We report on distributed Bragg reflector tapered lasers having 6^th order surface gratings and ridge waveguides simultaneously fabricated by wafer stepper lithography and reactive ion etching. Single longitudinal mode emission at 978 nm and a beam propagation ratio of M² = 1.1 at 4.4 W have been obtained in quasi-continuous wave operation. In CW operation, a maximal output power of 2.5 W with a side-mode suppression ratio of more than 20 dB and a beam propagation ratio of M² < 1.4 for the central lobe has been achieved.

The performance of high-power pump-laser modules is strongly influenced by their thermal properties. In this paper we discuss the optimization of the device performance with respect to thermal properties, output power, wavelength stability, and device reliability using the example of our newest pump-laser generation that has been developed and qualified to support the high-end market of erbium-doped fiber amplifiers. A comparison of device properties obtained from modeling and measurements is presented at each design step. We report on the performance of fiber Bragg grating-stabilized telecom-grade modules yielding 600 mW fiber-coupled light output power.

A number of up-to-date applications, including advanced optical radars with high single-shot resolution, precise 3 D imaging, laser tomography, time imaging spectroscopy, etc., require low-cost, compact, reliable sources enabling the generation of high-power (1-100 W) single optical pulses in the picosecond range. The well-known technique of using the gain-switching operation mode of laser diodes to generate single picosecond pulses in the mW range fails to generate high-power single picosecond pulses because of a lack of high-current switches operating in the picosecond range. We report here on the achieving of optical pulses of 45W / 70ps, or alternatively 5W / 40ps, with gain-switched commercial quantum well (QW) laser diodes having emitting areas of 250 × 200 μm and 75 × 2 μm, respectively. This was made possible by the use of a novel high-current avalanche switch based on a GaAs bipolar junction transistor (BJT) structure with a switching time (<200ps) comparable to the lasing delay. (The extremely fast transient in this switch is caused by the generation and spread of a comb of powerfully avalanching Gunn domains of ultra-high amplitude in the transistor structure.) A simulation code developed earlier but modified and carefully verified here allowed detailed comparison of the experimental and simulated laser responses and the transient spectrum.

Widely tunable ultra-high power monolithic multi-section tunable lasers have been a sought after dream for more than two decades. In recent years, tunable lasers have become critical components in the development of the next generation telecommunication networks and systems, due to their unique attributes and flexible functionalities. However, some stringent requirements have been imposed on tunable lasers by telecommunication applications regarding their tuning range, optical output power, side-mode suppression ratio (SMSR), linewidth, chirp, tuning speed, reliability, and so on. In addition, monolithic tunable lasers, requiring a regrowth process, suffer from butt-joint reflections from the regrowth interfaces of these multi-section devices, which have seriously affected their tunability, and greatly reduced their facet output power. Butt-joint reflection losses between active-passive interfaces are therefore the crucial and decisive factors in multi-section tunable laser operation. In this paper, original design ideas and novel approaches to the design of ultra-high power InGaAsP-InP based multi-section widely-tunable lasers are introduced. Simulation results show that the facet output power in the proposed new design can be greatly increased compared with a conventional design. The optimized butt-joint angles and the arrangements of these angles at the active-passive interfaces in a multi-section tunable laser can largely reduce the total adverse interface reflection in the device, and tremendously improve the operation performance of the multi-section tunable laser. Finally, an integrated curved semiconductor optical amplifier design is introduced that would be able to futher increase the total optical output power of the device and reduce the backward optical reflection into the device.

We review three two-mode models for different semiconductor laser structures: Vertical-Cavity Surface-Emitting Lasers (VCSELs), Twin-Stripe Semiconductor-Lasers (TSSL), and Semiconductor Ring Lasers (SRL). The VCSELs model and TSSL model display rich dynamic behavior when a saturable absorber is embedded in the cavity. VCSELs with saturable absorber showed polarization chaos, which found applications in encoded communications; TSSLs with saturable absorber show coherent locked states as well as chaotic behavior; and SRLs show a complex two-mode dynamics giving rise to bidirectional operation, alternate oscillations and spontaneous symmetry breaking toward quasi-unidirectional bistable solutions, with potential applications to all-optical switching.

A novel laterally-coupled dual-wavelength distributed feedback (DFB) laser having two different grating periods, one on each sidewall, has been successfully realised. Single-mode DFB and distributed Bragg reflector (DBR) lasers have also been fabricated alongside in order to compare the lasing operation characteristics of the dual-wavelength DFB laser. The lasers were fabricated on InP/InAlGaAs epitaxial heterostructure material emitting at 1.35 μm. Measurements show stable dual-mode emission, with threshold currents around 50 mA and good extinction ratio of about 30 dB. At low current levels, two longitudinal modes having different transversal spatial distribution oscillate inside the laser cavity. The emission wavelengths of the two modes are selected by the grating periods defined on the sidewalls of the waveguide. At higher current levels, a strong single transversal mode appears at longer wavelengths. To gain a wider understanding on the different transversal and longitudinal modes, the dual-wavelength laser behaviour was assessed under external optical injection locking. Linewidth measurements of both the single modes and the mode beating are also reported.

We investigate the continuous wave solutions of a system of two mutually delay coupled semiconductor lasers. These continuous wave solutions, which we refer to as compound laser modes (CLMs), are locked solutions of the coupled laser system where both lasers lase at a common frequency. We model the system by a set of delay differential rate equations, where we assume that, apart from a possible detuning in their free running optical frequencies, the lasers are identical. We show how the structure and the stability of the CLMs depend on the main parameters, namely, the feedback phase, the feedback rate, the pump parameter, and the detuning. We identify two mechanisms for creating CLMs. First, CLMs emerge from the off-state of the coupled laser system in Hopf bifurcations. Second, CLMs are created in pairs in saddle-node bifurcations. For the special case of zero detuning we also find pitchfork bifurcations that organize the CLM structure. We show in which parameter regions CLMs exist, where they are stable, and which bifurcation curves form the boundary of the stable locking region.

We have theoretically investigated the bifurcation scenario that leads to the emergence of a bistable regime in a two-mode model for a Semiconductor Ring Laser. The bistability takes place between two quasi-unidirectional solutions for the electric field, which are selected as stable solutions via gain-crossaturation, for well-above threshold operating conditions. Furthermore, we analyzed the switching properties of a single Semiconductor Ring Laser (SRL) operating in the bistable regime, under coherent optical pulse injection, in view of the possible implementation of a single SRL an optically adressable memory element. The result is that the response time and the minimum switching energy respectively attain values the order of a few tenth of ps, and 1 fJ. Those values are espected to scale down with the device radius, due to the consequent decreasing of the cavity flight time. We have observed that the fast switching dynamic is due to an energy redistribution process between the two counterpropagating modes, that does not involve the (slow) carrier density through field-medium energy exchange processes. This allows to attain time scales much faster than the typical limit represented by the inverse of relaxation oscillation frequency.

