Showing papers in "Journal of Lightwave Technology in 2018"

Digital Signal Processing for Short-Reach Optical Communications: A Review of Current Technologies and Future Trends

Abstract: Driven primarily by cloud service and data-center applications, short-reach optical communication has become a key market segment and growing research area in recent years. Short-reach systems are characterized by direct detection-based receiver configurations and other low-cost and small form factor components that induce transmission impairments unforeseen in their coherent counterparts. Innovative signaling and digital signal processing (DSP) play a pivotal role in enabling these components to realize their ultimate potentials and meet data rate requirements in cost-effective manners. This paper presents an overview of recent DSP developments for short-reach communications systems and discusses future trends.

End-to-End Deep Learning of Optical Fiber Communications

Abstract: In this paper, we implement an optical fiber communication system as an end-to-end deep neural network, including the complete chain of transmitter, channel model, and receiver. This approach enables the optimization of the transceiver in a single end-to-end process. We illustrate the benefits of this method by applying it to intensity modulation/direct detection (IM/DD) systems and show that we can achieve bit error rates below the 6.7% hard-decision forward error correction (HD-FEC) threshold. We model all componentry of the transmitter and receiver, as well as the fiber channel, and apply deep learning to find transmitter and receiver configurations minimizing the symbol error rate. We propose and verify in simulations a training method that yields robust and flexible transceivers that allow—without reconfiguration—reliable transmission over a large range of link dispersions. The results from end-to-end deep learning are successfully verified for the first time in an experiment. In particular, we achieve information rates of 42 Gb/s below the HD-FEC threshold at distances beyond 40 km. We find that our results outperform conventional IM/DD solutions based on two- and four-level pulse amplitude modulation with feedforward equalization at the receiver. Our study is the first step toward end-to-end deep learning based optimization of optical fiber communication systems.

Creation and Detection of Vector Vortex Modes for Classical and Quantum Communication

Abstract: Vector vortex beams are structured states of light that are nonseparable in their polarisation and spatial mode, they are eigenmodes of free-space and many fiber systems, and have the capacity to be used as information carriers for both classical and quantum communication. Here, we outline recent progress in our understanding of these modes, from their creation to their characterization and detection. We then use these tools to study their propagation behavior in free-space and optical fiber and show that modal cross-talk results in a decay of vector states into separable scalar modes, with a concomitant loss of information. We present a comparison between probabilistic and deterministic detection schemes showing that the former, while ubiquitous, negates the very benefit of increased dimensionality in quantum communication while reducing signal in classical communication links. This work provides a useful introduction to the field as well as presenting new findings and perspectives to advance it further.

Indoor Optical Wireless Systems: Technology, Trends, and Applications

Abstract: Indoor wireless traffic is evolving at a staggering pace, and is quickly depleting radio spectrum resources. Optical wireless communication (OWC) offers powerful solutions for resolving this imminent capacity crunch of radio-based wireless networks. OWC is not intended to fully replace radio wireless techniques such as WiFi, but to complement these and offload their high traffic loads. After discussing OWC's application domains, this paper gives a tutorial overview of two major directions in OWC: wide-coverage visible light communication which builds on LED illumination techniques and shares capacity among multiple devices, and communication with narrow 2-D steered infrared beams which offers unshared high capacity to devices individually. In addition, supporting techniques for wide field-of-view receivers, device localization, bidirectional hybrid optical/radio networks, and bidirectional all-optical wireless networks are discussed.

10-Mb/s Quantum Key Distribution

Abstract: We report the first quantum-key-distribution (QKD) systems capable of delivering sustainable, real-time secure keys continuously at rates exceeding 10 Mb/s. To achieve such rates, we developed high-speed postprocessing modules, achieving maximum data throughputs of 60 MC/s, 55 Mb/s, and 108 Mb/s for standalone operation of sifting, error correction, and privacy amplification modules, respectively. The photonic layer of the QKD systems features high-speed single-photon detectors based on self-differencing InGaAs avalanche photodiodes, phase encoding using an asymmetric Mach–Zehnder interferometer, and active stabilization of the interferometer phase and photon polarization. An efficient variant of the decoy-state BB84 protocol is implemented for the security analysis, with a large dataset size of $10^8$ bits selected to mitigate finite-size effects. Over a 2-dB channel, a record secure key rate of 13.72 Mb/s has been achieved averaged over 4.4 days of operation. We confirm the robustness and long-term stability on a second QKD system continuously running for 1 month without any user invention.

