The selection mechanism is blue, the coating surface is orange and the output beam is red.
1. The simplest structure is an F-P cavity laser (FP-QCL). In the F-P structure, the cutting surface provides feedback for the laser, and sometimes a dielectric film is used to optimize the output.
2. The second structure is to carve the distributed feedback grating directly on the QC chip. This structure (DFB-QCL) can output a narrow spectrum, but the output power is much lower than FP-QCL. Through the maximum range of temperature tuning, DFB-QCL can also provide limited wavelength tuning (the tuning range of 10~20cm- 1 through slow temperature tuning, or the tuning range of 2~3cm- 1 through rapid injection current heating tuning).
3. The third structure is to combine QC chip and external cavity to form ECqcL. This structure can not only provide narrow spectral output, but also provide fast tuning (the speed exceeds 10ms) in the whole gain bandwidth of QC chip (hundreds of cm- 1). Because ECqcL structure adopts low-loss components, it can work efficiently under the condition of portable battery power supply.