Beryllium incorporation in InGaAsN quantum well improves the optical properties of this dilute nitride material significantly. After annealing, the intensity of the photoluminescence of this new dilute nitride material (InGaAsNBe) is about 20 times higher and its wavelength is even 25 nm longer. After a certain time of this heat treatment, the photoluminescence quenched slowly for InGaAsN structures because of the strain relaxation due to the thermal activation. The photoluminescence of InGaAsNBe increased rapidly and show no saturation even after a very long time of annealing. Beryllium incorporation in InGaAs which was grew at the same temperature as dilute nitrides also improves the optic properties. But the improvement for InGaAsNBe is 10 times more than for InGaAsBe. Laser processing based on the new InGaAsNBe structures resulted in one half of the threshold current density compare to conventional InGaAsN.

Atomic clocks will be used in the future European positioning system Galileo. Among them, the optically pumped clocks provide a better alternative with comparable accuracy for a more compact system. For these systems, diode lasers emitting at 852nm are strategic components. The laser in a conventional bench for atomic clocks presents disadvantages for spatial applications. A better approach would be to realise a system based on a distributed-feedback laser (DFB). We have developed the technological foundations of such lasers operating at 852nm. These include an Al-free active region, a single spatial mode waveguide and a DFB structure. The device is a separate confinement heterostructure with a GaInP large optical cavity and a single compressive-strained GaInAsP quantum well. The broad-area laser diodes are characterised by low internal losses (<3 cm^-1), a high internal efficiency (94%) and a low transparency current density (100A/cm²). For an AR/HR coated 2mm long around 4μm wide ridge diode, we obtain a low threshold current (40mA) and a high slope efficiency (0.90W/A). With the Fabry-Perot laser structure we obtain 852nm wavelength at 145mW (I=200mA, 15°C). We measure an optical power of 230mW (I=280mA) in a single spatial mode with the beam quality parameter M²=1.3. With the DFB laser structure, we have obtained single frequency (side-mode-suppression ratio : SMSR over 30dB) and single mode lasers (M²<1.5) with a high optical power. An optical power of 150mW was obtained at 854nm wavelength and 20°C for AR-HR coated 2mm long, ~ 4μm wide devices. At this power, both near and far fields in the slow axis are gaussian-shaped with respective full widths at 1/e² of 8μm and 9.2° respectively, corresponding to a single spatial mode emission with a beam quality parameter M²=1.29. The SMSR is over 30dB. Furthermore, the preliminary results of the linewidth obtained with a Fabry-Perot interferometer give a value of less than 2MHz.

At the present time, there is a considerable demand for long wavelength (1.3μm-1.5μm) laser diodes for low cost data-communication applications capable of operating at high speed and at high ambient temperatures without the need for thermoelectric coolers. First proposed in 1995 by M. Kondow, the GaInNAs/GaAs material system has attracted a great deal of interest as it promises good temperature performance. The broad gain observed in GaInNAs/GaAs QW samples suggests that wavelength tuning should be possible by the application of gratings to select an optical mode. In addition, splitting the contact has been shown to improve modulation speed in other materials. These two methods should be able to be used jointly and processed together. The use of split-contact lasers has the advantage of that no change is made in the processing steps, since there is only need for a new metal mask to define a new top p-contact. Despite the bandwidth enhancement of two-contact lasers compared to the single contact case is well known, to the authors' knowledge, so far it has not being applied to GaInNAs/GaAs lasers. The use of Bragg-gratings on the ridge waveguide of the laser will generate a periodic modulation inducing an interaction between the forward and backward travelling modes. The effect of this interaction is the one of a band pass filter on the gain shape of the laser, allowing filtering out the actual lasing wavelength, and tuning the lasing wavelength in the range of wavelengths with substantial optical gain. Therefore, this method can be used optimally in lasers with broad gain, as is the case of GaInNAs/GaAs. In this paper, we reveal experimental investigations in how to apply these two post-processing methods to 600m-long 1.25μm-Ga₀.66In₀.34N₀.01As0.₀.99/GaAs 6nm single quantum-well ridge waveguide lasers.

We report the on the characterisation of 1.3μm emitting GaInNAs quantum well (QW) lasers grown by molecular beam epitaxy using a plasma nitrogen source. Through the optimization of the structural and optical properties as a function of substrate temperature and nitrogen flux conditions, we show that high optical quality structures, which exhibit good room temperature photoluminescence intensity and photoluminescence linewidths <10meV at low temperature, can be routinely achieved. To obtain 1.3μm emission, we employed a structure containing quantum wells with an indium content of 40% and a nitrogen content of 2.5% which have low nitrogen content (1%) lattice matched quaternary GaInNAs barriers, the latter enabling us to grow thick barrier structures without introducing further strain. For unmounted and uncoated 15μm ridge waveguide lasers we have achieved threshold current densities as low as 377Acm^-2 for a 3 QW and record low value of 178Acm^-2 for a single QW device emitting above 1310nm. The devices show excellent temperature characteristics with characteristic temperatures >90°C observed in several structures. In comparison to GaInAs quantum well lasers, the results show that at this composition (2.5%) there is no appreciable degradation of performance due to the presence of nitrogen in these samples. Increasing the nitrogen content by 1% was observed to shift the wavelength to 1390nm, but with a threshold current density increased by a factor of 2 to 830Acm^-2. The results also indicate that although high quality GaInNAs lasers can be achieved at wavelengths suitable for the 1.31μm optical fibre waveband, the performance of devices with higher N content, and therefore with emission at longer wavelength, are degraded.

In this contribution, microscopic simulation of optical gain in GaN-based short-wavelength lasers is presented. The model is used to perform a design study of different active regions, and to discuss the impact of inhomogeneous broadening, carrier-induced screening of the piezo charges, and well thickness on material gain and laser threshold current. As a reference, the model parameters are calibrated with temperature dependent Hakki-Paoli measurements of spectral gain. Excellent agreement between measurement and simulation is achieved, which gives the design studies a quantitative character.

Frequency conversion of near infrared diode lasers provides an efficient method to generate laser radiation in the visible spectral range. There are several requirements for efficient frequency doubling like singlemode emission and good beamquality, which can be fulfilled by light sources based on master oscillator power amplifier (MOPA). This contribution reports on the generation of 600 mW output power at 488 nm by single pass frequency doubling. An InGaAs distributed feedback (DFB) laser was used as MO and an InGaAs tapered amplifier as PA in a MOPA diode laser system. A maximum output power of 4 W at 976 nm was achieved in continuous wave operation mode, at a heatsink temperature of about 0°C with this pump source. For frequency conversion a 30 mm long PPMgLN bulk crystal held at 65°C, was used in a simple single-pass configuration. A maximum conversion efficiency of 15% and an overall wall-plug efficiency of 4% were achieved.

In this work we present the reliability study of low dislocation density InGaN laser diodes grown on the top of GaN monocrystalline substrates obtained by high-pressure growth technique. The active region of our lasers consists of an InGaN/InGaN multiple quantum well (MQW) emitting blue light around 415nm, placed between GaN or InGaN guiding layers and GaN/AlGaN superlattices as n- and p-cladding. We discovered two basic mechanisms of degradation in our laser diodes. The first one is characterized by a gradual increase of threshold current and stable behavior of differential quantum efficiency. In case of this mechanism the results showing square root dependence of threshold current during aging suggest that the diffusion of point defects and an enhancement in nonradiative recombination are responsible for degradation processes in our laser diodes. The second mechanism leads to a decrease of differential quantum efficiency with threshold current remaining constant. We associate this degradation mode with a gradual deterioration of dielectric mirror coatings.

