We perform a field trial of end-to-end transmission of heterogeneous signals: digital coherent optical (DCO) channels up to 600 Gbps and analog radio-over-fiber (ARoF) carriers at 60 GHz (mmWave) and 210 GHz (sub-THz), across the HEAnet live production metro network, leveraging optical spectrum-as-a-service and a laboratory-based passive optical network. We then perform wavelength-dependent performance characterization of ARoF carriers across the 50 GHz ITU-T channel grid within the C-band, measuring the pre-FEC bit-error rate (BER). The channel whose BER lies within the acceptable FEC threshold is selected as the optimum spectral slot for co-launching ARoF with background WDM traffic. This analysis enables optimization of the spectrum allocation, enhancing performance, throughput, and spectral efficiency, and shows the seamless coexistence of analog and digital traffic services.

This talk presents a new 6G network concept using artificial intelligence-based orchestration and combining radio fixed wireless, free-space optical, and wavelength-division multiplexed transport to enable energy-efficient, low-latency, highly available confluent mesh edge networking.

The vision for 6G involves transforming telecommunications infrastructure from simply providing traditional communication services to offering more intelligent, adaptable, and energy-efficient solutions. These services will integrate and leverage new information sources acquired from the physical and digital worlds. Key enablers for this shift include sensing, localisation, and self-organising networks. In this context, research and development efforts focus on developing sensing at various network segments utilising both inbound and outbound network channels. Network intelligence is evolving in several forms, including as a core element of network optimisation, data management, and service functionalities. These advancements will introduce new roles and use cases within the 6G ecosystem, involving various service layers. This paper explores early developments in transport network sensing and network intelligence within 6G networks, as examined in the SNS-JU ECO-eNET project, and discusses how these innovations may reshape the ecosystem for future 6G applications.

Because of their simplicity, photonic transmitters utilizing dual-wavelength-modulation (dual-lambda-mod) are appealing alternatives to conventional heterodyne systems for the generation of mm-wave and THz signals. However, and contrary to existing literature, the authors argue that dual-lambda-mod systems employing double sideband with carrier (DSB-C) modulation suffer from power fading, making them unsuitable for high-speed mm-wave and THz communications. To address this issue, a dual-lambda-mod system based on single sideband with carrier (SSB-C) modulation is proposed. To demonstrate this concept, a 60 GHz SSB-C dual-lambda-mod system utilizing a gain switched (GS) laser is employed to transmit 2.5 GBd 16-QAM signals. A PD input power penalty of just 2.8 dB is measured compared to a conventional heterodyne transmitter at a BER of 10(-3) for both optical B2B and 10 km of fiber transmission.

We experimentally study transmission of digitally multiplexed 15 GBd PAM-8, wideband 16-QAM OFDM (WiGig) and narrowband 64-QAM OFDM (5G NR) waveforms over a 10 km fiber, undergoing up-conversion to 60 GHz and achieving FEC limited performance.

Fast-switching tuneable lasers with a wide wavelength coverage and with noise and linewidth levels suitable for high-order modulation formats can facilitate the implementation of highly flexible and reconfigurable optical metro, access and inter/intra data center networks. In this work, we show the characterization of a tuneable laser capable of covering a wavelength range of 35 nm in the C-band with nanosecond switching time and low linewidth and use it to demonstrate 480 Gbit/s 16QAM transmission over 25 km of single-mode fiber for a wavelength range of 19 nm.

We provide a vision for 6G fixed networks based on flexible and scalable high-capacity transmission technologies that form mesh edge networks to achieve ultra energy-efficient highly available networks with low latency. These networks will be controlled by AI-native orchestration across mobile, fixed, and compute domains. Mesh networking at the edge will be enabled by a seamless ‘confluence’ of radio fixed wireless (RFW), free space optical (FSO), and switched flex grid wavelength division multiplexed (Flex-WDM) transport using optical-spectrum-as-a-service (OSaaS) and integrated sensing and communication capabilities. In addition, in the frame of the European Smart Network Services Joint Undertaking, the ECO-eNET project will investigate key technologies and concepts to determine the full potential of confluent networks as a viable and scalable platform for 6G.

We demonstrate a flexible millimeter wave optical fronthaul system compatible with analog radio over fiber signals for beyond 5G/6G applications. We experimentally show the successful transmission of up to 32 Gbps data rate with filtered-orthogonal frequency division multiplexed (f-OFDM) signal, enabled using the power loading technique. The transmission of standardized signals using multicarrier f-OFDM and single-carrier QAM has been successfully implemented.

