| The squeezed state of light is a very important non-classical optical field.Due to its extremely low quantum noise,it has great potential for many applications,such as precision measurement,quantum information and quantum imaging.In the field of precision measurement,such as gravitational wave detection,using the vacuum squeezed state to fill the vacuum channel of the M-Z interferometer can suppress the vacuum background noise and improve the sensitivity of the interferometer to the extremely weak-signal detection.In the field of quantum information,the squeezed state can be used to prepare the entangled state.As the core of the quantum information,the entangled state can be further used to complete many tasks,which are impossible for the classical light field to complete,such as quantum teleportation,quantum dense coding and quantum secret communication.In the field of quantum imaging,the high resolution and high quality image information can be obtained by using the entangled state.In order to improve the sensitivity of the precision measurement,the fidelity of the quantum information transmission and the quality of the quantum imaging,the generation of the high-level and long-term stable squeezed state has become an important research in recent decades.There are several methods for generating squeezed state of light,but the optical parametric oscillator(OPO)below the threshold is proved to be the most effective method.However,in the squeezed state generation system,it is very difficult to obtain the high-level and long-term stable squeezed state due to the limitations of the optical loss and the phase noise.With the improvement of the coating technology,the crystal growth technology and the mode matching technology,the optical loss of the system can be reduced effectively.When the optical loss is reduced to a certain extent,the phase noise becomes the key factor,which limits the improvement of the squeezed state.The factors causing the phase noiseare not only the environmental vibration but also the performance of the servo control system.In the servo control system,which is based on the electro-optic phase modulation,the electro-optic phase modulator(EOM)inevitably introduces the residual amplitude modulation(RAM),which results in the zero baseline drift of the Pound-Drever-Hall(PDH)error signal for the cavity and phase locking,and hence it degrades the cavityand phase-locking performance.The cavity-and phase-locking point drift can be equivalent to the phase noise,which severely reduces the degree and the long-term stability of the squeezed state,and is especially detrimental for the obtaining of the high-quanlity squeezed state.In this paper,the theoretical analysis and the experimental investigation are carried out on the suppression of the RAM in the squeezed state generaiton system.The main contents include: Firstly,the development of the squeezed state,the basic theory of quantum optics and the influence of the phase noise caused by the OPO cavity detuning and the relative phase drift on the squeezed state are introduced.Secondly,the generation mechanism of RAM and its influence on the cavity-and phase-locking are analyzed.Finally,the experimental scheme to suppress RAM is proposed to improve the stability and accuracy of OPO cavity and relative phase locking,reduce the phase noise of the squeezed state,and obtain a high-quality squeezed state.In the thesis,the works that belongs to innovation are as follows:A: The influence of the phase noise,which is induced by the OPO cavity detuning and the relative phase dirft,on the squeezed state is analyzed theoretically.B: The PDH error signals for the cavity-and phase-locking comprising RAM are derived,and the influence of the relevant experimental parameters on the zero baseline drift of the PDH error signal is analyzed in detail,so as to provide theoretical guidance for the suppression of RAM.C: Using the characteristics of the OPO cavity,which is a severeimpedance mismatch and large-linewidth cavity,and the characteristics of the relative phase,where the amplitude of the local osilator is large from the squeezed state,we designded a optimal scheme for the cavity and phase locking,which effectively suppress the RAM and improve the stability of the output power and degree of the squeezed state.D: The method of suppression the RAM by using the wedged electro-optic crystal is proposed.By optical design of the wedge angle and the incident beam radius of the crystal,RAM can be effectively suppressed without increasing the system size,which is of great significance in the development of compact squeezed and entanglement sources. |
