Fan-Yi Lin

Chaotic radar using nonlinear laser dynamics

A novel chaotic radar (CRADAR) system utilizing laser chaos is investigated both numerically and experimentally. Compared with conventional radars, the proposed CRADAR has the advantages of very-high-range resolution, unambiguous correlation profile, possibility of secure detection, low probability of intercept, and high electromagnetic compatibility. Generated by an optically injected semiconductor laser, chaotic waveforms with bandwidths larger than 10 GHz can be readily obtained. In this paper, the time series, the phase portraits, and the power spectra of the chaotic states are presented. The correlation traces between the signal and the reference waveforms are plotted. The peak sidelobe level with different correlation lengths is investigated. The capability of anti-jamming and the performance under additive white Gaussian noise are studied. To show the feasibility of CRADAR, proof-of-concept experiments using a pair of planar antennas with a 1.5-GHz bandwidth covering the range from 1.5 to 3 GHz are demonstrated. A range resolution of 9 cm is achieved, which is currently limited not by the bandwidth of the chaotic states but by the detection bandwidths of the real-time oscilloscope and the antennas used.

Nonlinear dynamical characteristics of an optically injected semiconductor laser subject to optoelectronic feedback

Nonlinear dynamical characteristics of an optically injected semiconductor laser subject to optoelectronic feedback is studied numerically. The dynamic states including stable locking, periodic oscillation, chaotic oscillation, regular pulsing, quasiperiodic pulsing, and chaotic pulsing seen in a semiconductor laser subject to either optical injection or delayed optoelectronic feedback alone, can all be found in this hybrid system where the laser is subject to both optical injection and optoelectronic feedback. While this system can follow either the period-doubling or the quasiperiodic route to chaos, transition states bridging chaotic oscillation states and chaotic pulsing states are identified and shown. Mappings of dynamic states in the parameter space are plotted, where a large expansion and shifting of the chaos region is observed and is compared with an optically injected laser without optoelectronic feedback. As the injection strength increases, the bandwidths of the chaotic states in the broadened area of this hybrid system are significantly enhanced. The advantages and potential applications of this hybrid system are discussed.

Photonic Generation of Broadly Tunable Microwave Signals Utilizing a Dual-Beam Optically Injected Semiconductor Laser

We propose and study photonic generation of broadly tunable microwave signals utilizing a dual-beam optically injected semiconductor laser. By injecting a slave laser with two detuned master lasers at the stable locking states, microwave signals with frequencies corresponding to the frequency spacing of the master lasers can be generated. Without the need for a microwave reference source, the dual-beam optical injection scheme has the advantages of low cost and less system complexity. Moreover, without the limitations of period-doubling bifurcation and Hopf bifurcation, by utilizing the period-one oscillation state with a single-beam injection scheme, the microwave signals generated with the proposed scheme have a much broader tuning range. In this paper, optical and power spectra of the microwave signals generated with the dual-beam optical injection scheme are compared with those generated with the optical mixing, the single-beam injection, and the unlocked dual-beam injection schemes. Generation of tunable microwave signals up to 120 GHz is demonstrated, which is currently limited by the locking range of the slave laser determined by the frequency difference between the Hopf (higher frequency) and the saddle node (lower frequency) bifurcation curves.

Nonlinear dynamics of a semiconductor laser with delayed negative optoelectronic feedback

Nonlinear dynamics of a semiconductor laser with delayed negative optoelectronic feedback are studied both numerically and experimentally. Mappings of the dynamic states and bifurcation diagrams are compared between a delayed negative optoelectronic feedback system and a delayed positive optoelectronic feedback system. Both systems follow a quasiperiodic route to chaos, where regular pulsing, quasiperiodic pulsing, and chaotic pulsing states are observed. Frequency-locked pulsing states are also found in a delayed negative optoelectronic feedback system, but not in a delayed positive optoelectronic feedback system. These frequency-locked pulsing states are experimentally observed to exhibit a harmonic frequency-locking phenomenon, where the pulsing frequency is locked to a harmonic of the delay loop frequency instead of the delay loop frequency itself. The rotation numbers of these frequency-locked pulsing states show a Devils staircase structure.

Diverse waveform generation using semiconductor lasers for radar and microwave applications

The possibility of using semiconductor lasers to conveniently generate diverse microwave waveforms for radar and microwave applications is studied both numerically and experimentally. Such waveforms are generated from the dynamical states of semiconductor lasers in different perturbation schemes and varying operating conditions. Using an optical injection scheme, broad-band chaotic microwave waveforms and tunable narrow-band harmonic microwaves over a broad frequency range can be generated. Using an optoelectronic feedback scheme, chaotic pulsing, regular pulsing, frequency-locked pulsing, and quasi-periodic pulsing waveforms are generated. These optically generated microwave waveforms can be easily amplified and radiated out using microwave amplifiers and antennas. The power spectra, time series, and autocorrelation traces of such waveforms are studied. The peak-sidelobe level is calculated to quantitatively compare the correlation characteristics of these waveforms. A broad-band chaotic waveform with a clean single-spike /spl delta/-function-like correlation profile useful for radar and other applications that demand unambiguous correlation profile is demonstrated experimentally.

