Dynamics Of Laser Diodes Research Articles

Nonlinear dynamics of a laser diode subjected to both optical injection and optical feedback.

We analyse theoretically the nonlinear dynamics of a single-mode laser diode subjected to both optical injection and optical feedback. Detailed mappings of the laser dynamics reveal that, due to optical feedback (OF), the locking boundaries resulting from optical injection (OI) shift towards larger negative detunings and higher injection rates and display a periodic pattern of the injection locking boundaries. We demonstrate how feedback induces a cascade of quasiperiodic bifurcations associated with abrupt dynamic changes, hence altering the route to locking. A close inspection of the laser optical spectra for increasing feedback rate reveals the complex interplay between undamped relaxation oscillations and external cavity frequencies.

Influence of thermal effects in microresonators on the locking range in self-injection locking of laser diodes

Stable narrow-linewidth lasers generated by self-injection locking systems have revolutionized applications from optical frequency metrology to astronomy. However, the dynamics for the self-injection locking system are intrinsically intertwined with thermal effects, which can generate a nonnegligible resonance drift in the microresonator and result in large detuning from the required regime. In this paper, we introduce the thermal effect, depending on the photon number, into self-injection locking systems with Rayleigh backscattering. We obtain a set of time-domain rate equations to describe the dynamics of laser-diode–cavity–microresonator systems and derive analytical formulas for effective detuning. The analytical results match well with our numerical simulations, and the effective detuning locking position moves forward as the value of the thermal effect coefficient decreases. We also analyze the dependence of the locking range and stable range on thermal effects, and our calculations show that, based on our approach, the stable range can be optimized effectively and the locking range is extended. Our results have the potential to optimize laser diode frequency stabilization experiments.

High-frequency chaotic bursts in laser diode with optical-feedback

The diversity of observed nonlinear dynamics in laser diodes subjected to optical feedback shows promise as an excellent candidate for chaos-based commercial applications. Thus, works in the last decade have primarily focused on system performances, geometric configurations, and balancing their trade-offs. We demonstrate an optical feedback system operating on phase-conjugate feedback exhibiting state-of-the-art chaos bandwidth values reaching ≈ 30 GHz. We report numerous high-frequency, spatiotemporally complex, chaotic dynamics undocumented in the past four decades. We highlight the underlying physics involving a three-tier temporal interaction mechanism between laser relaxation oscillations, phase-conjugate feedback induced external cavity modes, and chaotic bursts repeating each delay time in the extended cavity. We show supporting real-time high-definition system outputs captured by modern large bandwidth oscilloscopes. The presented work shows to our knowledge, the highest bandwidth and complexity entropy to-date in an optical chaos from a single laser, thereby proving the unnecessary need for further complexity using cascading lasers.

Effects of electron blocking layer configuration on the dynamics of laser diodes emitting at 450 nm

In this paper, a theoretical study is presented, analysing the AlxGa(1−x)N electron blocking layer (EBL) at different Al content and Mg-doping levels for the InGaN-based laser diode (LD) emitting at 450 nm. It is observed that the performance of LDs not only depends on the Al content in the EBL but also on the Mg doping levels in the EBL and the In content in the InGaN waveguide. The optimum selection of AlGaN EBL strongly depends upon the In content in the InGaN waveguide. It is found that, for an In0.08Ga0.92N waveguide, the higher Al content in the EBL degrades the performance due to the increase in leakage current, thus an Al-free EBL i.e. a GaN EBL, is optimal for an In0.08Ga0.92N waveguide. However, the increased Mg doping in the p-GaN (Al = 0) EBL shows improvement in the performance of LDs. For the p-GaN EBL with a Mg-doping level of 1 × 1019 cm−3, the output power is 138 mW, for 3 × 1019 cm−3 doping it is 364 mW and for 5 × 1019 cm−3 doping it increased to 556 mW. For the p-GaN EBL, the threshold current at 1 × 1019 cm−3 is 319 mA, at 3 × 1019 cm−3 doping it falls to 231 mA and for 5 × 1019 cm−3 doping it is 227 mA. For the heavily doped p-GaN EBL, the threshold current dependency is negligible at higher Al content in the EBL, but power output shows a strong dependency on the Al content. In the case of an In-free waveguide i.e. a GaN waveguide (In = 0), the performance of the LD is optimal at 15% Al content in the EBL.

