The output spectrum of both gas and semiconductor lasers usually contains more than one frequency. Multimode operation in gas versus semiconductor lasers arises from different physics. In gas lasers, slow equilibration of the electron populations at different energies makes each frequency an independent single-mode laser. The slow electron diffusion in semiconductor lasers, combined with the spatially varying optical intensity patterns of the modes, makes each region of space an independent single-mode laser. We develop a rate equation model for the photon number in each mode which captures all these effects. Plotting the photon number versus pumping rate for the competing modes, in both subthreshold and above threshold operation, illustrates the changes in the laser output spectrum due to either slow equilibration or slow diffusion of electrons.
We show that semiconductor Fano lasers strongly suppress dynamic instabilities induced by external optical feedback. A comparison with conventional Fabry-Perot lasers shows orders of magnitude improvement in feedback stability, and in many cases even total suppression of coherence collapse, which is of major importance for applications in integrated photonics. The laser dynamics are analysed using a generalisation of the Lang-Kobayashi model for semiconductor lasers with external feedback, and an analytical expression for the critical feedback level is derived.
In this work we study a possibility of waveguide fabrication on the basis of active quantum wells in semiconductor lasers. The efficiency of such a waveguide for an InP structure with In0.53Ga0.47As quantum wells is demonstrated experimentally. An optically-pumped laser on this basis is realized.
We introduce a simplified version of the steady-state ab initio laser theory for calculating the effects of mode competition in continuous wave lasers using the passive cavity resonances. This new theory harnesses widely available numerical methods that can efficiently calculate the passive cavity resonances, with negligible additional computational overhead. Using this theory, we demonstrate that the pump profile of the laser cavity can be optimized both for highly multi-mode and single-mode emission. An open source implementation of this method has been made available.
The generation of optical frequency combs via direct electrical pumping of semiconductor lasers is an attractive alternative to the well-established mode-locked laser sources in terms of compactness, robustness and integrability. However, the high chromatic dispersion of bulk semiconductor materials can prevent the generation of frequency combs or lead to undesired pulse lengthening. In this letter, we present a novel dual waveguide for intracavity dispersion compensation in semiconductor lasers. We apply the concept to a short mid-infrared wavelength quantum cascade laser operating in the fir…
The three goals of this PhD thesis are to improve the understanding of the mechanisms underlying the dynamical instabilities observed in semiconductor lasers subject to external optical feedback, to propose a technique to suppress these instabilities and finally to take advantage of them, for instance for secure communications or to generate microwave time-periodic oscillations.
We discuss our recent progress in iimproving the phase noise of a semiconductor laser using self-injection locking of to a mode of a high-Q whispering gallery mode resonator. Locking efficiency is analyzed for semiconductor distributed feedback (DFB) as well as Fabry-Perot (FP) lasers operating at 690nm, 1060nm, 1550nm, and 2000nm. Instantaneous linewidth below 300 Hz is realized with telecom DFB lasers. Tunability of the lasers is demonstrated. Commercially available packaged "plug-and-play" devices are manufactured.
The influence of nonlinear properties of semiconductor saturable absorbers on ultrashort pulse generation was investigated. It was shown, that linewidth enhancement, quadratic and linear ac Stark effect contribute essentially to the mode locking in cw solid-state lasers, that can increase the pulse stability, decrease pulse duration and reduce the mode locking threshold
A novel and simple model is proposed for the measurement of the linewidth enhancement factor (LEF) α of multiwavelengths semiconductor laser. It is based on the suppression characteristics of an arbitrary mode while other modes are optically injection locked individually. The proposed model can be used to measure α value of individual modes of multi-wavelengths laser with large mode spacing. As a proof of the concept, the model is used to experimentally measure α of a mode of a slotted Fabry- Pérot laser source.
This work reports single-frequency laser oscillation at 1003.4 nm of an optically pumped external cavity semiconductor laser. By using a gain structure bonded onto a high conductivity substrate, we demonstrate both theoretically and experimentally the strong reduction of the thermal resistance of the active semiconductor medium, resulting in a high power laser emission. The spectro-temporal dynamics of the laser is also explained. Furthermore, an intracavity frequency-doubling crystal was used to obtain a stable single-mode generation of blue (501.5 nm) with an output power around 60 mW.
