Dynamics Of Semiconductor Lasers Research Articles

Spin modulation in semiconductor lasers

We provide an analytic study of the dynamics of semiconductor lasers with injection (pump) of spin-polarized electrons, previously considered in the steady-state regime. Using complementary approaches of quasistatic and small signal analyses, we elucidate how the spin modulation in semiconductor lasers can improve performance, as compared to the conventional (spin-unpolarized) counterparts. We reveal that the spin-polarized injection can lead to an enhanced bandwidth and desirable switching properties of spin-lasers.

Nonlinear dynamics of semiconductor lasers with feedback and modulation

The nonlinear dynamics of two semiconductor laser systems: (i) with optical feedback, and (ii) with optical feedback and direct current modulation are evaluated from multi-GHz-bandwidth output power time-series. Animations of compilations of the RF spectrum (from the FFT of the time-series) as a function of optical feedback level, injection current and modulation signal strength is demonstrated as a new tool to give insight into the dynamics. The results are contrasted with prior art and new observations include fine structure in the RF spectrum at low levels of optical feedback and non-stationary switching between periodic and chaotic dynamics for some sets of laser system parameters. Correlation dimension analysis successfully identifies periodic dynamics but most of the dynamical states are too complex to be extracted using standard algorithms.

Chaos dynamics in semiconductor lasers with polarization-rotated optical feedback

By using polarization-rotated optical feedback from the transverse-electric (TE) mode to the transverse-magnetic (TM) mode, chaotic oscillations for both polarization modes are excited in a semiconductor laser. We find different correlations between these chaotic oscillations than those found in previous studies. In this study, the dynamics are strongly dependent on their radio-frequency (RF) components and they are divided into three RF regions. For low-pass filtered signals lower than the laser relaxation oscillation, there is an antiphase correlation between the two polarization modes. On the other hand, the two polarization modes have an in-phase correlation for the RF components of the high-pass filtered signals, which are higher than the relaxation oscillation. However, no correlations were observed between the two modes for the intermediate RF components that include the relaxation oscillation frequency. We also perform numerical calculations for the model and obtain good agreement between the theoretical and experimental results.

Nonlinear Dynamics of Multi-Section Tunable Lasers

Nonlinear dynamics of an optically-injected tunable three-section semiconductor laser have been investigated numerically. For the first time, to the best of our knowledge, we present stability maps, showing different types of the nonlinear behavior versus optical injection parameters, for different points of the tuning curve. Areas of stable locking, limit-cycle, and chaos change in a periodic manner as the lasing frequency undergoes staircase-shaped tuning controlled by the index of the distributed Bragg reflector section. Physical explanation relating this behavior to that of the relaxation oscillation frequency and damping factor is provided. These phenomena suggest that tuning can be an effective way to control laser stability properties.

Demonstration of ultra-wideband (UWB) over fiber based on optical pulse-injected semiconductor laser

We experimentally demonstrated the ultra-wideband (UWB) signal generation utilizing nonlinear dynamics of an optical pulse-injected semiconductor laser. The UWB signals generated are fully in compliant with the FCC mask for indoor radiation, while a large fractional bandwidth of 93% is achieved. To show the feasibility of UWB-over-fiber, transmission over a 2 km single-mode fiber and a wireless channel utilizing a pair of broadband antennas are examined. Moreover, proof of concept experiment on data encoding and decoding with 250 Mb/s in the optical pulse-injected laser is successfully demonstrated.

Chaos synchronization and communication of mutual coupling lasers ring based on incoherent injection

A chaos secure communication system of mutual coupling lasers ring based on incoherent optical injection is proposed, in which fine tuning of optical frequency is not required compared with other schemes based on coherent optical injection. Therefore the secure communication scheme is attractive for experimental investigation. The dynamics of semiconductor lasers in the coupling ring are examined. Numerical investigations indicate that zero lag synchronization can be achieved under equal coupling time and strength of mutual coupling. Furthermore, by chaos shift keying (CSK), secure communication is simulated with a random bit stream of 1.0 Gbit/s. The results confirm the possibility of applying incoherent schemes of mutual coupling lasers ring to realize chaotic secure communication.

