G. Maisons

Optical{Feedback Cavity{Enhanced Absorption Spectroscopy with a Quantum Cascade Laser.

Optical-feedback cavity-enhanced absorption spectroscopy is demonstrated in the mid-IR by using a quantum cascade laser (emitting at 4.46 μm). The laser linewidth reduction and frequency locking by selective optical feedback from the resonant cavity field turns out to be particularly advantageous in this spectral range: It allows strong cavity transmission, which compensates for low light sensitivity, especially when using room-temperature detectors. We obtain a noise equivalent absorption coefficient of 3 × 10(-9)/cm for 1 s averaging of spectra composed by 100 independent points. At 4.46 μm, this yields a detection limit of 35 parts in 10(12) by volume for N(2)O at 50 mbar, corresponding to 4 × 10(7) molecules/cm(3), or still to 1 fmol in the sample volume.

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.

Effect of emitter number on quantum cascade laser monolithic phased array

We present the optical analysis of spatial single-mode monolithic quantum cascade laser arrays in the mid-IR. Subwavelength parallel microstripe waveguides are buried into InP:Fe and phase locked by evanescent coupling. Lasing at room temperature is obtained at λ=8.4 μm. We describe the near- and far-field of stripe arrays comprising up to 32 emitters. One hundred percent coherent emission is shown experimentally and well accounted for by a standard optical simulation.

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.

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.

Drug precursor vapor phase sensing by cantilever enhanced photoacoustic spectroscopy and quantum cascade laser

Chemical control is a crucial element for controlling the manufacturing and distribution of illegal narcotics and synthetic substances. This work is focusing on the vapor phase point detection methodology due to its applicability in customs, airport and harbor check point scenarios where inspection of trucks, cars, containers, as well as people and baggage is required. There are several techniques available that are able to screen and identify specific molecules even at very low concentration at laboratory or in controlled environment. However, a portable system which would be simple to use, sensitive, compact, and capable of providing screening over a large number of compounds and discriminate them with low probability of false alarms with short response time scale is still demanded. Our solution is to combine cantilever enhanced photoacoustic spectroscopy with external cavity quantum cascade laser (EC-QCL), which is capable of measuring infrared gas phase spectra of the analyte substances. High sensitivity in a wide dynamic range is achieved with a silicon MEMS cantilever sensor coupled with an optical readout system and high power laser source, which is operating at the fundamental vibrational absorption wavelengths. High selectivity is achieved by measuring the infrared spectra of the sample gas utilizing widely tunable EC-QCL technology and novel signal processing methods. Measurements with the breadboard demonstrator of the described system and detection limit estimation were performed to a selected drug precursor target molecules. The measurement results indicate low ppb-level gas phase sensitivity to selected drug precursor substances also in the presence of typical interfering molecules.

Mid-infrared wavelength multiplexer in InGaAs/InP waveguides using a Rowland circle grating

We report the monolithic integration of a 15-channel multiplexer on indium phosphide. It covers the 7.1-to-8.5 µm wavelength range suitable for combining the outputs of several individual lasers. The fabrication is compatible with the growth of active layers, therefore enabling a fully integrate broadband laser source in the mid-infrared spectral range. Channels are accurately spaced in wavelength (97 nm) in good agreement with design.

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.