State-of-the-art vertical-cavity surface-emitting laser (VCSEL) based optical interconnects for application in high performance computers and data centers are reviewed. Record energy-efficient data transmission is demonstrated with 850 nm single-mode VCSELs for multimode optical fiber lengths up to 1 km at bit rates up to 25 Gb/s. Total power consumption of less than 100 fJ/bit is demonstrated for VCSELs for the first time. Extremely temperature stable 980-nm VCSELs show lasing up to 200 °C. Error-free 44 Gb/s operation at room temperature and 38 Gb/s up to 85 °C is achieved with these devices. We present record-high bit rates in a wide temperature range of more than 160 °C. Record energy-efficient data-transmission beyond 30 Gb/s is achieved at 25 °C for this wavelength range. In view of the high speed and advanced temperature stability we suggest long wavelength VCSELs for energy-efficient short and very short-distance optical interconnects for future high performance computers.

The latest results on InP based 1550 nm short-cavity VCSELs will be presented. Important design criteria will be discussed in order to manufacture high-power, high-speed or widely tunable VCSEL devices, respectively.

In recent years, optical manipulation has gained increasing interest, especially in combination with microfluidics. This combination offers promising tools for a fast and cost-effective sample analysis and manipulation. The contamination-free handling of micrometer-sized particles without any mechanical contact is an attractive tool for biology and medicine. VCSELs (vertical-cavity surface-emitting lasers) are an excellent choice for the trapping lasers, offering the opportunity of parallel particle manipulation by using two-dimensional VCSEL arrays, and of miniaturization by means of integration. In this paper, we present two novel concepts for the realization of the so-called integrated optical trap, resembling a strongly miniaturized version of the typically bulky setup of an optical trap. For this purpose, AlGaAs-GaAs-based VCSEL arrays with a very small device pitch were fabricated. We show the realization of integration-ready particle manipulation devices, both with top-emitting and with bottom-emitting densely packed VCSEL arrays. The smallest pitch of 18 μm is achieved with bottom-emitting VCSEL arrays, having mesa diameters of only 16 μm.

In the current work, we show a detailed analysis of the transverse beam profile and polarization characteristics of devices with one and three oxide apertures. A Gaussian transverse beam profile is achieved with an oxide aperture diameter of less than 6 μm. The laser light is linearly polarized with a high degree of polarization (> 97 %) in the complete current range. The stable polarization direction can be attributed to ordering effects ocurring during epitaxial growth of the GaInP material system and a reduction in crystal symmetry. Different oxide aperture diameters can be implemented in one device due to high oxidation selectivity of the Al_xGa_1-xAs layer depending on aluminum content. These deep oxidation layers lead to a reduction of the parasitic capacitance, while beam profile and polarization characteristics are not affected.

A novel type of all-optical pressure sensor has been developed. In this context, a vertical-cavity surface-emitting laser (VCSEL) has been modified in its design to provide simultaneous light emission from both facets. One beam serves as measuring signal while the other establishes a reference; and both paths lie on the same optical axis. The VCSELs are based on active InGaAs quantum wells for laser output close to 960 nm wavelength where the GaAs substrate is transparent. From both top and bottom facet, single-polarization and single-mode beams are observed, having a power ratio of 1:2 to 1:4. In this paper we give insight into this new sensing application for VCSELs, describe the laser fabrication and the static operation characteristics as well as the noise properties which have paramount importance for high performance of the sensor. With regard to the sensor application in acoustics, the focus of the noise measurements is put on the low-frequency, i.e. kHz, regime. While laser diode noise performance is readily available for the MHz to GHz frequency range, only very limited data exists in the Hz to kHz domain. The relative intensity noise of both beams is measured and compared and the mutual correlation properties are investigated. The frequency noise is quantified.

We present a comparison of epitaxial designs for non-resonantly pumped vertical external cavity surface-emitting lasers for emission in the red spectral range around 665 nm. Here, the VECSEL chip is based on a metal-organic vapor-phase epitaxy grown (Ga_xIn_1-x)_0.5P_0.5/[(Al_xGa_1-x)_yIn_1-y]_0.5P_0.5 multi-quantum-well structure with 20 compressively-strained quantum wells. The wells are placed in packages in a separate confinement heterostructure with quaternary AlGaInP barriers and cladding layers, respectively. The active region is fabricated on a 55 λ/4 pairs Al_0.50Ga_0.50As/AlAs distributed Bragg reflector. We compare two designs with different quantum well distributions in the chip: one design which includes 4 quantum wells in 5 packages whereas the other contains 10 quantum well pairs to have a larger absorption length. Laser parameters like output power, differential efficiency and threshold pump power of the different chip designs measured in a v-shaped cavity configuration are examined. By using the 10 × 2 quantum well distribution in the chip, we could improve the absorption efficiency by nearly 40% and output power by 25% compared to the 5 × 4 design. Additionally, by introducing tensile strained quaternary barriers and cladding layers in the 5 × 4 QW design, we could compensate for the compressive strain introduced by the quantum wells. Photoluminenscence measurements of structures with different numbers of quantum well packages reveal a more homogenous quantum well growth due to the strain-compensation technique. Furthermore, with the strain compensation technique, the output power could be increased over 30% compared to our conventional structures.

