M. Garcia

Top grating index-coupled distributed feedback quantum cascade lasers

We report on the modeling and design of top grating distributed feedback (DFB) quantum cascade lasers (QCLs). A low loss, index-coupled, DFB design that is very robust against technological spreads is proposed. Strong DFB coupling conditions are obtained while maintaining a high laser output power. Following this design, DFB QCL lasers with InP cladding layers and InGaAs∕AlInAs active regions have been fabricated. Room temperature monomode QCLs with 30dB side mode suppression ratios are demonstrated over a 4–8μm wavelength range.

Room-temperature continuous-wave metal grating distributed feedback quantum cascade lasers

New design rules allow room temperature continuous wave operation Distributed Feedback Quantum Cascade Lasers using top metal gratings. Lasing between 4.5 and 7.5 µm and above 20 mW is achieved.

Substrate emitting index coupled quantum cascade lasers using biperiodic top metal grating

We report design of specific grating profile to perform substrate emission of metal grating Distributed Feedback Quantum Cascade Lasers. We achieve room temperature operation around 5.6 µm.

InAs/AlAsSb based quantum cascade lasers

The advantages and drawbacks of the different semiconductor materials which can be used for the fabrication of quantum cascade laser (QCL) emitting in the 3–4μm wavelength range bring us to propose a material combination which can be lattice matched to InAs substrate. It is shown that using InAs quantum wells and AlAsSb barriers, it is possible to balance the strain in QCL structures made on InAs whatever the active region design and the wavelength targeted. A first InAs∕AlAsSb QCL structure has been grown and fully characterized by x-ray diffraction. The devices emit at 3.5μm at 300K in pulsed mode.

Directional single mode quantum cascade laser emission using second-order metal grating coupler

We report on the design and experimental demonstration of a substrate emitting quantum cascade laser (QCL) with low beam divergence in the two directions. A low-loss, index-coupled, distributed feedback laser is coupled to a monolithic extraction area. Both functions are performed with a top metal grating spatially differentiated for improving the divergence of the QCL in the two directions. Spectrally single-mode InGaAs/AlInAs QCL emitting at a wavelength of 5.65 μm with a low beam divergence, represented by a full width at half maximum of 2.3° and 4°, is demonstrated at room temperature with a threshold current of 2.1 kA/cm2.

Measurement of semiconductor waveguide optical properties in the midinfrared wavelength range

We propose a technique based on Fabry-Perot fringes to analyze, in a broad wavelength range, the waveguide properties of semiconductor lasers in the midinfrared spectrum. This technique has been applied to strain-balanced Ga0.32In0.68As∕Al0.64In0.36As quantum cascade lasers, with a double phonon active region, in order to determine propagation losses and the effective index between 2.5 and 8μm wavelength. These results are in good agreement with the values obtained using another method.

Very narrow linewidth of high power DFB laser diode for Cs pumping

We obtain (Fig. 1) a low threshold current at 30°C around 50mA and a high slope efficiency of 1W/A. At this measurement temperature, we have also obtained the D2 line of Cs (852.12nm) for a current of 170mA and so, a high optical intensity of 110mW (Fig. 2). The side mode suppression ratio (SMSR) for these operating conditions is higher than 50dB. We also measured by the self-heterodyne method the linewidth of our DFB laser at 30°C. We obtained at the D2 line of Cs (Fig.3) a very narrow linewidth of 200kHz for a white noise approximation (lorentzian fit) and 446kHz for a low frequency noise approximation (Gaussian fit). Furthermore, we can see (Fig.4) the usual decrease of the linewidth with the optical power, without any further increase at high power. From this linewidth evolution with power the Henrys factor is evaluated to be around 2.5.

Towards an engineering model of Optical Space Cs Clock

Thales Electron Devices and RUAG currently develop the engineering model of the Optical Space Cs Clock (OSCC) in the framework of an ESA/CNES project. Recent progress of the project is reported. Emphasis is put on the performance tests using new laser sources delivered by III-V Lab. The implementation of an isolator-free optics subsystem and the space evaluation of the laser and photodiode are discussed.

The optical feedback spatial phase driving perturbations of DFB laser diodes in an optical clock

Frequency perturbations of a laser seeding an optically pumped Cs clock are likely to reduce the achievable clock stability. They can be induced by residual back reflections in the optical system. It is shown here that the sensitivity of DFB laser diodes to low-level back-reflections significantly depends on the spatial phase of the reflected beam, i.e. the surface roughness of the reflecting element.

DFB-ridge laser diodes at 894 nm for Cesium atomic clocks

Time and frequency applications are in need of high accuracy and high stability clocks. Optically pumped compact industrial Cesium atomic clocks are a promising approach that could satisfy these demands. However, the stability of these clocks relies, among others, on the performances of the laser diodes that are used. This issue has led the III-V Lab to commit to the European Euripides-LAMA project that aims to provide competitive compact optical Cesium clocks for ground applications. This work will provide key experience for further space technology qualification. III-V Lab is in charge of the design, fabrication and reliability of Distributed-Feedback diodes (DFB) at 894 nm (D1 line of Cesium) and 852 nm (D2 line). LTF-Unine is in charge of their spectral characterisation. The use of D1 line for pumping will provide simplified clock architecture compared to the D2 line pumping thanks to simpler atomic transitions and a larger spectral separation between lines in the 894 nm case. Also, D1 line pumping overcomes the issue of unpumped “idle states” that occur with D2 line. The modules should provide narrow linewidth (<1 MHz), very good reliability in time and, crucially, be less sensitive to optical feedback. The development of the 894 nm wavelength is grounded on III-V Lab results for 852 nm DFB. We show here results from Al-free active region with InGaAsP quantum well Ridge DFB lasers. We obtain the D1 Cs line (894.4 nm) at 67°C and 165 mA (optical power of 40 mW) with a high side mode suppression ratio. The wavelength evolution with temperature and current are respectively 0.06 nm/K and 0.003 nm/mA. The laser linewidth is less than 1 MHz. The Relative Intensity Noise (RIN) and the frequency noise are respectively less than 10-12 Hz-1 @ f ≥ 10 Hz and 109 Hz2/Hz @ f ≥ 10 Hz.