Tunable fiber lasers based on fiber bragg grating arrays and a theta ring cavity
Fiber lasers feature unique properties, for instance an excellent beam quality, high power efficiency and the possibility to realize robust as well as compact systems by a fiber-integrated layout. To access new applications in the rising fields of life sciences and biophotonics, advanced operation concepts are desired, such as versatile tunable lasers, exploiting the broad spectral gain regions of rare-earth doped fibers. In this work, a new discrete tuning concept is developed for pulsed fiber lasers, utilizing fiber Bragg grating arrays as monolithic filters. Based on its discrete spectral sampling, this spectral filter uniquely enables tailored tuning ranges and ultrabroad bandwidths. The distributed filter is implemented in a novel theta resonator geometry that ensures a constant cavity length for each emission wavelength as well as a steady repetition rate along the tuning range. In this scheme, the electrical tuning mechanism is based on optical gating of pulses with a modulator. This thesis introduces the concept of the Theta Cavity Fiber Laser (TCFL) and experimentally investigates its characteristics. The system features superb emission properties including high spectral signal contrast (~40dB), narrow linewidth (~150pm), adjustable pulse durations (4ns - 15ns) and fast sweep speeds (spectral switching time <10s). These features are combined with an extended tuning range of up to 50nm (around 1m). The special resonator layout, ensuring a constant repetition rate for all emission wavelengths, as well as the scalability in the optical gating scheme enable advanced operation concepts, extending the potential application range of this tunable laser. A novel multi-wavelength mode is developed, featuring two or more independently tunable and synchronized emission wavelengths. Furthermore, an intra-cavity method is established to measure dispersion properties of fiber components based on evaluating minor pulse shape variations along the tuning range of the TCFL.