Perfection Of Theory Of Mode Cleaner For Intensity Noise Surpression And Investigation For Extracavity Frequency Doubling Of1560nm Fibre Laser

With the development of atomic clocks, the precision of time has gone beyond thetraditional time synchronization technology of precision, therefore timesynchronization technology become the bottleneck of the new generation time andfrequency system. The precision of the traditional time synchronization technology islimited by the Heisenberg limit, over the past twenty years, based on quantumentanglement, quantum time synchronization technology developing rapidly, its limitbroke the Heisenberg limit, is expected to increase the time synchronization accuracyfrom the nanosecond to the picosecond order of magnitude. Not only that, the timesynchronization technology have the advantages of can’t eavesdropping and not beingaffected by medium, etc. Which traditional time synchronization technology does nothave. Therefore, as a newtechnology of time synchronization, quantum timesynchronization has huge potential.In quantum time synchronization technology, the first is to get the high qualitysource of quantum entanglement in optical fiber communication band, timesynchronization technology requires frequency source for continuous variables of theentanglement, the commonly used method is Spontaneous Parameter DownConversion (SPDC), which making happens through the interaction between laser andnonlinear crystal. Compared to780nm pulse light single passing through thenonlinear crystal to1560nm entangled light method, we use1560nm continuoussingle mode fibre laser, for frequency doubling by extracavity before the downconversion by optical parameter oscillator to generate entangled light, greatlyimproving the conversion efficiency and entangled light source power, and lays thefoundation for the application of time synchronization technology.This paper mainly focus on these work:1560nm single frequency fiber laserintensity noise suppressed through a mold cleaner, to improve the quality of the laser,and through the homemade balance homodyne detector for detecting, laser noise at10MHZ to shot noise limit. However, the result of the experiment differs from theprediction of traditionaltheoretical model. With a new theory, we explain the reason of the difference, The noise suppression effect of the acoustic optical modulator isfurther analyzed by inserting it into the setup and providing a frequency modulationon it, making the laser line width from26kHz narrower to16kHz.Through a nonlinearcrystal (PPKTP) in quasi phase matching, outer cavity resonant frequency doublinghappens, producing about67%of the780nm second harmonic light.