Quantification of orbital instability of chaotic laser diode

We studied two methods that quantify the orbital instability of a laser diode (LD) in two typical chaotic systems. In one method, a coefficient named the orbital expansion exponent (OEE) is calculated from only the time series of the laser intensity. In the other method, the Lyapunov exponent is calculated from the rate equations. Then we compared the OEE and the Lyapunov exponent to discuss the appropriateness of the OEE. In an optical feedback LD system, the OEE cannot represent the dynamics of the chaotic LD satisfactorily for the large feedback ratio. However, when the LD has a larger drive current and the inherent parameters of the LD are dominant in the dynamics, the OEE represents the dynamics of the chaotic LD as well as the Lyapunov exponent. On the other hand, in an optical injection LD system, the correlation coefficient between the OEE and the Lyapunov exponent is large even if the injection ratio is large. To find the reason for this, we replaced the optical feedback system with a multistage optical injection system, and showed that the feedback terms prevent the OEE from accurately representing the orbital instability of a chaotic laser.

Second-harmonic-generation-based technique for examining laser diode wavelength dynamics in the μs to ms range.

Wavelength information is essential for any researcher in optics and photonics, and for this reason, a wide range of devices is available for measuring it. However, the techniques available today are limited either to a resolution of nanometers or a measurement rate of kHz. In this paper, we present a simple but highly versatile technique based on second-harmonic generation to measure fast wavelength dynamics of laser diodes. We demonstrate a resolution of 0.7pm and a measurement rate in the MHz range. The measurement rate is limited only by the photodetector, and the wavelength resolution is limited mainly by the length of the nonlinear crystal and the noise of the detectors. The technique can, e.g., be used to investigate the mode-hop behavior of laser diodes during pulsed operation. To demonstrate this, we show the wavelength changes of a laser diode during a single pulse.

The influence of gain suppression on dynamic characteristics of violet InGaN laser diodes

The influence of gain suppression factor on dynamic characteristics of violet InGaN laser diode (LD) with an emission wavelength near 415nm has numerically been investigated. Different values of gain suppression factor have been used to examine the dynamic characteristics of violet InGaN LD. Simulation results indicate that the gain suppression factor in the non-linear gain equation has potential effects on the carrier and photon dynamics of violet InGaN LD. It is found that the non-linearity of the carrier increases as the injunction current is increased.

Stabilisation of chaotic dynamics in semiconductor lasers with optical feedback using optimal control

The application of a method for controlling time-delay chaotic systems to the control of external-cavity laser diode dynamics is reported. The approach is based on optimal control theory and, in general, aims to stabilise nonlinear time-delay systems by the use of an approximating sequence technique. The goal of the approximating sequence technique is to reduce a given nonlinear system into a sequence of linear time-varying equations, with the purpose of approximating to the solution of the nonlinear system. In each of these equations, the linear-quadratic optimal tracking control is implemented. It is shown that in the case of chaotic external-cavity lasers, a feedback control via the laser bias current enables the selection of the desired dynamical behaviour.

Spectral and time resolved scanning near‐field microscopy of broad area 405 nm InGaN laser diode dynamics

AbstractRidge widths of GaN laser diodes (LDs) are typically in the order of few mm. In contrast to GaAs material systems, beam quality of GaN broad area lasers is still a critical point. By time resolved scanning near‐field optical microscopy (SNOM) on pulsed electrically pumped LDs with different ridge widths we observe dynamic features caused by thermal and carrier induced changes of the refractive index like filamentation and lateral mode competition, which strongly influence the far‐field of the LDs. Using a high spectral resolution spectrometer we can additionally resolve the individual longitudinal modes of the laser spectrum both time resolved and correlated to the lateral position in the waveguide. Especially on samples with broad ridges we observe complex spectral and spatial dynamics of the laser mode like different filaments lasing on different longitudinal mode combs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analysis of chromatic dispersion-induced second-harmonic distortions including laser dynamics to the second order

We perform analysis of chromatic dispersion-induced second-harmonic distortions including laser diode dynamics. Investigating laser diode dynamics fully to the second order, we derive analytical expressions for intensity and frequency modulation indices. Using these, we accurately model chromatic dispersion-induced second-harmonic distortions for signals produced by a directly modulated distributed feedback laser. The results agree well with numerical solutions, as well as with experimental results for a wide range of modulation frequencies and fiber lengths.