The frequency and phase fluctuations of free-running lasers limit the performance of optical heterodyne sub-THz systems - especially for low subcarrier spacing OFDM signals. Digital impairment compensation is implemented here for the successful generation of 170 - 260 GHz sub-THz OFDM signals over 10km analog-RoF link.

Dual-wavelength-modulation (dual- $\lambda$ -mod) photonic mm-wave/THz transmitters are an attractive alternative to conventional heterodyne systems for their simplicity. In this article, dual- $\lambda$ -mod systems are analysed, paying special attention to the impact of fiber dispersion and signal-signal beat interference. In contrast to what has been reported in the literature, it is concluded here that dual- $\lambda$ -mod systems based on optical double sideband (DSB) modulation are subjected to power fading, rendering them useless for high-speed mm-wave/THz communications. To solve this, the use of optical single sideband (SSB) modulation – which is immune to power fading – is proposed here. Using a gain-switched (GS) laser, a 60-GHz SSB dual- $\lambda$ -mod system transmitting 2.5-GBd 16-QAM signals is demonstrated experimentally. A penalty of around 2.8 dB is measured with respect to the conventional dual-path heterodyne transmitter over optical B2B and 10-km transmission. The reduction in complexity enabled by the demonstrated system aids in the deployment of cost-effective mm-wave/THz networks.

We demonstrate a 4-channel SOA-amplified 100 Gbit/s/λ probabilistically shaped PAM-8 C-band transmission for next-generation optical access networks. Power budgets up to 30.25 dB were obtained using T-spaced equalization on a 20-GHz bandwidth-limited system.

Efficient use of spectral resources will be an important aspect of converged access network deployment. This work analyzes the performance of variable bandwidth Analog Radio-over-Fiber signals transmitted in the unfilled spectral spaces of telecom-grade ROADM channels dedicated for coherent signals transmission over the OpenIreland testbed.

High-capacity data transmission for intra/inter-data centre links has become necessary to accommodate the massive increase in data traffic. Data transmission needs to be reconfigured based on instantaneous demand or based on certain cyclical and predictive traffic patterns. In this work, we demonstrate a record high transmission rate of 200 Gbps/$\lambda$ and 160 Gbps/$\lambda$ with 40 GHz 32QAM and 40 GHz 16QAM OFDM signal (over C-band) using the wavelength-tunable InP-Si$_{3}$N$_{4}$ laser source from the integrated dual laser module for short-reach application. We also demonstrate the data transmission with bandwidth reconfigurability and flexible higher-order modulation allocation enabled by this laser source's low relative intensity noise ($< $ −160 dB/Hz). We successfully show that the data transmission performance in back-to-back and over-fibre is within the standard FEC limits and goes beyond our previous works by leveraging wideband multi-carrier to achieve rates not yet shown before with this device.

Optical heterodyne analog radio-over-fiber (A-RoF) links can provide a cost-effective and spectrally efficient solution for the generation and distribution of millimeter-wave/Terahertz (mm-wave/THz) carriers for the next-generation wireless systems. The use of an optical frequency comb (OFC) source in such a system can facilitate carrier generation free from frequency fluctuation. However, decorrelation between tones, due to path length difference, can lead to phase noise on the generated mm-wave carrier — limiting the performance of low subcarrier spacing multi-carrier signals specified in the 5G standard. In this work, we analyze the effect of comb tones decorrelation due to path length difference on the performance of 5G compatible 244 kHz subcarrier spacing 59 GHz OFDM signal over an optical heterodyne A-RoF link using a gain switched laser (GSL) OFC source. Furthermore, we demonstrate the ability of the OFC-based A-RoF optical/mm-wave system to support flexible and interoperable mm-wave functionality through signal generation at 27 GHz, 43 GHz and 59 GHz using different pairs of GSL OFC tones for remote heterodyning. The capability of multi-frequency 5G NR compatible mm-wave signal generation and potential for photonic integration make the demonstrated GSL OFC based optical heterodyne A-RoF system a suitable candidate for deployment in the next generation wireless systems.