A novel explanation of observed enhanced longitudinal mode spacing in InGaN semiconductor lasers has been proposed. It has been demonstrated that e-h plasma oscillations, which can exist in the laser active layer at certain driving conditions, are responsible for mode clustering effect. The resonant excitation of the plasma oscillations occurs due to longitudinal mode beating. The separation of mode clusters is typically by an order of magnitude larger that the individual mode spacing.
Based on self - consistent field theory we study a soliton generation in cw solid-state lasers with semiconductor saturable absorber. Various soliton destabilizations, i.e. the switch from femtosecond to picosecond generation (''picosecond collapse''), an automodulation regime, breakdown of soliton generation and hysteresis behavior, are predicted.
Thanks to a new derivation of the fundamental equations governing multimode dynamics for a semiconductor laser near its threshold, we identify regimes of existence of a pure phase instability (and of a mixed phase-amplitude turbulence regime) which give an alternative satisfactory interpre- tation of the deterministic multimode dynamics observed in some devices. The existence of intrinsic noise generated by the phase instability reconciles in the same description the deterministic and random features of the semiconductor dynamics.
We demonstrate a technique for shaping current inputs for the direct modulation of a semiconductor laser for digital communication. The introduction of shaped current inputs allows for the suppression of relaxation oscillations and the avoidance of dynamical memory in the physical laser device, i.e., the output will not be influenced by previously communicated information. On the example of time-optimized bits, the possible performance enhancement for high data rate communications is shown numerically.
The realization of a cavity soliton laser using a vertical-cavity surface-emitting semiconductor gain structure coupled to an external cavity with a frequency-selective element is reported. All-optical control of bistable solitonic emission states representing small microlasers is demonstrated by injection of an external beam. The control scheme is phase-insensitive and hence expected to be robust for all-optical processing applications. The motility of these structures is also demonstrated.
We demonstrate lasing mode selection in nearly circular semiconductor microdisks by shaping the spatial profile of optical pump. Despite of strong mode overlap, adaptive pumping suppresses all lasing modes except the targeted one. Due to slight deformation of the cavity shape and boundary roughness, each lasing mode has distinct emission pattern. By selecting different mode to be the dominant lasing mode, we can switch both the lasing frequency and the output direction. Such tunability by external pump after the laser is fabricated enhances the functionality of semiconductor microcavity lasers…
Semiconductor laser generation begins at a critical injection when the gain and loss spectra touch each other at a singular frequency. In the framework of the standard (Schawlow-Townes-Lax-Henry) theory, the finite linewidth results from the account of fluctuations associated with the random spontaneous emission processes. This approach is based on the assumption that in the mean-field approximation the singular frequency generation persists for injection levels higher than critical. We show that this assumption in the framework of the Boltzmann kinetic equation for electrons and photons is in…
A novel model of a semiconductor laser with optical feedback is presented, generalizing Lang-Kobayashi equations to the case of incoherent feedback. The equations are supplemented by a stochastic variable which models random phase difference between the field inside laser cavity and the feedback field. It is shown that for weak-to-moderate feedback the transition from coherent to incoherent feedback leads to replacement of dynamical chaos by almost stationary lasing with slightly fluctuating intensity. Nevertheless, incoherent feedback can lead to chaotic oscillations, but at considerably larg…
An experimental study of the delayed threshold phenomenon in a Vertical Extended Cavity Semiconductor Emitting Laser is carried out. Under modulation of the pump power, the laser intensity exhibits a hysteresis behavior in the vicinity of the threshold. The temporal width of this hysteresis is measured as a function of the modulation frequency, and is proved to follow the predicted scaling law. A model based on the rate equations is derived and used to analyze the experimental observations. A frequency variation of the laser around the delayed threshold and induced by the phase-amplitude coupl…
A semiconductor laser subject to delayed optical feedback is investigated in the limit of extremely intense feedback power. In a range of feedback polarization rotation angles the emission spectra of the laser reveal a giant gap with width of more than a terahertz. The position of the gap and its width are shown to be regulated by means of feedback polarization rotation angle. We demonstrate that a theoretical approach, based on carrier density grating induced potential, explains our experimental results.
