We report on the design and characterization of a high-power and high dynamic range directly modulated analog fiber optic link in the S (2-4 GHz) band. The link is amplifier free, and uses passive impedance matching networks associated to high power laser diode and high power photodiode. Thanks to the high components efficiencies, together with the benefit of reactive impedance matchings, we achieved a high gain (≥ 0 dB) over 500 MHz bandwidths. Moreover, the use of high power and high linearity components allowed us to achieve simultaneously an output -1dB compression point higher than 20 dBm, and an output third order intercept point (OIP3) of more than 31 dBm. The measured spurious free dynamic range is as high as 114 dB.Hz2/3.

High power 14xx laser pumps are more and more required for eye safe industrial, medical, safety and defense applications as well as for increased telecom network capability (e.g. for 100 Gb Ethernet). However, this need of high power requires to control the overall power consumption in a range in line with systems requirements. In this respect, 3S PHOTONICS has developed a 14xx nm single mode laser diode with record internal losses of 1.5 cm-1 compared to the 2.7 cm-1 reported up to now. These lasers are based on p/nBH technology and use the asymmetric waveguide concept to reduce internal losses. The record loss value, coupled to an internal efficiency higher than 0.8, allows realization lasers of 3 mm length with external efficiency higher than 0.5 W.A-1 at 25°C in AR/HR coating configuration. Modules using direct coupling technology were realized. High coupling efficiency is obtained thanks to the 8° x 14° far field pattern of the diode. Output power of 550 mW at 1.8 A is thus obtained, with or without FBG stabilization, with maximum output power above 700mW. Thanks to the lasers' length, voltage at this current level is below 1.9 V, which gives a reduced thermal load. Thus, the overall modules electrical consumption remains lower than 10 W at case temperatures ranging from 0°C to 75°C. The 3 mm length also guaranties high reliability of these laser diodes.

Most Pulsed Fiber Lasers (FLs) are built on a Master Oscillator - Power Amplifier (MOPA) architecture, as this configuration has the advantage, among others, of exploiting direct modulation of the diode laser seed (the MO) to reach high repetition rates and high peak-power pulsed operation. To enhance the FL global performance and reliability, high power single-lateral-mode 1064 nm diodes with outstanding long-term behavior are needed. The reliability of these devices at high power has been a challenge for years, due to the high built-in strain in the Quantum Well (QW). In this paper, we present excellent reliability results obtained, in both cw and pulsed conditions, on the latest generation of 1064 nm single-lateral-mode diodes developed at 3S PHOTONICS. Aging tests in cw conditions prove the intrinsic robustness of the diode even at very high junction temperatures, while specific tests in pulsed operation at 45 °C heat-sink temperature, and high repetition rates of several hundred kHz, confirm the stability of the devices in accelerated conditions directly derived from real applications. Both free-running and wavelength stabilized (by means of a Fiber Bragg Grating (FBG)) packaged devices show very stable performances under pulsed conditions. Reliable operation at higher average power than currently commercially available diode lasers seeds is demonstrated.

Low levels of intensity noise in semiconductor lasers is a key feature for numerous applications such as high resolution spectroscopy, fiber-optic sensors, signal distribution in broadband analog communications as CATV, and more generally for microwave photonics systems. In particular, a DFB laser with very low relative intensity noise (RIN) levels from 0.1 to 20 GHz is a key component as it correspond to the whole frequency bandwidth of interest for radars. Several approaches have been reported but most suffer from the compromise between RIN level and power out level and stability, with RIN level in the range -150 dB.Hz(-1) to -155 dB.Hz(-1) in this frequency range [1,2]. We report here results from a new AlGaInAs DFB laser developed at 3S PHOTONICS. Excellent device performance is observed across an operating range from the laser threshold up to the thermal roll-over. Pure longitudinal single mode at 1545 nm is obtained over the whole current operating range with side mode suppression ratio higher than 50dB. The maximum output power reaches up to 130 mW. In these conditions, RIN levels below -160 dB.Hz(-1) is obtained in up to 20 GHz. These are the best results to our knowledge combining such high single mode output power with such low RIN level in the frequency range 0.4-20 GHz.

Single-mode 980 nm pump lasers are mature products needed in an increasing range of applications and their power level has been constantly raised in the last fifteen years from a few tens of mW for the first generations of devices up to the current maximum level of 750 mW fiber-coupled output power. As the fiber output power increases, new applications provide positive feed-back to continue the development of these devices, although severe constraints are imposed both by reliability and the need for wavelength stabilization, which is generally built on the utilization of Fiber Bragg Gratings (FBGs). We have developed in 2005 a record saturation power device [1] (P-sat=2.35W @ 25 degrees C, for 3.9 mm cavity lengths) whose fiber-coupled power has reached 750 mW for 25 C cooled applications, limited mainly by reliability as wavelength stabilization was already demonstrated up to levels above 1 Watt. 3S PHOTONICS has now developed a new generation of powerful and reliable devices that allow foreseeing operation at or close to 1W for cooled applications. We have further optimized the vertical structure to reduce the internal losses, and to reduce the junction temperature for increased reliability. High kink-currents around 2.5 A have been measured on the best devices. The gain bandwidth has been engineered to allow maintaining the wavelength stabilization even on very long laser cavities. Encouraging preliminary reliability results have also been obtained.

