The invention concerns a quantum cascade laser comprising in particular a gain region (14) consisting of several layers (20) each including: alternating strata of a first type (28) defining each an AllnAs quantum barrier and strata of a second type (28) defining each an InGaAs quantum barrier, and injection barriers (22), interposed between two of the layers (20). The layers of the gain region (14) form each an active zone extending from one to the other of the injection barriers (22) adjacent thereto. The strata (26, 28) are dimensioned such that: each of the wells comprises, in the presence of an electric field, at least a first upper subband, a second median subband, and a third lower subband, and the probability of an electron being present in the first subband is highest in the proximity of one of the adjacent injection barriers, in the second subband in the median part of the zone and in the third subband in the proximity of the other adjacent barriers. The laser is formed by a succession of active zones and injection barriers, without interposition of a relaxation zone.

https://science.sciencemag.org/content/sci/264/5158/553.full.pdf

Quantum cascade laser

Semiconductor devices have become indispensable for generating electromagnetic radiation in everyday applications. Visible and infrared diode lasers are at the core of information technology, and at the other end of the spectrum, microwave and radio-frequency emitters enable wireless communications. But the terahertz region (1-10 THz; 1 THz = 10(12) Hz) between these ranges has remained largely underdeveloped, despite the identification of various possible applications--for example, chemical detection, astronomy and medical imaging. Progress in this area has been hampered by the lack of compact, low-consumption, solid-state terahertz sources. Here we report a monolithic terahertz injection laser that is based on interminiband transitions in the conduction band of a semiconductor (GaAs/AlGaAs) heterostructure. The prototype demonstrated emits a single mode at 4.4 THz, and already shows high output powers of more than 2 mW with low threshold current densities of about a few hundred A cm(-2) up to 50 K. These results are very promising for extending the present laser concept to continuous-wave and high-temperature operation, which would lead to implementation in practical photonic systems.

Terahertz semiconductor-heterostructure laser

Terahertz semiconductor heterostructure laser

Six years after their birth, terahertz quantum-cascade lasers can now deliver milliwatts or more of continuous-wave coherent radiation throughout the terahertz range — the spectral regime between millimetre and infrared wavelengths, which has long resisted development. This paper reviews the state-of-the-art and future prospects for these lasers, including efforts to increase their operating temperatures, deliver higher output powers and emit longer wavelengths.

Terahertz quantum-cascade lasers

Continuous wave operation of quantum cascade lasers is reported up to a temperature of 312 kelvin. The devices were fabricated as buried heterostructure lasers with high-reflection coatings on both laser facets, resulting in continuous wave operation with optical output power ranging from 17 milliwatts at 292 kelvin to 3 milliwatts at 312 kelvin, at an emission wavelength of 9.1 micrometers. The results demonstrate the potential of quantum cascade lasers as continuous wave mid-infrared light sources for high-resolution spectroscopy, chemical sensing applications, and free-space optical communication systems.

/pdf/continuous-wave-operation-of-a-mid-infrared-semiconductor-2k5hjfw5ul.pdf

Continuous wave operation of a mid-infrared semiconductor laser at room temperature.

Recent advances in quantum-cascade (QC) laser active-region design are reviewed. Based on a rate equation model of the active region, we show why new gain regions. based on a two-phonon resonance or a bound-to-continuum transition exhibit significantly better performance than the traditional design based on a three-quantum-well active region. Threshold current densities as low as 3 kA/cm/sup 2/ at T=300 K, operation with a peak power of 90 mW at 425 K, single-mode high-power operation up to temperatures above 330 K at /spl lambda//spl ap/16 /spl mu/m and continuous wave operation up to T=311 K are demonstrated. QC lasers able to operate at high duty cycles (50%) on a Peltier cooler were used in a demonstration of a 300-MHz free-space optical link between two buildings separated by 350 m.

/pdf/bound-to-continuum-and-two-phonon-resonance-quantum-cascade-26bsd0vj75.pdf

Bound-to-continuum and two-phonon resonance, quantum-cascade lasers for high duty cycle, high-temperature operation

A quantum-cascade structure combining the advantages of the three-quantum well and superlattice active regions is demonstrated. In these devices, the emission occurs between a state localized close to the injection barrier and a miniband. A low threshold current density (3.6 kA/cm2), large slope efficiency (200 mW/A for 35 periods), and peak power (700 mW) are achieved at 30 °C while a peak power of 90 mW is obtained at temperatures as high as 150 °C.

https://www.alpeslasers.ch/Conference-Papers/bound-to-continuum.pdf

Quantum-cascade lasers based on a bound-to-continuum transition

High-temperature operation of a low-threshold 5.3 μm quantum-cascade distributed feedback laser is presented. The emission spectrum was single mode with more than 20 dB side mode suppression ratio for all investigated temperatures and up to thermal rollover. For 1.5% duty cycle and at 0 °C, the laser emitted 1.15 W of single mode peak power; at 120 °C, a value of 92 mW was seen. For a 3 mm long device, we observed a room-temperature threshold current density of 3.6 kA/cm2. This remarkable performance is mainly due to a 4 quantum-well active region using a double phonon resonance for the lower laser level.

High-temperature operation of distributed feedback quantum-cascade lasers at 5.3 μm

High average power quantum cascade lasers at 9.3 μm using InP top cladding layers and both junction up and junction down mounting are presented. A 3 mm long, junction up mounted device emitted 54 mW average power at 30 °C and 11.5% duty cycle with a threshold current density of 3.72 kA/cm2. A similar, but only 1.5 mm long device with high reflection coating on both facets was mounted junction down and tested at even higher duty cycles. At −27 °C, we achieved continuous wave operation with a threshold current density of 3.3 kA/cm2.

/pdf/continuous-wave-operation-of-a-9-3-mm-quantum-cascade-laser-338snpabs0.pdf

Thierry Aellen

Papers

Continuous wave operation of a mid-infrared semiconductor laser at room temperature.

Bound-to-continuum and two-phonon resonance, quantum-cascade lasers for high duty cycle, high-temperature operation

Quantum-cascade lasers based on a bound-to-continuum transition

High-temperature operation of distributed feedback quantum-cascade lasers at 5.3 μm

Continuous wave operation of a 9.3 μm quantum cascade laser on a Peltier cooler