This PDF file contains the front matter associated with SPIE Proceedings Volume 11711, including the Title Page, Copyright information and Table of Contents

Plasmonics has emerged as a promising technological solution for realizing high-performance nanoscale communication photonic devices. This paper reports our recent advances on high-performance plasmonic modulators and photodetectors.

Graphene has been proposed to be integrated with Si Photonics because of its very high mobility, fast carrier dynamics and ultra-broadband optical properties. High speed graphene photodetectors have been demonstrated so far, however the most are based on the photo-bolometric or photo-conductive effect. These devices are characterized by large dark current, in the order of milli-Amperes. Photothermal effect (PTE) photodetectors can be used in voltage detection mode with no dark current, it is ultra fast and it operates near zero-bias. Graphene PTE-based photodetectors have been reported so far but high-speed optical telecommunication signal detection has not been shown yet. Here, we report on a graphene PTE-based photodetector on SOI waveguide. Thanks to the optimized design we show a direct detection of 105Gb/s non-return to zero (NRZ) and 120Gb/s 4-level pulse amplitude modulation (PAM) optical signals.

Radio-frequency integrated circuits (RFICs) play key roles in new emerging broadband access technologies. At imec, we have been working on densely integrated photonic and electronic ICs for high-speed passive optical networks (PONs), Radio-over-Fiber (RoF) and future coherent optical access. This presentation will review our recent and on-going research activities related to ultra-wideband RFIC front-ends.

In this invited paper, we discuss how optical fibers, the de-facto choice for last-mile connectivity of radio access network equipment, can rise to the challenges of 5G. We start by addressing technologies and trends for point- to-point connectivity, from fully passive to auto-tunable wavelength division multiplexing. Then, we assess niche solutions based on point-to-multipoint optical connectivity and possible scenarios allowing fixed-mobile convergent topologies. Finally, we brie y exploit the potential of abstraction of optical and radio access equipment through software defined networking for intelligent and multi-tenancy ready traffic management compliant with the constraints of mobile interfaces and hosting locations of cloud infrastructures.

In recent years, high-speed visible light communications (VLC) have been identified as an essential part of communication technologies for next generation wireless network owing to the increasing demand for faster data transmission speeds. VLC offers the unique advantages of ultra-high data rate, unregulated and secure channels, free of EM interference. Compared with the LED-based VLC system, laser-based photonic systems are promising for compact, droop-free, and high-speed white lighting and VLC applications, making them ideal alternatives for building ultra-fast optical wireless data link. Besides the potential for achieving high data rate free-space communication links, i.e., the Li-Fi network, laser based VLC, or visible laser light communication (VLLC) technology can also enable underwater wireless optical communications (UWOC) for many important applications. This paper summarizes the recent progress in high-speed laser based VLC devices and explore VLLC-enabled networks, systems, and applications. I will describe state-of-the-art VLC transmitter and receiver technologies. Novel designs to overcome the inherent limitations will be covered. Finally, the innovations in VLC systems for industrial IoT, vehicular communication, and underwater wireless networks applications will be discussed.

RoFSO technology can easily transmit radio frequency signals using optical carriers in the atmosphere. On the other hand, MIMO transmission have widely used in recent mobile communication, and there are some reports about FSOMIMO transmission. This paper demonstrates a RoFSO- MIMO transmission system which combines technologies of FSO-MIMO and RoF to enhance the flexibility of mobile front-haul. The proposed system uses pilot RF signals to estimate the FSO channel which is affected by atmospheric turbulence and so on. In this paper, we theoretically analyze RF signal quality for various turbulence conditions and show some experimental results of 2x2 RoFSO-MIMO transmission. Performance comparison results will show the effectiveness of the proposed technology.

In this paper, we propose free space optical (FSO) communication using laser light in the 2μm wavelength. FSO using the mid-infrared 2μm band can reduce the effects of turbulence and particles generated in free space and improve link performance. In addition, it has a large allowable exposure because it can be operated in a transparent window in the atmosphere or in a safety for human eyes. We will analysis link visibility, transmission characteristics and SNR of 2μm FSO, demonstrate the BER of the FSO link with fog experimentally. The theoretical analysis will show that visibility and transmission loss will be improved by 2μm FSO, and experimental results also show that BER performance can be improved about 2dB.

We investigate the computational complexity of adaptive equalization in coherent receiver digital signa l processing (DSP) for data center interconnect (DCI) systems. We propose modified DSP procedures with a first-stage static filter and a second-stage short-length adaptive equalizer. Typically, coherent DSP requires 11 and 17 adaptive equalizer taps respectively for 60 Gbaud and 80 Gbaud signals in the 100 km fiber link. The modified DSP procedures combine matched filter, chromatic dispersion compensation (CDC), and non-ideal channel effects and polarization effect s in to a static filter. Since polarization demultiplexing is partially realized by the static filter, the size of the following adaptive equalizer is substantially reduced. Results showed 35% - 87% overall complexity reduction in adaptive equalization a s compared with the reference DSP, depending on link length and symbol rate.