We show that a topological investigation of the phase space of a Semiconductor Ring Laser can be used to devise switching schemes which are alternative to optical pulse injection of counter-propagating light. To provide physical insight in these switching mechanisms, a full bifurcation analysis and an investigation of the topology is performed on a two-dimensional asymptotic model. Numerical simulations confirm the topological predictions.
We characterize the operation of semiconductor microring lasers in an excitable regime. Our experiments reveal a statistical distribution of the characteristics of noise-triggered optical pulses that is not observed in other excitable systems. In particular, an inverse correlation exists between the pulse amplitude and duration. Numerical simulations and an interpretation in an asymptotic phase space confirm and explain these experimentally observed pulse characteristics.
A room temperature operating Vertical External Cavity Surface Emitting Laser is applied around 1550 nm to intracavity laser absorption spectroscopy analyzed by time-resolved Fourier transform interferometry. At an equivalent pathlength of 15 km, the high resolution spectrum of the semiconductor disk laser emission covers 17 nm simultaneously. A noise equivalent absorption coefficient at one second averaging equal to 1.5 10^{-10} cm^{-1}.Hz^{-1/2} per spectral element is reported for the 65 km longest path length employed.
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-equations 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 openi…
We demonstrate a miniature self-injection locked DFB laser using resonant optical feedback from a high-Q crystalline whispering gallery mode resonator. The linewidth reduction factor is greater than 10,000, with resultant instantaneous linewidth less than 200 Hz. The minimal value of the Allan deviation for the laser frequency stability is 3x10^(-12) at the integration time of 20 us. The laser possesses excellent spectral purity and good long term stability.
The transition between the class-B and class-A dynamical behaviors of a semiconductor laser is directly observed by continuously controlling the lifetime of the photons in a cavity of sub-millimetric to centimetric length. It is experimentally and theoretically proved that the transition from a resonant to an overdamped behavior occurs progressively, without any discontinuity. In particular, the intermediate regime is found to exhibit features typical from both the class-A and class-B regimes. The laser intensity noise is proved to be a powerful probe of the laser dynamical behavior.
Injection-locked semiconductor lasers can be brought to a neuron-like excitable regime when parameters are set close to the unlocking transition. Here we study experimentally the response of this system to repeated optical perturbations and observe the existence of a refractory period during which perturbations are not able to elicit an excitable response. The results are analyzed via simulations of a set of dynamical equations which reproduced adequately the experimental results.
Using metal-clad (or plasmonic) waveguide structures in semiconductor lasers carries a promise of reduced size, threshold, and power consumption. This promise is put to a rigorous theoretical test, that takes into account increased waveguide loss, Auger recombination, and Purcell enhancement of spontaneous recombination. The conclusion is that purported benefits of metal waveguides are small to nonexistent for all the band-to-band and intersubband lasers operating from UV to Mid-IR range, with a prominent exception of far-IR and THz quantum cascade lasers. For these devices, however, metal wav…
We present an experimental and theoretical study of modal nonlinear dynamics in a specially designed dual-mode semiconductor Fabry-Perot laser with a saturable absorber. At zero bias applied to the absorber section, we have found that with increasing device current, single mode self-pulsations evolve into a complex dynamical state where the total intensity experiences regular bursts of pulsations on a constant background. Spectrally resolved measurements reveal that in this state the individual modes of the device can follow highly symmetric but oppositely directed spiralling orbits. Using a g…
We report on the development of a frequency modulatable 795 nm semiconductor laser based on self-injection locking to a high quality factor whispering gallery mode microresonator. The laser is characterized with residual amplitude modulation below -80 dB and frequency noise better than 300 Hz/Hz^(1/2) at offset frequencies ranging from 100 Hz to 10 MHz. The frequency modulation (FM) speed and span of the laser exceed 1 MHz and 4 GHz, respectively. Locking of the laser to Doppler-free saturated absorption resonance of 87Rb D1 line is demonstrated and frequency stability below 10^(-12) is measur…
We theoretically investigate optical injection in semiconductor ring lasers and disclose several dynamical regimes. Through numerical simulations and bifurcation continuation, two separate parameter regions in which two different injection-locked solutions coexist are revealed, in addition to a region in which a frequency-locked limit cycle coexists with an injection-locked solution. Finally, an antiphase chaotic regime without the involvement of any carrier dynamics is revealed. Parallels are drawn with the onset of chaos in the periodically forced Duffing oscillator.