We present the optimization of the carrier injection, heat flow and optical confinement aimed for single mode operation. The analyzed structure incorporates InAlGaAs quantum wells within InP cavity. The cavity is bounded by AlGaAs/GaAs DBRs The tunnel junction is responsible for carrier funneling into the active region. The air-gap etched at the interface between cavity and top DBR provides the confinement of the lateral modes. To rigorously simulate the physical phenomena taking place in the device we used multi-physical model, which comprises three-dimensional models of optical (Plane Wave Admittance Method), thermal and electrical (Finite Element Method) phenomena. We perform the exhaustive modal analysis of the 1x3, 1x4 and 2x4 VCSEL arrays. In the analysis we investigate the influence of the distance between emitters. The analysis is performed for broad range of injected currents from threshold to the rollover. As the result we illustrate the complex competition of the modes, influence of the optical confinement on structure of the modes and determine the geometrical parameters, which favor the array modes in the considered array designs.

Applications of long-wavelength (λ > 1 μm) vertical-cavity surface-emitting lasers (VCSELs) generally require close control over wavelength and polarization of the emitted light. In most cases, single mode and polarization stable lasing is desired. We report here on the detailed modal analysis of wafer-fused 1550-nm wavelength VCSELs incorporating an AlGaInAs/InP active region, a re-grown circular tunnel junction (TJ) and undoped AlGaAs/GaAs distributed Bragg reflectors (DBRs). We experimentally determined the diameter of the TJ that optimizes the output power and threshold current, finding a value between 7.0 μm and 9.5 μm depending on the temperature. Moreover, we investigated the impact of the TJ aperture diameter on the mode structure. A large batch of devices was investigated, allowing drawing conclusions on typical behavior of these devices. The measured emission spectra show that the fundamental spatial mode is split into two orthogonal polarization modes, which are spectrally separated in wavelength by δ, used as a birefringence parameter. We observed that this parameter is independent of current but depends on the particular chip, suggesting that it is caused by stress, growth inhomogeneities, or etched mesa shape. The higher order spatial modes show similar polarization doublets with a splitting also equal to δ. This suggests that the birefringence results from effects not particular to the mechanism of mode confinement. Finally, the spectral separation Δ_0;1 between the fundamental mode and the first-order transverse mode increases linearly with current, with a slope that depends only on the TJ aperture diameter. This confirms that the mode confinement is induced by the structured TJ, and possibly also by the temperature distribution induced by the current injection.

Vertical-Cavity Surface-Emitting Lasers, due to their properties, are one of the best choices for optical communication purposes. Although direct modulated VCSELs have reached error free operation at speed of 40 Gbit/s, however, their cut-off frequency is limited by the relaxation oscillation phenomenon and is not likely to be further increased. Recently, it has been suggested that properly designed Coupled Cavity VCSEL with one cavity used as a reverse-biased Electro-Optic Modulator, can be only limited by the 3 dB electrical bandwidth cut-off frequency. Therefore, it is important to develop a high-speed electrical design for such VCSELs. In this paper we first present an analysis of an electrical equivalent circuit of EOM CC-VCSEL with lumped electrodes. We base our design on record high-speed structures reported in the literature. We optimize our structure with respect to modulator cavity length, number of top and middle distributed Bragg reflectors, doping levels of layers, radii of both mesas and non-ion implantation region in the DBR as well as the contact pad area. We show that the most influencing parameters are the mesa capacitance, series resistance and polyimide capacitance. The 3 dB bandwidth is enhanced by reducing the contact pad area and modulator cavity diameter, together with increasing the modulator cavity length. Faster operation is provided by pnp structure, instead of npn - one. A realistic structure design that is theoretically able to work with a 90 GHz modulation speed is suggested. Finally we also discuss the possibility of using a design concept of a EOM CC-VCSEL based on traveling wave electrode configuration.

Studying cavity quantum electrodynamical effects is an emerging and important field of research for the understanding of the many body quantum theory as well as for the generation of a new type of efficient lasers. Here we report a dramatic change in the photon statistics of quantum dot based micropillar lasers where a finite fraction of the emission is reflected back into the microcavity after a roundtrip time τ in an external cavity, where τ greatly exceeds the coherence time. Photon bunching was observed above the threshold current where the second order autocorrelation function g(2)(τ) at zero-lag can reach values up to 3.51±0.06. The change in the photon statistics of the two non-degenerated fundamental modes were found to be correlated, indicating non-trivial interactions between both cavity modes. Furthermore the optical feedback led to revivals of the bunching signal in integer multiples of the round trip time of the external cavity and to a decrease in the coherence time of the laser. These phenomena compare well with milliwatt chaotic lasers induced by an external feedback, indicating that chaos might occur in the nanowatt lasing regime where fluctuations in the photon statistics are in the leading order.