We fabricated wide-stripe laser diodes operating between 380 and 430 nm. The threshold current density for 380 and 430 nm devices (6-7 kA/cm²) was only slightly higher than for our main stream 415 nm devices (4-6 kA/cm²). Thanks to the use of high-pressure-grown low-dislocation-density substrates we succeeded in demonstration of high power optical emission both under CW and pulse operation. For the device emitting at 415 nm we were able to demonstrate 200 mW of CW optical power (20 μm wide device) and 2.7 W under pulse current operation (peak power, 50 μm device). The main obstacle for achieving CW operation of 50 μm device was to remove the excess of heat from laser chip-diamond submount assembly.

Theoretical results concerning injection locking in complex cavity semiconductor lasers are reported. A general equation for the complex temporal envelope of the optical field is derived. The injection direction influence is taken into account and the difference between front and rear phase noise is pointed out and demonstrated. Numerical results are given concerning the feed-in rate of different DFB lasers.

A reflective semiconductor optical amplifier is modeled using a rate equation for the inversion and an expression for the outgoing field in terms of the incoming field and the instantaneous inversion, for both the cases of linear and nonlinear gain, while assuming modulation speeds well below the round-trip frequency. Simulations are performed on the basis of these equations. Results for both the static and dynamic performance are presented and discussed.

We combine a scanning near-field microscope (SNOM) with a time-resolved detection scheme to measure the mode dynamics of InGaN laser diodes emitting at 405 nm. Observed phenomena are filaments, mode competition, near-field phase dynamics, near-field to far-field propagation, and substrate modes. In this article we describe in detail the self-built SNOM, specialized for these studies. We also provide our recipe for SNOM tip preparation using tube etching. Then we compare the mode dynamics for a 3 μm narrow and a 10 μm wide ridge waveguide laser diode.

We study the identification of the delays of several chaotic optical cryptosystems subjected to one or two delayed feedbacks. We show that the delay of a single-delay system can be identified, even if highly complex chaos is used. For certain types of systems with two delays, the same identification techniques that work for single-delay systems also work for multiple-delay systems. These systems thus do not provide a significant increase of the security level. A careful choice of the architecture of multiple-delay system can, however, make these techniques fail. We propose some higher-dimensional techniques that lead to the identification of the delays for these architectures too. The increased complexity of these techniques means, however, that it takes a significantly longer time to identify the delays.

We investigate the evolution of short-duration pulses injected into laser diodes biased above threshold with the use of spectrally and temporally resolved experimental and numerical methods. We show that stable transients may be formed as a result of spatially re-distributing the cavity energy. By controlling the phase of injected pulses with respect to the diode cavity radiation we show through simulation that it is possible to directly generate and control stable streams of pulses.

DFB lasers, microcavity and External-cavity VCSELs exhibit narrow single-frequency operation and wide mode-hop-free tuning range, especially well adapted for gas spectroscopy application in the 2-2.7μm window. We will present a review of the results achieved and a systematic comparison, with such Sb-based lasers emitting near 2.3μm. These sources operate in CW above 300K, with up to 5mW output power in a single transverse mode and linear light polarization. Diode-pumped V(E)CSELs and electrically-pumped DFB lasers were designed, grown, processed, and the spectral, spatial, thermal properties characterized. These sources are now being applied in high sensitivity spectroscopy instruments for in-situ measurements.

To achieve high power and high brightness, we have developed tapered diode lasers based on an Al-free active region at 915 nm. The material structure was grown by MOCVD (Metallorganic Chemical Vapor Deposition). It shows very low internal losses of only 0.5 cm^-1, a very low transparency current density of 86 A/cm², an excellent internal quantum efficiency of 86%, and a high characteristic temperature T₀ of 171 K. Based on these good results, at first, we have realised index-guided tapered lasers (IG1) with a narrow output width and a narrow taper angle, which deliver 1 W CW, together with an M² beam quality parameter of 2.9 at 1/e², and a narrow divergence angle in the slow axis of 5.1° FWHM and 7.5° at 1/e². We have also fabricated new index-guided tapered lasers with a Clarinet shape, which were recently proposed to achieve high brightness together with a very narrow divergence angle. The Clarinet lasers deliver 0.6W CW, together with an excellent M² beam quality factor of 1.2 at 1/e², and a very narrow divergence angle in the slow axis of only 2.5° FWHM, and 3.9° at 1/e², which is stable with current. These very narrow divergences are very advantageous for the collective coupling of tapered bars into optical fibers. In this work we have also investigated the influence of taper length on the output power and beam quality.

This paper approaches the problem of catastrophic optical mirror damage from a geometrical waveguide point of view. Instead of engineering the characteristics of the semiconductor material at the facet of the laser using quantum-well intermixing or other sophisticated wafer growth technique, a simple intra-cavity diverging lens concept is proposed and demonstrated to be capable of effectively expanding the lateral optical mode in order to counter the effect of SHB and thermal lensing effect, thereby reducing the risk of COMD. The Gaussian output beam profile is maintained throughout the whole of the current range tested, showing that expanding the nearfield at facet using integrated lens does not compromise the brightness of the laser. A key finding in this work is that the diverging effect on an optical mode is a thoroughly scalable effect that can be engineered by varying the etch-depth of the integrated lens. Fabrication of the lens is compatible with existing laser manufacturing process flow in that it can be easily implemented either by post-processing technology or by an additional lithographical step. This opens up new possibility in device design, with the beam width along the lateral direction being a parameter that can be optimized in isolation.

The input power dynamic range (IPDR) of a semiconductor optical amplifier (SOA) is extended using a moderate power holding beam, which could be readily achieved with a single DFB laser. The associated reduction of gain with improved IPDR is studied and assessed in parallel with power penalty to explore the optimum operating powers in switching applications. Holding beam powers of less than +10 dBm facilitate IPDR enhancement to 27 dB, representing an order of magnitude improvement. The achievable gain remains sufficiently high to find applications in a number of switching and routing applications.

Theoretical investigation and device measurements are reported to demonstrate the strict fabrication requirements of small diameter shallow etched semiconductor ring lasers. A very accurate control over the dry etching depth is crucial to both minimise the bending losses and achieve very precise control of the coupling ratio in directional couplers. A reactive ion etching process was developed on Aluminium-quaternary wafer structures, showing selectivity greater than 30 between the AlInAs core layer and the InP upper cladding. The process proved very effective in providing a complete and controllable etching of directional couplers with 500nm wide gaps. Assessment on the effect of the bending losses and on the minimum ring radius was performed through characterisation of half ring lasers. A minimum current threshold of 34mA is reported on 150μm ring radius devices emitting at 1300nm.

