Incoherently Pumped Tunable Raman Fibre Laser Operating Across 1625-1653nm

Nura Adamu, Hao Liu, Kyle R. H. Bottrill, Periklis Petropoulos, Optoelectronics Research Centre, University of Southampton

Fibre laser systems operating in the U-band (1625-1675 nm), are attractive for a range of applications, such as methane sensing, deep tissue imaging, eye surgery and LIDAR. However, achieving efficient laser operation in this region based on doped optical fibres is very challenging. This makes Raman fibre lasers (RFLs) attractive, due to their design simplicity and versatility in their operating wavelength. We demonstrate a RFL based on an incoherently pumped ring cavity configuration realized using a non-zero dispersion shifted fibre (NZDSF). Amplified spontaneous emission (ASE) from an erbium-doped fibre amplifier (EDFA), shaped with a gain flattening filter, was used as the incoherent pump source, giving rise to a broad gain bandwidth. An optical signal-to-noise ratio (OSNR) greater than 55 dB was obtained at 1650 nm. This work shows feasibility of constructing RFLs using off-the-shelf components to deliver efficient gain in the challenging 1625-1675nm region.

Automating Network Growth: Graph Machine Learning Approaches to Fibre Expansion

Akanksha Ahuja, Sam Nallaperuma, Albert Rafel, Paul Wright, Andrew Lord and Seb J. Savory, Department of Electrical Engineering, Darwin College, University of Cambridge

 Optical network providers must expand the physical infrastructure of national-level core networks efficiently and regularly by adding new fibre onto the network to increase capacity, maintain optimal utilisation and ensure resilience. Physical topologies can be represented as graphs, where each node represents a geolocation hosting network equipment, and each edge represents an optical fibre connecting these regions. Fibre prediction or edge prediction is the forecasting of new connections in optical networks and is critical for automating the scalability of the infrastructure. Our research aims to predict edges among existing nodes to inform optical network expansion planning and infer patterns of network design. We represent the physical topology as a graph and develop machine learning and graph embedding techniques to predict fibre connections, quantitatively demonstrating high edge prediction accuracy on real-world core networks. The predictive graph learning approach outperforms heuristic methods and captures the intelligence of network design.

Optimization of Fibre Optical Parametric Amplifiers for QAM Signal Amplification

Mariia Bastamova, Aston Institute of Photonic Technologies

Fiber optical parametric amplifiers (FOPA) offer theoretically unlimited bandwidth of operation in almost arbitrary wavelength ranges, the capability of phase-sensitive noiseless amplification, high gain, and applicability for ultra-fast transient-free applications. These features are crucial for applications involving the amplification of extremely low-power or few-photon signals, such as space or quantum communications.
We demonstrated that the challenge of gain fluctuations in FOPA arising from pump phase modulation, necessary for mitigating Stimulated Brillouin Scattering, does not cause degradation for coherently detected QAM signals compared to OOK signals. The reason is that QAM signals rely on the electric field amplitude being the square root of power.
The design of a polarization-diverse FOPA architecture allows for further compensation of the impact of pump phase modulation by adjusting the pumps’ optical path difference and the pump phase modulation frequencies. Theoretically this approach can decrease the required optical signal-to-noise ratio penalty by a factor of 10.

Training Strategies for Learned Volterra MIMO Equalizers in WDM Systems

Nelson Castro, Aston Institute of Photonic Technologies

This research advances training strategies for a learned Volterra MIMO equaliser tailored for Wavelength Division Multiplexing (WDM) systems. Building upon prior success with minimal steps per span, our current focus is improving training efficiency. The equaliser integrates filters to address key signal impairments, and our work delves into refining training strategies for these filters. As part of the considered techniques, we explore the potential of applying transfer learning among the channels in the equaliser. This investigation yields valuable insights into the interplay of training strategies and filter optimisation, contributing to the enhanced performance of learned Volterra MIMO equalisers in WDM systems. Authors: Nelson Castro, Sonia Boscolo, Andrew Ellis, Stylianos Sygletos

Introducing Automatic Initialization Procedure and Temperature-Independent Detection Anticipation Technique for a Plug-and-Play Quantum Key Distribution System

Márton Czermann(1,2,), Benjámin Ott(1,2), Áron Szabó(2), Péter Trócsányi(3), Attila Róka(1), Benedek Kovács(2)

