| With the development of optical clock,optical frequency standard signal,as a new generation of high stability frequency source,plays an important role in the physical constant measurement,high precision GPS navigation and time synchronization and other fields.As the background oscillator of the optical clock system,the acquisition and application of clock laser is particularly important.In order to obtain optical frequency signal of high stability,fiber is used to transfer with high precision the laser frequency to the physical system so as to lock the frequency.The high stability optical frequency signal also needs to be transferred with high precision to achieve signal sharing and comparison via fiber links.However,the optical frequency signal transferred via the fiber will introduce random phase noise,and as a result,the frequency signal after transmission will be broadened and the frequency stability decreased.Therefore,it is necessary to study the fiber transmission of optical frequency standard signal.This paper mainly studies and analyzes the principle and method of fiber phase noise suppression,and designs the circuit to achieve the purpose of phase noise suppression.First,a set of fiber phase noise cancellation system is built,and the frequency of 698 nm laser is transferred via a short fiber.The performance of the phase noise cancellation system is verified by analyzing the additional line width and the frequency stability introduced by the fiber.The results show that the frequency stability introduced by the fiber is 6.9×10-18 at 1 s averaging time and reduced to4.9×10-19 at 100 s averaging time,and the additional linewidth of the noise is suppressed to the order of the millihertz.Then,the above system is used to complete the transmission of the frequency of1.5?m ultra-stable laser via a 808 m fiber linked two different laboratories.It can test the linewidth and frequency characteristics of two commercial ultra-stable laser systems.The results show that the frequency stability introduced by the 1.6 km real fiber link is 1.2×10-17 at 1 s averaging time after the phase noise is suppressed.It proves the fiber phase noise cancellation system can be used to transfer the frequency of ultra-stable laser via real fiber links.This method verifies the linewidth of two ultra-stable laser systems are 0.5 Hz,and the frequency stability of beat signal is1.2×10-15 at 1 s averaging time.Finally,the application of the fiber phase noise suppression system in the self-designed clock laser system is introduced.Since the power fluctuation after fiber transmission has a significant effect on the cavity length of the long cavity,the acousto-optic modulator is used to stabilize the power of laser.The results show that the power of the laser can be stabilized at the order of 10-4. |
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