Student Project Abstracts 2005 - Pluto - University of Washington

The Design of a Fluid Delivery System for Micro-Core Optical FiberGreg WinchellEverett Community CollegeAnn MescherMechanical Engineering, University of WashingtonINTRODUCTION TO POLYMER FIBER DRAWThe objective of this research has been to develop a methodfor drawing a single-hole polymer optical fiber from a pre-drilledacrylic preform, with accurate control ( +/- 2 microns) of the fiberouter diameter and internal channel diameter. Polymer fiberoffers superior design capabilities compared to currently manufacturedglass fiber, along with potential savings in energy andmanufacturing cost. The most significant advantages of polymerfiber are: 1) the ability to incorporate unique organic optical materials,and 2) much greater flexibility in designing and processingpolymer materials as opposed to glass into photonic bandgapstructures. The next paragraph will discuss how polymer fiber ismade.The basic approach to making polymer fiber is to first trimand machine the polymer preform (which is an acrylic rod) tospecifications inherent to the fiber making procedure. Then thepreform is attached via cross pin to the draw mechanism and isslowly fed downward into the furnace as shown in Figure 1. Thefurnace heats the preform (with wall temperatures peaking at approximately184°C) such that polymer fiber can be drawn mechanicallyby the Draw Tower spindle and spooled. While thefiber is drawn a Laser Diameter Gauge measures the outer diameterof the fiber produced by the process. This is the basic processfor producing polymer fiber.If we take a polymer preform and drill a hole in the radialcenter along the axis of the preform (thus forming a “thick-walledtube”), and we then heat this preform, the resultant fiber will havethe same aspect ratio (i.e. the inner hole diameter divided by theouter diameter of the fiber) as the original drilled preform beforeheating. Now if we take another polymer preform and drill a holein the radial center and this time place fluid in the hole, the aspectratio of the resultant fiber will not be the same as the preformaspect ratio before heating. Why is this happening?Figure 1. The Polymer Fiber Draw ProcessFluid Core and the Effect Of Fluid PressureWhen the preform with a hole (but no fluid inside the hole)is heated, the experimental evidence consistently shows thatthe aspect ratio of the fiber produced does not differ from thatof the unheated preform. This suggests that mere atmosphericpressure inside the drilled hole is not enough to alter the aspectratio. However when fluid is added to the drilled hole, this isenough to change the aspect ratio of the fiber indicating thatatmospheric pressure in combination with fluid pressure willalter the aspect ratio of the resultant fiber compared to the aspectratio of the unheated preform. Fluid Pressure is equal tothe density of the fluid multiplied by gravitational accelerationmultiplied by height of the fluid column (Fluid Pressure=ρgh).The illustration below (Figure 2) shows that the fluid pressure ishighest in the region where the polymer radius is rapidly changing.As the fiber is created below the fluid column, the aspectratio increases and therefore fluid is gradually removed from thepreform. This results in a continuous drop in the fluid columnheight which means that the fluid pressure itself will also beginto decline.CMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005 127