| Ultra-narrow linewidth laser,also known as ultra-stable laser,which has the best coherence.Ultra-narrow linewidth lasers play a very important role in the generation and transmission of high-precision time-frequency signals.As one of the three com-ponents of the optical clock,the ultra-narrow linewidth laser is often called the clock laser.It is used for the detection of clock transition signals.Its frequency stability de-termines the short-term frequency stability of the output frequency of the optical clock.The combination of ultra-narrow linewidth laser and femtosecond optical comb can realize a frequency-tunable photo-generated microwave source,which can replace the constant-temperature crystal oscillator in the cesium atom fountain clock system,elim-inate the influence of the Dick effect,and improve the short-term frequency stability of the current reference clock.At the same time,the ultra-narrow linewidth laser is used as the transmission light source in the high-precision fiber optic frequency transmission system,which provides a reliable guarantee for improving the transmission accuracy of optical frequency signals.In addition,ultra-narrow linewidth lasers are widely used in quantum optics,ultra-precision spectroscopy,gravitational wave detection,basic phys-ical quantity measurement and other fields.Currently,the National Time Service Center(NTSC)of the Chinese Academy of Sciences(CAS)has undertaken two important engineering development projects for the 921 space station high-precision time-frequency laboratory cabinet space strontium atomic optical clock and the“13th Five-Year”high-precision ground-based time ser-vice system.The main research contents of this thesis are carried out around the above engineering tasks,with ultra-narrow line wide lasers as research objects.We studied the key technology of the space external cavity diode laser,laser frequency automatic locking technology with high control bandwidth and key technology of the space inte-grated optical system.The main research contents and innovations of the thesis are as follows:(1)As the optical source of the space ultra-narrow linewidth laser system,the 698nm external cavity diode laser is one of the most important critical devices.Commer-cially available diode lasers,which terms of volume,weight and space environmental adaptability are unable to meet the needs of the space narrow linewidth laser system.A new type of 698 nm tunable anti-vibration external cavity diode laser with a“cat's eye”structure using narrow-band interference filters for mode selection was developed,and its environmental adaptability was verified by mechanical tests.An external cav-ity semiconductor laser suitable for space environment was realized for the first time in China,and a key technical problem in the development of space narrow linewidth laser was solved.Theoretical analysis studies the characteristics of narrowing the laser line width based on the interference filter mode selection and the“cat's eye”structure of the ex-ternal cavity to improve the laser's anti-vibration ability.On this basis,a new type of mechanical structure is designed.The IF-ECDL developed is small in size,stable in structure,and does not have any adjustable device for elastic loading.The free-running linewidth of the IF-ECDL is about 175 k Hz,and the frequency stability is less than1×10-9at an averaging time of 1?10 s.Based on the finite element method,the modal analysis of the IF-ECDL and the deformation analysis under the gravitational environment are carried out.The first or-der resonant frequency of the laser is 2316 Hz,which is greater than the requirements of the base frequency 70 Hz.The space application system payload environmental test requirements(qualification level)of the IF-ECDL are half the order of magnitude Me-chanical environment test.The laser spot shape,wavelength and output optical power parameters remained basically unchanged before and after the test.Experiments show that the IF-ECDL can resist the impact of 450 g of acceleration.(2)Aiming at the unattended characteristics of space narrow linewidth lasers in orbit operation,the laser automatic frequency stabilization experiment was carried out.Innovatively proposed a laser automatic frequency stabilization system and its locking algorithm based on the combination of analog and digital circuits.In order to obtain a faster control speed,the core of the frequency stabilization system is an analog PID circuit,and all parameter adjustments are operated by a microcontroller through digital circuits and programs.By optimizing the locking algorithm,the functions of automatic peak finding,automatic locking,and relocking after losing lock are realized.The au-tomatic frequency stabilization system achieves a control bandwidth of up to 2 MHz,which can determine that the laser is out of lock and relock the laser frequency in less than 4 s.After more than 4,000 repeated experiments,each time the laser frequency loses lock,it can automatically relock.(3)Narrow linewidth lasers for space applications are limited by system resource conditions.Factors such as weight and volume must be considered.At the same time,the impact of vibration and shock during the launch process and the impact of the optical circuit board in the microgravity environment from the ground to the space must also be considered.Deformation influence and so on.In view of the above influencing factors,a miniaturized design of the laboratory's narrow linewidth laser optical system is carried out,and an innovative solution for the optimization of the integrated optical platform using the structural topology optimization design method is proposed.On the basis of the miniaturization of the optical path in the laboratory,the design of the optical system of the spatial narrow linewidth laser electrical components was carried out.All the optical and mechanical components were integrated on both sides of a 310 mm×210mm optical substrate through a miniaturized and modular design.Through mechanical simulation analysis,the maximum deformation of the optical plate under the influence of gravity is only 0.36?m,which initially meets the requirements of space applications.The electrical properties of the space narrow-line laser have been tested.The laser linewidth is about 4.6 Hz,and the frequency stability is better than 3.5×10-15/s.(4)Carried out the engineering research of 1550 nm narrow linewidth laser ap-plied to high-precision fiber optic frequency transmission.For applications in mobile,transportable,and telecom room environments,the optical module,physical module,and circuit module have been miniaturized and integrated optimized design.The entire system is integrated in a 19-inch 6 U of the soundproof chassis,with a total mass of less than 30 kg.The key technical problems such as optical reference cavity sensitivity optimization,system integration,etc.have been solved,which lays a solid foundation for the ultra-narrow linewidth laser engineering of communication bands.The research work in this thesis solves the key technologies for the development of removable,transportable,and future-facing space-oriented interfacial laser engineering.Laying the foundation for the production of future space atomic frequency standards and the transmission of high precision optical frequency signal via fiber. |
PDF Full Text Request