We proposed and experimentally demonstrated a novel point-to-point (P2P) coherent optical link based on optical frequency comb and injection-locking optical process, featuring single wavelength and wavelength division multiplexing (WDM) full-duplex coherent transmission over a fiber link up to 100-km distance. With light sources and local oscillators that are injection locked to an optical frequency comb, simultaneous down-stream and up-stream operations at the same wavelength using full-duplex coherent optical transceivers have been experimentally demonstrated.

Optical switches represent an appealing option to address the upcoming scaling challenges facing electrical switches in data-center networks with the slowdown of Moore’s Law and the exponential increase in network demands posed by emerging cloud workloads. Wavelength switching based on tunable lasers and passive arrayed waveguide grating routers is a particularly promising technology for optical switching due to its amenability to fast switching and the passive nature of the core, which leads to lower power consumption and higher fault tolerance. We investigated the potential of this technology in the context of Sirius, a scalable, optically-switched network architecture for data centers, which can achieve ultra-fast switching time. At its core lies a novel tunable laser that can tune across wavelengths in less than 930 ps. The laser uses a disaggregated architecture where the carrier generation is separated from the wavelength tuning, which significantly reduces the wavelength tuning time compared to conventional tunable lasers. In this paper, we describe the different instantiations of this architecture that we developed and present the experimental evaluation.

This paper describes and evaluates experimentally two versions of Si3N4 photonic integrated devices based on optical ring resonators (ORRs) and multi-core fiber (MCF) that enable radio beamsteering for operating 5G and beyond in the K-band. The RF beamsteerer depends on the optical delay induced by the ORRs that can be modified by heater tuning (slow switching) or by wavelength shift (fast switching). The first version of the beamforming chip permits multi-wavelength operation by keeping the heaters’ configuration and changing the wavelength. The second version of the chip includes independent dual-wavelength operation with dedicated heaters’ configurations for each wavelength. The experimental evaluations are performed for both short-reach and long-reach applications with the transmission of the photonic TTD over 150-m of 4-core MCF and over 1-km of 7-core MCF for the first and second version of the chip, respectively. In addition, the stability and delay variation were measured experimentally over 1-hour run time for different heater configurations. A maximum delay variation of 4 ps was measured, which translates to a 9° steering angle resolution at 19 GHz RF. The impact of the delay variation applied to one of the antenna elements in the resulting beam steering is analyzed in more detail in this work, confirming the suitability of the proposed technique.

To support enhanced mobile broadband (eMBB) communication, 5G is going to use new radios (NRs) at frequencies above 24.25 GHz in the millimeter-wave (mm-wave) bands with abundant available bandwidths. The photonic generation, modulation and distribution of such ultra-high speed broadband RF signals in the optical domain is more promising compared to the bandwidth limiting electrical technology, however, it requires low noise coherent optical sources. In this paper, we present a highly coherent low noise InP-based p-n block buried heterostructure (BH) C-band InAs/InP quantum dash (QD) passively mode-locked laser (MLL) for photonic aided broadband wireless communication systems. The device features repetition rates of 25 GHz resulting in an optical coherent frequency comb (CFC) with a 6-dB optical bandwidth of around 9 nm providing over 46 channels. Each individual channel of the CFC exhibits an average phase noise and integrated relative intensity noise (RIN) of less than 500 kHz and -130 dB/Hz in the frequency range from 10 MHz to 20 GHz, respectively. Its timing jitter and RF beat-note linewidth between any two adjacent channels are as low as 5.53 fs and 3 kHz, respectively. By using this QD MLL, a photonic aided radio-over-fiber (RoF) broadband quadrature amplitude modulated (QAM) signal wireless delivery at around 25 GHz (K-band) is successfully demonstrated over 2-m free space wireless distance through 25.22 km standard single-mode fiber (SSMF) with a total link capacity of 16Gbit/s and error vector magnitude (EVM) below the standard requirements of 12.5%.

The rising traffic demand in mobile networks is pushing the capacity need, especially in the access network. Wireless access integrated with the operator optical fiber network offers mobility and easiness of deployment. The challenge is the provision of wireless broadband capacity paired with the increasing traffic demands. The paper describes a point-to-multipoint fronthaul distribution wireless network at D-band (141 – 148.5 GHz) fed with point-to-point backhaul transport links at G-band (275 – 305 GHz), providing tens of Gb/s data rate. The system is under development in the frame of the European Commission Horizon 2020 ULTRAWAVE “Ultra capacity wireless layer beyond 100 GHz based on millimeter wave”. The D-band transmission hubs are connected to the optical core network through Gb/s class G-band links, based on a microwave photonic transmitter employing uni-traveling-carrier photodiodes (UTC-PD). A field test in real environment is planned to demonstrate the ULTRAWAVE system breakthrough.