We report on the characteristics of (AlGaIn)(AsSb)-based optically pumped vertical-external-cavity surface-emitting lasers (VECSELs) emitting at wavelengths around 2.35 μm. For barrier-pumped VECSELs mounted substrate-side down without substrate thinning, typical room temperature cw output powers of 2 mW were achieved, limited by premature thermal rollover due to strong device overheating. The thermal impedance of the VECSEL semiconductor chip could be considerably reduced by bonding an intra-cavity polycrystalline CVD diamond heat spreader to the top surface of the chip. This way, at -18°C a maximum cw output power of 0.6 W and a slope efficiency of 10% were obtained for a multiple transverse mode output beam limited by the available pump power rather than by thermal rollover. Optimising the resonator for TEM₀₀ mode operation (M²≈1.1), an output power exceeding 0.4 W was achieved. To reduce the large quantum deficit of more than 50% inherent to barrier-pumped (1.06 μm pump wavelength) GaSb-based VECSELs which emit at wavelengths above 2 μm, we realized a first in-well pumped (AlGaIn)(AsSb) VECSEL where the pump light is absorbed directly in the quantum wells, with the amount of absorbed light enhanced by a higher order microcavity resonance. Using a pump wavelength of 1.94 μm, the quantum deficit is reduced to only 18% and an output power of 5mW, limited by the available pump power, and a slope efficiency of 10% were achieved. Further optimisation of the pump optics is expected to result in a significant increase in device performance.

The square-wave response of edge-emitting diode lasers subject to a delayed polarization-rotated optical feedback is studied experimentally and theoretically. Square-wave self-modulated polarization intensities of a period close to twice the delay τ of the feedback gradually appear through a sequence of bifurcations starting with a Hopf bifurcation (Gavrielides et al, Proc. SPIE 6115, to appear, 2006). In Gavrielides et al (submitted, 2006), squarewave solutions were determined analytically from the laser equations in the limit of large τ. A condition on the laser parameters was derived explaining why square-wave oscillations are preferentially observed for suffciently large feedback strength. In this paper, we concentrate on the relaxation oscillations that always appear at each intensity jump between the plateaus of the square-wave. We show analytically that if the feedback strength is progressively decreased, a bifurcation to sustained relaxation oscillations is possible for one of the two plateaus.

We present a detailed analysis of the external filter mode (EFM) structure of a semiconductor laser subject to filtered optical feedback (FOF). These EFMs form the 'backbone' of the dynamics of the system. Specifically, from the governing delay differential equations, we find analytic, transcendental expressions for both the solution curves, which define the frequency and amplitude of the EFMs, and their envelopes. We use numerical continuation to find and follow solutions of these equations. This approach allows us to show how the structure depends on the key parameters of filter width, filter detuning, and feedback phase. In other words, we identify the external influence of the filter on an otherwise fixed laser.

In the filtered optical feedback (FOF) scheme a part of the emission of the laser is spectrally filtered, for example by a Fabry-Perot filter, and than fed back into the laser. If a semiconductor laser is subject to such delayed FOF qualitative different types of oscillations are possible: the well known relaxation oscillations and, more remarkably, frequency oscillations. We explain how the continuous wave operation of the FOF laser - the external filtered modes - lose their stability and the different types of oscillations arise due to the presence of the filter. This study is restricted to the case of a narrow filter. This means that there are only a few external filtered modes within the width of the filter, so that the influence of the feedback phase can be studied explicitly.

We use an asymptotic method to simplify the rate equations for a semiconductor laser subject to filtered optical feedback. The simplified equations provide insights on the physical mechanisms involved in two different oscillatory instabilities, namely: relaxation oscillation undamping, and the onset of optical frequency oscillations. We proceed to an analytical stability analysis of the external cavity modes and determine simple scaling laws for their stability boundaries in parameter space. We also point out a couple of remarkable properties of the frequency oscillation regime; in particular, we draw analogies with a related dynamical response predicted for semiconductor lasers subject to both conventional feedback and optical injection.

We investigate a semiconductor laser with delayed optical feedback due to an external cavity formed by a regular mirror. We discuss similarities and differences of the well-known Lang-Kobayashi delay differential equation model and the traveling wave partial differential equation model. For comparison we locate the continuous wave states in both models and analyze their stability.

The output polarization of an optically pumped InGaAs/GaAs vertical cavity surface-emitting laser (VCSEL) is analyzed at room temperature as a function of the circular input polarization degree. The emission of the VCSEL is unambiguously controlled by the exciting polarization and only 30% of spin-polarized electrons are needed in the active region to generate an output polarization degree of up to 100% at short-pulsed pumping. This testifies that a VCSEL can be used as an effective amplifier for spin information even at room temperature. Measurements with a continuous wave excitation were executed to demonstrate the possibility of spin-amplification by electrical spin-injection in a VCSEL. All measurements were confirmed by a phenomenological spin flip model. Our paper is completed with the introduction of Fe/Tb-Multilayers used for spin injection. These contacts enable spin injection without external magnetic fields, i.e. in remanence. Finally, we suggest a combination of these multilayers with a VCSEL-structure to create the first spin-optoelectronic device working both at room temperature and without external fields.

An overview of the idiosyncratic emission characteristics of pulsed broad-area VCSELs is presented, together with a statistical model which describes these devices as quasi-homogeneous sources. The predicted properties of such sources, which include two reciprocity relations between near and far field aspects of the cross-spectral density as well as its propagation, are verified experimentally. We finish by showing how and which thermal effects are at the origin of this nonmodal emission.

Monolithically integrated surface gratings have proven to control the polarization of vertical-cavity surface-emitting lasers (VCSELs) very reliably and effectively. To overcome the drawbacks of these devices with respect to threshold current or differential quantum efficiency we will present in this paper monolithically integrated surface gratings with a modified longitudinal position relative to the standing wave inside the laser cavity. It turns out that an optimum is reached for an additional quarter-wave layer on top of the upper Bragg mirror. In that way the diffraction from the grating and therefore its influence on the other laser properties like threshold, differential quantum efficiency or maximum output power can be reduced significantly, while the polarization control is still maintained. At the same time the requirements on the fabrication accuracy are very relaxed. 118 out of 120 fabricated devices with grating periods between 0.5 and 1.2 μm and grating depths between 35 and 105 nm exhibit a stable polarization orthogonal to the grating grooves. If one limits the lateral extension of the grating to a diameter smaller than the oxide aperture of the laser, the single-mode output power can be increased simultaneously.

We investigate experimentally and theoretically nonlinear dynamics and polarization bistability in a vertical-cavity surface-emitting laser (VCSEL) submitted to an external optical injection with orthogonal polarization, i.e., the injected light from a master laser (ML) is linearly polarized and orthogonal to the polarization direction of the free-running VCSEL (slave laser, SL). Depending on the injection power level and the frequency detuning between ML and SL, our experimental results show that the injected VCSEL may undergo complex dynamics including subharmonic resonances and period-doubling route to chaos that are associated to polarization switching (PS). Using continuation method, we carry out a detailed bifurcation analysis and report on qualitatively different dynamics as we change the injection strength and/or the detuning. We show that PS may be strongly influenced by the presence of those dynamics. Our numerical results reveal period doubling dynamics that emerge from a Hopf bifurcation associated to an elliptical polarized injection locking state. Pure frequency-induced polarization bistability, i.e., when the detuning is changed for fixed injection power, is studied theoretically. Our results show that, depending on the level of the fixed injection strength, frequency induced PS may be achieved with or without hysteresis.

