Proceedings Article | 25 February 2008
Proc. SPIE. 6873, Fiber Lasers V: Technology, Systems, and Applications
KEYWORDS: Optical fibers, Mirrors, Femtosecond phenomena, Oscillators, Dispersion, Mode locking, Fiber lasers, Near field, Ytterbium, Femtosecond fiber lasers
Femtosecond fiber lasers are currently of great interest due to their small size, stable operation, long lifetime and low
cost compared to bulk lasers. However, for operation in the 1 µm wavelength range of Yb lasers, a major obstacle has
been the lack of suitable fibers with anomalous dispersion that can compensate for the normal dispersion of the
conventional active and passive fibers used. However, a new promising fiber device using a higher order mode (HOM)
with anomalous dispersion in the 1 μm range has recently been demonstrated. The device comprises integrated all fiber
mode converters based on long period gratings (LPG), and hence has the potential to be low loss and easy to splice,
while offering a large effective area, and the possibility of third order dispersion compensation.
In this paper, optimization of HOM fibers with anomalous dispersion in the 1 μm range has been investigated
theoretically and experimentally. Fibers with dispersion coefficients ranging from +50 to +300 ps/(nm·km) at 1060 nm
have been fabricated and devices including integrated LPG mode converters have been characterized. Modeled and
measured properties of the modules, such as dispersion, grating bandwidth etc., are found to correlate well. It is shown
that there is a tradeoff between a high dispersion coefficient and the bandwidth of LPG mode converters.
The characteristics of such HOM devices have been studied in a linear, passively mode-locked laser-cavity using
SESAM as saturable absorber.
