Tailoring enhanced chaos in optically injected semiconductor lasers

We demonstrate theoretically and experimentally that the injection of two optical signals into a semiconductor laser can be a feasible and practical method of enhancing chaos, influencing the stability map and generating various nonlinear dynamics.     

Synchronization between optically injected semiconductor lasers on undamped relaxation oscillations

Seeding light from a laser into the cavity of a second one is a simple experiment largely encountered in optical domain (Stover, H.L., Steier, W.H.: Appl. Phys. Lett. 8, 91–93 (1966); Lang, R.: IEEE J. Quant. Elect. 18(6), 976–983 (1982)). With an unidirectional coupling, optical injection is a basic tool to study synchronization process between oscillators. The dynamics induced in this experiment have been extensively described, theoretically and experimentally (Simpson, T.B. et al.: Quant. Semiclassical Opt. 9(5), 765–784 (1997); Wieczorek S.: Opt. Commun. 172, 279–295 (1999); Blin, S.: Comptes Rendus de la Phys. 4(6), 687–699 (2003)) but mainly when the seeded light is a continuous wave (CW). In this paper, we describe the synchronization on an undamped relaxation regime. In order to study the degree of correlation between the two synchronized lasers (TL and RL), we use a cascade of two optical injections (Guignard, C.: Conference on Lasers and Electro Optics—the Europeen Quant. Electronics Conference (CLEO-EQEC), Munich (Germany), EC1M (2003)) thus three lasers: Master-transmitter laser (TL)-receiver laser (RL). The seeding by a field showing undamped relaxations can be directly compared with the optical injection by a CW signal, especially when the injected power and the detuning between the TL and RL frequencies are varied. Synchronization on undamped relaxation are shown to occur at values of the optical injected power and detuning, for which the RL is in the locked or wave-mixing regime when it is seeded by a CW. However, additional tongues of synchronization also exist at detuning equal to the relaxation oscillation frequency (ROF).     

Route to broadband optical chaos generation and synchronization using dual-path optically injected semiconductor lasers

The generation and synchronization of broadband optical chaos in dual-path optically injected (DPOI) semiconductor lasers (SLs) are numerically demonstrated. The effective bandwidth enhancement is achieved up to about 35.84 GHz, under appropriate injection strength and frequency detuning. We systematically study and compare the bandwidth enhancement in single-path optically injected SLs (SPOI-SLs) and DPOI-SLs, and find that better performance can be obtained for the latter over a larger parameter span. Furthermore, two schemes for synchronization of bandwidth-enhanced chaos generated in two similar or identical (twin) DPOI-SLs are proposed, where the twins are driven by a common DPOI signal injected from another chaotic SL. High-quality chaos synchronization, an isochronous type, is observed between the twin DPOI-SLs. Also, the effect of parameter mismatch and frequency detuning is numerically examined. The simple technique of bandwidth enhancement using dual-path injection may pave way for various applications such as high-speed random number generators (RNGs) and chaos-based communications.     

Labyrinth bifurcations in optically injected diode lasers

Although pulsating and chaotic regimes in injection-locked semiconductor lasers have been described often in the literature, so far their relative abundance has remained poorly explored. Here, for two popular laser models, we report detailed Lyapunov phase (stability) diagrams characterizing the extension in parameter space of pulsating phases. Our phase (stability) diagrams discriminate regular from chaotic laser emissions and indicate where multistability is to be expected in injection-locked semiconductor lasers.     

Narrow spectral linewidth semiconductor lasers

Developments of narrow-linewidth distributed-Bragg-reflection (DBR) and distributed-feed-back (DFB) lasers are described. The design of a narrow-linewidth DBR laser is described in detail. Kl optimization from the viewpoint of narrow-linewidth operation and stable single mode operation is discussed. The linewidth dependences on cavity length, facet reflectivity and threshold current density are investigated. Some approaches to suppressing spatial hole burning in DFB lasers are described.     

Switching time in optically bistable injection-locked semiconductor lasers

Switching between states in a dispersive bistable injection-locked slave laser has been theoretically investigated. We show that the switching can be achieved by relatively small and short (≈10-50?ps) variation of the master laser injection power or frequency, which, besides the variation of the slave laser optical power, leads to significant variation of its photon phase (≈5π/6). By using an analytical model, we calculate the switching time dependence on the magnitude of the injection power and the frequency detuning variation.     

Radio-over-fiber AM-to-FM upconversion using an optically injected semiconductor laser

A radio-over-fiber system uses light to carry a microwave subcarrier on optical fibers. The microwave is usually frequency modulated for wireless broadcasting. A conventional optical communication system usually operates at the baseband with amplitude modulation. The interface of the two systems thus needs an upconversion from the baseband to the microwave band with AM-to-FM transformation. An all-optical solution employing an optically injected semiconductor laser is investigated. The laser is operated in a dynamic state, where its intensity oscillates at a microwave frequency that varies with the injection strength. When the injection carries AM data, the microwave is frequency modulated accordingly. We demonstrate optical conversion from an OC-12 622-Mbps AM baseband signal to the corresponding FM microwave signal. The microwave is centered at 15.90 GHz. A bit-error rate of less than 10(-9) is measured.     

Sudden chaotic transitions in an optically injected semiconductor laser

We study sudden changes in the chaotic output of an optically injected semiconductor laser. For what is believed to be the first time in this system, we identify bifurcations that cause abrupt changes between different chaotic outputs, or even sudden jumps between chaotic and periodic output. These sudden chaotic transitions involve attractors that exist for large regions in parameter space.     

