RareEarthDoped Fiber Lasers www rpphotonics com Anneke Batenburg

Rare-Earth-Doped Fiber Lasers www. rp-photonics. com Anneke Batenburg 0123137

Introduction Fiber Lasers : lasers having a doped fiber as gain medium or (sometimes) just lasers where most of the laser cavity consists of fibers. Dopants usually are rare-earth ions, like erbium, neodymium, ytterbium. . .

Erbium Energy Levels • Transition between 4 flevels: actually forbidden (parity), but can occur through interaction with lattice electrons. • 4 f electrons are very well shielded from crystal: little collisional decay and long u. • Transition at 1. 53 μm: very useful for telecom • Inhomogeneous broadening in glass.

Pumping Scheme Possible pumping wavelengths: 0. 98 and 1. 48 μm. Usually pumped with laser diodes.

Parameters. . .

Advantages of Fibers • Large surface-to active-volume ratio → good heat dissipation, less thermal effects • Low losses in the fiber, permits construction of very long lasers and amplifiers, leading to very high single-pass gain and low pump treshold values • Broad gain bandwidth (glass) • Easily integrable in communication systems, compactness, stability

Output Fluctuations • Spiking is common in three-level solid-state laser systems, and also in erbium-doped fiber lasers. • Spiking can be suppressed by choosing suitable pumping wavelength (Loh et al) 980 nm 1510 nm

Double-Clad Fibers • Ordinary single-mode fibers have to be pumped by single -mode diode lasers, typically limited in power (~W). • Solution: double-clad fibers. Laser light propagates in core, pump light in highly multimode inner cladding. Allows for higher power laser diode pumping (and higher gain)

Photonic Crystal Fibers • Nonlinear effects restrict ultimate power of fiber lasers. Desired: single mode fibers with large mode area (low power density) The renaissance and bright future of fibre lasers, Tünnermann et al.

Photonic Crystal Fibers 2 • More missing air holes lead to larger mode -areas (but take care of bending losses).

Double-Clad PCF (Makes in-coupling of pump light easier by larger numerical apertures) 80 W output power, could be scaled up to 260 W, authors expect 4 k. W in the future

Questions? • • www. erbium. nl/nanophotonics www. rp-photonics. com Laser Funadementals Optical Fiber Sensors: Principles and Components, edited by John Dakin and Brian Culshaw, Artech House • The renaissance and bright future of fibre lasers, A Tünnermann, T. Schreiber, F. Röser, A. Liem, S. Höfer, H. Zellmer, S. Nolte and J. Limpert, Journal of Physics B • Suppression of self-pulsing behaviour in erbium-doped fiber lasers with resonant pumping: experimental results, W. H. Loh and J. P. de Sandro, Optics Letters 1996