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Semiconductor nanostructures with low dimensionality like quantum dots and quantum dashes are one of the best attractive and heuristic solutions for achieving high performance photonic devices. When one or more spatial dimensions of the nanocrystal approach the de Broglie wavelength, nanoscale size effects create a spatial quantization of carriers leading to a complete discretization of energy levels along with additional quantum phenomena like entangled-photon generation or squeezed states of light among others. This article reviews our recent findings and prospects on nanostructure based light emitters where active region is made with quantum-dot and quantum-dash nanostructures. Many applications ranging from silicon-based integrated technologies to quantum information systems rely on the utilization of such laser sources. Here, we link the material and fundamental properties with the device physics. For this purpose, spectral linewidth, polarization anisotropy, optical nonlinearities as well as microwave, dynamic and nonlinear properties are closely examined. The paper focuses on photonic devices grown on native substrates (InP and GaAs) as well as those heterogeneously and epitaxially grown on silicon substrate. This research pipelines the most exciting recent innovation developed around light emitters using nanostructures as gain media and highlights the importance of nanotechnologies on industry and society especially for shaping the future information and communication society., Quantum dot are one of the best practical examples of nanotechnologies. Owing to the discrete energy levels, quantum dot lasers output unique features like thermal stability, feedback insensitivity and spectral purity.

Speech emotion recognition is a challenging task in natural language processing. It relies heavily on the effectiveness of speech features and acoustic models. However, existing acoustic models may not handle speech emotion recognition efficiently for their built-in limitations. In this work, a novel deep-learning acoustic model called attention-based skip convolution bi-directional long short-term memory, abbreviated as SCBAMM, is proposed to recognize speech emotion. It has eight hidden layers, namely, two dense layers, convolutional layer, skip layer, mask layer, Bi-LSTM layer, attention layer, and pooling layer. SCBAMM makes better use of spatiotemporal information and captures emotion-related features more effectively. In addition, it solves the problems of gradient exploding and gradient vanishing in deep learning to some extent. On the databases EMO-DB and CASIA, the proposed model SCBAMM achieves an accuracy rate of 94.58% and 72.50%, respectively. As far as we know, compared with peer models, this is the best accuracy rate.

Photonic integrated circuits (PICs) have enabled numerous high performance, energy efficient, and compact technologies for optical communications, sensing, and metrology. One of the biggest challenges in scaling PICs comes from the parasitic reflections that feed light back into the laser source. These reflections increase noise and may cause laser destabilization. To avoid parasitic reflections, expensive and bulky optical isolators have been placed between the laser and the rest of the PIC leading to large increases in device footprint for on-chip integration schemes and significant increases in packaging complexity and cost for lasers co-packaged with passive PICs. This review article reports new findings on epitaxial quantum dot lasers on silicon and studies both theoretically and experimentally the connection between the material properties and the ultra-low reflection sensitivity that is achieved. Our results show that such quantum dot lasers on silicon exhibit much lower linewidth enhancement factors than any quantum well lasers. Together with the large damping factor, we show that the quantum dot gain medium is fundamentally dependent on dot uniformity, but through careful optimization, even epitaxial lasers on silicon can operate without an optical isolator, which is of paramount importance for the future high-speed silicon photonic systems.

To schedule wind power efficiently and to mitigate the adverse effects caused by wind's intermittency and variability, an advanced wind power prediction model is proposed in this paper. This model is a combined model via switching different data-driven chaotic time series models. First, inputs of this model come from the reconstructed data based on the chaotic characteristics of wind power time series. Second, three different data mining algorithms are used to construct wind power prediction models individually. To obtain a regime for switching optimal models, a Markov chain is trained. Then, weights of different data-driven modes are calculated by the Markov chain switching regime, and used in the final combined model for wind power prediction. The industrial data from actual wind farms is studied. Results of the proposed model are compared with that of non-reconstructed input data, traditional data-driven models and two typical combined models. These results validate the superiority of proposed model on improving wind power prediction accuracy.

