This PDF file contains the front matter associated with SPIE Proceedings Volume 9892, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We describe the lasing characteristics of a compact tunable laser source formed by the butt-coupling of a reflective indium phosphide optical amplifier to an SU8 waveguide coupled to few-mode photonic crystal reflector. The short cavity length ensured that only a single longitudinal mode of the device could overlap with each photonic crystal reflection peak.

Spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) provide novel opportunities to overcome several limitations of conventional, purely charge-based semiconductor lasers. Presumably the highest potential lies in the spin-VCSEL's capability for ultrafast spin and polarization dynamics which can be significantly faster than the intensity dynamics in conventional devices. By injecting spin-polarized carriers, these coupled spin-photon dynamics can be controlled and utilized for high-speed applications. While relaxation oscillations provide insights in the speed and direct modulation bandwidth of conventional devices, resonance oscillations in the circular polarization degree step in for the spin and polarization dynamics in spin-VCSELs. These polarization oscillations can be generated using pulsed spin injection and achieve much higher frequencies than the conventional intensity relaxation oscillations in these devices. Furthermore polarization oscillations can be switched on and off and it is possible to generate short polarization pulses, which may represent an information unit in polarization-based optical communication. The frequency of polarization oscillations is mainly determined by the birefringence-induced mode splitting between both orthogonal linearly polarized laser modes. Thus the polarization modulation bandwidth of spin-VCSELs can be increased by adding a high amount of birefringence to the cavity, for example by incorporating mechanical strain. Using this technique, we could demonstrate tunable polarization oscillations from 10 to 40 GHz in AlGaAs-based 850nm VCSELs recently. Furthermore a birefringence-induced mode splitting of more than 250 GHz could be demonstrated experimentally. Provided that this potential for ultrafast dynamics can be fully exploited, birefringent spin-VCSELs are ideal devices for fast short-haul optical interconnects. In this paper we review our recent progress on polarization dynamics of birefringent spin-VCSELs and investigate numerically how ultrafast polarization oscillations can be utilized for data communication using simulations based on the spin-flip model.

We have devised a novel oxide-free and regrowth-free approach for optically controlled current confinement in vertical-cavity surface-emitting lasers (VCSELs). This is realized with a monolithically integrated phototransistor (PT), which is configured as an optical switch and embedded between the two Bragg reflectors. We have fabricated functional PT-VCSELs by one-step epitaxial growth plus metal deposition with different top contact sizes. We present light–current–voltage characteristics of the lasers as well as a simple theoretical model explaining the occurrence of a distinct turn-on point and clarify epitaxial design requirements to reach strong optically controlled current confinement.

An overview is given about the recent improvement in 1.5 μm QD lasers for direct modulation. Based on improved QD epitaxy with a reduced inhomogeneous size distribution, record values in small signal modulation bandwidth of more than 15 GHz and in digital modulation of up to 36 GBit/s were obtained. Due to the high modal gain and robust ground state transition, the temperature dependence of the laser performance could be very much improved with characteristic temperatures of T₀ = 125 K and T₁ near to 400 K. Also the impact of the temperature on the digital modulation speed will be discussed.

In this work, the sensitivity to external optical feedback of two different InAs/GaAs QD Fabry-Perot (FP) lasers is investigated under long cavity regime. The first, which has a 1.5 mm-long cavity, emits on the GS while the second one, which is 1 mm long, radiates solely on the ES transition. The results indicate that for the same bias level, the ES laser presents a larger sensitivity to external feedback, the critical level being under 1% versus above 9% for the GS laser. In particular, the ES laser exhibits a route to chaos such that the first destabilization occurs for a lower feedback strength than for the GS laser.

Phase noise of a single mode semiconductor laser is reduced drastically by introducing a newly proposed optical negative feedback scheme. Proof-of-concept experiment confirms that the spectral linewidth of a semiconductor laser can be reduced to 1/1,000 successfully by applying the scheme.

Semiconductor lasers under external perturbations can manifest a broad variety of complex dynamics in their output power, from periodicity to high dimensional chaos. One of their characteristic behaviors, when submitted to optical feedback, is their excitability. These optical excitable devices, that mimic neuronal behavior, can serve as building-blocks for novel, brain-inspired information processing systems. Neuronal systems represent and process the information of a weak external input through correlated electrical spikes. Semiconductor lasers with low to moderate optical feedback, i.e. in the low frequency fluctuations (LFF) regime, display optical spikes with intrinsic temporal correlations, similar to those of biological neurons. Here we study the laser optical spiking dynamics under the influence of direct pump current modulation, focusing on the influence of the modulation frequency and amplitude. We characterize time correlations in the sequence of optical spikes by using symbolic ordinal analysis. This powerful tool allows detecting symbolic patterns in the laser output, and to quantify the effect of the frequency and amplitude of the modulation on the patterns probabilities. The experimental results are in good qualitative agreement with simulations of the Lang and Kobayashi model.