Influence of the injection current dependence of gain suppression on the nonlinear dynamics of semiconductor lasers

A detailed numerical analysis of the nonlinear dynamics of a directly modulated 1.55 μm InGaAsP distributed-feedback laser diode (LD) is carried out. Results show that when simulating the nonlinear dynamics of LDs, it is important to account for the gain suppression being dependent on the injection current. Only when this dependency of gain suppression is included in the conventional single-mode rate equations, can excellent agreement between simulated and measured results be achieved.

Is noise a crucial factor in rate equation modeling of nonlinear dynamics in laser diodes?

The effect of noise on the accuracy of single-mode rate equations in predicting laser diode (LD) behavior is evaluated. Inclusion of noise increases the relaxation oscillation damping. Nonlinear dynamics analysis reveals that noise has disguised an important factor that governs the agreement between calculated and measured results. Instead, simulations show that the LD active layer temperature has a major impact on the accuracy of modeling LD behavior.

Period tripling and chaos in the dynamic behavior of directly modulated diode lasers

The paper presents the relevance of period-tripling behavior that has recently been found in different experimental studies of directly modulated laser diodes. Applying different numerical techniques to the rate equation model of the laser diode, among which we highlight the continuation method to calculate the unstable solutions of the system, we show that period-tripling behavior appears and disappears in two tangent bifurcations. Therefore, the period-three solutions form a closed bifurcation curve called isola. In between these two tangent bifurcations, the period-three solution coexists with the chaotic attractor reached by a period-doubling cascade, giving rise to a hysteresis loop in the deterministic case. Also, we have found that a boundary crisis might be behind the chaotic behavior that is observed for the highest values of the modulation index. The effects of random noise fluctuations in the laser diode dynamics are also studied. Langevin noise sources are included in the rate equation model and appropriate stochastic integration methods have been used. The route to chaos that we have obtained points out the relevant role that noise has in achieving agreement between numerical studies and experimental results that have been published. The introduction of noise has been proved to be of major importance in determining the system behavior in the regions of the coexistence of solutions.

Targeting in nonlinear dynamics of laser diodes

The authors propose a simple experimentally accessible method of targeting periodic and chaotic dynamics appearing in a semiconductor laser subject to optical feedback. Robustness of the method to the feedback strength have been demonstrated. The possible application of the technique in chaotic communications is identified, and its advantages in chaos control are discussed.

Wigner distribution and spectral dynamics of laser diodes

The Wigner distribution is a simultaneous representation of a signal in both time and frequency domains. We discuss the Wigner distribution as an instrument-independent method of displaying the time–frequency response of a laser transmitter. This is important in long-haul communication systems that use semiconductor lasers, which exhibit chirp. If the type of spectrometer for measuring the spectrum as a function of time is known, so that the instrument's impulse response is known, then the Wigner distribution can be recovered. This distribution is then identical to that obtained with a different instrument with a different resolution. Examples of the calculated time-resolved spectra, obtained with two different instruments, are shown for a gain-switched laser. They are compared with the Wigner distribution obtained by deconvolution.

Transformation of rate equations and approximate transient solutions for semiconductor lasers

Effects of the gain saturation, spontaneous emission, Auger recombination, and fast saturable absorption on the dynamics of laser diodes are studied approximately in a unified manner by transforming the rate equation to generalized coordinates. By applying the multiple-scales expansion method to the transformed nonlinear rate equations, the transient solutions of relaxation oscillation in laser diodes are derived. Analytic expressions for the photon density and the electron density agree well with numerical calculations. >