The end-to-end speech recognition technology solves the problem that each component is independent and models cannot be jointly optimized in the traditional speech recognition model. It incorporates such components as the acoustic model, language model, and decoding unit of the hybrid model into a single neural network, that can avoid the inherent defects of multiple modules and greatly reduces the complexity of the speech recognition model. In this research, an Amdo-Tibetan speech recognition system is constructed based on Listen, Attend and Spell (LAS) model by the end-to-end speech recognition technology. It can realize the direct conversion from Amdo-Tibetan speech sequence to the corresponding character sequence and greatly reduces the difficulty of building the Amdo-Tibetan speech recognition model. To further improve the performance of the proposed system, the following improvements have been made: firstly, the Multi-Head Attention mechanism is introduced to improve the alignment accuracy between state vectors of decoder and encoder; secondly, the label smoothing technique is adopted to solve the problem of over-fitting; thirdly, an N-gram language model is combined with the LAS model to increase the accuracy of speech recognition and the maximum mutual information (MMI) criterion is employed for discriminative training; and finally, transfer learning is utilized to overcome the problem of insufficient training data. Experimental results show that the proposed model can significantly enhance the performance of Amdo-Tibetan speech recognition.

This paper investigates the intensity noise and pulse oscillation characteristics of an InAs/GaAs quantum dot laser epitaxially grown on germanium. We show that the relative intensity noise of the free-running laser generally decreases with increasing pump current, and the minimum value reaches down to about $-$ 126 dB/Hz. The intensity noise is hardly affected by the optical feedback, unless there is a resonance or pulse oscillation in the noise spectrum. The laser pumped at a high current is more sensitive to the optical feedback. Interestingly, it is found that the free-running Ge-based quantum dot laser generates self-sustained pulse oscillations with one period or two periods upon the pump current, without incorporating saturable absorbers. This behavior is valuable for both self-generation of photonic microwaves and for understanding nonlinear dynamics of semiconductor lasers.

To mitigate the threat to power system caused by ramp events – large wind power fluctuation, this study proposes an advanced ramp prediction approach based on event detection framework. This approach contains two successive stages of work, including wind power forecasting and ramp detection. Considering high-performance ramp prediction requires long-term and accurate wind power prediction results; this study also proposes a hybrid prediction model at the first stage. By using wind power curve to reflect the physic mechanism of wind power generation, data from numerical weather prediction system could be used to realise long-term trend prediction. Then, a multivariate model is built with a data-mining algorithm to correct system errors of the primary prediction, which is addressed to improve long-term prediction performance. At the second stage, a modified swinging door algorithm is applied for ramp detection. Performance of both the proposed long-term wind power prediction and the corresponding ramp prediction are computed and compared with conventional models on an actual wind dataset. Comprehensive results validated the feasibility and superiority of the proposed ramp prediction approach.

This letter reports on a 1.3- $\mu \text{m}$ reflection insensitive transmission with a quantum dot laser directly grown on silicon in the presence of strong optical feedback. These results show a penalty-free transmission at 10 GHz under external modulation with −7.4-dB optical feedback. The feedback insensitivity results from the low linewidth enhancement factor, the high damping, the absence of off-resonance emission states, and the shorter carrier lifetime. This letter paves the way for future on chip high-speed integrated circuits operating without optical isolators.

This work reports on a high-efficiency InAs/GaAs distributed feedback quantum dot laser. The large optical wavelength detuning at room temperature between the lasing peak and the gain peak causes the static, dynamic, and nonlinear intrinsic properties to all improve with temperature, including the lasing efficiency, the modulation dynamics, the linewidth enhancement factor, and consequently the reflection insensitivity. Results reported show an optimum operating temperature at 75°C, highlighting the potential of the large optical mismatch assisted single-frequency laser for the development of uncooled and isolator-free high-speed photonic integrated circuits.

This work investigates the dynamics of two-state quantum dot lasers through semi-analytically solving a set of rate equations. Simulations reveal that the occurrence of excited state lasing reduces the damping factor and relaxation oscillation frequency of the laser while increases the linewidth enhancement factor associated to the ground state transition. These results are in good agreement with the experimental observation showing that the quantum dot laser becomes more sensitive to external optical feedback at excited state lasing threshold. This work brings novel insights in the understanding of quantum dot laser physics that are useful for designing feedback resistant lasers in photonic integrated technologies.

Photonic integrated circuits enable energy efficient and compact technologies for modern information communications. Here, we explore semiconductor epitaxial quantum dots lasers on silicon and demonstrate their high suitability for addressing the important issues associated to photonic integration on silicon.

