“…Widely tunable continuous-wave (CW) middle infrared (mid-IR) laser sources are very useful for applications in trace-gas detections, medical diagnosis, biological and chemical analysis because the fundamental rotation and vibration lines for many gas molecules are located in the mid-IR region where the absorptions are stronger than those of their overtones in the near-infrared region by 2-3 orders of magnitude [1,2]. Several laser sources, such as lead-salt diode laser, quantum cascade laser [3], colorcenter laser, Raman lasers [4,5] and optical parametric oscillator (OPO) [6,7], can emit CW laser radiations in the mid-infrared region. However, all these sources have their own issues when they are put into practical applications.…”