The readiness of Quantum Communication Technologies has already been demonstrated all around the globe. A European initiative, called EuroQCI, aims to realize a quantum communication infrastructure by the end of 2027, throughout the continent. Therefore, our focus is making these technologies integrable into our classical telecommunications infrastructure, while improving their quality parameters, following plug-and-play principles.
In our poster, we present an automatic initialization process and patent-pending synchronization technique for a fiber-based plug-and-play Quantum Key Distribution (QKD) system that implements phase-encoding BB84 protocol. The initialization process helps us to configure the system with optimal parameters for a low QBER to achieve secure operation, while the synchronization technique allows photon detection anticipation even under continuously changing environmental conditions. Finally, our architecture enables us to choose between quantum protocols, giving flexibility to serve diverse application requirements.
The system has been developed at Budapest University of Technology and Economics, in cooperation with Ericsson Hungary.

Affiliation: (1) Department of Networked Systems and Services, Faculty of Electrical Engineering and Informatics, Budapest University of Technology and Economics, (2)Ericsson Hungary, Budapest, Hungary (3) Department of Theoretical Physics, Faculty of Natural Sciences, Budapest University of Technology and Economics

Forward Error Correction for High-Capacity Transmission Systems

Safiya Dabwan, Nelson Castro, Stylianos Sygletos, Aston Institute of Photonic Technologies

We studied the interplay between forward error correction FEC and fibre nonlinearity compensation performed with digital backpropagation DBP in long-haul fibre channels. A state-of-the-art scheme based on Bit Interleaved Coded Modulation BICM was developed and built up with concatenated FEC implementation. Several Implementations were then evaluated in a comprehensive setup with DBP of different complexities to determine configurations suitable for diverse applications. Our findings suggest that integrating 3 steps/span DBP can enhance the reach of 300 km channels by 30% to be 400 km, while maintaining a fixed coding overhead 27.5%. Interestingly, the same distance extension can be achieved without the need for DBP but at the cost of increasing the coding overhead from 27.5% to 41.67%. The utilized BICM scheme was proven to be equivalently efficient without a bit interleaving function, thereby, the elimination of that has contributed to reducing the overall complexity of the system.

E-band amplifier based on combined neodymium-doped fibre and bismuth-doped fibre amplification

Dr Aleksandr Donodin, Aston University

The conventional optical networks exploit a bandwidth of only 10 THz allowed by commercially available Er-doped fibre amplifiers (EDFAs) in C- and L- optical bands (1530-1620 nm). The multi-band transmission (MBT) maximizes the return on investments in the existing infrastructures by the transmission in the so-called O, E, S, and U optical bands. However, it requires a substantial advance in efficient optical amplifiers for these spectral bands, similar to a major breakthrough in telecommunications made by the development of Er-doped fibre amplifiers.Here we report a concept of a novel hybrid bismuth-doped fibre and neodymium-doped fiber amplifier with high optical gain and extended bandwidth of operation in the E-band. The developed amplifier features a maximum gain of 43 dB and a minimal noise figure of 5.5 dB enabled by 150-m Bi-doped fibre length and 2x7m 𝑁𝑑3+-doped fibre. The performance demonstrates a high potential of combining both NDFA and BDFA.

Weight Clustering for Simplified Time-Domain Chromatic Dispersion Mitigation in Optical Fiber Communications

Geraldo Gomes, Pedro J. Freire, Jaroslaw E. Prilepsky, Sergei K. Turitsyn, Aston University

This study explores weight clustering to reduce chromatic dispersion compensation (CDC) complexity in optical fiber links, focusing on a 16-QAM transmission across 1280km of standard single-mode fiber (SSMF) at 32Gbd. Simulations show that the integration of time domain-based CDC and weight clustering effectively reduces the number of required filter taps, with a plus finding that as the power and nonlinearity increase, fewer clustered filter taps are needed for CDC, leading to reduced processing complexity. This counter-intuitive finding can be attributed to the interplay between anomalous dispersion and nonlinear self-phase modulation in SSMF and can be leveraged to simplify CDC complexity and free up hardware resources for other equalizers in digital coherent receivers.

