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This paper proposes a dynamic secure key distribution scheme based on dispersion equalization and cellular automata (CAs). The scheme effectively eliminates the key inconsistency problem caused by imperfect channel reciprocity, and dynamic key sequences can be conveniently generated with large key space in long-haul optical transmission. In the process of communication, the legitimate parties obtain the secure core parameter from the frequency domain equalizer algorithm, and a final key sequence is generated through CA iterations on the basis of the core parameter. The randomness and reciprocity characteristics of the channel ensure the security and uniqueness of the core parameter and final key sequence. With 10G Baud 16 quadrature amplitude modulation over 400 km standard single-mode fiber transmission, the proposed scheme is verified with a free key error rate and an unlimited key generation rate. The security robustness of this scheme was theoretically analyzed and verified by sweeping the eavesdropper’s tapping position and improving CA operation processing. The proposed key distribution scheme is compatible with the existing transmission system for different signal modulation formats.

An all-optical aggregator consisting of time-lens and a phase reloader for two four-channel multiplexed quadrature phase shift keying (QPSK) signals to a wavelength division multiplexed (WDM) 16-ary quadrature amplitude modulation (16QAM) signal is proposed. The feasibility of the scheme is confirmed by the waveforms of the intermediate process and the constellations of input-output signals. The performance of bit error rate (BER) and error vector magnitude (EVM) values under different optical signal-to-noise ratios (OSNR) are analyzed to evaluate the system, and the OSNR penalties of the aggregated signal at the forward error correction (FEC) threshold are between 2.25 dB and 2.45 dB. This scheme potentially enables reconfigurable service and improves compatibility in elastic optical networks (EON).

Wavelength-division-multiplexed passive optical network (WDM-PON) has been widely deployed for the high-speed, reliable transmission and low-cost properties. The physical layer identity authentication in WDM-PON becomes increasingly prominent. Recently, many device fingerprint based identity authentication schemes are proposed. However, these schemes only realize constant fingerprint, which will be acquired by illegal ONU after optical spectrum analysis. Therefore, the higher-level security requirement cannot be satisfied. To solve the problem, we propose a physical layer identity authentication method in WDM-PON by exploiting the channel characteristics based adjustable fingerprint with deep neural networks (DNNs). By secretly negotiating with legal optical network units (ONUs) on the lengths of the local fibers applied by them, the optical line terminal (OLT) can acquire the unique channel characteristics fingerprint obtained by each legal ONU. It should be noted that the fingerprint can be adjusted by modifying the length of the local fiber. Moreover, the same number of DNNs as legal ONUs are trained for fingerprint identification. Simulation results show 100% identification accuracy for illegal ONU when the length deviation between two fibers applied by legal ONU and illegal ONU is greater than 1.5 km. Meanwhile, the identity of each legal ONU can be recognized with 100% accuracy.

With the development of Fifth-generation (5G) mobile communication, mobile networks are dedicated to accommodating more subscribers and diversified service scenarios. 5G is then expected to significantly enhance the quality of experience on services, and pave way for the interconnection of everything. Starting from the development trends of radio accoss network (RAN), this paper investigates its evolution progress and key technologies, including wireless access, optical bearing, interfaces for fronthaul and midhaul, control and management, as well as network slicing. Finally, the urgent challenges are described from the perspective of RAN evolution towards 5G.

The integration of 5G and vertical industries promotes the development of the energy Ethernet while putting forward fine granularity, flexibility, high reliability, and deterministic low-latency service requirements for the smart grid and the ubiquitous power Internet of Things (UPIoT). As the bearer architecture supporting the next-generation optical transmission network, the Slicing Packet Network (SPN) slice granularity decreases from 5 Gbps to 10 Mbps fine granularity and the frame period of 5 Gbps large-granularity slices is short, so the non-deterministic delay caused by timeslot conflicts has a negligible impact on the end-to-end delay, and the timeslot scheduling is unnecessary. However, due to the reduction in timeslot granularity and the change in frame structure in 10 Mbps slices, the scheduling of conflicting timeslots and the complex device computing management problems need to be solved urgently. In this paper, we establish a model of routing embedded timeslot scheduling for the routing of fine-granularity slices and timeslot scheduling problems in SPN-based FlexE interfaces, for which we propose a deterministic timeslot allocation mechanism supporting end-to-end low-latency transmission. According to the timeslot symmetry, the mechanism can reduce the space of feasible solutions through ant colony optimization and unidirectional neighborhood search (ACO-UNS), so as to efficiently solve the scheduling of conflicting timeslots and provide end-to-end delay guarantee for delay-sensitive services. Finally, we make a comparison between the ACO-UNS algorithm and the timeslot random dispatching algorithm (ACO-RD); the results show that, relative to the ACO-RD, the reduction in the proposed ACO-UNS is 98.721% for the end-to-end delay of fine-granularity slices.

It is essential to estimate the quality of transmission (QoT) of lightpaths before their establishment for efficient planning and operation of optical networks. Due to the nonlinear effect of fibers, the deployed lightpaths influence the QoT of each other; thus, multi-channel QoT estimation is necessary, which provides complete QoT information for network optimization. Moreover, the different interfering channels have different effects on the channel under test. However, the existing artificial-neural-network-based multi-channel QoT estimators (ANN-QoT-E) neglect the different effects of the interfering channels in their input layer, which affects their estimation accuracy severely. In this paper, we propose a self-attention mechanism-based multi-channel QoT estimator (SA-QoT-E) to improve the estimation accuracy of the ANN-QoT-E. In the SA-QoT-E, the input features are designed as a sequence of feature vectors of channels that route the same path, and the self-attention mechanism dynamically assigns weights to the feature vectors of interfering channels according to their effects on the channel under test. Moreover, a hyperparameter search method is used to optimize the SA-QoT-E. The simulation results show that, compared with the ANN-QoT-E, our proposed SA-QoT-E achieves higher estimation accuracy, and can be directly applied to the network wavelength expansion scenarios without retraining.