Photonic ultrawideband signal generator using an optically injected chaotic semiconductor laser

We propose and demonstrate a method to generate ultrawideband (UWB) signals in the optical domain based on the chaotic dynamics of an optically injected semiconductor laser with optical feedback. The chaotic-UWB pulses with a fractional bandwidth of 116% and central frequency of 6.88?GHz are experimentally generated by controlling the injection strength and frequency detuning of the chaotic laser. The spectrum of the UWB signals is in full compliance with the Federal Communications Commission spectral mask, and the experimental results are qualitatively consistent with the simulated results.     

The frequency noise and spectral linewidth in semiconductor ring lasers

Numerical analyses for power spectral density of frequency noise (FN) and spectral linewidth in monolithic semiconductor ring laser (SRL) operating in the bistable unidirectional regime are performed in this paper. The Langevin noise sources for electric field and carrier density fluctuations are also taken into account in the frequency-domain theoretical model. The influences of several important physical parameters on the FN properties and laser linewidth are clearly demonstrated, including the injection current, linewidth enhancement factor and the particular backscattering coefficient. Due to the particular backscattering in SRLs, the calculated linewidths are relatively higher than that from the conventional Henry formula. The laser linewidth shows an exponential relationship with the backscattering strength.     

Emission properties of printed organic semiconductor lasers

We investigated the emission properties of a distributed-feedback resonator based on an organic semiconductor patterned by a novel printing technology. We observed the peak splitting of the photonic bandstructure of the periodic grating and extracted the effective refractive index of the outcoupled guided modes. The laser works at the second diffraction order, exhibiting narrow single-mode emission at 637 nm, with a threshold as low as 37 microJ/cm2. The results suggest that direct printing is a promising fabrication technique for optically confined integrated optoelectronics.     

外腔半导体激光器中激光二极管端面反射率的谱特性分析

考虑到端面反射率与波长有关 ,且带宽有限的实验事实 ,以及增益谱随载流子密度变化的因素 ,着重分析了激光二极管 (L D)镀膜端面反射率带宽、极小波长位置参量对光栅外腔激光器 (ECL D)调谐范围的影响。分析表明 ,除了 L D镀膜端面剩余反射率值、外腔反馈效率等因素之外 ,增大反射率带宽、精确控制极小波长位置是进一步挖掘 ECL D调谐范围的有效措施。增大反射率带宽 ,可更有效地提高参考载流子密度 ,延伸长波长端调谐区域 ,抑制 F- P腔影响。在确定的条件下 ,优化后的极小波长位置对应于调谐范围的极大值。理论分析结果较好地解释了实验现象     

Random bit generation using an optically injected semiconductor laser in chaos with oversampling

Random bit generation is experimentally demonstrated using a semiconductor laser driven into chaos by optical injection. The laser is not subject to any feedback so that the chaotic waveform possesses very little autocorrelation. Random bit generation is achieved at a sampling rate of 10 GHz even when only a fractional bandwidth of 1.5 GHz within a much broader chaotic bandwidth is digitized. By retaining only 3 least significant bits per sample, an output bit rate of 30 Gbps is attained. The approach requires no complicated postprocessing and has no stringent requirement on the electronics bandwidth.     

Hysteretical and spectral behaviour of bistable cleaved coupled cavity semiconductor diode lasers

Cleaved coupled-cavity GaAs/AlGaAs diode lasers have been fabricated which display optical bistability with wide hysteresis loops in their light current (L/I) characteristics. The single longitudinal mode output of these devices has been investigated under several operating conditions. The observed spectral changes associated with mode hopping, shifting and jumping across the band have been explained qualitatively.     

Observation of the synchronization of chaos in mutually injected vertical-cavity surface-emitting semiconductor lasers

Synchronization of chaotic oscillations was observed in mutually injected vertical-cavity surface-emitting lasers (VCSELs) in a low-frequency fluctuation regime. In the experiments, only one of the two polarization modes (x mode) showed synchronized oscillations, and the other polarization components (y mode) were synchronized as a result of the effect of anticorrelated oscillations that is a characteristic feature of VCSELs.     

Self pulsing properties of optically pumped FIR NH3 lasers

We report on measurements of periodic and chaotic self-pulsing beyond the second threshold of far-infrared NH₃ lasers. While the instabilities of the 81 m¹⁴NH₃ laser follow a simple pattern, for the 374 m¹⁵NH₃ laser different pulsing properties are found in different parameter ranges.Pulses under conditions of high pumping power are measured in detail, in view of possible applications of these coherent, high-repetition rate far-infrared pulsed lasers.     

Dependence of the experimental stability diagram of an optically injected semiconductor laser on the laser current

An experimental study of the dynamical properties of a semiconductor laser subjected to external optical injection is presented. The effect of the laser current on the dynamical regions as found in an experiment is reported on for the first time. The nonlinear dynamical regions are mapped in the parameter plane consisting of the detuning between lasers and the injection strength, by utilizing a method of condensing the information in output spectra to two-dimensional images. Corresponding maps for different values of the slave laser current are recorded. The recordings present conclusive experimental evidence that the overall locations of the dynamical regions scale with respect to the relaxation–oscillation frequency and the injection strength relative to the free running laser power. The results further support the theoretical prediction that the linewidth-enhancement factor is the parameter which most strongly affects the dynamics. Locally, specific chaotic regions are found to grow for higher operating points of the slave laser. A complete characterization of the parameters that enter the rate-equations for the visible output AlGaInP laser used in this experiment is performed.     

Time behaviour of the spectral properties of dye lasers

The spectral narrowing that occurs in the build-up regime of lasers with strongly homogeneously broadened emission lines, is studied numerically in the dye laser case. It turns out that in the first stage (up to a few nanoseconds, depending on the pumping power) this narrowing process is rather rapid, reducing the linewidth by a factor of about five, while it becomes slower and slower during further evolution.