This PDF file contains the front matter associated with SPIE Proceedings Volume 10945, Including the Title Page, Copyright information, Table of Contents, Introduction, Author and Conference Committee lists

Graphene is a suitable material for optoelectronic applications that reveals several advantages and complementarities compared with other technologies. Graphene is a gapless material that absorbs radiation from visible to far-infrared and beyond including the terahertz range. The absorption can be modified by changing the material doping, i.e. Fermi level energy, by applying an external electric field. The change in absorption can be very fast and, for this reason, graphene can be used to realize optical modulators. Moreover, the absorption change occurs along with refractive index change. In particular, conditions, i.e. for Fermi level above the Pauli blocking, light is not absorbed anymore and only phase change occurs. Phase change has been demonstrated to be good for fast Mach Zehnder interferometer based modulation. The broadband absorption of Graphene is also exploited to realize efficient photodetectors. Generation of hot electrons upon light absorption in graphene is the cause of photo-thermal effect (PTE) that leads to photo voltage generation. PTE is an ultrafast process that is used for fast photodetection. In this work, the vision for graphene-based integrated photonics is presented. We review state-of-the-art graphene-based modulators and detectors and outline a roadmap matching the technology readiness requirements with the datacom and telecom market demands. We show that graphene-based integrated photonics could enable ultra-high spatial density, low power consumption for board and intra- data centre connectivity, access networks, metropolitan, core, regional and long-haul optical communications.

In this paper, we present an optical fiber that is single-mode at 1310 nm window and few-mode at 850 nm window with high bandwidth. The fiber is compatible with standard single-mode fiber at 1310 nm, which can meet long reach requirements for hyper-scale data centers. In addition, the fiber can be used for few-mode transmission at 850 nm using single-mode or few-mode VCSELs, providing low-cost solutions for short links. We discuss fiber design considerations and present fiber properties and 25 Gb/s transmission results at 850 nm.

Microwave photonics will play an important role in 5G systems to support wideband and low loss operations. In this paper, recent development in microwave photonic techniques for 5G will be discussed. In particular, coherent radio over fiber techniques for fiber wireless access will be discussed. Associated microwave photonic sub-systems for 5G, including silicon-based photonic integrated optoelectronic oscillator and programmable silicon-based on-chip photonic signal processor, will also be discussed.

In order to support the 1,000 times increase in data rates expected from next-generation wireless communications (5G), radically novel technological approaches will be needed. Integrated microwave photonics (IMWP) techniques are identified as an enabling technology for 5G, thanks to their potential to improve the performance of electronics by leveraging the broadband characteristics and flexibility of operation of photonic integrated circuits. Relevant applications of IMWP are optical signal generation and distribution of mm-waves towards antenna terminals, optical control of antenna arrays, frequency-reconfigurable filtering, and more. The rapidly growing field of plasmonics has shown a breakthrough in performance for optical modulators with fast operation (500 GHz) and ultra-compact footprint (10s μm2). This paper reports recent achievements on the use of integrated plasmonic devices for millimeter-wave signal conversion and processing for next-generation wireless systems.

The 5G-induced paradigm shift from traditional macro-cell networks towards ultra-dense deployment of small cells, imposes stringent bandwidth and latency requirements in the underlying network infrastructure. While state of the art TDM-PON e.g. 10G-EPON, have already transformed the fronthaul networks from circuit switched point-to-point links into packet based architectures of shared point-to-multipoint links, the 5G Ethernet-based fronthaul brings new requirements in terms of latency for an inherently bursty traffic. This is expected to promote the deployment of a whole new class of optical devices that can perform with burst-mode traffic while realizing routing functionalities at a low-latency and energy envelope, avoiding in this way the latency burden associated with a complete optoelectronic Ethernet routing process and acting as a fast optical gateway for ultra-low latency requiring signals. Wavelength conversion can offer a reliable option for ultra-fast routing in access and fronthaul networks, provided, however, that it can at the same time offer both packet power-level equalization to account for differences in optical path losses and comply with the typical, in optical fronthauling, NRZ format. In this paper, we demonstrate an optical Burst-Mode Wavelength Converter using a Differentially-Biased SOA-MZI that operates in the deeply saturated regime to provide optical output power equalization for different input signal powers. The device has been experimentally validated for 10Gb/s NRZ optical packets, providing error-free operation for an input packet peak-power dynamic range of more than 9dB.