A novel nanocavity-based polymer-on-insulator (POI) electro-optic modulator (EOM) is proposed. It consists of a polymeric photonic-crystal nanobeam cavity (PCNC) with ultra-low index-contrast (ncavity/nbg = 1.17). Based on three-dimensional (3D) finite-difference time-domain (FDTD) method, the PCNC design and optimization are investigated theoretically. A high quality-factor (Q) of 3.4 × 104 and small mode-volume of 22.8 (λ/nSEO)3 can be achieved. In order to judge the efficiency of the cavity design for electro-optic (EO) modulation, the optical modes and the electric field distribution are computed using an electromagnetic finite-element solver. Benefiting from the fast and strong EO effect in polymers, the modulator shows an EO modulation efficiency of up to 16 pm/V, which is over an order of magnitude higher than that in lithium niobate (LN) PCNCs. Moreover, the device is only 80 μm in length, leading to a voltage-length product Vπ × L = 0.05 V·cm, which is much smaller than those of Mach-Zehnder modulators. To the best of our knowledge, this is the first on-chip POI-based EOM that features both ultra-compact size and high modulation efficiency. Hence, it is potentially an ideal platform for applications in optical communications, electric-field sensing, and tunable photonic circuits.

The convergence of optical and wireless networks, and the marginalization of centralized data centers are required for next-generation telecommunications. According to the operators' concern of cost-efficient deployment combined with latency-sensitive requirements, network planning will lay a foundation for the development of next-generation networks. In particular, the network planning of mobile edge computing (MEC)-enabled cloud radio access networks (C-RAN) in a cost-effective and low-latency manner becomes exceedingly challenging. However, most research studies focus on the cost-effective deployment of C-RAN without considering the optimal placement of MEC servers simultaneously. Moreover, deployment costs and access latency will be directly affected by the optimal deployment of both the MEC servers and access networks. Therefore, we investigate how to coordinate the optimal deployment of MEC servers and C-RAN for latency-sensitive services. In detail, a MILP model is proposed to minimize the joint cost of latency and network deployment of time division multiplexing-passive optical network (TDM-PON) based MEC-enabled C-RAN. Given the model's complexity, a heuristic algorithm is also proposed to solve the mixed integer linear programming (MILP) model. Simulations are conducted to evaluate the performance comparisons of different approaches under different network scenarios. The impacts of some key parameters on comparisons of different approaches are also analyzed.

The development of new techniques to rapidly and accurately detect bacteria has drawn continuous attention due to the potential threats posed by bacteria to human health and safety. Recently, a novel strategy based on fluorescent probes has drawn considerable interest for the detection of bacteria due to its high selectivity, fast response, and simple operation. In this review, we summarize the recent progress on fluorescent probes for the specific recognition and discrimination of Gram-negative and Gram-positive bacteria. In particular, we outline current design strategies, such as targeting of the differences in surface components, cell wall components, endogenous enzymes, surface charge, and hydrophobicity of various kinds of bacteria to develop various fluorescent sensors (organic small-molecule fluorescent probes, nanoprobes, and metal ion probes). We also emphasize the application of organic molecules in probe recognition elements. We hope that this review can stimulate this research area in bacterial detection and imaging in the future.

As a typical high-order modulation format optimization technology, constellation probability shaping enhances generalized mutual information (GMI) by optimizing the probability distribution of each constellation point of the signal. It can improve the transmission capacity of the same order M Quadrature Amplitude Modulation (QAM) signal under the condition of limited average transmission power, and further narrow the gap with the Shannon limit capacity. The distribution matcher is a key part of constellation probability shaping since it not only ensures the one-to-one mapping of input and output sequences but also realizes the function of probability shaping. The constant composition distribution matcher (CCDM) structure is a widely utilized distribution matcher in the current probability shaping technology. Based on CCDM, a parallel distribution matcher scheme is proposed in this paper. It has a lower rate loss than CCDM for short output lengths (n is less than 100). Block lengths can be reduced by up to 30% with the same rate loss. When the GMI is the same as for the probability shaping (PS) 64QAM signal using CCDM, the OSNR required by the PS-64QAM signal using this scheme can be enhanced by 0.12dB, the block length can be reduced by 40%, and the transmission distance in a standard single-mode fiber can be slightly extended.

A simultaneous all-optical channel aggregation and de-aggregation scheme is proposed for two 8QAM modulation formats by employing four-wave mixing (FWM) in highly nonlinear fiber. The scheme consisting of two FWM processes is simple without photoelectric conversion, which is promising to improve efficient use of the fiber resources in elastic optical networking. The feasibility of the scheme has been confirmed by the input-output constellations and waveforms. System performance is also studied as a function of the optical signal-to-noise ratio of the two 8QAM signals. Finally, some potential application scenarios have also been discussed based on the same setup.

The increasing demand of mobile internet and Internet of Things poses challenging requirements for indoor wireless communication. Visible light communication (VLC) is a promising technology to alleviate the growing traffic problem. In addition, nonlinear distortion of light emitting diodes (LEDs) results in a poor link quality. In this paper, we propose multiple access with polarity division sparse code (PDSC) for VLC, which is based on nonorthogonal multiple access and spatial characteristic of LEDs. The experimental results indicate that the PDSC significantly enhances capacity and spectral efficiency of VLC network compared with orthogonal frequency division multiple access. We also demonstrate that the PDSC can optimize the problem of nonlinear distortion with polarity division. The experimental results reveal that PDSC is a promising multiple access scheme for the indoor VLC networks.

