Modeling and simulations of beam stabilization in edge-emitting broad area semiconductor devices

A 2+1 dimensional PDE traveling wave model describing spatial-lateral dynamics of edge-emitting broad area semiconductor devices is considered. A numerical scheme based on a split-step Fourier method is presented and implemented on a parallel compute cluster. Simulations of the model equations are used for optimizing of existing devices with respect to the emitted beam quality, as well as for creating and testing of novel device design concept

Modeling and simulations of beam stabilization in edge-emitting broad area semiconductor devices

A 2+1 dimensional PDE traveling wave model describing spatial-lateral dynamics of edge-emitting broad area semiconductor devices is considered. A numerical scheme based on a split-step Fourier method is presented and implemented on a parallel compute cluster. Simulations of the model equations are used for optimizing of existing devices with respect to the emitted beam quality, as well as for creating and testing of novel device design concept

Stabilization of class-B broad-area lasers emission by external optical injection

We theoretically examine the effect of external optical injection on the spatio-temporal dynamics of class-B broad-area lasers. We demonstrate that optical injection can efficiently stabilize the intrinsic transverse instabilities in such lasers associated with both the boundaries of the pumping area and with the bulk nonlinearities of the active medium. Stabilizing action of optical injection is shown to be closely related to the suppression of inherent relaxation oscillations behavior.Comment: 8 pages, 7 figure

Modeling and efficient simulations of broad-area edge-emitting semiconductor lasers and amplifiers

We present a (2+1)-dimensional partial differential equation model for spatial-lateral dynamics of edge-emitting broad-area semiconductor devices and several extensions of this model describing different physical effects. MPI-based parallelization of the resulting middlesize numerical problem is implemented and tested on the blade cluster and separate multi-core computers at the Weierstrass Institute in Berlin. It was found, that an application of 25-30 parallel processes on all considered platforms was guaranteeing a nearly optimal performance of the algorithm with the speedup around 20-25 and the efficiency of 0.7-0.8. It was also shown, that a simultaneous usage of several in-house available multi-core computers allows a further increase of the speedup without a significant loss of the efficiency. Finally, an importance of the considered problem and the efficient numerical simulations of this problem were illustrated by a few examples occurring in real world applications

Modeling and efficient simulations of broad-area edge-emitting semiconductor lasers and amplifiers

We present a (2+1)-dimensional partial differential equation model for spatial-lateral dynamics of edge-emitting broad-area semiconductor devices and several extensions of this model describing different physical effects. MPI-based parallelization of the resulting middlesize numerical problem is implemented and tested on the blade cluster and separate multi-core computers at the Weierstrass Institute in Berlin. It was found, that an application of 25-30 parallel processes on all considered platforms was guaranteeing a nearly optimal performance of the algorithm with the speedup around 20-25 and the efficiency of 0.7-0.8. It was also shown, that a simultaneous usage of several in-house available multi-core computers allows a further increase of the speedup without a significant loss of the efficiency. Finally, an importance of the considered problem and the efficient numerical simulations of this problem were illustrated by a few examples occurring in real world applications

Chirped photonic crystal for spatially filtered optical feedback to a broad-area laser

We derive and analyze an efficient model for reinjection of spatially filtered optical feedback from an external resonator to a broad area, edge emitting semiconductor laser diode. Spatial filtering is achieved by a chirped photonic crystal, with variable periodicity along the optical axis and negligible resonant backscattering. The optimal chirp is obtained from a genetic algorithm, which yields solutions that are robust against perturbations. Extensive numerical simulations of the composite system with our optoelectronic solver indicate that spatially filtered reinjection enhances lower-order transversal optical modes in the laser diode and, consequently, improves the spatial beam quality

Chirped photonic crystal for spatially filtered optical feedback to a broad-area laser

We derive and analyze an efficient model for reinjection of spatially filtered optical feedback from an external resonator to a broad area, edge emitting semiconductor laser diode. Spatial filtering is achieved by a chirped photonic crystal, with variable periodicity along the optical axis and negligible resonant backscattering. The optimal chirp is obtained from a genetic algorithm, which yields solutions that are robust against perturbations. Extensive numerical simulations of the composite system with our optoelectronic solver indicate that spatially filtered reinjection enhances lower-order transversal optical modes in the laser diode and, consequently, improves the spatial beam quality