In this contribution we investigate both experimentally and by simulations a quantum dot absorber of a two-section quantum dot laser as an intra-cavity photodiode with a focus on the photo-generated absorber current. The escape of the photo-generated ES carrier sweep-out from the absorber can be controlled by variably biasing the absorber either with a variable external resistor in resistor Self-electro-optic-effect device (resistor-SEED) configuration or by applying a reverse bias. This escape is directly observable in the absorber photocurrent. In the resistor-SEED regime where the absorber is operated in so-called photoconductive mode, a steep increase in photocurrent is observed when the ES joins the GS emission and is attributed to increased losses, as reported recently. In contrast, GS emission and a low photocurrent in the resistor-SEED regime corresponds to a large carrier occupation probability corresponding to a reduced escape. In reverse bias operation, sole ES emission is observed together with a shallow increase in photocurrent with increasing reverse bias, in analogy to the p-n photodiode characteristics. By joining both resulting photocurrent regimes, the respective contributions of carrier capture and escape in the absorber to the averaged photocurrent is identified by numerical simulations. The obtained numerical results are in excellent qualitative agreement with the experiment.

In this paper we present the development of mid-infrared GaAs/AlGaAs QCLs technology and discuss basic characteristics of lasers fabricated at the Institute of Electron Technology. We also show that reliable simulation methods which can deal with the complicated physical phenomena involved in the quantum cascade lasers operation are necessary to predict the behaviour of new structures and optimize their performance. The developed lasers show the record pulse powers of 6 W at 77 K and up to 50 mW at 300 K. This has been achieved by careful optimization of the epitaxial process and by applying a high reflectivity metallic coating to the back facet of the laser. The devices have been successfully used in prototype ammonia detection system working in ppb range.

The authors present a technique to reduce the facet reflectivity in quantum cascade lasers (QCLs) by tilted facets. In order to minimize the Fabry-Pérot resonances, the feedback from the laser facets into the cavity must be minimized. Due to intersubband selection rules, the light generated inside QCLs is TM polarized. This polarization purity in QCLs enables the reduction of the facet reflectivity through the angle of light incidence at the laser facet. We observed a maximum threshold current density when the facet is tilted 17° towards the surface normal. This is in agreement with the calculated Brewster's angle for the QCL heterostructure.

We report on detailed investigation of thermal performance of AlGaAs/GaAs quantum cascade lasers (QCL) emitting at wavelength of 9.4 ìm, with a particular emphasis on the influence of different mounting options and device geometries, which are compared in terms of their influence on the relative increase of the active region temperature. The spatially resolved thermoreflectance (TR) is used to register temperature distribution over the facet of pulse operated QCLs. The devices' thermal resistances are derived from experimental data. Thermal resistances of 15 ìm devices are the highest among the investigated device widths. By combining the experimental and numerical results, an insight into the thermal management in QCLs is gained. The thermal design focuses on optimization of heat dissipation in the device, improving the thermal behavior of QCLs. This is essential in order to increase the maximal operation temperature to further progress the applications of QCLs.

The wavelength range from 3 μm to 4 μm is of special interest for gas-sensing applications. We present systematic design optimizations of interband cascade laser (ICL) layers to reduce the dissipated threshold power at room temperature with the aim to facilitate high performance room temperature operation in this wavelength range. Furthermore, we show that slight variations of the active region design enable us to easily obtain emission in this target wavelength range and beyond. Based on the epitaxial material grown, ridge waveguide lasers and distributed feedback interband cascade lasers with vertical sidewall gratings are fabricated. We obtain single mode emitting devices operating in continuous wave mode at room temperature. The devices exhibit side mode suppression ratios up to ~25 dB and typical fine tuning rates of 0.09 nm/mA and 0.3 nm/K. Therewith, the presented devices are ideally suitable for highly sensitive gas sensing of hydrocarbons.

One of the failure mechanisms preventing diode lasers in reaching ultra high optical output powers is the catastrophic optical damage (COD). It is a sudden degradation mechanism which impairs the device functionality completely. COD is caused by a positive feedback loop of absorbing laser light and increasing temperature at a small portion of the active material, leading to a thermal runaway on a nanosecond timescale. We analyze commercial gain-guided AlGaAs/GaAs quantum well broad area diode lasers in single pulse step tests. The near-field emission on the way to and at the COD is resolved on a picosecond time scale by a streak-camera combined with a microscope. In the final phase of the step tests the COD is occurring at ~50 times threshold current. The growth of the COD defect site is monitored and defect propagation velocities between 30 and 190 μm/μs are determined. The final shape of the damage is verified by opening the device and taking a micro-photoluminescence map of the active layer.

The spatial "rocking" is a dynamical effect converting a phase-invariant oscillatory system into a phase-bistable one, where the averaged phase of the system locks to one of two values differing by π. In this paper we consider theoretically the spatial rocking of irregularly operating edge emitting broad area semiconductor laser. The stabilization of the laser is realized by the injection of an optical field formed by two, coherently interfering at some angle, beams. We demonstrate that this stabilization is preserved if one or both injected beams are weakly focused, and analyze a corresponding focusing of the emitted field.

We report on discrete mode laser diodes designed for narrow linewidth emission and demonstrate a linewidth as low as 96 kHz. A discrete mode laser diode with a minimum linewidth of 189 kHz was also characterised in a coherent transmission setup using quadrature phase shift keying modulation. Similar performance to an external cavity laser is demonstrated at baud rates as low as 2.5 Gbaud. The effect of increased linewidth on transmission performance is also investigated using lasers with linewidths up to 1.5 MHz.