Vertical Cavity Surface Emitting Lasers (VCSELs) often present switching between two orthogonal polarization states when varying parameters like e.g. current or temperature. Around such a switching point, the system randomly jumps between these two polarization states (mode hopping), driven by noise. In this contribution, we present experimental and numerical results showing the effect of coloured noise, externally added to the current, on the switching characteristics of a VCSEL.

We theoretically investigate the polarization-resolved dynamics of two vertical-cavity surface-emitting semiconductor lasers that are mutually coupled through coherent optical injection. We find a sequence of bistable polarization switchings that can be induced by either changing the coupling strength or the optical propagation phase. The successive polarization switchings are correlated to the creation of new compound-cavity modes when these parameters are continuously varied. The switching dynamics and the role of asymetries are also discussed.

Quantum-dot semiconductor lasers have several distinctive features when compared with bulk and quantum-well devices. The phase-amplitude coupling of such devices was predicted to be near zero, but several experiments have shown this not to be generally the case. Here, we review several experimental investigations and their theoretical underpinnings.

A high-growth-temperature step used for the GaAs spacer layer is shown to significantly improve the performance of 1.3-μm multilayer InAs/GaAs quantum-dot (QD) lasers. The high-growth-temperature spacer layer inhibits threading dislocation formation, resulting in enhanced electrical and optical characteristics and hence improved laser performance. The combination of high-growth-temperature GaAs spacer layers and high-reflectivity (HR) coated facets has been utilized to further reduce the threshold current and threshold current density (J_th) for 1.3-μm InAs/GaAs QD lasers. Very low continuous-wave room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A/cm² are achieved for a 3-layer device with a 1-mm long HR/HR cavity. For a 2-mm cavity the continuous-wave threshold current density is as low as 17 A/cm² at room temperature for an HR/HR device. An output power as high as 100 mW is obtained for a device with HR/cleaved facets. The high-growth-temperature spacer layers have only a relatively small effect on the temperature stability of the threshold current above room temperature. To further increase the characteristic temperature (T₀) of the QD lasers, 1.3-μm InAs/GaAs QD lasers incorporating p-type modulation doping have been grown and studied. A negative T₀ and J_th of 48 A/cm^-2 at room temperature have been obtained by combining the high-growth-temperature GaAs spacer layers with the p-type modulation doping of the QDs.

We report on the growth and characterization of low threshold 1.32-μm quantum dots (QDs) laser diodes. The quantum dot active region was optimised to get the highest photoluminescence emission and the lowest Full Width at Half Maximum (FWHM). From samples containing multilayer QDs and using the Limited-Area Photoluminescence (LAPL) technique we have shown that the gain of an N-layer structure is higher than N times that of a single layer. This enhancement is attributed to the increase of the quantum dot density in the upper layers and also to the use of the high growth temperature spacer layer. Broad area laser diodes were processed from the grown samples containing three layers of InAs QDs grown directly on GaAs and capped with 4-nm-thick In_xGa_1-xAs layer. Than measurements were performed at room temperature under pulsed excitation. The laser diodes operate at room temperature and emit between 1.29 and 1.32-μm which is beyond the strategic telecommunication wavelength. The characteristic temperature is around 80 K and very stable in the hole range of the operating temperature (from 0 to 90 °C). The internal quantum efficiency is 53% and the modal gain per QD layer was estimated to be ~ 6 cm^-1. For an infinite cavity length a threshold current density of 8 A/cm² per QD layer was obtained. From the calculation of the optical confinement of QDs, we have estimated a material gain of 1979 cm^-1.

We analyzed effective masses for In_yGa_1-yAs_1-xN_x/GaAs quantum-well structures within self-consistent approach by solving 10-band k.p Hamiltonian matrix with the Poisson equation. Both single well and double well systems were considered. Numerical results have been presented for a large range of material and structural parameters. Our results show that significant variation in the effective masses is possible by adjusting the relevant parameters and that the effects due to self-consistency are small.

We present a comprehensive description of electrically-driven vertical-external-cavity surface-emitting diode lasers (VECSELs) at 980 nm, mode-locked by saturable absorber mirrors. A novel partially-integrated time-domain model combines accuracy and flexibility, allowing for a semi-analytical stability analysis of the compound-cavity modes, tracking the mode-locking onset and an optimization analysis. The linear stability analysis of the monochromatic solutions (i. e., the compound cavity modes) indicates that single mode solutions exist and are stable only in a limited current range around threshold. Increasing the current above this current level leads to a multimode solution through a Hopf bifurcation. This bifurcation point is followed by a continuous transition leading from harmonic oscillations to fully-developed pulses that correspond to the mode-locked solution. We obtain stable, fully-developed mode-locked pulses of few tens of picoseconds at 15 GHz repetition rate in good agreement with reported experimental results. We discuss the dependence of the mode-locking regimes on the reflectivity of the distributed Bragg reflectors, spot area of the spatial mode, and number of quantum wells in the emitter and absorber cavities. The optimization analysis reveals that, in order to favor the mode-locking onset, the effective coupling between the emitter and saturable absorber cavities has to be optimized through the standing wave pattern in the composite cavity and spot-area of the spatial modes.

We apply the self-mixing method for the measurement of the linewidth enhancement factor of several types of semiconductor lasers. The α-factor value above threshold is determined by analysing the small perturbations that occur to the laser when it is subjected to moderate optical feedback, relying on the well-known Lang-Kobayashi equations. The method is applied to Fabry-Perot, VCSEL, External Cavity Laser (ECL), DFB, Quantum Cascade Laser. It is found that for some lasers the α-factor varies with the emitted power, and these variations can be correlated with variations in the laser linewidth.

We present measurements of the linewidth enhancement factor of a distributed feedback quantum cascade laser (DFB-QCL) using the so-called self-mixing technique. The linewidth enhancement factor is investigated by analyzing optical feedback induced changes of the emission properties of the laser. We will demonstrate that our self-mixing setup works well with QCLs in the mid infrared wavelength regime, and that it is possible to use the obtained signal to extract the linewidth enhancement factor. We present a setup that records the self-mixing signal with the voltage signal across the laser device using the laser as a detector itself. In this contribution we will show the advantages of this measurement technique. First measurements of the linewidth enhancement factor yield values that rise from 0.24 to 2.6 with an increase of the injection current of the QCL. We will discuss the influence of the injection current on the linewidth enhancement factor.

Through absorber length optimisation, sub-picosecond pulse generation and low timing jitter are demonstrated in a 20GHz passively mode-locked quantum-dot laser diode. Pulse-widths as low as 800fs and timing jitter performance of 390fs (20kHz-50MHz) are achieved.

