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We propose and demonstrate a mode-division-multiplexed transmitter by employing a VCSEL-based 2-D matrix and a multi-plane light converter (MPLC). The triangular matrix light spots from VCSELs are designed with a 250-μ pitch in both x- and y- directions for scalable and low-loss mode multiplexing. The VCSELs are directly modulated by co-packaged BiCMOS drivers on a silicon interposer, fabricated on a wafer level. The MPLC is utilized to form seven phase masks to convert the individual Gaussian beams to multiplex Hermite-Gaussian modes, which can be coupled into a multi-mode fiber. In the demonstration, we packaged ten 10-G class VCSELs with the drivers, and the form factor of the co-packaged optics is 10-mm × 10-mm. With the fan-out evaluation board, the sub-module is characterized for short and long transmissions by multiplexing the ten directly modulated outputs from VCSELs. The testing results indicate 200-Gb/s capacity over 100-m MMF with direct detection and 28-km few-mode fiber with coherent detection.

We design an optical interface system for vertically coupling between Vertical-Cavity Surface-Emitting Lasers and 3-μm silicon waveguides. The system includes a photoresist lens and a total internal reflection mirror, which allows for passive alignment and flip-chip bonding of VCSELs. The simulated coupling loss is 0.7dB, in optimal conditions, which increases to 1 dB when 3-μm and 20-μm alignment tolerances are considered in lateral and longitudinal directions, respectively. The system is built by post-processing lens and metallic wiring on the backside of a 3-μm silicon photonic platform. After flip-chip bonding and embedding of the VCSELs, the system performance is characterized, and VCSEL-to-waveguide coupling efficiency of -7.5 dB is obtained.

Semiconductor lasers have been rapidly evolving to meet the demands of next-generation optical networks. This imposes much more stringent requirements on the laser reliability, which are dominated by degradation mechanisms (e.g., sudden degradation) limiting the semiconductor laser lifetime. Physics-based approaches are often used to characterize the degradation behavior analytically, yet explicit domain knowledge and accurate mathematical models are required. Building such models can be very challenging due to a lack of a full understanding of the complex physical processes inducing the degradation under various operating conditions. To overcome the aforementioned limitations, we propose a new data-driven approach, extracting useful insights from the operational monitored data to predict the degradation trend without requiring any specific knowledge or using any physical model. The proposed approach is based on an unsupervised technique, a conditional variational autoencoder, and validated using vertical-cavity surface-emitting laser (VCSEL) and tunable edge emitting laser reliability data. The experimental results confirm that our model (i) achieves a good degradation prediction and generalization performance by yielding an F1 score of 95.3%, (ii) outperforms several baseline ML based anomaly detection techniques, and (iii) helps to shorten the aging tests by early predicting the failed devices before the end of the test and thereby saving costs, Published in: Journal of Lightwave Technology (Volume: 40, Issue: 18, 15 September 2022)

A mode-multiplexed transmitter combining a 2-D VCSEL matrix on a Si interposer and a multi-plane light converter is demonstrated. This enables 200-Gb/s transmission using 10G-class VCSELs over 100-m multimode fiber with direct detection and 28-km few-mode fiber with coherent detection.

To deal with the challenging requirements of metropolitan area networks (MANs), it is essential to design cost-effective systems that can support high capacity and dynamic adaptation, as well as a synergy of programmability and efficient photonic technologies. This becomes crucial for very large MANs that support 5G, where multihop connections will need to be dynamically established at target capacities beyond Tb/s. Programmability, automation, and modularity of network elements are key desired features. In this work, a modular photonic system, programmable via a software-defined networking platform, designed for dynamic 5G-supportive MANs, is described and analyzed. We consider modular sliceable bandwidth/bit rate variable transceivers (S-BVTs) based on vertical-cavity surface-emitting laser (VCSEL) technology and dense photonic integration. The proposed system and its programmability are experimentally assessed using a VCSEL with 10 GHz bandwidth. The experiments are performed over connections as long as six-hop and 160 km, from low-level aggregation nodes to metro-core nodes, thereby enabling IP off-loading. Furthermore, a numerical model is derived to estimate the performance when adopting higher bandwidth VCSELs ( ≥ 18 G H z ) and integrated coherent receivers, as targeted in the proposed system. The analysis is performed for both 50 GHz and 25 GHz granularities. In the former case, 50 Gb/s capacity per flow can be supported over the targeted connections, for optical signal-to-noise ratio values above 26 dB. When the granularity is 25 GHz, the filter narrowing effect severely impacts the performance. Nevertheless, 1.2 Tb/s capacity (scalable to higher values if spectral/spatial dimensions are exploited) can be achieved when configuring the S-BVT to enable 40 VCSEL flows. This confirms that the system is promising to support Tb/s connections in future agile MANs.