The Gaussian Noise Model in the Presence of Inter-Channel Stimulated Raman Scattering

Abstract: A Gaussian noise (GN) model, precisely accounting for an arbitrary frequency dependent signal power profile along the link, is presented. This allows accurate evaluation of the impact of inter-channel stimulated Raman scattering (ISRS) on the optical Kerr nonlinearity. Additionally, the frequency dependent fiber attenuation can be taken into account and transmission systems that use hybrid amplification schemes can be modeled, where distributed Raman amplification is partly applied over the optical spectrum. For the latter two cases, a set of coupled ordinary differential equations must be numerically solved to obtain the signal power profile yielding a semianalytical model. However for lumped amplification and negligible variation in fiber attenuation, a less complex and fully analytical model is presented denoted as the analytical ISRS GN model. The derived model is exact to first-order for Gaussian modulated signals and extensively validated by numerical split-step simulations. A maximum deviation of only 0.1 dB in nonlinear interference power between simulations and the ISRS GN model is reported. The model is applied to a transmission system that occupies the entire C + L band (10 THz optical bandwidth). At optimum launch power, changes of up to 2 dB in nonlinear interference power due to ISRS are reported. The ISRS GN model is quantitatively compared with other models published in the literature and found to be significantly more accurate.

Achievable Information Rates for Fiber Optics: Applications and Computations

Abstract: In this paper, achievable information rates (AIR) for fiber optical communications are discussed. It is shown that AIRs such as the mutual information and generalized mutual information are good design metrics for coded optical systems. The theoretical predictions of AIRs are compared to the performance of modern codes including low-parity density check and polar codes. Two different computation methods for these AIRs are also discussed: Monte-Carlo integration and Gauss-Hermite quadrature. Closed-form ready-to-use approximations for such computations are provided for arbitrary constellations and the multidimensional AWGN channel. The computation of AIRs in optical experiments and simulations is also discussed.

Kramers–Kronig Receivers for 100-km Datacenter Interconnects

Abstract: In this paper, we review in detail experimental demonstrations of Kramers–Kronig (KK) based direct detection systems with high per-carrier interface rates, high spectral efficiencies, and ∼100-km reach Two realizations of KK-based receivers are summarized, including single-polarization and dual-polarization versions Critical aspects of the KK receiver such as the carrier-to-signal power ratio and receiver bandwidth limitations are discussed We show 220-Gb/s single-diode detection and 4 × 240-Gb/s dual polarization (dual-diode) detection in a WDM system at 53 bits/s/Hz spectral efficiency

Multi-Vendor Experimental Validation of an Open Source QoT Estimator for Optical Networks

Abstract: Dramatic increase in data traffic, future diffusion of bandwidth-hungry 5G connectivity and evolving services like virtual reality and cloud will require the implementation of the open and elastic network paradigm on backbone optical networks. To support such growth, operators are aiming at lowering optical network costs by deploying multi-vendor disaggregated optical networks supporting white boxes while maintaining target performances. To make this effort successful, a vendor-agnostic assessment of optical performance is needed, and operators and vendors are working together to achieve this. In this paper, we present the vision of the Open Optical Packet Transport Physical Simulation Environment (PSE) Group of the Telecom Infra Project consortium, which aims at developing an open source framework for quality-of-transmission (QoT) assessment for design and operation of multi-vendor optical networks. We validate the PSE QoT estimator—the optical link emulator (OLE) based on the Gaussian noise (GN) model for nonlinear fiber propagation—by comparison with experimental results on the mixed-fiber test-bed network at Microsoft labs, operated in the C-band by commercial transceivers from eight different vendors, with propagation distances up to 1945 km. An excellent agreement between OLE predictions requiring milliseconds of computational time and measurements has been observed for all channels. The observed $\pm$ 0.75 dB of accuracy in OLE predictions can be further reduced by including the stimulated Raman scattering in the GN model and with a more accurate capability to estimate power levels and the amount of amplified spontaneous emission noise. Further work will be also required to automate the measurement process of operational parameters from network equipment, especially optical amplifiers, to streamline the overall QoT estimation process.

