Research On Distrbuted Bragg Reflector Single-frequency Fiber Laser

The works in this thesis are on the basis of two projects: New Single Longitudinal-mode Laser Array Source in WDM All Optical Communications funded by Science and Technology Development of Jilin Province, China. Single longitudinal-mode fiber laser adopts short erbium/ ytterbium codoped fiber (EYDF) as gain medium, it is of high coupling efficiency, low noise, and single longitudinal-mode stability. This kind of fiber laser is one of the most attractile light source in high speed optical communications and high accuracy optical sensor. It is significance to research on the single longitudinal-mode fiber laser for the development of the high speed all optical communications and high accuracy optical sensing.This works mainly focuses on the single longitudinal-mode and high-speed modulation in the 1.55μm fiber laser in order to meet the requirements of modern telecommunication. We develop the single longitudinal-mode short cavity fiber laser according to communications demand as the aim. In this paper, the characteristics of the mode, the fiber Bragg gratings in the high concentration Er/Yb fiber, fiber laser array, and high-speed modulation have been studied experimentally and theoretically, which include:1. The three energy level stabilization characteristic of the fiber laser is deduced and the cavity configuration of the fiber is optimized.2. The single longitudinal-mode operation is realized by a short Er/Yb codoped as resonant cavity pumped by 980nm laser diode (LD). Two fiber Bragg gratings are written in the Er/Yb codoped fiber directly.3. The resonant cavity characteristics of the short cavity fiber laser are studied. The length of Er/Yb co-doped fiber is optimized, and 11mW output power is obtained by using 13cm Er/Yb co-doped fiber as resonant cavity.4. The longitudinal-mode is observed by the interferometer with free spectrum range (FSR) of 7.5GHz and the single longitudinal-mode is approved.5. A fiber laser array is experimented which two short cavity single longitudinal-mode fiber laser are pumped by a LD and the wavelength spacing is 0.8nm. This kind of the fiber laser array can be used in WDM systems and distributed fiber sensing.6. The high-speed rates, 10Gb/s and 12.5Gb/s, are used in the modulation experiment of single longitudinal-mode fiber laser. The eye diagrams of optical transmission and reception are measured by an optical sampling broadband oscilloscope, the transmission performance with high-speed modulation is perfect.7. In addition, the cross-sensitivity between strain and temperautre in the fiber sensor is studied. Then we described the physical mechanics of the cross-sensitivity in fiber sensor and the cross-sensitivity coefficient is obtained.The measurement matrix of the strain and temperature simultaneously are deduced. With highly elliptical core two-mode fiber and double wavelength single detecting the change of strain and temperature simultaneously, the cross-sensitivity can be solved. The relationship of the strain (and temperature) against the two wave phases shifts and Bragg wavelengths are showed. The feasibility of using this type of embedded sensors configuration for simultaneous strain and temperature measurements was demonstrated.With the experimental and theoretical analysis, there are some novel findings in the key technology and its application to fiber lasers in this paper as follows:1. Two fiber Bragg gratings are written in the short Er/Yb co-doped fiber directly and the short cavity is relized. The processing technology of writing gratings on short Er/Yb do-doped fiber is very difficult. 2. Two resonant cavitis are pumped by a 980nm LD simultaneously, and the fiber laser array is realized. The fiber laser array will be applied in the WDM systems, distributed fiber sensing systems and microwave source.3. For the first time the fiber laser is experimented in the high-speed electro-optical externally modulated transmission tests, and the results according with optical communications requirements are achieved through 21km transmission of signal. This system employed NRZ format, LiNbO3 electro-optic modulator, modulation rate from 10Gb/s to 12.5Gb/s. The signal eye diagrams of the multi-rate transmission and reception are measured, and the eyelids are thin. The results show that the coding jam and signal aberrance were not observed and signal-to-noise ratio for better. The high-speed transmission error rate is 10-12, and the system has run error free continuously for 24 hours.The single longitudinal-mode fiber laser in this paper can emit single longitudinal-mode laser, with low noise, no chirp with high-speed modulation, and the laser couples with optical system efficiently, small size array, low cost. This product will be the most potential carrier sources in the new generation all optical communication systems.