The monolithic integration of photonic circuits will open new perspectives for optical communication networks. It will enable higher transmission rates, new functionalities, higher functional densities, leading to all-optical networks and reduced cost for telecommunication. Mode-locked laser diodes (MLLDs) will play an important role for short pulse generation in Tb/s networks for the transmitters, as well as for clock recovery for the receivers and optical regenerators. To overcome the limitations of conventional monolithically integrated MLLDs, where the pulse width is limited by the relatively slow absorption recovery, we demonstrate an ultrafast semiconductor saturable absorber based on the uni-traveling-carrier (UTC) concept. The UTC absorber is designed to be monolithically integrated in InGaAsP/InP mode-locked laser diodes grown by MOVPE. The absorber shows a saturation energy of E_sat,abs of 1pJ at 1.55μm and a voltage-dependent recovery time of 2ps at 2V reverse bias. The importance of an optimum absorption-bandgap to absorber-length ratio is demonstrated to keep the saturation energy low. The voltage-dependent absorption and absorption recovery time make this absorber ideal for hybrid mode-locking and synchronization to an external RF-source.

An uniform Bragg grating as InGaAsP/InP integrated chirped pulse compressor in transmission is studied. An exhaustive numerical analysis in Bragg grating parameters as length, coupling coefficient and detuning related to chirp compensation and the quality of the output ultrafast pulses is presented. The influence of the time-width and chirp of the input pulse has been also taken into account.

The sensitivity to optical feedback of 1.55 μm AR/HR distributed feedback semiconductor lasers (DFB) is presented in this paper. The onset of the coherence collapse which is the most critical feedback regime for optical transmissions is theoretically investigated and with a stress on its dependence with facet phase effects (FPE). Taking into account FPE on both facets, the sensitivity to optical feedback is evaluated with respect to both the coupling strength coefficient and the feedback level. The first part of the paper shows that due to the HR-facet, a distribution up to several dB on the coherence collapse thresholds is predicted over the whole DFB laser population. The second part concentrates on the coherence collapse dependence with respect to the antireflection (AR) coating. Calculations show an enhancement of the coherent collapse threshold distribution up to 5 dB due to AR coating impairment. Those simulations are of first importance for optical transmissions since they show that for AR coatings beyond 10^-4, the sensitivity to optical feedback of AR/HR DFB lasers is extremely difficult to evaluate from a laser to another. On the other hand, for AR coatings below 10^-4, all feedback performances are directly connected to the laser wavelength and lasers can be selected for high bit rate isolator-free transmission.

In the paper, the problem of the effective enhancement of electron capture efficiency has been considered for MQW structures. Different approaches to the problem are used. The most effective one is based on embedding of additional layers in SQH region. We have investigated the influence of such layers on two types of carriers' capture. The first one is the capture of bound carriers from reservoir states in SQH region and the second one is the capture of free carriers from quasi-continuum states. As a result, we have obtained up to tenfold increase of electron capture efficiency.

In this article, we investigate the anomalous temperature characteristics of InGaN/GaN multiple quantum-well (MQW) blue light emitting diodes (LEDs), with multiquantum barriers (MQBs) and GaN barriers, in depth via an examination of the luminescence intensity and carrier transport temperature evolution. The experimental evidences for electrical properties of two diodes exhibited the ideality factor extremely departure from unity, and the anomalies were characterized by pseudo-temperature T_o and carrier tunneling behavior. With respect to conventional GaN barrier devices, devices with MQBs inherently exhibit a small pseudo-temperature To with a small characteristic energy and charge population of the multilayer interface, over a variety of temperature and voltage ranges. Due to the less interface state distribution and the more effective density of state (DOS), the excitons formed in the MQB sample augment the spectral radiations at the temperature higher than 180 K. Furthermore, the carrier tunneling processes via the extent of the charge population consequently cause anomaly more T_o and further characteristic energy, result in the abnormal deterioration of the EL intensities with small DOS for these two LEDs below 180 K. These results also demonstrate that an introduction of well-designed barriers within a heterojunction configuration can be used to perform device improvements by governing the coupling of dynamical transports to spontaneous emissions. All observed correlations suggest that the carrier transport process is essentially responsible for the improvement of the luminescence characteristic. Accordingly, the MQW with the well-designed MQB structures not only exhibited the thermal-insensitive luminescence, but also inhibited the energetic carrier overflow.

We numerically study a novel scheme of generating linearly chirped signal utilizing the nonlinear dynamics of an optically injected semiconductor laser. With proper adjustment, the optically injected semiconductor laser can be operated in an instable region where the output of the laser exhibits periodic oscillation. The oscillation frequency of the injected laser can be controlled by simply varying the strength of the injection light. By sweeping the injection strength in time, desired chirped signal with very high linearity can readily be obtained. Without modulating the frequency of the laser through either direct current modulation or external frequency modulation, large modulation frequency exceeding 7 GHz is achieved. To suppress the amplitude modulation, a cascaded scheme is further considered that the chirp light generated from the second laser is further injected into a third laser. By tuning the third laser to an injection-locked state, the third laser reproduces the chirp signal injected but with an amplitude modulation greatly suppressed. In this paper, chirp bandwidths, chirp rates, and linearity of the chirp signals generated are studied. A chirp rate of more than 100 GHz/μs is obtained, while the bandwidth of the chirp signal exceeds 7 GHz. The relation between amplitude suppression and chirp rate is also presented. Moreover, the dependence of peak-to-peak intensity modulation suppression on the injection strength is investigated as well.

A theoretical investigation of the static and dynamic behaviour of an optically injected multitransverse mode vertical-cavity surface-emitting laser is performed. Selection of the fundamental transverse mode is induced by injecting light with a polarization that is parallel to the one of the fundamental mode. We analyze two different situations. The first one corresponds to operation in the fundamental and first higher-order transverse modes. Selection of the fundamental mode is achieved when the polarization of both transverse modes is parallel or orthogonal. The second situation corresponds to operation in more than two transverse modes. Selection of the fundamental mode is obtained when the higher order modes are orthogonally polarized to the fundamental mode. The injected power required for that selection is much higher than in the two-mode operation. That selection is not obtained when the higher order modes are parallel to the fundamental mode. A rich variety of nonlinear dynamics have been found out of the stable locking operation. A regime where the fundamental and first higher order mode evolve in a chaotic way is found for small positive detunings and small injection powers.

We present results on the characterization of the main parameters of DFB lasers for its use in direct modulation: chirp parameter, linewidth, relaxation frequency and RIN, obtained from measurements of the emitted optical spectrum in continuous operation mode using a high resolution (10 MHz) and high dynamic range (80 dB) optical spectrum analyzer. Results obtained from the characterization of commercial grade available DFB lasers with this method, present typical parameter values, but are also checked with well-know, but more resource demanding, methods involving modulation and optical to electrical conversion.

