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.
We report a novel ultra-short light pulse emitters utilizing transient charge carrier behaviour in a multiple wide-quantumwell (WQW) heterostructure. The optical waveguide is implemented as a tandem-cavity laser diode with electro absorber section in the middle, surrounded by two end-firing gain sections. The ultrashort pulse production is achieved by employing the gain region with three wide GaAsP tensile strained quantum wells separated by GaInP barriers in an unintentionally doped active region of the p-i-n laser diode structure. At large negative absorber bias, lasing emission spiking starts with an unusually long delay of 7 μs. By applying the current pulses of duration smaller than 7 μs it is possible to quench entirely the lasing emission. With selection of the parameters of the electrical pump pulse and the absorber voltage it is possible to obtain ultra-short light pulse regime. This optical pulse appears at the end of the electrical pump pulse, as a single optical pulse on top of wide pedestal, due to amplified spontaneous emission. The duration of the pulse is 1.2 ps and pulse energy is 80 pJ. We attribute this behaviour to quantum confined Stark effect. Removal of the external bias field, enabling stronger overlap of carriers yields a sudden increase in the radiative recombination rate and optical gain enabling SR emission. We provide a detailed report on the pulse width and optical spectral behaviour as well as on possible nonclassical correlation in the emitted light state seen from comparison to CW lasing regime.
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