Mode Locked Fiber Laser And The Application In Optical Fiber Frequency Transfer

Mode-locked fiber lasers the advantages of short pulse,wide spectrum,light weight,stable output and high signal-to-noise ratio.They have a broad application prospect in optical clocks,frequency transfer,low-phase-noise microwaves,astronomical spectrograph calibration,coherent LIDAR,military,optical sensing,laser ranging and optical arbitrary waveform generation.It has become one of the most popular research hotspots in laser technology field.Nowadays,mode-locked fiber lasers are being improved in the research of simple structure,ultra-short pulses and high power.Therefore,the study and research of fiber mode-locking technologies have great theoretical significance and application value.High quality optical frequency comb and low-phase-noise radio frequency signal can be obtained from mode-locked fiber laser.It plays an important role in improving the performance of radar,navigation and positioning system.Nowadays,satellite navigation and positioning,radar and deep space detection are developed toward collaborative networking.In order to work in coordination of above systems,the time and frequency of the whole system must achieve unification and synchronization.Thus,frequency transfer with mode-locked fiber laser have a significant meaning in improving the stability of fr-equency in optical fiber.Theoretical and experimental resear-ches of mode-locked fiber lasers oin the dispersion management,super-continuum spectrum,high repetition frequency and all polarization maintain fiber mode locking and its application in frequency transfer are carried out.The pulse state caused by the dispersion management,the pulse compression with super-continuum spectrum and unlocking problem during move and long-term working are analyzed.What's more,the application of mode-locked fiber laser in frequency transfer is discussed.A phase compensation based on optical-microwave phase locking loop is proposed.It is used for an optical comb based stable frequency transfer system over a multi-access optical fiber loop link.The main achievements are as follows:1.A simple and efficient femtosecond nonlinear polarization evolution(NPE)mode-locked laser is presented.Different form conventional NPE fiber laser,the polarization beam splitter(PBS)is three-dimensionally manipulated to achieve polarization control and state selection in our NPE laser.The polarizer,half-wave plate and quarter-wave plate from conventional NPE fiber lasers is replaced by this PBS.Thus,the configuration and the system gain of our proposed laser is simply and efficiently improved.As a result,transfer efficiency of 24.17%is experimentally demonstrated.In addition,measured self-started pulses with average power of 49 mW and center wavelength of 1584 nm,are generated with single pulse energy of 1.51 nJ.2.A phase compensation based on optical-microwave phase locking loop is designed.An optical comb based stable fr-equency dissemination system is achieved with the compensation and optical comb.In the system,a mode-locked fiber laser at a repetition rate of 100 MHz is used to provide an optical source at local site,then it transmits along a 150 km fiber loop link.To testify the proposed system,two accessing nodes are measured in the loop link.The dissemination frequency instability is measured at 3.65×10-15/1 s and 7.8×10-18/1000 s at the intermediate node.The similar performance is shown at the other node.Hence,the system has the potential application in high-precision frequency transmission system via a long-haul multi-access loop link.3.A transmission model is established and simulated by analyzing the principle of nonlinear amplifying loop mirror.The results show that the mode-locking performance of the mode-locked fiber laser is related to inot only the ratio of the optical fiber coupler but also the difference value of optical pulse phase shift in the loop part.Then,a 30.8 MHz mode-locked fiber laser which is based on a nonlinear amplifying loop mirror with an electrically tunable optical delay line is constructed.The laser outputs stable optical pulse and the cavity length is electrically adjustable with the range of 13 kHz.The super-continuum spectrum is obtained by pulse compression and the pulse duration of the laser is only 58 fs.4.Optical integration techniques are introduced to realize a 100 MHz high repetition frequency mode-locked fiber laser.The stable mode locking is established only by two integrated optical devices.In order to meet the requirement of high repetition frequency on the cavity length,the wavelength division multiplexer,optical coupler,isolator and polarizer are integrated together.In addition,polarization controller and optical delay line are made to integrate together for large adjustable range.This can not only reduce the cavity length more than 1.1 m,but also adjust repetition frequency manually in a wide range.The adjustable range is up to 1.9 MHz.At the same time,the relation of temperature and repetition frequency on the mode-locked fiber laser is analyzed,the effective thermal expansion coefficient is deduced as 1.05×10-51/?.