In this work we report on a novel optical design for beam shaping and focalization of high-power diode laser bars. The goals of our study are: the increase the optical throughput of the beam shaping device with respect to standard solutions and either to enhance the irradiance on a target or to inject the laser beam into a smaller fibre than with respect to beam shaping system based on plane surfaces. The high power diode laser bars pose serious difficulties in their optical handling due to their strong difference between the two transverse axes, which induce a strong astigmatic and asymmetric output radiation. As is well known, the beam quality is very different in the two axes called slow axis and fast axis, and in particular the slow axis is composed by the superposition of several multimodal sources. The beam quality in this axis is very low (its etendue may exceed 2000 mm mrad). On the other hand, the fast axis has a very high beam quality, near diffraction limited, although with very high divergence (30°-50°). The common solution for the application of the laser radiation is a fast axis aspheric micro lens in front of the emitters, in order to achieve its collimation. Typical values of the fast axis collimated beam are 0.7mm and less than 6mrad. However, the so obtained collimated beam is poorly focusable with a standard lens, and a few methods were proposed to overcome the problem. The more relevant solutions include: the stepped mirror technique, the plane parallel mirrors pair, micro prisms array and confocal micro lens array. Each of these techniques is based on the equalization of the beam parameter product by the subdivision of the beam in the slow axis and its reshaping. For all these techniques the efficiency spans from 50% to 70%. The best focalization results allow the coupling in a fibre of 400μm diameter, with NA-0.22. The aim of this work is the design and the realization of a new device, that is considered as target the following aspects: 1) the maximum optical efficiency in the beam shaping process, 2) the optimal equalization of the beam parameter product for the two axes, 3) the use of few optical elements and 4) a very compact size. These goals are addressed by a scheme that splits the collimated beam from the laser diode into different portions while the length of the optical paths of each sub element is kept constant, and by the subsequent use of short focal length aspheric lenses for the focalization of the transformed beam. Each sub-beam is deflected by a couple of plane parallel mirrors, whose normal is directed to equalize the BPP without any mutual shadowing. An optimal solution can be easily envisaged for a laser source of common size of 0.7 x 10 mm. The condition on equal optical path length has the noticeable property of placing the virtual position of the individual portions into which the original beam is split at the same distance with respect to target. Thanks to this, their subsequent focusing is unaffected by the axial displacement of the common solution by the stepped mirrors. In fact, to correct this effect, this latter technique requires the use of a prism pair, involving complexity, size enlargement and higher costs. In this work both an extensive ray tracing and optical analysis is presented as well as the experimental characterization of an experimental model. Moreover, we also report on the technique for the realization of th tilted-face plane mirrors of which is composed our beam shaping device. The scheme of beam shaping here reported can be extended to higher power beam by means of the technique of the beam combination by polarization coupling or that of the optical beam compression. Examples of theses developments are discussed in the paper, and experimental results presented. The most direct applications of the class of optical devices here reported are the high power diode laser direct application in material processing or manufacturing, the coupling into multimode optical fiber of the diode laser radiation as well as the fiber laser end pumping.

The authors propose a simple source based on mode-locked semiconductor lasers using linearly chirped fibre Bragg gratings external cavities to generate transform-limited pulses. Effects of the apodisation of Bragg grating on the source performances are experimentally investigated.

We present a fully digital stabilized semiconductor laser system designed to operate as a fiber-optic front-end of a pulsed power laser PALS (Prague Asterix Laser System). The replacement of the PALS master oscillator is a part of a broader effort to rebuild PLAS into a laser generating shorter pulses with higher pulse power by the technique of optical parametric chirped pulse amplification. With an operating wavelength of 1315.15 nm the stabilized laser is based on a telecommunication single-frequency DFB diode. The frequency stabilization is derived from the same transitions in dissociated iodine as those employed in the following power amplifiers. The lines are detected by means of linear absorption in a heated cell filled with thermally dissociated iodine. The technique of laser frequency stabilization folows the demands of a fully automated self-contained system operated by a remote control. The detection scheme is based on a derivative spectroscopy with a current frequency modulation and thermal wavelength control. The detection chain together with stabilization servo loop is fully digital represented by two signal-processing single-chip controllers.

We present a laser system based on a tunable high-power laser diode optimized for maximum efficiency of the optical pumping process of Rb atoms. The system represents the crucial part of the HpG (hyperpolarized gasses) production process. It is designed to operate in medical and industrial applications to come. We concentrated on the laser diode emission linewidth reduction because of the efficiency of the optical pumping process. The emission linewidth was reduced approximately from 1 THz to 69 GHz with only half of the total optical power loss and quadruple increase of the power spectral density at the wavelength of desire. Furthermore we present the cooling system for high-power laser diode bar and the measured laser diode bar emission line too.

Numerical and experimental results of output dynamics investigations of AR-coated broad area lasers (BALs) above laser threshold are presented. The BALs are subject to feedback from a free-space external Fourier-optical 4f-setup with a spatial reflective filter in the Fourier-plane for transverse mode selection. It is shown theoretically and experimentally that under certain pump current conditions the BALs are operating in a repetitive self-pulsation mode. Pulse duration is approx. 1 ns at repetition rates of 200 to 500 MHz. Using the same setup active mode-locking of a BAL is achieved experimentally. Pulse durations of 103 ps are obtained. The Gaussian-like fundamental and higher order transverse modes up to mode No. 4 can be adjusted while the laser is operating in a mode-locked state. Experimentally, the simultaneous combination of mode-locking, transverse mode selection, and pulse shaping of a BAL in a modified 4f-setup implementing a spectral filter is investigated. Employing an optimized spectral sinc-like function as amplitude and phase filter the mode-locked BAL emits nearly square-shaped pulses with a pulse duration of 705 ps, while running close to the Gaussian-like transverse mode.

We study the time evolution of the polarization state of the light emitted by a Nd:YAG laser as the direction of the linearly polarized pump beam is changed. The accurate description of the emitted polarization state is an exciting topic encountered in many laser systems and often depends on the peculiarities of the laser structure. However, we expect that the behavior of our Nd:YAG laser will highlight key polarization properties of many Class B lasers which include semiconductor lasers. As we shall demonstrate experimentally, numerically, and analytically, the slow evolution of the inversion of population relative to the laser fields is responsible for unusual polarization switching properties.

Anisotropy has been predicted of the energy flux of radiation in 'isotropic' semiconductor stripe laser pumped with an electron beam. The physical basis of the effect has been delivered by the worked out model of an acoustically active laser medium that directly results in the sought anisotropy of the output energy flux of radiation emanating from the cavity if a rate of the acoustic phonons generation is taking into account. Profound exposing of an integral output lasing power to an excited phonon fluxes has been derived for the pulsed strip-light-emitters designed on the basis of 6mm semiconductors. Quantitative analysis has been done for the strip laser with a fixed slit aperture on the basal plane of the (0001) CdS plate. For the longitudinal geometry of pumping, in the framework of the model put forward a difference has been predicted in the integral output power of lasing delivered through the output (0001) face of the devices in the form ΔP = A_mτ_wj²f, where A_m is the medium factor, τ_w is the photon lifetime relatively to the output, j is the pumping current density, f is the cavity form factor. Overall, acoustic impact has been revealed on the lasing anisotropy, an additional source has been manifested of the pumping losses, relationship has been established between the strip laser beam shape and the laser performance, the method based on the carrier lifetime approach has been additionally proposed to study phenomenon, understanding and direct calculating have been advanced of the performance of the considered type emitters.

This work reports single-frequency laser oscillation at λ = 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 (λ = 501.5 nm) with an output power around 60 mW.

