High-capacity Wavelength-division Multiplexing Research Articles

High-Capacity Coherent WDM Networks Empowered by Probabilistic Shaping and End-to-End Deep Learning

To optimize the functionality of coherent optical fiber communication (OFC) systems and enhance their capacity related to long-haul transmissions, wavelength-division multiplexing (WDM) and probabilistic constellation shaping (PCS) techniques have been used. This paper develops an end-to-end (E2E) deep learning (DL)-based PCS algorithm, i.e., autoencoder (AE) for a high-order modulation format WDM system that minimizes nonlinear effects while ensuring high capacity and considers system parameters, in particular those related to the OFC channel. Only the AE of the central channel is trained to meet the specified performance objective, as the system design employs identical AEs in each WDM channel. The simulation results show that the architecture should consist of two hidden layers, with thirty two nodes per hidden layer and a ”32×modulation order” batch size to obtain optimal system performance, when designing AE using a dense layer neural network. The behavior of the AE is examined to determine the optimum launch-power ranges that enhance the system's performance. The developed AE-based PCS-WDM provides a 0.4 shaping gain and outperforms conventional solutions.

Mitigating network adaptation and QoT prediction challenges in WDM networks

Abstract The capacity and efficiency of optical communication networks have been completely transformed by wavelength division multiplexing (WDM) technology, which allows many wavelengths to be transmitted simultaneously over a single optical fibre. Conventional QoT prediction is based on analytical models that consider physical layer characteristics including dispersion, optical power and signal-to-noise ratio. But these models frequently oversimplify complex real-world situations, which reduces their accuracy for modern high-speed WDM networks. A data-driven solution is provided by machine learning(ML), which may boost the accuracy of QoT predictions by utilising real-time measurements, historical data and a variety of network situations. The creation of a ML-based framework for QoT prediction is investigated in the current research. This research proposes an effective ML-based routing computation model that uses a non-linear autoregressive recurrent neural network (ML-RCNA-RNN) to ensure QoT for every wavelength channel in high-capacity and high-speed WDM networks. Through simulations, more accurate QoT metrics, such as bit error rate (BER) 68.42 %, QoT prediction accuracy (Q-Factor) 5.9 %, network adaption time (ms) 48.3 %, latency (ms) 0.28 % and throughput (Gbps) 14.29 %, have been obtained compared to conventional QoT predictions. These results were obtained using Gaussian noise Python simulation (GNPy). As a result, the proposed framework that makes use of GNPy demonstrates that it substantially enhances optical communication networks’ performance and dependability. This facilitates the development of high-capacity, low-latency and reliable communication infrastructure, and makes it more adaptable and able to manage the complexity of high-speed WDM optical networks while preserving signal quality in the modern digital era.

Ultra-Wide Free-Spectral-Range Silicon Microring Modulator for High Capacity WDM

Silicon microring modulators (MRM) are a promising technology for next generation datacenter interconnects, where migration to higher data capacities will require the increasing use of wavelength division multiplexing (WDM). However the periodic repetition of wavelength resonances, and the limited free-spectral range (FSR) of MRMs, can limit the number of WDM channels when we use the wavelength selectivity of the MRM to modulate a particular wavelength from frequency comb sources or other multi-wavelength sources propagating in the bus waveguide. In this paper, we realize an ultra-compact, high bandwidth, CMOS compatible MRM which has an ultra-wide FSR of 4 THz, 3-dB electro-optic (EO) bandwidth of >67 GHz and which can operate at high datarates for standard single mode fiber transmission in the C-band. Using the modulator, we demonstrate 100 Gbaud PAM-4 intensity modulation-direct detection (IM-DD) with 4 wavelengths within a single FSR in the wavelength range of 1540 nm–1570 nm. The bit-error-rate (BER) of the transmission was below the general 7% hard-decision forward-error correction (HD-FEC) of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> .

SOA-Integrated Silicon Photonics Switch and Its Lossless Multistage Transmission of High-Capacity WDM Signals

We experimentally demonstrate the lossless transmission of wavelength division multiplexing (WDM) signals through a silicon-photonics 4 × 4 switch with a flip-chip bonded 4-channel semiconductor optical amplifier (SOA). We first optimized the input power and gain of the SOA-integrated switch to obtain the optimum operation point in terms of the transmitted signal quality. We then performed simultaneous transmission of 8-ch, 32-Gbaud, SP 16-QAM WDM (800 Gb/s) signals through all the four paths of the switch. The effect of crosstalk on the switch was very small, and thus could not be observed. We also examined multistage (up to four stages) transmission of the signals with circulating configurations. We show that even for a 4-stage transmission, the bit error rate of the transmitted signal is below the 20% forward-error-correction limit. Finally, we discuss approaches to improve the optical signal-to-noise ratio of the transmitted signals to enlarge the signal quality margin and increase the possible number of the cascading stages and/or WDM channels for wide applications.

