In this paper, we present the design and analysis of an adaptive cost-effective discrete multitone transponder (DMT) using direct detection (DD) suitable for data center interconnections. Levin Campello margin adaptive (LC-MA) algorithm is applied to the transponder digital signal processing modules to enhance fiber chromatic dispersion (CD) resilience, while achieving highdata rate transmission. The bit error rate (BER) performance and the rate/distance adaptive capabilities of the proposed transponder have been numerically analyzed and compared to bandwidth variable uniform loading, taking into account the transmission impairments at the varying of the fiber length. Specifically, the performance of the designed transponder has been assessed from 20 to 112 Gb/s, extending the achievable reach at 50 Gb/s beyond 80 km of standard single mode fiber (SSMF). The numerical simulations have been compared with experimental results, evidencing good agreement in presence of transmission impairments.

Real-time transmission of 400G (8x50G DWDM) PAM-4 signals for data center interconnects up to 100 km SSMF is successfully demonstrated. All channels stay well below the 802.3bj KR4 FEC limit, thus allowing error free transmission.

Fixed optical transport is the predominant fronthaul technology for 4G mobile access networks, carrying the traffic between the central office and subtended antenna sites. With the new functional splits and related standards introduced in 5G, new capacity and quality-of-service requirements are imposed on optical transport. In this paper, we discuss low-cost high-capacity optical fronthaul solutions enabled by advanced modulation formats and wavelength-agnostic passive wavelength division multiplexing (WDM) technology. As the key component, a low-cost remotely tunable WDM transceiver is introduced, specifically designed on a hybrid InP-polymer platform. We also explain why an Ethernet-based 5G fronthaul solution requires additional means to improve the latency and timing performance of the conventional packet forwarding and multiplexing. We review the recent standardization effort on time-sensitive networking in support of 5G fronthaul and present an FPGA-based implementation providing low latency and low packet delay variation following the latest IEEE 802.1CM specification. These advanced technologies can facilitate an effective packet-optical transport for 5G.

For a future 5G Ethernet-based fronthaul architecture, 100G trunk lines of a transmission distance up to 10 km standard single mode fiber (SSMF) in combination with cheap grey optics to daisy chain cell site network interfaces are a promising cost-and power-efficient solution. For such a scenario, different intensity modulation and direct detect (IMDD) formats at a data rate of 112 Gb/s, namely Nyquist four-level pulse amplitude modulation (PAM4), discrete multi-tone transmission (DMT) and partial-response (PR) PAM4 are experimentally investigated, using a low-cost electro-absorption modulated laser (EML), a 25G driver and current state-of-the-art high speed 84 GS/s CMOS digital-to-analog converter (DAC) and analogto-digital converter (ADC) test chips. Each modulation format is optimized independently for the desired scenario and their digital signal processing (DSP) requirements are investigated. The performance of Nyquist PAM4 and PR PAM4 depend very much on the efficiency of pre-and post-equalization. We show the necessity for at least 11 FFE-taps for pre-emphasis and up to 41 FFE coefficients at the receiver side. In addition, PR PAM4 requires an MLSE with four states to decode the signal back to a PAM4 signal. On the contrary, bit-and power-loading (BL, PL) is crucial for DMT and an FFT length of at least 512 is necessary. With optimized parameters, all modulation formats result in a very similar performances, demonstrating a transmission distance of up to 10 km over SSMF with bit error rates (BERs) below a FEC threshold of 4.4E-3, allowing error free transmission.

Leveraging client optics based on intensity modulation and direct detection for point-to-point inter data center interconnect applications is a cost and power efficient solution, but challenging in terms of optical signal-to-noise ratio (OSNR) requirements and chromatic dispersion tolerance. In this paper, real-time 8x28.125 GBd dense wavelength division multiplexing (DWDM) PAM-4 transmission over up to 80 km standard single mode fiber (SSMF) in the C-Band is demonstrated. Using a combination of optical dispersion compensation and electronic equalization, results below a bit error rate (BER) of 1e-6 are achieved and indicate sufficient margin to transmit over even longer distances, if an FEC threshold of 3.8e-3 is assumed. Moreover, single channel 28.125 GBd PAM-4 is evaluated against optical effects such as optical bandwidth limitations, chromatic dispersion tolerance and optical amplified spontaneous emission (ASE) noise.