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In this paper, we propose a dynamic key technique based on Cellular Neural Network (CNN) for security improvement in the orthogonal frequency division multiplexing passive optical network (OFDM-PON). To enhance the encryption scheme security, a six-dimensional CNN hyperchaotic system is employed to encrypt the data. And, the keys are divided into the dynamic and static. The dynamic key is randomly extracted from a key set by incorporating the random feature of the input data. Then, the chaotic sequence generated by the dynamic key is served as the synchronous sequence for encryption. Moreover, the chaotic sequences generated by the static keys are used to resist the chosen-plaintext attacks (CPAs) and scramble the phase of QAM symbols on the frequency domain. With these processing techniques, the multi-fold data encryption can create a key space of ∼10315 to protect against the exhaustive trial. The transmission of 10-Gb/s encrypted 16-QAM-based OFDM signal is demonstrated over 20-km single mode fiber (SMF) by experiment. The results show that our proposed scheme can provide excellent confidentiality of data transmission against the CPAs and brute-force attack.

The scattered Optical Network Units (ONUs) in an optical access network have different propagation delays. In an Ethernet passive optical network (EPON) adopting the traditional Interleaved Polling with Adaptive Cycle Time (IPACT) scheme, such ONU propagation delay difference will waste network resources and will degrade both network delay performance and network energy efficiency in delivering low-latency services. In this article, to deal with the heterogeneous ONU propagation delays problem, two solutions are proposed and investigated. The first solution, namely the Upstream Postponing with ONU Dozing (UP-OD) scheme, is to properly postpone the upstream transmissions of those ONUs having relatively short propagation delays to improve channel utilization efficiency, and ONU doze mode is incorporated to enhance network energy efficiency. The second solution, namely the Identical Fiber Length with ONU Sleeping (IFL-OS) scheme, is to adopt an identical distribution fiber length for ONUs to enhance channel utilization, and ONU sleep mode is incorporated for energy consumption reduction. Simulation results show that both the UP-OD scheme and the IFL-OS scheme reduce network delay and improve network energy efficiency in delivering low-latency (

For hospital e-health systems, a novel medium access control (MAC) scheme that achieves delay-sensitive healthcare traffic (DSHT) delivery in the uplink direction of wireless local area networks (WLANs) is proposed and investigated. By introducing a slotted request uploading period and informing hubs to upload their transmission requests orderly during the period, overhead cost associated with frequent transmitter/receiver transitions can be reduced and polling empty hubs can be eliminated. Consequently, the proposed scheme results in in-time polling of hubs, thereby optimizing packet queuing delay. Moreover, due to centralized coordination, the proposed scheme avoids contention and back-off. Such an MAC scheme is critical to the Internet of Things (IoT)-based delay-sensitive healthcare applications (DSHAs), such as unmanned patient tending and tele-diagnose/surgery in future e-health systems. Our simulation results show that under a delay constraint of $200~\mu \text{s}$ , the proposed scheme outperforms both the conventional point coordination function (PCF) and distributed coordination function (DCF) schemes in terms of DSHT throughput and has a good DSHT delivery stability performance.

We present a latency optimization scheme based on double polling mechanism for TDM-PON fronthaul network. And by conducting the simulation, its feasibility is manifested.

An energy-efficient and survivable optical access network structure is proposed and investigated. Based on a structure model of multilayer-ring, the access network is divided into four layers and modules on a same layer are interconnected as a ring. Therefore, multiple paths are available for optical network units to access an optical line terminal, which not only provides convenience in traffic aggregation, but also guarantees the survivability of network. With this structure, quantities of standby modules are reduced to decrease both capital cost and power cost. Large part of power can also be saved by turning off idle modules through traffic aggregation. Moreover, by controlling the optical switches deployed in remote node, elastic reach access is realized as well since amplification is optional on transmission links. Theoretical and numerical analyses indicate that the scheme shows great advantages on power saving, network survivability, as well as the system flexibility, and its energy efficiency performance can be further improved by operating in conjunction with energy-efficient resource scheduling scheme. It provides a potential structure for next generation optical access network.

An energy-efficient optical access network scheme based on sub-band grouping and allocating is proposed and studied for the digital filter multiple access adopted passive optical network (DFMA-PON). In this scheme, sub-bands generated in digital sdomain are grouped as band groups and properly allocated for optical network unit (ONU) transmissions to reduce the transmission time. Based on this, longer sleeping time can be provided to each ONU, and some more energy can be saved. Numerical evaluations indicate that comparing with basic DFMA-PON, significant energy is saved by the proposed scheme, and a promoted energy saving performance can be achieved by properly arranging the number of sub-bands assigned in a band group. Furthermore, the technology improvement and its impact on the performance of the scheme are also investigated. It is demonstrated that comparing with the conventional network, the proposed scheme possesses prominent energy saving potential. It can be considered as a potential solution for future energy-efficient optical access network.