The effect of SOA-based MAN node crossing on DMT high-capacity transmission is experimentally evaluated. A capacity of more than 50 Gb/s per channel is demonstrated for a multi-hop multi-channel transmission up to 116 km SSMF.

C-band InP vertical cavity surface emitting laser (VCSEL) exploitation can be appealing also for high-capacity transmission over hundreds of kilometres. Long-wavelength VCSELs can represent an alternative solution for the development of transmitters with reduced cost, power consumption and footprint by adopting direct modulation (DM) and single sideband (SSB) discrete multitone (DMT) modulation to achieve dense wavelength division multiplexing (WDM) granularity. Due to numerous hops between nodes inside metropolitan area networks the effect of filtering can severely impact the transmission performance. We present preliminary experimental assessments of DM VCSEL sources with multi-carrier modulation formats, for more than 50 Gb/s per-channel transmission to target a metro network including nodes, handling 25-GHz granularity.

Wavelength division multiplex (WDM) passive optical network (PON) is considered for converged fixed mobile broadband access networking. We propose to utilize low-cost tunable lasers at the remote sites, together with a centralized wavelength locker. Practical implementations require a transparently added downstream signaling channel and upstream per-channel pilot tones for channel tagging and remote wavelength control. We demonstrate, for the first time, 26-Gbps discrete multitone transmission modulated on a low-cost wide tunable vertical surface emitting laser over up to 40 km of standard single-mode fiber. The results confirm that converged fixed mobile WDM-PON systems based on low-cost lasers carrying discrete multitone modulation are a technically viable approach.

We demonstrate 84-Gb/s four-level pulse amplitude modulation (PAM-4) over up to 1.6-km standard single mode fiber using a 20-GHz single mode short cavity vertical cavity surface emitting laser diode at a transmission wavelength of 1525 nm. Different equalizer approaches including a common feedforward equalizer, a nonlinear Volterra equalizer (NLVE), a maximum likelihood sequence estimator (MLSE) and their combinations are evaluated working either as an equalizer for a standard PAM-4 or a partial response PAM-4 signal with seven levels. It is demonstrated that a standard FFE is not enough for a transmission distance of >0.6 km, while the use of an NLVE or FFE + MLSE is able to improve the transmission distance towards 1 km. The use of partial-response PAM-4 FFE in combination with a short memory MLSE is able to efficiently equalize the bandwidth limitations, showing more than 10-times BER improvement compared to standard NLVE or FFE + MLSE at a transmission distance of 1.6 km. Using a partial-response NLVE instead of an PR-FFE further performance improvement is achieved, resulting in BERs below the KP4 FEC-threshold with a BER-limit of 2E-4 after 1.6-km transmission distance, allowing error free operation.

Innovative photonic solutions designed and developed in the H2020 research project PASSION are presented for the future metropolitan area network (MAN) supporting different aggregated data traffic volumes and operating at heterogenous granularities. System performance evaluated both by simulations and experimentation regarding the proposed vertical cavity surface emitting laser (VCSEL) -based modular sliceable bandwidth/bitrate variable transceiver (S-BVT) are shown in realistic MANs organized by hierarchical levels with the crossing of multiple nodes characterized by new switching/aggregation technologies. The capabilities and challenges of the proposed cost-effective, energy-efficient and reduced footprint technological solutions will be demonstrated to face the request of huge throughput and traffic scalability.