5G C-RAN With Optical Fronthaul: An Analysis From a Deployment Perspective

Abstract: The fifth generation (5G) wireless technology is designed to provide significantly faster Internet access, with lower latency, and ubiquitous mobile coverage compared to its predecessors. However, as there will be hundreds and thousands of wireless cells deployed in the 5G network, transporting the enormous volume of data instigated from high capacity 5G wireless cells to the core network in a cost-effective and greener manner with a low latency still remains one of the major hurdles. Therefore, in this paper, we exploit different optical transport network architectures and technologies that can be used to build an efficient fronthaul network for 5G, in order to carry data between wireless cells and the central office. Particularly, we equitably compare multiple fronthaul architectures in terms of major requirements of 5G fronthaul network such as bandwidth requirements, delay budgets, deployment costs, complexity of radio remote head, and the ability to support advanced wireless functions. In order to analyze the deployment cost of entire 5G transport and wireless networks, we develop a joint optimization framework to optimally deploy fiber-based fronthaul network and 5G wireless network simultaneously. Our framework is also capable of setting limits on the required network coverage and capacity. We analyze the optimal deployment costs under different deployment scenarios and different fronthaul technologies. Our analyses provide insights into modeling future-proof optical transport networks to realize 5G network deployment.

Photonic Integrated Circuit-Based FMCW Coherent LiDAR

Abstract: We present the demonstration of an integrated frequency modulated continuous wave LiDAR on a silicon platform. The waveform calibration, the scanning system, and the balanced detectors are implemented on a chip. Detection and ranging of a moving hard target at upto 60 m with less than 5 mW of output power is demonstrated in this paper.

Integration of IoT, Transport SDN, and Edge/Cloud Computing for Dynamic Distribution of IoT Analytics and Efficient Use of Network Resources

Abstract: Internet of Things (IoT) requires cloud infrastructures for data analysis (e.g., temperature monitoring, energy consumption measurement, etc.). Traditionally, cloud services have been implemented in large datacenters in the core network. Core cloud offers high-computational capacity with moderate response time, meeting the requirements of centralized services with low-delay demands. However, collecting information and bringing it into one core cloud infrastructure is not a long-term scalable solution, particularly as the volume of IoT devices and data is forecasted to explode. A scalable and efficient solution, both at the network and cloud level, is to distribute the IoT analytics between the core cloud and the edge of the network (e.g., first analytics on the edge cloud and the big data analytics on the core cloud). For an efficient distribution of IoT analytics and use of network resources, it requires to integrate the control of the transport networks (packet and optical) with the distributed edge and cloud resources in order to deploy dynamic and efficient IoT services. This paper presents and experimentally validates the first IoT-aware multilayer (packet/optical) transport software defined networking and edge/cloud orchestration architecture that deploys an IoT-traffic control and congestion avoidance mechanism for dynamic distribution of IoT processing to the edge of the network (i.e., edge computing) based on the actual network resource state.

The First 0.14-dB/km Loss Optical Fiber and its Impact on Submarine Transmission

Abstract: We achieved the lowest-ever transmission losses of 0.1419 dB/km at 1560 nm wavelength and 0.1424 dB/km at 1550 nm in a Ge-free silica-core optical fiber. It was an improvement by 4 mdB/km from the previous record realized in 2015. The Ge-free silica core included fluorine co-doping, which helps to reduce disorder in the microscopic glass network structure that causes Rayleigh scattering loss without a significant increase in waveguide imperfection loss. A two-layered polymer coating with an inner layer having lower elastic modulus than before also contributed to the ultralow loss without influence of microbending loss increase even with an enlarged effective area of 147 μm2. The present fiber with ultralow loss and a large effective area benefits an ultralong haul optical transmission system including transoceanic submarine cable systems. We estimate system performance based on the fiber figure of merit theory that the present fiber enables a 0.10 bit/s/Hz increase in spectral efficiency or 7% reduction in the number of repeaters, compared to the previous record-loss fiber.