Ambiguity functions of laser-based chaotic radar

The ambiguity functions of a newly developed laser-based chaotic radar (CRADAR) system are studied. In the CRADAR system, the chaotic waveforms can be generated either by an optically injected (OI) semiconductor laser, or a semiconductor laser with optoelectronic feedback (OEF). The ambiguity functions of the chaotic pulsation and chaotic oscillation waveforms obtained experimentally from the CRADAR system with the respective OEF and the OI schemes are examined and compared. In the cross-ambiguity functions, both types of the chaotic waveforms demonstrate their excellent capabilities in the electrical counter-countermeasures (ECCM) that civilian and military applications desire. In the auto-ambiguity functions, the chaotic oscillation waveform shows better unambiguous detection quality than the chaotic pulsation waveform that an ideal thumbtack-like ambiguity function with minimal sidelobes is found. Moreover, variations in the peak value and the full width at half-maximum of the auto-ambiguity function of the chaotic oscillation waveform along the principal axes are also investigated. By having the features of both ultrawideband radar and random signal radar, the chaotic oscillation waveform of the CRADAR system with the OI scheme is shown to possess the advantages of high range resolution, excellent ECCM capability, ideal thumbtack-like ambiguity function, and uncoupled range and range rate resolution functions.

Effective Bandwidths of Broadband Chaotic Signals

We propose and study a new definition for the effective bandwidths of the broadband chaotic signals, which sums up only those discrete spectral segments of the chaos power spectrum accounting for 80% of the total power. Compared to the definitions used conventionally, which tend to overestimate the effective bandwidths of the chaotic signals, the proposed definition measures only the bandwidths that possess significant amounts of power in the chaos spectra. With the proposed definition, the broadband chaos states can be clearly distinguished from the narrowband periodic oscillation states, based on just the values of the effective bandwidths measured. In this paper, the bandwidths of the dynamical states generated with an optically injected semiconductor laser under different definitions are studied and compared. To demonstrate the usefulness of the proposed definition in applications, such as ranging using chaos, the relations between the chaos bandwidths and the peak to sidelobe levels of the autocorrelations of the chaotic signals are also investigated.

Chaotic communication in radio-over-fiber transmission based on optoelectronic feedback semiconductor lasers

Performance of chaotic communication in radio-over-fiber (ROF) transmission based on optoelectronic feedback semiconductor lasers is studied numerically. The chaotic carrier is generated by optoelectronic feedback semiconductor lasers, where chaotic communication is realized by synchronizing a receiver laser with a transmitter laser. Transmission quality of different message encoding schemes, including additive chaos modulation (ACM) and on-off shift keying (OOSK), are investigated and compared. In this study, the dispersion and nonlinearity effects in the fiber transmission module and the amplified spontaneous emission noise from the optical amplifiers are considered. In the wireless channel, effects of additive white Gaussian noise, multipath, and path loss are included. To quantitatively study the performance of this chaotic communication system in the ROF transmission, bit-error-rates (BER) of different transmission lengths, message bit-rates, and signal-to-noise ratios are studied. The optimal launched power and message strength that minimize the BER while assuring effective communication security are discussed. While the ACM scheme is shown to perform better in a fiber only configuration, the OOSK scheme shows better immunity to the random effects and waveform distortions presented in the wireless channel.

Chaos time delay signature suppression and bandwidth enhancement by electrical heterodyning.

We numerically investigated the chaos time delay signature (TDS) suppression and bandwidth enhancement by electrical heterodyning. Chaos signals generated with a semiconductor laser subject to optical feedback typically have distinct loop frequency peaks in their power spectra corresponding to the reciprocals of the time delays, which deteriorates the performance in applications including chaos radar/lidar and fast random bit generation. By electrically heterodyning the chaos signal with a single frequency local oscillator, we show that the power in the chaos spectrum can be redistributed and a smoother spectrum with a broader effective bandwidth can be obtained. Compared with the chaos directly generated from a semiconductor laser subject to optical feedback, the amplitudes of the TDS (ρ(TDS)) measured under different feedback strengths can be suppressed up to 63% and the effective bandwidths can be enhanced up to 46% in average after the electrical heterodyning is applied.

Harmonic frequency locking in a semiconductor laser with delayed negative optoelectronic feedback

The locking states of a delayed negative optoelectronic feedback system are studied experimentally. Harmonic locking is observed in this system. Instead of locking to the frequency of the delay loop, the pulsing frequency of the system locks to a harmonic of the loop frequency. Moreover, a period-adding route of the locking states is found and locking states of Farey fractions up to order 17 are reported. The plot of the rotation number of the locking states shows a Devil’s staircase structure.