In this paper, a simple optical vector quadrature de-multiplexer (QD) scheme is proposed for de-aggregating input 10 Gbaud 16/32/64 quadrature amplitude modulation (QAM) signals into two pulse amplitude modulation (PAM) streams. The proposed QD is based on a single bi-directional degenerate phase-sensitive amplifier (PSA), where the wavelength and the polarization status of the extracted in-phase and quadrature components stay the same as the input signal. Since the proposed QD is realized using PSA based on semiconductor optical amplifier (SOA), it is also possible to realize an on-chip QD system, providing an integrated platform for optical signal processing. Through numerical simulation, the transfer characteristics of the proposed QD system show that the SOA-based PSA has a high phase-sensitive gain extinction ratio of 44.1 dB. The constellations, error vector magnitudes (EVMs), and bit-error rates (BERs) of the data streams after the de-aggregation are numerically investigated to verify the proposed QD scheme. For the 10 Gbaud 16/32/64 QAM signals with an input optical signal-to-noise ratio (OSNR) of 25 dB, the de-aggregated PAM4/PAM6/PAM8 signals show 6.1, 5.6, and 8.2 dB receiver OSNR improvements at the BER of 10−3, respectively. Also, to optimize the performance of the subsystem, the BER performance dependence on the phase difference between two arms in the subsystem is also examined. The simulation results reveal that the proposed QD can accomplish the function of optical vector de-aggregation well for the high-level QAM signals. The proposed QD can be applied to information de-aggregation, format conversion, and direct detection for optical vector signals, which may have great potential values for the flexible optical networks.

The wide coverage of satellite networks and the large bandwidth of terrestrial networks have led to an increasing research on the integration of the two networks (ISTN) for complementary advantages. However, most researches on routing mainly focus on the internal routing of the satellite network. Due to the point-to-area coverage of the channel characteristics between the satellites and the ground stations, the heterogeneity of ISTN has increased, which makes that the routing algorithm of the traditional satellite networks cannot be applied to the end-to-end routing of ISTN. Meanwhile, the data flows with elastic quality of service attribute make the routing pre-assign and resource allocation in ISTN much more complicated, which has been rarely researched before. In this paper, we first describe the unified network architecture based on software-defined network and model the data flow. Then, based on the considerations of latency, capacity, wavelength fragmentation, and load balancing, a heuristic service-oriented path computation algorithm for elastic data flows is proposed for the complex heterogeneity of the ISTN. The simulation shows that, the end-to-end routing mechanism can reduce the blocking rate of the ISTN, and our proposed algorithm greatly reduces the wavelength fragmentation and bandwidth consumption, and has a better performance on load balancing, with a slight disadvantage in latency when the network load is high.

Flexible conversion between modulation formats enables intelligent grooming techniques for an elastic optical network (EON) aimed at dynamical spectral efficiency allocation in optical fiber transmission. In this paper, we propose and demonstrate an all-optical modulation format conversion scheme between an 8-ary phase shift keying (8PSK) signal and two quadrature phase shift keying (QPSK) signals based on phase-sensitive amplification in highly nonlinear fiber. Benefiting from two simultaneous but different phase-squeezing processes, the two QPSK signals can be obtained simultaneously to avoid the loss of original information. The system transfer functions show the feasibility of the proposed scheme, and the system performance is evaluated by input-output constellations, calculated error vector magnitude (EVM), and bit error rate (BER) in numerical simulation. At BER of 3.8 × 10-3, about 5-dB optical signal-to-noise-ratio (OSNR) improvement between the input 8PSK signal and output QPSK signals can be observed. Furthermore, several potential applications in optical fiber transmission can also be found based on the converter.

Recently, a hybrid multiple access (MA) scheme, non-orthogonal MA (NOMA) combined with orthogonal frequency-division MA (OFDMA), has attracted significant attention in the fifth-generation (5G) wireless communication due to its superior spectrum efficiency. However, the advantage of the hybrid MA scheme cannot be fully realized in visible light communication (VLC) networks, since current optical orthogonal frequency-division multiplexing (OFDM) technologies are unable to provide high spectrum efficiency and power efficiency at the same time. In this paper, a hierarchical pre-distorted layered asymmetrically clipped optical OFDM (HPD-LACO-OFDM) scheme is proposed for NOMA, which offers superior spectrum efficiency as well as high optical power efficiency. In HPD-LACO-OFDM, multiple layers of asymmetrically clipped optical OFDM (ACO-OFDM) signals are generated to fill the odd subcarriers successively, and the inter-layer interference is eliminated with successive signal pre-distortion. A comparison of the bit-error-rate (BER) performance between the traditional dc-biased optical OFDM (DCO-OFDM), the layered ACO-OFDM (LACO-OFDM), and the proposed HPD-LACO-OFDM scheme is experimentally performed. The results show that with the same signal power, the HPD-LACO-OFDM-based NOMA-VLC network shows the best BER performance, whereas the demand for direct current voltage is reduced by half of the signal voltage compared to the traditional DCO-OFDM-based NOMA-VLC network.