Common applications using optical chaos in a semiconductor laser include, among others, random number generation and chaos-encrypted communications. They rely on chaos of high dimension with a large bandwidth and a high entropy growth rate to achieve good results. Optical chaos from a semiconductor laser with conventional optical feedback (COF) is typically used as the primary source of chaos. Additional enhancing techniques are used to enlarge the chaos bandwidth. In this contribution, we show experimentally how using phase-conjugate feedback (PCF) can naturally produce a chaos of higher bandwidth than COF. PCF is an alternative to COF which consists of feeding the conjugate of the optical output back into the laser cavity, with a time-delay. Thanks to an oscilloscope with a fast sampling rate, and a large bandwidth, we were able to measure and observe the time-resolved frequency dynamics with a good precision. In the regime of low-frequency fluctuations (LFF), where dropouts of optical power occur randomly, we were able to compare the difference in dynamics before and after a dropout, for PCF and COF. In the range of attainable reflectivities, we measured a bandwidth increase of up to 27 % with PCF when compared to COF. Interestingly, we found that high-frequency dynamics are enabled before dropouts in PCF, where it was theoretically shown that the system jumps between destabilized self-pulsing states at harmonics of the external-cavity frequency, the so-called external-cavity modes (ECMs). This observation tends to confirm that ECMs in PCF are indeed fundamentally different than ECMs in COF, where they are simple steady-states. Finally, we believe that the enhancing techniques used with COF could also be used with PCF to obtain even wider chaotic bandwidths. These results could lead to studies about the dimension and the entropy growth rate of chaos from a laser diode with PCF.

We demonstrate experimentally that optical chaos generated by a laser diode with optical feedback is suitable for compressive sensing of sparse signals. Specifically, we find that the coherence collapse regime guarantees that the generation of a sensing matrix, necessary for sparse reconstruction, has a comparable level of performance to those constructed with Gaussian random sequences. Our result opens new avenues for the use of optical chaotic devices for signal processing applications at ultra-high speed.

A set of differential equations with distributed delay is derived for modeling of multimode ring lasers with intracavity chromatic dispersion. Analytical stability analysis of continuous wave regimes is performed and it is demonstrated that sufficiently strong anomalous dispersion can destabilize these regimes.

We study both analytically and numerically the rate equations of a laser diode subject to a filtered phase-conjugate optical feedback (FPCF). We formulate dimensionless equations for the FPCF and determine the Hopf bifurcation conditions. The coalescence of different Hopf bifurcations as the filter width decreases suggests the disappearance of the external cavity modes for a narrow width. We confirm our analytical predictions with direct numerical simulations of the FPCF equations.

Fibre lasers have been shown to manifest a laminar-to-turbulent transition when increasing its pump power. In order to study the dynamical complexity of this transition we use advanced statistical tools of time-series analysis. We apply ordinal analysis and the horizontal visibility graph to the experimentally measured laser output intensity. This reveal the presence of temporal correlations during the transition from the laminar to the turbulent lasing regimes. Both methods allow us to unveil coherent structures with well defined time-scales and strong correlations both, in the timing of the laser pulses and in their peak intensities.

The complexity of chaos generated in two systems has been studied experimentally. The complexity of the chaos is quantified by calculating average normalized permutation entropy (HS(P)). In the first system, a chaotic output from a master laser (ML) is injected into a CW slave laser (SL). The results show that the complexity of chaos generated in the SL decreases with absolute value of the frequency detuning Δf₁, which means the complexity of the chaos is compromised with enhancing the bandwidth, as Δf₁ is increased. The second system comprises three vertical-cavity surface-emitting lasers (VCSELs); the first VCSEL (used as ML) was rendered chaotic by optical feedback, the second VCSEL is used as intermediate laser (IL), which is rendered chaotic when it is subject to optical injection from the chaotic ML and the third VCSEL is used as a SL and is a subject of optical injection from the chaotic IL, thus entering chaotic dynamics. In this three-VCSEL system, small, intermediate and wide bandwidths of the injecting chaos signals, have been used to study the effect of the bandwidth of the injecting chaos on the complexity of chaos generated in the SL. The results show that the bandwidth of the chaotic injection beam does not impact the complexity of the chaos generated in the SL for positive frequency detuning; however, for large negative frequency detuning, the complexity of the chaos in the SL has been reduced significantly for the intermediate and lower bandwidth of the chaotic injection beam.

We experimentally show how the nonlinear amplification properties of a micro-laser operating in the threshold region, sinusoidally modulated near its resonance (relaxation oscillations), can lead to several important advantages. First, suitably adjusting the bias point and the modulation amplitude, it is possible to obtain reliable trains of large amplitude, synchronous, well-resolved, narrow pulses, with injection currents moderate values of the injection current: the extension to nano-laser modulation is discussed. Second, adjusting the modulation amplitude and the working point it is possible to investigate the threshold properties of the laser: the computation of the second-order autocorrelation as a function of modulation amplitude shows a resonance-like phenomenon where the degree of correlation is degraded by the presence of the external action, only for small modulation amplitude, until true coherence sets in. This allows for a determination, with good accuracy, of the onset of E.M. field coherence. Since this resonance is quite sensitive to the modulation frequency, it also allows for a good determination of the optimal frequency at which the pulse trains can be generated. A physical discussion of these properties, in the context of threshold and coherence, is offered.

We report a theoretical and experimental analysis of the polarization switching found in a single-transverse mode VCSEL when subject to parallel optical injection. We have found a novel situation in which injection locking of the parallel polarization and excitation of the free-running orthogonal polarization of the VCSEL are simultaneously obtained. Analytical expressions for the power of both linear polarizations in the previous steady state are determined. We show that considering two linear polarization modes in a model of a VCSEL subject to parallel optical injection leads to simpler expressions than those found for a VCSEL with only a single linear polarization. We show that the power emitted in both linear polarizations depend linearly on the injected power. The stability region of this solution is measured in the plane injected power versus frequency detuning.

