Efficient generation of radiation in the mid- and far- infrared relies primarily on lasers and coherent nonlinear optical phenomena driven by lasers. This wavelength range lacks of luminescent devices because the spontaneous emission rate becomes much longer than the nonradiative energy relaxation processes and therefore emitters have to count on stimulated emission produced by linear or non-linear optical gain. However, spontaneous emission is not a fundamental property of the emitter. By engineering metamaterials composed of arrays of nano-emitters into microcavities coupled to patch antennas, we have demonstrated mid-infrared electroluminescent devices emitting a collimated beam with excellent spatial properties and a factor 100 increase in the collected power, compared to standard devices. Our results illustrate that by reshaping the photonic environment around emitting dipoles, as in the Purcell effect, it is possible to enhance the spontaneous emission and conceive efficient optoelectronic light emitting devices that operate close to the thermodynamical equilibrium as LEDs in the visible range.

Atomically resolved Z-contrast and strain mappings are used to extract a model of the composition of an InGaAs/InAlAs asymmetric coupled quantum-well structure grown on InP by using metal-organic vapor phase epitaxy. The model accounts for grading across multiple alloy interfaces and is used to compute intersubband absorption in the structure. The simulation accurately predicts the experimental absorption spectrum of the structure within only a few meV, an almost 10-fold improvement over simulations using a square-band profile with nominal alloy compositions. This work thus provides a significant step forward in accurate and predictive simulations of the optical properties of epitaxial heterostructures for emission, modulation, and detection in mid-infrared.

Interband cascade lasers (ICLs) are semiconductor lasers emitting in the mid-wave infrared (MWIR 3–6 μm) and can operate as frequency combs (FCs). These demonstrations are based on double section cavities that can reduce dispersion and/or are adapted for radio frequency operation. Here, we show that ICL FCs at long wavelengths, where the refractive index dispersion reduces, can be realized in a single long section cavity. We show FC generation for ICLs operating at λ ∼ 4.2 μm, demonstrating narrow electrical beatnotes over a large current range. We also reconstruct the ultrafast temporal response through a modified shifted wave interference Fourier transform spectroscopy setup with two fast MWIR detectors, which shows a frequency modulated response in free running operation. Further, we show that, through active mode-locking, the ICL can be forced to generate short pulses on the order of 3 ps. This temporal response is in agreement with Maxwell–Bloch simulations, highlighting that these devices possess long dynamics (∼100 ps) and potentially makes them appropriate for the generation of large peak powers in the MWIR.

Through an efficient linearization of the optical frequency chirps of a quantum cascade laser (QCL), we demonstrate and compare two methods of coherent ranging in the long-wave infrared (LWIR) window. The first method is based on the coherent detection of the light reflected by the target on an external quantum cascade detector (QCD). The second method relies on the measurement of disturbances of the laser properties caused by the reinjection of the collected light inside the laser cavity. Both of the methods are compared in terms of precision and accuracy through the ranging of an outdoor static target up to 54 m. Via a linear optical frequency modulation with a bandwidth of about 8 GHz in a period of 65 $\mu s$ and thanks to linearity errors as low as 0.03%, measurements with a relative precision below 1% of the absolute distance are achieved, paving the way to high-speed and precise mid-infrared ranging systems.

Il y a 30 ans je faisais partie de l’équipe des Laboratoires Bell qui a conçu et démontré le laser à cascade quantique, une puissante source de lumière infrarouge, réalisée par une complexe ingénierie qui combine plusieurs phénomènes quantiques, tels que l’effet tunnel et la discrétisation des niveaux d’énergie. Dans cet article, je raconte l’aventure de sa découverte, les conditions qui l’ont permise, le plaisir et la fierté d’être un jeune chercheur.

Free space optical (FSO) communication is considered a critical part of future ICT infrastructure, particularly in non-terrestrial communication segments. In this context, the ability to achieve fast and reliable FSO propagation through long-distance atmospheric channels is the most important factor in choosing technological solutions. One property of optics directly related to this factor is the choice of wavelength. It has been identified that the mid-infrared (mid-IR) regime, which includes two atmospheric transmission windows-the mid-wave IR (MWIR, 3-5 mu m) and the long-wave IR (LWIR, 8-12 mu m)-can potentially offer a promising solution for achieving such performance. Additionally, viable semiconductor sources and detectors that support high-speed and efficient signal transmission are also considered critical to generating sufficient critical mass to advance the application of mid-IR FSO. Unipolar quantum optoelectronics, including quantum cascade lasers (QCL), Stark modulators, quantum cascade detectors (QCD), and quantum-well IR photodetectors (QWIP), among other components, emerge as potential candidates to build such FSO subsystems and systems. We present our recent efforts in conducting subsystem and system-level studies with different variants of these unipolar quantum optoelectronics and demonstrate the potential for feasible transmitter and receiver performance in a laboratory environment. We also discuss the key challenges and considerations of such technologies towards practical development. Finally, we summarize recent research and development efforts worldwide in advancing this highly promising direction.