This paper describes and evaluates experimentally a Si₃N₄ photonic chip based on optical ring resonators (ORRs) assisted by multi-core fiber (MCF) that enables radio beamsteering in 5G by the continuous tuning of the time delay applied to an antenna array. Each ORR includes two heaters: one for tuning the resonance wavelength and another to set the coupling coefficient. In this way, the configuration for beamsteering can be implemented by heater tuning or by wavelength shifting. Each optical path of the photonic chip comprises a thermally tunable optical side band filter (OSBF) and an ORR in cascade configuration. The output of each optical path is transmitted through a core of a MCF to distribute the modulated 5G signals to each array element at the transmitter antenna. This ensures that all the optical paths have the same length and enables the delay tuning of each array antenna element directly set from the photonic chip. Experimental demonstration is carried out with a four-core MCF with 26 GHz signals suitable for 5G transmission.

This paper reports and analyses the hybrid 5G NR (new-radio) fronthaul technology with emphasis in the different functional splitting points, and the associated silicon-photonics technologies which enable a completely integrated electro-optical transceiver. Different silicon photonics solutions have been proposed so far targeting an integrated solution combining electronics and photonics, where electronics deal with digital coding and MAC forming, and photonics implement modulation (enabling QPSK, QAM and PAM4 transmissions above 100 Gbit/s) and switching functionalities (reducing the switching time to the ns range). High-speed transceivers integrated in bulk CMOS would enable Tbit/s optical interconnects. In particular, this work firstly summarizes the recent advances and challenges of silicon photonics technology that will have an impact on 5G applications in a near future. Next, an experimental demonstration of a radio-over-fiber fronthaul for the simultaneous provision of multiple radio-access technologies including 2G, 3G and 4G is included. Enhanced capabilities enabled by silicon photonics including MIMO and beamforming are also evaluated.

This paper proposes and evaluates experimentally the performance of single-carrier QAM (SC-QAM) and OFDM-QAM signals for next-generation backhaul over a deep fiber-to-the-home (FTTH) network comprising up to 50 km SSMF combined with in-building transmission over 150 m of 4-core multi-core fiber in order to reach the cellular transmission equipment usually located in the roof. The data signals are generated with commercial off-the-shelf (COTS) components using QAM modulation orders up to 256QAM. OFDM and SC-QAM transmission after 10-km SSMF PON and 150-m MCF in-building riser employing 256QAM provides 14.22-14.36 Gb/s per channel. 50-km PON is reached employing 128QAM signals. Channel aggregation is also investigated to increase the system capacity. The experimental results point out that aggregation of a second data channel is feasible employing the same components with a 3-dB received power penalty. The minimum received optical power level is evaluated experimentally for each signal. This approach enables operators to select the optimum modulation order depending on the distance and the received power level, providing up to 28.44 Gb/s per user with two 256QAM channels.

In this paper we present the urgency for the optical transport networking evolution for 5G delivery and ultra-broadband services to users and communities of users, in the followings: (a) Cloud core, Metro-cloud core and edge cloud networking structure with optical SDN and SDN/NFV. (b) Photonic enabled technologies including principal devices and photonic processors. (c) Security aspects and transmission technology for secret keys in co-transmission of massive data transport.

A new function split option 9 based on delta-sigma modulation is proposed for the next generation fronthaul interface (NGFI). All existing low layer split (LLS) options, such as 6 (MAC-PHY), 7 (high-low PHY), and 8 (CPRI) require a complete RF layer implemented in the analog domain at remote cell sites; whereas the proposed option 9 can implement RF layer in the digital domain and moves the split point between the distributed unit (DU) and remote radio unit (RRU) into the RF layer. With the help of delta-sigma modulation, high-RF layer functions are centralized in the DU and lowRF layer distributed in RRUs. Although it splits at a lower level than conventional option 8 (CPRI), option 9 offers improved spectral efficiency and reduced fronthaul traffic than CPRI. Moreover, it implements all RF functions in the digital domain and eliminates the need of analog devices required by other LLS options, such as DAC, local oscillator, mixer, power amplifier. Therefore, option 9 enables all-digital RF transmitter and RF layer virtualization, which makes low-cost, energy-efficient, and small-footprint cell sites possible for the wide deployment of 5G small cells.