Frequency dynamics of semiconductor lasers with atomic absorbers: theory and experiments

In this paper we discuss the spectral behavior of monomode semiconductor laser systems whose output amplitude is constant, but whose frequency may be bistable, multistable, locked or present instabilities. The explored configurations are: (i) a laser diode (Fabry-Perot) under orthogonal filtered optical feedback; and (ii) an extended-cavity diode laser with an intracavity strongly-saturated resonant vapor. Starting from rate equations for the carrier density and for the radiation field oscillating in the cavity of these systems we describe spectral features which are in very good quantitative agreement with experimental observations.

Dynamics of Optically-Injected Semiconductor Lasers Using the Travelling-Wave Approach

The dynamics of optically-injected semiconductor lasers are of great practical interest for various applications such as chaotic signal transmission. For the first time, a method is presented to obtain a complete picture of the dynamics for optically-injected systems simulated with the travelling-wave model by investigating their trajectories. The method uses the distribution of intersection points of the trajectory on a Poincare plane to distinguish between different dynamical states of the system. It is then applied to obtain stability maps for the reflected and transmitted light of three quarter-wave-shifted distributed-feedback lasers with different Bragg coupling coefficients and it is shown that, firstly, the dynamics are different for the reflected and transmitted light and, secondly, the locking bandwidth for the case with lower Bragg coupling coefficient is significantly increased. Both findings are in agreement with published results obtained by a different analysis. The obtained stability maps are then applied to find three points inside each locking region for which the longitudinal power and carrier distributions along the cavity are displayed. These distributions are compared with the solitary laser and the relation between the Bragg coupling coefficient and its influence on the shape of the power and carrier distributions is shown.

Control of Spatio-Temporal Dynamics of Broad-Area Semiconductor Lasers by Strong Optical Injection

Control of spatio-temporal dynamics in broad-area semiconductor lasers is investigated numerically under the condition of strong optical injection. Irregular filamentation of the laser emissions are considerably suppressed as the optical injection ratio is increased. At high optical injections ratios, the laser oscillates with a regular structure in the time-resolved near-field pattern. At the same time, the time-averaged near-field pattern at the exit facet exhibits a good top-hat distribution.

Dynamics of a multimode semiconductor laser with optical feedback

A new model of a multi-longitudinal-mode semiconductor laser with weak optical feedback is proposed. This model generalizes the well-known Tang-Statz-deMars equations, which are derived from the first principles and adequately describe solid-state lasers to a semiconductor active medium. Steady states of the model and the spectrum of relaxation oscillations are found, and the laser dynamics in the chaotic regime of low-frequency fluctuations of intensity is investigated. It is established that the dynamic properties of the proposed model depend mainly on the carrier diffusion, which controls mode-mode coupling in the active medium via spread of gratings of spatial inversion. The results obtained are compared with the predictions of previous semiphenomenological models and the scope of applicability of these models is determined.

Excitable phase slips in an injection-locked single-mode quantum-dot laser

An experimental study of the dynamics of a single-mode quantum-dot semiconductor laser undergoing optical injection is described for the first time, to our knowledge. In particular, the first observation of excitable pulses near the locking boundaries for both positive and negative detuning is reported, indicating locking via a saddle-node bifurcation for both signs of the detuning. The phase evolution of the slave electric-field during pulsing was measured and confirmed that the pulses result from 2pi phase slips. The interpulse-time statistics were analyzed, and a Kramers-like distribution was obtained.