Here we present a device concept utilizing GaSb-based laterally-coupled DFB-lasers. Fabrication procedure to define the ridge waveguide and the grating makes use of nanoimprint lithography. This technology addresses issues related to mass fabrication and cost of the DFB-lasers. We demonstrate state-of-the-art devices on a range of wavelengths around 2 μm. These lasers exhibit single-mode operation with a maximum side-mode suppression ratio of more than 55 dB and high output power of ~25 mW.

This paper presents the development and narrow-linewidth characteristics of an optically-pumped vertical external-cavity surface-emitting laser emitting light near 1120 nm. The laser development is motivated by the need to achieve narrowlinewidth, frequency-stable laser emission near 280 nm for cooling of Mg⁺ ions. The laser is capable of emitting ~0.8 W at 1118.542 nm in a less than 300 kHz linewidth.

We present a non-resonantly pumped vertical external cavity surface-emitting laser in a compact v-shaped cavity configuration. By using intra-cavity frequency doubling in combination with a birefringent filter, a tunable high power UV laser source with an emission wavelength around 335 nm is realized. The fundamental red laser emission is based on a metal-organic vapor-phase epitaxy grown (Ga_xIn_1-x)_0.5P_0.5/[(Al_xGa_1-x)_yIn_1-y]_0.5P_0.5 (abbr. GaInP/AlGaInP) multi-quantum-well structure. Five quantum well packages with four compressively strained quantum wells are placed in a separate confinement heterostructure in a resonant periodic gain design in strain-compensating quaternary AlGaInP barriers and cladding layers, respectively. The 3 λ cavity is fabricated on a 55 λ/4 pairs Al_0.45Ga_0.55As/AlAs distributed Bragg reflector. By using a beta barium borate non-linear crystal for second harmonic generation, output powers up to 150mWat a wavelength of 335 nm could be realized. Tuning of the laser resonance was accomplished with a birefringent filter. A tuning of 9 nm in the UV will be shown.

We compared the performance of DQW and TQW edge-emitters in a passively mode-locked 1GHz MOPA system at 1075 nm wavelength. Passive mode-locking is induced by applying a reverse DC voltage to the absorber section. The average power is increased up to 0.9Wby a single-stripe pre-amplifier and a tapered amplifier. After compensation of the quadratic chirp in a grating compressor we achieved a pulse duration of 342 fs. We found that the oscillator gain current and the absorber bias voltage have significant impact on the pulse duration. Both parameters were used to optimize the MOPA system with respect to the shortest pulse length after compression.

When a semiconductor laser is subject to an incoming optical carrier, equivalently an external optical injection, it can enter nonlinear period-one dynamics through Hopf bifurcation due to the radical modification in field-carrier coupling of the injected laser which results from the dynamical competition between injection-imposed laser oscillation and injection-shifted cavity resonance. Equally-separated spectral components appear, of which intensity and frequency depend strongly on the injection level and frequency. This suggests that a dynamical amplitude or frequency variation of the incoming optical signal, such as amplitude-shift keying (ASK) or frequency-shift keying (FSK), respectively, would lead to corresponding dynamical variation in amplitude and frequency of each spectral component. Therefore, by properly selecting the optical frequency of the output optical carrier and by minimizing the residual ASK and FSK modulation, both ASK-to-FSK and FSK-to-ASK conversions can be achieved, where bit-error ratio down to 10^-12 is achieved with a slight power penalty. Only a typical semiconductor laser is necessary as the key conversion unit. In addition, frequency shifts of the optical carrier can also be achieved, which allows a simultaneous frequency conversion of the optical carrier if required.

We investigate the dynamical properties of broad area lasers with a V-shaped external cavity formed by two off-axis feedback mirrors that allow to select a single transverse mode with transversely modulated intensity distribution. We derive and study a reduced model of a multi-stripe array. Bifurcation analysis of this system reveals the existence of single mode and multimode instabilities leading to a periodic and irregular time dependence of the output intensity. We observe within reduced model the multimode instability leading to a periodic regime, where the fields traveling in the opposite directions oscillate in antiphase. This result is in agreement with that obtained with the help of 2+1 dimensional traveling wave model.

Optical chaos is easily observed in a laser diode with either conventional (COF) or phase-conjugate optical feedback (PCF). We focus here on the so-called chaotic low-frequency fluctuations (LFF) where the laser exhibits slow power dropouts together with fast picosecond dynamics. We report here on a systematic study of LFF in a laser diode when subjected to PCF for which the bifurcations leading to those LFF remain to be elucidated. Qualitatively different dynamics are observed when increasing the phase-conjugate mirror (PCM) reflectivity or the injection current level. A combination of spectral and temporal measurements unveils the transition to LFF dynamics. The statistical properties of the time between power dropouts -mean dropout time and standard deviation- are studied as a function of the laser and feedback parameters and show that the laser may undergo what we call here a deterministic coherence resonance for a particular value of the PCF ratio. Interestingly, the phase conjugation build-up time here in SPS crystal is around 3 ms, hence is three orders of magnitude faster than what has been reported in previous dynamical studies of chaos in lasers with PCF using BaTiO₃ photorefractive crystals. How the phase conjugation time-scale impacts on the laser dynamics remains an interesting question to which we contribute here.

