1.5 ?m Squeezed Light Generation In Fiber-based System

With the development and maturity of squeezed light generation technology,the related applications have also developed rapidly.In the research fields of quantum precision measurement and quantum sensing,squeezed light has become an important tool for many optical measurement to break through the classical quantum noise limit due to its unique noise distribution characteristics;in the fields of quantum information,the squeezed light has also become the important continuous-variable quantum resource due to the virtue of the inter-correlation of noise on its orthogonal components.At present,squeezed light sources based on parametric oscillation and parametric amplification technologies in space optical systems have been able to meet requirements in terms of technical parameters such as the degree of squeezing and stability.However,this type of system requires fine adjustment of a large number of spatial optical components,precise mode matching of multiple spatial beams,and coordination of multiple electronic locking systems.This undoubtedly imposes many restrictions on the large-scale application of the squeezed light field.Therefore,research on miniaturization and compactness has become one of the key technologies that promote the large-scale application of quantum squeezed light sources in the fields of quantum information and quantum sensing.This dissertation aims at the all-fiber miniaturization of 1.5?m communication band squeezed light preparation,and explores the related technology of realizing the all-fiber compressed light preparation system based on fiber-coupled crystal waveguides.The main content and results obtained are as follows:(1)Experimentally researched and analyzed the polarization-related characteristics in the process of suppressing RIN based on the SOA gain saturation effect.Based on the high polarization extinction ratio of the polarization device and the polarization"post-selection"technology,successfully eliminated the polarization-dependent characteristics of the RIN.The RIN of the final output of 1550 nm laser in the frequency range of 300 k Hz-50 MHz is suppressed to-151 d B/Hz,which is only 1.9 d B above the quantum noise limit(-152.9 d B,0.5 m W@1550 nm).The linearly polarized low-noise 1550 nm single-frequency fiber laser can be used as an ideal seed laser for squeezed light generation systems.(2)Based on the on-line polarization low-noise 1.5?m laser,combined with the frequency doubling of the fiber-coupled periodic polarization lithium niobate waveguide,a low-noise laser output of 775 nm is realized.When the input pump light power is 1.74 W,the output second-harmonic power is 348 m W.The relative intensity noise in the frequency range of0.3-50 MHz reaches-148.5 d B/Hz,which is about 1.5 d B higher than the quantum noise limit(-149.9 d B,0.5 m W@775 nm).The linearly polarized low-noise 775 nm compact frequency-doubling laser can be used as the pump source of the squeezed light preparation system.The double-pass PPLN waveguide structure with end-face coating is designed.Through the double-pass frequency doubling technology,the output power of the 775 nm laser is increased to 404 m W under the same pump power.The feasibility of improving the nonlinear conversion efficiency by coating the end face when the physical length of the waveguide is limited is verified,which provides an experimental basis for the preparation of bright squeezed light in the two-pass parametric amplifier.(3)The influence of system loss,nonlinear gain,and pump power on the preparation of squeezed light in the non-resonant waveguide structure have been researched and analyzed;based on the homemade low-noise single-frequency fiber laser,and the frequency doubling and parametric down conversion process in the all-fiber coupled waveguide During the conversion process;according to the difference between fiber optical system and space optical system in the squeezed light preparation in terms of mode matching and interference efficiency,the system structure was optimized and the maximum squeezed degree of the vacuum squeezed light at 2.5 MHz is finally measured to be 2.13 d B.The fluorescence spectrum of the spontaneous parameter down-conversion in the PPLN waveguide was measured by the integrated spectroscopy technique based on a single photon counter,and the bandwidth was measured to be about 5 THz.(4)With the peculiarity of the high nonlinear efficiency of pulsed light in the nonlinear waveguide,the average pump power required for the preparation of the vacuum squeezed state is reduced.When the average pump power is 45 m W,a vacuum squeezed state of 1.74d B is generated.For low-repetition pulses,the influence of pulse synchronization on the detection of squeezed state was analyzed.This scheme is expected to replace the pulse synchronous pump parametric oscillator in space optical system for squeezed light preparation,which greatly reduces the complexity of the system.(5)An experimental system of bright squeezed light based on a double-pass waveguide structure was proposed and built for the first time.On this basis,the parametric amplification gain of the structure is measured,and the parametric gain factor g=0.153 m W^-1is estimated;the vacuum squeezed state and the bright squeezed state prepared in the double-pass parametric amplifier experimentally,and the measured degree of squeezing of vacuum squeezed light and bright squeezed light are 1.85 d B and 1.12 d B,respectively,when the effective pump power is at 60 m W.This result is the first reported result of bright squeezed light based on optical fiber system.