A physically enhanced secure wavelength division multiplexing chaos communication scheme in virtue of the chaos synchronization of two multimode semiconductor lasers (MSLs) is introduced. In this scheme, two communicating MSLs are subjected to identical optical injections from a chaotic external-cavity MSL, and each mode of the communicating MSLs is used as a chaotic carrier. The messages are divided into a set of blocks, and these blocks are transmitted by different modes in different time slots, according to a pre-negotiated pattern. The numerical results indicate that high-quality chaos synchronization with a wide operation region and relatively strong frequency detuning tolerance can be achieved between the communicating MSL modes, which can afford multiple simultaneous bidirectional message transmissions. Moreover, because of the carrier-consumption competition in the MSL cavity, the peak average power ratios of the chaotic carriers are much larger and more widely distributed with respect to selected single-mode injection or feedback cases, which can obviously enhance the link security against the attack of linear filtering. Also, the carrier-consumption competition induces a cross talk between the transmission messages, which can greatly improve the link security when eavesdroppers adopt the synchronization utilization method to attack the public link. Furthermore, with the non-fixed wavelength transmission technology, the system security can also be further improved greatly. The proposed scheme provides a new way to implement high-speed multichannel chaos communication with high physically enhanced security.

An external-cavity semiconductor laser with nonlinear optical feedback to generate broadband chaos with time delay signature (TDS) suppression is investigated. The system is composed of three semiconductor lasers, one of which is regarded as the chaos generator, while the other two play a role of a built-in nonlinear modulator in the external cavity of the generator. The results show that by properly setting the feedback strength and time delay of the first semiconductor laser in the nonlinear modulator, the TDS embedded in the intensity and phase time-series of the chaos can be effectively concealed in a wide range of frequency detuning.

To benefit Tactile Internet (TI) grade uplink healthcare data transmission in hospital wireless local area networks (WLANs), the effect of polling sequence is investigated and two polling sequence arrangement schemes are proposed and evaluated.

We propose an efficient energy-saving scheme by dividing the optical network units (ONUs) into groups composed of one master-ONU (M-ONU) and several slave-ONUs (S-ONUs). The S-ONUs are primarily selected to communicate with the M-ONU and, second, with the remote node (RN), which can reduce the usage of high-power ports at the RN and subsequently decrease energy consumption. It is demonstrated that obvious energy-saving effects can be achieved, and moreover, the energy-saving efficiency can be further improved by expanding the capacity of the links between RN and M-ONUs and properly selecting the scale of the ONU group.

An energy-efficient scheme based on the interconnection of optical network unit (ONU) is introduced, which can significantly reduce the energy consumption of the low-traffic operation. The energy consumption model for the ONU-interconnected optical access network (OAN) based on the electronic switch (ES) technology is established, and the energy efficiency of the proposed scheme is analyzed and compared with that of the OAN using optical switch (OS). The simulation results demonstrate that the ONU-interconnected scheme can efficiently reduce the energy consumption of OAN, and it shows a good energy consumption performance under daily traffic model.

We have numerically demonstrated a high-speed bidirectional chaotic communication, where chaotic optical signal with suppressed time delay signature is used. In this scheme, the output of a third semiconductor laser is used as the common signal driving the other two identical lasers with self-feedback to be synchronized. To enhance the bandwidth of the chaotic signal employing in the communication, part of output of the driven laser is coupled into the third laser and appropriate frequency detuning is also considered. Since the relative strong wide-bandwidth optical injection, the native time delay signature of chaos generated by the driven laser is suppressed. Moreover, the results shows that high-speed chaotic communication over 10Gb/s can be achieved due to the enhancement of the chaotic bandwidth.

We propose and numerically demonstrate a secure key distribution scheme based on the dynamic chaos synchronization of two external cavity vertical-cavity surface-emitting lasers (VCSELs) subject to symmetric random-polarization injections. By exchanging the random parameters that control the polarization angles of the driving injection, Alice and Bob can identify the time slots in which high-quality private chaos synchronization is achieved and independently generate a shared key from the synchronized polarization difference signals of their local VCSELs. The results show that Gb/s key distribution with a low bit error ratio can be achieved, and the shared key can pass all NIST tests, which guarantee the randomness of the key. In the proposed scheme, the exchange messages do not contain any information about the key generation, which affords a high-level of security for key distribution.

Chaos generated by a semiconductor laser subject to self-phase-modulated optical feedback is proposed, where the time-delay-signature is concealed and complexity is enhanced. Fascinatingly, the probability density distribution of its output intensity is close to symmetry.

Chaotic semiconductor laser is a good candidate for secure communication and high-speed true random bit generator, for its characteristics of broad bandwidth and prominent unpredictability. Based on the synchronization property and true random bit generation characteristic of chaotic semiconductor lasers, physical secure key distribution is available. In this work, we majorly show three key distribution schemes stemming from synchronized chaotic semiconductor lasers or chaos-based key exchange protocol. The numerical results demonstrate that the security of the chaos-synchronization-based key distribution scheme can be physically enhanced by adopting dynamic synchronization scheme or encrypted key generation, and that of key distribution with chaos-based key exchange protocol is dependent on the security of the exchange protocol and finally determined by the difficulty of regeneration the chaos system accurately.