Orthogonally Polarized RF Optical Single Sideband Generation and Dual-Channel Equalization Based on an Integrated Microring Resonator

Abstract: We demonstrate narrowband orthogonally polarized optical radio frequency (RF) single sideband generation as well as dual-channel equalization based on an integrated dual-polarization-mode high- Q microring resonator. The device operates in the optical communications band and enables narrowband RF operation at either 16.6 or 32.2 GHz, determined by the free spectral range and TE/TM mode interval in the resonator. We achieve a very large dynamic tuning range of over 55 dB for both the optical carrier-to-sideband ratio and the dual-channel RF equalization.

Broadband RF Channelizer Based on an Integrated Optical Frequency Kerr Comb Source

Abstract: We report a broadband RF channelizer based on an integrated optical frequency Kerr micro-comb source, with an RF channelizing bandwidth of 90 GHz, a high RF spectral slice resolution of 1.04 GHz, and experimentally verify the RF performance up to 19 GHz. This approach of realizing RF channelizers offers reduced complexity, size, and potential cost for a wide range of applications to microwave signal detection.

On the Interplay of Nonlinear Interference Generation With Stimulated Raman Scattering for QoT Estimation

Abstract: To effectively operate multivendor disaggregated networks, the performance of the physical layer needs to be assessed by a quality-of transmission estimator (QoT-E) delivering quick results with a given reliability range. Current state-of-the-art wavelength-division-multiplexing channels are based on multilevel modulation formats relying on DSP-operated coherent receivers, propagating on uncompensated and amplified optical links. In this transmission scenario, beside amplified spontaneous emission noise accumulation, nonlinear propagation impairments are well summarized by the accumulation of a Gaussian-distributed disturbance: the nonlinear interference (NLI). When exploiting a transmission bandwidth exceeding the C-band, the interaction of NLI generation with the stimulated Raman scattering (SRS) must be properly considered. We present the derivation of the generalized Gaussian noise (GGN) model for NLI generation, including the SRS and, in general, a spectral and spatial variation of gain/loss. We validate its accuracy by comparing performances predicted by a QoT-E based on the GGN model with measurements on a testbed exploiting commercial equipment, including 100 Gb/s transponders. Considering that operational parameters of the commercial equipment are known with a large range of uncertainty, an excellent agreement with errors within 0.5 dB on the generalized Signal-to-noise ratio ( $\text{SNR}$ ) is shown, demonstrating that the GGN-model can be used for the QoT-E in multivendor network scenarios. Moreover, the GGN model has shown the capability to predict the spectral tilting due to SRS in $\text{SNR}$ performances, enabling its application to evaluate the impact of linear pretilting for SRS precompensation and NLI generation.

10.16-Peta-B/s Dense SDM/WDM Transmission Over 6-Mode 19-Core Fiber Across the C+L Band

Abstract: Space-division multiplexing (SDM) is an attractive technique for dramatically enhancing the transmission capacity in a single optical fiber. Recently, ultradense SDM transmission experiments with a spatial multiplicity of over 100 have been reported by using few mode multicore fibers (FM-MCFs). Considering the maximum capacity of around 100 Tb/s reported in single-mode single-core fiber transmission experiments, the capacity in FM-MCF transmission with more than 100 spatial channels is expected to reach 10 peta-b/s; however, the maximum capacity has been limited to 2 peta-b/s. In this paper, we demonstrate ultradense SDM transmission of 739 WDM 12-Gbd dual polarization—64-quadrature amplitude modulation (QAM)/16-QAM signals over 11.3-km 6-mode 19-core fiber using the C+L band, achieving a record fiber capacity of 10.16 peta-b/s with an aggregate spectral efficiency of 1099.9 b/s/Hz.

