Research On Tunable CW All-fiber Optical Parametric Oscillator Based On The Multimode Interference Filter

The all-fiber optical parametric oscillators(FOPOs)based on four-wave mixing(FWM)effect has received great attention of the researchers in recent years due to the particularity of output wavelength and wide wavelength tunability.Among of the FOPOs,the continuous wave(CW)FOPOs as a kind of tunable CW coherent light sources have gradually demonstrated its potential value of applications in many related fields.In this thesis,aiming at the problem of high ring cavity losses caused by the use of a high-insertion-loss filter components to tune the output wavelengths in a CW FOPO,we propose a tunable CW all-fiber FOPO based on multimode interference(MMI)filters,and theoretically and experimentally study its output characteristics.The main contents of this thesis are summarized as follows:(1)The recent research status of the FOPOs are introduced.The main problems faced in FOPOs researches,as well as the solutions mainly used at present,are summarized.In addition,the research status of the MMI filters are also elaborated.(2)The phase matching principles of the FWM effect in FOPOs are elaborated.The procession of parametric amplification is theoretically analyzed.The influencing factors of the parametric amplification gain spectrum in single pump situation are simulated,which provide an important theoretical basis for the experimental research.(3)The related theories of MMI effect are briefly introduced.The influences of incident light wavelengths,multimode fiber lengths and core sizes on the filtering characteristics of Single-mode-Multimode-Single-mode(SMS)fiber structures are theoretical and experimental studied.Compared the experimental results of changing external temperature and applying axial pulling force,the experimental suitable scheme for the tunable CW FOPO is determined,which provides a theoretical basis for subsequent experiment.(4)A tunable CW all-fiber FOPO based on the MMI filters is demonstrated.Cascaded SMS fiber structures are fabricated as filter devices by selecting multimode fibers with different lengths and core-sizes.And their insertion-losses at selected wavelengths are less than 1 dB,and the total losses of the FOPO ring cavity are not more than 5 dB.By applying axial pulling force to the multimode fiber of the SMS structure,the transmission spectrum of the filter devices can be tuned.The double-sideband output wavelengths could be tunable in the range of 1494-1501 nm and 1629-1638 nm.The output power is stable within the range of 21.8-22.6 mW.