Yves Bidaux

Extended tuning of mid-ir quantum cascade lasers using integrated resistive heaters

We present single mode quantum cascade lasers including a microscopic heater for spectral emission tuning. Through the use of a buried heater element, the active region temperature can be modified without changing the submount one. Emission frequency tuning in continuous-wave as large as 9 cm(-1) at 1270 cm(-1) and 14 cm(-1) at 2040 cm(-1) are observed, corresponding to an increase of the active region temperatures of ∼ 90 K. Due to the proximity of the heaters to the active region, emission can be modulated at several kHz range and the absence of moving parts guarantees the mechanical stability of the system. This method can be successfully applied to all buried heterostructure lasers, becoming an attractive solution for molecular spectroscopy in the IR. Using the presented devices, molecular absorptions of N(2)O have been measured between 1270 cm(-1) and 1280 cm(-1) and are in agreement with data from the HITRAN database.

Extended and quasi-continuous tuning of quantum cascade lasers using superstructure gratings and integrated heaters

In this work, we demonstrate broad electrical tuning of quantum cascade lasers at 9.25 μm, 8.5 μm, and 4.4 μm in continuous wave operation using Vernier-effect distributed Bragg reflectors based on superstructure gratings. Integrated micro-heaters allow to switch from one Vernier channel to the other, while predictable and mode-hop free tuning can be obtained in each channel modulating the laser current with a side mode suppression ratio as high as 30 dB. The resulting device behaves effectively as a switchable multicolour tunable source. Tuning up to 6.5% of the central wavelength is observed. To prove the importance of the developed devices for high resolution molecular spectroscopy, a N2O absorption spectrum has been measured.

Measurements and simulations of the optical gain and anti-reflection coating modal reflectivity in quantum cascade lasers with multiple active region stacks

We report spectrally resolved gain measurements and simulations for quantum cascade lasers (QCLs) composed of multiple heterogeneous stacks designed for broadband emission in the mid-infrared. The measurement method is first demonstrated on a reference single active region QCL based on a double-phonon resonance design emitting at 7.8 μm. It is then extended to a three-stack active region based on bound-to-continuum designs with a broadband emission range from 7.5 to 10.5 μm. A tight agreement is found with simulations based on a density matrix model. The latter implements exhaustive microscopic scattering and dephasing sources with virtually no fitting parameters. The quantitative agreement is furthermore assessed by measuring gain coefficients obtained by studying the threshold current dependence with the cavity length. These results are particularly relevant to understand fundamental gain mechanisms in complex semiconductor heterostructure QCLs and to move towards efficient gain engineering. Finally, the method is extended to the measurement of the modal reflectivity of an anti-reflection coating deposited on the front facet of the broadband QCL.

Dual comb operation of λ ∼ 8.2 μm quantum cascade laser frequency comb with 1 W optical power

In this work, we report the characterization of a quantum cascade laser frequency comb with an optical power of 1.05 W at λ∼8.2 μm. A 4.5 mm long device has a high reflectivity coating on the back facet as well as a top cladding designed to lower the group velocity dispersion and is operated at 258 K. Very strong (more than 60 dB) narrow beatnotes are shown, and frequency comb operation is obtained on a bandwidth of 85 cm−1 in a very large range of light-versus current characteristics. A bandwidth of 82 cm−1 has a power per mode of more than 1 mW and an average power per mode of 4.1 mW. Finally, a multi-heterodyne spectrum with 215 lines covering an optical bandwidth of more than 70 cm−1 measured with lasers showing similar performances is presented with very good line separation.

High power and single mode quantum cascade lasers

We present a single mode quantum cascade laser with nearly 1 W optical power. A buried distributed feedback reflector is used on the back section for wavelength selection. The laser is 6 mm long, 3.5 μm wide, mounted episide-up and the laser facets are left uncoated. Laser emission is centered at 4.68 μm. Single-mode operation with a side mode suppression ratio of more than 30 dB is obtained in whole range of operation. Farfield measurements prove a symmetric, single transverse-mode emission in TM00-mode with typical divergences of 41° and 33° in the vertical and horizontal direction respectively. This work shows the potential for simple fabrication of high power lasers compatible with standard DFB processing.

Purely wavelength- and amplitude-modulated quartz-enhanced photoacoustic spectroscopy

We report here on a quartz-enhanced photoacoustic (QEPAS) sensor employing a quantum cascade laser (QCL) structure capable of operating in a pure amplitude or wavelength modulation configuration. The QCL structure is composed of three electrically independent sections: Gain, Phase (PS) and Master Oscillator (MO). Selective current pumping of these three sections allows obtaining laser wavelength tuning without changes in the optical power, and power modulation without emission wavelength shifts. A pure QEPAS amplitude modulation condition is obtained by modulating the PS current, while pure wavelength modulation is achieved by modulating simultaneously the MO and PS QCL sections and slowly scanning the DC current level injected in the PS section.

All-electrical frequency noise reduction and linewidth narrowing in quantum cascade lasers

A novel all-electrical method of frequency noise reduction in quantum cascade lasers (QCLs) is proposed. Electrical current through the laser was continuously adjusted to compensate for fluctuations of the laser internal resistance, which led to an active stabilization of the optical emission frequency. A reduction of the linewidth from 1.7 MHz in the standard constant current mode of operation down to 480 kHz is demonstrated at 10-ms observation time when applying this method to a QCL emitting at 7.9 μm.

Mid infrared quantum cascade laser operating in pure amplitude modulation for background-free trace gas spectroscopy.

We present a single mode multi-section quantum cascade laser source composed of three different sections: master oscillator, gain and phase section. Non-uniform pumping of the QCLs gain reveals that the various laser sections are strongly coupled. Simulations of the electronic and optical properties of the laser (based on the density matrix and scattering matrix formalisms, respectively) were performed and a good agreement with measurements is obtained. In particular, a pure modulation of the laser output power can be achieved. This capability of the device is applied in tunable-laser spectroscopy of N2O where background-free quartz enhanced photo acoustic spectral scans with nearly perfect Voigt line shapes for the selected absorption line are obtained.

Waveguide engineering for low dispersion mid-infrared quantum cascade lasers frequency combs

Quantum Cascade Lasers (QCLs) have become one of the most used light sources in the Mid-IR. It has been demonstrated that QCLs can operate as frequency combs (FCs) [1] and that the performance of QCL FCs can be significantly improved by compensating for their waveguide dispersion using dielectric coating based Gires-Tournois interferometers [2]. However, the latter are incompatible with high optical output power since due to the optical absorption of the materials they overheat and burn. In this work we investigate how the properties of mid-IR QCL FCs can be improved by tailoring their waveguide dispersion.

Pure amplitude and wavelength modulation spectroscopy for detection of N2O using a three-section quantum cascade laser

We report on a novel quantum cascade laser (QCL) capable of operating in pure amplitude or wavelength modulation configuration thereby allowing the acquisition of background-free gas absorption-line profiles using quartz-enhanced photoacoustic spectroscopy (QEPAS). The QCL is composed of three electrically independent sections: Gain, Phase (PS) and Master Oscillator (MO). The non-uniform pumping of these three QCL sections allows laser wavelength tuning with constant optical power and vice-versa. Pure QEPAS amplitude modulation operating conditions were obtained by modulating the PS current, while pure wavelength modulation was obtained by modulating the MO section and slowly scanning the PS current.