We report on experimental observation of localized structures in two mutually coupled broad-areahttp://hal.archives-ouvertes.fr/images/calendar.gif semiconductor resonators. These structures coexist with a dark homogeneous background and they have the same properties as cavity solitons without requiring the presence of a driving beam into the system. They can be switched individually on and off by means of a local addressing beam.
We provide a numerical proof of concept of a stabilization mechanism for BAS laser sources. The scheme is based on the simultaneous introduction of in-phase two-dimensional modulations on the refractive index and pump (gain). We numerically proof total stabilization in BAS laser sources, both in space and time. We also examine the interplay between the index and gain modulations and the effect of the slow relaxation of carriers on the stabilization performance.
We experimentally demonstrate the difference between a ridge polariton laser, and a conventional edge-emitting ridge laser operating under electron-hole population inversion. The horizontal laser cavities are 20 -- 60 $μ$m long GaN etched ridge structures with vertical Bragg reflectors. We investigate the laser threshold under optical pumping and assess quantitatively the effect of a varying optically-pumped length. The laser effect is achieved for an exciton reservoir length of just 15% of the cavity length, which would not be possible in a conventional ridge laser, with an inversion-less pol…
We demonstrate that a semiconductor laser perturbed by the distributed feedback from a fiber random grating can emit light chaotically without the time delay signature. A theoretical model is developed based on the Lang-Kobayashi model in order to numerically explore the chaotic dynamics of the laser diode subjected to the random distributed feedback. It is predicted that the random distributed feedback is superior to the single reflection feedback in suppressing the time-delay signature. In experiments, a massive number of feedbacks with randomly varied time delays induced by a fiber random g…
Stability control in laser is still an emerging field of research. In this paper the dynamics of External cavity semiconductor lasers (ECSLs) is widely studied applying the methods of chaos physics. The stability is analyzed through plotting the Lyapunov exponent spectra, bifurcation diagrams and time series. The oscillation of the electric field E has been reported to be either periodic (P1,P2,..) or chaotic. The results of the study show that the rich nonlinear dynamics of the electric field |E|^2 includes saddle node bifurcations, quasi-periodicity and regular pulse packages. The issue of f…
We show that the emission of broad area semiconductor amplifiers and lasers can be efficiently stabilized by introducing, two-dimensional periodic modulations simultaneously on both the refractive index and the pump (gain-loss) profiles, in the transverse and longitudinal directions. The interplay between such index and gain-loss modulations efficiently suppresses the pattern forming instabilities, leading to highly stable and bright narrow output beams from such sources. We also determine the stabilization performance of the device as a function of pump current and linewidth enhancement facto…
We investigate both theoretically and experimentally the stochastic switching between two counter-propagating lasing modes of a semiconductor ring laser. Experimentally, the residence time distribution cannot be described by a simple one parameter Arrhenius exponential law and reveals the presence of two different mode-hop scenarios with distinct time scales. In order to elucidate the origin of these two time scales, we propose a topological approach based on a two-dimensional dynamical system.
We presented a detailed experimental study on lasing in GaAs microstadium with various shapes. Unlike most deformed microcavities, the lasing threshold varies non-monotonically with the major-to-minor-axis ratio of the stadium. Under spatially uniform optical pumping, the first lasing mode corresponds to a high-quality scar mode consisting of several unstable periodic orbits. By tuning the shape of GaAs stadium, we are able to minimize the lasing threshold. This work demonstrates the possibility of controlling chaotic microcavity laser.
In the present article we investigate optical near fields in semiconductor lasers. We perform finite element simulations for two different laser types, namely a super large optical waveguide (SLOW) laser, which is an edge emitter, and a vertical cavity surface emitting laser (VCSEL). We give the mathematical formulation of the different eigenvalue problems that arise for our examples and explain their numerical solution with the finite element method. Thereby, we also comment on the usage of transparent boundary conditions, which have to be applied to respect the exterior environment, e.g., th…
We report detailed measurements of the pump-current dependency of the self-pulsating frequency of semiconductor CD lasers. A distinct kink in this dependence is found and explained using rate-equation model. The kink denotes a transition between a region where the self-pulsations are weakly sustained relaxation oscillations and a region where Q-switching takes place. Simulations show that spontaneous emission noise plays a crucial role for the cross-over.
