Quasi-continuous-wave operations of quantum cascade lasers

Abstract

In this paper, quasi-continuous-wave (quasi-CW) operation of quantum cascade lasers (QCLs) is studied. A group of strain-balanced InGaAs/InAlAs QCLs emitting around λ~4.8μm were used in the experiment. QCLs were tested at different driving conditions (i.e. pulsed mode, CW mode and quasi-CW mode) at various temperatures. Experimental measurements show that thermal effect plays an important role in deteriorating QCL performance. This is especially true at high temperatures. At low temperature (~100K), L-I curves with different pulse widths exhibit no significant difference. While at a higher temperature (~200K), we observed that the longer the pulse width, the lower the roll-over power and the worse the laser performance. At 100K, the roll-over power increases as duty cycle increases until it reaches CW operation, indicating that the thermal generation difference for quasi-CW mode and CW mode is negligible. At 200K, however, a maximum roll-over power is about 50mW at duty cycle of 65% corresponding to a CW roll-over power of 40mW. It reveals that at high temperature, quasi-CW operation generates less heat and more average output power. Therefore, quasi-CW operation is obviously a favorable way to achieve high performance operations at high temperature.