Fiber Optic Cable Processing
Automating the processes for stripping fiber optic cable is key to continued growth for manufacturers in the fiber optic marketplace.
Although basic fiber optic cable constructions have not changed significantly since the early 1990s, there has been an increase in the number of processing methods. New processes have been developed that allow the fiber optic assembly to meet certain application requirements. A few new fiber optic cable constructions have been introduced that require new production processes. All of these processes have largely been performed using manual tools, but now manufacturers feel pressure to automate for quality and labor-saving reasons.
Types of Materials
In order to recognize all of the application requirements that manufacturers have in the fiber optic sector, one must first identify the different types of materials that are now common and those that are emerging (see Table 1).
- Coated fiber
- Tight-buffered fiber
- Loose-buffered fiber
- Simplex jacketed cable with Kevlar
- Duplex (zipcord) jacketed cable with Kevlar
- Flat fiber ribbon
- Jacketed flat fiber ribbon
Common Processes
Many fiber optic cables used in photonics production require customization. This involves treating the cable in a certain way that will alter its inherent characteristics to yield a specific performance.
Figure 1. Window-stripped example
One common customization is used when producing bragg gratings. A bragg grating is produced by a process that changes the optical characteristics of a fiber using a photo mask and an ultraviolet laser. This process usually requires that the acrylate coating of the fiber (typically 250 mm) be removed prior. Normally, removal of this coating is done in the center portion of the fiber's given length.
This is commonly referred to as a window strip (see Figure 1). Window stripping is the process of stripping the acrylate coating from a fiber to expose the bare glass near the middle of a length of coated fiber. Then, the bare glass (125 mm) is cleaned and set in place under a special laser below a custom photo mask that is set 50 mm above the cable. Once the laser performs its cycle, the assembly is now customized. The window-stripped area is recoated or otherwise protected to prevent damage.
Another reason for use of a window strip is thermally expanded core (TEC) optical fiber applications. A TEC-treated fiber is produced by window stripping and then cutting the fiber in the center of the window area. The ends then are treated with heat, which expands the core and allows for easier optical alignment in subsequent operations.
Success Factors
Performing a window strip presents a challenge when trying to achieve consistent results. The success of this operation is dependent on two factors:
- The amount of delamination that may occur as a result of the window strip
- The tensile strength achieved once the window strip is performed
Delamination occurs at the edge of a window strip when the stripped acrylate coating gets pushed under the remaining coating at the end of the window. Tensile strength is measured in Newtons or thousands of pounds per square inch (kpsi) and must be at a consistent high level. Tensile strength value is determined by using a pull tester and performing a destructive pull test. The desired value depends on the application and is defined by each individual company. The range of values is from 100 to 600 kpsi. A value of approximately 700 kpsi is typically what the strength of the fiber is before stripping.
Positioning
Once the challenges of delamination and tensile strength are resolved, the user must find a way of providing accurate positioning. Positioning a fiber optic cable involves producing the window strip at an exact and repeatable location along the given fiber length. A number of manual processes are now commonly used to do this, but all of these involve excessive handling of the delicate fiber. This leaves the door open to possible damage during the process.
The ultimate solution to resolving the positioning issue while achieving desired tensile strength values and minimizing delamination is to automate the process. Automating this operation requires a reliable high-resolution transport system along with a reliable blade-positioning system. Such a system can cut and strip on the same axis while allowing the fiber to remain stationary. All dimensions and functions should be programmable and repeatable. To achieve consistency, all axes of motion should have high resolution and user-definable speeds, as well as accelerations that are independently controllable.
In-line System
The use of an in-line fiber optic cable window stripping system can reduce delamination and produce accurately positioned window strips that consistently test to high tensile strength values (see Figure 2). The same system can be used to perform other fiber optic cable processes such as end stripping of acrylate coating, end stripping of buffered fiber down to 250 mm and window slitting of tight-buffered fiber down to 250 mm. Combinations of processes on the same assembly are also possible when the system is configured with appropriate tooling and programming.
Figure 2. In-line fiber optic cable window stripping system
When dealing with tight-buffered fiber (where outer buffer material is bonded to acrylate coating), traditional stripping processes cannot be used, especially when performing a long strip. The in-line system must perform a slit on the top and bottom of the buffer material along the entire region to be stripped. This allows the buffer to be easily peeled off once the cable exits the machine. At the start of the slit, a ring cut is also performed with different blades to define the beginning of the slit area. The same process is also used when performing window strips in the buffer, except another ring cut is placed to define the window's total length.
Conclusion
The need for automation in end stripping and window stripping processes for fiber optic cable is rapidly increasing. Because the volume has been expanding, there is a need to reduce manual operations in order to achieve higher yields. The programmable approach (an in-line fiber optic cable window stripping system) is a good solution to many of the "operator skill and handling issues" that exist today.
Manufacturers that need to produce optoelectronic components for the global marketplace are often faced with challenges to mass produce rapidly. The justifications for automating the traditional manual approaches have never been clearer. Programmable and repeatable quality is the ultimate goal that these manufacturers must reach. For those manufacturers that still have manual processes in place for stripping fiber optic cable, automation of these processes is the key to continued growth in the global fiber optic marketplace.
Main Point
The need for automation in end and window stripping processes for fiber optic cable is rapidly increasing. Because the volume has been expanding, there is a need to reduce manual operations. A programmable approach is a good solution to many of the "operator skill and handling issues" that exist today.
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