In this paper, an all-optical quadrature phase shift keying (QPSK) phase regeneration scheme using vector phase sensitive amplification (PSA) is proposed, analyzed, and simulated. Compared with the conventional scalar PSA scheme, the vector superposition of harmonics makes it easy to obtain high gain extinction ratio (GER) with low pump powers. A subsequent phase-preserving amplitude regenerating device is also introduced to achieve full-quadrature regeneration of signal without phase conjugation and frequency conversion. In addition to the theoretical analysis of the implementation principle, a series of simulation results' analysis, including comparison with traditional scheme and regeneration performance assessment, is also included. The results show that undesired harmonics are greatly reduced by nearly 40 dB, and high GERs are available independent of input power. What is more, various levels of phase and amplitude noise can be effectively compressed for 10-Gbd QPSK signal. The regeneration system also reduces the signal bit error rate and gets 2-dB receiver optical signal noise ratio (OSNR) improvements at 13-dB OSNR input, which has potential applications in enhancing transmission distance in the future optical communication network.

Quantum access networks allow a large number of users to access quantum networks, which can be regarded as an important part of the practical application for quantum communication. However, current quantum access networks have not considered as the peer-to-peer multimedia service between optical network units (ONUs) that have become the dominant service in the access networks. Thus, we propose a quantum access network that can support direct quantum and classical ONU-ONU communication by using an N:N splitter. In addition, we improve the efficiency of quantum key distribution (QKD) from both the physical and the data link layer. For the former, we analyze spontaneous Raman scattering (SRS) that is the main impairment source to QKD due to the co-propagation of the classical and quantum signal. Then, we propose a collision-avoiding scheme to reduce the influence of the SRS. For the latter, a dynamic time slot assignment protocol is proposed to reduce discarding secure keys greatly. The two methods are verified by simulations, and the results show that each method can effectively optimize QKD performance.

WDM-PON-based mobile edge computing (MEC)-enabled fiber wireless access networks (MFWAN) have been identified as a promising technology for next-generation broadband access. Low-latency oriented network planning of the WDM-PON-based MFWAN would be required for low-latency access to newly emerging latency-sensitive applications in the fifth-generation (5G) era. However, this would require a low-latency oriented network design in the network planning phase and has thus become a crucial challenge. In this paper, we investigate low-latency oriented network planning of the WDM-PON-based MFWAN under physical and management constraints. To this end, we develop a mathematical model to minimize total transmission latency for all latency-sensitive services. Our model is composed of the propagation latency on the paths and the processing latency on the network equipment and is subject to constraints of maximal transmission distance, maximal PON power budget, bandwidth requests, and the fronthaul latency limit under some functional split options. Given the model's complexity, we also propose a heuristic algorithm called latency-minimized integrated multi-associated positioning and routing algorithm (LMI-MAPRA). The simulation results show that the proposed algorithm outperforms the benchmark algorithm with more total transmission latency reductions in both sparse and dense networks. We also analyze the impact of key parameters on comparisons of different approaches in terms of low-latency optimal performances.

Typical energy-efficient dynamic grooming solutions may find a detour and longer path where delay from both the IP layer and optical layer is increased on extra nodes and links. In this paper, analysis of both delay and energy is made on typical grooming operations. An integer linear programming (ILP) model for minimization of both delay and energy is formulized and an alternative model is given with more delay consideration on the distribution over expected IP links. By considering the expected resource distribution of service requests, the available network resource can be re-priced by amortized cost over the expected distribution and a delay proactive control algorithm is designed over this distribution. A proactive delay heuristic is then proposed as an independent policy by a sorting function which is distinguished from other policies by cost functions on a virtual graph. By mining a frequent subset of IP links between node pairs, the problem is simplified without loss of statistical advantage over the resource distribution. The proposed grooming heuristic is performed on a simulation platform in terms of path delay, optical energy consumption, and electrical energy consumption. The simulation results show that the proposed grooming heuristic decreased average path delay without impacting energy performance. Different factors such as sliceability of a network resource, frequent degrees of expected resource, and grooming control periods, which affect the performance of the proposed heuristic, are compared to give thorough evaluations.

In this paper, a novel electro-optic feedback phase chaotic system based on nonlinear coupling of two delayed interfering branches is proposed and analyzed by numerical simulation. The feedback loop of the proposed system contains two delay branches and a Mach-Zehnder modulator. The chaotic voltages generated from two branches are nonlinearly converted in order to reduce their temporal correlations. The dynamic characteristics and the complexity of the generated chaotic signal are evaluated by the bifurcation diagram and permutation entropy, respectively. Besides, the simulated results show that the time-delay signature can be concealed effectively with a lower feedback gain, meanwhile the key space is extended considerably since more tunable parameters are nonlinearly coupled, thus the security can be improved greatly. Furthermore, the communication system based on the proposed scheme is discussed, and the results demonstrate that this system can be applied in secure communication.

The optical datacenter networks need periodical reconfiguration in response to traffic change. Before the networks reconfigure, the tenant requests are given and should be served within fixed transfer time and spectrum capacity. In this paper, the planning problem of serving the requests in optical orthogonal frequency division multiplexing datacenter networks is investigated. We introduce the knapsack-based spectrum and time allocation (KSTA) problem. The objective of this paper is to maximize the network throughput. We formulate the KSTA problem as an integer linear programming (ILP) model. However, ILP cannot find the optimal solution for large input requests within shorter time. To solve the problem, three fast heuristic algorithms, i.e., the most spectrum first, the most time first, and the most data volume first, are proposed to achieve suboptimal solutions. Furthermore, the simulated annealing (SA) algorithm is employed to yield a better suboptimal solution. The simulation results indicate that ILP provides an optimal solution for small input requests, whereas the three heuristic algorithms and SA can yield suboptimal solutions for large input requests. The results also show that the suboptimal solution to SA is better than those provided by the three heuristic algorithms.