Very diverse and sometimes extreme requirements in the 5G mobile and IoT services pose significant challenges to wireless backhaul networks. Particularly, their edge, namely fronthaul(FH), has to be high-capacity, low-latency, reliable and flexible than ever before. To fulfill such 5G/IoT FH demands, some ‘overloading’ techniques to enable much better utilization of the FH infrastructure are indispensable. In this talk, recent advancements on the overloading techniques will be introduced such as including; a low-latency space-time compression technique for massive MIMO RF waveforms for the FH bandwidth efficiency, a signal detection technique for the overloaded FH in massive IoT scenarios, and a latency-aware packet-based transport technique for the FH flexibility.

Weakly-coupled multicore fibers (MCFs) have been proposed to support the huge data capacity demanded by future 5G fronthauls. However, in MCFs, intercore crosstalk (ICXT), i.e., power coupling between different MCF cores, can degrade significantly the performance of the 5G fronthaul, particularly, when using Common Public Radio Interface (CPRI) signals and direct-detection at the optical receiver. In this work, the performance degradation induced by ICXT in 5G fronthauls with MCFs and direct-detection is assessed by numerical simulation. We show that the study of the outage probability is essential to ensure the reliability and the good quality of service in 5G fronthauls supported by MCFs impaired by ICXT with CPRI signals transmission. The ICXT level that leads to an outage probability of 104 is more than 5.6 dB lower than the ICXT level necessary to reach the power penalty of 1 dB. Our results also indicate that fronthaul systems with lower extinction ratio exhibit an higher tolerance to ICXT.

With the approach of the 5G era, stringent requirements are imposed on the data transport solutions, including both of the supported transmission reach and the capacity. Radio-over-fiber technologies are considered to be promising candidates to cope with both aspects, owing to the low-loss and broad-bandwidth nature of the optical fibers. Meanwhile with such optical transport solutions, signals can be collected from the distributed remote radio sites and processed in a centralized manner. In this report, we target on the digital radio-over-fiber systems, and discuss about several key technologies, focusing on the aspects of coding and transmission, which could potentially enable terabit-scale data transport.

In this paper we present two different techniques for photonic generation of millimeter and THz waves. Each of them tackles the phase noise problem associated with optical sources in a different way. The first one relays on the heterodyne down-conversion of two phase noise correlated optical tones. The correlation is achieved by generation of an optical frequency comb. To select one of the optical lines we use an optical phase lock loop, which besides enabling a frequency offset between output and input, can provide optical gain and is highly selective. The second one relays on the envelope detection of a single sideband-with carrier signal. In this approach the photonic remote antenna unit is implemented as monolithically integrated photonic chip.

For high-speed train communication system, broadband analog radio-over-fiber based backhaul networks with a centralized processing unit can reduce hard hand-over processes by prediction of train location and be tracking the train by adaptive optical path routing. In the system, an automatic bias control technique without any dither signals is important to avoid the degradation of the throughput. In the study, we design and demonstrate a single-sideband optical modulation using an optical IQ modulator.

In the last decade data-centers have become a crucial element in our society. As a result, in the coming years there will be increased threat from hackers, who could cause outage of the data-center, extract millions of account details, or steal financial and sensitive information. One way to reduce these threats is to divide the data-center into sub data-centers, and connect them by secure links which prevent access by unauthorized users. A possible technology to connect between the sub data-centers is optical wireless communication (OWC) or free space optics (FSO). An OWC link includes an optical receiver and laser transmitter. The transmitter transmits a light beam that carries information which propagates to the receiver. The light beam carrying the information propagates through the air. In order to increase the security and make the penetration and intrusion difficult quantum key distribution (QKD) is added to the link. By doing so the information exchange between the sub data-centers is encrypted. In this paper we review up to date literature in the field, propose an implementation scheme of an OWC network in sub data-centers, and discuss ways to hack the system.

Data centers (DCs) are intrinsic to emerging technologies which require to store and process massive amounts of versatile data through large-scale networks of computing and storage units. Conventional wired DC networks (DCNs) with static links and finite network interfaces suffer from cabling cost and complexity as scalability increases, lack the flexibility to handle the dynamic and large volume of traffic outbursts (i.e., hotspots), and have limited bisection bandwidths mainly due to the switching speeds. Therefore, optical wireless DCNs have recently attracted attention by their capability to augment the inherent restrictions of wired DCNs. In addition to the reduced cost of wiring, wireless communication can provide a flexible topology to overcome oversubscriptions and hotspots. Moreover, it is possible to adapt the link capacities in accordance with the quality of service demands of different services and flow classes. Furthermore, wireless communication can also make it possible to eliminate switches by establishing direct links among the servers. In this paper, we first present potential state- of-art optical wireless technologies. Second, practical challenges of design and provisioning of optical wireless communications in real-life DCNs are outlined along with a survey of recent advances and implementations. Finally, we motivate researchers with the exciting prospects of optical wireless DCNs including physical and virtual topology design, interference management, multiple access techniques, traffic management and grooming, and flow classification.

