The impact of additional injected signals on the stability and bandwidth of the quantum cascade lasers with external cavities

Abstract

- In recent years, special attention has been paid to the injection lock of quantum cascade lasers, which leads to the improvement of their small signal properties and output power. In this paper, the operation of an injection-locked quantum cascade laser including the output characteristics and modulation response has been investigated. By using one external cavity for optical lock, the resulted structure has complexities may cause instability of a laser that limit the use of this system. In this paper, for the first time, to solve this problem, an optical self-locking system was proposed and the properties of laser under these conditions were investigated. By adding a second external cavity to a single external cavity laser, output power will reach a constant value. The output power of the single cavity laser in free-running mode was about 400 mw while the output power of the laser with two external cavities has been increased to 700 mw. In addition to stabilizing the output power, we also see an increase in bandwidth. We found that for different lengths and reflectivity, the output power of the proposed one external cavity laser in free-running mode does not reach a fixed value and even in some cases, it becomes unstable. But by adding a second cavity to the laser in the free-running mode, it will be able to produce a stable laser with constant output power. Adding external cavities can be used as an effective tool to improve frequency stability or increase bandwidth.