In this work, we investigate data transmission in the long wavelength infrared spectrum employing a directly-modulated quantum cascade laser and a quantum cascade detector in ridge architecture, both operating at a wavelength around 9 mu m. We were able to measure bit rates of 200 Mbps for a two-level (OOK) modulation scheme in a back-to-back configuration at room temperature. The findings of this study pave the way for further development of these devices to be employed in integrated photonic circuits for advanced applications in secure and high-speed free-space optical communications.

Electrically injected supersymmetric (SUSY) quantum cascade laser (QCL) array of the wavelength at around 13.4 μm has been demonstrated. By applying SUSY transformations to the main array with five laser elements, a lossy superpartner array with four laser elements is constructed. As a result, except for the fundamental supermode, which is confined in the main array, other high order supermodes penetrating into the superpartner array are suppressed. By selectively pumping the main array, the fabricated SUSY QCL array can emit light with a near-diffraction-limited (D.L.) beam over the whole dynamic range, with the full-width half-maximum up to 11.7° in the lateral direction and the output peak power up to 406 mW in pulsed operation at room temperature, which is 3.6 times the power of a single ridge laser of the same laser length. Furthermore, the far field tuning through the mode switching of fundamental and high order supermodes is realized experimentally, by electrically adjusting the gain and loss in the superpartner array, which agrees well with the designs. The electrically far field tunability has great potential to find applications in beam steering.

The volume plasmon modes of a confined electron gas are engineered in a step-like semiconductor potential, which induces the formation of adjacent regions of different charge density. Each region supports spatially localized collective modes. Adjacent modes are theoretically demonstrated to couple, forming delocalized modes, which are well-described with a hybridization picture. Exploiting the thin-film Berreman effect, the engineered plasmon modes are directly observed in optical measurements. Using a quantum microscopic theory, the asymmetry of the single-particle electronic states is shown to be directly imprinted on the nonuniform polarization of the collective modes.

Colloidal nanocrystals are becoming an increasingly viable alternative to epitaxially grown semiconductors for infrared optoelectronics. Nanocrystal-based imagers have reached a commercial status in the short-wave infrared, while the midwave infrared (3-5 mu m) appears as a promising playground. Beyond the evident requirement to grow less confined particles, the design of the sensor architecture for colloidal materials requires a complete overhaul compared to their visible and near-infrared counterparts. Here, we focus on designing transparent conductive electrodes in a spectral range where transparent conductive oxides become inefficient. We propose an optimized design of a metallic multiresonant grating that allows a strong spatial overlap between the confined electromagnetic field and the built-in electrostatic field from a diode stack, thus simultaneously enhancing light absorption and charge collection. The device is then expanded to a 2D metasurface to prevent a polarization dependence for maximized light absorption. Finally, we explore the lateral size downscaling of this type of resonator and show its behavior when the size matches the pixel size of infrared focal plane arrays.

This study investigates the potential of long-wave infrared (LWIR) free-space optical (FSO) transmission using multilevel signals to achieve high spectral efficiency. The FSO transmission system includes a directly modulated-quantum cascade laser (DM-QCL) operating at 9.1 μm and a mercury cadmium telluride (MCT) detector. We conduct small-signal characterization of the system, including the DM-QCL chip and MCT detector, evaluating the end-to-end response of both components and all associated electrical elements. For large-signal characterization, we employ a range of modulation formats, including on-off keying (OOK), 4-level pulse amplitude modulation (PAM4), and 6-level PAM (PAM6), with the objective of optimizing both the bit rate and spectral efficiency of the FSO transmission by applying pre- and post-processing equalization. At 15˚C, the studied LWIR FSO system achieves gross rates of 16 Gbps with an OOK signal and 18 Gbps with PAM4, both below the 6.25% overhead hard decision-forward error correction (6.25%-OH HD-FEC) limit, and 10 Gbps OOK below the KR-FEC limit. At 20˚C, we obtain 15 Gbps with OOK, 18 Gbps with PAM4, and 17.4 Gbps with PAM6. Furthermore, we evaluate the BER performance as a function of the decision feedback equalization (DFE) tap number to explore the role of equalization in enhancing signal fidelity and reducing errors in FSO transmission. Our findings accentuate the competitive potential of DM-QCL and MCT detector-based FSO transceivers with digital equalization for the next generation of FSO communication systems.

