Alfredo Bismuto

Electrically tunable, high performance quantum cascade laser

A quantum cascade laser design for wide voltage-tuning, emitting at ∼8.5 μm, is presented based on a diagonal bound-to-continuum design. The relatively short period length and the diagonal nature of the laser transition guarantees a wide tuning of the emission due to the linear Stark shift effect. Tuning of both the spontaneous and stimulated emission is presented over almost 100 cm−1. In spite of the large tuning, laser performance are comparable with the best results present in literature in this spectral range. In particular, continuous wave operation up to 450 mW and pulsed wall plug efficiencies up to 11.5% were measured at 300 K. A transport model, based on the density matrix formalism, was used to simulate spontaneous and stimulated emission as function of the applied field. Same model was also used to predict light-current-voltage characteristics of the lasers.

High power Sb-free quantum cascade laser emitting at 3.3 μm above 350 K

The design and implementation of a short wavelength strain-compensated quantum cascade laser based on In0.72Ga0.28As/In0.52Al0.48As–AlAs on InP is presented. We demonstrate watt-level room temperature emission at 3.3 μm. Lasers operate in pulsed mode above 350 K. Threshold current densities of 3.6 kA/cm2 and slope efficiencies of more than 600 mW/A are observed at room temperature. The laser performance is comparable with Sb-containing quantum cascade lasers.

Direct link of a mid-infrared QCL to a frequency comb by optical injection.

A narrow-linewidth comb-linked nonlinear source is used as master radiation to injection lock a room-temperature mid-infrared quantum cascade laser (QCL). This process leads to a direct lock of the QCL to the optical frequency comb, providing the unique features of narrow linewidth, absolute frequency, higher output power, and wide mode-hop-free tunability. The QCL reproduces the injected radiation within more than 94%, with a reduction of the frequency-noise spectral density by 3 to 4 orders of magnitude up to about 100 kHz, and a linewidth narrowing from a few MHz to 20 kHz.

Influence of the growth temperature on the performances of strain-balanced quantum cascade lasers

The effect of substrate temperature, during epitaxial growth, on the performances of strain-balanced quantum cascade lasers based on a three quantum well active region and operating at λ≈4.6 μm is presented. Based on a comparison with a density matrix model of these devices, the optimum performances obtained at a growth temperature of 515 °C, are interpreted as arising from a value of the interface roughness correlation length (Λ=85 A) close to the optimum one computed by the model (Λ=100 A).

High performance, low dissipation quantum cascade lasers across the mid-IR range

In this work, we present the development of low consumption quantum cascade lasers across the mid-IR range. In particular, short cavity single-mode lasers with optimised facet reflectivities have been fabricated from 4.5 to 9.2 μm. Threshold dissipated powers as low as 0.5 W were obtained in continuous wave operation at room temperature. In addition, the beneficial impact of reducing chip length on laser mounting yield is discussed. High power single-mode lasers from the same processed wafers are also presented.

Fully automatized quantum cascade laser design by genetic optimization

Using a transport model based on the density matrix formalism, a fully automatized technique to design quantum cascade structures in the mid-infrared is presented that implements a genetic algorithm where the wallplug efficiency has been used as merit factor. Starting from a reference design, the model converges after few generations on an optimized design that presents a better carrier injection in the upper lasing state. Both the designs have been fabricated using buried heterostructure process and the optimized design shows a pronounced increase in the laser operation range and higher output powers. In good agreement with the simulations, the laser efficiency increases from 5% to 12%.

Broadband external cavity tuning in the 3-4 μm window

In this work, a continuous external cavity spectral tuning of 556 cm−1 in the 3–4 μm region is shown for a heterogeneous bound-to-continuum active region design based on the strain-compensated Sb-free material system. The two active regions have center wavelengths at 3.3 μm and 3.7 μm with a total modal overlap factor of 86%. We also show an effective multilayer broadband anti-reflectivity coating in the 3–4 μm region reducing the overall reflectivity over the whole tuning range below 1.4%.

Asymmetric heterostructure for photovoltaic InAs quantum dot infrared photodetector

A photovoltaic InAs quantum dot-under-a-well photodetector is reported with a peak responsivity at 7 μm wavelength. In this structure, we implement an improved injection scheme, which allows a controlled feeding of the quantum dots through a modulation-doped InGaAs quantum well injector. A thin Al0.3Ga0.7As barrier significantly reduces the dark current and, at the same time, is responsible for the photovoltaic behavior. At 4 K and no applied bias, a responsivity of 2.5 mA/W and a detectivity of D∗=2.3×1010 cm Hz1/2/W in the dark is measured. The TBLIP of the device is 60 K and the D∗ at this temperature is 2×109 cm Hz1/2/W.

Large cavity quantum cascade lasers with InP interstacks

Multicore quantum cascade lasers with large cavities show low optical losses, high saturation intensity, and low beam divergence. We present a four active core laser based on InGaAs–AlInAs material system emitting at 10.5 μm. To improve thermal conductance, InP interstacks were used to separate active regions. Selective lateral etching of the active regions was used to reduce optical losses. Peak powers up to 4.6 W, average powers up to 310 mW, and wall-plug efficiencies up to 4.6% were measured at 300 K. A far field with full width at half maximum of 18.7° and 49.8° in the lateral and in the growth direction, respectively, was observed.

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.