In recent years, an interest in the detection of the ShortWave Infra-Red (SWIR) band has grown. On the ground, the development of telescopes (ELTs) requires the construction of large focal planes in the SWIR for imaging, spectroscopy, or wavefront sensing applications. In space, the SWIR band can have many applications whether for communications or for imaging space and earth. The state-of-the-art III-V detectors in the SWIR are InGaAs photodiodes on InP substrate that are limited by a 1.7μm cut-off wavelength. Superlattice (SL) based detectors, that have been increasingly studied in recent years, make it possible to reach new cut-off wavelengths. Starting from the InGaAs on InP detector technology that has been mastered for more than ten years by THALES, the III-V Lab we propose to extend the detection range beyond 1.7μm by introducing a SL in the active region of an InGaAs photodiode. We will present the results obtained up to 2.6μm, as well as the solutions implemented to limit the carrier localization in the superlattice and the associated QE degradation. We will also discuss the consequence of minority carrier lifetime on the performance and the consequence of localization on MTF.
In recent years, an interest in the detection of the Short Wave Infra-Red (SWIR) band has grown. In these wavelengths, we benefit both from the properties of the visible and thermal infrared, offering new information and a different contrast to the image. In the defense field, this band offers the possibility of passive and active imaging, as well as the detection of laser or thermal radiation from bodies above ambient temperature. The state-of-the-art III-V detectors in the SWIR are InGaAs photodiodes on InP substrate that are limited by a 1.7 μm cut-off wavelength. Super-lattice (SL) based detectors, that have been increasingly studied in recent years, make it possible to reach new cut-off wavelengths. Starting from the InGaAs on InP detector technology that has been mastered for more than ten years by THALES, the III-V Lab we propose to extend the detection range beyond 1.7 μm by introducing a SL in the active region of an InGaAs photodiode. We will present the results obtained up to 2.5 μm, as well as the solutions implemented to limit the carrier localization in the super-lattice and the associated QE degradation.
Time and Frequency applications, such as time synchronization of complex networks, are in need of high accuracy and stability clocks. Optically pumped Cesium tube atomic clocks satisfy these demands. However, Size, Weight and Power (SWaP) are very important parameters considering easier implementation of atomic clocks in systems. The innovative principal of Coherent Population Trapping (CPT) clocks can meet these challenges. They require a 894nm (Cs D1 line) DFB laser modulated at half the clock frequency (4.6GHz). The modulation generates the side bands separated by 9.2GHz. The laser should also keep a linewidth below 1MHz. We grow the layers of our laser structure two steps Metal Organic Vapor Phase Epitaxy, with an Aluminum free active region. It includes a single GaInAsP compressively strained Quantum Well (QW) and a GaInP waveguide, on GaAs substrates. The use of Al free materials allows for the realization of a buried Bragg grating which induces a very stable single frequency operation as a function of current and temperature. We have investigated our actual 2mm long laser in light current characteristics, optical spectra, linewidth and direct modulation, showing high stability at different temperatures. The Cs D1 line is achieved near room temperature with a very high SMSR (50dB) and a low linewidth (<1MHz). The actual -3dB bandwidth is 2.3GHz at 80mA (48mW) at 25°C. We have designed a new laser structure allowing 10 GHz bandwidth, without reducing the cavity length.
In the area of smart mobility, a major challenge is to insure secure transportation. LIDAR are acknowledged as key enablers for Advanced Driver Assistance Systems (ADAS) and autonomous driving. Our approach for the Time of Flight (ToF) LIDAR is to use an Optical Phase Array (OPA), for the optical beam steering, together with a high peak power and high beam quality laser diode emitting at 905nm. To the best of our knowledge, a high-power laser diode at 905nm directly compatible with an OPA does not exist. We report on the design, realization and characterization of laser diode, with different geometries, emitting several watts (>10W) in a short pulse (typically 10ns) operation, in order to be coupled into the silicon nitride waveguide input of the OPA developed by the CEA LETI. The high power 905nm LASER coupled into the OPA, and their respective drivers, will constitute the optical steerable source, without no moveable parts, of the medium range TOF LIDAR developed within the European VIZTA project. The Aluminum free active region laser structure have been grown by Metal Organic Vapor Phase Epitaxy (MOVPE) on 3” GaAs substrates. It contains a single GaInAsP compressively strained Quantum Well (QW) for emission at 905nm, located in a GaInP waveguide. This structure exhibits high internal quantum efficiency ηqi of 0.99, low internal losses αi of 1.3cm-1 and low transparency current density J0 of 59A/cm2. Peak optical powers of 11.4W at 15.4A and 7.7W at 10.2A are obtained, respectively, for two different geometries.
European Space Agency (ESA) considers Mode-Locked Semi-Conductor Lasers as a promising technology for precision metrology systems in space such as High Accuracy Absolute Long Distance Measurement. We report our progress towards challenging ESA requirements: picosecond pulse duration, pulse energy 200 pJ, Pulse Repetition Frequency (PRF) 1-3 GHz, PRF stability < 5·10-9 at 1 second and PRF tunability 20 MHz. The laser should have small power consumption, be compact and robust against launch vibrations. We have reported in the past two such mode-locked (ML) laser diodes, each reaching only 90 pJ pulse energies: (i) very long (13.5mm) monolithic tapered laser and (ii) inverse bow-tie external cavity (EC) laser. The subject of the present communication is a novel passively mode-locked monolithic tapered laser achieving 201 pJ pulses. Large optical cavity with 2QWs heterostructure provides a low internal loss (~1 cm-1) together with high quantum efficiency (< 90 %) and low series resistance. To reach high energy output pulses, the tapered gain section gets a low (< 0.1 %) reflectivity dielectric coating. For passive mode-locking at fundamental cavity frequency, the saturable electroabsorber section is located at the back side of the gain chip with a high reflectivity coating (< 95 %). The monolithic cavity is made 13.5mm long by introducing an intermediate section for PRF tuning around 3 GHz. We reached passive ML at 2.9 GHz PRF with pulse energy of 201 pJ, compressed pulse width of 2.6 ps and electric power consumption of 8.2 W. PRF can be continuously tuned by 9.8 MHz. Active current modulation for hybrid ML resulted in PRF relative stability at 9.16·10-10 level on 1s intervals, while with a phase lock loop (PLL) acting on the DC gain section current we reached PRF stability of 1.15·10-10 on 1 s measurement interval.
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