Investigation of noise correlations in the phase-locked class-A VECSEL array.

We theoretically and experimentally study the noise correlations in an array of lasers based on a VECSEL (Vertical External Cavity Surface Emitting Laser) architecture. The array of two or three lasers is created inside a planar degenerate cavity with a mask placed in a self-imaging position. Injection from each laser to its neighbors is created by diffraction, which creates a controllable complex coupling coefficient. The noise correlations between the different modes are observed to be dramatically different when the lasers are phase-locked or unlocked. These results are well explained by a rate equation model that takes into account the class-A dynamics of the lasers. This model permits the isolatation of the influence of the complex coupling coefficients and of the Henry α-factor on the noise behavior of the laser array.

Non-linear dynamics of multimode semiconductor lasers: dispersion-based phase instability and route to single-frequency operation.

Emission dynamics of a multimode broadband interband semiconductor laser have been investigated experimentally and theoretically. Non-linear dynamics of a III-V semiconductor quantum well surface-emitting laser reveal the existence of a modulational instability, observed in the anomalous dispersion regime. An additional unstable region arises in the normal dispersion regime, owing to carrier dynamics, and has no analogy in systems with fast gain recovery. The interplay between cavity dispersion and phase sensitive non-linearities is shown to affect the character of laser emission with phase turbulence, leading to regular self-excited oscillations of mode intensity, self-mode locking, and single-frequency emission stabilized by spectral symmetry breaking. Such physical behavior is a general phenomenon for any laser with a slow gain medium relative to the round trip time, in the absence of spatial inhomogeneities.

Merging and disconnecting resonance tongues in a pulsing excitable microlaser with delayed optical feedback.

Excitability, encountered in numerous fields from biology to neurosciences and optics, is a general phenomenon characterized by an all-or-none response of a system to an external perturbation of a given strength. When subject to delayed feedback, excitable systems can sustain multistable pulsing regimes, which are either regular or irregular time sequences of pulses reappearing every delay time. Here, we investigate an excitable microlaser subject to delayed optical feedback and study the emergence of complex pulsing dynamics, including periodic, quasiperiodic, and irregular pulsing regimes. This work is motivated by experimental observations showing these different types of pulsing dynamics. A suitable mathematical model, written as a system of delay differential equations, is investigated through an in-depth bifurcation analysis. We demonstrate that resonance tongues play a key role in the emergence of complex dynamics, including non-equidistant periodic pulsing solutions and chaotic pulsing. The structure of resonance tongues is shown to depend very sensitively on the pump parameter. Successive saddle transitions of bounding saddle-node bifurcations constitute a merging process that results in unexpectedly large regions of locked dynamics, which subsequently disconnect from the relevant torus bifurcation curve; the existence of such unconnected regions of periodic pulsing is in excellent agreement with experimental observations. As we show, the transition to unconnected resonance regions is due to a general mechanism: the interaction of resonance tongues locally at an extremum of the rotation number on a torus bifurcation curve. We present and illustrate the two generic cases of disconnecting and disappearing resonance tongues. Moreover, we show how a pair of a maximum and a minimum of the rotation number appears naturally when two curves of torus bifurcation undergo a saddle transition (where they connect differently).

Metamaterial engineering for optimized photon absorption in unipolar quantum devices.

Metamaterials have played a major role in the development of optoelectronic devices due to their capability of coupling free-space radiation with active materials at the nanometer scale. In particular, unipolar photodetectors display highly improved performances when implemented into patch-antenna arrays. We study light-coupling and absorption in patch-antenna metamaterials by combining an experimental investigation, an analytical approach based on coupled mode theory and numerical simulations in order to understand how the geometrical parameters influence the electromagnetic energy transfer from the free-space to the active material. Our findings are applied to the design of optimized unipolar photodetectors with improved quantum efficiency.

Semiconductor disk laser in bi-frequency operation by laser ablation micromachining of a laser mirror.

We present bi-frequency continuous wave oscillation in a semiconductor disk laser through direct writing of loss-inducing patterns onto an intra-cavity high reflector mirror. The laser is a Vertical External Cavity Surface Emitting Laser which is optically pumped by up to 1.1 W of 808 nm light from a fibre coupled multi-mode diode laser, and oscillates on two Hermite-Gaussian spatial modes simultaneously, achieving wavelength separations between 0.2 nm and 5 nm around 995 nm. We use a Digital Micromirror Device (DMD) enabled laser ablation system to define spatially specific loss regions on a laser mirror by machining away the Bragg layers from the mirror surface. The ablated pattern is comprised of two orthogonal lines with the centermost region undamaged, and is positioned in the laser cavity so as to interact with the lasing mode, thereby promoting the simultaneous oscillation of the fundamental and a higher order spatial mode. We demonstrate bi-frequency oscillation over a range of mask gap sizes and pump powers.