An SDN-enabled modular photonic system architecture, including VCSEL-based bandwidth/bitrate variable transceivers, for multi-terabit capacity transmission and agile spectrum/space switching in optical metro networks is presented, providing the proposed technological solutions, programmability aspects and preliminary assessment.

The use of vertical cavity surface emitting laser (VCSEL) at long wavelengths, especially if characterized by large bandwidth or tunable capability, is appearing as an attractive technology for the implementation of advanced transceivers to be used in optical metro networks at 100G and beyond. In this work, we report recent promising results on the adoption of different types of VCSEL for the sliceable bandwidth/bitrate variable transceiver (S-BVT) design. Special attention will be devoted to technological aspects and challenges, focusing on the added value of exploiting novel photonic technologies for the implementation of cost-effective transceivers, suitable for future optical metro networks targeting high capacity and flexibility., Grant numbers : DESTELLO - Dynamic flexible orchestration of data centers and programmable elastic optical networks and systems (TEC2015-69256-R).

Long-wavelength vertical-cavity surface-emitting lasers (LW-VCSELs) with emission wavelength in the 1.3$\mu$m region for intensity modulation/direct detection (IM/DD) optical transmissions, enable longer fiber reach compared to C-band VCSELs, thanks to the extremely low chromatic dispersion impact at that wavelength. A lot of effort has been recently dedicated to novel cavity designs in order to enhance LW-VCSELs modulation bandwidth to allow higher data rates. Another approach to further improve VCSEL-based intensity modulation speed consists of making use of dedicated driver circuits implementing feed forward equalization (FFE). In this manuscript we present a transmitter assembly incorporating a 4-channel 0.13-$\mu$m SiGe driver circuit wire-bonded to a novel dual 1.3$\mu$m-VCSEL array. The short-cavity Indium Phosphide (InP) Buried Tunnel Junction (BTJ) VCSEL design minimizes both the photon lifetime and the device parasitic currents. The integrated driver circuit requires 2.5 V supply voltage only due to the implementation of a pseudo-balanced regulator, it includes a 2-tap asymmetric FFE where magnitude, sign, relative delay and pulse width distortion (PWD) of the taps can be modified. Through the proposed transmitter, standard single-mode fiber reach of 20 km and 4.5 km respectively for 28 Gb/s and 40 Gb/s data rate has been demonstrated with state-of-the-art power consumption. Transmitter performance has been analyzed through pseudorandom bit sequences of both 27-1 and 231-1 length and the additional benefit due to the use of the driver circuit has been discussed in detail. A final comparison with state-of-the-art VCSEL drivers is also included.

We present results from 400G transceiver development based on the hybrid integration of vertical-cavity surface emitting lasers and photodiode arrays on 3 and 12 μm silicon-on-insulator (SOI) chips. The integration of waveguide circuits, amplifiers and modulators on SOI is also reported.

Unprecedented standard single-mode fiber reach of 20km and 4.5km respectively for 28Gb/s and 40Gb/s VCSEL-based intensity-modulation/direct detection optical transmission was obtained with a low-power transmitter assembly including a 4-channel 0.13-μm SiGe driver wire-bonded to a novel 2×1 1.3pm-VCSEL array.

Directly modulated long-wavelength vertical cavity surface emitting lasers (VCSELs) are considered for the implementation of sliceable bandwidth/bitrate variable transceivers for very high capacity transmission (higher than 50 Gb/s per wavelength) in metropolitan area systems characterized by reduced cost, power consumption, and footprint. The impact of the frequency chirp measured for InP VCSELs with different kinds of design (high-bandwidth very short cavity and widely-tunable with micro electro-mechanical systems (MEMS) top mirror) is analyzed in case of discrete multitone (DMT) direct modulation in combination with 25-GHz wavelength selective switch (WSS) filtering. The maximum transmitted capacity for both dual side- and single side-band DMT modulation is evaluated as a function of the number of crossed nodes in a mesh metro network, comparing VCSEL based transmitters performance also with the case of external electro-absorption modulator use. Finally, the maximum reach achieved based on the received optical signal to noise ratio (OSNR) and the fiber span length is discussed. The results confirm the possibility to use directly-modulated long-wavelength VCSELs for the realization of sliceable bandwidth/bitrate variable transmitters targeting 50-Gb/s capacity per polarization, also in the presence of 5 crossed WSSs for reaches of hundreds of kilometers in multi-span Erbium-doped fiber amplified (EDFA) metro links supported by coherent detection.

