J. Faist

Frequency noise of free-running 4.6 μm distributed feedback quantum cascade lasers near room temperature

The frequency noise properties of commercial distributed feedback quantum cascade lasers emitting in the 4.6 μm range and operated in cw mode near room temperature (277 K) are presented. The measured frequency noise power spectral density reveals a flicker noise dropping down to the very low level of <100 Hz(2)/Hz at 10 MHz Fourier frequency and is globally a factor of 100 lower than data recently reported for a similar laser operated at cryogenic temperature. This makes our laser a good candidate for the realization of a mid-IR ultranarrow linewidth reference.

Sb-free quantum cascade lasers in the 3–4 μm spectral range

In this work, the design and implementation of Sb-free short wavelength strain-compensated quantum cascade lasers in the 3–4 μm spectral range is presented. Due to the presence of highly strained AlAs-barrier layers, the optimization of the epitaxial growth process is firstly discussed. The used active region design is then presented together with the observed laser performance. Watt-level room temperature emission at 3.3 μm is shown for Fabry–Perot devices and laser operation in pulsed mode is observed above 350 K. The laser performance is comparable with Sb-containing quantum cascade lasers. Spectral tuning of the lasers in an external cavity configuration over more than 275 cm−1 is achieved with an emission wavelength as short as 3.15 μm. For the first time in this spectral range, results on single-mode buried heterostructure distributed feedback lasers are shown.

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.

Physical origin of frequency noise and linewidth in mid-IR DFB quantum cascade lasers

Frequency noise and linewidth properties of different mid-infrared DFB-QCLs using buried-heterostructures and ridge waveguides are compared. The physical origin of frequency noise and the impact of the different lasers parameters are discussed.

Recent progress on single-mode quantum cascade lasers

Since the first demonstration of distributed feedback quantum (DFB) quantum cascade (QC) lasers in 1997 tremendous progress has been made in the development of single-mode emitting QC lasers. Such kind of devices are of particular interest because a lot of different molecules, like CO2, N2O or CH4, have their fundamental modes in the mid-infrared spectral region (3-12 μm).

Multi-wavelength QCL based MIR spectroscopy for fluids and gases

We demonstrate multi-color DFB QCLs with separated electrical pumping for independent single-mode emission of several wavelengths from the same ridge. This will be implemented in our mid-infrared spectroscopy sensors for gases (CO2) and liquids (cocaine).

Photocurrent spectroscopy of site-controlled pyramidal quantum dots

Intraband photocurrent spectroscopy of site-controlled pyramidal quantum dots by inserting them into the intrinsic region of n-i-n like quantum dot infrared photodetector structure is reported. The photovoltaic response is observed in the mid-infrared region. A peak responsivity of 0.4 mA/W at 120 meV (λ = 10 μm) is observed at 10 K at −2 V bias. The ability to engineer states in the conduction band of the QDs has been exploited to tune their photocurrent response from 10 μm to 18 μm with a narrow spectral width of Δλ/λ = 0.17.

Terahertz quantum cascade lasers frequency combs: Wide bandwidth operation and dual-comb on a chip

Terahertz (THz) quantum-cascade lasers (QCLs) constitute a very promising candidate for compact, wide bandwidth, integrated frequency combs [1, 4-7]. QCLs based on heterogeneous cores display the widest spectral coverage reaching more than one octave [2]. The possibility to engineer the gain profile turns out to be fundamental also with respect to dispersion compensation in order to extended the comb spectral bandwidth [2, 7]. In the effort of extending the comb operation to a full-octave to implement the laser self-referencing [3], we present here a new here a new THz QCL active region that allows the generation of a frequency comb with a spectral bandwidth exceeding of 1 THz centered at 3.1 THz. It fully exploits the capability of QCLs to integrate different active region designs within one laser cavity. The used building block is the three-active region design reported in Ref. [2], where a design at 3.4 THz has been added to increase the bandwidth towards higher frequencies. The four designs have central frequencies of 2.3, 2.6, 2.9, and 3.4 THz, the number of periods per design has also been rearranged in order to provide a flat gain resulting in a similar threshold for all the active regions and more dynamic range. Additionally, the doping level has been increased. Laser performance results in a largely extended dynamic range with respect to the original three-stack structure. Peak powers above 8 mW are recorded at 30 K and the lasing spectrum spans over 1.94 THz from 1.88 THz to 3.82 THz covering more than a full octave in frequency (Fig.1(a, b)). Dry-etched lasers with side-absorbers for lateral mode suppression similar as in [5] were fabricated for continuous wave (CW) operation and comb operation is probed through the beatnote analysis. Fig. 1(c, d) shows the beatnote as a function of the injected current with a maximum comb span of 1.1 THz which is the broadest demonstrated so far. Further proof of comb regime comes from the simultaneous measurements of two laser ridges on the same chip that show multiheterodyne spectra working in a dual-comb configuration [6].

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.

Amplification of broadband terahertz pulses in a quantum cascade heterostructure

We demonstrate an amplification of broadband terahertz pulses in the bandwidth of 500 GHz centered at 2.5 THz. The amplification is based on gain switched quantum cascade structure width the heterogeneous active region.