dc.contributor.authorMeng, Bo
dc.date.accessioned2015-05-04T02:35:09Z
dc.date.accessioned2017-07-23T08:35:50Z
dc.date.available2015-05-04T02:35:09Z
dc.date.available2017-07-23T08:35:50Z
dc.date.copyright2015en_US
dc.date.issued2015
dc.identifier.citationMeng, B. (2015). Tunable mid-infrared quantum cascade lasers. Doctoral thesis, Nanyang Technological University, Singapore.
dc.identifier.urihttp://hdl.handle.net/10356/62926
dc.description.abstractThe tremendous developments of quantum cascade lasers (QCLs) have proven themselves as powerful tools for spectroscopy, homeland security, thermal imaging, and free-space communication applications. Compact broadly tunable QCLs in both mid-infrared (3-24 μm) and terahertz (1.2-5 THz) spectrum regions are especially important for high sensitivity spectroscopy due to their intrinsic narrow linewidth, high output power, robustness, and versatile emission wavelength designability. To achieve single-mode emission from QCLs, a number of schemes have been employed to exploit the broad gain spectrum of QCLs, e.g. external cavity QCLs (EC-QCLs), distributed feedback QCLs (DFB-QCLs), DFB QCL array, and sampled grating QCLs (SG-QCLs) etc. However, the above approaches either suffer from complex fabrication processes, e. g. InP regrowth and e-beam lithography, or reduced robustness due to the mechanically moving parts. Monolithic single-mode QCLs with broad tuning range and simple fabrication process through photolithography are thus necessary for both real-life applications and laboratory researches. Therefore, the main objective of this thesis is to develop novel tunable single-mode QCLs with easy fabrication and high performances. In this thesis, first, we have proposed and experimentally demonstrated compact tunable single-mode QCLs based on slot waveguide tunable structure at wavelength of ~10 μm. The slot-QCLs demonstrates a tuning range of 77 cm-1, which corresponds to ~7.8 % of relative tuning, while maintaining ~20 dB side mode suppression ratio (SMSR) within the whole tuning range. Compared with DFB-QCLs, the broader tuning range together with significantly simplified fabrication process makes slot-QCLs better candidates for high resolution spectroscopy. To further increase the wavelength modulation speed, we have also proposed and investigated tunable single-mode mid-infrared quantum cascade lasers based on surface acoustic-wave (SAW) modulation mechanism. The air-waveguide and surface plasmon waveguide structures with two-section active regions were proposed, together with Zinc Oxide (ZnO) thin film deposited on top of these devices to enhance the piezoelectricity of the materials. Coupling coefficients of ~2.5 cm-1 were calculated for both waveguide structures, showing the possibility of achieving tunable single-mode emission by using SAW modulation. Furthermore, to improve the single-mode QCLs performances in terms of power and modulation bandwidth, we have studied the high modulation bandwidth injection-locked single-mode QCLs. Mid-infrared QCLs with wavelength of 4.6 μm and 9 μm were investigated for comparison. Enhanced modulation Bandwidths of ~30 GHz and ~70 GHz were obtained for 4.6 μm and 9 μm, respectively, under a 5-dB optical injection ratio, showing threefold increases of modulation bandwidth for both wavelengths. These injection-locked QCLs are expected to be important components in mid-infrared free space communications.en_US
dc.format.extent142 p.en_US
dc.language.isoenen_US
dc.subjectDRNTU::Engineering::Electrical and electronic engineeringen_US
dc.titleTunable mid-infrared quantum cascade lasersen_US
dc.typeThesis
dc.contributor.schoolSchool of Electrical and Electronic Engineeringen_US
dc.contributor.supervisorWang Qijieen_US
dc.description.degreeDOCTOR OF PHILOSOPHY (EEE)en_US


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