The unexpected growth of cloud services lead to a dramatic increase in the network capital expenditure (CAPEX) and latency in geographically distributed inter-datacenter networks. In this paper, an adaptability analysis is proposed on CAPEX and forwarding delay for IP switching and optical transport network (OTN) switching in distributed inter-datacenter networks. By abstracting the switching behavior of the IP routers and OTN equipment, the IP nodes, and OTN nodes are mapped to the switching matrix of CLOS switching network. A unified network-level connection model is established based on CLOS switching network to meet the needs of connectivity. Then, the hardware costs and the forwarding delay are evaluated to find out the bandwidth threshold (BDT) which decides the most suitable switching mode for a specific switching granularity. The adaptability of IP switching and OTN switching under different switching granularities and port rates is performed based on the simulation platform in terms of hardware cost, optical port cost, and forwarding delay. Simulation results show that the BDT based on hardware cost is 280 Mbps when switching granularity is 1.25 Gb/s. For 2.5 Gb/s switching granularity, when average bandwidth between multiple datacenters is higher than 600 Mbps, OTN switching has more advantages than IP switching on capital expenditure, especially when port rate of the equipment is high. In addition, the simulation results also verify that the forwarding delay is reduced obviously with OTN switching.

Using free-space optics (FSO) in the mobile fronthaul/backhaul networks is a promising solution that can potentially enhance the capacity of mobile networks. The main challenge of establishing FSO-based fronthaul/backhaul networks is the dynamic feature of the networks, i.e., the fragile links under adverse weather conditions and the dynamic traffic demands among small cells. Topology reconfiguration is proposed to dynamically rearrange the FSO links. In this paper, two types of network reconfigurations are investigated, in which the proactive network reconfiguration is to proactively optimize the topology of the FSO-based fronthaul/backhaul networks for each specific time period based on the statistics of the network, and the reactive reconfiguration is to actively adjust the topology when traffic demands and link states are changed. The proactive network reconfiguration is formulated as a mixed integer nonlinear programming (MINLP) problem, which jointly optimizes the network throughput and power consumption of the FSO-based fronthaul/backhaul networks. A greedy algorithm is proposed to derive the solution of the proposed problem. After the network topology having been reconfigured by solving the MINLP problem, two reactive reconfiguration algorithms are designed to optimally adjust the network topology once a link failure and demand explosion occur, respectively, to further enhance the network throughput and reduce the power consumption. The performance of the algorithms is demonstrated via extensive simulations.

Abstract Recently, to bridge the gap between security of Measurement-device-independent quantum key distribution (MDI-QKD) and a high key rate, a novel protocol, the so-called detector-device-independent QKD (DDI-QKD), has been independently proposed by several groups and has attracted great interest. A higher key rate is obtained, since a single photon bell state measurement (BSM) setup is applied to DDI-QKD. Subsequently, Qi has proposed two attacks for this protocol. However, the first attack, in which Bob’s BSM setup is assumed to be completely a “black box”, is easily prevented by using some additional monitoring devices or by specifically characterizing the BSM. The second attack, which combines the blinding attack and the detector wavelength-dependent efficiency, is not explicitly discussed, and its feasibility is not experimentally confirmed. Here, we show that the second attack is not technically viable because of an intrinsically wavelength-dependent property of a realistic beam splitter, which is an essential component in DDI-QKD. Moreover, we propose a feasible attack that combines a well-known attack—detector blinding attack with intrinsic imperfections of single-photon detectors. The experimental measurement and proof-of-principle test results confirm that our attack can allow Eve to get a copy of quantum keys without being detected and that it is feasible with current technology.

Free-space optics (FSO) and visible light communication (VLC) share the same optical wireless features, such as high data rate, license free, energy efficient, flexible access, and high degree of security. A hybrid optical wireless network based on FSO/VLC heterogeneous interconnection is presented here for future space-air-ground-ocean-integrated communication architecture, especially in the radio-frequency-sensitive (RF) or security-required environments. The functional modules of the hybrid network coordinator are defined, along with the implementation and deployment details. Three fundamental network-layer mechanisms are designed in the coordinator including user identification and localization, user mobility and handoff control, and routing and traffic management. An experimental platform is built to evaluate the transmission performance of the presented hybrid network, and a complete data aggregation/transmission/distribution procedure based on heterogeneous interconnection is first realized, which includes two-segment 1.0-m 450-Mb/s orthogonal-frequency-division-multiplexing-based VLC transmissions interconnected by one-segment 430-m 0.96-Gb/s on-off keying (OOK)-based nonturbulent FSO transmission, with the bit error rate under the forward-error-correction limit (3.8 × 10-3 ). The VLC transmission performances under three speed levels and FSO transmission performances under five typical air-quality conditions are experimentally demonstrated, which validate the feasibility of the proposed hybrid optical wireless network.

A scheme of all-optical multilevel phase quantization with high accuracy based on multiwave interference is proposed. The influences of the amplitude ratios of the conjugate (N - 1)th and (N + 1)th harmonics to the signal on phase quantization accuracy are researched. The characteristics of the phase quantization output with the amplitude ratios variation are discovered. By using the proposed scheme, the output phase is more concentrated than that of the traditional method for multilevel phase quantization. The simulations show the effectiveness of the scheme for the three levels quantization and the application of four levels quantization to the quadrature phase shift keying signal regeneration.

