Ginni Khanna

Nonlinearity compensation is considered as a key enabler to increase channel transmission rates in the installed optical communication systems. Recently, data-driven approaches — motivated by modern machine learning techniques — have been proposed for optical communications in place of traditional model-based counterparts. In particular, the application of neural networks (NN) allows improving the performance of complex modern fiber-optic systems without relying on any a priori knowledge of their specific parameters. In this work, we introduce a novel design of complex-valued NN for optical systems and examine its performance in standard single mode fiber (SSMF) and large effective-area fiber (LEAF) links operating in relatively high nonlinear regime. First, we present a methodology to design a new type of NN based on the assumption that the channel model is more accurate in the nonlinear regime. Second, we implement a Bayesian optimizer to jointly adapt the size of the NN and its number of input taps depending on the different fiber properties and total length. Finally, the proposed NN is numerically and experimentally validated showing an improvement of 1.7 dB in the linear regime, 2.04 dB at the optimal optical power and 2.61 at the max available power on Q-factor when transmitting a WDM 30×200G DP-16QAM signal over a 620 km SSMF legacy link. The results highlight that the NN is able to mitigate not only part of the nonlinear impairments caused by optical fiber propagation but also imperfections resulting from using low-cost legacy transceiver components, such as digital-to-analog converter (DAC) and Mach-Zehnder modulator.

We propose and experimentally demonstrate an all-optical architecture for data center interconnect networks with reconfiguration times of a few seconds. Filtering and amplification transient effects have minimal impact on BER performance.

An adaptive digital pre-compensation scheme to jointly compensate for the linear and non-linear effects for high baud rate and higher order modulation formats optical transmitters is discussed.

Digital pre-compensation (DPC) is an indispensable block of state-of-the-art optical transceivers, and a key enabler for high-order modulation formats (HOMFs) transmission. A crucial component, which enables the transmission of the precompensated HOMFs, is the digital-to-analog-converter (DAC). However, as data and symbol rates grow, the implementation of such devices becomes highly challenging in terms of performance, power consumption, and costs. In this paper, a digital-resolution-enhancer (DRE) algorithm is discussed, conjoined with high-end DPC methods. Simulation results demonstrate that the DRE reduces the effect of DAC quantization noise power by more than 8 dB for the considered cases of 400G with 64QAM. The proposed scheme is experimentally verified by transmitting a 4-bit DP-64QAM 400 Gbit/s signal in a WDM scenario over 95 km of single mode fiber.

In recent years, digital pre-distortion has emerged as a powerful approach to compensate for linear and nonlinear imperfections of the transmitter. Previous solutions are either based on factory calibration or use a local auxiliary receiver. Here we present a digital pre-distortion architecture to compensate transmitter frequency response and I/Q skew, which relies upon a feedback from the far-end receiver and uses the signal propagated over the optical link. The effectiveness of the proposed solution is validated over different transmission systems for dual-polarization 64QAM net 400 Gb/s and 16QAM net 200 Gb/s signals.

An adaptive digital pre-distortion method based on memory polynomials to compensate for non-linearities in high power optical transmitters is presented. Gains up to 2dB for DP-64QAM are achieved beyond linear pre-distortion

We report on the results of a field trial carried out on a Telecom Italia metro link, targeting short data center interconnect applications. The test-bed presented realistic transmission conditions, such as an average ~0.3-dB/km attenuation and usage of legacy erbium-doped fiber amplifier (EDFA) only. We transmitted a net bit rate of 400 Gb/s on a single carrier with 64 quadrature amplitude modulation (QAM) and 128QAM over 156 km. Error-free transmission over 80 km for single carrier dense wavelength-division multiplexing (DWDM) 30 × 400G 64QAM and 30 × 400G 128QAM (one half of the C-band) is reported. The net spectral efficiency, for both schemes, is 7.11 b/s/Hz.