800 Gb/s (8 × 100 Gb/s) Nyquist Half-Cycle Single-Sideband Modulation Direct-Detection Transmission Over 320 km SSMF at C-band

Direct detection shows great attraction in short- and medium-reach transmission for its low cost and easy integration. Especially, single-sideband (SSB) Nyquist subcarrier modulation is a promising technology due to its high spectral efficiency and strong tolerance to chromatic dispersion. In this paper, we experimentally demonstrate 800 Gb/s (8 × 100 Gb/s) direct-detection wavelength-division multiplexing (WDM) transmission over 320 km standard single-mode fiber (SSMF) with Nyquist 16-ary quadrature amplitude modulation (16-QAM) and half-cycle SSB subcarrier modulation. Each channel carries 25 Gbd 16-QAM SSB signal and the channel spacing is 35 GHz. The nonlinear performance is discussed for both single channel and WDM systems. The bit error rate of the WDM system transmitting over 320 km SSMF is 6.73 × 10–3. Considering 20% hard-decision forward error correction and frame redundancy, a net bit rate of 650.4 Gb/s is achieved with a spectral efficiency of 2.32 b/s/Hz. With this spectral efficient modulation technique, our study achieves C-band high-capacity direct-detection WDM systems with metro distance transmission as long as 320 km SSMF.

An efficient fault localization or detection mechanism for high speed optical networks

Optical burst switching (OBS) has been considered as the gate through which the envisaged world of optical Internet will be conquered by implementing Internet Protocol (IP) software directly over a wavelength-division-multiplexing (WDM) optical layer (IP/WDM). The main feature for designing next generation optical networks is protecting and restoring high capacity WDM networks from the failures. Quick detection, identification and restoration make networks more strong and consistent even though the failures cannot be avoided. Hence, it is necessary to develop fast, efficient and dependable fault localization or detection mechanisms. In this paper, an efficient scheme for OBS networks has been proposed to provide fast restoration of links with minimum delay as well as blocking probability. By simulation results, it is shown that the proposed OBS scheme achieve less blocking probability and delay while getting higher throughput in comparison to conventional schemes.

Visible to infrared high-speed WDM transmission over PCF

We achieved high-speed wavelength division multiplexing (WDM) transmission in the visible to infrared region over a 1km photonic crystal fiber (PCF). We realized ultra-wide and high-speed WDM transmission using six wavelengths in the 658 to 1550nm wavelength range, which corresponds to a frequency bandwidth of 263THz. We demonstrated WDM transmission of 1Gbit/s at 658nm and 10Gbit/s at 780nm and four infrared wavelengths. Our experimental results show that low loss PCF is very attractive for use in future high capacity WDM systems with an ultra wide bandwidth.

Impact of Fiber Non-linearity in High Capacity WDM Systems and in Cross-Connected Backbone Networks

The rapidly increasing data traffic volumes will demand for very high transmission capacity and network nodes’ throughput. Wavelength division multiplexing (WDM) technology will be asked to support many channels on the same fiber, both in point-to-point links and in WDM optical networks. The transmission of a high number of wavelength channels in all these systems is a key issue. This paper analyzes this topic, in both high capacity links and optical networks, highlighting the impact of fiber non-linearity, and addressing the main source of impairments. This is done through the use of a semi-analytical model recently upgraded to account for all the contributions deriving from Kerr effects, particularly four-wave mixing and cross-phase modulation. The analysis reveals that more than one hundred of channels at 2.5 Gbit/s can be transmitted in point-to-point links whose length can span until the order of 1000 km, and 32 channels per fiber, at the previous bit rate, can be handled in WDM networks, without dispersion compensation. For a higher number of channels (e.g., 64) dispersion compensation is needed.

Development of IR-emitting colloidal II-VI quantum-dot materials

The current state-of-the-art of colloidal II-VI nanocrystal formation using the aqueous/thiol synthesis route is described. Work on single component and heterostructures and mixed compound quantum dots is discussed. The purpose of the work is to provide a range of infrared (IR)-emitting materials with high quantum efficiency (QE) as potential gain media for future ultrawideband optical amplifiers for high-capacity wavelength-division multiplexing (WDM) telecommunications systems. Physical and chemical factors influencing particle sizes are described.

Key building blocks for high-capacity WDM photonic transport networks

The objective of this paper is to give an overview of the different studies we have performed at the research level regarding the design and implementation of a photonic wavelength division multiplexing (WDM) layer providing transparent transport services to client layers (SONET/SDH, ATM, etc.). Such a network requires a number of enabling factors to be assessed in order to become a reality. Among these factors are the availability of high-capacity WDM transmission systems and efficient optical routing nodes based on mature technology, the design of robust networks optimizing the utilization of resources, and the development of a management system in accordance with presently applied standards for transport networks. We review our achievements in these different fields.