Widely tunable 2.3-μm-wavelength superstructure grating (SSG) DBR laser with InAs/InGaAs multiple quantum wells grown on InP substrate

The wavelength range around the 2.3-μm band is promising for gas sensing systems used with CO and other gases such as N₂O, NH₃, and CH₄ due to the strong absorption lines of these gases. Widely tunable diode lasers emitting in the 2.3-μm-wavelength band enables simultaneous detection of multiple gas species using a single laser cavity. We previously developed a 2.3-μm-wavelength distributed Bragg reflector laser with InAs/InGaAs multiple quantum wells (MQWs), and demonstrated a wavelength tuning range of over 4 nm. In this study, to further extend the wavelength-tuning range in a single laser cavity, we implemented a superstructure grating (SSG), a special type of grating structure with multiple reflection-peak characteristics, in this DBR laser. The newly designed SSGs with seven reflection peaks are formed on the front and rear DBR regions. Experimental results indicate that, with our SSG-DBR laser, the lasing wavelength could be controlled over a wide range from 2300 to 2347 nm by selectively switching between oscillating SSG modes corresponding to the seven reflection peaks. Two of the seven SSG modes were used to detect absorption lines in a CO gas cell; thus, three CO-gas-absorption lines at 2313.7, 2315.0, and 2316.3 nm, as well as two absorption lines at 2337.4 and 2339.3 nm, could be detected by sweeping the 3rd and 6th SSG modes, respectively. These results indicated that multiple gas-absorption lines over a wide wavelength range can be detected simultaneously using a single laser cavity.