Neck Down and Thermally Induced Defects in High-Speed Optical Fiber Drawing

Abstract

The drawing speeds employed in the manufacturing of optical fibers have been rising in recent years due to growing worldwide demand. However, increasing speeds have placed stringent demands on the manufacturing process, mainly because of large temperature gradients that can generate thermally induced defects and undesirable variations in fiber characteristics. Heat transfer and glass flow that arise in drawing fibers of diameters 100–125 microns from cylindrical silica preforms of diameters 5–10 cm play a critical role in the success of the process and in the maintenance of fiber quality. This paper presents an analytical and numerical study of the optical fiber drawing process for relatively large diameter preforms and draw speeds as high as 20 m/s. The free surface, which defines the neck-down profile, is not assumed but is determined by using a balance of forces. An iterative numerical scheme is employed to obtain the profile under steady conditions. The transport in the glass is calculated to obtain the temperature, velocity and defect distributions. A zone radiation model, developed earlier, is used for calculating radiative transport within the glass. Because of the large reduction in the diameter of the preform/fiber, the velocity level increases dramatically and the geometry becomes complicated. A coordinate transformation is used to convert the computational domains to cylindrical ones. The numerical results are compared with experimental and numerical results in the literature for smaller draw speeds for validation. The effects of high draw speeds and of other physical variables on defects generated in the fiber, on the neck-down profile, and on the feasible domain for the process are determined. [S0022-1481(00)02302-1]

Optimization of a thermal manufacturing process: Drawing of optical fibers

“…This can cause the redistribution of the material dopants and impurities and, therefore, impact the fiber quality [13,20,22]. The variation of the maximum velocity lag in the neck-down region is shown in Fig.…”

“…Details of the method and the radiative properties used are given in [16][17][18]. In order to avoid computation of the direct exchange areas every time the neck-down profile is corrected, since this is very time-consuming, the optically thick approximation is first used to generate the neckdown profile [21,22]. This profile is used as the initial guess to generate the final neck-down profile with the zonal method.…”

Computational thermal fluid models for design of a modern fiber draw process

“…where is the iris temperature and 2 (15) In the air domain, we extend the application of the pressure-implicit with splitting of operators (PISO) numerical algorithm [23] to solve (1)-(4), along with the boundary conditions (10)- (25) in curvilinear coordinates with staggered grids. The staggered grids (as illustrated in Fig.…”

“…More recently, Yin and Jaluria [15] and Cheng and Jaluria [16] investigated the effects of some parameters on high-speed fiber drawing (up to 20 m/s). As most of the previous studies, they assumed that the glass was drawn into the specified fiber diameter of 125 m before leaving the furnace exit.…”

The evolution of a viscous thread pulled with a prescribed speed

“…Long-wavelength models for liquid bridges of various non-Newtonian fluids have been solved numerically by Olagunju (1999) and Balmforth et al (2010), with the latter authors including experimental comparisons. Such problems have also received attention in the context of the drawing of Newtonian fibres (Gupta & Schultz 1998;Forest, Zhou & Wang 2000;Yin & Jaluria 2000;Fitt et al 2001).…”