Recently, spectral measurement becomes an important tool in astronomy to find exoplanets etc. The fibers are used
to transfer light from the focal plate to spectrometers. To get high-resolution spectrum, the input slits of the
spectrometers should be as narrow as possible. In opposite, the light spots from the fibers are circle, which diameters are
clearly wider than the width of the spectrometer slits. To reduce the energy loss of the fiber-guide star light, many kinds
of image slicers were designed and fabricated to transform light spot from circle to linear. Some different setup of fiber
slicers are introduced by different research groups around the world. The photonic lanterns are candidates of fiber slicers.
Photonic lantern includes three parts: inserted fibers, preform or tubing, taped part of the preform or tubing. Usually the
optical fields concentrate in the former-core area, so the light spots are not uniform from the tapered end of the lantern.
We designed, fabricated and tested a special kind of photonic lantern. The special fibers consist polymer cladding and
doped high-index core. The polymer cladding could be easily removed using acetone bath, while the fiber core remains
in good condition. We inserted the pure high-index cores into a pure silica tubing and tapered it. During the tapering
process, the gaps between the inserted fibers disappeared. Finally we can get a uniform tapered multimode fiber end. The
simulation results show that the longer the taper is, the lower the loss is. The shape of the taper should be controlled
carefully. A large-zone moving-flame taper machine was fabricated to make the special photonic lantern. Three samples
of photonic lanterns were fabricated and tested. The lanterns with cladding-removable fibers guide light uniform in the
tapered ends that means these lanterns could collect more light from those ends.
Optical fibres play more and more important roles in astronomy, for example, to transfer light from the focus point of
telescopes to spectrometers. In this paper, a novel designed, a fibre-brush-shape converter was designed to transfer circle
input of a fibre to a line-shape output. The brush-shape converter consists of several bare fibres at one end, one fibre at
the other end and a taper between them. The light propagating from the bare fibres to the single fibre will be coupled.
According to the theoretical and calculated results, the power of the light could be confined in the core of the fibre if the
parameters of the taper are appropriate.
A special designed fiber with double layers of cores was investigated theoretically and experimentally. This fiber is
widely used in astronomy to transform light from the telescope to the optical spectrum analyzer. The refractive index
profile of this fiber was measured firstly. The testing result showed that the fiber has three layers of refractive index. A
special layer of the highest refractive index is between the uniform general fiber core and the general
low-refractive-index fiber cladding. This highest layer has higher local numeric aperture (NA), which can absorb more
light when the incidence angle is little larger. A series of experiments have been done to prove that the NA is larger than
normal fibers due to the higher-index layer. Two special incidence angles were measured respect to uniform and circle
mode pattern.
In order to detect the weak light of the protostars in astronomy, we design a new type of photonic crystal fibers with high
numerical aperture. Through controlling the number and the diameter of the air holes around the central fiber core, the
numerical aperture can also be adjusted to apt different applications. With the help of the big air holes, the loss can be
reduced to less than 0.1dB/km. So this kind of high numerical aperture fibers has the strong ability to collect light and the
loss is very low.
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