# Experimental Study on Partially Coherent Optical Coherent Detection
## 4 Conclusions  
This study theoretically derived and experimentally verified the relationship between the polarization state and mixing efficiency of EGSM signal light and local oscillator light beams. The results indicate that:  
When both the local oscillator light and the signal light are linearly polarized, the degree of coincidence of the polarization directions directly affects their mixing efficiency. From the simulation results, it can be seen that when the angle between the local oscillator vector and the horizontal direction is 45\({}^{\circ}\), and the angle between the signal vector and the horizontal direction is 45\({}^{\circ}\), the mixing efficiency is the highest, and the efficiency varies with the cosine function of the polarization direction angle between the two. Circularly polarized EGSM beams can be seen as the combination of two linearly polarized light signals with a phase difference of 90\({}^{\circ}\) in the vertical direction, with two components of equal amplitude but perpendicular phases. If the signal light is circularly polarized, a higher mixing efficiency can be maintained. Elliptically polarized EGSM beams can be regarded as a general case of linear polarization and circular polarization, consisting of  
Figure 16: 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.  
two orthogonal components with unequal amplitudes and a phase difference of 90\({}^{\circ}\). The mixing efficiency depends on the degree of matching between these two components and the corresponding component of the local oscillator light. When the main axis of the ellipse is aligned with the polarization state of the local oscillator, the mixing efficiency is higher, but the greater the deviation of the ellipse shape from the polarization state of the local oscillator, the lower the efficiency. When both the signal light and the local oscillator light are in the same polarization state (whether that is linear polarization, circular polarization, or elliptical polarization), the mixing effect is better.  
Conceptualization, Y.M. and X.K.; methodology, J.L., Y.M., X.K. and M.H.; software, Y.M.; validation, J.L., Y.M. and M.H.; formal analysis, X.K.; investigation, Y.M. and X.K.; resources, X.K.; data curation, M.H.; writing--original draft preparation, Y.M.; writing--review and editing, Y.M.; visualization, Y.M.; supervision, X.K.; project administration, X.K.; funding acquisition, X.K. All authors have read and agreed to the published version of the manuscript. Funding was received from the following: the Key Industrial Innovation Chain Project of Shaanxi Province [grant number 2017 ZDCXL-GY-06-01]; the General Project of National Natural Science Foundation of China [grant number 61377080]; the Xi'an Science and Technology Plan (22 GXFW0115); the Scientific Research Team of Xi'an University (D202309); and the Xi'an Science and Technology Program Fund (2020 KJRC0083). Institutional Review Board StatementThis study did not require ethical approval. Informed Consent StatementThis study did not require ethical approval. Data Availability StatementThe data that support the findings of this study are available from the corresponding author upon reasonable request. Conflicts of InterestThe authors declare no conflicts of interest. References