Silicon High-Order Mode (De)Multiplexer on Single Polarization

Abstract: Mode-division multiplexing on an integrated photonic chip is critical for future optical networks. High-order mode multiplexing is desired to increase the transmission capacity. Here, we propose and experimentally demonstrate a silicon on-chip high-order mode (de)multiplexer using subwavelength grating (SWG) structure, which supports 11-mode (de)multiplexing on a TE-polarized light (TE0–TE10). The proposed mode (de)multiplexer comprises three directional couplers and seven SWG-based directional couplers. Measurement results show that all the 11 channels have low crosstalk values (−15.4 to −26.4 dB) and low insertion losses (0.1 to 2.6 dB) at 1545 nm. To the best of our knowledge, our device achieves the highest-order-mode (de)multiplexing on a silicon photonic chip.

Physical Explanation of Fabry–Pérot Cavity for Broadband Bilayer Metamaterials Polarization Converter

Abstract: We propose a wideband linear polarization converter in transmission mode by bilayer metamaterial. The polarization converter operates from 0.55 to 1.37 THz with polarization conversion ratio maintaining nearly 100%. The distribution of surface current and electrical field was numerically simulated to clarify physical mechanism of polarization conversion. Importantly, we introduced the Stokes method to assess the polarization state of transmitted converter. The Fabry-Perot-like cavity model was established to reveal the enhancement of polarization conversion ratio. The clear expressions including ideal and approximate model were deduced to provide an excellent explanation of Fabry-Perot cavity in subwavelength bilayer metamaterials structure.

1.032-Tb/s CPRI-Equivalent Rate IF-Over-Fiber Transmission Using a Parallel IM/PM Transmitter for High-Capacity Mobile Fronthaul Links

Abstract: We report high-capacity intermediate-frequency-over-fiber (IFoF) transmission using parallel intensity/phase modulators (IM/PM). Thanks to the parallel IM/PM transmitter, we can avoid all the null frequencies caused by dispersion-induced RF power fading. Compared to other techniques to avoid RF power fading, the parallel IM/PM transmitter offers a simple solution because it does not rely on any sophisticated digital signal processing. We transmitted 14 $\times$ 1.2-GHz orthogonal-frequency-division-multiplexed signals over a 20-km single-mode fiber using the parallel IM/PM transmitter and achieved a Common Public Radio Interface equivalent data rate of 1.032 Tb/s. Thus, an IFoF system with the parallel IM/PM transmitter shows great potential to be applied to high-capacity mobile fronthaul links in the upcoming fifth-generation mobile system and beyond.

An Operator view on the Introduction of White Boxes into Optical Networks

Abstract: Hardware and software disaggregation is a recognized strategy for achieving efficiency and cost reduction within datacentre warehouse. More recently this approach has been applied to high-bandwidth inter-datacenter connectivity at the transport layer. Telecom Operators look with great interest at this approach which promises savings that could make the difference in years of ever decreasing margins on revenues. This paper presents and analyzes how disaggregation models in the wavelength division multiplexing (WDM) transport layer could replace the established aggregated model based on mono-vendor systems. Three optical disaggregation models are presented implying different levels of involvement of the telecom operator in WDM system design, assembly, and integration. The impact on the network lifecycle of each model is then analyzed with particular reference to the roles of the operator, the equipment vendors, and the system integrator. The issue of organizational changes and heavy redefinition of processes is addressed and a comparative techno economic analysis is also offered.

Cost-Optimized Submarine Cables Using Massive Spatial Parallelism

Abstract: We study the techno-economics of submarine systems constrained by a fixed electrical power supply. We show significant cost savings for high-capacity submarine systems using massive space-division multiplexing (SDM), even without assuming any savings from SDM-specific subsystem integration. Systems with about 100 parallel optical paths, e.g., $\sim$ 50 fiber pairs are shown to provide minimum cost/bit, operating at reduced spectral efficiencies and deep within the linear regime. While advanced nonlinearity-optimized fibers and digital nonlinearity compensation schemes provide little to no gain in such systems, SDM integration of amplifiers and transponders is shown to be a source for significant additional cost savings. We further examine the permissible cost premium for multicore fibers in such massively parallel systems and revisit various design tradeoffs for optical amplifiers, showing that a reduced noise figure can be traded for better power conversion efficiency. We also evaluate potential gains from increasing the available electrical supply power and discuss reliability aspects of massively parallel submarine systems.

