Impact of Wavelength Detuning on the Performance of Mid-IR Distributed Feedback Quantum Cascade Lasers

We present the design and the performance of mid-infrared distributed feedback quantum cascade lasers made of strain-balanced GaxIn_1-xAs/AlyIn_1-yAs material on InP substrates for wavelength near 5 μm. By changing the grating period within one wafer, we demonstrated wide wavelength coverage of 325 and 282 cm^-1 (16.3% and 14.1% of the center wavelength) under room temperature pulsed and continuous wave (CW) operation, respectively. The variation of pulsed and CW laser performance as a function of wavelength detuning from the gain peak was studied and correlated to the amplified spontaneous emission spectra. We conclude that a slight positive detuning within 5% of the center wavelength favors CW performance especially for high-temperature operation.