Fig. 1. Structure of the tapered microstrip line and parameters

Fig. 2. Parameter optimization process and results

Fig. 3. The S parameter obtained by processing technology of Ti coating and Au plating on Cu metal were compared with the simulated S parameter

Fig. 4. Electric field distribution diagram of gradient microstrip line

Fig. 5. Equivalent circuit model and comparison of S parameters between equivalent circuit and simulation model

Fig. 6. Measured light-current-voltage characteristics in continuous wave mode of the QCL

Fig. 7. Schematic diagram of experimental set-up

Fig. 8. Intermode beat note mapping of laser measured with RBW of 100 kHz and VRW of 10 kHz and stable beat note of current at 790 mA and temperature at 20K

Fig. 9. Stability test of beat note signal