High-Power Mid-Infrared (λ∼3-6 μm) Quantum Cascade Lasers

Abstract

The performances of mid-infrared (IR) quantum cascade lasers (QCLs) are now reaching a maturity level that enables a variety of applications which require compact laser sources capable of watt-range output powers with high beam quality. We review the fundamental design issues and current performance limitations, focusing on InGaAs/AlInAs/InP QCLs with emission in the 3-6 m wavelength range. Metamorphic materials broaden the available compositions for accessing short emission wavelengths (≤3.5 m) or for integration with GaAs-and Si-photonics platforms. Conductionband engineering through the use of varying compositions throughout the active-region structure has been utilized to achieve the highest performance levels to date. Interface roughness scattering plays a dominant role in determining both the lower-laser-level lifetime as well as the carrier-leakage current. Numerous approaches have been implemented in attempts to control, scale, and stabilize the spatial mode to high output powers. Of all approaches photonic-crystal structures with high built-in index contrast, thus capable of maintaining modal properties under strong self-heating, are the most promising device configuration for achieving single-spatial-mode, single-lobe reliable CW operation to multiwattrange power levels. Such devices have demonstrated to date > 5W front-facet output powers with diffraction-limited beams in shortpulse operation.

Compact multi-watt QCL module

“…Second, the efficiency of the high power QCL chips is on the order of η = 5 -10 % (Popt,out / Pel,in) around λ ≈ 4 µm [7], which is substantially lower than in typical semiconductor laser chips. An output power level of about Popt,out = 1 W thus leads to heat dissipation of easily more than 10 W. Heating of the QCL chip initiates a negative feedback-loop by reducing its efficiency and further increasing the dissipated heat.…”

Pushing the Room Temperature Continuous‐Wave Operation Limit of GaSb‐Based Interband Cascade Lasers beyond 6 µm

“…[15] The wavelength region around 6 µm is contested by both ICLs and quantum cascade lasers (QCLs), that are also realized in this wavelength window. [16][17][18] However, QCLs usually show higher threshold current densities and threshold voltages than ICLs. By extending the wavelength range of ICLs beyond 6 µm combined with the low power consumption, we envision that these light sources will successfully compete with QCLs and InAs-based ICLs in low-power applications.…”

Room temperature continuous-wave operation of a dual-wavelength quantum cascade laser

“…Since the experimental demonstration in 1994 [1] , with continuous optimization in structure design, material quality, and device processing, the performances of quantum cascade lasers (QCLs) have been greatly improved in terms of high output power, low power consumption, wide spectral coverage, and other characteristics [2][3][4] . QCLs have now become superb and versatile laser sources in the mid-infrared spectral region with a wide range of applications, such as chemical sensing, free space optical communication, high-resolution spectroscopy, and medical diagnosis [5][6][7] .…”