An electro-optical system with a delay loop based on semiconductor lasers is investigated for information processing by performing numerical simulations. This system can replace a complex network of many nonlinear elements for the implementation of Reservoir Computing. We show that a single nonlinear-delay dynamical system has the basic properties to perform as reservoir: short-term memory and separation property. The computing performance of this system is evaluated for two prediction tasks: Lorenz chaotic time series and nonlinear auto-regressive moving average (NARMA) model. We sweep the parameters of the system to find the best performance. The results achieved for the Lorenz and the NARMA-10 tasks are comparable to those obtained by other machine learning methods.

We numerically and analytically study the dynamics of two semiconductor lasers which are delay-coupled via a semitransparent mirror. We vary the transmission and reflection of the mirror, while keeping their sum constant. For equal transmission and reflection of the mirror, the lasers show identical chaos synchronisation. If the reflection is zero, the lasers show generalised synchronisation of leader-laggard type. Setting the transmission to zero results in uncoupled delay dynamics. We study the transition between these types of dynamics via autocorrelation and spectral properties. As the system evolves from uncoupled dynamics to identical synchronisation, the dynamics of the individual elements does not change significantly, but the crosscorrelation function increases with crosscoupling. As the lasers evolve from identical to generalised synchronisation, some extrema disappear in the correlation functions, while new maxima appear in the spectral density. To interpret this dynamical behaviour, we replace the lasers by delay-coupled linear stochastic maps. In this case, we are able to compute the correlation functions and spectral densities analytically. Surprisingly, we find that the correlations and spectra of delay-coupled stochastic maps are generally a good approximation for the laser dynamics, even becoming exact in the limit of face-to-face coupling.

Optical injection is one of the key methods for invoking nonlinear dynamical outputs in laser systems. The system parameters that are used to control the nature of the output from such a system are the injection strength and the frequency detuning between the optical frequency of the free running master and slave lasers. A map of the dynamics can be generated using a number of measurands to facilitate identifying the fundamentally different dynamical regions in the injection-strength/frequency-detuning parameter space. Herein we describe a set of automated algorithms used to establish several measures to identify transients and instabilities in the nonlinear dynamical output of an optically injected vertical cavity surface emitting laser (VCSEL), for set and unchanging driving parameters.

We present a theoretical and experimental study of the polarization-resolved nonlinear dynamics of a 1550nm single-mode linearly polarized VCSEL when subject to orthogonal optical injection. Anticorrelated (correlated) dynamics between the two linear polarizations emitted by the VCSEL is found for negative (positive) frequency detuning. Our theoretical analysis show that deterministic dynamics with appreciable values of the standard deviation of the period of the signal can be found for negative values of the frequency detuning. We study the effect of spontaneous emission noise on the dynamics by analyzing the dependence of the average and standard deviation of the interpulse time on the injected power. We find that in general the effect of spontaneous emission noise is to increase the standard deviation of the interpulse time.

We report a theoretical study of the polarization and transverse mode properties of single and multi-transverse mode VCSELs when they are subject to two-frequency, or dual-beam, orthogonal optical injection. We analyze the nonlinear dynamics of the system making special emphasis in the double injection locking observed at large injection strengths, useful for photonic microwave signal generation. Simulation of single and multi-transverse mode VCSELs show that the double injection locking can be obtained when these devices are subject to dual-beam orthogonal optical injection. We show that the extra degree of freedom given by the multi-transverse mode operation of the VCSEL under dual-beam orthogonal optical injection is useful for enhancing the performance of the photonic microwave generation system. In fact we obtain that the higher-order transverse mode is excited with a much larger amplitude than that of the fundamental transverse mode. The response of the multi-transverse mode VCSEL is enhanced with respect to that obtained with a similar single-transverse mode VCSEL subject to the same dual-beam orthogonal optical injection. Wide tuning ranges, beyond the THz region, and narrow linewidths are also demonstrated in our system.

We consider a broad area vertical-cavity surface-emitting laser (VCSEL) subject to injection and to time-delayed feedback. We show that near the nascent optical bistability regime, the space-time dynamics of this device is described by a generalized Swift-Hohenberg equation with delay. We classify different regime of stability of the homogeneous steady states in terms of dynamical parameters. We show that the delay modifies strongly the stability domain of both periodic and localized structures solutions. Finally, we show that the delay feedback induces a spontaneous motion of bright peaks in one and in two-dimenional transverse plane. Bifurcation diagram associated with these localized structures is constructed.

Experiments on quantum well and recently quantum dot VCSELs have shown that the increase of injection current may lead to a transition from a linearly polarized light emission at threshold to a region of nonlinear dynamics (self-pulsing) accompanying polarization switching between either two orthogonal linearly polarized states or non-orthogonal elliptically polarized states. The dynamics occurs on a nanosecond time-scale and relates either to the birefringence induced frequency splitting or to the relaxation oscillation frequency. In this contribution, we bring new light into the bifurcation mechanisms explaining the occurrence of deterministic self-pulsing accompanying polarization switching. We demonstrate theoretically that depending on the laser parameters, different polarization switching scenarios may be observed with self-pulsing dynamics at a dominant time-scale related to either linear cavity birefringence or relaxation oscillation, and with additional period doubling or quasiperiodicity. Our work therefore not only reconciles previous experiments with different conclusions on dynamical states, but also provides an improved understanding of the bifurcations underlying the commonly used spin flip model for VCSEL - hence motivating new in depth experiments of polarization dynamics at nanosecond time scale.