Beamsteering systems offer the potential to extend the fibre-based telecommunications infrastructure with wireless point-to-point data links that are transparent to modulation scheme and data rate. In this paper we introduce beamsteering, and discuss the challenges in implementing and using such systems that use this approach in indoor environments. Results from a number of demonstration systems are presented, including ultra-high data rate indoor optical wireless, operating at up to 400Gbit/s.

Most Data Center Networks (DCNs) deployed today can be classified as wired DCNs in which copper and optical fiber cables are used for intra- and inter-rack connections in the network. Despite recent advances, wired DCNs face two inevitable problems; cabling complexity and hotspots. To address these problems, recent research works suggest the incorporation of wireless communication technology into DCNs. Wireless links can be used to either augment conventional wired DCNs, or to realize a pure wireless DCN. Moreover, wireless links can be fixed or reconfigurable. Optical Wireless Communication (OWC) [also known as free space optical (FSO) communication] and 60 GHz radio frequency (RF) are the two key candidate technologies for implementing wireless links in DCNs. In this paper, we focus our discussion on OWC-based wireless DCNs. We review and summarize major research in this area until 2018. We also discuss open questions and future research directions in the area of OWCs.

The architectural issues related to growth capability, dynamicity, and bandwidth requirements in data centres (DCs) impact the connectivity requirements. The larger the DC, the more challenging and complex the cabling becomes. The traditional approach, which is still the case for smaller DCs, uses long individual patch cords between different DC network tiers. However, in medium to large DCs, a large number of patch cords are required, which are less robust and create the prospect for problems resulting from bending, crushing and scalability. Additionally, the progression toward 40 and 100 Gbit/sec transmission rates is paving the way for parallel optics in place of serial connections. Therefore, the way forward would be to exploit the dual benefits of optical fibre and free space optical communications for both inter- and intra-rack links to address the challenges facing future DCs, in particular their energy efficiency. This hybrid optical fibre-optical wireless architecture can provide unprecedented degrees of flexibility thus offering a number features including (i) relatively easy reconfiguration of the connectivity within DC; (ii) drastically reducing the number of cable interconnections; (iii) acting as an enabler for network operators to deploy topologies that would otherwise remain impossible due to the substantial cabling complexity. This talk gives an overview of optical wireless communications (mostly FSO), which and its use in DCs. The FSO technology is compact, low power and energy efficient, where it uses mirror arrays with flat and concave mirrors to establish links between server, switches, rack, etc.

With the digitalization of industry and society, data centers have grown into an essential key strategic infrastructure, centralizing the processing, storage and distribution of vast amounts of information. Through continuing centralization, their size grows ever larger, while at the same time they need to remain flexible and dynamic to adapt to the temporary nature and diverse requirements of many tasks. Modular data centers can fulfil this requirement, allowing quick deployment and provisioning, while being highly reconfigurable - however, in such data centers interconnectivity is a complex and difficult issue. Wired connections based on optical fibers are the standard in data centers, but come at a significant cost and lack reconfigurability. The introduction of wireless connectivity at millimeter and tera-Hertz frequencies offers similar capacities, while allowing dynamic and re configurable deployment and wireless or hybrid data center architectures have been suggested. In this context, the innovations in high capacity millimeter wave communications and in the convergence of optical and wireless networking developed for 5G mobile networks may offer a potential technology candidate for high-density and high-capacity data center network deployments. Such networks allow the layout and topology of the network to be changed on demand and to adapt to the changing needs of different applications, creating a data center network that matches the multi-purpose nature of the computation and storage hardware. In this paper, the recent trends in wireless technologies for data centers are reviewed and connected to the innovations of optical and wireless convergence seen in 5G networks, perceiving a data center network that is better able to cope with the demanding requirements in terms of network reconfigurability, installation and running cost, as well as power consumption and cooling efficiency.

