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The effect of optical feedback on the stability and linewidth of a photonic microwave generated in an optically injected single-mode vertical-cavity surface-emitting laser has been investigated in both cases of single feedback and double feedback. The stability of the photonic microwave is quantified by measuring the microwave frequency range using the long sweep time of the radio frequency spectrum analyzer. The effect of the feedback phase on the side peaks in the single feedback has also been studied. The experimental results show that both single feedback and double feedback can reduce the linewidth of the photonic microwave and improve its stabilization. A narrow linewidth photonic microwave spectrum with suppressed side peaks has been achieved in a single feedback configuration at the optimal feedback phase condition. The simulated results using the spin-flip model confirm that side peaks suppression in the single optical feedback configuration is sensitive to the feedback phase. For nonoptimal feedback phase conditions, single optical feedback can generate many side peaks which are related to external cavity. These side peaks can be suppressed by introducing the second feedback.

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.

Enhanced photonic microwave generation by using a filtered optical feedback in an optically injected semiconductor laser operating at period-one (P1) dynamics is numerically demonstrated. In the simulation, the frequency tunability of the generated narrow-linewidth photonic microwave with the filtered optical feedback has been investigated. The results show that the frequency of the narrow-linewidth photonic microwave can be widely tuned by adjusting the injection parameters only or adjusting both the injection parameters and the center frequency of the filter. Moreover, the influence of the delay time, feedback strength, filter bandwidth and detuning on the linewidth, side-peak suppression and phase noise of the generated microwave have also been investigated in detail. The results show that with increasing feedback strength or delay time, evident reduction of the linewidth is observed. The side-peak suppression also increases with increasing feedback strength; however, side-peak suppression decreases with increasing feedback delay time. In addition, the linewidth reduction and side-peak suppression are relatively robust to the filter detuning, especially for higher feedback strengths and microwave frequencies. This is mainly attributed to the self-adaptive shifting of the red-shifted cavity resonance frequency to the center frequency of the filter in the FOF configuration.

We numerically and experimentally demonstrated the generation flat-spectrum wideband chaos with efficient bandwidth of several tens of GHz and perfect time delay signature suppression using external-cavity semiconductor laser subject self-phase modulation and dual optical feedback.

A physical encryption scheme converting messages into noise-like signals is proposed, whose features include inherent transparency to modulation formats, bidirectional transmission suitability, plug-and-play in conventional optical communication systems and use of existing dispersion compensation modules.

We experimentally demonstrate a broadband chaos generation using semiconductor laser subject to self-phase-modulation and microsphere resonator, and a subsequent fast physical random bit generation beyond 300-Gbps by using the broadband chaos as entropy source.

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.

Characteristics of microwave photonic signal generation based on the period-one dynamic in an optically injected vertical-cavity surface-emitting laser are studied systematically. The evolutions of the linewidth, power, and second-harmonic ratio of the generated microwave are investigated as a function of injection strength and frequency detuning. The effect of optical feedback on the linewidth and the phase noise of the generated microwave photonic signal is also studied in detail. With the help of optical feedback, the linewidth can be effectively reduced by increasing the feedback strength and feedback delay time. However, there is an optimal feedback delay time to minimize the phase noise.

We propose and experimentally demonstrate a broadband chaos generation scheme by introducing self-phase modulation (SPM) in the feedback loop of an external-cavity semiconductor laser and propagating the chaos through a microsphere resonator (MR). Four chaos generation cases—conventional optical feedback (COF), COF+MR, individual SPM optical feedback (SPMOF), and the proposed SPMOF+MR—are experimentally discussed. The experimental results demonstrate that with respect to the other three cases, in the proposed scheme with the joint effects of SPMOF and MR, the relaxation oscillation effect in chaos can be eliminated and a flat RF spectrum with much more significant bandwidth enhancement can be achieved. Simultaneously, the time delay signature (TDS) in the chaos can be perfectly suppressed at a very low level close to 0 in a wide operation range of feedback. This work shows a novel scheme to generate broadband chaos with flat spectrum and perfect TDS suppression.

We propose a new stream-cipher generation scheme based on the correlated physical random bit generation with synchronized chaotic lasers and pseudo-random bit extension RC4 algorithm. The proposed scheme shows high-security, extensible rate and strong robustness.