Smart control of light in edge-emitting lasers

Tesi en modalitat de compendi de publicacions, amb diferents seccions retallades per drets dels editorsThe invention of the laser triggered the study of light-matter interactions. In turn, the advent of artificial structured materials on micro- and nanometer scales has become a fruitful playground to tailor the propagation and generation of light, even in exotic or counterintuitive ways, uncovering novel physical phenomena. In this thesis, we precisely propose using recently discovered properties of artificial photonic materials, and new schemes, to control the spatiotemporal dynamics of broad area semiconductor lasers and improve their performance. Semiconductor lasers are replacing other laser sources due to their efficiency, compactness and affordable prices, however suffering from a major drawback. The quality of the emitted beam intrinsically deteriorates when power increases, if the aperture of the laser is very broad as compared to wavelength. The highly multimode and unstable emission limits possible applications of these lasers. Although different mechanisms have been proposed to save this obstacle, obtaining a stable and bright emission remains a longstanding open question. This thesis aims at contributing to this goal without compromising their compact design, and to the new field of non-Hermitian Photonics providing new insights into the control of wave dynamics in artificial complex media. Indeed, the physics of open-dissipative, non-Hermitian systems offers new possibilities to utilize the gain and loss for steering optical processes, and is beyond the recent focus on non-Hermitian Photonics. As initially demonstrated in the frame of Quantum Mechanics, systems with gain and losses may still present real eigenvalues of the Hamiltonian (energy) as the purely conservative ones, yet holding other unexpected physical behaviors, derived from an asymmetric coupling between modes. In particular, this was first observed in systems invariant under parity (P-) and time (T-) symmetry ¿ referred as PT-symmetric ¿. Optical systems with complex permittivity are flexible and achievable classical analogs of such quantum systems to realize and explore these effects. As a first step, we propose to use a chirped modulation of the refractive index (chirped photonic crystal) for intracavity filtering the multimode emission of EELs. To numerically assess the filtering performance, we developed a full (2+1)-dimensional spatio-temporal model, including both transverse and longitudinal dimensions plus time, for the evolution of the electric field and carriers. The good agreement between predictions with actual experimental results demonstrates the proposal while validating the model which is used throughout the thesis, with corresponding modifications. We then analyze the effect of intrinsically imposing in phase refractive index and gain modulations within the semiconductor laser, and use the interplay between real and imaginary parts of the non-Hermitic potential to achieve spatial and temporal stabilization. Taking one step further, we propose to divide the EEL cavity into two mirror-symmetric half-spaces, both holding PT-symmetry but with opposite mode coupling. With this geometry, we expect to obtain a two-fold benefit: on the one hand, achieving a spatial-temporal stabilization of the laser, and on the other, localizing the generated field along the symmetry axis. We numerically demonstrate regimes of simultaneous localization and stabilization leading to an enhanced output and improved beam quality. Finally, while thinner lasers show a more stable new temporal and synchronization instabilities arise in EELS arrays (bars) from the coupling between neighboring lasers, leading again to irregular spatiotemporal behaviors. We show that the proposed mirror symmetric non-Hermitian configuration may be extended to couple individual EELs in the array, by a lateral shift between the pump and index profiles. In all cases, the obtained localized and stable output beam may facilitate a direct coupling of the emitted beam to optical fibers.La invenció del làser va representar el tret de sortida per nombrosos estudis de la interacció entre la llum i la matèria. A banda, el desenvolupament de nous materials fotònics artificials en escales micro i nanomètriques ha esdevingut un camp fructífer per al control de la propagació i generació de la llum, fins i tot de maneres exòtiques o contra intuïtives, revelant nous fenòmens físics. En aquesta tesi proposem, precisament, utilitzar nous materials fotònics artificials i nous esquemes per controlar la dinàmica espai-temporal dels làsers de semiconductor d'apertura ampla, per millorar-ne les propietats. Els làsers de semiconductor estan reemplaçant altres fonts de llum làser gràcies a la seva eficiència, format compacte i preu assequible. Malgrat tot, pateixen un gran inconvenient: el deteriorament del feix emès en augmentar la potència, especialment si l'amplada del làser és molt gran respecte la longitud d'ona. Quan l'emissió esdevé altament multimode i inestable en limita les possibles aplicacions. Encara que s'han proposat diferents mecanismes per superar aquest problema, aconseguir una emissió estable sense comprometre'n el format compacte, és encara una qüestió oberta. Aquesta tesi té com a objectiu contribuir a la millora dels làsers de semiconductor i a l'estudi del control de la dinàmica dels làsers mitjançant el nou camp de la fotònica no hermítica. De fet, la física dels sistemes oberts no Hermítics ofereix noves possibilitats per utilitzar la permitivitat complexa per dominar processos òptics i és la causa del recent interès en la fotònica no hermitiana. Primer, es va demostrar en el marc de la Mecànica Quàntica que els sistemes oberts o no Hermítics, tot i tenir guanys o pèrdues poden presentar autovalors reals del Hamiltonià (valors constants de l'energia) i altres comportaments físics inesperats, derivats d'acoblaments asimètrics entre modes. Efecte observat inicialment en sistemes invariants sota la paritat (P-) i la simetria de temps (T-), anomenats PT-simètrics. Els sistemes òptics amb permitivitat complexa són anàlegs clàssics, flexibles i assequibles d’aquests sistemes quàntics per realitzar i explorar aquests nous efectes. Primer, proposem fer servir una modulació de l’índex de refracció per al filtrat, intacavitat, de l'emissió multimode d'amplificadors i làsers de semiconductor. Per l'anàlisi numèrica desenvolupem un model espai-temporal complet, que inclou dues dimensions espacials, transversal i longitudinal, més l'evolució temporal del camp elèctric i dels portadors. Aquest model s'utilitza al llarg de tota la tesis amb les modificacions corresponents i és contrastat també experimentalment. A continuació, analitzem l'efecte d'imposar modulacions intrínseques de l’índex de refracció i el guany, en fase i, dins del làser de semiconductor. Gràcies a la interacció entre parts reals i imaginàries del potencial no hermític s’aconsegueix una estabilització espacial i temporal. Fent un pas més, dividim la cavitat làser en dos espais PT-simètrics (simetria de mirall) amb un acoblament en sentit oposat. Amb aquesta geometria, esperem obtenir un doble benefici: d'una banda, aconseguir una estabilització espacial-temporal del làser, i per una altra banda, localitzar el camp generat en l'eix de simetria. Es demostra numèricament règims de localització i d'estabilització simultànies, augmentant la potència emesa tot millorant la qualitat dels feix. Finalment, tot i que els làsers més estrets mostren una emissió més estable, els làsers propers s’acoblen quan formen part d'una matriu. Demostrem que l'acoblament asimètric també pot ser utilitzat en barres de làsers de semiconductor per estabilitzar-los temporalment i concentrar-ne l’emissió. L'acoblament asimètric es produeix mitjançant un desplaçament lateral entre el bombeig i l'índex de refracció. En tots els casos, el feix de sortida localitzat i estable obtingut pot facilitar un acoblament directe del feix emès a les fibres òptiques.Postprint (published version