Nonlinear Dynamics of Semiconductor Lasers Under Repetitive Optical Pulse Injection

In this paper, nonlinear dynamics of semiconductor lasers under repetitive optical pulse injection are studied numerically. Different dynamical states, including pulsation and oscillation states, are found by varying the intensity and the repetition rate of the injection pulses. The laser is found to enter the chaotic pulsation (CP) states and chaotic oscillation (CO) states through individual period-doubling routes. Mapping and corresponding Lyapunov exponents of these dynamical states are plotted and examined in the parameter space. Moreover, the bandwidths of the chaos states found are investigated, where the bandwidths of the CP states observed at the strong injection regime are two to four times broader than the bandwidths of the CO states found at the weak injection regime. In this paper, frequency-locked states with different winding numbers, the ratio of the oscillation frequency, and the repetition frequency of the injection pulses are also studied. Both the cases for repetition frequency above and below the relaxation oscillation frequency are examined. The winding numbers of the frequency-locked states reveal a Devil's staircase structure, where a Farey tree showing the relations between the neighboring states is constructed.

Chaotic dynamics in semiconductor lasers subjected to polarization-rotated optical feedback

In-phase or synchronized oscillations between transverse electric (TE) and transverse magnetic (TM) modes with a loop delay are common phenomena in the numerical studies of semiconductor lasers subjected to polarization-rotated optical feedback. However, we experimentally find antiphase oscillations of laser output powers with zero time lag under appropriate conditions of orthogonal polarization optical feedback. Antiphase oscillations are well reproduced by the numerical simulations for the experimental model taking into account the frequency detuning between the two modes.

Dynamics of semiconductor lasers with external multicavities

Extending a semiconductor laser by means of an external resonator providing a weak optical feedback causes high-dimensional chaotic fluctuations of the light intensity. Adding a second resonator with different round-trip time may turn these fluctuations into more ordered oscillations or even lead back to a stable steady-state operation. The stability range of periodic or continuous wave solutions can be increased by adding a third resonator to the system. This stabilizing effect of multicavities is shown experimentally and theoretically using numerical simulations based on an extended Lang-Kobayashi model and corresponding linear stability analysis of continuous wave solutions.

Dynamics of semiconductor laser with optical feedback: Evolution from low-frequency fluctuations to chaos

The low-frequency fluctuations and high-dimensional chaos with 12.2 correlation dimensions were generated experimentally by a semiconductor laser with optical feedback. Extensive experimental and numerical studies were performed to reveal the evolution process from low-frequency fluctuations to chaos. Our results showed that there exists a obvious critical point for the semiconductor laser's bias current. When the bias current Ib is set below 1.03Ith, the peak-to-peak value of the low-frequency fluctuations increases at first and then decreases with the feedback strength decreasing, while its average period keeps decreasing. In this process, the output of the semiconductor laser never goes chaos. However, when the bias current Ib is set beyond 1.03Ith, chaos appears and is persistent in this range. Moreover, the peak-to-peak value of the low-frequency fluctuations increases continuouslly and its duration decreases with the decrease of the feedback strength. Three stages experienced in the process leading from stable emission and low-frequency fluctuation to chaos are established. Numerical simulations are well consistent with the experimental results.

Novel photonic applications of nonlinear semiconductor laser dynamics

With a proper perturbation, even a single-mode semiconductor laser can exhibit highly complex dynamical characteristics ranging from stable, narrow-linewidth oscillation to broadband chaos. In recent years, three approaches to invoke complex nonlinear dynamical states in a single-mode semiconductor laser have been thoroughly studied: optical injection, optical feedback, and optoelectronic feedback. In each case, the nonlinear dynamics of the semiconductor laser depends on five intrinsic laser parameters and three operational parameters. The dynamical state of a given laser can be precisely controlled by properly adjusting the three operational parameters. This ability to control the dynamical behavior of a laser, combined with the understanding of its characteristics, opens up the opportunity for a wide range of novel applications. This paper illustrates the utilization of the rich nonlinear dynamics of single-mode semiconductor lasers by focusing on the period-one oscillation for its applications in tunable photonic microwave generation, AM-to-FM conversion, and dual-frequency precision Doppler lidar.

