Development of a 4 GHz mode locked laser

In this thesis, it is aimed to develop an active mode locked fiber laser with low phase noise at 4GHz frequency. Fiber lasers are divided into two part according to change of the light they emit over time as continuous wave or pulsed. In this study, a laser that produces a short pulse sequence is designed. In the first part of the thesis, general information about lasers is given and it is aimed to introduce the usage areas, development processes, concepts and used terms. In the second part of the thesis, the fiber optic technology and working principle used for the laser, which is aimed to be developed, are introduced, and the methods used to produce the pulse sequence of the laser are specified. Information is given about the doped fiber to be used as a gain medium in the light amplification of the laser to be developed and the light amplification process. In the third part of the thesis, the physically installed active mode locking fiber laser is shown. The materials used are introduced. All components in the laser are selected with polarization protection in order to avoid an unstable state in the laser. All fiber optic connectors have been chosen as APC type with 8 degrees inclination in order to prevent the Fresnel reflection that may be backwards in the laser. The characterization of the erbium doped fiber amplifier has been made and the unwanted ASE noise has been filtered out by using a band-pass filter after the optical amplifier in the laser due to the high ASE noise. The optical modulator has been characterized and it has been seen that the laser we designed works smoothly in the frequency range we want. The laser, which was developed according to the measurements obtained after the characterization of the components, was tested to operate at another frequency and worked without any problems in accordance with the results. In order to make active mode locking, the phase noises of the RF signal source connected outside the laser and the signal source coming from the laser were compared and it was determined that the mode locking laser filtered the phase noise. In the last part of the thesis, the results of the experimental studies carried out with the laser were summarized and suggestions were made for future studies in order to obtain better results.