We present a novel approach to determine the thermal resistance and the internal temperature of vertical-cavity surface-emitting lasers (VCSELs) based on easily accessible laser parameters. The described method does not use any empirical parameters or pulsed measurements that are often mentioned in literature. We explain how to determine the thermal resistance and show the computation of the internal temperature for any operation point. Furthermore the data evaluation can be used for characteristic parameter extraction that enables us to establish an isothermal and temperature-dependent modeling of the VCSEL operation curves.

We report on the dynamic properties of 1.31 μm InAs/GaAs and 1.55 μm InAs/InP quantum-dot Fabry-Perot lasers with the main focus on the increase of their large-signal modulation capabilities. A GaAs-based edge-emitter structure incorporating a standard p-doped active region with ten quantum-dot layers enables 15 Gbit/s data transmission at 70 °C upon direct modulation. The large number of layers and wide barriers cause significant carrier transport limitations. Since the carrier distribution across the stack is not uniform, a graded p-doping profile is implemented leading to an increased data rate of 20 Gbit/s, but at the expense of somewhat lower temperature stability. GaAs-based lasers operating exclusively from the first excited state demonstrate a further data rate increase to presently 25 Gbit/s, due to the larger degeneracy of the higher quantum-dot energy levels. 25 Gbit/s data transmission at 70 °C is also achieved with InAs/InP quantum-dot devices emitting in the C-band. Four- and eight-level pulse-amplitude modulation formats are utilized to increase the data rate at a given bandwidth compared to a standard on-off keying scheme. Data rates up to 35 Gbit/s are presented for both wavelength bands. Monolithically integrated two-section mode-locked lasers based on the graded pdoping structure provide low-jitter optical pulse trains and are utilized as optical sources for non-return-to-zero transmitters. 80 Gbit/s on-off keying and 80 GBd (160 Gbit/s) differential quadrature phase-shift keying data transmission based on optical time-division multiplexing are demonstrated using a packaged 40 GHz module.

Frequency conversion using highly non-degenerate four-wave mixing is reported in InAs/GaAs quantum-dot Fabry- Perot lasers. In order to compress the spontaneous emission noise, the laser is optically injection-locked. Under proper injection conditions, the beating between the injected light frequency and the cavity resonant frequency dominates the dynamic behavior and enhances a carrier modulation resonance at frequencies higher than the relaxation oscillation frequency. Conversion efficiencies as high as -12 dB associated to a large optical signal-to-noise ratio of 36 dB are reported. The conversion bandwidth is extended up to 2.1 THz for down-conversion (resp. 3.2 THz for up-conversion) with a quasi-symmetrical response between up- and down-converted signals.

We investigate the spectrally-resolved relative intensity noise (RIN) of a dual state emitting quantum-dot (QD) laser in dependence on the laser biasing conditions. We study the RIN under free-running conditions as well as under external optical feedback (OFB). We find an improvement in RIN of the free-running laser when ground-state (GS) and excited-state (ES) emit simultaneously as compared to a single-state emission. Furthermore, we find an improvement in RIN under external OFB.

Depending on device and operating parameters, the emission of lasers based on InAs quantum dot (QD) material may come from the ground state (GS) only, from the first excited state (ES) only or simultaneously from both states. When the emission is from the ES only, optical injection at the GS frequency can completely suppress the ES output and instead, phase-locked emission from the GS can be obtained. We report on a variety of non-linear phenomena obtained when the frequency of the master laser is varied revealing two antiphase, dual-state excitable regimes.

We investigate the behaviour of a multimode two-color quantum dot laser subject to optical feedback. In particular, we focus on the effects of a variation of the external cavity length at the micrometer scale on the laser emission characteristics and especially on its optical spectrum. For each mode, we observe oscillations of the output power with different spectral amplitudes. No clustering or mode grouping effect is observed. Theoretically, we demonstrate a good agreement with a multimode two-color quantum dot laser model.

ABSTRACT The Vertical-Cavity Surface-Emitting Laser (VCSEL) is an established optical source in short-distance optical communication links, computer mice and tailored infrared power heating systems. Its low power consumption, easy integration into two-dimensional arrays, and low-cost manufacturing also make this type of semiconductor laser suitable for application in areas such as high-resolution printing, medical applications, and general lighting. However, these applications require emission wavelengths in the blue-UV instead of the established infrared regime, which can be achieved by using GaN-based instead of GaAs-based materials. The development of GaN-based VCSELs is challenging, but during recent years several groups have managed to demonstrate electrically pumped GaN-based VCSELs with close to 1 mW of optical output power and threshold current densities between 3-16 kA/cm². The performance is limited by challenges such as achieving high-reflectivity mirrors, vertical and lateral carrier confinement, efficient lateral current spreading, accurate cavity length control and lateral optical mode confinement. This paper summarizes different strategies to solve these issues in electrically pumped GaN-VCSELs together with state-of-the-art results. We will highlight our work on combined transverse current and optical mode confinement, where we show that many structures used for current confinement result in unintentionally optically anti-guided resonators. Such resonators can have a very high optical loss, which easily doubles the threshold gain for lasing. We will also present an alternative to the use of distributed Bragg reflectors as high-reflectivity mirrors, namely TiO₂/air high contrast gratings (HCGs). Fabricated HCGs of this type show a high reflectivity (>95%) over a 25 nm wavelength span.