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.

By introducing sinusoidal phase-modulated feedback to semiconductor lasers of closed-loop chaos-based communication system, the efficient bandwidth of chaotic carrier can be broadened greatly, the BER performance can be improved, and the communication security is enhanced.

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.

We propose a security-enhanced communication scheme with time delay signature suppression and phase encryption, by using cascaded random phase modulation for the feedback. Moreover, the low frequency signature is well hidden in the frequency spectrum.

A wideband complexity-enhanced chaos generation scheme is proposed by using a semiconductor laser subject to delay-interfered self-phase-modulated optical feedback. The influences of feedback strength, phase modulation index, and interference delay on the effective bandwidth and time-delay-signature (TDS) characteristics of the proposed scheme-generated chaos are extensively investigated both experimentally and numerically. The results demonstrate that with the joint effects of phase modulation-induced spectrum expansion and nonlinear filtering of delayed interference, wideband chaos with flat spectrum and excellent TDS suppression characteristics can be generated over a wide dynamic operation range. In comparisons with the relevant chaos generation schemes under conventional optical feedback, individual self-phase modulated optical feedback, and delay-interfered optical feedback, the proposed scheme cannot only significantly enhance the effective bandwidth of chaos but also considerably enhance the complexity of chaos by suppressing the TDS toward an indistinguishable level close to 0.

We propose and demonstrate a novel physical, secure high-speed optical communication scheme based on synchronous chaotic spectral phase encryption (CSPE) and decryption (CSPD). The CSPE is performed by a module composed of two dispersion components and one phase modulator (PM) between them, and the CSPD is carried out by a twin module with reverse dispersions and inverse PM driving signals. The PM driving signals of the CSPE and CSPD modules are privately synchronized chaotic signals that are independently generated by local external-cavity semiconductor lasers subject to common injection. The numerical results indicate that with the CSPE, the original message can be encrypted as a noise-like signal, and the timing clock of the original message is efficiently hidden in the encrypted signal. Based on the private synchronization of the chaotic PM driving signals, only the legal receiver can decrypt the message correctly, while the eavesdropper is not able to intercept a useful message. Moreover, the proposed scheme can also support secure symmetric bidirectional high-speed WDM transmissions. This work shows a prospective way to implement high-speed secure optical communications at the physical layer.

We propose and demonstrate a closed-loop chaos system composed of external-cavity semiconductor lasers subject to common chaotic phase-modulated optical feedback (CCPMOF). The efficient-bandwidth and time-delay signature (TDS) characteristics of the chaotic carrier, the properties of chaos synchronization, as well as the performance and security of chaos communication are systematically investigated. The numerical results demonstrate that wideband chaotic carrier with effective TDS suppression can be easily obtained, high-quality chaos synchronization with considerable mismatch robustness, frequency detuning tolerance, and phase fluctuation tolerance can be achieved in a wide operation range, and high-speed chaos communication is available. With respect to the conventional closed-loop systems, the bandwidth and complexity of chaotic carrier is greatly enhanced, and the performances of chaos synchronization and communication are obviously improved.

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.

A physical-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, the messages are divided into a set of blocks, and these blocks are transmitted by different modes with different wavelengths, according to a pre-negotiated pattern. The numerical results indicate that the proposed scheme affords multiple simultaneous bidirectional message transmissions, and the security can be greatly enhanced. The proposed scheme provides a new way to implement high speed multichannel chaos communication with high security.

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.

We propose a flat wideband chaos generation scheme that shows excellent time delay signature suppression effect, by injecting the chaotic output of general external cavity semiconductor laser into an optical time lens module composed of a phase modulator and two dispersive units. The numerical results demonstrate that by properly setting the parameters of the driving signal of phase modulator and the accumulated dispersion of dispersive units, the relaxation oscillation in chaos can be eliminated, wideband chaos generation with an efficient bandwidth up to several tens of GHz can be achieved, and the RF spectrum of generated chaotic signal is nearly as flat as uniform distribution. Moreover, the periodicity of chaos induced by the external cavity modes can be simultaneously destructed by the optical time lens module, based on this the time delay signature can be completely suppressed.

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.