In this letter, we report on the advances toward the integration of our developed continuous variables (CV) quantum key distribution (QKD) system in existing optical infrastructure and wavelength division multiplexed (WDM) networks. First, we investigate the tolerance of the CV-QKD system to spontaneous Raman scattering (SRS) noise, the latter being the most dominant impairment in a WDM co-existence environment for QKD. In particular, we investigate by experiment the impact of a WDM 10 × 10 Gb/s ON-OFF-keying signal in terms of induced SRS noise in the QKD channel. The spontaneous SRS noise influence is assessed for different transmission scenarios, i.e., for various optical launch powers of the WDM signal, and for different transmission links of 20, 40, 60, and 80 km. Based on the experimental data and on the measured system's parameters, we estimate the key rates and reach capabilities of the proposed CV-QKD system. The scheme supports a key rate of 90 kbit/s over 20 km, for an ideal QKD system multiplexed with 2-mW optical power. A step further, we demonstrate for first time the use of the aforementioned CV-QKD system to encrypt a 10GE client service over deployable optical transport network legacy equipment over 20 km. Our results prove the feasibility of the integration of our proposed scheme with legacy telecom equipment in existing WDM optical networks.

The introduction of low-cost coherent signal reception is one of the great challenges in optical telecommunications since its opto-electronic sub-systems are associated to a high degree of complexity. In this work we propose a disruptive approach: the re-use of widely deployed direct-detection technology for simultaneous coherent homodyne reception and transmission. We first show that an externally modulated laser (EML) is sufficient to perform both, coherent reception and transmission functionality. Second, we prove that homodyne detection applies to the EML-based scheme in virtue of an injection-locked local oscillator, which for low input power levels is pulled to the optical carrier frequency of the incident data signal. The proposed methodology for coherent reception enables a greatly simplified transceiver as optical-layer hardware. As we will demonstrate it just requires single fiber access, a single radio frequency port and can be implemented in a transistor-outline package. Full-duplex transmission with coherent homodyne reception is experimentally validated, showing 2.5 Gb/s transmission over 27.5 km reach and a loss budget of 28 dB, and coherent Gigabit Ethernet connectivity - without use of optical-layer digital signal processing functions.

We investigate two trellis-coded modulation (TCM) schemes for use in next-generation low-cost 400G optical networks. Their performance is evaluated against that of four-level pulse amplitude modulation (PAM-4). We experimentally demonstrate that TCM outperforms PAM-4 at bit rates between 56 and 80 Gbps and thus is a valid candidate for 8λ × 50G implementations of future 400G wave division multiplexing (WDM) networks. Due to the severe bandwidth limitations of the experimental setup, the feed-forward equalizer and the maximum likelihood sequence estimation equalizer are employed in order to achieve bit error rates below the KP4 threshold of 3 × 10-4. We also show that, at 56 Gbps and 1300 nm wavelength, TCM enables optical links of up to 40 km, whereas PAM-4 can only provide transmissions of up to 30 km. We observe that TCM performance degrades faster than that of PAM-4 when we increase the bit rate. For rates higher than 80 Gbps, TCM is not able to improve upon PAM-4 anymore. Thus, only PAM-4 is fit for 4λ × 100G WDM networks, unless higher bandwidth components are used.

Integrated magneto‐optic (MO) modulators are an attractive but not fully explored alternative to electro‐optic (EO) modulators. They are current driven, structurally simple, and could potentially achieve high efficiency in cryogenic and room temperature environments where fJ bit⁻¹optical interfaces are needed. In this paper, the performance and energy efficiency of a novel MO modulator at room temperature are for the first time assessed. First, a model of the micro‐ring‐based modulator is implemented to investigate the design parameters and their influence on the performance. Then, a fabricated device is experimentally characterized to assess its performance in terms of bit rate and energy efficiency. The model shows efficient operation at 1.2 Gbps using a 16 mA drive current, consuming only 155 fJ bit⁻¹. The experimental results show that the MO effect is suitable for modulation, achieving error‐free operation above 16 mA with a power consumption of 258 fJ bit⁻¹at a transient limited data rate of 1.2 Gbps.

The densification of radio access and the massive deployment of radio heads calls for efficient optical fronthaul technologies. The adoption of analogue radio-over-fiber schemes promises greatly simplified equipment that can be distributed at the antenna sites for the purpose of radio signal conditioning and electro-optic conversion. Towards this direction, we propose and experimentally evaluate a full-duplex interface at the intersection between the optical and the radio frequency layer, aiming at bidirectional radio signal transmission over a single wavelength (1577 nm) and a single carrier frequency (5.375 GHz). Analogue coherent optical reception is performed through an electro-absorption modulated laser, which is employed as multi-functional element that accomplishes wavelength re-use for full-duplex radio-over-fiber transmission. The directional split is shifted to the electrical domain through adoption of a crosstalk-cancelling circulation stage, ensuring compatibility with a high dynamic power range for the simultaneous transmission and reception of up- and downlink radio signals, respectively, without the need for further duplexing methods subject to frequency translation or time slotting. We prove that margins of >2% in terms of error vector magnitude can be accomplished for an unpaired spectral configuration, where down- and uplink radio signals share the same spectrum in the optical and electrical domains.

The continuing drive towards broadband access necessitates cost-effective optical access and mobile fronthaul solutions. While the fixed-mobile convergence motivates high-speeds for the antenna remoting through broadband digitized radio-over-fiber, the access segment still uses time division multiplexed access equipment. Although the steadily increasing line rates call for 50 Gb/s solutions, the unshared per-user rate remains in the 1-Gb/s range. It is a question whether such data rate can be facilitated without high-speed components, at the same time supporting higher passive splits for the optical distribution networks. We experimentally demonstrate a simplified receiver based on an electro-absorption modulated laser, co-integrated on a die-level with a transimpedance amplifier. We investigate its sensitivity for the phase-agnostic coherent heterodyne downstream detection of data signals in a passive optical network scenario. We will show that despite the omission of a high-performance local oscillator, balanced detection and digital signal processing, the proposed receiver accomplishes reception of 1 Gb/s phase-modulated signals over a link reach of 57 km and an optical budget of 48 dB, thus enabling high passive splits of 1:128. We study the implications raised by this single-ended coherent receiver architecture under multi-channel transmission and investigate the susceptibility of its integrated local oscillator to optical feedback.