High-capacity multi-span transmission performance characterization of broadband discrete Raman amplifier

The performance of a multi-span transmission link compensated with a >75nm broadband discrete Raman amplifier is experimentally evaluated using multiple DP-x-QAM modulation formats over a multi-channel C + L band WDM grid with up to 182 ×50 GHz spaced channels

Repurposable hardware in smart photonic components

Key to the development of cost effective integrated components is low cost, low power circuitry capable of being repurposed from providing manufacturing based functions, such as characterisation and calibration, to operational control functions. Although these individual functions are well known, efficient and low cost implementations are required to enable competitive module pricing. In the case of an optical Mach Zehnder Modulator (MZM), bias currents require complex control functions, for example based around digitally synthesized sinusoidal pilot tones and harmonic detection via filters [1][2]. Control methods making use of calibrated laboratory equipment have been proposed [2], whereas here we consider the practical adoption of these methods with low cost and low power components which could be readily integrated into an optical module. In particular we investigate the behaviour and capabilities required for automatic digital bias control functionality implemented in a small gate count, low cost Field Programmable Gate Array (FPGA) when used in conjunction with a MZM. We assess the suitability of highly efficient implementations of DSP functions within the bias controller, such as digital filters, for example investigating the use of a computationally efficient algorithm for computing a single component of a discrete Fourier transform [3], and demonstrate the viability of using low cost digital hardware to implement a circuit capable of monitoring the MZM transfer function. The concept of creating cost effective, repurposable hardware is crucial for implementation and inclusion in optical devices deployed in communications networks and beyond

Hybrid discrete Raman/EDFA design for broadband optical amplification in metro WDM systems

A novel design of a broadband discrete Raman/EDFA hybrid amplifier is proposed. A broadband signal of 84 channels across 75 nm is experimentally amplified and the gain contribution of each amplifier stage is shown. The amplifier consists of a discrete Raman amplifier using a DCF fibre pumped at three 14×× nm wavelengths, which is followed by a 1480 nm pumped erbium doped fibre. An average gain of 15.4 dB and gain flatness of ± 1.7 dB with no gain equalising elements is achieved

Low penalty, dual stage, broadband discrete Raman amplifier for high capacity WDM metro networks

We present a broadband (>70nm), dual stage, discrete Raman amplifier built with small and standard core fibre with ~19.5dB net gain. We transmit 120Gb/s DP-QPSK signals over 3040km with 38 amplifications for a preFEC BER<3.8×10-3

Nonlinearity Tolerant LUT-based Probabilistic Shaping for Extended-Reach Single-Span Links

We propose Huffman-coded sphere shaping (HCSS) as a method for probabilistic constellation shaping which provides improved tolerance to fiber nonlinearities in single-span links. An implementation of this algorithm based on look-up-tables (LUTs) allows for low-complexity, multiplier-free shaping. The advantage of short-length shaping for mitigating fiber nonlinear impairments is experimentally demonstrated for a system employing dual–polarization 64–ary quadrature amplitude modulation (DP-64QAM) at 56 GBd and operating over 210 km of standard single-mode fiber (SSMF). A gain in achievable information rate (AIR) of 0.4 bits/4D-symbol compared with uniform signaling is measured, corresponding to a 100% improvement in shaping gain compared with ideal Maxwell–Boltzmann (MB) shaping. The combinatorial mapping and demapping algorithms can be implemented with integer addition and comparison operations only, utilizing an LUT with 100 kbit size

Impact of pump-signal overlap in S+C+L band discrete Raman amplifiers

We experimentally investigate the impact of pump-signal overlap in ultra-wideband (>13THz) Raman amplifiers and measure the transmission penalty on 30GBaud PM-QPSK signals due to adjacent Raman pumps in a 15dB gain, 150nm (∼18.8THz) S+C+L-band discrete Raman amplifier. We present an efficient numerical model to predict the performance penalty induced by crosstalk from Rayleigh backscattered light from backward-propagating Raman pumps showing good agreement with the experimental results. A 4nm guard-band must be retained around an overlapping Raman pump based on typical, commercial semiconductor laser pump diodes to ensure a negligible transmission penalty in S-ban

Nonlinear Noise of Low Transmission Penalty Dual-Stage Discrete Raman Amplifier

We experimentally characterise the linear and nonlinear performance of a >70nm, dual-stage, 19.5dB average net gain discrete Raman amplifier using different nonlinear fibres in the second stage. We propose an architecture built with a combination of IDF and SMF, and compare its performance with amplifiers built with conventionally used nonlinear fibre types (IDF-IDF, IDF-DCF). The measured FWM product power shows the IDF-SMF architecture to generate less nonlinear interference when compared to other schemes. We test the amplifiers with 5x120Gb/s DP-QPSK WDM signals in a recirculating loop at 10 recirculations of 93.4km SMF fibre, where the power sweep shows up to 2dB optimum launch power difference, with the maximum Q2 factor varying by up to 1.6dB. Using the optimum transmission point we measure a Q2=8.8dB at 35 recirculations of 93.4km transmission (3269km) with the proposed IDF-SMF scheme, which is >460km further than the other tested architectures. All characterised schemes performed similarly in the linear noise regime

RIN-penalty mitigation and transmission performance improvement using forward propagated broadband first order Raman pump

We demonstrate that using a broadband pump enables forward-propagated first order distributed Raman amplification by mitigating RIN-associated penalty. This extends the reach of 10 × 120 Gb/s DP-QPSK WDM transmission up to 7499 km, compared with other commercially available pumps. Moreover, using this Raman scheme maintains uniform/symmetric signal power distribution and requires low pump power

Characterisation of Linear and Nonlinear Noise of a Dual-Stage Broadband Discrete Raman Amplifier

The linear and nonlinear noise performance of a 70nm, dual-stage, ∼20dB-gain discrete Raman amplifier is characterised experimentally using different second-stage fibres. An advantageous IDF-SMF configuration is identified with an improvement in the nonlinear performance by >1dBQ 2 compared with IDF-DCF configurations

Linear and Nonlinear Noise Characterisation of Dual Stage Broadband Discrete Raman Amplifiers

We characterise the linear and nonlinear noise of dual stage broadband discrete Raman amplifiers (DRAs) based on conventional Raman gain fibres. Also, we propose an optimised dual stage DRA setup that lowers the impact of nonlinear noise (generated in the amplifier) on the performance of a transmission link (with 100-km amplifier spacing). We numerically analyse the design of a backward pumped cascaded dual stage 100-nm DRA with high gain (∼20 dB) and high saturated output power (>23 dBm). We show that the noise figure (NF) of the dual stage DRA is mainly dominated by the first stage irrespective of the type of gain fibre chosen in the second stage, and we also demonstrate that optimising the length and the type of Raman gain fibre can have significant impact on the size of inter/intrasignal nonlinearities generated. Here, we report a theoretical model to calculate the nonlinear noise power generated in transmission spans with dual stage DRAs considering piecewise signal power evolution through the Raman gain fibres. The predicted signal-to-noise ratio (SNR) performances are calculated from the combined contributions from NF and nonlinear product power obtained using the proposed analytical model for transmission systems deployed with 100-km transmission span compensated by different dual stage DRAs. Finally, an optimised IDF 6 km-SMF 10 km dual stage configuration has been identified using the theoretical model, which allows maximum SNR of 14.6 dB at 1000 km for 1 THz Nyquist wavelength division multiplexed signal and maximum transmission reach of 3400 km at optimum launch power assuming 8.5 dB HD-FEC limit of the Nyquist PM-QPSK signal