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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 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.

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.

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.

A security-enhanced chaos communication scheme by expanding and compressing the spectrum of modulated chaotic carrier is proposed, in virtue of a spectrum expansion module composed of two phase modulators and two dispersion mediums. The numerical results demonstrate that the efficient bandwidth of modulated chaotic carrier can be expanded up to several tens of GHz and the RF spectrum is uniformly flat. Moreover, the security of the proposed system is discussed by comparing the bit error ratio (BER) of legitimate receiver and that of eavesdroppers who try to extract message from the public link by the ways of direct filtering and synchronization utilization. It is indicated that the BER of illegal interception message is much larger than the legal one. The security of the proposed scheme is much higher than the conventional scenario without spectrum expansion and compression.

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 a scheme for fast random number generation with a bandwidth-enhanced chaotic signal generated by injecting the signal of a traditional chaotic external-cavity semiconductor laser (ECSL) into a spectrum expansion module (SE). Our simulation results show that the bandwidth-enhanced chaotic can be generated and its efficient bandwidth can be greatly enhanced up to 70 GHz. Random bits in our scheme are generated by bitwise exclusive-OR(XOR) operation on corresponding bits in samples of the bandwidth-enhanced chaotic signal and its time-delayed signal. An output bit rate of 300 Gb/s is attained by retaining 6 least significant bits (LSBs) per sample at the sampling rate of 50GSa/s.

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 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.

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.

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 novel secure passive optical network (PON) configuration jointly based on the chaos synchronization of wavelength division multiplexed (WDM) chaotic signals and the subcarrier modulation multiplexing is introduced. The upstream and downstream carriers consist of a set of wavelength division multiplexed chaotic signals, and each wavelength takes on several bidirectional optical line terminal (OLT)-optical network unit (ONU) transmissions in virtue of the subcarrier modulation multiplexing technology. The numerical results demonstrate that with proper selection of the wavelength spacing, high-quality chaos synchronization can be achieved on each wavelength, and each wavelength can afford several OLT-ONU transmissions by properly allocating the frequency spacing of subcarriers. The proposed scheme can improve the bandwidth utilization efficiency and obviously enhance the information security at the physical layer of the WDM-PON.

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.