Design And Research Of Related Devices Of Optical Fiber Image Slicer

Astrophotonics is an intersecting subject of astronomy and photonics,with the research purpose:how to apply optical technology for astronomical observations.One of the important means for astronomical observations is spectrum analysis technique,so high resolution spectrograph is indispensable.But on the cost of high resolution,the light input efficiency is lower and lower.The image slicer,as an optical device,is a solution to the problem.It can be used to cut the image into some sub-images and then direct the light intercepted by the slit jaws into the slit to improve the light input efficiency.The traditional image slicers consisting of lens and mirrors require high processing precision,and there are defects of structural complexity,big size and difficulty of installation.Since optical fiber comes up,it is favored by researchers in different fields and opens up a new orientation to deal with the defects of traditional image slicer.The optical fiber image slicer has the advantages of being made easily,simple structure and installation swiftly.Besides,optical fiber could be made into various devices to realize different function because of its great variety.In this paper,a novel optical fiber image slicer is designed according to the principle of the image slicer.It consist of three part-optical fiber lantern,optical fiber brush and the connecting fibers.The optical fiber lantern and the optical fiber brush are all formed by tapering preform.The lantern with a circle core is used to receive the light signal,and the fiber brush with linear multi-cores used to direct the light into the spectrograph.The main topics of this thesis are followed:1.The local-mode theory of slowly varying fibers and the coupling theory of the multi-core fibers are explained.If the fiber is slowly varying,the modes in the taper are accurate approximations to local modes and the local modes propagated without losing significant power.Cross-coupling arises when there are several cores in the waveguide.The coupling coefficient is related to the normalized frequency and the distance between the fibers.Both of the normalized frequency and distance change along the taper,so the cross-coupling also changes.The coupling is obvious at the thinner end of the taper.2.A large-heating-zone moving planner-flame taper system is designed and manufactured for tapering fiber preform to special components,such as fiber lanterns or fiber brushes.The most specialty of the system is the adjustable large heating zone formed by the moving heater whose speed and distance are adjustable.The taper is lengthened due to the large heating zone,and as a result,the loss of the device is reduced.Seven blow holes with the diameter of 0.5 mm are in a straight row to form a planner flame.On one hand the width of the flame is decreased witch helps to control the shape of the taper.On the other hand the length of flame could heat preforms of different diameters.The heating temperature could be adjusted by controlling the proportion of butane and oxygen.3.A special kind of photonic lanterns was designed and fabricated by inserting some large-core plastic cladding fibers.The cladding of this kind fiber is soluble in acetone and the core is in good condition.After removed the cladding,the fibers are inserted into a pure silica capillary and tapered.Consequently,the core of taper end is uniform and so is the light power distribution,which overcomes the defect of un-uniform power distribution at the taper end formed by inserting single mode fibers.4.A novel design,optical fiber brush was fabricated to couple the light signal into the spectrometer.The fiber brush is made by tapering a photonic crystal fiber preform inserted with seven bare fibers.The seven bare fibers are inserted into a straight row of air holes.So at the taper end,the fiber brush has linear multi-cores.When the modes propagated along the taper,they will couple among the cores.Therefore,the circle mode transfers to a strip type.The major innovation works of this paper are as follow:1.Design and manufacture the large-heating-zone moving planner-flame taper system which realizes the adjustable large zone heating method.The length and the shape of taper are controlled easily with this taper system.2.Fabricate a special kind of photonic lantern by inserting the large core plastic cladding fibers.At the end of the taper,the field is uniform.3.Design and fabricate a novel optical fiber device-optical fiber brush.This device combined with the photonic lantern transfers the circle mode to a trip one.