A security-enhanced chaos communication scheme with time delay signature (TDS) suppression and phase-encrypted feedback light is proposed, in virtue of dual-loop feedback with independent high-speed phase modulation. We numerically investigate the property of TDS suppression in the intensity and phase space and quantitatively discuss security of the proposed system by calculating the bit error rate of eavesdroppers who try to crack the system by directly filtering the detected signal or by using a similar semiconductor laser to synchronize the link signal and extract the data. The results show that TDS embedded in the chaotic carrier can be well suppressed by properly setting the modulation frequency, which can keep the time delay a secret from the eavesdropper. Moreover, because the feedback light is encrypted, without the accurate time delay and key, the eavesdropper cannot reconstruct the symmetric operation conditions and decode the correct data.

We numerically investigate the time delay signature (TDS) properties of a chaotic semiconductor laser subject to nonlinearly-modulated feedback. In the proposed scheme, two semiconductor lasers that play the role of a built-in nonlinear modulator is positioned in the external cavity of the chaos generator laser, which forms a structure of semiconductor laser ring. The simulation results show that the TDS of the chaos generator in the laser ring is quite smaller than that of the chaos induced by the conventional optical feedback. Moreover, the TDS embedded in the intensity and phase time-series of the chaotic signal can be further concealed, by introducing an additional optical feedback into the built-in nonlinear modulator.

An energy-efficient and robust optical access network structure is proposed and investigated. By adopting the ring structure with network interconnection, substantial energy saving is achieved and all access links are simultaneously protected.

An energy-efficient ONU interconnection scheme is proposed for electronic switch based optical access networks. By separately performing traffic aggregation in downstream and upstream, substantial energy is saved and elastic capacity can be provided.

A new scheme for key distribution based on variant properties of chaos synchronization in cascaded semiconductor lasers with phase-modulation feedback. The security of the scheme relies on the practical difficulty of completely observing chaotic signals.

A new secure key distribution scheme based on the dynamic chaos synchronization of two cascaded semiconductor laser systems (CSLSs) subject to common chaotic injection and random phase-modulated optical feedback is demonstrated. In this scheme, Alice and Bob adopt two independent random sequences to control the phase modulators of CSLSs, which induces a dynamic perturbation to the chaos synchronization. We thoroughly investigate the chaos synchronization performance under different phase-shift conditions with cross-correlation function, and systematically discuss the feasibility and security of the system. The results show that, with proper injection and feedback strength, the correlation coefficient gap between phase shift match and mismatch is clear and robust to the parameter mismatches in the CSLSs and those between the two CSLSs. Based on this, high-quality key distribution can be performed by picking out the identical random bits from the two independent random sequences according to the computational correlation. Moreover, the investigations on the information theoretic security and rate of the key distribution show that the security of the key distribution scheme can be further enhanced by properly increasing the number of layers in the CSLSs or employing high-order modulation format.

We propose and numerically demonstrate a new scheme for key distribution on the physical layer based on the chaos synchronization and physical random bit generation. In this scheme, two chaotic semiconductor lasers are commonly driven by a third semiconductor laser, their output chaotic signals are employed as the physical sources of the random bit generators (RBGs). Under symmetry operation scenario, the two RBGs are well synchronized and the random bits generated by them are used to generate identical secret keys for Alice and Bob by the way of a dynamic post-processing technology. The feasibility and security of the proposed scheme are investigated by testing the parameters mismatch tolerance and the sensitivity to the systematic noise. The numerical results indicate that the dynamic and unpredictable post-processing can provide a great enhancement for the security of the secret key distribution. The security of the proposed scheme mainly determined by the post-processing, not confidential source, which provides a new potential way for implementing high-speed secure secret key distribution.

An energy-efficient scheme termed as load adaptive sequence arrangement (LASA) is introduced. Based on changing the polling sequence of optical network units (ONUs) according to traffic load, the scheme can improve the energy efficiency of passive optical access networks. The polling sequence arrangement is performed by processing a label that is added in the gate/report message and allocating each ONU an uneven idle time. When the polling sequence is changed, the ONUs that have been allocated longer idle times could sleep much longer. Theoretical analysis indicates that the polling sequence arrangement has a significant effect on the energy efficiency of the network. It can provide ONUs longer total sleeping time, and barely lengthen the average cycle time. Moreover, to optimize the energy consumption performance under a low-traffic scenario, the LASA scheme jointly working with the fixed minimal transmission time (FMT) of the ONU scheme, which is called the LASA-FMT scheme, is further investigated. By ensuring the minimal transmission time of an ONU, the LASA-FMT scheme further extends the total sleeping time of ONUs and improves the energy efficiency. The performance on packet delay of both the LASA scheme and the LASA-FMT scheme is acceptable to support delay sensitive services, which shows the practical value of the two schemes in green network progress.