The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well, giving rise to new and novel applications for medical, industrial, display and scientific purposes. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with high optical powers of >100mW with high reliability. Low defectivity and highly uniform GaN substrates allow arrays and bars of nitride lasers to be fabricated. We demonstrate the operation of monolithic AlGaInN laser bars with up to 20 emitters giving optical powers up to 4W cw at ~395nm with a common contact configuration. These bars are suitable for optical pumps and novel extended cavity systems. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space and/or fibre optic system integration within a very small form-factor.

In this paper we analyze the influence of the thickness of two oxide layers in a typical oxide-confined vertical-cavity surface-emitting laser (VCSEL) on the capacitance of the device and its electrical modulation properties. An analysis of the distribution of the potential and the energy of the electric field in this device is presented, and the influence of these fields on the laser's capacitance is described. It is shown that the oxide layer closest to the active region contributes in a very different way to the laser's capacitance compared to the second slightly more distant oxide layer, and a quantitative analysis of the impact of the thicknesses of these layers on the modulation time constants is presented.

We review our recent studies on capsule-shaped InP/InGaAs metallic-cavity lasers. By introducing an optimal curvature at the metallic sidewalls of conventional rectangular metallic lasers, the electric fields of the resonant mode are pushed effectively into the center of the mesa, which allows dramatic reduction of the plasmonic loss. The validity of the scheme is verified both numerically and experimentally. From three-dimensional finite-difference time-domain simulation and rate-equation analysis, we estimate that the threshold current can be reduced to as low as 60 μA with the effective modal volume of 0.45 μm³. Up to 4-fold increase in Q value is confirmed experimentally for the cavity structure with an optimal curvature.

We present numerical results on the effect of backscattering at the junctions of double bus ring resonators in a Vernier ring hybrid laser design. The structure is comprised off a pair of III-V gain media evanescently coupled to a silicon on insulator racetrack comprised of a pair of double bus ring resonators coupled together through straight and flared waveguide sections. We show how the small backscattering at the ring resonator junctions has the effect of splitting and shifting the resonances off the clockwise and counter clockwise propagating modes thereby modifying the feedback spectrum from the ideal case. We then simulate results such as light current (LI) curves, relative intensity noise (RIN) and laser spectrum, and compare the laser performance including backscattering effects with the ideal case.

In this paper, we present a novel 1x2 multi-mode-interferometer-Fabry-Perot (MMI-FP) laser diode, which demonstrated tunable single frequency operation with more than 30dB side mode suppression ratio (SMSR) and a tuning range of 25nm in the C and L bands, as well as a 750 kHz linewidth. These lasers do not require material regrowth and high resolution gratings; resulting in a simpler process that can significantly increase the yield and reduce the cost.

A novel approach is demonstrated for overcoming the trade-off relationship between the power consumption and transmission distance of an electro-absorption modulator integrated with a DFB laser (EADFB laser). We demonstrate that the monolithic integration of a short semiconductor optical amplifier (SOA) with an EADFB laser is effective in overcoming the limitation imposed by the Kramers-Kronig (K-K) relation of the EA modulator, which cannot be overcome with the conventional method of optimizing the MQW structure of the EA modulator. Our approach provides an EADFB laser with two advantages. One is that we can realize a higher optical output power with smaller power consumption than with a conventional EADFB laser by reducing the DFB laser injection current and allocating it to the SOA section. We design the SOA length based on this concept. The other advantage is the chirp compensation of the EA modulator with the SOA. To confirm the validity of this approach, we investigate the SOA length dependence on the basic characteristics. By using an EADFB laser integrated with a 50-μm-long SOA, we achieve a 2 dB increase in the modulated output power compared with a stand-alone EADFB laser with the same power consumption. We realize an extended transmission distance of 5 km at 40 Gbit/s, and a 1.55-μm-wavelength window, which is conventionally achieved for a 2-km SMF transmission with an EADFB laser. These results indicate that this approach is a promising way to realize a high-speed light source with low power consumption for future large capacity optical network systems.

We increased the Al content in the single quantum well InGaP/InAlGaP laser by strain-induced quantum well intermixing, and obtained a considerable enhancement (close to ten-fold increase) in the photoluminescence (PL) intensity. Among the annealing process investigated, we achieved lasing at 638 nm in conjunction with reduction in the lasing threshold current by close to 500 mA in a moderately intermixed laser. Lasing in orange color, as well as spontaneous emission in the yellow and green color regime, were also achieved by extending the annealing conditions. The significance of the current work became apparent when one considers that achieving these tunable wavelengths by increasing the Al content in quantum wells during epitaxy growth leads to severe lattice-mismatch and poor material quality. Hence, our Al "drive-in" intermixing process is a viable approach for forming Al-rich InAlGaP quantum well, which is essential for realizing efficient optoelectronic devices in the "green-yellow-orange gap".

