Abstract
This thesis presents two designs for high power linearly polarized all-fiber linear cavity lasers, continuous wave (CW) and mode-locked. The cavity designs use Polarization Maintaining (PM) fibers for both gain medium and Fiber Bragg Gratings (FBGs). The FBG pairs select lasing wavelength and polarization. The fiber lasers incorporating specialty designed FBGs achieve an extinction ratio larger than 23 dB. Firstly, an all-fiber linear cavity design of a high power picoseconds mode-locked laser is introduced. The proposed configuration is based on Non-Linear Polarization (NPR) using PM Yb-doped active fiber and two matching FBGs to form the laser cavity. The combination of nonlinearity, gain and birefringence in cavity made the laser generate mode-locked pulses in picoseconds range and with high average output power. The output mode-locked pulses amplitude is modulated with an envelope whose mechanism is also investigated in this thesis project. Experimental data and numerical simulations of the self mode-locking fiber laser are presented. Main parameters affecting mode-locked pulses and its envelope are identified. In addition, a new theoretical model based on Nonlinear Schrödinger Equation (NLSE) is developed and implemented on the MATLAB platform. The model explains the self mode-locking mechanism and the source of the pulse envelope. In this model, it is proven that self phase modulation (SPM) plays an essential role in pulse formation and shaping. The theoretical model and experimental results are in a very good agreement at different pumping levels. A method of regulating the mode-locked pulses is presented. This is achieved by applying a pulsed current to pump diode. This method successfully stabilizes the mode-locked pulses underneath a Q-switched pulse envelope. Further scale-up of average power and pulse energy is realized by adding an amplifier stage. Secondly, a CW dual-wavelength all-fiber laser is presented. The laser consists of two pairs of FBGs and a PM Er/Yb co-doped fiber as a gain medium. The laser emits at both 1 μm and 1.5 μm wavelengths simultaneously with a stable output. This laser provides a compact fiber-based pumping source that is suitable for mid-IR generation.
Highlights
Experimental Results of Mode-Locked all-Polarization Maintaining (PM) Fiber Laser applying pulsed current to laser diodes, the laser output has a Q-switched form with a repetition rate determined by the current signal
The numerical simulation starts with a 1 ns Gaussian pulse as an initial condition and we examine the output after 10000 round trips
Since the active fiber is optimized for C-band operation, the 1057 nm cavity was made as an inner cavity to reduce its cavity loss in order and better match the power of 1554 nm laser output
Summary
In order to design a robust compact all-fiber mode-locked laser with high average and peak powers, the above stated limitations have to be overcome. The use of SESAMs and nanotubes should be avoided They have low damage threshold which will limit the maximum realized pulse energy and peak power from the laser cavity. High power CW fiber lasers with linearly polarized output are essential for many applications, such as Second Harmonic Generation (SHG), polarized laser beam combining, and interferometer sensing. The lasers reported in [87, 88] used dichroic mirrors to separate pump and lasing wavelengths and bulk optics to couple the light in and out of the gain fiber
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