Frequency-modulated (FM) combs are produced by mode-locked lasers in which the electric field has a linearly chirped frequency and nearly constant amplitude. This regime of operation occurs naturally in certain laser systems and constitutes a valuable alternative to generate spectra with equidistant modes. Here, we use a low-noise fs-pulse comb as the local oscillator and combine dual comb heterodyne detection with time domain analysis of the multi-heterodyne signal to reveal the temporal trace of both amplitude and phase quadratures of FM comb lasers' electric field. This technique is applied to both a dense and a harmonic mid-infrared free-running quantum cascade laser frequency comb and shows direct evidence of the FM behavior together with the high degree of coherence of these sources. Our results furnish a deeper insight on the origin of the FM combs and pave the way to further improvement and optimization of these devices.

Mechanical forces induced by high-speed oscillations provide an elegant way to dynamically alter the fundamental properties of materials such as refractive index, absorption coefficient and gain dynamics. Although the precise control of mechanical oscillation has been well developed in the past decades, the notion of dynamic mechanical forces has not been harnessed for developing tunable lasers. Here we demonstrate actively tunable mid-infrared laser action in group-IV nanomechanical oscillators with a compact form factor. A suspended GeSn cantilever nanobeam on a Si substrate is resonantly driven by radio-frequency waves. Electrically controlled mechanical oscillation induces elastic strain that periodically varies with time in the GeSn nanobeam, enabling actively tunable lasing emission at >2 μm wavelengths. By utilizing mechanical resonances in the radio frequency as a driving mechanism, this work presents wide-range mid-infrared tunable lasers with ultralow tuning power consumption.

We experimentally demonstrate a room-temperature LWIR FSO link with a 9.1-μm directly modulated QCL and an MCT detector. Net bitrate of up to 16.9 Gb/s is achieved at both 15°C and 20°C over a 1-meter distance.

We summarize our recent experimental studies of free-space communications enabled by directly modulated quantum cascade lasers at both MWIR and LWIR regions. Different detector types with different characteristics are compared.

Abstract The large mid-infrared (MIR) spectral region, ranging from 2.5 µm to 25 µm, has remained under-exploited in the electromagnetic spectrum, primarily due to the absence of viable transceiver technologies. Notably, the 8–14 µm long-wave infrared (LWIR) atmospheric transmission window is particularly suitable for free-space optical (FSO) communication, owing to its combination of low atmospheric propagation loss and relatively high resilience to turbulence and other atmospheric disturbances. Here, we demonstrate a direct modulation and direct detection LWIR FSO communication system at 9.1 µm wavelength based on unipolar quantum optoelectronic devices with a unprecedented net bitrate exceeding 55 Gbit s−1. A directly modulated distributed feedback quantum cascade laser (DFB-QCL) with high modulation efficiency and improved RF-design was used as a transmitter while two high speed detectors utilizing meta-materials to enhance their responsivity are employed as receivers; a quantum cascade detector (QCD) and a quantum-well infrared photodetector (QWIP). We investigate system tradeoffs and constraints, and indicate pathways forward for this technology beyond 100 Gbit s−1 communication.

We report room temperature heterodyne detection of a quantum cascade laser beaten with a local oscillator on a unipolar quantum photodetector in two different atmospheric windows, at 4.8 µm and 9 µm. A noise equivalent power of few pW is measured by employing an active stabilization technique in which the local oscillator and the signal are locked in phase. The measured heterodyne noise equivalent power is six orders of magnitude lower than that obtained with direct detection.

Optoelectronic devices rely on conductive layers as electrodes, but they usually introduce optical losses that are detrimental to the device performances. While the use of transparent conductive oxides is established in the visible region, these materials show high losses at longer wavelengths. Here, we demonstrate a photodiode based on a metallic grating acting as an electrode. The grating generates a multiresonant photonic structure over the diode stack and allows strong broadband absorption. The obtained device achieves the highest performances reported so far for a midwave infrared nanocrystal-based detector, with external quantum efficiency above 90%, detectivity of 7 × 1011 Jones at 80 K at 5 μm, and a sub-100 ns time response. Furthermore, we demonstrate that combining different gratings with a single diode stack can generate a bias reconfigurable response and develop new functionalities such as band rejection.