Broad area Vertical-Cavity Surface-Emitting Lasers (VCSELs) have peculiar polarization properties which are a field of study by itself.^1-3 These properties have already been used for localized structure generation, in a simple configuration, where only one polarization component was used.⁴ Here, we present new experimental and theoretical results on the complex polarization behavior of localized structures generated in an optically-injected broad area VCSEL. A linear stability analysis of the spin-flip VCSEL model is performed for the case of broad area devices, in a restrained and experimentally relevant parameter set. Numerical simulations are performed, in one and two dimensions. They reveal existence of vector localized structures. These structures have a complex polarization state, which is not simply a linear polarization following the one of the optical injection. Experimental results confirm theoretical predictions. Applications of this work can lead to the encoding of small color images in the polarization state of an ensemble of localized structures at the surface of a broad area VCSEL.

We consider an optical ring cavity filled with a metamaterial and with a Kerr medium. The cavity is driven by a coherent radiation beam. The modelling of this device leads to the well known Lugiato-Lefever equation with high order diffraction term. We assume that both left-handed and right-handed materials possess a Kerr focusing type of nonlinearity. We show that close to the zero-diffraction regime, high-order diffraction effect allows us to stabilise dark localised structures in this device. These structures consist of dips or holes in the transverse profile of the intracavity field and do not exist without high-order diffraction effects. We show that high order diffraction effects alter in depth the space-time dynamics of this device. A weakly nonlinear analysis in the vicinity of the first threshold associated with the Turing instability is performed. This analysis allows us to determine the parameter regime where the transition from super- to sub-critical bifurcation occurs. When the modulational instability appears subcritically, we show that bright localised structures of light may be generated in two-dimensional setting. Close to the second threshold associated with the Turing instability, dark localised structures are generated.

We are interested in spatio-temporal dynamics of cavity solitons (CSs) in a transverse section of a broad area vertical cavity surface emitting laser (VCSEL) with saturable absorbtion subjected to time-delayed optical feedback. In the absence of delayed feedback, a single branch of localized solutions appears in the parameter space. However, in the presence of the delayed feedback, multistability of CS solutions emerges; The branches of CSs fill the surface of the "solution tube" in the parameter space, which is filled densely with increasing delay time. Further, our study reveals that the multistability of stationary solutions is caused by a delayed-induced phase bifurcation of CSs. Furthermore, it was shown that stability properties of CSs strongly depend on the delayed feedback parameters. In particular, the thresholds of the drift and phase bifurcations as well as corresponding bifurcation diagrams are obtained by a combination of analytical and numerical continuation methods. It turns out that both thresholds tend to zero in the limit of large delay times. In addition, we demonstrate that the presence of the delayed optical feedback can induce Andronov-Hopf bifurcation and a period doubling route to chaos. Moreover, a coupling between this bifurcation scenario with aforementioned delay-induced multistability leads to a complex spatio-temporal behavior of the system in question. The results of analytical bifurcation analysis are in agreement with those obtained by direct numerical integration of the model equation.

Tunable laser diodes are needed in a range of applications including wavelength division multiplexing, optical instrument testing, optical sensing and tera hertz generation. In this work, we investigate the stability of lasers which use filtered optical feedback for wavelength tuning. We investigate experimentally the dynamics induced by this on-chip filtered optical feedback.

In this study, we choose to use a compact device which combines a semiconductor ring laser with on-chip filtered optical feedback to achieve wavelength tunability. The filtered optical feedback is realized by employing two arrayed waveguide gratings to split/recombine light into different wavelength channels. Semiconductor optical amplifiers are placed in the feedback loop in order to control the feedback of each wavelength channel independently.

Experimental observations show that the stability of the clockwise and counterclockwise propagation modes depends on the feedback strength. Experiments also show that for a specific range of the feedback strength, anti-phase oscillations in the intensity of the clockwise and counterclockwise propagating modes can be induced. These oscillations could not be seen in the same semiconductor ring laser without filtered optical feedback. We investigate how the frequency and the amplitude of these oscillations change under the effect of filtered optical feedback. We also discuss how these anti-phase oscillations can be suppressed by properly choosing the feedback strength.

Catastrophic optical damage (COD) in semiconductor lasers is a major limiting effect for high-power operation. Several techniques like microphotoluminescence (μPL) mapping, focused ion beam (FIB) microscopy, and micro- Raman spectroscopy were employed to reveal the physics behind catastrophic optical damage, its related temperature dynamics, as well as associated defect and near-field patterns. High-resolution μPL images demonstrated that during COD, nonradiative dark line defects (DLDs) originate from the front mirror of the laser and propagate deep inside the cavity. Furthermore, FIB microscopy identified the epitaxial layers affected by COD, revealing that the DLDs are confined to the active region. In addition, deep-etching uncovered the DLDs by making them visible, and showed that they are composed of complex dislocation networks. Lasers that underwent a spontaneous breakdown where also studied. One missing piece to complete the characterization of COD is to analyze if the DLDs actually follow certain crystal direction lines inside the laser cavity, which are in general perpendicular to the output facet, or follow the path of the light-field intensity-maximum. Using a specially designed innovative device, namely an asymmetrical AlGaInP tapered laser, it is proven in this study that the COD is strongly dependent on the light-field intensity inside the laser cavity and not on certain crystal direction lines.

We discuss the impact of asymmetries and noise on the nonlinear dynamics of vertical-cavity surface-emitting lasers (VCSEL). We focus in particular on the effects of these features on the chaotic dynamics that can be generated by a free-running VCSEL due to the intrinsic competition between polarization modes taking place in these devices. Experimentally, we observe significant asymmetries especially in the statistics of the chaotic dynamics. We show that these behaviour can be explained theoretically by a combined effect of the system asymmetries and the noise. This work therefore brings new light on the interplay between deterministic and stochastic processes taking place in VCSELs.

