Study On Fabricating Polymer Segmented Cladding Fiber By Bicomponent Spinning

Polymer optical fibers（POFs） offer many advantages over their glass counterparts,for instance,low manufacturing cost and more flexible.Microstructured polymer optical fibers（MOFs） has become more and more popular in recent years because of their single mode operation over a wide range of wavelengths.There are many kinds of microstructured optical fibers proposed till now,including but not limited to hollow-core MOF,twin-core MOF and ring structure MOE Among them, segmented cladding fiber（SCF） is consisted of a uniform core of high refractive index and a cladding with alternate regions of high and low refractive indices in the angular direction and single-mode operation can be realized theoretically.So far,only Yeung et al.experimentally demonstrated fabrication of polymer SCF by polymer casting method.However,only short fiber（up to a few tens centimeters） of sufficient uniformity can be obtained.It has been a challenge to fabricate such an optical fiber continuously.Fabricating segmented cladding fiber by bicomponent spinning method was proposed firstly in this study.The obtained fiber is even and continuous.The splice loss can be decreased and the productivity is high.The aim of this article is to study on the fabrication of polymer segmented cladding fiber by bicomponent spinning,including the design of spin pack and the quenching system,the modification of winding up system,the selection of material for melt spinning,the study on bicomponent spinning technology and the characterization of the obtained polymer segmented cladding fiber.The details are as follows:（1） Designing a spin pack to meet the requirements of fabrication of optical fiber;（2） Studying on the technology of bicomponent spinning;（3） Studying on the properties of optical fiber.The following results were obtained with the research above:The cross-section of segmented cladding fiber can be obtained by considering the high refractive index component of segments and core as a whole and controlling the cross-section of the high refractive index component.PMMA-3#、PC-1#、PC-2#、PS-1# and PS-2# are suitable for melt spinning.The experiment results of refractive index match and viscosity analysis showed that it is suitable to use PC-2# and PMMA-3# as high refractive index component and low refractive index component respectively.During the bicomponent spinning with PC-2# and PMMA-3#,the temperatures of different screw region are 170/220/240/260/275℃and 160/210/230/250/265℃, the extruding temperature is 275℃.During the course of spinning,the ratio of the frequency of metering pump for low refractive index component to that of metering pump for high refractive index component should be rational to avoid the mixing of two components.During the quenching of filament,make sure that the fiber is perpendicular to the spinneret before the first force bearing point,avoiding the unquenched filament deformation because of the shear force.The requirements of quenching the polymer segmented cladding fiber of 500μm in diameter can be satisfied by water tank of 80 cm in height.Gearbox with low speed and large diameter is suitable to wind up the brittle optical fiber.For fabrication of the aimed polymer segmented cladding fiber,the ratio of the frequency of the metering pumps for high and low refractive index component is 1:2.88,the suitable quenching mode is that the air gap is 25 cm and the immersion deepth is 80 cm.According to the existed metering pumps,the spinning speed for fabrication of the aimed polymer segmented cladding fiber is from 83.6 m/min to 290.4m/min.The polymer segmented cladding fibers with different core diameter of 36μm～46μm and different duty cycleγ=2θ₂/Λof 0.375～0.625 were fabricated using polycarbonate and polymethyl methacrylate.The output spectrum of obtained fiber was investigated using white light as the light source.From the output spectra,it was seen that the intensity in the wavelength of 730nm～830nm is comparatively higher in the test range of 500 nm-1000nm.It also can be seen from the output spectra that the intensity is decreased with the length of the fiber.The transmission loss in the wavelength of 500nm-1000 nm was tested by the cut-back method.The result showed that the transmission loss of the obtained fiber is up to 80dB/m.The comparison of transmission loss values of fiber with different diameter shows that the transmission loss is the minimum when the diameter is around 0.43 mm for the polymer segmented cladding fiber with duty cycle of 0.5 and the ratio of core diameter to cladding diameter of 1:10.The comparison of transmission loss values of fiber with different duty cycle shows that the transmission loss is the maximum when the duty cycle is 0.5 for the polymer segmented cladding fiber with diameter of 0.36mm and the ratio of core diameter to cladding diameter of 1:10.The output light pattern of the obtained fiber of 60 cm was collected by a chare-coupled device（CCD） with laser light of 532 nm as the input.The output light pattern was a uniform circle for far-field and was similar to the cross-section designed for the near-field.The results showed that fabricating polymer segmented cladding fiber by bicomponent spinning is feasible with rational spin pack design and modification of the existed melt spinning system and suitable materials as well as spinning parameters and that the cross-section of the obtained fiber was in accordance with the designed cross-section.Fabricating polymer segmented cladding fiber by bicomponent spinning can easily obtain the polymer segmented cladding fiber with different duty cycle and different size.By adjusting the ratio of the frequency of metering pumps,the polymer segmented cladding fiber with different duty cycle can be obtained with the same spin pack.Under the condition of fixing other process prameters,the polymer segmented cladding fiber with different diameter can be obtained by changing the spinning speed.