This paper has four goals. Firstly, we present, for the first time to the best of our knowledge, a minimalist-design, Linear Optical Electric Field Frequency Discriminator (LOEF-FD) for Microwave Photonic Link (MPL) using only a single Mach-Zehnder Interferometer (MZI) configured in unique folded-back arrangement. The standard configuration of LOEF-FD requires two MZI elements in serial arrangement with additional interferometric arm. The original minimalistdesign structure was first proposed by our group and used as an active device known as linear optical field modulator (LOFM) [8]. Here, we use it as a passive LOEF-FD for MPL application. Secondly, we layout the benefits of the new design such as: (i) reduced chip footprint, (ii) decreased component cost by one-half, and (iii) avoidance of the troublesome engineering problem associated with perfectly matching of the two MZIs in the original design. However, due to the folded-back architecture of the new simplified LOEF-FD, we need to be attentive to the negative impact of the back-reflected electric field on the overall linearity of the frequency discriminator. Thus, for our third goal, we investigated and quantified its effect on the (i) amplitude linearity, (ii) bandwidth, (iii) phase response, and (iv) group delay. We show that a 5% back reflection from the final output reduces the performance of the ideal LOEF-FD’s effective bandwidth utilization (BWU) by about 10%. Lastly, we present a common mitigated scheme to reduce the back reflection.

In this work, the possibility of interference exploitation (IE) in heterogeneous networks is investigated. Based on the shared channel state information (CSI) and the transmitted data among the coordinated heterogeneous base stations (BS)s, we first formulate an IE-based coordinated multi-point (CoMP) scheme, which is able to utilize inter-cell interference as well as multiuser interference as constructive elements. Considering the effect of imperfect CSI at the BSs, we then minimize the transmission power consumption subject to users' statistical signal-to-interference-and-noise ratio (SINR) requirements. Simulation verifies that the proposed IE-based heterogeneous CoMP scheme significantly outperforms the benchmarks in terms of low power consumption..

Indoor visible light communication (VLC) systems commonly make use of non-tunable, fixed optical components to achieve best communication performance at fixed transmitter and receiver separation distance. In practice suitable tuning mechanism to achieve maximum throughput for user equipment held at variable link length is desirable. This becomes more relevant when optical illumination spot with narrow beam profile are used as VLC transmitters. In this paper, we simulate the effect of a focus tunable liquid lens-based transmitter system for variable link length collection efficiency optimization in phosphor down-converted white light VLC link. We use a remote phosphor as a secondary source, which down-converts the narrow-angle incident blue laser light into wide-angle white light with Lambertian mode number 1.54. We perform optical simulations using non-sequential ray-tracing to calculate the overall light collection efficiency at the detector plane as a function of varying liquid lens radius of curvature. Optical rays at the blue wavelength at the phosphor plane are directed to the receiver using a focus-tunable lens followed by a fixed 100 mm focal-length aspherical-lens. At the receiver side a single aspherical-lens of 32 mm focal-length is used in front of photodetector. The liquid lens focal length is tuned to vary the position of the peak of the optical throughput along the optical path relative to the transmitter. The tuning of the liquid lens from -10 to 0 dioptres results in maximum optical throughput to shift from ~2 m to 30 cm, without moving any optical component in the path. Liquid lenses are promising addition to indoor VLC systems to achieve focus tunable optical link with best optical throughput for communication at varying link lengths..

This paper evaluates experimentally a centralized radio access network (C-RAN) based on multi-core fiber (MCF) for the transmission of high-bandwidth signals in the sub-THz band. We compare the system performance when the data and carrier wavelengths to be mixed at the receiver for optical heterodyning are transmitted over the same or over different cores of a MCF link. Full-duplex transmission on MCF is evaluated using the same received wireless signal downconverted and transmitted back as uplink over the same carrier wavelength. The performance with different digital signal processing (DSP) configurations and with higher-power interference in the other cores are also analyzed in this work. Successful provision of 12.5 GBd 16QAM signals is achieved after 1-km of 7-core MCF transmission including a short wireless link at 182 GHz, obtained with optical heterodyning. C-RAN implementation with MCF simplifies the remote nodes as all the lasers can be located in the central office, while minimizing the number of lasers needed at the central office thanks to wavelength re-use. It also provides more flexibility to the system, as it enables using the same LO for different purposes (i.e. THz generation of other data or optical modulation for uplink transmission).

Photonics-assisted image suppression photonic down-converter is an effective way to eliminate image frequency interference in microwave receiver. Due to the performance of the converter largely relies on the local oscillator (LO) signal quality, the frequency converter based on frequency doubling can reduce the demand of the frequency of LO signal. In this paper, we propose and demonstrate an all-optical broadband image-reject photonic down-converter with wideband photonic phase shifting and LO frequency doubling based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). The experimental results show that the phase shift of I and Q channel can be varied continuously in the range of 360°. And the image rejection ratio of our image-reject photonic down-converter reaches ∼50 dB at the single-tone. For a broadband image signal, the signal-to-noise (SNR) has an improvement of 24 dB. The spurious-free dynamic range (SFDR) value is 102.4 dB⋅Hz2/3.