We investigate theoretically the synchronization properties of the polarization chaos dynamics generated by a free-running vertical-cavity surface-emitting laser (VCSEL). Here, we focus on a one-way master-slave configuration - or unidirectional coupling - with two chaotic VCSELs. The spin-flip model is used to model the two devices and derived to account for the coupling between them. We demonstrate that the chaotic dynamics generated by the two lasers can indeed synchronize in the proposed configuration. The synchronization appears to be of high quality as we obtain a high-level of similarity between the emission characteristics of the master and slave laser dynamics.

In this contribution, we experimentally report recurrent switching between ground and excited state emission in a quantum dot laser controlled by optical feedback. We demonstrate that changing the phase of the optical feedback can efficiently induce switching between the two emission processes of the laser. Experimentally, by using an external mirror placed on a piezo-actuator, we were able to achieve incomplete switching between ground and excited state emission, i.e. without complete extinction of the modes. The switching takes place for variations of the external cavity length at the wavelength scale, i.e. around 1.2 um. Theoretically, we successfully link this switching behaviour with the evolution of the modal gain difference between the two modes induced by the variations of the optical feedback phase.

In this paper, we numerically demonstrate a new extraction scheme for generating ultra-fast physically random sequence of bits. For this purpose, we utilize a dual-channel optical chaos source with suppressed time delayed (TD) signature in both the intensity and the phase of its two channels. The proposed technique uses M 1-bit analog-to-digital converters (ADCs) to compare the level of the chaotic intensity signal at time t with its levels after incommensurable delay-interval T_m, where m = {1,2, … , M}. The binary output of each 1-bit ADC is then sampled by a positive-edge-triggered D flip flop. The clock sequence applied to the flip-flops is relatively delayed such that the rising edge of the clock triggering the m flip-flop precedes the rising edge of the clock of a subsequent m+1 flip-flop by a fixed period. The outputs of all flip flops are then combined by means of a parity-check logic. Numerical simulations are carried out using values of parameters at which TD signature is suppressed for chosen values of setup parameters. The 15 statistical tests in Special Publication 800-22 from NIST are applied to the generated random bits in order to examine the randomness quality of these bits for different values of M. The results show that all tests are passed from M = 1 to M = 39 at sampling rate up to 34.5 GHz which indicates that the maximum generation rate of random bits is 2.691 Tb/sec using a chaotic source of single VCSEL and without employing any pre-processing techniques.

The huge increase of datacom capacities requires lasers sources with more and more bandwidth performances. Vertical-Cavity Surface-Emitting Lasers (VCSEL) in direct modulation is a good candidate, already widely used for short communication links such as in datacenters. Recently several different approaches have been proposed to further extend the direct modulation bandwidth of these devices, by improving the VCSEL structure, or by combining the VCSEL with another high speed element such as lateral slow light modulator or transistor/laser based structure (TVCSEL).

We propose to increase the modulation bandwidth by vertically integrating a continuous-wave VCSEL with a high-speed electro-modulator. This vertical structure implies multiple electrodes with sufficiently good electrical separation between the different input electrical signals. This high frequency modulation requires both good electrical insulation between metal electrodes and an optimized design of the coplanar lines. BenzoCyclobutene (BCB) thanks to its low dielectric constant, low losses, low moisture absorption and good thermal stability, is often used as insulating layer. Also, BCB planarization offers the advantages of simpler and more reliable technological process flow in such integrated VCSEL/modulator structures with important reliefs. As described by Burdeaux et al. a degree of planarization (DOP) of about 95% can be achieved by simple spin coating whatever the device thickness. In most of the cases, the BCB planarization process requires an additional photolithography step in order to open an access to the mesa surface, thus involving a tight mask alignment and resulting in a degraded planarization.

In this paper, we propose a self-aligned process with improved BCB planarization by combining a hot isostatic pressing derived from nanoimprint techniques with a dry plasma etching step.

We present an experimental study of the nonlinear dynamics and the chaos synchronization using an asymmetric all-fiber setup in mutually coupled but nonidentical 1550-nm VCSELs with a large total coupling delay time of 274.2 ns. The linear polarization of the two VCSELs is adjusted to be parallel to each other, i.e. to achieve parallel coupling. The results are analyzed in terms of the frequency detuning and the coupling strength between the two lasers. We define the frequency detuning as the emitting frequency difference between the solitary VCSEL 1 and VCSEL 2. For positive frequency detuning, limit cycle and period doubling have been observed. For zero and negative frequency detuning, periodic dynamics, polarization switching and chaotic behavior have been found. Novel results have been obtained for the suppressed polarization of both parallel mutually coupled VCSELs. CW emission and dynamics in the orthogonal polarization can appear for negative frequency detuning. We have analyzed the accuracy of chaos synchronization in both VCSELs given by the cross-correlation function. Good achronal chaotic synchronization is found, with a time shift that corresponds to the large coupling delay time between the lasers. The leader-laggard relationship is also investigated.