In recent years, extensive investigations have been made on high-speed visible light communication (VLC) for indoor applications including data centres. For high-speed VLC systems, precise alignment between the VLC transceivers is usually required to establish an optical link with less optical loss. In this paper, an effective scheme of auto-alignment and tracking of transceivers is proposed for practical VLC systems with a high-speed camera for location of the target light source and a two-axis gimbal for initial auto-alignment between transceivers. To explore the feasibility of the proposed scheme, real-time dynamic 200 Mb/s carrierless amplitude-phase (CAP)-VLC transmission is experimentally demonstrated in ≥ 3 m VLC links with red light emitting diodes (LEDs) at an angular accuracy of ≤ 0.02º (0.35 mrad), a tracking speed of ≤ 27º/s and a latency of ≤ 21 ms. The proposed scheme can also be applied for coarse alignment in highspeed laser-based free space optical communication (FSO) systems with visible beacons. 10 Gb/s on-off keying (OOK) transmission is successfully demonstrated over a 1.8 m FSO link with the coarse alignment and the spatial light modulator (SLM)-based fine alignment. Experimental results indicate good flexibility and effectiveness of the proposed scheme for an FSO system with high spatial efficiency and low cabling complexity in data centres.

We designed and fabricated a high-bandwidth, 32-pixel, two-dimensional photodetector array (2D-PDA) for receiving transmission signals from multi-core and few-mode fibers. Pixel sizes of 10, 20, and 30 μm were employed, with a pixel gap of 14 μm. We obtained 3 dB bandwidths of 23.8~29.8 GHz, 19.1~20.8 GHz, and 9.0~13.7 GHz for pixel sizes of 10, 20, and 30 μm, respectively. The device exhibited increasing noise due to RF crosstalk, which was caused by neighboring wires or pixels. In this study, we explored different pixel arrangements to reduce the crosstalk between neighboring pixels, and confirmed the frequency characteristics of the 2D-PDA pixels. Moreover, using electromagnetic simulation software, the RF crosstalk of -30 dB between neighboring pixels was confirmed up to the 10–20 GHz range. The crosstalk analysis, crosstalk reduction design in 2D-PDA devices, and its experimental results are displayed and discussed.

Carrier-less amplitude and phase (CAP) modulation schemes have been actively explored in visible light communication (VLC) because of its high spectral efficiency and simpler transceiver design. Conventionally, CAP with root-raised-cosine filter (CAP-RRC) has been explored for VLC. However, in this paper, we have implemented CAP with a Gaussian minimum shift keying filter (CAP-GMSK) in order to improve the system performance. The proposed scheme is compared against CAP-RRC and baseline DCO-OFDM, on the basis of symbol error rate (SER) and peak-to-average power ratio (PAPR) performance. The result shows that as compared to DCO- OFDM, CAP-GMSK and CAP-RRC provides a SNR gain of 8 and 1 dB and PAPR improvement of 2.5 and 2.3 dB respectively.

The conventional visible light (VL) communication signals based on the LED array and photodiode severely decreases at the far away receiving point in the VL channel by the path loss effect and the insufficient compensation capability of the receiver, which results in failure of long-range VL communication for smart indoor service. In this paper, we consider the long-range VL communication technique that the compensation extent of the path loss distortion provides in advance by threshold map, and utilizes the optimal transceiver circuit for long-range VL communication. And so we can see that the proposed long-range VL communication technique overcomes the path loss problem through the compensation effect from utilizing the optimal threshold voltages into VL receiver, and attains the success of longrange VL communication test in the overall range from zero to 1070 cm distance.

The cellular system goes through significant power loss due to indoor channel fading, the height of the building, wall reflections, etc. Visible Light Communication (VLC) in conjunction with the radio frequency (RF) communication can provide potential solutions to address issues wireless network is facing in the indoor environment. VLC uses existing illumination infrastructure for communication. VLC is more secure because light cannot penetrate through the wall, can offer high bandwidth and is environmentally safe green technology, unlike RF. This paper analyses and compares the RF and VLC link for indoor communication with respect to symbol-error-rate (SER) performance and power saving. The RF link path loss inside the building is modeled using WINNER-II path loss model, and VLC channel is modeled including the movement of the people. The same constellation-based modulation schemes are used in both the links for fair comparison such as binary phase shift keying (BPSK) for RF and on-o keying (OOK) for VLC, M^thorder quadrature amplitude modulation (M-QAM) for RF and colour shift keying (M-CSK) for VLC. VLC link provides better SER performance as compared to RF link at the same signal-to-noise-ratio (SNR) for both BPSK (OOK) and 4-QAM (4-CSK) modulation schemes. There is an outstanding amount of power saving using VLC link as compared to RF link inside the room. Further, the SER gap between VLC and RF decreases as the constellation size increases.