A 20-channel distributed feedback (DFB) quantum cascade laser (QCL) arrays based on uniform buried grating have been demonstrated. In pulsed mode, peak power reaches 80 mW and slope efficiency reaches 167 mW/A for 2.5-mm-long laser in the arrays at room temperature. The loss difference of two band-edge mode increases when reflectivity of the front facet becomes small, which prevents the mode hopping. The device shows linear tuning after the anti-reflectivity coating is deposited in the front facet, maintaining peak power of 64 mW. The whole chip covers a tuning range of 64 cm -1 , centering at 8.3 μm, with side-mode-suppression-ratio over 20 dB at room temperature.
KeywordsQCL array • Uniform buried grating • Band-edge mode • Anti-reflectivity coating 1 Introduction Mid-infrared quantum cascade lasers (QCLs) are unipolar semiconductor lasers based on resonant tunneling and optical transitions within the conduction band of a multi-quantum well structure (Faist et al. 1994). There are various application including gas sensing (Kosterev et al. 2002), industrial process monitoring (Yao et al. 2012), spectroscopy (Namjou et al. 1998), and free space communication (Corrigan et al. 2009), which demands widely tunable and single-mode QCLs. External cavity (EC)-QCLs are broadly tunable light sources and have achieved a tunability of over 300 cm −1 (Centeno et al. 2014).However, the system is usually bulky and requires fine optical alignment. DFB-QCLs are compact with side-mode-suppression-ratio (SMSR) about 30 dB. Although a single DFB-QCL has a limited tuning range of a few cm −1 (~ 10 cm −1 ) via temperature tuning, we can still achieve wide tunability by fabricating a large amount lasers of different periods of gratings in one chip (Lee et al. 2009;Rauter et al. 2015). In this way, we can develop this tunable source called DFB-QCL arrays combining the advantages of external cavity and DFB devices, and DFB-QCL array has reached an impressive tunability above 230 cm −1 (Slivken et al. 2013).However, DFB-QCL arrays still have the problem of mode hopping which can be detrimental for this