A method for the dense integration of one-dimensional (1-D) photonic crystal nanobeam cavity (PCNC) based integrated sensor array (1-D-PCNC-ISA) is proposed. The 1-D-PCNC-ISA consists of multiple parallel-connected sensing channels with airgap separations. On each channel, only a single flexible 1-D-PCNC sensor with large free spectral range (FSR) and high Q-factor is contained. With proper engineering of the FSR, multiple ultracompact high-sensitivity 1-D-PCNC sensors can be integrated into microarrays without resonance overlap, and be interrogated simultaneously between a single input/output ports. Using 3-D finite-difference-time-domain (3-D-FDTD) method, the performance of the device is investigated theoretically in the whole paper. With optimization design, a large FSR as wide as 197 nm and high Q-factor 2 x 105 can be achieved. Moreover, the refractive index sensitivities of a 5-channel 1-D-PCNC-ISA as high as 170.6, 152.7, 138.5, 128.1, and 120.5 nm/RIU are obtained. Particularly, the footprint of a 5-channel 1-D-PCNC-ISA is ~7μm x 65μm (width by length), which is decreased by three orders of magnitude compared to the sensor arrays based on 2-D-PC cavity platforms. To the best of our knowledge, this is for the first time that a 1-D-PCNC based multichannel parallel-connected sensor array has been displayed with channel spacing as small as 0.195μm, extinction ratio > 20 dB and Q-factor > 105, respectively, without using particular materials or complexities in fabrication. Both the specific result and the general idea are promising in future ultracompact lab-on-a-chip applications and nanophotonic integrations.

Smart home technologies are growing actively all around the world. As a result, great pressures are imposed on internet of things networks by dynamic traffic and plenty of devices. The passive optical network is considered one of the most promising fronthaul technologies. In particular, the time and wavelength division multiplexing passive optical network has shown the advantage of high capacity and received attention recently. In support of internet of things networks, the energy and transmission efficiency has emerged as an important issue on the time and wavelength division multiplexing passive optical network enabled fronthaul networks. In this paper, we try to enhance the energy and transmission efficiency of the time and wavelength division multiplexing passive optical network enabled reconfigurable fronthaul. Fronthaul links’ load balancing is also taken into consideration. An integer non-linear programming model is employed to formulate the joint optimization problem. We also provide an adaptive genetic algorithm-based approach with fast convergence. The simulation results show that the active units of fronthaul can be dynamically switched on/off with the traffic variation and a significant energy saving is achieved. In addition, the maximum transmission efficiency increases by 87% with integer non-linear programming method in off-peak periods.

A novel method for integration of high-performance 1-D photonic crystal nanobeam bandgap filter (1-D PC-NBF) and high-sensitivity 1-D PC nanobeam cavity sensor (1-D PC-NCS) is proposed on a monolithic silicon chip. The 1-D PC-NBF consists of a simple 1-D PC nanobeam waveguide, in which the bulk air-hole grating radii are kept the same. The 1-D PC-NCS consists of a common 1-D PC nanobeam cavity, in which the air-hole grating radius is parabolically tapered from center to end. By using the 3-D finite-difference time-domain (3-D-FDTD) method, the proposed 1-D PC-NBF with an effective low-pass bandgap ranging from 1533 to 1785 nm (with width > 250 nm) is demonstrated, where the resonant wavelengths lying in the bandgap are not guided. Then, by connecting an additional 1-D PC-NBF to a 1-D PC-NCS in series, a transmission spectrum only containing the specific fundamental mode of the 1-D PC nanobeam cavity for sensing purposes is created, while the other high-order modes are filtered out. Moreover, the additional 1-D PC-NBF has no influence on the properties (e.g., Q-factor, resonance position, and sensitivity) of the fundamental resonant mode of 1-D PC-NCS. In particular, the footprint of the proposed 1-D PC nanobeam integrated sensor is ultracompact around 0.7 μm × 10 μm, which is improved more than three orders of magnitude compared with the integrated sensor devices based on 2-D PC. Thus, the method presented here is promising to build highly parallel integrated sensor arrays for lab-on-a-chip applications and accurate detections.

Separation by IMplantation of OXygen (SIMOX) 3-D sculpting is considered as a new method for 3-D strain engineering in buried silicon waveguides. A model capable of analyzing the stress distribution and strain gradient of buried silicon waveguides is developed. The modeled stress shows agreement with experimental measurements obtained using Raman spectroscopy. Our method not only provides a new way to engineer strain in silicon but allows for the integration of strained-silicon-based devices with other optical and/or electronic devices on the same substrate as well, improving the device density and enhancing the functionality of the optical chip.

Strain in silicon plays a significant role in exploring electro-optical material, boosting transistor performance, tuning birefringence of optical silicon waveguides, and so on. In this paper, we measured, for the first time, the nanoscale strain in the SIMOX 3-D sculpted silicon waveguides using tip-enhanced Raman spectroscopy (TERS). A model, which relates the observed Raman peak shifts to the localized stresses for our TERS experiments, was presented. The tip-induced electric-field enhancements, tip-induced depolarization of incident light, and oblique incidence geometry of the TERS system were included in the model. Both polarizations of incident light and Raman scattered light are selected appropriately with the guidance of the model for obtaining enough electric-field enhancements and accurately calculate the stresses. A 2-D stress map inside the silicon waveguide with spatial resolution of about 20 nm was obtained, and corresponding strains were calculated based on Hooke's law. We observed that the stresses are compressive, and the strains show inhomogeneity. The origins of strain and the strain-induced second-order optical susceptibility inside the SIMOX 3-D sculpted buried silicon waveguides are discussed and analyzed. The mapping of 2-D nanoscale strain and the analysis of second-order optical susceptibility in this work suggest that the SIMOX 3-D sculpted strained silicon might be a potential metamaterial for electro-optical modulation and optical signal processing. Moreover, the presented TERS model could be a valuable tool for probing strain in strained silicon devices.