We present application of methods for calculation of parameters of apodized fiber Bragg gratings (FBG). We used combination of methods based on layered dielectric media (LDM) and the transfer matrix. On the contrary to the other calculation techniques the LDM method is based on sequence of thin films of dielectric media assembled in the direction of wave propagation. The combination of the LDM method and the transfer matrix method can be used to the calculation of arbitrary fiber gratings with high precision. For this designed apodized FBG we calculated the phase mask to manufacture by interference patterns. The phase mask and the fixation bottom of the fiber were made by e-beam lithography to achieve highly precise stability during manufacturing. We present the set-up of this system for writing FBG by pulsed UV laser with wavelength 266nm. Measurement of commercially available FBG with comparison to our calculated FBG is presented. We put together the absolute fiber laser interferometer where Vertical Cavity Surface Emitting Laser (VCSEL) is used to easy employment of FBG to stabilization and control the tuning range of the wavelength. The first set-up is presented.

In this work we present to our knowledge the first spatial and dynamical model of semiconductor vertical-cavity surface-emitting laser (VCSEL) incorporating a spatial built-in optical waveguide created by the defect in the two-dimensional photonic crystal (PC). The PC is created by an array of air-holes etched in VCSEL. Results of investigations of power versus current and dynamic characteristics of a conventional proton-implanted VCSEL and VCSELs incorporating PC defect waveguides operating with effective index and photonic band-gap guidances are presented and discussed. Results show that the VCSELs with incorporated PC between laser mirrors provide a dramatic decrease of the power of the fundamental laser mode. Application of multiple-defect photonic band-gap (PBG) waveguides provides an additional dominance of the fundamental mode, and thus, the PC creates high-power but single-mode radiation of VCSELs which is impossible in conventional VCSELs. The VCSELs with PCs made in top mirror are characterized by an extremely low power of the radiation comparing to same VCSELs without the PC. Preliminary analysis of dynamical responses of the VCSELs show that VCSELs with PCs incorporated between laser mirrors could have slightly better modulation properties than VCSELs without PCs.

The conventional measuring system of laser feedback noise for an optical pickup was implemented specifically only for laser diodes by using a static optical system. With no close-loop servo control, it is impossible to measure the genuine laser noise distribution of a pickup while operating in an optical drive. With modifying the optical system of a commercial pickup, this study was integrated with precision mechanical design, optical design, servo control design, and opto-electronic signal measurement for providing a dynamic real-time laser feedback noise measurement system. With this system, some experimental results were obtained. The laser feedback noise is responsible to the focusing point within the linear range of an optical pickup head. It has the maximum value while the lens is on the best focus. The central frequency of noise is dependent on the disk rotation speed and the noise level is reducible by increasing the disk rotation speed.

Nowadays, vertical cavity surface emitting lasers (VCSELs) provide a very exciting area of research. The unique geometry of VCSELs results in several significant advantages over their edge-emitting counterparts, including low threshold current, single-longitudinal-mode operation, circular output-beam profile. The optimization of the DBR structure is of fundamental importance to increase the performance of optical systems based on the VCSEL technology. To this aim, sophisticated modelling techniques are needed, where only negligible or no approximations are included in the calculations. Therefore, we have used the Floquet-Bloch theory (FBT) formalism to simulate the DBR performance of VCSEL structures. In this paper we explain the general VCSEL theory and propose a number of simulations to individuate the optimal configuration of DBR mirrors with the aim to maximise the output power laser and reduce the threshold current density. The VCSEL optimization is carried out by considering the best trade off among various parameters, including period number, materials, and doping concentration and profile. It is clearly shown the superiority of the FBT approach in the prediction of the best DBR performance and VCSEL properties by comparing results (reflectivity, spectrum, peak wavelength, gain) with other well-known methods, such as the transfer matrix method (TMM) and coupled-mode theory (CMT).

We develop a rate equation model describing the polarization switching phenomenon in vertical-cavity surface-emitting lasers taking into account the major underlying physical origins of this behavior: spin flip relaxation effects, temperature variations and both residual strain in the quantum well and stresses externally applied to the device. To include effects of temperature and stress or strain, we describe the optical material properties of the quantum well by way of a recently derived analytical approximation for the optical susceptibility of uniaxially stressed quantum-well lasers at low temperatures. We review the influence of temperature and stress on the polarization-dependent gain and the linewidth enhancement factor. Combining this information with cavity anisotropies and spin carrier dynamics, we present a model that provides a unified overview of the polarization switching phenomenon. By way of a linear stability analysis, the polarization mode stability is discussed and compared with earlier experimental results.

Short pulsed laser sources have recently been under investigation for applications in high speed optical communications systems. A key issue to achieve high quality reliable short pulses is the need to compress and improve the shape of the pulse train. Nonlinear Optical Loop Mirrors (NOLM) provides both compression and reshaping of the optical pulses. The present work turns the attention to the influence of noise in the compression behavior of NOLM. Characteristics such as compression factor, signal to noise ratio, dynamic RIN level, BER and timing jitter are considered. The results obtained will be the basis for the design of a compact high quality ultrashort optical pulse source at 40 GB/s with monolithic semiconductor compressor. This device is under investigation within the MONOPLA European Project.

The study of the coupling phenomena and of the operation regions in laterally coupled diode lasers is a major key parameter for the understanding and development of these devices as a solution for the new optical communications systems. To understand the behaviour of these devices a complete study of their dynamics must be performed. In order to do so, in this paper a study of both the noise spectrum and frequency response is made. The aim of this study is to compare the performance of these devices as a single ridge laser and as a twin stripe operation.

Theoretical analysis of the emission line broadening in quantum-well lasers is carried out taking into account the Coulomb interaction of current carriers in the approach of two-dimensional electron-hole gas. The principal idea of the used method consists in the determination by means of the perturbation theory for many-body systems the functional behavior of tails of the emission line and in the subsequent extrapolation of the central part of the line according to a normalization requirement. Based on the obtained in the parabolic band approximation analytical shape function for the homogeneously broadened spectral line, the influence of various factors on the optical spectrum is analyzed. An explanation of the experimental data, including the spectral line asymmetry and the linewidth change versus temperature and power excitation, is given. Results of the numerical calculations are presented for quantum-well heterostructure laser diodes in the GaInAsSb-AlGaAsSb-GaSb system. Spectra of luminescence and gain in dependence on the quantum well width, temperature, and excitation level are examined. Spectrum transformation in the long-wavelength range and tuning curves for the GaSb-based laser emitters are also discussed. New possibility to overlap the spectral emission diapason of 2.2-2.9 μm is examined due to asymmetric multiple-quantum-well heterostructure configuration of the active region.

In this work we numerically calculate the linewidth of a single-mode monolithic Semiconductor Ring Laser (SRL) operating in the unidirectional regime. A new expression for the SRL linewidth is derived from the conventional Henry's formula, and the importance of different physical parameters is discussed. In particular, the linewidth is mainly determined by the SRL diameter, because the waveguide bending loss have a very strong dependence on the diameter. We show that circular SRLs with diameter smaller than 180 μm are unlikely to be operated CW. As a general rule, the linewidth decreases for increasing SRL diameter, and it varies from 15 MHz for 200 μm diameter down to 1 MHz for 2000 μm diameter.

We summarize the recently developed approach to modelling quantum well based semiconductor lasers based on Green's functions. The derivation of quantum Boltzmann equations is outlined and Langevin approach to spontaneous emission is described. The DFB structure is discussed. The resulting small-signal equations are derived. Finally, the application to simulations of practical structure is illustrated and some numerical results are presented.