We demonstrate a practical wavelength reuse bidirectional analog radio-over-fiber (A-RoF) system served by a single distributed feedback (DFB) laser. Frequency interleaving of downlink and uplink signals is proposed to ameliorate the spectral efficiency and mitigate the interference raised by the bidirectional transmission. Pre-emphasis is exploited to counteract the performance impairment brought about by the interaction between laser chirp and fiber chromatic dispersion. Through employing 64-QAM modulated 16 bands and 16-QAM modulated 12 bands filtered orthogonal frequency division multiplexing (f-OFDM) signals with 200 MHz bandwidth, asymmetric transmission with superior flexibility over 25 km fiber is attained, with an aggregate capacity of 20 Gb/s for downlink and 10 Gb/s for uplink. The mutual interference between the downlink and uplink is explored by overlapping the downlink and uplink signal spectra to varying degrees. Using the optimum frequency configuration, system performance is evaluated in terms of EVM and phase noise. To further investigate the effects caused by the Rayleigh backscattering and the stimulated Brillouin scattering (SBS), simulations are conducted on the proposed architecture, validating the conclusion from the experiment that the bidirectional transmission is primarily limited by the Rayleigh backscattering than the stimulated Brillouin scattering.

In this work we analyse and demonstrate the coexistence of digital coherent and analogue radio over fibre signals over an access-metro transmission network and field fibre. We analyse how the spectral proximity of the two signals and the non-ideal filter alignment of typical telecomms-grade ROADMs affect the signal performance. Our results show that coexistence is indeed possible, although performance deteriorates with the increase in number of ROADMs in the network topology. Thus, while today's access-metro networks will be able to support future 5.5 and 6G cell densification operating at mmWave and THz frequency, using spectral efficient analogue radio over fibre transmission, there will be trade-offs to be considered. In our experiment setup, we show that the limit for ARoF accessible performance is reached after transmission over 3 ROADMs and a total of 49 km of fibre.

A highly flexible wavelength and space switched analog radio-over-fiber (ARoF) fronthaul transmission of a millimeter-wave (mmWave) emerging 6G waveform over a centralized/cloud radio access network (C-RAN) is experimentally demonstrated in this work. A spread spectrum multiplexing technique — orthogonal chirp division multiplexing (OCDM) — which is highly resilient to inter-channel interference and enables enhanced channel estimation is utilized in the fronthaul transmission demonstration. The flexible properties of a low noise silicon photonic (SiP) microring resonator (MRR) based tunable laser and a low cross-talk $4\times 4$ SiP optical wavelength/space switch are combined to form a reconfigurable 10 km fronthaul system enabling 64-QAM OCDM transmission at 24 GHz with consistent performances ~5% EVM across all test wavelengths/ports. A signal constituting Wi-Fi and 5G NR standard compatible 64-QAM orthogonal frequency division multiplexing (OFDM) bands, at 10 GHz and 24 GHz respectively, are also transmitted and evaluated in the proposed system with EVM performances below 64-QAM EVM limit (8%) achieved, thus demonstrating the system’s potential in a future converged multi-service environment.

The emergence of the millimeter wave (mm-Wave; 30 GHz to 300 GHz) frequency band holds a lot of promise for addressing the congestion at low frequency in future mobile networks. Among many mm-Wave generation schemes, optical heterodyning is considered one of the most promising approaches due to its scalability and potential for integration on chip. Employing optical frequency combs (OFC) for optical heterodyning alleviates the significant phase distortions/noise introduced by the optical sources. However, any residual phase noise in these systems can deteriorate the transmission performance. Here we demonstrate a high-capacity mm-Wave radio-over-fiber (RoF) system using Fabry-Pérot (FP) laser comb overcoming the typical limitations of this source. The temporal phase perturbation induced by the frequency fluctuation of the FP laser is theoretically analyzed, and then estimated and compensated by a pilot-based phase equalizer. Performance evaluation of the proposed phase equalizer is conducted through experiment and simulation. Enabled by the proposed compensation scheme, ten 200 MHz filtered orthogonal frequency division multiplexing (f-OFDM) signal bands modulated by 16-quadrature amplitude modulation (QAM) are transmitted over 10 km fiber, with the ability to serve multiple users. The transmission of 16-QAM modulated single carrier signals with 2 GBd and 8 Gbps data rate is also performed for comparison, which offers better resilience to phase noise, demonstrating the first commercial Quantum Well FP laser-based optical heterodyning mm-Wave RoF system for both multi-carrier and single carrier signals.