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This article highlights the potential of photonic-assisted analog fronthaul solutions, particularly analog radio-over-fiber (ARoF) and analog radio-over-free-space-optics (ARoFSO), as prospective alternatives for the development of 6G applications. First, we present (New-Radio) NR/5G conformance testing of ARoF and ARoFSO fronthaul links, including the assessment of the error vector magnitude (EVM) and adjacent channel leakage power ratio (ACLR) to demonstrate compliance with the minimum transmitter requirements outlined by the 3rd Generation Partnership Project (3GPP) standards. Then, with focus on future 6G Distributed-MIMO (D-MIMO) networks, we conduct experimental validations of coherent joint transmissions (CJT) using ARoF and ARoFSO fronthaul links in a 2-transmitter D-MIMO network, demonstrating MIMO gains of up to 5.35 dB and that these links meet the stringent synchronization demands for CJT. These tests represent the first realizations of CJT utilizing ARoF and ARoFSO links. Finally, for consistency, we validate CJT in a 4-transmitter D-MIMO network with ARoF fronthaul links, with MIMO gains up to 9.4 dB and confirming our previous results. This evidence indicates that these technologies hold significant potential for applications in future 6G systems.

Development of Data Center based computing technology require energy efficient high-speed transmission links. This leads to optical amplification-free intensity modulation and direct detection (IM/DD) systems with low complexity equalization compliant with IEEE standardized electrical interfaces. Switching from on-off keying to multi-level pulse amplitude modulation would allow to reduce lane count for next generation Ethernet interfaces. We characterize 106.25 Gbaud on-off keying, 4-level and 6-level pulse amplitude modulation links using two integrated transmitters: O-band directly modulated laser and C-band externally modulated laser. Simple feed forward or decision feedback equalizer is used. We demonstrate 106.25 Gbaud on-off keying links operating without forward error correction for both transmitters. We also show 106.25 Gbaud 4-level and 6-level pulse amplitude modulation links with performance below 6.25% overhead hard-decision forward error threshold of 4.5 × 10−3. Furthermore, for EML-based transmitter we achieve 106.25 Gbaud 4-level pulse amplitude modulation performance below KP-FEC threshold of 2.2 × 10−4. That shows that we can use optics to support (2x)100 Gbps Ethernet on single lambda at expense of simple forward error correction.

With the exponential growth of internet traffic, driven by the increasing number of connected devices and data-intensive applications, there is an urgent need to address the surging demand for higher capacity in datacenter communications. This article proposes using O-band single-carrier coherent transmission to achieve 1.6 Tbps for intra-datacenter reach (2-10 km), leveraging the advancements in next-generation DACs and the TFLN platform. To support our proposal, we assess experimentally the gain of employing 256 GSa/s interleaved DACs compared to the current state-of-the-art 128 GSa/s DACs. Additionally, we explore the feasibility of utilizing cost-effective DFB lasers in these short-reach systems. Using the 128 GSa/s DAC and DFB lasers, we transmit 120 Gbaud DP-64QAM over 10 km of SSMF under the 20% overhead SD-FEC threshold, featuring a net rate of 1.2 Tbps. Switching to 256 GSa/s DAC, we achieve net 1.6 Tbps transmission over 10 km with 167 Gbaud DP-64QAM below the 25% SD-FEC BER threshold. We observe that the power penalty of using DFB lasers compared to ECLs is less than 1 dB. Furthermore, this study includes a comprehensive analysis of the power consumption envelope for various candidate configurations targeting 1.6 Tbps operation. The comparison reveals the competitiveness of the O-band single-carrier coherent solution, attributed to its simpler architecture and the inherent features of the TFLN platform. The analysis highlights the potential of the proposed solution as a power-efficient and high-performance option for meeting the demanding requirements of 1.6 Tbps Ethernet.

As internet traffic demand continues to increase, high-speed electro-optic modulators and high-bandwidth RF components are needed to stretch intensity modulation direct detection (IMDD) systems to their limits. In this study, we experimentally demonstrate the transmission performance using the next generation of digital-to-analog converters (DAC) and high-bandwidth thin-film lithium niobate (TFLN) modulators. In the C-band, we transmit 172 Gbaud PAM6 and 180 Gbaud PAM8 over 120 m of SSMF under the 6.7% overhead hard-decision forward error correction (HD-FEC) and the 20% overhead soft-decision (SD)-FEC thresholds, which respectively correspond to net 400 and 450 Gbps. We also demonstrate the first transmission of net 400 Gbps over 10 km in the O-band (1310 nm) using 172 Gbaud probabilistically shaped (PS)-PAM8 under the 20% SD-FEC BER threshold. Our results indicate that the TFLN platform has the potential to support even higher data rates with the development of high-bandwidth RF components.

In this paper, we demonstrate up to 260-GBaud single-wavelength coherent transmission by employing an optical transmitter based on two wide-bandwidth devices: a novel 260-GS/s arbitrary waveform generator with a 10-dB bandwidth of 90-GHz and a thin-film Lithium Niobate I/Q modulator with a 3-dB bandwidth of 110-GHz. We first assess the performance of our high symbol rate transmitter for generating spectrally efficient Nyquist multilevel modulation format signals at symbol rates up to 210-GBaud with >1.4-Tbps achievable information rates and by using linear digital signal processing only. We achieve up to 1.84-Tbps at 185-GBaud using PCS-64QAM, highlighting the linear behavior of our transmitter for high symbol rate Nyquist signaling. We then switch to dual-polarization QPSK coherent transmission and further increase the symbol rate up to 260-GBaud. Without using nonlinear digital-signal-processing nor advanced inter-symbol-interference mitigation techniques, we successfully transmit 260-GBaud QPSK at 800-Gbps net rate over 100-km of standard single mode fiber.