We have developed electroabsorption modulated ridge waveguide-based DFB Lasers for 4x25Gbit/s that comply with the IEEE 100GBASE-ER4 Standard for 100Gbit-Ethernet. An identical InGaAlAs MQW layer stack is used in the DFB and the EAM section. Devices from a single wafer show excellent 25Gbit/s modulation performance at all four wavelengths with dynamic extinction ratios exceeding 9dB. All devices have facet output powers over +2.5dBm and are operated semi-cooled at 45°C.

In this work we show the analysis of high contrast vertical-cavity surface-emitting lasers (VCSEL) mirror with etched photonic crystal, which provide the true photonic band-gap (PBG) for TE-like polarized light. We confirm that PBG is the main light confinement mechanism by analyzing a low-index line-defect as well as a low-index cavity mode. In the latter case we are able to obtain very high cavity Q-factor. Such PBG-VCSELs are compatible with the VCSEL technology and do not require a complicated assembly of three-dimensional photonic crystals.­

In the following paper a simulation of optically pumped vertical external cavity surface emitting lasers (VECSEL) with a novel approach for the improvement of the heat management is presented. In recent VECSEL structures, it was common to use one top diamond heat spreader in order to decrease the thermal resistance of the device by redistributing the heat flow to the lateral regions and thus transporting heat down to the copper heat sink more efficiently. We present here further improvement of the heat management by eliminating the bottom DBR from the heat flow path and substituting it for a diamond with a High Contrast Grating (HCG). Hence the active region, which consists of 5 pairs of AlGaInAs quaternary alloy quantum wells, is sandwiched between two diamond heat spreading layers. The structure of Si HCG deposited on a diamond provides broad wavelength range in which reflectivity is close to 100% for the emitted beam for perpendicular mode polarization with respect to the direction of the HCG trenches. The HCG assures less than 20% reflection and near zero absorption of pumping light, hence it allows for on-axis bottom pumping scheme and integration of the VECSEL with the pumping laser. According to the simulations 300 μm thick top diamond heat spreader is enough to assure effective heat dissipation mechanism. Replacing the bottom DBR with the diamond heat spreader will provide additional 10% reduction of the thermal impedance. The minimum of thermal impedance is achieved for about 450 μm thick bottom diamond heat spreader.

Semiconductor Ring Lasers (SRLs) are a modern class of semiconductor lasers whose active cavity is characterized by a circular geometry. This enables the laser to support two counterpropagating modes, referred to as the clockwise (CW) and the counterclockwise (CCW) mode. Semiconductor ring lasers have been shown to have a regime of operation in which they are excitable, when the linear coupling between the counterpropagating modes is asymmetric. This can be achieved by increasing the reflection of, for example, the CW mode into the CCW mode. This will stabilize lasing in the CCW mode. In the excitable regime, the SRL will fire optical pulses (spikes) in the CW mode as a response to noise perturbations. In this contribution we experimentally and theoretically characterize these spikes. Our experiments reveal a statistical distribution of the characteristics of the optical pulses that is not observed in regular 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 [L. Gelens et al., Phys. Rev. A 82 063841, 2010]. We will also theoretically consider asymmetric SRLs coupled through a single bus waveguide. This is a first step towards an integrated optical neural network using semiconductor ring lasers as building blocks. We will show that for weak coupling, excitatory excursions still persist due to the similar phase space structure. Moreover, the coupled SRLs can excite pulses in each other and can thus function as communicating neurons [W. Coomans et al., Phys. Rev. E 84 036209, 2011]. This type of neural network can be fully integrated on chip and does not suffer from the drawback of needing extra-cavity measures, such as optical injection or saturable absorbers.

Quantum-dot (QD) lasers exhibit unique properties when subjected to optical injection, e.g. lower sensitivity and less complex dynamics when compared to conventional quantum-well (QW) lasers. These features can be explained by a lower phase-amplitude coupling and a higher damping of relaxation oscillations in QD laser devices. In this work, we investigate an optically injected QD laser and clarify the role of many-body effects. We model the QD laser device using a semi-classical approach based on the semiconductor-Bloch and Maxwell's equations. The QD optical transition is modeled with a finite spectral width, accounting for inhomogeneous broadening due to QD imperfections. Furthermore, many-body Coulomb interactions, leading to renormalizations of the single-particle energies, are taken into account assuming the screened Hartree-Fock approximation. Throughout the literature the phase dynamics of the electric field inside the laser cavity is implemented by assuming a constant α-factor. Our model accounts for the effects of α via a more rigorous treatment of light-semiconductor interaction. As a result the model allows to extract a value for the α-factor from the intrinsic phase dynamics of the system. The extracted α-factor is not a constant, but rather changes on the one hand dynamically throughout the simulations, and on the other hand with all operation conditions. Furthermore, the dynamical shift of the band-gap energy due to the Coulomb interactions gives rise to modifications in the locking behavior of the laser, that can not be explained with the simpler free-carrier models.