This work experimentally investigates the impact of p-doping on the relative intensity noise (RIN) properties and subsequently on the modulation properties of semiconductor quantum dot (QD) lasers epitaxially grown on silicon. Owing to the low threading dislocation density and the p-modulation doped GaAs barrier layer in the active region, the RIN level is found very stable with temperature with a minimum value of − 150 d B / H z . The dynamical features extracted from the RIN spectra show that p-doping between zero and 20 holes/dot strongly modifies the modulation properties and gain nonlinearities through increased internal losses in the active region and thereby hinders the maximum achievable bandwidth. Overall, this Letter is important for designing future high-speed and low-noise QD devices integrated in future photonic integrated circuits.

This work reports on an investigation of the optical feedback in an InAs/InGaAs passively mode-locked quantum dot (QD) laser epitaxially grown on silicon. Under the stably-resonant optical feedback condition, experiments demonstrate that the radio-frequency linewidth is narrowed whatever the bias voltage applied on the saturable absorber (SA) is; on the other hand, the effective linewidth enhancement factor of the device increases with the reverse bias voltage on the SA, hence it is observed that such an increase influences the mode-locking dynamic and the stability of device under optical feedback. This work gives insights for stabilizing epitaxial QD mode-locked lasers on silicon which is meaningful for their applications in future large-scale silicon electronic and photonic applications requiring low power consumption as well as for high-speed photonic analog-to-digital conversion, intrachip/interchip optical clock distribution and recovery.

Soft robotic pneumatic grippers have been shown to be versatile, robust to impacts, and safe for use on delicate objects. One type, fluidic elastomer grippers, are characterized by fingers with an inextensible gripping surface backed by extensible pneumatic chambers; when inflated, this mismatch in extensibility results in the finger curling. However, one drawback of these simple fingers is that they have one preprogrammed grasp, usually a simple constant-curvature wrap. While well-suited for finger-sized round objects, they do not grasp flat or small objects well. Here, we present an adaptable tri-stable soft robotic finger that can form either a pinch or wrap grasp based on the shape of the grasped object. We enable this by incorporating two bi-stable springs into the inextensible layer. The three stable positions are: i) open (unpressurized), ii) pinch (with only the proximal section bending), and iii) wrap (with the entire finger bending). We present a simple model of the behavior of our finger and experimental results verifying the model. Further, we apply forces and moments to grasped objects, and show that the tri-stable finger increases the grasping performance when compared to a control gripper with equal gripping force. Our work presents a novel design modification that is unobtrusive, simple, and passive. Our introduction of inexpensive programmable hardware advances the versatility and adaptability of soft grippers.

International audience; This work reports on the optical feedback dynamics of InAs/GaAs QD lasers epitaxially grown on silicon operating in both the short and long delay regimes. Both undoped and p-doped QD lasers are considered. Whatever the external cavity length, no chaotic oscillations are observed on both samples as a result of the small α-factor observed in the silicon QD lasers. Despite that, experiments conducted in the short-cavity region raise period-one oscillation for the undoped QD laser. In addition, the transition from the short to long delay regimes can be finely covered by varying the external cavity length from 5 cm to 50 cm, and the boundaries associated to the appearance of the periodic oscillation are identified. In the short-cavity region, boundaries show some residual undulations resulting from interferences between internal and external cavity modes; whereas in the long-delay regime, the feedback ratio delimiting the boundaries keeps decreasing, until it progressively becomes rather independent of the external cavity length. Overall, our results showed that the p-doped device clearly exhibits a much higher tolerance to the different external feedback conditions than the undoped one, seeing that its periodic oscillation boundaries are barely impossible to retrieve at the maximum feedback strength of-7 dB. These results show for the first time the p-modulation doping effect on the enhancement of feedback insensitivity in both short-and long-delay configurations, which is of paramount importance for the development of ultra-stable silicon transmitters for photonic technologies.

In Opt. Lett. 44, 5755 (2019)OPLEDP0146-959210.1364/OL.44.005755, a factor is missing in the result of Eq. (1). Thus, the width of the comb spectrum Δ ν becomes Δ ν = 2 3 Γ α e .

This work investigates the performance of 1.3-μm quantum dot lasers epitaxially grown on silicon under optical feedback sensitivity with different temperature and doping profiles. Experiments show that these quantum dot lasers exhibit a very high degree of resistance to both incoherent and coherent optical feedbacks. 10 Gbps penalty-free transmissions are also unveiled under external modulation and at different temperatures. The paper draws attention on quantum dot lasers with p-doping that exhibit a better thermal resistance, a lower linewidth enhancement factor, a higher critical feedback level, and a better spectral stability with less intensity noise. Together, these properties make epitaxial quantum dot lasers with p-doping more promising for isolator-free and Peltier-free applications, which are meaningful for future high-speed photonic integrated circuits.

