# Experimental Study on Partially Coherent Optical Coherent Detection
## 3 Experimental Study
### Partial Coherent Polarization Measurement and the Coherent Detection Experiment
Figure 10: _Cont._  
Figure 9: Intermediate frequency signal waveforms: (**a**) intermediate frequency signal diagram when the signal light is linearly polarized and the local oscillator light is linearly polarized; (**b**) intermediate frequency signal diagram when the signal light is linearly polarized and the local oscillator light is circularly polarized; and (**c**) intermediate frequency signal diagram when the signal light is linearly polarized and the local oscillator light is elliptically polarized. When the output power of the local oscillator laser is set to 1.5 mW, the power of the signal laser is modified, and the EGSM beam is circularly polarized, the power of the signal light is 1.5 \(\upmu\)W.  
As shown in Figure 11, the waveform of the intermediate frequency signal collected by the oscilloscope shows that when the signal light is in a circularly polarized state and the local oscillator light is linearly polarized, the peak-to-peak value of the intermediate frequency signal is 446.4 mV; when the signal light is in a circularly polarized state and the local oscillator light is circularly polarized, the peak-to-peak value of the intermediate frequency signal is 504.0 mV; and when the signal light is in a circularly polarized state and the local oscillator light is elliptically polarized, the peak-to-peak value of the intermediate frequency signal is 159.2 mV. Similarly, following the same operation, elliptically polarized signal light was generated, as shown in Figure 12a. Concurrently, the local oscillator light was engineered to be linearly polarized, circularly polarized, and elliptically polarized, respectively, as shown in Figure 12b-d. The output power of the local oscillator laser was set to 1.5 mW and the power of the signal laser was modified when the EGSM beam was elliptically polarized. At this time, the power of the signal light was 1\(\upmu\)W.  
Figure 11: _Cont._  
Figure 10: Circularly polarized signal light and three polarization states of local oscillator light: linear polarization, circular polarization, and elliptical polarization. (**a**) Circularly polarized signal light; (**b**) linearly polarized local oscillator light; (**c**) circularly polarized local oscillator light; and (**d**) elliptically polarized local oscillator light. Figure 11: Intermediate frequency signal waveforms: (**a**) intermediate frequency signal diagram when the signal light is circularly polarized and the local oscillator light is linearly polarized; (**b**) intermediate frequency signal diagram when the signal light is circularly polarized and the local oscillator light is circularly polarized; and (**c**) intermediate frequency signal diagram when the signal light is circularly polarized and the local oscillator light is elliptically polarized. Figure 12: Elliptically polarized signal light and three polarization states of local oscillator light: linear polarization, circular polarization, and elliptical polarization. (**a**) Elliptically polarized signal light; (**b**) linearly polarized local oscillator light; (**c**) circularly polarized local oscillator light; and (**d**) elliptically polarized local oscillator light. The waveform of the intermediate frequency signal collected by the oscilloscope is shown in Figure 7:0 It can be seen from the figure that when the signal light is in an elliptical polarization state and the local oscillator light is elliptically polarized, the peak-to peak-value of the intermediate frequency signal is 254.8 mV; when the signal light is in an elliptical polarization state and the local oscillator light is circularly polarized, the peak-to-peak value of the intermediate frequency signal is 124.0 mV; and when the signal light is in an elliptical polarization state and the local oscillator light is linearly polarized, the peak-to-peak value of the intermediate frequency signal is 94.4 mV. The mixing efficiency is higher when the signal light's polarization state is the same as or similar to that of the local oscillator light, as demonstrated in Figures 9, 11 and 13.