The theoretical investigation of the double-state lasing phenomena in InAs/InGaAs quantum dot lasers has been carried out. The new mechanism of the ground-state lasing quenching, which takes place in quantum dot (QD) laser operating in double-state lasing regime at high pump level, was proposed. The difference between electron and hole capture rates causes the depletion of the hole levels and consequently leads to the decrease of an output lasing power via QD ground state with the growth of injection. Moreover, it was shown that the hole-to-electron capture rates ratio strongly affects both the light-current curve and the key laser parameters. The model of the simultaneous lasing through the ground and excited QD states was developed which allows to describe the observed quenching quantitatively.

We study the gain in an acousto-optical cavity made of an indirect bandgap semiconductor with simultaneous confinement of photons and photons. We obtain that the phonon confinement in such a cavity can give rise to optical gain at room temperature.

We present self-consisted approach for calculating output characteristics of quantum cascade lasers. Presented model is based on the analysis of 1½ period of the structure. The model solves self-consistently Schrödinger equation, Poisson equation and a full rate equations including electron-phonon scattering, electron-electron scattering, spontaneous emission and stimulated emission. Results of calculation are in good agreement with experimental data which shows validity of the model.

In this paper, we have theoretically studied the dynamical behavior of current modulated semiconductor ring lasers (SRLs). As we vary the amplitude and frequency of the modulation around a fixed bias current, difference dynamical states including periodic, quasi-periodic and chaotic states are found. As in other single mode semiconductor lasers, the modal intensities in an SRL present chaotic behavior for driving frequencies comparable to the relaxation oscillation frequency. In this regime the two counter-propagating modes vary in phase. However, for modulation frequencies significantly lower than the relaxation oscillation frequency, we reveal the existence of chaotic oscillations where the two counter-propagating modes are in anti-phase.

We study experimentally and numerically a new dynamical regime in the operation of semiconductor ring lasers (SRLs) subject to delayed optical feedback. When employing an asymmetric feedback scheme, we find experimentally that the SRL can show square-wave intensity oscillations with a 50 % duty cycle. In this scheme, where the output in one direction is delay-coupled to the other direction but not vice versa, the laser switches regularly between the clockwise (CW) and counter-clockwise (CCW) propagating modes. The measured period of the square-waves is slightly longer than twice the roundtrip time in the external cavity. We analyze the regularity and the shape of the square-waves as a function of the pumping current and the feedback strength. For higher pump currents on the SRL,the output displays stochastic mode hopping between the square waves attractor and stable unidirectional operation in the CW mode. To understand the origin of this dynamical regime, we rely on numerical simulations based on the Lang-Kobayashi equations. We demonstrate a novel mechanism leading to square wave oscillations based on the cross-feedback overcoming backscattering asymmetries present in the device's structure. Our numerical results are in close agreement with the experimental ones.

We report on the study of the temperature influence on optical and electrical performance of the mid-IR GaAs/AlGaAs QCLs. The temperature dependence of the threshold current, output power, slope efficiency, wall-plug efficiency, characteristic temperatures T₀ and T₁, and waveguide losses is investigated. In addition, the influence of different mesa dimensions on the QCL parameters is analyzed. Experimental results clearly indicate that among the examined geometries the 25μm wide mesa devices exhibit the best operational parameters i.e., the highest T_max and T₀, highest wall-plug and slope efficiency, as well as a small temperature increases and the smallest thermal resistivity in the active area. The knowledge of the above parameters is crucial for designing GaAs/AlGaAs-based devices for high temperature operation.­¬«

We demonstrate 40 Gb/s all-optical clock recovery by using a monolithic integrated amplified-feedback laser (AFL) with coherent injection-locked method. The AFL consists of a gain-coupled DFB laser and an optical amplified feedback external cavity. With proper design and operation of AFL, the device can work at self-pulsation state that resulted from the beating between two lasing modes. The self-pulsation can be injection-locked to the optical clock embedded in input data streams. Due to different work mechanisms, there are two all-optical clock recovery operation modes: incoherent injection-locked and coherent injection-locked. It's predicted that the coherent injection method has various advantages: 1) requiring low injection power recovery, 2) independent of the bit rate and 3) introducing little timing jitter to the recovered clock. The robustness of coherent clock recovery is confirmed by our experimental results. We set up a return-to- zero (RZ) pseudorandom binary sequence (PRBS) data streams all-optical clock recovery system. This coherent injection-locked based clock recovery method is optical signal noise ratio (OSNR) and chromatic dispersion (CD) degeneration tolerant, and has low timing jitter and high sensitivity.

PM optical fiber with a PM single mode couplers or splitters at each fiber end can be used as a sensitive structure for fiber sensing applications. The sensitive structure is created with two lasers at λ = 1550 nm. Each laser is connected to the opposite sides of two the single mode PM couplers with PM fiber connecting both PM couplers. One DFB laser is isolated and its light goes through variable attenuator. Isolation is necessary for DFB laser stability. The second laser is F-P laser without any isolator. Its radiation is driven as with driven current so with DFB laser passing through SM optical fiber. Small changes of DFB laser light spectrum passing through PM optical fiber activate large changes in FP laser radiation spectra. DFB laser is tunable with temperature and its radiation is a stimulated light for FP laser. If the power of DFB laser is above threshold power, FP laser losses its multimode behavior. Threshold powers, tunable range of DFB laser, changes in mode structures of FP laser will be presented together with application possibilities of coupled laser diodes system.