Blockchain is changing science and technology in a revolutionary way for its decentralized, incorruptible computing mechanism. This work explores blockchain applications in speech recognition via investigating decentralized deep learning models. The decentralized deep learning models demonstrate a good potential to handle large scale acoustic data by fusing distributed deep learning models to achieve better learning results. To the best of our knowledge, it is a pioneering work to explore blockchain technologies in speech recognition.

International audience; This work reports on the influence of bias voltage applied on saturable absorber (SA) on sub-threshold linewidth enhancement factor (LEF) in hybrid-silicon quantum dot optical frequency comb lasers (QD-OFCLs). Results show that the reverse bias voltage on SA contributes to enlarge the LEF and improve the comb dynamics. Optical injection is also found to be able to improve the comb spectrum in term of 3-dB bandwidth and its flatness. Such novel findings are promising for the development of high-speed dense wavelength division multiplexing (DWDM) photonic integrated circuits (PICs) in optical interconnects and datacom applications.

Achieving high-performance by an effective and convenient preparation method is of great significance to the application of thermoelectric materials. Herein, we propose a facile method combined one-step solid state reaction (SSR) with hot pressing (HP) to fabricate Mg2(Si0.3Sn0.7)0.99Sb0.01. Although the main products after the SSR are Mg2Si and Mg2Sn compounds as well as various Mg2Si1−xSnx phases, the compact bulk sample with anti-fluorite structure is obtained in 2 h of HP process by controlling HP temperature. The obtained Mg2(Si0.3Sn0.7)0.99Sb0.01 exhibits a decent figure of merit of 1.37 at 673 K associated with a flexural strength of 74 MPa, which is fully comparable with the samples prepared by the method of two-step SSR combined with sintering technique, but the process of our method is obviously simplified.

Achieving the simultaneous improvement of thermoelectric and mechanical properties is of great significance for the application of thermoelectric materials. Here, we fabricate the bulks of Mg2(Si0.3Sn0.7)0.99Sb0.01 hybrid composites reinforced by graphene oxide nanosheets (GOs) and multi-walled carbon nanotubes (MWCNTs). The influences of GOs and MWCNTs on the thermoelectric and mechanical properties of the composites are characterized in detail. It is found that the hybrid composites exhibit obvious improvements in flexural strength and fracture toughness with respect to both the matrix and the samples reinforced by GOs or MWCNTs alone, owing to the remarkable synergistic effect of GOs and MWCNTs. Meanwhile, the dimensionless figures of merit are basically maintained or even slightly enhanced when dual reinforcements of GOs and MWCNTs are introduced. Our work provides a feasible path to obtain excellent mechanical and thermoelectric properties simultaneously.

Prediction of wind power ramp events is important to the stability operation of power system, it is realized by combining wind power prediction of several continuous units for long-term power prediction, then using detecting algorithms to extract ramps. A prediction unit is a prediction time window. Its size impacts the accuracy of predicting ramps, and an optimization model is proposed to select the suitable window size. First, a swinging door algorithm is applied to extract ramp events from historical data. A model for optimizing the time window size is established based on the minimum non-ramp data in a ramp window. The solution of the proposed model is discussed, including the selection of variables, constraints and algorithm. The model presented in this paper is tested, and performance of selected time window is discussed. Computational analysis demonstrates the validity of the model.

To reduce the harm of wind power ramp events in advance, an effective wind power ramp prediction system is needed. A new ramp prediction approach utilizing suitable selected time windows as units is proposed in this paper. Two risk factors are defined based on the performance analysis of ramp prediction, and the risk minimization principle is applied to build the risk model. Combining the correlation analysis and the statistical analysis of ramp duration, model constraints are studied. The optimal time window of industrial data is computed for ramp prediction based on a support vector regression model. Four evaluation indicators are chosen to verify that the proposed approach improves the performance of ramp prediction, and that the risk model is effective to select an optimal time window for prediction.

This work investigates the effect of the polarization anisotropy on the linewidth enhancement factor and the reflection sensitivity of InAs/InP quantum dash semiconductor lasers. The results show that the small linewidth enhancement factor and high stability against external optical feedback are obtained for nanostructures oriented perpendicular to the cavity axis as opposed to those oriented parallel to the cavity axis. Effective simulations on the critical feedback level of these two lasers are also in agreement with experimental results. Such anisotropy is attributed to the polarization dependence of the transition matrix element in these quantum nanostructures.

