| Summary: | Quantum Cascade Laser is a unipolar semiconductor optoelectronic device based on inter-subband electron leap with wavelengths covering the mid- and far-infrared to terahertz bands, which has important applications in gas composition detection, medical diagnosis, hazardous materials telemetry, and free-space communication. The long-wave infrared band contains many fingerprint absorption peaks of gas molecules and is located within a low-loss atmospheric window, so the development of high-power long-wave infrared quantum cascade laser research is of great importance in the fields of gas sensing, free-space communication and infrared countermeasures. Current quantum cascade lasers have achieved watt-level continuous output in the 3-5 μm band range, however, the inherent technical limitations of 8-14 μm long-wave devices (e.g., increased optical loss of free carriers, reduced inter-subband gain, and
weakened optical confinement) cause the performance of long-wave devices to decrease rapidly with increasing wavelength.
In this article, different designs and performances of active regions of quantum cascade lasers are discussed, including several commonly used active region designs for quantum cascade lasers at long wavelengths, such as bound to continuum, resonant-phonon, and chirped superlattice. In addition, the waveguide structure of the laser also largely determines the performance of the quantum cascade laser, and the design of the waveguide structure not only focuses on the optimization and enhancement of the device performance, but also takes into account some problems
encountered in the device fabrication process. I will use a software named “erwinjr” to do the simulation of the design of structure. After this section, I will learn about spectroscopy and how to measure the performance of a quantum cascade laser. In characterizing the performance of a device, there are several important parameters such as light-current-voltage, and spectral characteristics. The process of making a
pulsed laser and the devices and processes to characterize the corresponding properties of a laser will also be mentioned in this article.
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