C. Castro

Digital Compensation of Bandwidth Limitations for High-Speed DACs and ADCs

In this paper, we present a novel digital preemphasis algorithm to compensate for the electrical bandwidth limitations at the transceiver also by taking into account the quantization noise introduced by the signal digitalization. The proposed method is based on the minimization of the mean square error between the desired input signals and the output signals of the digital-to-analog converter/analog-to-digital converter (DAC/ADC), when assuming the knowledge of the DAC/ADC frequency responses. Though this paper focuses on the DAC/ADC compensation, the introduced method could be applied to electrical bandwidth limitations caused by any other component within the transponder. The performance of the algorithm is assessed in optical back-to-back configuration by comparing it against the case without digital preemphasis and with a previously published method to compensate for DAC bandwidth limitations. Our analysis shows that when utilizing realistic descriptions of the DAC/ADC, the proposed digital preemphasis (at the transmitter) or digital compensation (at the transmitter and receiver) can considerably increase the maximum transmittable symbol rate for the case of advanced modulation formats. For example, the maximum symbol rate can be ideally increased up to ~ 60% for the case of 16QAM when employing the high-speed DAC with a -3 dB electrical bandwidth of ~16 GHz and with six effective number of bits. Furthermore, we evaluate the impact of additional noise sources, based on experimental measurements, envisioning potential for further improvements of the digital preemphasis module. Finally, we experimentally verified our algorithm, for the specific case of polarization-multiplexed 16QAM, showing a considerable match between simulation and lab results.

Demonstration of Single-Mode Multicore Fiber Transport Network With Crosstalk-Aware In-Service Optical Path Control

Multicore fiber (MCF) transmission is considered as one of the promising technologies for breaking the capacity limit of traditional single mode fibers. Managing the crosstalk (XT) and configuring optical paths adaptively based on the XT as well as achieving longer distance and larger capacity transmission are important, because intercore XT could be the main limiting factor for MCF transmission. In a real MCF network, the intercore XT in a particular core is likely to change continuously as the optical paths in the adjacent cores are dynamically assigned to match the dynamic nature of the data traffic. If we configure the optical paths while ignoring the intercore XT value, the Q-factors may become excessive. Therefore, monitoring the intercore XT value continuously and configuring optical path parameters adaptively and flexibly are essential. To address these challenges, we develop an MCF transport network testbed and demonstrate an XT-aware traffic engineering scenario. With the help of a software-defined network controller, the modulation format and optical path route are adaptively changed based on the monitored XT values by using programmable devices such as a real-time transponder and a reconfigurable optical add–drop multiplexer.

In-service crosstalk monitoring for dense space division multiplexed multi-core fiber transmission systems

We present in-service inter-core crosstalk monitoring for MCF transmission systems. We transmit 54-WDM PDM-16QAM signals over 111.6-km 32-core DSDM transmission line incorporating cladding-pumped 32-core MC-EYDFA, and demonstrate −30 dB crosstalk monitoring without affecting transmission performance.

Simulation and verification of a multicore fiber system

In this paper, a simulation model of a multicore fiber in the linear regime is presented. We describe how to digitally represent the fiber and introduce a modelling scheme based on Coupled-Mode theory and Power-Coupled theory to analyze the system performance of multicore fibers. In order to validate the investigated model, the obtained simulation results are compared to our own measurements of a 7-core multicore fiber transmission link and to results from previously published experiments.

50 ch × 250 Gbit/s 32-QAM transmission over a fully integrated 7-core multicore link

A transmitted distance of 180 km over an integrated multicore link is demonstrated for a C-band 32-QAM WDM system, where the complete usable amplification region of the integrated 7-core amplifiers, supporting 50 channels per core, is exploited.

32-Core Erbium/Ytterbium-Doped Multicore Fiber Amplifier for Next Generation Space-Division Multiplexed Transmission System

We present a high-core-count 32-core multicore erbium/ytterbium-doped fiber amplifier (32c-MC-EYDFA) in a cladding pumped configuration. A side pumping technique is employed for ease of pump coupling in this monolithic all-fiber amplifier. A minimum gain of >17 dB and an average noise figure (NF) of 6.5 dB is obtained over all cores in the wavelength range 1534 nm-1561 nm for −4 dBm input signal power. The core-to-core variation for both amplifier gain and NF is measured to be 1850 km was successfully demonstrated. We also compare the total power consumption of our MC-EYDFAs with that of 32 conventional single core erbium doped fiber amplifiers (EDFAs) to illustrate the potential power saving benefits.