear noise due to fibre chromatic dispersion and nonlinear coefficient(γ). Nonlinear fibres such as inverse dispersion fibre (IDF), dispersion compensation fibre (DCF) and a development fibre known as the Corning Raman fibre (CRF) with the opposite sign of CD to the other two, were taken as the gain fibre in the DRA stage of the long-haul transmission setup. To study the performance penalty with these Raman gain fibres a 30 GBaud 120 Gb/s DP-QPSK channel @1550 nm was combined with 9 spectrally shaped 50 GHz amplified spontaneous emission (ASE) channels for transmission over a recirculation loop with a per loop length of 63 km single mode fibre (SMF). Our modelling and experimental results show that a fibre with positive dispersion >10ps/nm/km and a nonlinear coefficient of ∼ 4W−1km−1 is a good choice of gain fibre for DRA-assisted coherent transmission system

E-, S-, C- and L-band coherent transmission with a multistage discrete Raman amplifier

We report for the first time an ultra-wideband coherent (UWB) WDM transmission over a 70 km standard single mode fibre (SSMF) solely using a multistage discrete Raman amplifier (DRA) over the E-, S-, C- and L-bands of the optical window. The amplifier is based on a split-combine approach of spectral bands enabling signal amplification from 1410-1605 nm over an optical bandwidth of 195 nm (25.8 THz). The proposed amplifier was characterized with 143 channelized amplified spontaneous emission (ASE) dummy channels in the S-, C- and L-bands and 4 laser sources in the E-band (1410–1605 nm). The amplification results show an average gain of 14 dB and a maximum noise figure (NF) of 7.5 dB over the entire bandwidth. Coherent transmission with the proposed amplifier was performed using a 30 Gbaud PM-16-QAM channel coupled with the ASE channels over a 70 km SMF. The ultra-wideband transmission using the tailored multistage DRA shows transmission bandwidth of 195 nm with a maximum Q2 penalty of ∼4 dB in E- and S-band, and ∼2 dB in C- and L-band

Multi-band Transmission over E-, S-, C- and L-band with a Hybrid Raman Amplifier

Capacity enhancement by utilising the unused spectral bands of the low-loss optical window of standard single-mode fibre (SSMF) is a cost-effective solution for meeting the future demand of data traffic. The development of optical amplifiers that can operate in different spectral bands is expected to play an integral part in the establishment of multi-band networks. In this work, we perform experimental, analytical and numerical modelling of a multi-band transmission system using a hybrid distributed-discrete Raman amplifier enabling signal amplification from 1410-1605 nm. The developed amplifier was tested over 50km of SSMF using 200 Gbit/s channels, where successful transmission was achieved, well above the HD-FEC threshold of 8.5 dB. Further study on the multi-band transmission performance was carried out using a semi-analytical closed-form approximation and split-step Fourier method-based simulations for various related test cases. The analytical and numerical models are also compared with experimental results, showing reasonable agreement in terms of system performance estimation

Multi-band ESCL transmission supported by bismuth-doped and Raman fiber amplification

Ultra-wideband transmission utilizes bandwidths beyond the standard C-band to enable significant network capacity upgrades. Upgrading the standard C-band to a C+L-band transmission scenario is already feasible, and exploratory transmission is being performed in the S-, E-, and O-bands to investigate quality of transmission (QoT) impairments in these spectral regions. In this paper, experimental transmission through a SCL- and partial E-band spectral region is performed, with use of a hybrid amplifier that exploits discrete Raman amplification for the SCL-bands, and a bismuth-doped fiber amplifier (BDFA) for the E-band. Through this transmission bandwidth, we demonstrate that 36 Tbit/s transmission is possible, with 150 coherent channels over 70 km of standard, single-mode fiber. This result is compared to a wideband physical layer model that considers a realistic full spectral load transmission scenario, where the E-band is occupied by 74 channels, providing a total of 221 channels. This comparison demonstrates that, for both scenarios in this experiment, the greatest impairment is present within the S-band, and the addition of the E-band to a SCL-band scenario has a negligible impact upon the QoT within the C- and L-bands