Gallium Phosphide as a Piezoelectric Platform for Quantum Optomechanics.

Recent years have seen extraordinary progress in creating quantum states of mechanical oscillators, leading to great interest in potential applications for such systems in both fundamental as well as applied quantum science. One example is the use of these devices as transducers between otherwise disparate quantum systems. In this regard, a promising approach is to build integrated piezoelectric optomechanical devices that are then coupled to microwave circuits. Optical absorption, low quality factors, and other challenges have up to now prevented operation in the quantum regime, however. Here, we design and characterize such a piezoelectric optomechanical device fabricated from gallium phosphide in which a 2.9 GHz mechanical mode is coupled to a high quality factor optical resonator in the telecom band. The large electronic band gap and the resulting low optical absorption of this new material, on par with devices fabricated from silicon, allows us to demonstrate quantum behavior of the structure. This not only opens the way for realizing noise-free quantum transduction between microwaves and optics, but in principle also from various color centers with optical transitions in the near visible to the telecom band.

Pulse train interaction and control in a microcavity laser with delayed optical feedback.

We report experimental and theoretical results on the pulse train dynamics in an excitable semiconductor microcavity laser with an integrated saturable absorber and delayed optical feedback. We show how short optical control pulses can trigger, erase, or retime regenerative pulse trains in the external cavity. Both repulsive and attractive interactions between pulses are observed, and are explained in terms of the internal dynamics of the carriers. A bifurcation analysis of a model consisting of a system of nonlinear delay differential equations shows that arbitrary sequences of coexisting pulse trains are very long transients towards weakly stable periodic solutions with equidistant pulses in the external cavity.

High-power tunable low-noise coherent source at 1.06 µm based on a surface-emitting semiconductor laser.

Exploiting III-V semiconductor technologies, vertical external-cavity surface-emitting laser (VECSEL) technology has been identified for years as a good candidate to develop lasers with high power, large coherence, and broad tunability. Combined with fiber amplification technology, tunable single-frequency lasers can be flexibly boosted to a power level of several tens of watts. Here, we demonstrate a high-power, single-frequency, and broadly tunable laser based on VECSEL technology. This device emits in the near-infrared around 1.06 µm and exhibits high output power (>100 mW) with a low-divergence diffraction-limited TEM00 beam. It also features a narrow free-running linewidth of <400 kHz with high spectral purity (side mode suppression ratio >55 dB) and continuous broadband tunability greater than 250 GHz (<15 V piezo voltage, 6 kHz cutoff frequency) with a total tunable range up to 3 THz. In addition, a compact design without any movable intracavity elements offers a robust single-frequency regime. Through fiber amplification, a tunable single-frequency laser is achieved at an output power of 50 W covering the wavelength range from 1057 to 1066 nm. Excess intensity noise brought on by the amplification stage is in good agreement with a theoretical model. A low relative intensity noise value of -145 dBc/Hz is obtained at 1 MHz, and we reach the shot-noise limit above 200 MHz.

Coherent continuous-wave dual-frequency high-Q external-cavity semiconductor laser for GHz-THz applications.

We report a continuous-wave highly-coherent and tunable dual-frequency laser emitting at two frequencies separated by 30 GHz to 3 THz, based on compact III-V diode-pumped quantum-well surface-emitting semiconductor laser technology. The concept is based on the stable simultaneous operation of two Laguerre-Gauss transverse modes in a single-axis short cavity, using an integrated sub-wavelength-thick metallic mask. Simultaneous operation is demonstrated theoretically and experimentally by recording intensity noises and beat frequency, and time-resolved optical spectra. We demonstrated a >80 mW output power, diffraction-limited beam, narrow linewidth of <300 kHz, linear polarization state (>45 dB), and low intensity noise class-A dynamics of <0.3% rms, thus opening the path to a compact low-cost coherent GHz to THz source development.

High Q factor InP photonic crystal nanobeam cavities on silicon wire waveguides.

High-quality (Q) factor indium phosphide (InP)-based 1D photonic crystal nanobeam cavities are fabricated on silicon on insulator waveguides. Through the optimization of the fabrication process, the intrinsic Q factor of these fully encapsulated nanocavities is demonstrated to attain values higher than 100,000. Experimental and numerical investigations are carried out on the impact, on the Q factor, of the strength of the evanescent wave coupling between the cavity and the waveguide. We reveal that this coupling can result in a modification of the electromagnetic field distribution in the resonant mode, which gives rise up to a factor 4 reduction in the intrinsic Q factor for the structures under study.