Spatial field control of broad area semiconductor lasers with integrated grating couplers

In this research, a method of designing a grating outcoupler to obtain the desired 2D-intensity profile and improved field distribution of the optical beam emitted by a grating coupled surface emitting laser is presented. The method is based on variation of the periodicity, duty cycle, and the groove tilt angle of the grating. Grating design involves numerical analysis of the optical field propagated through the grating, by applying the Rigorous Coupled Wave Approach method. Experimental evaluation of the designed grating components was done by fabrication and testing the broad area semiconductor lasers with the monolithically integrated grating outcouplers. Another grating design is presented that provides the spreading of a single optical output into multi-beams at different outcoupling angles in the emitting plane. Using field distribution presentation, an approach to provide uniform optical intensity profile from the grating outcoupler based on varying duty cycle is described. Furthermore, this work presents experimental evaluation of 1D, and 2D (8x8) square, arrays of phase-locked surface-emitters including semiconductor optical amplifiers spaced by grating outcouplers. The phase-locked multi-emitter design was based on the master oscillator power amplifier (MOPA) array approach. As the MO for the 1D array we used a monolithically integrated grating coupled laser with wavelength stabilization and a fiber coupled external laser source was used for the 2D array. Mutual coherence was experimentally evaluated by interference investigation and the obtained results were compared to numerical modeling