This thesis studies optical fiber lasers for microwave photonics applications. Performance of traditional electronics counterparts turns out to be limited for high frequencies ranging tens of GHz. In this context, optics has found potential application to contribute towards the extension of microwave system features. In particular, fiber lasers have shown to be cost-effective reliable sources which are gaining increasing interest as a compact solution in comparison with solid-state lasers. The aim of this thesis is the design, fabrication and characterization of compact fiber laser optical sources for microwave photonics applications such as microwave-millimeter wave generation and photonic-assisted analog to digital conversion.

A tunable dual-wavelength distributed feedback (DFB) fiber laser for continuous wave microwave generation by photomixing is presented. A fiber Bragg grating written in an erbium–doped fiber with two induced phase shifts constitutes the laser cavity. The dynamic wavelength difference tunability is achieved through two piezoelectric actuators controlled by a DC voltage source. After photodetection of the dual-wavelength laser output, a microwave signal with a continuously 0.12-7 GHz tuning range is photogenerated. The tuning range is ultimately limited by the grating spectral bandwidth. A second configuration of the dual-wavelength DFB fiber laser is studied to further increase the tuning range. Implementing two DFB cavities with different Bragg wavelengths in the same erbium-doped fiber allows a more versatile control of the single longitudinal mode emission frequencies. A photogenerated millimeter signal of tunable frequency from 0.72 to 92 GHz is obtained from an extremely compact and simple fiber laser.

We also propose different mode-locked fiber lasers for photonic-assisted analog to digital conversion. Active and passive mode-locking techniques are studied in erbium-doped fiber cavities to satisfy target specifications in terms of pulse repetition frequency, pulse width and time jitter. The harmonically active mode-locking is carried out through high bandwidth optical Mach-Zehnder modulators inserted in the cavity, while semiconductor saturable absorbers were used for passive mode-locking. The use of intracavity polarizing fibers is also explored: control of the mode-locking operation regime is demonstrated via polarization state adjustment. Repetition rates of tens of GHz, subpicosecond pulsewidths and time jitters below 180 fs have been accomplished through the different mode-locking approaches.

Apart from semiconductor saturable absorbers, single-walled carbon nanotubes have shown ultrafast optical nonlinearities suitable for passive mode-locking. Fiber lasers passively mode-locked using carbon nanotubes as saturable absorbers are being proposed in the last years, and great effort is dedicated to implement nanotubes saturable absorbers in fiber lasers. The thesis also deals with the study of a new approach to deposit carbon nanotubes in optical fibers, in which tilted fiber Bragg gratings are used to enable optical light to interact with the nanotubes. Ultrafast optical switching is demonstrated using such carbon nanotube-based fiber device.