We report the injection locking of specific spatial modes and polarization modes of 1.3μm wavelength vertical surface emitting lasers (VCSELs) in single-aperture devices and phase-coupled arrays. The optical injection is realized using a master laser (ML) VCSEL, the beam of which is directed onto the output facet of the slave laser (SL) VCSEL or VCSEL array. We measured the emission spectra of the SL as the ML operating conditions (frequency, power) were varied systematically, and present the results on two-dimensional stability maps of power versus detuning of the ML from the injected modes. In single-aperture devices, the high degree of circular symmetry allows the support of two modes with orthogonal polarizations with ~75 GHz frequency difference. With optical injection, we could induce a polarization mode switching and decrease the power of the free running mode by 25 dB. Model calculations confirm injection locking and specify the stability region. In a 1×2 VCSEL array defined by tunnel junction patterning and biased below threshold, we injection locked the fundamental mode (1×2 mode) and a « broad area » mode (1×3 mode). The spatial overlap between the ML spot and the array mode is shown to be a key factor in injection locking. Locking of the non-lasing 1×3 mode results in suppressed output power of the free running 1×2 mode. These studies are useful for understanding the mode structure of these VCSELs and suggesting ways for their discrimination.

We developed an in- house technology to overlay liquid crystal (LC) on top of a 850nm Vertical Cavity Surface Emitting Laser (VCSEL) creating a so-called LC-VCSEL. Prior to this, the effect of the cell thickness on the planar alignment of the E7 LC is investigated. It is observed that the LC orientation is planar, uniformly aligned over the whole cell with an average pre-tilt of 22.5⁰ in a thin a cell of 13μm thickness; such alignment uniformity is not observed in a thick cell of 125μm. Nevertheless, several domains of good uniformity are still present. Further, the polarization resolved LI characteristics of LC-VCSEL are investigated with and without the insertion of LC in a cell glued directly onto VCSEL package. Before filling in the LC, the VCSEL emits linearly polarized light and this linear polarization is lost after LC filling. The output intensity as a function of polarizer angle shows partial planar alignment of the E7 LC, which is very important for the further advancement of the LC-VCSEL integrated system.

We study experimentally and numerically the synchronization dynamics of two laser modes, coupled by a coherent optical feedback injection. For a given coupling strength, we observe three synchronization regimes, depending on the initial detuning between the modes. If this detuning is sufficiently weak, the phase of the beat between the two modes remains constant. In contrast, for very large detuning, this relative phase drifts. Besides these two familiar cases, we identify an intermediate situation, in which the relative phase oscillates while remaining bounded. The frequency locking is preserved, even in the absence of phase locking.

Discrete Mode Laser Diodes (DMLDs) present an economic approach with a focus on high volume manufacturability of single mode lasers using a single step fabrication process. We report on a DMLD designed for operation in the 1550 nm window with high Side Mode Suppression Ratio (SMSR) over a wide temperature tuning range of -20 °C < T < 95 °C. Direct modulation rates as high as 10 Gbit/s are demonstrated at both 1550 nm and 1310 nm. Transmission experiments were also carried out over single mode fibre at both wavelengths. Using dispersion pre-compensation transmission from 0 to 60 km is demonstrated at 1550 nm with a maximum power penalty measured at 60 km of 3.6 dB.

Broad area semiconductors lasers and amplifiers are of technological relevance because of their high conversion efficiency and high output power, in a wide range of wavelengths. However, due to their specific waveguiding planar geometry, which is unique to this kind of heterostructures, the beam is usually of low spatial and temporal quality. Therefore, the beam quality restricts their potential use. We propose to improve the beam quality of semiconductors lasers and amplifiers using a two-dimensional spatial modulation of both the refractive index and the optical gain/loss, on the scale of the wavelength. The modulation of the refractive index and gain/loss function on a small scale modifies the spatial dispersion and introduces anisotropic gain on a large scale. As a result, the modified dispersion gives rise to interesting and technologically useful effects, such as spatial filtering or focalization behind the amplifier. We show that such effects can be achieved considering a modulated injection current which imposes a periodic spatial modulation of the active layer of the semiconductor.

The three-dimensional confinement of electrons and holes in the semiconductor quantum dot (QD) structure profoundly changes its density of states compared to the bulk semiconductor or the thin-film quantum well (QW) structure. The aim of this paper is to theoretically investigate the microwave properties of InAs/InP(311B) QD lasers. A new expression of the modulation transfer function is derived for the analysis of QD laser modulation properties based on a set of four rate equations. Analytical calculations point out that carrier escape from ground state (GS) to excited state (ES) induces a non-zero resonance frequency at low bias powers. Calculations also show that the carrier escape leads to a larger damping factor offset as compared to conventional QW lasers. These results are of prime importance for a better understanding of the carrier dynamics in QD lasers as well as for further optimization of low cost sources for optical telecommunications.

We consider a multi-transverse mode Vertical Cavity Surface Emitting Laser (VCSEL) subject to optical feedback. When the field profile can be described in terms of few Gauss-Laguerre modes we show that the self-mixing interferometric signal exhibits features peculiar of the spatial distribution and/or polarization state of the re-injected field. Based on these results we provide both theoretically and experimentally the proof-of-principle of an operational scheme for a sensor that can be used to simultaneously measure target translations along the optical axis and target rotations in the orthogonal plane.