Ultrawideband (21.9 THz) Ytterbium Doped Fibre Amplifiers for 1 µm Data Transmission

Xin Huang, Sijing Liang, Lin Xu, David J. Richardson, Yongmin Jung, Optoelectronics Research Centre, University of Southampton

Ytterbium-doped fibre amplifiers (YDFAs) are renowned for their broad emission bandwidth, but the focus on designing wideband YDFAs tailored specifically for data transmission has been limited, owing to the challenges posed by relatively high propagation losses in conventional silica fibres. Recent breakthroughs, highlighted by the development of a record low-loss hollow core fibre operating at 1 µm (0.3 dB/km @1060 nm), have opened new possibilities for 1 µm data transmission.
This study introduces an innovative ultrawideband ytterbium-doped fibre amplifier particularly engineered for optimal performance in 1 µm data transmission. The amplifier showcases an impressive 21.9 THz bandwidth spanning from 1025 to 1110 nm, featuring an >20 dB average gain coupled with a <5.1 dB noise figure. This advancement marks a significant step towards unlocking the full potential of ytterbium-doped fibres in high-speed, long-distance data transmission applications.

Within microseconds: An ultra-fast, low-loss and non-blocking free space optical switch based on a piezo-actuator and a multi-lens beam-steering system

Yanwu Liu, George Zervas, UCL

Conventional data centre networks (DCNs) with multi-layer switching structures are inherently limited by oversubscription, hotspots, congestions and cabling complexities. All optical circuit switching in free space (FSO) provides a potential solution to reconfigure the scalability of a DCN and serve as a dynamic interface between multiple processing blocks. However, commercial switches such as POLATIS Series 7000 are limited by the mechanical switching speed of milliseconds. In this research, an ultra-fast (around 1.5 us), low-loss, low-crosstalk and non-blocking (5×5) FSO switch based on a piezo-actuator and a multi-lens beam-steering system at 1550nm has been theoretically proposed and simulated in an end-to-end configuration in an optical design software Code V, aiming to address the key requirements of a classical switching task in DCNs. This research also plans to manufacture an error-tolerant prototype, and experimentally explore its operational limits in a variety of computing technologies.

Photonic Reservoir Computing for Kramers-Kronig Receiver Linearization

Sarah Masaad and Peter Bienstman, Photonics Research Group, Department of Information Technology, Ghent University – imec, Belgium

We numerically demonstrate the use of a photonic reservoir co-trained with an electronic feed forward equalizer (FFE) for the linearization of a Kramers-Kronig (KK) receiver operating at restricted sampling rate and low carrier powers. The KK receiver is operated at 3 samples per symbol instead of the required 6, and using carrier-to-signal power ratios between 5 and 8 dB instead of the required 9 dB. This causes the receiver to behave nonlinearly, thus distorting the signal post-detection and limiting the successfulness of the necessary digital signal processing (DSP) blocks like chromatic dispersion compensation. Our proposed reservoir-FFE network sandwiches the receiver and is trained to improve its linearity. The network is trained on back-to-back systems and then tested in a plug-and-play manner in varying short-reach links. Numerical results show successful linearization with up to 4 times reduction in bit error rate. ©2023 The Author(s)

Direct Laser Diode Interconnection with a Hollow Core Fibre

Jing Meng, Sijing Liang, Qiang Fu, Ian A. Davidson, Hesham Sakr, Gregory Jaison, Natalie Wheeler, Francesco Poletti, David J. Richardson, Yongmin Jung, Optoelectronics Research Centre, University of Southampton

Direct interconnection of a laser diode or photodiode with a hollow-core fibre (HCF) – without the need for an intermediate solid core fibre – is a very important requirement for fully leveraging the unique characteristics of HCFs, such as low-loss, low-latency, low dispersion and low nonlinearity.
This study explores two specific methods for HCF interconnection – butt coupling and a two-lens system. Using an 850 nm VCSEL, butt coupling achieved an efficiency of ~69%, while the two-lens system demonstrated an outstanding ~96% efficiency, accompanied by superior beam quality. Extending our investigation to mid-IR QCL sources, we achieved an efficiency of ~70%. These findings highlight the versatility and efficiency of HCF interconnection methods across diverse laser sources, promising enhanced performance in optical communication systems.