We experimentally and theoretically study the characteristics of semiconductor ring lasers bidirectionally coupled by a single bus waveguide. This configuration has, e.g., been suggested for use as an optical memory and as an optical neural network motif. The main results are that the coupling can destabilize the state in which both rings lase in the same direction, and it brings to life a state with equal powers at both outputs. These are both undesirable for optical memory operation. Although the coupling between the rings is bidirectional, the destabilization occurs due to behavior similar …
We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in laser…
A detailed experimental study of antiphase dynamics in a two-mode semiconductor laser with optical injection is presented. The device is a specially designed Fabry-Perot laser that supports two primary modes with a THz frequency spacing. Injection in one of the primary modes of the device leads to a rich variety of single and two-mode dynamical scenarios, which are reproduced with remarkable accuracy by a four dimensional rate equation model. Numerical bifurcation analysis reveals the importance of torus bifurcations in mediating transitions to antiphase dynamics and of saddle-node of limit cy…
Semiconductor ring lasers are miniaturized devices that operate on clockwise and counterclockwise modes. These modes are not coupled in the absence of intracavity reflectors, which prevents the formation of a standing wave in the cavity and, consequently, of a population inversion grating. This should inhibit the onset of multimode emission driven by spatial hole burning. Here we show that, despite this notion, ring quantum cascade lasers inherently operate in phase-locked multimode states, that switch on and off as the pumping level is progressively increased. By rewriting the master equation…
We report the first experimental observation of multi-stable states in a single-longitudinal mode semiconductor ring laser. We show how the operation of the device can be steered to either monostable, bistable or multi-stable dynamical regimes in a controlled way. We observe that the dynamical regimes are organized in well reproducible sequences that match the bifurcation diagrams of a two-dimensional model. By analyzing the phase space in this model, we predict how the stochastic transitions between multi-stable states take place and confirm it experimentally.
We analyze theoretically and experimentally the influence of current noise on the longitudinal mode hopping dynamics of a bulk semiconductor laser. It is shown that the mean residence times on each mode have different sensitivity to external noise added to the bias current. In particular, an increase of the noise level enhances the residence time on the longitudinal mode that dominates at low current, evidencing the multiplicative nature of the stochastic process. A two-mode rate equation model for semiconductor laser is able to reproduce the experimental findings. Under a suitable separation …
We propose in this communication an experimental study of the relaxation oscillations behavior in mode-locked lasers. The semiconductor self-pulsating laser diode is composed by two gain sections, without saturable absorber. It is made of bulk structure and designed for optical telecommunication applications. This specific device allows two different regimes of optical modulation: the first one corresponds to the resonance of the relaxation oscillations and the second one, to the mode-locking regime at FSR value. This singular behavior leads us to characterize the self-pulsations which are coe…
We design and fabricate an on-chip laser source that produces a directional beam with low spatial coherence. The lasing modes are based on the axial orbit in a stable cavity and have good directionality. To reduce the spatial coherence of emission, the number of transverse lasing modes is maximized by fine-tuning the cavity geometry. Decoherence is reached in a few nanoseconds. Such rapid decoherence will facilitate applications in ultrafast speckle-free full-field imaging.
The wavelength switching dynamics of two-colour semiconductor lasers with optical injection and feedback are presented. These devices incorporate slotted regions etched into the laser ridge waveguide for tailoring the output spectrum. Experimental measurements are presented demonstrating that optical injection in one or both modes of these devices can induce wavelength bistability. Measured switching dynamics with modulated optical injection are shown to be in excellent agreement with numerical simulations based on a simple rate equation model. We also demonstrate experimentally that time-dela…
Driven by narrow-linewidth bench-top lasers, coherent optical systems spanning optical communications, metrology and sensing provide unrivalled performance. To transfer these capabilities from the laboratory to the real world, a key missing ingredient is a mass-produced integrated laser with superior coherence. Here, we bridge conventional semiconductor lasers and coherent optical systems using CMOS-foundry-fabricated microresonators with record high $Q$ factor over 260 million and finesse over 42,000. Five orders-of-magnitude noise reduction in the pump laser is demonstrated, and for the firs…