We present a simple and robust structure to realize Fano resonance for refractive index sensing applications. The Fano resonance with ultrahigh Q factors (Q > 5.0 × 104) and high reflections (near 100%) is realized in a 2-D defect-free pillar array photonic crystal (PAPC) with optimized geometry (e.g., pillar array periodicity, height, and radius). We analyze its band structure, polarization, and transmission characteristics in detail with numerical methods (plane wave expansion and 3-D finite-difference time-domain (3-D-FDTD) simulations). The numerical results show that FOM ~6.85 × 103 (FOM being the figure of merit) can be achieved, which is an order of magnitude improved over the previous work. In addition, the unique simplicity of this system in which a long-lifetime delocalized electromagnetic field exists and interacts with the surrounding media permits new opportunities for point-of-care applications. Furthermore, the proposed architecture makes the implementation of lab-on-a-chip refractive index sensing possible, which is enabled by integrating PAPC on the tip of an optical fiber.

With the increasing number of Internet of Things (IoT) devices, a huge amount of latency-sensitive and computation-intensive IoT applications have been injected into the network. Deploying mobile edge computing (MEC) servers in cloud radio access network (C-RAN) is a promising candidate, which brings a number of critical IoT applications to the edge network, to reduce the heavy traffic load and the end-to-end latency. The MEC server’s deployment mechanism is highly related to the user allocation. Therefore, in this paper, we study hierarchical deployment of MEC servers and user allocation problem. We first formulate the problem as a mixed integer nonlinear programming (MINLP) model to minimize the deployment cost and average latency. In terms of the MINLP model, we then propose an enumeration algorithm and approximate algorithm based on the improved entropy weight and TOPSIS methods. Numerical results show that the proposed algorithms can reduce the total cost, and the approximate algorithm has lower total cost comparing the heaviest-location first and the latency-based algorithms.

We propose a theoretical model to quantitatively estimate the intercore spontaneous Raman scattering (ICSRS) in multicore fiber based on intercore crosstalk. We analyze the properties of ICSRS through numerical simulations. Then, the impact of ICSRS on quantum key distribution (QKD) is evaluated with a classical dense wavelength division multiplexing system in a seven-core fiber. We evaluate the impact in two scenarios, long-distance transmission and metropolitan area transmission. For long-distance transmission, it is revealed that both the forward-ICSRS and backward-ICSRS will reduce the maximum transmission distance of QKD and backward-ICSRS has more impairment to QKD. However, over the range of metropolitan area networks, QKD is not impaired seriously by ICSRS with typical power of classical signal. Finally, we compare the properties of SRS generated in single-core fiber and the properties of ICSRS.

We present a novel optical sensor based on the design of ultrahigh-Q and low-mode-volume 1-D single photonic crystal (PhC) slot nanobeam cavity (SNC) in which the air-hole radius is parabolically tapered. The performance of the device is investigated theoretically. In order to achieve high Q-factor and high sensitivity simultaneously, the slot geometry is exploited to make the optical field strongly localized inside the low index region and overlaps sufficiently with the analytes. With the three-dimensional finite-difference time-domain (3D-FDTD) method, we demonstrate that the proposed single 1-D PhC-SNC sensor device possess an ultrahigh sensitivity (S) up to ~900 nm/RIU (refractive index unit, RIU) and a high Q-factor in air up to > 107 at the telecom wavelength range. The optimized figure of merit is > 107. In addition, an ultrasmall mode volume of Vm ~0.01 (λ/ηair)3 has been achieved, which is more than three orders of magnitude smaller than our previous works [Appl. Phys. Lett. 105, 063118 (2014)] and, thus, is potentially an ideal platform for realizing ultracompact laboratory-on-a-chip applications with dense arrays of functionalized spots for multiplexed gas sensing.

We theoretically demonstrate a low crosstalk ring-slot array structure used for label-free multiplexed sensing. The proposed sensors array is based on an array of three ring-slot and input/output line defect coupling waveguides. Each ring-slot cavity has slightly different cavity spacing and different resonant frequency. Results obtained using two dimensional finite-difference time-domain (2D-FDTD) simulation indicate that the resonant frequencies of each sensor unit in response to the refractive index variations are independent. The refractive index sensitivity is 134 ~ 145.5 nm/RIU (refractive index unit) and the Q factors more than 104 can be achieved. The calculated detect limit lower than 1.13 × 10−4 RIU is obtained. In addition, an extremely small crosstalk lower than −25.8 dB is achieved among the array of three ring-slot cavities. The results demonstrate that this multiplexed sensor array is a promising platform for integrated optical devices and enables highly parallel label-free detection.

We theoretically investigate a flexible design of building nanoscale photonic crystal (PhC) integrated sensor array with low crosstalk. The proposed device consists of array of side-coupled PhC resonant cavities with high Q-factors over 2 ×103. The extinction ratio of well-defined single resonance exceeds 30 dB. Each resonant cavity has different resonant wavelengths and independently shifts its resonance in response to the refractive index variations. With three-dimensional finite-difference time-domain (3D-FDTD) method, simulation results demonstrate that the proposed sensor array is desirable to perform monolithically integrated sensing and multiplexed detection. Particularly, the design method here makes it possible to effectively enhance sensor array integration density and simultaneously restrain crosstalk between each other adjacent sensors. The refractive index sensitivity of 100 nm/RIU and the crosstalk lower than -4 dB are observed, respectively. Both the specific result and the general idea are promising in future optical multiplexed sensing and nanophotonic integration.