International audience; A common way of extracting the chirp parameter (i.e., the α-factor) of semiconductor lasers is usually performed by extracting the net modal gain and the wavelength from the amplified spontaneous emission (ASE) spectrum. Although this method is straightforward, it remains sensitive to the thermal effects hence leading to a clear underestimation of the α-factor. In this work, we investigate the chirp parameter of InAs/GaAs quantum dot (QD) lasers epitaxially grown on silicon with a measurement technique evaluating the gain and wavelength changes of the suppressed side modes by optical injection locking. Given that the method is thermally insensitive, the presented results confirm our initial measurements conducted with the ASE i.e. the α-factor of the QD lasers directly grown on silicon is as low as 0.15 hence resulting from the low threading dislocation density and high material gain of the active region. These conclusions make such lasers very promising for future integrated photonics where narrow linewidth, feedback resistant and low-chirp on-chip transmitters are required.

International audience

This work investigates the dynamic and nonlinear properties of quantum dot (QD) lasers directly grown on silicon with a view to isolator-free applications. Among them, the chirp parameter, also named the αH factor, is featured through a thermally insensitive method analyzing the residual side-mode dynamics under optical injection locking. The αH at threshold is found as low as 0.32. Then, the nonlinear gain is investigated from the gain compression factor viewpoint. The latter is found higher for epitaxial QD lasers on silicon than that in heterogeneously integrated quantum well (QW) devices on silicon. Despite that, the power dependence of the αH does not lead to a large increase of the chirp coefficient above the laser’s threshold at higher bias. This effect is confirmed from an analytical model and attributed to the strong lasing emission of the ground-state transition, which transforms into a critical feedback level as high as −6.5 dB, which is ∼19 dB higher than a comparable QW laser. Finally, the intensity noise analysis confirms that QD lasers are overdamped oscillators with damping frequencies as large as 33 GHz. Altogether, these features contribute to fundamentally enhancing the reflection insensitivity of the epitaxial QD lasers. This last feature is unveiled by the 10 Gbit/s error-free high-speed transmission experiments. Overall, we believe that this work is of paramount importance for future isolator-free photonics technologies and cost-efficient high-speed transmission systems.

Bad data must be detected in the microgrid because they mislead the decision making of energy management systems (EMSs). The authors propose a robust detection approach that combines an imp...

© 2018 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved. The optical feedback dynamics of two multimode InAs/GaAs quantum dot lasers emitting exclusively on sole ground or excited lasing states is investigated. The transition from long- to short-delay regimes is analyzed, while the boundaries associated to the birth of periodic and chaotic oscillations are unveiled to be a function of the external cavity length. The results show that depending on the initial lasing state, different routes to chaos are observed. These results are of importance for the development of isolator-free transmitters in short-reach networks.

In this paper, we investigate the temperature dependence of spectral linewidth of InAs/InP quantum dot distributed feedback lasers. In comparison with their quantum well counterparts, results show that quantum dot lasers have spectral linewidths rather insensitive to the temperature with minimum values below 200 kHz in the range of 283K to 303K. The experimental results are also well confirmed by numerical simulations. Overall, this work shows that quantum dot lasers are excellent candidates for various applications such as coherent communication systems, high-resolution spectroscopy, high purity photonic microwave generation and on-chip atomic clocks.

International audience; This work reports on the ultra-low linewidth enhancement factor (αH-factor) of semiconductor quantum dot lasers epitaxially grown on silicon. Owing to the low density of threading dislocations and resultant high gain, an αH value of 0.13 that is rather independent of the temperature range (288 K–308 K) is measured. Above the laser threshold, the linewidth enhancement factor does not increase extensively with the bias current which is very promising for the realization of future integrated circuits including high performance laser sources.

A 10 Gb/s transmission by direct modulation of a distributed feedback semiconductor laser heterogeneously integrated onto silicon is studied with optical feedback. Its impact on the bit error rate and power penalty degradation is analyzed.