Silicon photonics with micron-scale Si waveguides offers most of the benefits of submicron SOI technology while avoiding most of its limitations. In particular, thick silicon-on-insulator (SOI) waveguides offer 0.1 dB/cm propagation loss, polarization independency, broadband single-mode (SM) operation from 1.2 to >4 μm wavelength and ability to transmit high optical powers (>1 W). Here we describe the feasibility of Thick-SOI technology for advanced optical interconnects. With 12 μm SOI waveguides we demonstrate efficient coupling between standard single-mode fibers, vertical-cavity surface-emitting lasers (VCSELs) and photodetectors (PDs), as well as wavelength multiplexing in small footprint. Discrete VCSELs and PDs already support 28 Gb/s on-off keying (OOK), which shows a path towards 50-100 Gb/s bandwidth per wavelength by using more advanced modulation formats like PAM4. Directly modulated VCSELs enable very power-efficient optical interconnects for up to 40 km distance. Furthermore, with 3 μm SOI waveguides we demonstrate extremely dense and low-loss integration of numerous optical functions, such as multiplexers, filters, switches and delay lines. Also polarization independent and athermal operation is demonstrated. The latter is achieved by using short polymer waveguides to compensate for the thermo-optic effect in silicon. New concepts for isolator integration and polarization rotation are also explained.

We propose an SDN-enabled S-BVT adopting directly-modulated tunable VCSEL with direct-detection for optical metro networks and spectrum defragmentation. We experimentally assess it over different network paths up to 185km and in presence of adjacent slices., Grant numbers : This work has been partially supported by the Spanish DESTELLO project TEC2015-69256-R.© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

We demonstrate DSP-free and real-time NRZ transmission at 50Gb/s over 15km SSMF, 60Gb/s over 5km SSMF and 64Gb/s back-to-back using a directly modulated 1326nm short cavity VCSEL supported by a SiGe BiCMOS 6-tap feedforward equalizer.

VCSEL links typically require multiple supply voltages for high-speed and low-power operation. We report a 40-Gb/s 1.5-μm VCSEL link achieving 8.7 pJ/bit of energy efficiency with a 0.13-μm SiGe VCSEL driver and TIA operated at 2.5 V.

We report full C-band tunable, 10 Gbit/s capability, directly modulated MEMS-VCSEL for next generation converged mobile fronthaul and backhaul applications. Bit error rates below 10(-9) were achieved over up to 40 km SSMF.

We present a vision for the hybrid integration of advanced transceivers at 1.3 μm wavelength, and the progress done towards this vision in the EU-funded RAPIDO project. The final goal of the project is to make five demonstrators that show the feasibility of the proposed concepts to make optical interconnects and packet-switched optical networks that are scalable to Pb/s systems in data centers and high performance computing. Simplest transceivers are to be made by combining directly modulated InP VCSELs with 12 μm SOI multiplexers to launch, for example, 200 Gbps data into a single polymer waveguide with 4 channels to connect processors on a single line card. For more advanced transceivers we develop novel dilute nitride amplifiers and modulators that are expected to be more power-efficient and temperatureinsensitive than InP devices. These edge-emitting III-V chips are flip-chip bonded on 3 μm SOI chips that also have polarization and temperature independent multiplexers and low-loss coupling to the 12 μm SOI interposers, enabling to launch up to 640 Gbps data into a standard single mode (SM) fiber. In this paper we present a number of experimental results, including low-loss multiplexers on SOI, zero-birefringence Si waveguides, micron-scale mirrors and bends with 0.1 dB loss, direct modulation of VCSELs up to 40 Gbps, ±0.25μm length control for dilute nitride SOA, strong band edge shifts in dilute nitride EAMs and SM polymer waveguides with 0.4 dB/cm loss.