1550 nm AlGaInAs DFB lasers and PIN receptors were developed for analog transmission up to 20 GHz. Over 20 GHz bandwidth are measured for both laser and detector. Highly linear characteristics and low RIN < -150 dB/Hz have been obtained for lasers.

We demonstrate very high reliability level on 980-1060nm high-power single-mode lasers through multi-cell tests. First, we show how our chip design and technology enables high reliability levels. Then, we aged 758 devices during 9500 hours among 6 cells with high current (0.8A-1.2A) and high submount temperature (65°C-105°C) for the reliability demonstration. Sudden catastrophic failure is the main degradation mechanism observed. A statistical failure rate model gives an Arrhenius thermal activation energy of 0.51eV and a power law forward current acceleration factor of 5.9. For high-power submarine applications (360mW pump module output optical power), this model exhibits a failure rate as low as 9 FIT at 13°C, while ultra-high power terrestrial modules (600mW) lie below 220 FIT at 25°C. Wear-out phenomena is observed only for very high current level without any reliability impact under 1.1A. For the 1060nm chip, step-stress tests were performed and a set of devices were aged during more than 2000 hours in different stress conditions. First results are in accordance with 980nm product with more than 100khours estimated MTTF. These reliability and performance features of 980-1060nm laser diodes will make high-power single-mode emitters the best choice for a number of telecommunication and industrial applications in the next few years.

3S PHOTONICS demonstrates record power levels for 1060 nm single-lateral mode diode lasers based on a new lowloss (α~1 cm) vertical structure derived from our 980 nm diodes design. This technology enables a vertical far-field divergence of 22-23° and saturation powers well above 1.5 W at 25°C. It opens the way for improved fiber coupling and long-term reliability through the use of long cavities up to 5 mm. The power-current curve shows linear behavior for currents as high as 2 Amps, and a maximum kink-free power of 1.25 W. The reliability level of our 980 nm design has been assessed in a multi-cell test which demonstrates 428 FIT at 1 A or 800 mW for telecommunications lasers. This robustness allows to guarantee 20 khrs MTTF for industrial applications at more than 1.1 W for our 980 nm chips. Preliminary robustness assessment data of our 1060 nm chip will be presented. They indicate the suitability of this exciting technology for industrial applications requiring high brightness in the form of single emitters or bars. Markets such as laser marking, cutting and printing as well as direct diode frequency doubling (DDFD) promising new lower-cost portable instruments in the near future can now be addressed.

Resonant tunnelling through two impurities has been observed in a vertical double-barrier GaAs/AlGaAs tunnelling diode. It manifests itself as a peak in the I-V characteristic near the conductance threshold. Analysis of the position of the current peak, its shape and the shift in magnetic field parallel to the current provides information about the characteristics of the two impurities. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We demonstrate record kink-free output powers, over 1.2 W, for 1060-nm single-mode lasers. Saturation powers of 1.9 W are observed at room temperature that guarantee high-power and kink margins with respect to typical operation conditions.

We report on the development of a new generation of very high power 980 nm single lateral mode ridge-waveguide quantum-well lasers. An asymmetric-waveguides vertical structure has been optimized for very low internal losses while keeping the vertical mode-size large, thus allowing a low vertical far-field beam angle of less than 19°. Careful optimization of the doping profiles, and epitaxial interfaces optimization for reduced scattering, allowed to obtain internal losses as low as 0.6-0.7 cm-1. Such low losses are necessary to keep the external efficiency high in very long cavities, together with a high internal quantum efficiency. We thus reached our goal of keeping the external efficiency above 70% even for cavity lengths of 4.5 mm. The flared ridge waveguide has been designed to strongly filter higher order lateral modes, and kink-free operation has been obtained up to over 1.5 W output power, with very stable vertical and horizontal beam patterns. High saturation powers above 2 W have also been demonstrated at 25°C, and over 1.5 W at 75°C. Wavelength stabilized chips, by means of a fiber Bragg grating, reached linear fiber powers above 1.0 W with strong suppression of gain-peak lasing at all currents and good power stability.

The low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE) of tensile AlGaInAs multi-quantum wells (MQWs) for transverse magnetic (TM) 1.3 μm emitting lasers is presented. Al-containing wells have been mostly studied with compressive strain for transverse electric (TE) lasers. In this study, we report on highly tensile-strained AlGaInAs well layers (−0.72 to −1.65%) grown with compressive-strained AlGaInAs barrier layers (0.64%). The good agreement of high-resolution X-ray curves and simulated curves indicates that good crystalline quality and abrupt hetero-interfaces are obtained. An enhanced separation between light hole and heavy hole transitions is clearly observed by room-temperature photoluminescence as the strain increases. From broad-area laser results, it was observed that the strain had a low impact on the laser internal loss, the quantum efficiency and the transparency current density, which was as low as 0.32 A/cm2 for a 6 QW structure. On the opposite, a doubling of the gain parameter g0 when the strain increases from −0.72 to −1.65% was clearly observed. This result is associated with a 40% threshold density reduction on 300 μm long lasers. These investigations show that highly tensile-strained layers are very promising for the realisation of high-speed lasers.