International audience

Iron loaded zeolites like Fe-ZSM-5 are potent candidates for the catalytic abatement of nitrogen oxides from car exhaust, e.g. from Diesel engines. Recent problems in this field show that there is an urgent need in further improvement of such catalysts, for which a full analysis of Fe species present in them under different conditions is highly desirable. We have studied Fe-ZSM-5 catalysts prepared via solid-state ion exchange by using field dependent Mossbauer spectroscopy at low temperature in order to identify the different iron species present in this type of catalyst in the fresh state and after use in catalysis. Mossbauer spectroscopy proved to be the key technique for a full understanding of species structures, but due to the complexity of structures, guidance by parallel EPR experiments and control by SQUID magnetometry were essential to prove reliability of derived species distributions.

We investigate the interplay between linewidth and $\alpha$ -factor in quantum dot lasers using experimental data and a minimal quantum dot laser rate equation model. The rebroadening of the laser linewidth found experimentally at high injection currents is explained by analytical means and traced back to nonlinear scattering processes. Important differences of the pump current dependent linewidth evolution of quantum dot lasers are highlighted especially if compared to conventional laser devices. Furthermore, we provide a scheme to extract the amplitude-phase coupling as well as effective carrier scattering rates with standard characterization techniques, i.e., linewidth, light versus injected pump current and modulation response measurements.

This work reports on a systematic investigation of the influence of optical feedback in InAs/GaAs quantum dot lasers epitaxially grown on silicon. The boundaries associated to the onset of the critical feedback level corresponding to the first Hopf bifurcation are extracted at different bias conditions with respect to the onset of the first excited state transition. Overall, results show that quantum dot lasers directly grown onto silicon are much more resistant to optical feedback than quantum well lasers, mostly resulting from a small linewidth enhancement factor of high-quality quantum dot material. However, results also unveil that the onset of the critical feedback level strongly depends on the excited-to-ground-state ratio, hence a figure of merit showing that a small ratio of the excited-to-ground-state lasing thresholds is not beneficial for maintaining a high degree of stability. This work brings further insights in the understanding of quantum dot laser physics and is useful for designing feedback resistant lasers for isolator-free transmission in metro, access, and data center optical networks, as well as for integrated photonics.

International audience; Frequency conversion using highly non-degenerate four-wave mixing is investigated in optically injection-locked InAs/GaAs quantum-dot Fabry-Perot lasers with different ridge waveguide dimensions. Conversion efficiencies up to -16 dB with a large optical signal-to-noise ratios of 36 dB are unveiled. The conversion bandwidth is extended to 4 THz with a quasi-symmetrical response between up- and down-converted signals.

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.

Recently, an easily scalable process for the production of small (3 −7 nm) monodisperse superparamagnetic ferrite nanoparticles MeFe2O4 (Me = Zn, Mn, Co) from iron metal and octanoic acid has been reported (Salih et al., Chem. Mater. 25 1430–1435 2013). Here we present a Mossbauer spectroscopic study of these ferrite nanoparticles in external magnetic fields of up to B = 5 T at liquid helium temperatures. Our analysis shows that all three systems show a comparable inversion degree and the cationic distribution for the tetrahedral A and the octahedral B sites has been determined to (Zn0.19Fe0.81) A [Zn0.81Fe1.19] B O4, (Mn0.15Fe0.85) A [Mn0.85Fe1.15] B O4 and (Co0.27Fe0.73) A [Co0.73Fe1.27] B O4. Spin canting occurs presumably in the B-sites and spin canting angles of 33°, 51° and 59° have been determined for the zinc, the manganese, and the cobalt ferrite nanoparticles.

Quantum dot lasers are envisioned to be the next generation of optical transmitters used for short-reach communication links, owing to their low threshold current and high temperature operation. However, in a context of steady increase in both speed and reach, quantum dot lasers emitting on their upper energy levels have been recently of greater interest as they are touted for their faster modulation dynamics. This work aims at further evaluating the potential impact of such lasers in communication links by characterizing their long-delay optical feedback responses as well as the role of the lasing states on the multimode dynamics of InAs/GaAs quantum-dot Fabry-Perot devices sharing the same design. Results unveil that the excited-state laser shows a much larger sensitivity to optical feedback, with a more complex route to chaos, and a first destabilization point occurring at lower feedback strengths than for a comparable ground-state laser, which remains almost unaffected.