We study the dynamics of semiconductor lasers with optical feedback and direct current modulation, operating in the regime of low frequency fluctuations (LFFs). In the LFF regime the laser intensity displays abrupt spikes: the intensity drops to zero and then gradually recovers. We focus on the inter-spike-intervals (ISIs) and use a method of symbolic time-series analysis, which is based on computing the probabilities of symbolic patterns. We show that the variation of the probabilities of the symbols with the modulation frequency and with the intrinsic spike rate of the laser allows to identify different regimes of noisy locking. Simulations of the Lang-Kobayashi model are in good qualitative agreement with experimental observations.

Monolithic High refractive index Contrast Grating (MHCG) allows several-fold size reduction of epitaxial structure of VCSEL and facilitates VCSEL fabrication in all photonic material systems. MHCGs can be fabricated of material which refractive index is higher than 1.75 without the need of the combination of low and high refractive index materials. MHCGs have a great application potential in optoelectronic devices, especially in phosphide- and nitride-based VCSELs, which suffer from the lack of efficient monolithically integrated DBR mirrors. MHCGs can simplify the construction of VCSELs, reducing their epitaxial design to monolithic wafer with carrier confinement and active region inside and etched stripes on both surfaces in post processing. In this paper we present results of numerical analysis of MHCGs as a high reflective mirrors for broad range of refractive indices that corresponds to plethora of materials typically used in optoelectronics. Our calculations base on a three-dimensional, fully vectorial optical model. We investigate the reflectance of the MHCG mirrors of different design as the function of the refractive index and we show the optimal geometrical parameters of MHCG enabling nearly 100% reflectance and broad reflection stop-band. We show that MHCG can be designed based on most of semiconductors materials and for any incident light wavelength from optical spectrum.

Optoacoustic (OA) effect refers to the generation of the acoustic waves due to absorption of light energy in a biological tissue. The incident laser pulse is absorbed by the tissue, resulting in the generation of ultrasound that is typically detected by a piezoelectric detector. Compared to other techniques, the advantage of OA imaging (OAI) technique consists in combining the high resolution of ultrasound technique with the high contrast of optical imaging. Generally, Nd:YAG and OPO systems are used for the generation of OA waves but their use in clinical environment is limited for many aspects. On the other hand, high-power diode lasers (HPDLs) emerge as potential alternative. However, the power of HPDLs is still relatively low compared to solid-state lasers. We show a side-by-side combination of several HPDLs in an optical fiber bundle to increase the amount of power for OA applications. Initially, we combine the output optical power of several HPDLs at 905 nm using two 7 to 1 round optical fiber bundles featuring a 675 μm and 1.2 mm bundle aperture. In a second step, we couple the output light of these fiber bundles to a 600 μm core diameter endoscopic fiber, reporting the corresponding coupling efficiencies. The fiber bundles with reasonable small diameter are likely to be used for providing sufficient light energy to potential OA endoscopy (OAE) applications.

New phenomena are observed in the optical response of InGaAs/AlGaAs 1060nm Laser Diodes (LDs) and Laser Diode Modules (LDMs) driven under high peak current condition: two segments of parasitic oscillations appear in the optical response of every tested LD and LDM, when increasing the current above two respective thresholds. In order to understand their origins and to discuss their influence over the operation range and reliability of seed LDs, we designed a test bench, based on an Electro-Optical Modulator, devoted to the time-spectral analysis of LD optical responses under such conditions. A correlation was found between the presence of the first segment of oscillations on the optical response and a temporal broadening of the LD spectrum. The presence of the second segment of oscillations is associated with a red-shift of the LD spectrum, but not with a significant spectral broadening, suggesting different causes for these phenomena. Step-stress ageing tests have then been carried out, in order to estimate the evolution of those parasitic oscillations over the lifetime of these LDs for reliability investigations.

We use a laser diode from a commercial CD/DVD-ROM drive to detect changes in the surface of a diffraction grating without a photodiode. Specifically, we exploit the changing terminal voltage in the laser-diode due to changing feedback strength as the laser is rastered across the grating's surface.

Since the original demonstration of terahertz quantum-cascade lasers (QCLs), the performance of these devices has shown rapid improvement. QCLs can now deliver milliwatts or more of continuous-wave radiation throughout the terahertz frequency range (300 GHz to 10 THz). Therefore, QCLs have become widely used in various applications such as spectroscopy, metrology or free-space telecommunications. For many of these applications there is a need for compact tuneable quantum cascade lasers. Nowadays most tuneable QCLs are based on a bulky external cavity configuration. We explore the possibility of tuning the operating wavelength through a fully integrated on-chip wavelength selective feedback applied to a dual wavelength QCL. Our numerical and analytical analyses are based on rate equation models describing the dynamics of QCLs extended to include delayed filtered optical feedback. We demonstrate the possibility to tune the operating wavelength by altering the absorption and/or amplification of the signal in the delayed feedback path. The tuning range of a laser is limited by the spectral width of its gain. For inter-band semiconductor lasers this spectral width is typically several tens of nm. Hence, the laser cavity supports the existence of multiple modes and on chip wavelength selective feedback has been demonstrated to be a promising tuning mechanism. We have selected a specific QCL gain structure with four energy levels and with two lasing transitions in the same cascade. In this scheme, the two lasing modes use a common upper level. Hence, the two modes compete in part for the same carriers to account for their optical gain. We have added delayed wavelength specific filtered optical feedback to the rate equation model describing these transitions. We have calculated the steady states and their stability in the absence of delay for the feedback field and studied numerically the case with non-zero delay. We have proven that wavelength tuning of a dual wavelength QCL through filtered optical feedback is possible in this system under certain circumstances.