We report on photon correlation measurements on a single quantum dot formed at fluctuations of the interface of a GaAs/GaAlAs quantum well. We demonstrate that under pulsed nonresonant excitation, the quantum dot emits a single photon per pulse. This shows that after the photon emission, there is no refill of the quantum dot by the nearby two-dimensional reservoir of delocalized states. The possibility of delivering Fourier transform limited single photons makes this system a good candidate for exciton- and photon-based quantum information processing schemes.

We perform low-temperature optical experiments on remotely doped lateral superlattices epitaxially grown on vicinal GaAs substrates. This quantum wire system provides a degenerate electron gas of density n s ≃8 × 10 1 1 cm - 2 subjected to a tunable one-dimensional periodic potential of amplitude ≃20 meV and period ≃30 nm, i.e., at the scale of its Fermi energy (E F ≃25 meV) and Fermi wavelength (λ F ≃30 nm). The enhancement of Fermi-edge singularities in tilted lateral superlattices [T. Melin and F. Laruelle, Phys. Rev. Lett. 76, 4219 (1996) is examined in the framework of the Fano resonance scheme that we recently proposed for two-dimensional systems in presence of alloy disorder [T. Melin and F. Laruelle, Phys. Rev. Lett. 85, 852 (2000)]. Including periodic intersubband couplings as extrinsic scatterings in the Fano model, we obtain a nice agreement with experimental data. This thus rules out possible many-body scenarios for the enhancement of Fermi-edge singularities in lateral superlattices, where multiple Coulomb diffusions of Fermi-sea electrons by charged photocreated valence holes would be boosted by the reduced dimensionality.

We perform low-temperature optical experiments on remotely doped lateral superlattices epitaxially grown on vicinal GaAs substrates. This quantum wire system provides a degenerate electron gas of density n(s)similar or equal to8x10(11) cm(-2) subjected to a tunable one-dimensional periodic potential of amplitude similar or equal to20 meV and period similar or equal to30 nm, i.e., at the scale of its Fermi energy (E(F)similar or equal to25 meV) and Fermi wavelength (lambda(F)similar or equal to30 nm). We show that the one-dimensional quantum confinement strongly affects both photoluminescence and photoluminescence excitation properties of the degenerate electron system. Through a careful analysis of the optical emission and absorption linear polarization spectra together with their temperature dependence, we distinguish between features due to (i) the periodic one-dimensional confinement and (ii) the localization anisotropy of photocreated valence-band carriers.

Summary form only given. Devices using quantum wires (QWR) are of much current interest. In recent times, several investigations have focussed attention on optical properties of QWRs at high excitation densities. In comparison, studies of excitonic interactions in QWRs are few. We perform femtosecond degenerate four wave mixing (DFWM) and picosecond photoluminescence measurements at 8 K on GaAs/AlAs QWRs and QWs. Our results show that while exciton-exciton scattering is reduced in the QWRs, exciton-phonon scattering is enhanced. The QWRs are MBE grown on a vicinal GaAs substrate in the form of a low disorder AlGaAs lateral superlattice with a period of 32 nm and a vertical width of 10 nm.

We have found that the local density of state fluctuations (LDOSF) in a disordered metal, detected using an impurity in the barrier as a spectrometer, undergo enhanced (with respect to Shubnikov-de Haas and de Haas-van Alphen effects) oscillations in strong magnetic fields, omega(c)tau>/=1. We attribute this to the dominant role of the states near the bottom of Landau bands which give the major contribution to the LDOSF and are most strongly affected by disorder. We also demonstrate that in intermediate fields the LDOSF increase with field B in accordance with the results obtained in the diffusion approximation.

We perform time integrated degenerate four-wave mixing (DFWM) measurements to investigate exciton dephasing in a GaAs/AlAs lateral superlattice (LSL) with a tunable band gap modulation. The excitons are resonantly excited by femtosecond laser pulses. Under optimal conditions of growth layer alignment, the ground state excitons in the LSL are 1D. When the LSL growth is highly tilted, the 1D confining potential vanishes and the LSL effectively becomes a 2D system. The DFWM measurements for the 1D and 2D excitons show that the exciton–exciton scattering strength is significantly reduced in the 1D case. We find that disorder in the LSL cannot fully explain the observed large reduction. It is likely that reduction in dimensionality plays an important role in this.

We study the magneto-transport in vertical quantum dots boththeoretically and experimentally. We focus our attention onthe non-linear transport regime. We demonstrate that the peakamplitudes in the I–V characteristics show a dramaticallydifferent behaviour as a function of the magnetic field,depending on the value of the angular momentum of the dotstate through which tunnelling occurs. The investigationallows us to probe details of the quantum dot wavefunctionsand to distinguish tunnelling through localised states relatedto impurities or to quantum dots.