Design And Implementation Of Key Parts Of Electronic System For POP Rb Atomic Clock

Pulsed optical pumping rubidium atomic clock is composed of the optical system, the physical system and the electronic system, wherein the electronic system is crucial for the realization of the long-term unattended stable and reliable operation of the atomic clock under the space-borne circumstance. On the basis of space-borne POP rubidium atomic clock prototype system, according to the current requirements of the engineering prototype miniaturization, this paper focuses on the digiti zation and integration of key functional electronic modules of POP rubidium atomic clock circuit system, specifically including:(1) the long-term automatic frequency stabilization system of the DFB diode laser;(2) the driving RF signal generating circuit for AOM;(3) the digital probe-pulse laser power stabilization system;(4) the frequency-locking closed loop servo control circuit of the atomic clock.As the pumping laser source of POP rubidium atomic clock, the DFB diode laser frequency stability affects the medium-term and long-term stability of the clock. On the basis of the previous manually frequency stabilization system with analog circuit, this paper introduces the embedded development platform which uniformly control the laser driving current module, temperature control unit, and frequency-locking circuits, and realize the long-time automatic frequency stabilization of the laser source with the form of digital control and analog PI by saturated absorption harmonic frequency stabilization technique. The digital system achieves long-time auto-locking of the laser frequency and real-time monitoring of frequency-locking state. Under the laboratory environment, the DFB diode laser is locked stably and continuously to Rb line in more than a month and relocked again within one second, with a linewidth of 5MHz, which meet the experimental requirements.Acousto-optic modulator mainly acts as the laser switch used to achieve a pulsed laser, and also adjusts detuning of the pumping laser. Based on direct digital frequency synthesis technology, with FPGA+DDS scheme, the designed system generates 80 MHz pulsed RF driving signal by synchronizing timing signals. In the system, FPGA controls DDS AD9910 with serial port by its internal state machine conversion. The system replaces the signal generator and lays the foundation for optical detection.It is necessary to ensure the laser power stabilization within the detection window time for optical detection. So the laser power stabilization digital control loop is carried out.In the control system, FPGA+DDS which generates pulsed RF driving signal for AOM serves as a digital actuator,and DSP+FPGA dual-core system which is shared by atomic clock frequency-locking closed loop in Part IV acts as digital PID controller. What’s more, it is necessary to add an ADC module in the system. Finally, the designed system achieve a stable detecting-pulse laser power, and the stabilized laser power mean is 1.8917 m W, the maximum fluctuation of which does not exceed ±0.004 m W.The servo control system of atomic clock frequency-locking closed loop is proposed, the analog input/output channel of which select the high precision and high speed ADC/DAC chip respectively, with the core of DSP+FPGA development platform. In the system, FPGA is responsible for controlling the peripheral ADC and DAC module, and DSP processes and computes the data of the input/output channel to implement the digital PID controller. The system takes the place of the previous servo control closed loop, in which the PC serves as the hardware platform, and the NI data acquisition board acts as the analog signal input/output channel, and the control algorithm is implemented under the Labwindows/CVI development environment. The system with clear functional definition and more reliable performance, which takes full advantage of each chip, achieves a digital integrated system on chip and reduces the volume of the servo control system.These four parts works in the paper lay the foundation of next experimental study on the optical detection and the POP rubidium atomic clock engineering prototype.