Microcomb-Based True-Time-Delay Network for Microwave Beamforming With Arbitrary Beam Pattern Control

Abstract: Microwave phased array antennas (PAAs) are very attractive to defense applications and high-speed wireless communications for their abilities of fast beam scanning and complex beam pattern control. However, traditional PAAs based on phase shifters suffer from the beam-squint problem and have limited bandwidths. True-time-delay (TTD) beamforming based on low-loss photonic delay lines can solve this problem. But it is still quite challenging to build large-scale photonic TTD beamformers due to their high hardware complexity. In this paper, we demonstrate a photonic TTD beamforming network based on a miniature microresonator frequency comb (microcomb) source and dispersive time delay. A method incorporating optical phase modulation and programmable spectral shaping is proposed for positive and negative apodization weighting to achieve arbitrary microwave beam pattern control. The experimentally demonstrated TTD beamforming network can support a PAA with 21 elements. The microwave frequency range is 8-20 GHz; and the beam scanning range is ±60.2°. Detailed measurements of the microwave amplitudes and phases are performed. The beamforming performances of Gaussian, rectangular beams, and beam notch steering are evaluated through simulations by assuming a uniform radiating antenna array. The scheme can potentially support larger PAAs with hundreds of elements by increasing the number of comb lines with broadband microcomb generation.

Long-Haul Transmission Over Few-Mode Fibers With Space-Division Multiplexing

Abstract: Space-division multiplexing (SDM) has been intensively proposed in recent years to overcome the capacity limitations of the current single-mode fiber infrastructure and to increase the efficiency of optical transmission systems. Few-mode fibers offer the potential of transmitting several signals at the same wavelength over different modes of a fiber with one single core. In this paper, we demonstrate the potential of using few-mode fiber-based SDM systems for long-haul transmission. We analyze system limitations such as mode-dependent loss and Kerr-effect-based nonlinear signal distortions for different modulation formats and distances up to 3500 km. We find that mode-dependent loss poses the major limitation in the analyzed transmission system, masking most intermodal nonlinear interactions.

Enabling Technologies for High-Speed Visible Light Communication Employing CAP Modulation

Abstract: High-speed light emitting diode (LED) based visible light communication (VLC) system is restricted by the limited LED bandwidth, low detector sensitivity, and linear and nonlinear distortions. Thus, single- and two-cascaded constant-resistance symmetrical bridged-T amplitude hardware pre-equalizers, carrierless amplitude and phase (CAP) modulation, and a three-stage hybrid postequalizer are investigated to increase transmission data rate for a high-speed LED-based VLC system. The schemes utilized by the hybrid postequalizer are modified cascaded multimodulus algorithm, Volterra series based nonlinear compensation algorithm and decision-directed least mean square algorithm. With these technologies, we successfully implement high-speed CAP32, CAP64, and CAP128 VLC experimental system over 1-m free space transmission with bit error rate under the hard decision-forward error correction threshold of 3.8 × 10–3. System performance improvement employing these key technologies is also validated through experimental demonstration. With the superposition of each stage of the hybrid postequalizer, system performance will be improved. And utilizing two-cascaded hardware pre-equalizer will provide more accurate channel compensation than a single pre-equalizer.

The Impact of Solar Irradiance on Visible Light Communications

Abstract: This paper aims to address the perception that visible light communication (VLC) systems cannot work under the presence of sunlight. A complete framework is presented to evaluate the performance of VLC systems in the presence of solar irradiance at any given location and time. The effect of solar irradiance is investigated in terms of degradations in signal to noise ratio, data rate, and bit error rate. Direct current (DC) optical orthogonal frequency division multiplexing is used with adaptive bit and energy loading to mitigate DC wander interference and low-frequency ambient light noise. It was found that reliable communication can be achieved under the effect of solar irradiance at high-speed data rates. An optical bandpass blue filter is shown to compensate for half of the reduced data rate in the presence of sunlight. This work demonstrates data rates above 1 Gb/s of a VLC link under strong solar illuminance measured at 50350 lux in clear weather conditions.

