Real-time monitoring of the impact of cascaded wavelength-selective switches in digital coherent receivers

A simple real-time monitoring algorithm for the impact of cascaded WSSs in elastic optical networks, which exploits the information available in a digital coherent receiver, is proposed and demonstrated through both numerical simulations and experiments

Autonomous Raman Amplifiers using Standard Integrated Network Equipment

Practical needs related to infrastructure management are driving optical network operators to include Raman amplification in order to improve the performance of long fiber spans. Compared to standard erbium-doped fiber amplifier (EDFA) management, Raman amplifiers require a greater degree of control and monitoring due to their distributed nature. Inevitably, this update leads to a key consideration; the introduction of additional telemetry devices with respect to standard EDFA photodiodes, resulting in an increase in required investments. In this work, we present an embedded controller architecture in combination with an ad-hoc probing procedure to manage Raman amplification within disaggregated optical networks, using only standard integrated equipment, allowing an efficient implementation without the introduction of optical channel monitors (OCMs). This proposal is validated using a fully representative experimental campaign, testing both the probing procedure on a single fiber span and the operation of a Raman amplifier using the extracted information

Phase Noise Impact and scalability of self-homodyne short-reach coherent transmission using DFB lasers

We investigate on a two-fiber short-reach self-homodyne coherent transmission system without optical amplification, where the same transmission laser is used to generate a modulated signal carrying useful data and a continuous wave signal, which serves as a local oscillator at the receiver side. Target of the work is to determine by experiments and theoretical models under which conditions DFB lasers can be used instead of more expensive ECL lasers. After careful characterization of lasers phase noise in terms of linewidth as a function of the mismatch between the optical paths of the signal and of the local oscillator, the performance of two laser technologies is investigated in the proposed transmission setup, showing that commercial DFB laser can be used, provided that the optical path mismatch between the two fibers is kept below 1.8 meter for 28 GBaud PM-QPSK and 0.8 meter for PM-16QAM modulation format in combination with a soft-decision forward error correction algorithm. After an experimental demonstration, we theoretically investigate the scalability laws of the proposed systems in different configuration flavours

Two-Fiber Self-Homodyne Transmission for Short-Reach Coherent Optical Communications

We experimentally evaluate the performance of two-fiber self-homodyne short-reach transmission, showing that it enables the use of DFB laser provided that the optical path mismatch is kept below 1 m for PM-QPSK and 0.5 m for PM-16QAM

Experimental demonstration of coherent transmission over MMF and of the impact of connectors offset

We experimentally demonstrate the possibility of coherent transmission over multimode fiber and discuss its tolerance to offsets in connectors

Adaptive Stokes-Based Polarization Demultiplexing for Long-Haul Multi-Subcarrier Systems

We experimentally evaluate the performance of the adaptive Stokes polarization demultiplexing (PolDemux) algorithm over a long-haul optical link considering the propagation of 31 × 192 Gb/s channels modulated as PM-16QAM multisubcarrier (MSC) signals. Initially, we consider 1 × 24 Gbaud channel under test, and subsequently, we assess the performance of the algorithm on an increasing number of subcarriers (up to 12 × 2 Gbaud) while keeping the same aggregate symbol rate. Taking advantage of the higher robustness of MSC signals toward chromatic dispersion (CD), we demonstrate that the memoryless Stokes-based PolDemux algorithm, originally designed for short reach links, can also be used for low-complexity and modulation transparent polarization demultiplexing in long-haul systems. In addition, we demonstrate that the PolDemux rotation matrix for the MSC signals can be estimated over a restricted group of Nref subcarriers and seamlessly applied to all Nsc subcarriers, thereby significantly reducing the overall complexity by a factor of ∼Nsc/Nref

Statistical Analysis of 100 Gbps per Wavelength SWDM VCSEL-MMF Data Center Links on a Large Set of OM3 and OM4 Fibers

We present a detailed statistical study on achievable reach of 100 Gbps data center optical links based on vertical cavity surface emitting lasers (VCSEL) and multimode fibers (MMF). Based on the characterization of the spectral and spatial properties of eight lasers and of the modal and dispersion behavior of a large set of 20233 OM3 and OM4 modeled fibers (obtained by properly extending an initial set of 500 measured fibers), we compute the resulting frequency responses of all of the VCSEL-MMF combinations. Then, we feed them to a numerical tool modeling PAM-4 transmission at 100 Gbps net bit rate per wavelength. Our model analyzes performance at distances up to 400 meters, using three different adaptive equalizers at the receiver and considering two forward error correction overheads. We show that 100 Gbps operation is feasible for 99% of the simulated links reaching up to 120 m over OM4 at 850 nm and using a decision feedback equalizer (DFE). Aggregated data rates of 200 Gbps and 400 Gbps per fiber using Shortwave Wavelength Division Multiplexing (SWDM) are achievable for 99% of the links reaching 80 m over OM4 using two wavelengths and feed-forward equalizer (FFE) and four wavelengths and maximum likelihood sequence estimation (MLSE)-based equalizer, respectively

MM-wave on-wafer characterization of electro-optic devices: a new, simple approach

A new simple experimental set-up both for on-wafer and in-package electrical and electro-optic characterization of electro-optic devices up to 40 GHz is presented. The technique makes only use of a conventional network vector analyzer (NVA) and of a calibrated high-speed photodetector. The electro-optic transmission coefficient is simply deembedded from the electrical S21 using the detector calibrated responsivity. The RF calibration of the set-up implements the RSOL technique. The results obtained are shown to be comparable with the ones given by commercially available instrumentation, both in terms of accuracy and repeatability. The frequency bandwidth is only determined by the NVA bandwidth provided that the photodetector RF output is well above the NVA noise floor. Firstly some comparison with commercially available instrumentation up to 40 GHz on in-package device will be shown to validate the technique, after that, results concerning both in-package and on-wafer devices up to 40 GHz will be reported

Quasi-3D coupled electro-optical simulation of MQW avalanche waveguide photodetectors

The physics-based modeling of InAlAs/InGaAs waveguide MQW avalanche photodiodes is addressed through a coupled electro-optical quasi-3D approach, based on selfconsistent application of drift-diffusion simulation and the effective refractive index method. The application of the model to two recently proposed waveguide MQW APD structures shows a good agreement with experimental results