We present experimental results showing alternating lasing and non-lasing regions for the short-wavelength longitudinal mode in a GaAs-based 850 nm coupled-cavity vertical-cavity surface-emitting laser (CC-VCSEL). These regions are situated between the laser threshold and roll-off for this mode. The analyzed structure consists of two identical AlGaAs cavities with GaAs quantum wells, separated with 11.5 pairs of middle DBR. The current apertures are realized by ion-implantation for the top cavity and selective oxidation for the bottom cavity. We then perform fully-vectorial three-dimensional cold-cavity optical simulations to theoretically investigate optical density radial and on-optical-axis profiles of the first order transverse modes corresponding to the two longitudinal modes. We show that the short-wavelength fundamental mode λS-LP01 is subject to periodic changes of its optical field distribution when changing the oxide aperture radius, which can lead to weaker resonance of the short-wavelength LP01 mode within the coupled cavity structure.

Using the elasto-optic effect we increase the frequency difference between the two orthogonally polarized modes, the so-called birefringence splitting, in standard single-mode oxide-confined GaAs-based vertical-cavity surface-emitting lasers (VCSELs). The birefringence may play an important role in the realization of ultrafast polarization modulation for high-speed data transmission. For practical implementation it is necessary to miniaturize the strain-inducing mechanism for birefringence tuning in VCSELs. The goal is the realization of integrated structures on the VCSEL chip. In this paper we discuss our work on miniaturized bending devices as the next step in achieving extremely high birefringence splitting. Furthermore measurements with integrated hotspot structures on VCSEL chips were made to reach much smaller scales for birefringence fine-tuning.

Controlling the coupled spin-photon dynamics in vertical-cavity surface-emitting lasers (VCSELs) is an attractive opportunity to overcome the limitations of conventional, purely charge based semiconductor lasers. Such spin-controlled VCSELs (spin-VCSELs) offer several advantages, like reduced threshold, spin amplification and polarization control. Furthermore the coupling between carrier spin and light polarization bears the potential for ultrafast polarization dynamics. By injecting spin-polarized carriers, the complex polarization dynamics can be controlled and utilized for high-speed applications. Polarization oscillations as resonance oscillations of the coupled spin- photon system can be generated using pulsed spin injection, which can be much faster than the intensity dynamics in conventional devices. We already demonstrated that the oscillations can be switched in a controlled manner. These controllable polarization dynamics can be used for ultrafast polarization-based optical data communication. The polarization oscillation frequency and therefore the possible data transmission rate is assumed to be mainly determined by the birefringence-induced mode-splitting. This provides a direct tool to increase the polarization dynamics toward higher frequencies by adding a high amount of birefringence to the VCSEL structure. Using this technique, we could recently demonstrate experimentally a birefringence splitting of more than 250 GHz using mechanical strain. Here, we employ the well-known spin-flip model to investigate the tuning of the polarization oscillation frequency. The changing mechanical strain is represented by a linear birefringence sweep to values up to 80πGHz. The wide tuning range presented enables us to generate polarization oscillation frequencies exceeding the conventional intensity modulation frequency in the simulated device by far, mainly dependent on the birefringence in the cavity only.

The amplitude jitter and timing jitter characteristics of a monolithic two-section tapered mode-locked quantum dot laser are experimentally investigated in dependence on the injection current and reverse bias voltage. Stable operating regimes with amplitude jitter below 10 % and timing jitter smaller than 10 fs are identified and the pulse widths and pulse peak power of the pulses are determined.

We study the formation of three-dimensional structures in type-I intracavity second harmonic generation model where polarization degrees of freedom due to the birefringence of the χ⁽²⁾ crystal is not considered. The device consists of an optical cavity filled with a quadratic nonlinear material and driven by an external beam at the fundamental frequency. The transmitted part of this field is coupled into the cavity where it undergoes second-harmonic conversion. These dissipative structures consist of regular or localized 3D lattices of bright spots travelling at the group velocity of light in the material. We show evidence of stable three dimensional structures such as stripes and cylinders.

In the present paper we investigated the spatio-temporal instabilities of stationary lasing in class-B broad-area lasers. The onset conditions of filamentary instability and its spatio-temporal characteristics were obtained analytically on the basis of Maxwell-Bloch equations without phase-amplitude coupling. The lasing stabilization capabilities through varying laser parameters were considered. We demonstrated that coherent external optical injection can effectively suppress the transverse filamentary instability. We considered the case of weak optical injection, so that the amplitude of injected field is small compared to the amplitude of intracavity laser field. The latter restriction is ascribed to active cavity where injected field doesn’t play a driving role in laser operation. We report that injected field can have the stabilizing impact even for such relatively weak injection. Moreover our findings show that both relaxation oscillations and spiking behaviour may be significantly suppressed up to complete elimination in broad-area laser submit to coherent optical injection. All the results were also found to stay principally valid for weak nonzero phase-amplitude coupling.

Temperature-induced laser dynamics of wide-aperture vertical cavity surface emitting semiconductor lasers (VCSELs) is under investigation. We describe the dynamics of VCSELs with circular and square apertures using the full system of two-dimensional Maxwell-Bloch equations. The results of numerical simulations in near and far fields are shown in dependence on frequency detuning, which can be presented as function of temperature. Results of simulations are compared with experimental data and theoretical predictions.