Research On Mode Control And Tunable Technique Of Single-frequency Fiber Laser

With the emergence of new services such as cloud computing and mobile 5G,promote the rapid growth of communication bandwidth requirements.As a core component in optical communication systems,high performance tunable laser has a decisive impact on device performance directly.Optical communication systems have strict requirements for laser wavelengths.DBR single-frequency fiber lasers with compact all-fiber structure,narrow spectral linewidth of kHz order,stable single longitudinal mode operation and good beam quality,and it has become a research hotspot in the fields of fiber laser.However,there are many technical difficulties in mode control and tuning technique for the DBR single-frequency fiber laser.Due to the compact structure of the short straight cavity,the tunable filter is difficult to operate in the resonant cavity,which has brought great difficulty to realize the wide tuning range of DBR narrow linewidth single frequency laser.Meanwhile,the Bragg grating and the cavity length are sensitive to temperature,which is easy to generate mode-hop phenomenon when the temperature change.The single-frequency laser hard to keep mode-hop-free in a wide temperature range which restricted the application of single-frequency laser.Therefore,it is important to develop the research of its mode control principle and expand the tunable range of the single-frequncy laser.This paper focuses on the research of mode control and tunable technique in single-frequency fiber laser,and the research contents and the main results are as follows:?1?A broad continuous temperature tunable DBR fiber laser based on a temperature dependent longitudinal-mode-selection model was proposed.The model can simulate the range of mode-hop-free temperature tunable range and wavelength tunable range for DBR fiber laser under different parameters.Base on the guidance of this model,effectively expand the temperature modulation range of short straight cavity DBR fiber laser which is helpful for the cavity length selection and mode control design of DBR laser.?2?Simulated and predicted the temperature modulation of single-frequency DBR fiber laser and analyzed the situation of laser mode change by temperature modulation.By using different packaging materials for the active fiber and the FBG,the change in cavity resonance wavelength can be well matched the Bragg wavelength change in FBG when thermal variation is applied to the cavity.Based on the model and the experiments,further broadening of the SLM temperature range of the fiber laser can be realized.Effectively increases the mode-hop-free temperature tuning interval from 2.1°C to 20.4°C and the wavelength tuning range increased from 9 pm to 149 pm which expanding application of fiber lasers.?3?An ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser based on self-injection locking has been demonstrated.By the use of a tunable narrow-band fiber Fabry-Perot interferometer,the laser wavelength could be flexibly tuned from 1527 to 1563 nm with linewidths of<700 Hz.The measured side mode suppression ratio?SMSR?is larger than of 62.0 dB.Hz.The laser frequency noise is less than 40 dB re Hz/Hz¹/2/2 at low frequencies?<100 Hz?and reaches-5 dB re Hz/Hz^1/2 at around 25 kHz.And a tunable single-frequency fiber laser prototype has been developed,which can be used for the laser source of long distance transmission communication and the fiber sensing application.