We propose optical injection locking (OIL) injecting for the first-time a hybrid InP-Si3N4 laser source using another laser integrated on the same chip for microwave generation through optical heterodyning in Ka-, Q- and V-bands. A study of the drift exhibited by the devices will be performed as key parameter of lasers. The amount of free-running drift exhibited by the lasers and a way to minimize as much as possible. According to the measured drift that goes in the worst case up to 520 MHz. However, the electric drift of the beat-note RF signal keeps below 50 MHz thanks of being thermally stabilize over the same conditions. To eliminated the drift, an optical injection locking of one InP/Si3N4 hybrid integrated laser have been done by injecting another hybrid laser integrated on the same chip for the first time. We have demonstrated a locking range demonstrated a locking range of 1.86 GHz.
We propose a microwave photonic band-pass filter in the TriPleX® waveguide technology, capable of performing channel selection in flexible DEMUX satellite systems. The proposed channel selector consists of 2 stages of filtering, that enable fully reconfigurable central frequency and channel bandwidth tuning in the Ka-, Q- and V-band. The first stage of filtering is based on a Coupled Ring Optical Waveguide (CROW) filter and serves as channel bandwidth regulator. The CROW filter includes 8 ring resonators, each with a length of 7.38 cm, corresponding to a Free Spectral Range (FSR) of 2.6667 GHz. Bandwidth reconfigurability is achieved by using ultra low-loss, stress-optic lead zirconate titanate (PZT)-based tunable couplers between the ring resonators, while central frequency tunability is enabled for the whole Ka-band by incorporating a tunable PZT-based phase shift on each ring resonator. The second stage of filtering consists of Asymmetric Mach-Zehnder Interferometer (AMZI) - lattice filters and serves as FSR extender. AMZI lattice filters with FSR of 5.3334 GHz and 10.6668 GHz, respectively, are used to expand the central frequency tunability of the channel selector in the Q- and V-band. The lattice filters are also equipped with tunable phase shifters to allow for tunability in the central frequency. The proposed 2-stage channel selector filter has a fFSR=10.6668 GHz and exhibits a tunable passband bandwidth from 125 MHz to 1000 MHz. The passband insertion loss and group delay variation are < 0.9 dB and 2.8 ns, while channel isolation is higher than 50 dB. Additional presentation content can be accessed on the supplemental content page.
We present ultra-low power stress optic actuators for high-speed switching in photonic integrated circuits using the standard silicon nitride TriPleX™ platform. The stress-optic actuator is created by a piezoelectric layer (lead zirconate titanate, PZT) on top of a Si3N4-based TriPleX™ waveguide in our standard Asymmetric Double Stripe (ADS) cross section. The top cladding thickness in between the actuator and the waveguide is chosen to achieve minimal optical loss (≤0.01dB/cm). The electrodes are placed on the top of- and directly below the PZT layer allowing the generation of a vertical electric field across the layer. This electrical field deforms the PZT layer by means of the piezoelectric effect. As a consequence of the PZT deformation stress is induced in the underlying waveguide. In this way, the refractive index of the waveguide is controlled by the stress-optic effect brought about by actuating the PZT layer. To demonstrate the stress-optic based phase actuation experimentally, a Mach-Zehnder Interferometer (MZI) is employed. The MZI is designed for operation at a wavelength of 1550 nm. We measure a half-wave voltage-length product (Vπ·cm) of 16 V·cm, while the half-wave-voltage length loss product (Vπ ·L·α) is 1.6 V·dB only. The 2π phase shift would be at 42 V. The measured response time is 4.25 μs. The quasi-DC power dissipation is able to go down to 1 μW. Compared with conventional thermo-optic actuators these characteristics show a dramatic improvement, being a factor of 50 faster in terms of switching speed and a factor of 100 000 lower in terms of quasi-DC power dissipation. This makes stress-optic actuators an attractive choice for the next generation integrated photonic circuits where ultra-low quasi-DC power dissipation and/or fast switching time and operation in the MHz range are required.
The ever-increasing energy consumption of Data Centers (DC), along with the significant waste of resources that is observed in traditional DCs, have forced DC operators to invest in solutions that will considerably improve energy efficiency. In this context, Rack- and board-scale resource disaggregation is under heavy research, as a groundbreaking innovation that could amortize the energy and cost impact caused by the vast diversity in resource demand of emerging DC workloads. However disaggregation, by breaking apart the critical CPU-to-memory path, introduces a challenging set of requirements in the underlying network infrastructure, that has to support low-latency and high-throughput communication for a high number of nodes.
In this paper we present our recent work on optical interconnects towards enabling resource disaggregation both on Rack-level as well as on board-level. To this end, we have demonstrated the Hipoλaos architecture that can efficiently integrate Spanke-based switching with AWGR-based wavelength routing and optical feedforward buffering into highport switch layouts. The proof-of-concept Hipoλaos prototype, based on the 1024-port layout, provide latency performance of 456ns, while system level evaluations reveal sub-μs latency performance for a variety of synthetic traffic profiles. Moving towards high-capacity board-level interconnects, we present the latest achievements realized within the context of H2020-STREAMS project, where single-mode optical PCBs hosting Si-based routing modules and mid-board optics are exploited towards a massive any-to-any, buffer-less, collision-less and extremely low latency routing platform with 25.6Tb/s throughput. Finally, we combine the Hipolaos and STREAMS architectures in a dual-layer switching scheme and evaluate its performance via system-level simulations.
