B. Simozrag

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.

Coherent quantum cascade laser micro-stripe arrays

We have fabricated InP-based coherent quantum cascade laser micro-stripe arrays. Phase-locking is provided by evanescent coupling between adjacent stripes. Stripes are buried into semi-insulating iron doped InP. Lasing at room temperature is obtained at 8.4μm for stripe arrays comprising up to 16 emitters. Pure supermode emission is demonstrated via farfield measurements and simulations. The farfield pattern shows a dual-lobe emission, corroborating the predicted phase-locked antisymmetric supermode emission.

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.

High thermal performance of μ-stripes quantum cascade laser

We demonstrate high thermal dissipation of quantum cascade lasers (QCLs) using multi-stripes array technology. Buried QCL arrays offer both lateral dissipation enhancements while keeping beam quality control for large active region lasers. Experimental thermal resistances down to 2 K/W are reported. InP:Fe regrowth morphology has been optimized to limit current leakage. Thermal resistance decreasing with both number and width of emitters is demonstrated. Comparison with simulation shows excellent agreement, with a reduction factor of 3 when comparing to standard ridges QCL. These low thermal resistances project up to 40 W in continuous wave operation using state-of-the-art QCL design.

Demonstration of a quick process to achieve buried heterostructure quantum cascade laser leading to high power and wall plug efficiency

This thesis addresses new methods in the growth of indium phosphide on silicon for enabling silicon photonics and nano photonics as well as efficient and cost-effective solar cells. It also addresses the renewal of regrowth of semi-insulating indium phosphide for realizing buried heterostructure quantum cascade lasers with high power and wall plug efficiency for sensing applications.As regards indium phosphide on silicon, both crystalline and polycrystalline growth methods are investigated. The crystalline growth methods are: (i) epitaxial lateral overgrowth to realize large area InP on Si, for silicon photonics (ii) a modified epitaxial lateral overgrowth method, called corrugated epitaxial lateral overgrowth, to obtain indium phosphide/silicon heterointerface for efficient and cost effective solar cells and (iii) selective growth of nanopyramidal frusta on silicon for nanophotonics. The polycrystalline growth method on silicon for low cost solar cell fabrication has been realized via (i) phosphidisation of indium oxide coating synthesized from solution chemistry and (ii) phosphidisation cum growth on indium metal on silicon. All our studies involve growth, growth analysis and characterization of all the above crystalline and polycrystalline layers and structures.After taking into account the identified defect filtering mechanisms, we have implemented means of obtaining good optical quality crystalline layers and structures in our epitaxial growth methods. We have also identified feasible causes for the persistence of certain defects such as stacking faults. The novel methods of realizing indium phosphide/silicon heterointerface and nanopyramidal frusta of indium phosphide on silicon are particularly attractive for several applications other than the ones mentioned here.Both the polycrystalline indium phosphide growth methods result in good optical quality material on silicon. The indium assisted phosphidisation cum growth method normally results in larger grain size indium phosphide than the one involving phosphidisation of indium oxide. These two methods are generic and can be optimized for low cost solar cells of InP on any flexible substrate.The method of regrowth of semi-insulating indium phosphide that is routinely practiced in the fabrication of buried heterostructure telecom laser has been implemented for quantum cascade lasers. The etched ridges of the latter can be 6-15 µm deep, which is more than 2-3 times as those of the former. Although this is a difficult task, through our quick and flexible regrowth method we have demonstrated buried heterostructure quantum cascade lasers with an output power up to 2. 5 W and wall plug efficiency up to 9% under continuous operation.

Monolithic tunable single source in the mid-IR for spectroscopy

We present a scheme for the realization of high performances, large tuning range, fully integrated and possibly low cost mid infrared laser source based on quantum cascade lasers and silicon based integrated optics. It is composed of a laser array and a laser combiner. We show that our metal grating approach gives many advantages for the fabrication yield of those laser arrays. We show the results of such a fabrication at 1350 cm-1 with 60 cm-1 tuning range. The silicon is a low cost option for the size consuming combiner. In the development of the SiGe platform, we present the loss measurement set up and we show losses below 1dB/cm at 4.5μm.

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.

Hydride vapour phase epitaxy assisted buried heterostructure quantum cascade lasers for sensing applications

Buried heterostructure (BH) lasers are routinely fabricated for telecom applications. Development of quantum cascade lasers (QCL) for sensing applications has largely benefited from the technological achievements established for telecom lasers. However, new demands are to be met with when fabricating BH-QCLs. For example, hetero-cascade and multistack QCLs, with several different active regions stacked on top of each other, are used to obtain a broad composite gain or increased peak output power. Such structures have thick etch ridges which puts severe demand in carrying out regrowth of semi-insulating layer around very deeply etched (< 10 μm) ridges in short time to realize BH-QCL. For comparison, telecom laser ridges are normally only <5 μm deep. We demonstrate here that hydride vapour phase epitaxy (HVPE) is capable of meeting this new demand adequately through the fabrication of BH-QCLs in less than 45 minutes for burying ridges etched down to 10-15 μm deep. This has to be compared with the normally used regrowth time of several hours, e.g., in a metal organic vapour phase epitaxy (MOVPE) reactor. This includes also micro-stripe lasers resembling grating-like ridges for enhanced thermal dissipation in the lateral direction. In addition, we also demonstrate HVPE capability to realize buried heterostructure photonic crystal QCLs for the first time. These buried lasers offer flexibility in collecting light from the surface and relatively facile device characterization feasibility of QCLs in general; but the more important benefits of such lasers are enhanced light matter interaction leading to ultra-high cavity Q-factors, tight optical confinement, possibility to control the emitted mode pattern and beam shape and substantial reduction in laser threshold.

Monolithic coupling of QCLs in evenescent waveguides on InP

In this work we present a significant step toward monolithic multiplexed distributed feedback (DFB) quantum cascade lasers (QCL) array on indium phosphide (InP). A multi-wavelength DFB-QCL array evanescently coupled to an underlying InGaAs waveguide on iron doped InP wafer is presented. We introduce the design, optimization, simulation and fabrication of the adiabatic coupler ensuring high transfer efficiency from the active to the passive waveguide. The active region designed in 7 μm - 10 μm wavelength range is grown by molecular beam epitaxy on top of an InGaAs waveguide. Components are defined during postgrowth processing, which eliminates the need for material regrowth or bonding techniques. With the present design, one could realize a broadly tunable, mechanically robust, single-mode output source which can be used in spectroscopic applications.

Broadband quantum cascade lasers monolithically multiplexed on Silicon for mid-infrared spectroscopy

We present the realizations of an array of Distributed Feedback (DFB) lasers and passive optical waveguides based on Silicon. The aim of these preliminary results is to realize a monolithic, widely tuneable, source in the mid-Infrared (mIR) for laser spectroscopy.