According to the IEEE 802.15.6 standard, interference within each wireless body area network (WBAN) can be well addressed by the time division multiple access (TDMA)-based media access control (MAC) protocol. However, the inter-WBAN interference will be caused after multiple WBANs are gathered together. This paper proposes a priority-aware price-based power control (PPPC) scheme for mitigating the inter-WBAN interference. Specifically, to maximize the transmission data rate of sensors and control the aggregate interference suffered by coordinators, a Stackelberg game is established, in which the coordinators issue interference prices and the active sensors adjust their transmission power accordingly. On the other hand, since the information about the identities of the active sensors in a specific time slot is kept private, a Bayesian game is designed to model the interaction among sensors. Moreover, the timeliness and reliability of data transmission are guaranteed by designing the sensors’ priority factors and setting a priority-related active probability for each sensor. At last, a power control algorithm is designed to obtain optimal strategies of game players. Simulation results show that compared with other existing schemes, the proposed scheme achieves better fairness with a comparable network sum data rate and is more energy efficient.

The body area network (BAN) is an emerging branch of wireless sensor networks for personalized applications. The services in BAN usually have a high requirement on security, especially for the medical diagnosis. One of the fundamental directions to ensure security in BAN is how to provide node authentication. Traditional research using cryptography relies on prior secrets shared among nodes, which leads to high resource cost. In addition, most existing non-cryptographic solutions exploit out-of-band (OOB) channels, but they need the help of additional hardware support or significant modifications to the system software. To avoid the above problems, this paper presents a proximity-based node authentication scheme, which only uses wireless modules equipped on sensors. With only one sensor and one control unit (CU) in BAN, we could detect a unique physical layer characteristic, namely, the difference between the received signal strength (RSS) measured on different devices in BAN. Through the above-mentioned particular difference, we can tell whether the sender is close enough to be legitimate. We validate our scheme through both theoretical analysis and experiments, which are conducted on the real Shimmer nodes. The results demonstrate that our proposed scheme has a good security performance.

RNA editing is one of the post- or co-transcriptional processes that can lead to amino acid substitutions in protein sequences, alternative pre-mRNA splicing, and changes in gene expression levels. Although several methods have been suggested to identify RNA editing sites, there remains challenges to be addressed in distinguishing true RNA editing sites from its counterparts on genome and technical artifacts. In addition, there lacks a software framework to identify and visualize potential RNA editing sites. Here, we presented a software - 'RED' (RNA Editing sites Detector) - for the identification of RNA editing sites by integrating multiple rule-based and statistical filters. The potential RNA editing sites can be visualized at the genome and the site levels by graphical user interface (GUI). To improve performance, we used MySQL database management system (DBMS) for high-throughput data storage and query. We demonstrated the validity and utility of RED by identifying the presence and absence of C→U RNA-editing sites experimentally validated, in comparison with REDItools, a command line tool to perform high-throughput investigation of RNA editing. In an analysis of a sample data-set with 28 experimentally validated C→U RNA editing sites, RED had sensitivity and specificity of 0.64 and 0.5. In comparison, REDItools had a better sensitivity (0.75) but similar specificity (0.5). RED is an easy-to-use, platform-independent Java-based software, and can be applied to RNA-seq data without or with DNA sequencing data. The package is freely available under the GPLv3 license at http://github.com/REDetector/RED or https://sourceforge.net/projects/redetector.

On the basis of photonics-assisted compressive sampling (CS), we demonstrate for the first time an integrated system with the capacity of multifrequency recognition and downconversion of intercepted radio frequency (RF) component. Using a single analog-to-digital converter (ADC) with sub-Nyquist analog bandwidth of 826.75 MHz, a multicomponent signal with unknown frequencies ranging from 15 to 20 GHz is precisely located with maximum detection error of 100 kHz. The system's ability of photonic downconversion of identified RF component is characterized in terms of spur-free dynamic range (SFDR) as well.

A broadband dispersion compensation scheme based on a 2-Ch phase modulator (2-Ch PM) is proposed and experimentally demonstrated in the long-haul analog optical link. Benefiting from the complementary power fading function for the phase and intensity modulated link, which are simultaneously obtained by using the 2-Ch PM, the broadband and long-reach dispersion compensation is implemented. The experimental results show that the dispersion-induced power fading is greatly mitigated for the radio frequency (RF) signal with a bandwidth up to 18 GHz over 24.45-km single-mode fiber (SMF) transmission. Meanwhile, the system spurious-free dynamic range (SFDR) is improved with a maximum value of 24 at the frequency of 17.5 GHz; the vector signal transmission performance has also been improved.

In low-duty-cycle wireless sensor networks, wireless nodes usually have two states: active state and dormant state. The necessary condition for a successful wireless transmission is that both the sender and the receiver are awake. In this paper, we study the problem: How fast can raw data be collected from all source nodes to a sink in low-duty-cycle WSNs with general topology? Both the lower and upper tight bounds are given for this problem. We use TDMA scheduling on the same frequency channel and present centralized and distributed fast data collection algorithms to find an optimal solution in polynomial time when no interfering links happen. If interfering links happen, multichannel scheduling is introduced to eliminate them. We next propose a novel Receiver-based Channel and Time Scheduling (RCTS) algorithm to obtain the optimal solution. Based on real trace, extensive simulations are conducted and the results show that the proposed RCTS algorithm is significantly more efficient than the link schedule on one channel and achieves the lower bound. We also evaluate the proposed data collection algorithms and find that RCTS is time-efficient and suffices to eliminate most of the interference in both indoor and outdoor environment for moderate size networks.