The rapid increase of bandwidth requirements across the entire hierarchy of Data Center (DC) networks, ranging from chip-to-chip, board-to-board up to rack-to-rack communications, puts strenuous requirements in the underlying network infrastructure that has to offer high-bandwidth and low-latency interconnection under a low-energy and low-cost envelope. Arrayed Waveguide Grating Router (AWGR)-based optical interconnections have emerged as a powerful architectural framework that can overcome the currently deployed electrical interconnect bottlenecks leveraging the wavelength division multiplexing (WDM) and the cyclic routing properties of AWGRs to offer one-hop, all-to-all communication when employed as N×N routers. However, the majority of previous silicon (Si)-based integrated AWGR demonstrations has either targeted C-band operation, despite the dominance of the O-band spectral region in the DC interconnection domain, or offered coarse-WDM (CWDM) functionality and, as such, were limited in terms of AWGR port count. In this article, we present for the first time to our knowledge, a Dense-WDM (DWDM) 16×16 Si-photonic cyclic-frequency AWGR device targeting O-band routing applications. The fabricated AWGR device features a channel spacing of 1.063 nm (189 GHz), a free spectral range of 17.8 nm (3.15 THz) and a 3-dB bandwidth of 0.655 nm (116 GHz). Its proper cyclic frequency operation was experimentally verified for all 16 channels with channel peak insertion loss values in the range of 3.9 dB to 8.37 dB, yielding a channel loss non-uniformity of 4.47 dB. Its compact footprint of 0.27×0.71 mm2 and low crosstalk of 21.65 dB highlight its potential for employment in future AWGR-based interconnection schemes.
Analog optical fronthaul for 5G network architectures is currently being promoted as a bandwidth- and energy-efficient technology that can sustain the data-rate, latency and energy requirements of the emerging 5G era. This paper deals with a new optical fronthaul architecture that can effectively synergize optical transceiver, optical add/drop multiplexer and optical beamforming integrated photonics towards a DSP-assisted analog fronthaul for seamless and medium-transparent 5G small-cell networks. Its main application targets include dense and Hot-Spot Area networks, promoting the deployment of mmWave massive MIMO Remote Radio Heads (RRHs) that can offer wireless data-rates ranging from 25Gbps up to 400Gbps depending on the fronthaul technology employed. Small-cell access and resource allocation is ensured via a Medium-Transparent (MT-) MAC protocol that enables the transparent communication between the Central Office and the wireless end-users or the lamp-posts via roof-top-located V-band massive MIMO RRHs. The MTMAC is analysed in detail with simulation and analytical theoretical results being in good agreement and confirming its credentials to satisfy 5G network latency requirements by guaranteeing latency values lower than 1 ms for small- to midload conditions. Its extension towards supporting optical beamforming capabilities and mmWave massive MIMO antennas is discussed, while its performance is analysed for different fiber fronthaul link lengths and different optical channel capacities. Finally, different physical layer network architectures supporting the MT-MAC scheme are presented and adapted to different 5G use case scenarios, starting from PON-overlaid fronthaul solutions and gradually moving through Spatial Division Multiplexing up to Wavelength Division Multiplexing transport as the user density increases.
As data centers constantly expand, electronic switches are facing the challenge of enhanced scalability and the request for increased pin-count and bandwidth. Photonic technology and wavelength division multiplexing have always been a strong alternative for efficient routing and their potential was already proven in the telecoms. CWDM transceivers have emerged in the board-to-board level interconnection, revealing the potential for wavelength-routing to be applied in the datacom and an AWGR-based approach has recently been proposed towards building an optical multi-socket interconnection to offer any-to-any connectivity with high aggregated throughput and reduced power consumption.
Echelle gratings have long been recognized as the multiplexing block exhibiting smallest footprint and robustness in a wide number of applications compared to other alternatives such as the Arrayed Waveguide Grating. Such filtering devices can also perform in a similar way to cyclical AWGR and serve as mid-board routing platforms in multi-socket environments. In this communication, we present such a 3x3 Echelle grating integrated on thick SOI platform with aluminum-coated facets that is shown to perform successful wavelength-routing functionality at 10 Gb/s. The device exhibits a footprint of 60x270 μm2, while the static characterization showed a 3 dB on–chip loss for the best channel. The 3 dB-bandwidth of the channels was 4.5 nm and the free spectral range was 90 nm. The echelle was evaluated in a 2x2 wavelength routing topology, exhibiting a power penalty of below 0.4 dB at 10-9 BER for the C-band. Further experimental evaluations of the platform involve commercially available CWDM datacenter transceivers, towards emulating an optically-interconnected multi-socket environment traffic scenario.
Future broadband access networks in the 5G framework will need to be bilateral, exploiting both optical and wireless technologies. This paper deals with new approaches and synergies on radio-over-fiber (RoF) technologies and how those can be leveraged to seamlessly converge wireless technology for agility and mobility with passive optical networks (PON)-based backhauling. The proposed convergence paradigm is based upon a holistic network architecture mixing mm-wave wireless access with photonic integration, dynamic capacity allocation and network coding schemes to enable high bandwidth and low-latency fixed and 60GHz wireless personal area communications for gigabit rate per user, proposing and deploying on top a Medium-Transparent MAC (MT-MAC) protocol as a low-latency bandwidth allocation mechanism. We have evaluated alternative network topologies between the central office (CO) and the access point module (APM) for data rates up to 2.5 Gb/s and SC frequencies up to 60 GHz. Optical network coding is demonstrated for SCM-based signaling to enhance bandwidth utilization and facilitate optical-wireless convergence in 5G applications, reporting medium-transparent network coding directly at the physical layer between end-users communicating over a RoF infrastructure. Towards equipping the physical layer with the appropriate agility to support MT-MAC protocols, a monolithic InP-based Remote Antenna Unit optoelectronic PIC interface is shown that ensures control over the optical resource allocation assisting at the same time broadband wireless service. Finally, the MT-MAC protocol is analysed and simulation and analytical theoretical results are presented that are found to be in good agreement confirming latency values lower than 1msec for small- to mid-load conditions.
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