This paper reports on the spectral linewidth of InAs/InP quantum dot distributed feedback lasers. Owing to a low inversion factor and a low linewidth enhancement factor, a narrow spectral linewidth of 160 kHz (80 kHz intrinsic linewidth) with a low sensitivity to temperature is demonstrated. When using anti-reflection coatings on both facets, narrow linewidth operation is extended to high powers, believed to be due to a reduction in the longitudinal spatial hole burning. These results confirm the high potential of quantum dot lasers for increasing transmission capacity in future coherent communication systems.

We experimentally compare the dynamics of InAs/GaAs quantum dot lasers under optical feedback emitting exclusively on ground states (GSs) or excited states (ESs). By varying the feedback parameters and putting focus either on their short or long cavity regions, various periodic and chaotic oscillatory states are found. The GS laser is shown to be more resistant to feedback, benefiting from its strong relaxation oscillation damping. In contrast, the ES laser can easily be driven into complex dynamics. While the GS laser is of importance for the development of isolator-free transmitters, the ES laser is essential for applications taking advantages of chaos.

Non-degenerate four-wave mixing effects are investigated in an injection-locked InAs/InP nanostructure Fabry-Perot laser. Locking a longitudinal mode at various wavelengths within the gain spectrum and using the locked mode as the pump for the wave mixing shows different levels of asymmetry between up- and down-conversion. Experiments reveal that the normalized conversion efficiency is less asymmetric when the pump is locked at wavelengths below that of the gain peak. The values of nonlinear conversion efficiencies are maintained above -60 dB for pump-probe frequency detunings up to 3.5 THz. The role of the linewidth enhancement factor on the asymmetry is discussed and the value of the nonlinear susceptibility is compared to similar InAs/InP nanostructure semiconductor optical amplifiers. From an end-user viewpoint, data transmission experiments have also confirmed the possibility to propagate up-converted signals over 100 km at a 5 Gb/s bit rate under an OOK modulation format. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only., SPIE OPTO, 7 February 2015, San Francisco, California, United States, Series: Proceedings of SPIE; no. 9357

Non-degenerate four-wave mixing in an InAs/InP quantum dot Fabry–Perot laser is investigated with an optical injection-locking scheme. Wavelength conversion is obtained for frequency detunings ranging from +2.5 THz to −3.5 THz. The normalized conversion efficiency is maintained above −40 dB between −1.5 and +0.5 THz with an optical signal-to-noise ratio above 20 dB and a maximal third-order nonlinear susceptibility normalized to material gain of 2 × 10−19 m3/V2. In addition, we show that injection-locking at different positions in the gain spectrum has an impact on the nonlinear conversion process and the symmetry between up- and down- converted signals.

For high-speed three-dimensional shape measurement, techniques with projector defocusing have become increasingly important. When the projector is defocused, structured patterns used for phase unwrapping are blurred. These blurred patterns need to be normalized into binary distributions in actual measurement. We propose a method to normalize these blurred structured patterns. The retrieved absolute phase is correct even when the measured objects contain discontinuous parts or contrasting colors.

A newly developed flexible calibration algorithm for telecentric 3D measurement systems is presented in this paper. We theoretically analyzed the similarities and differences between the telecentric and entocentric system. The telecentric system can be calibrated with the aid of the traditional 2D planar calibration method. An additional two-step refining process is proposed to improve the calibration accuracy effectively. With the calibration and refining algorithm, an affine camera can be calibrated with a reprojection error of 0.07 pixel. A projector with small field of view (FOV) is applied to achieve a full 3D reconstruction in our profilometry system. Experiments with a prototype demonstrate the validation and accuracy of the proposed calibration algorithm and system configuration. The reconstruction accuracy can achieve 5 µm with a measurement FOV of 28.43 mm×21.33 mm and a working distance of 110 mm.

This work reports on non-degenerate four-wave mixing under dual-mode injection in metalorganic vapor phase epitaxy grown InP/InAs quantum-dash and quantum dot Fabry-Perot laser operating at 1550 nm. High values of normalized conversion efficiency of −18.6 dB, optical signal-to-noise ratio of 37 dB, and third order optical susceptibility normalized to material gain χ(3)/g0 of ∼4 × 10−19 m3/V3 are measured for 1490 μm long quantum-dash lasers. These values are similar to those obtained with distributed-feedback lasers and semiconductor optical amplifiers, which are much more complicated to fabricate. On the other hand, due to the faster gain saturation and enhanced modulation of carrier populations, quantum-dot lasers demonstrate 12 dB lower conversion efficiency and 4 times lower χ(3)/g0 compared to quantum dash lasers.