Online digital compensation of phase and amplitude distortions in cascaded FOPA transmission links

Long Nguyen, Aston University

 Today mitigating stimulated Brillouin scattering (SBS) remains a significant challenge for the eventual penetration of fibre-optical parametric amplifiers (FOPAs) into future communication systems. The pump phase modulation that is often used for SBS mitigation causes temporal variation of the parametric gain, which is primarily a source of phase distortion for coherently detected quadrature-amplitude modulation (QAM) signals. Here, we introduce a new and fully online digital signal processing (DSP) scheme that enables compensation of the intrinsic dithering-induced phase distortion and its conversion into amplitude distortion when interacting with the dispersive fibre channel in transmission systems with cascaded FOPAs operating with multi-tone pump dithering to support sufficient SBS-limited gain. Through extensive numerical simulations, we identify the required dimensioning for performance improvement and evaluate the scheme’s robustness against non-ideal conditions. We demonstrate that enhancing a conventional DSP chain with the proposed algorithm achieves significant performance benefits in 28-Gbaud 16-QAM transmission. We believe that our scheme may become a key component of future FOPA-amplified links, where pump dithering will be necessary to achieve high amplification gains.

Experimental investigation of S-band optical amplifiers in long-haul coherent transmission systems

D Pratiwi, P. Hazarika, M. Tan, A. Donodin, and W. Forysiak, Aston University

 Ultra-wideband transmission techniques are being explored as an alternative and essential solution to address the expanding demand for data capacity. Distributed Raman amplifiers, discrete Raman amplifiers, and Thulium-doped fibre amplifiers (TDFA) are potential technologies to provide signal amplification in the S-band (1470 nm to 1520 nm). We experimentally compare the performance of these S-band amplifiers in long-haul coherent transmission systems.

Co-packaged 14xxnm Pump Chips for Raman Amplification

Mostafa Rady, Coherent

 Distributed Raman amplification is used through many parts of optical fibre networks. Raman pump modules require multiple high power dissipating lasers. With the drive to improve power efficiency in optical networks, co-packaging of pump chips in compact packages is essential to achieve this goal. Design and performance is described of a hermetically sealed Raman pump laser with two independently driven laser diodes, each coupled to a fibre tail with an integrated Bragg grating for wavelength locking. The wavelength selection for each laser diode is fully customisable, allowing for similar or dissimilar wavelength configurations. Power dissipation and thermal management considerations are discussed, as well as the evaluation of thermal and optical crosstalk.


Two-photon lithography for lanthanide-doped 3D ceramics microarchitectures with temperature promoted photoluminescence

Cristian Rosero Arias, University of Twente

Two-photon lithography (TPL) is revolutionizing the creation of submicrometric 3D designs, particularly in integrated photonics and precision manufacturing of ceramic microarchitectures like zirconia (ZrO2). Lanthanide-doped ZrO2 microarchitectures are of utmost importance due to high-refractive index ceramic that functions as a host and emitting-doping elements, which could enhance the functionalities of optical devices. However, suboptimal photoluminescence of lanthanide-doped ZrO2 microarchitectures is due to defects and non-ideal crystallinity in the manufacturing process. Here, we show that strategic thermal treatments can significantly refine the crystalline structure of ZrO2, thereby amplifying the luminescent response of lanthanide elements incorporated within these structures. Our results illustrate enhanced lanthanide photoluminescence in 3D microarchitectures, emphasizing the role of crystallinity. This approach diversifies the spectrum of sophisticated luminescent materials and paves the way for integrating additive manufacturing with microfabrication technologies within the micro-optics domain.

Dissipative soliton breathing dynamics driven by desynchronization of orthogonal polarization states

Qing Wang, Aston University

Breathing solitons, e. g. dynamic dissipative solitons with oscillating pulse shape and energy caused by different mechanisms of spatiotemporal instabilities, received considerable interest from the aspects of nonlinear science and potential applications. However, by far, the study of breathing solitons is still limited within the time scale of hundreds of cavity round trips, which ignores the slow dynamics. To fill this blank, we theoretically investigate a new type of vector dissipative soliton breathing regime and experimentally demonstrate this concept using mode locked fibre lasers, which arise from the desynchronization of orthogonal states of polarization in the form of complex oscillations of the phase difference between the states. The obtained results can reveal concepts in nonlinear science and may unlock approaches to the flexible manipulation of laser waveforms towards various applications in spectroscopy and metrology.