光学
饱和吸收
渐变折射率纤维
光纤激光器
保偏光纤
材料科学
克尔效应
光纤
纤维
色散位移光纤
模式音量
单模光纤
物理
非线性系统
光纤传感器
复合材料
量子力学
摘要
This dissertation reports on the research to design
and build a pulsed fiber laser with the Er doped fiber based on a
new mode locking technique. The numerical simulations begin by
launching an optical wave in a fiber which will be amplified during
propagation. The device to mode-lock the waves is outside the
fiber, but connecting to fibers at both ends; it is a nonlinear
optical material that can reshape the beam as it propagates using a
nonlinear change of the refractive index, which is called a Kerr
effect. The device is made with a nonlinear material sandwiched
between two fiber ends; it takes an optical field from one end of
the fiber and propagates it to the other fiber end. In between the
two ends, a nonlinear medium will be used to balance the
diffraction through Kerr effect (which can lead to Self-focusing of
the optical beam). With the second fiber end working as a soft
aperture, the combination of the self-focusing effect through the
nonlinear medium and the aperture will act as an intensity
dependent coupling loss; this effect is referred to as a fast
saturable absorber which means that higher intensity corresponds to
higher coupling efficiency and thus the cavity modes will be
gradually phase locked together to form pulses. The saturable
absorber action is calculated using different nonlinear mediums
( CS 2 ,
As 2 S 2
and
As 40 Se 60 )
and the fibers used are assumed to be of the same size.Whole cavity
simulation is then conducted using the proposed SA design and the
pulse energy produced from the laser cavity is generally below 1
nJ. In those simulations the pulse peak power is weak and the
saturable absorber action is not strong.Experiments are designed to
test the mode locking idea with the chalcogenide glass plate
( As 40 Se 60 ).
Firstly, a mode locked laser is constructed from a ring fiber laser
cavity with an Er doped fiber as the gain fiber. Three modes from
this cavity are routinely generated. Two modes have pulse durations
of 220 fs and 160 fs with spectral width of about 30 nm and 40 nm,
respectively. Mode 3 is more interesting since it covers a huge
spectrum range (1490 to 1640 nm) and the pulse duration is
estimated to be about 40 fs from the transform limited pulse
calculated from the spectrum, which could be the shortest pulse
ever reported from an Er doped fiber laser. Further efforts are
needed to better dechirp the pulse to verify the transform limited
calculation. Due to the weak saturable absorber action from the
original design, we use a telescope design to test our SA idea in
experiment; the ChG
As 40 Se 60
plate is placed inside a telescope which is then inserted into the
laser cavity explained in previous paragraph. The telescope design
is used to focus the pulse so that higher level of nonlinearity is
induced. Then an iris is placed behind the glass plate to create a
transmission discrimination mechanism against different powers
(Kerr…
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