RAN Revolution With NGFI (xhaul) for 5G

Abstract: From “Rethinking Ring and Young” in 2011 to proposing next generation fronthaul interface (NGFI, aka xhaul) in 2014, the radio access network (RAN) revolutionary path to meet ambitious 5G demands has been charted out. Traditional fronthaul solutions fell short both in required bandwidth and architecture flexibility. NGFI proposed by China Mobile targeting a packet-based, traffic-dependent, and antenna scale-independent interface will be central to the 5G RAN revolution. This paper presents its latest progress. Specifically, a two-level NGFI architecture will be highlighted, and the function split options with associated requirements in, e.g., latency, bandwidth, and synchronization will be presented. In addition, challenges as well as the potential solutions for NGFI realization will be discussed.

Physical-Enhanced Secure Strategy for OFDMA-PON Using Chaos and Deoxyribonucleic Acid Encoding

Abstract: Due to massive parallelism, huge storage, and ultralow power consumption characteristics of deoxyribonucleic acid (DNA), we propose a secure orthogonal frequency-division multiple access passive optical network (OFDMA-PON), using chaos encryption and DNA encoding. In this scheme, the transmitted bit data are interleaved according to DNA operation rules, and the encoding and operation rules are randomly controlled by using a chaotic map. This DNA encoding can improve the complexity and the random characteristic of the chaotic encrypted sequences. A physical layer secures OFDMA-PON system with 36.77-Gb/s downstream signal, and the 15.45-Gb/s upstream signal is successfully experimentally demonstrated. The experimental results verify that the chaos and DNA encoding based physical layer security enhancement technique can suggest an effective solution for future physically secured OFDMA networks.

Enhancing the Magnetic Plasmon Resonance of Three-Dimensional Optical Metamaterials via Strong Coupling for High-Sensitivity Sensing

Abstract: We report an effective method to enhance and modify the magnetic plasmon (MP) resonance in three-dimensional (3D) optical metamaterials consisting of periodic arrays of silver vertical split-ring resonators (VSRRs) for high-sensitivity sensing. By positioning the 3D metamaterials above a thick silver film separated by a silica dielectric spacer layer, the strong coupling between the MP resonance in the VSRRs and the surface plasmons polaritons (SPPs) propagating on the silver film can be realized and gives rise to an ultra-narrowband hybrid MP mode with a huge enhancement of magnetic fields. For the coupling to happen, the magnetic field direction of the SPPs should be parallel to the magnetic moment induced in the VSRRs. More importantly, because the ultra-narrowband hybrid MP mode is extremely sensitive to the surrounding media, the sensitivity and the figure of merit (FOM) of the 3D metamaterials can reach as high as 700 nm/RIU and 170, respectively, suggesting that the proposed 3D metamaterials hold potential applications in label-free biomedical sensing.

1.72-Tb/s Virtual-Carrier-Assisted Direct-Detection Transmission Over 200 km

Abstract: Supporting the ever-increasing data-center-inter-connect traffic in a cost-effective manner is a great challenge, which requires innovative transmission and digital signal processing (DSP) techniques. Recently, single-side-band (SSB) direct-detection (DD) transmissions have been actively considered for data rates beyond 100 Gb/s per channel and distance of hundreds of kilometers due to its capability of electronic chromatic dispersion compensation. In addition, several effective DSP techniques to mitigate or suppress the signal-signal beating interference (SSBI) due to the squared-law detection of the photodiode have been intensively investigated, such as Kramers–Knonig (KK) and SSBI cancellation schemes, showing promising performance at data rates over 200 Gb/s and distance beyond 100 km. In this paper, we demonstrate that high-performance low-complexity SSB DD transmissions can be achieved by generating a digital carrier (virtual carrier) together with the complex information-bearing signal at the transmitter using only two digital-to-analog converters. Combining this transmission technique with either the KK field reconstruction or a two-stage SSBI cancellation scheme at the receiver, eight-channel WDM signals with a net data rate of 1.72 Tb/s have been transmitted successfully over a record span length of 200 km at 1550 nm.