Resonant activation in bistable semiconductor lasers

We theoretically investigate the possibility of observing resonant activation in the hopping dynamics of two-mode semiconductor lasers. We present a series of simulations of a rate-equation model under random and periodic modulation of the bias current. In both cases, for an optimal choice of the modulation time scale, the hopping times between the stable lasing modes attain a minimum. The simulation data are understood by means of an effective one-dimensional Langevin equation with multiplicative fluctuations. Our conclusions apply to both edge-emitting and vertical cavity lasers, thus opening the way to several experimental tests in such optical systems.

Analysis of semiconductor laser dynamics under gigabit rate modulation

A theoretical study of the dynamics of semiconductor lasers subjected to pseudorandom digital modulation at gigabit rates is presented. The eye diagram, turn-on jitter (TOJ), and power fluctuations in the modulated laser wave form are analyzed. The study is based on numerical large-signal analysis of the laser rate equations. Influences of the biasing and modulation currents on the eye diagram and TOJ are examined. The degree of eye opening is measured in terms of a Q factor of the laser signal analogous to the Q factor determining the bit-error rate in transmission systems. Influence of optimizing both the sampling and decision times on the signal Q factor is modeled. We show that the most eye opening corresponds to shortening the sampling time associated with lengthening the decision time. We also assess the relative contributions of the laser intrinsic noise and pseudorandom bit pattern to the TOJ. The results show that the bit pattern is the major contributor to the TOJ when the setting time of the relaxation oscillation is longer than the bit slot.

Single–Frequency operation of External–Cavity VCSELs: Non-linear multimode temporal dynamics and quantum limit.

We present an experimental and theoretical investigation of the non-linear multimode dynamics of external-cavity VCSELs emitting at 1 and 2.3mm. We account for the stable single-frequency and linearly polarized emission by these laser sources, even in the presence of quantum noise and non-linear mode interactions originating from Four-Wave-Mixing via population pulsations in the quantum-wells. This fact is a consequence of the mode antiphase dynamics. Thanks to the high-Q external cavity configuration, the laser dynamics fall into the oscillation-relaxation-free class-A regime. The characteristic time to achieve single mode emission is ~ 1ms for a 15mm long cavity with an antireflection coated structure and no spectral filter, as for an "ideal" homogeneous gain laser. The side mode suppression ratio is as high as 40 dB, close to the quantum limit. The laser linewidth is at the quantum limit, and is ~ 1Hz at 1mW output. An experimental value <20 kHz has been established. Under standard conditions, without spectral filtering, the optimum cavity length for highly coherent single mode operation is expected in the range 5 to 30mm. Finally, for cavity lengths typically shorter than 5mm, we rather have an "ideal" homogeneous gain class-B laser, exhibiting oscillation-relaxation of the intensity in the 0.1GHz range. These properties contrast with the intrinsic strongly non-linear dynamics of conventional semiconductor lasers.

Picosecond Dynamics of Semiconductor Fabry–PÉrot Lasers: A Simplified Model

A simplified semiconductor laser model that is sufficient to describe laser dynamics on a picosecond time scale is presented. The model prescribes a time-domain differential equation regarding the complex amplitude of the light field. The simplification comes from an approximation of the semiconductor optical gain dynamics that typically exhibits two distinct time scales with a slow component on the order of hundreds of picoseconds and a fast component on the order of a few picoseconds or subpicoseconds. For laser dynamics concerning mainly the picosecond time scale, the slow component of the material gain dynamics can be treated as a static effect and the fast component can be treated as instantaneous. Such treatment also shines light on relations between semiconductor optical amplifier nonlinearities such as self-phase modulation and device parameters such as the linewidth enhancement factor and confinement factors. The model correctly predicts various picosecond laser dynamics of semiconductor lasers including the preference of a constant-power, FM mode-locking operation once the correct chirp condition is first established. A coupled multispatial mode (MSM) model based on the simplified time-domain laser model is used to successfully explain self-start AM mode-locking operations of single-contact Fabry-Perot laser diodes (FP-LDs) that have been observed experimentally. A mechanism for establishing the needed condition for single-contact FP-LD's self-FM mode-locking operations is also proposed based on the understanding of the MSM AM mode-locking operations.