# Experimental Study on Partially Coherent Optical Coherent Detection
## 3 Experimental Study
### Partial Coherent Polarization Measurement and the Coherent Detection Experiment
This is due to the fact that energy conversion and frequency conversion in nonlinear media require the signal light and the local oscillator light to have the same vibration direction and phase relationship during the mixing process. Their vibration directions are more consistent and energy conversion is more efficient when their polarization states are the same or comparable. Conversely, energy conversion efficiency will drop if there is a significant difference between the polarization states of the two. When the polarization state of the signal light is the same as that of the local oscillator light, we adjust the local oscillator light power to about 2 mW, adjust the signal light power so that the amplitude of the intermediate frequency signal is 450 mv, and measure the power of the signal light under three different states. From Figure 14, it can be seen that  
Figure 7:1 Intermediate frequency signal waveforms: (**a**) Intermediate frequency signal diagram when the signal light is elliptically polarized and the local oscillator light is linearly polarized; (**b**) intermediate frequency signal diagram when the signal light is elliptically polarized and the local oscillator light is circularly polarized; and (**c**) intermediate frequency signal diagram when the signal light is elliptically polarized and the local oscillator light is linearly polarized. when the signal light is a linearly polarized EGSM beam, the measured output power of the signal light fluctuates around \(-47\) dBm; when the signal light is a circularly polarized EGSM beam, the measured output power of the signal light fluctuates around \(-52\) dBm; and when the signal light is an elliptically polarized EGSM beam, the measured output power of the signal light fluctuates around \(-43\) dBm. The output power of the local oscillator was adjusted to around \(2.4\) mW and the amplitude of the intermediate frequency signal was measured to be around \(450\) mV. The signal light power was measured in three different states, as shown in Figure 7:2 When the signal light is a linearly polarized EGSM beam, the output power of the measured signal light fluctuates around \(-50\) dBm; when the signal light is a circularly polarized EGSM beam, the measured output power of the signal light fluctuates around \(-54\) dBm; and when the signal light is an elliptically polarized EGSM beam, the measured output power of the signal light fluctuates around \(-45\) dBm. From Figure 16, it can be seen that when the local oscillator power is \(3\) mw, and the signal power is adjusted so that the amplitude of the intermediate frequency signal  
Figure 7:3 Measurement curves of signal light and local oscillator power under different polarization states of EGSM beams. (**a**) Measurement curves of local oscillator power under different polarization states of EGSM beams; (**b**) measurement curves of signal light power under different polarization states of EGSM beams. Figure 7:4 Measurement curves of signal light and local oscillator power under different polarization states of EGSM beams. (**a**) Measurement curves of local oscillator power under different polarization states of EGSM beams; (**b**) measurement curves of signal light power under different polarization states of EGSM beams. is 450 mv, the signal power in three states can be measured. When the signal light is a linearly polarized EGSM beam, the output power of the measured signal light fluctuates around \(-\)54 dBm; when the signal light is a circularly polarized EGSM beam, the measured output power of the signal light fluctuates around \(-\)55 dBm; and when the signal light is an elliptically polarized EGSM beam, the measured output power of the signal light fluctuates around \(-\)48 dBm. It is evident from the three scenarios that the detection sensitivity increases with the local oscillator power.