(a)
(b) (c)
(a) SEM of the ytterbium holey fibre. (b) Output characteristics of the mode-locked
ytterbium holey fibre laser. (c) Output spectrum at high pump power.
m2 at the laser wavelength
(1.03m) as shown in Fig.1(a).
The fibres display huge birefringence at 1.55m
(beat length 0.3mm) owing to the high index contrast between the core and the
cladding, the small dimensions, and the elliptical core shape. Using this
fibre, we have demonstrated a low threshold and environmentally stable
mode-locked laser using frequency feedback technique (see Fig.1(b)).
Furthermore,
the fibre exhibits anomalous dispersion at the laser wavelength. Using
this feature along with the high nonlinearity, we have also demonstrated
broadly and continuously tunable Raman soliton generation by seeding with only
pico-joule femtosecond pulses into the fibre. In a single pulse regime, the
tuning range covers from 1.06 to 1.33m, a region
that is difficult to access using conventional solid state laser technology.
In a multiple pulse regime, we have obtained femtosecond pulses as long as
1.58m as shown in Fig.1(c).