We present a vision for transceiver integration on a 3 µm SOI waveguide platform for systems scalable to Pb/s. We also present experimental results from the first building blocks developed in the EU-funded RAPIDO project. At 1.3 µm wavelength 80 Gb/s per wavelength is to be achieved using hybrid integration of III-V optoelectronics on SOI. Goals include athermal operation, low-loss I/O coupling, advanced modulation formats and packet switching. An example of the design results is an interposer chip that consists of 12 µm thick SOI waveguides locally tapered down to 3 µm to provide low-loss coupling between an optical single-mode fiber array and the 3 µm SOI chip. First example of experimental results is a 4x4 cyclic AWGs with 5 nm channel spacing, 0.4 dB/facet fiber coupling loss, 3.5 dB center-tocenter loss, and -23 dB adjacent channel crosstalk in 3.5x1.5 mm2 footprint. The second example result is a new VCSEL design that was demonstrated to have up to 40 Gb/s operation at 1.55 µm.

This paper summarizes the research and technical achievements done under the EU project GigaWaM. The goal of this project was to develop a cost-effective solution that can meet the increasing bandwidth demands in access networks. The approach was to use a novel wavelength division multiplexing passive optical network (WDM-PON) architecture that can deliver symmetric 1 Gb/s to 64 users over 20 km standard single mode fiber using the L and C bands for down and upstream, respectively. During the course of the project, a number of key enabling technologies were developed including tunable transceivers, athermal 50 GHz spaced arrayed waveguide grating multiplexer devices, novel hybridization technologies for integration of passive and active electro-optic devices, and system-level algorithms that ensure the quality of service. The outcome of the project proved a reliable, cost-effective, flexible, and upgradable WDM-PON solution, achieving per-user datarates of 2.5 and 10 Gb/s for up and downstream, respectively. The proposed solution is not only suitable for access networks, but also for metro aggregation and mobile backhaul. QC 20141113

International audience; We demonstrate a free-running directly-modulated 1580 nm VCSEL suitable for hybrid wireless/optical interconnects supporting cloud data centers. Error-free transmission at 1.25 Gbps was achieved after 6.5 GHz wireless link and 1 km bend-insensitive fiber.

We report on migrating multiple lane link into a single WDM L-band VCSEL-based system. Experimental validation successfully achieves 10 km of SMF reach with 4×14Gbps and less than 0.5dB inter-channel crosstalk penalty.

We experimentally demonstrate 1.33-mum vertical-cavity surface-emitting laser characterization (linewidth and chirp measurements) and very good propagation performances at multi-Gb/s in single-mode-fiber transmission. Error-free measurements are presented both for 10.3 Gb/s over 40 km and for 12.5 Gb/s over 20 km at different operating temperatures.

The employment of long-wavelength directly-modulated VCSELs for applications in next-generation access networks is proposed. Suitable simulations are shown in case of DMT modulation and SSB filtering, demonstrating the capabilities of LW-VCSEL for future 50-Gb/s access networks.

Metro area network (MAN) connectivity is rapidly evolving towards a much more dense, complex and diverse scenario to be dynamically addressed with flexible cost-efficient and high-capacity technology and architecture solutions, dealing with an even more open and disaggregated paradigm. In this work, sliceable bandwidth/bitrate variable transceiver (SBVT) architectures adopting modular approach and suitable photonic technologies (such as VCSEL), enabling to efficiently and dynamically exploit both spectral and spatial dimensions, are discussed, considering design, implementation, cost and flexibility aspects. Recent numerical and experimental results are reported, showing how to enable scalability towards supporting multi-Tb/s connectivity in flexible and dynamic large MAN.