Tunable mid-infrared single-mode quantum cascade lasers

• Main Author: Shi, Hao
• Other Authors: Wang Qijie
• Format: Thesis-Master by Coursework
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/158753
• Institution: Nanyang Technological University

Since the concept of quantum cascade laser (QCL) first proposed in 1997, the technology of QCL has grown rapidly and QCLs have been applied in many aera such as gas sensing and optical communication. The property of unipolar and subbands transition makes quantum cascade laser (QCL) ideal both mid-infrared and terahertz sources with narrow linewidth, high output power and tunable emission wavelength. The common solutions to realize single-mode tunable QCL are distributed feedback QCL (DFB-QCL) and external cavity QCL (EC-QCL). However, both of them suffer from some undesired drawbacks like complex fabrication, limited tuning range, and reduced robustness caused by vibration sensitive. In this dissertation, we designed and characterized a new QCL named slot waveguide QCL, which shows satisfying tunable single-mode performance. In the first part of dissertation the history, category and applications of QCLs are reviewed. Then the working principle as well as theoretical analysis including rate equation models of the tunnable QCL were introduced. Two types of typical tunnable QCLs (DFB-QCL and EC-QCL) were also mentioned in chapter two. After that, an five-element slot waveguide QCL array in this work have been presented. With current tuning in both front and back section, the device realized continuous tuning range over 41cm-1 with the center wavelength around 7.3 m and a SMSR of around 15dB is achieved. Moreover, the application of the QCL in mid-infrared gas detecting was also demonstrated. The absorption spectra for 2500 ppm SO2 detection with slot QCL array is investigated and the experimental result is consistent with simulation result. In addition, the linear fitting for absorption signal recorded at 1369.4 cm-1 exhibit good linear relationship in a large dynamic range.