By Randy Reagan
Improvements in the fiber optic cable assembly process allow a new level of performance while reducing costs.
The slump in the fiber optics industry has put customers in the driver's seat with respect to setting expectations for fiber optic cable assemblies. Today, customers expect to buy cable assemblies that have higher quality and performance than ever before, yet pay significantly reduced prices vs. those of just a few years ago. Cable assembly suppliers are faced with seemingly impossible demands — improve product quality and performance while reducing costs. How can suppliers respond?
The approach taken by some suppliers is to focus on overall process and quality improvement. Process changes may include improvements in the areas of materials, calibration, assembly, testing, facilities, training, quality control and certification. These improvements can allow a new level of performance while achieving significant cost efficiencies.
Customers carefully select fiber optic cable assemblies based on low insertion loss, back reflection and endface geometry using the Telcordia standards as a basis. To ensure cable assemblies meet customer performance requirements, manufactures design their products and processes to conform to these Telcordia requirements. For instance, singlemode cable assemblies must conform to criteria found in Telcordia GR326-CORE, Issue 3, "Generic Requirements for Singlemode Optical Connectors and Jumper Assemblies." This standard is widely recognized as the most rigorous baseline for fiber optic cable assembly performance and reliability.
Materials
Materials used in fiber optic cable assemblies must be carefully specified to achieve performance and reliability over a range of applications and environmental conditions. Manufacturers specify design dimensions and material properties for components including cords, connector bodies, ferrules, strain relief and boots, with a goal of optimizing the cost-performance equation.
Often, changes to materials and components are required to achieve enhanced performance and improvements in cable assembly yields. Changes should be implemented only after thorough qualification testing to ensure that performance and reliability can be maintained while achieving low costs. Materials and components qualified using a complete analysis and testing regiment allow changes to be introduced without degrading the quality of the assembly process or the product.
Calibration
Equipment used in the manufacture of fiber optic cable assemblies is subject to repeated use and wear. Stripping tools and polishing pucks wear over time. Polishing paper can wear throughout the day. Test instruments need periodic adjustments and recalibration. Therefore, it is imperative to institute a program for calibration and periodic recalibration for each step and each piece of equipment in the cable assembly process.
A carefully designed program of calibration at optimal intervals is required to maximize the up time of the assembly line and avoid rework. Samples should be reviewed several times during each shift to ensure the overall process is in calibration and that products are meeting customer requirements. As an added step in the overall calibration, samples can be periodically reviewed to compare performance against Telcordia criteria.
Assembly
In the past, the cable assembly process has typically been dominated by manual operations. While most assembly types still involve some manual tasks, there is a trend toward increased automation throughout the process. Automation is especially effective where designs are standardized, such as when a single cable and connector type are specified. Automation results in greater consistency and can improve the throughput of the overall assembly line. The trend toward automation has helped to improve yields and performance in the overall process.
Manufacturers currently use automation in the stripping process to help improve consistency and eliminate fiber breakage. Automated crimps are used to overcome inconsistencies in hand operation by applying uniform and complete pressure, thus making the mechanical joining of fiber cord to connector much more reliable. Automated mixing and dispensing machines bring consistency to epoxy application. Newer automated curing ovens provide complete control of the cure temperature, thus providing uniform temperature distribution and duration of cure.
 Telcordia certification mark. |
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Each parameter of the polishing procedure should be optimized to bring tighter controls to the assembly process. This includes specifying polishing pucks and paper to achieve high quality and following a prescribed algorithm for the polishing machine speeds and pressures.
Testing
Testing cable assemblies is still a critical part of the cable assembly process. Insertion loss testing and return loss testing ensure that product meets desired performance levels. Data can be collected and used to monitor the assembly process and indicate where further improvements can be made.
Also, a geometry check should be instituted on fiber ends using highly automated interferometers to ensure proper radius and fiber protrusion on the connector ferrule endface. The geometry testing data can be correlated and used as feedback to continuously maintain tight controls over the endface geometry. Finally, techniques have been developed that aid technicians in visual inspection, which results in endfaces that are free of defects.
 Multifiber connector polishing. |
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Facilities
Particulates and contaminants having sub-micron dimensions can adversely affect key cable assembly procedures such as polishing and testing. To achieve the high performance now required in fiber optic cable assemblies, upgrades to manufacturing facilities are often needed to improve the assembly environment. This involves constructing a cleanroom environment to provide a controlled and monitored atmosphere for finishing and testing cable assemblies. It is often necessary to provide appropriate training and monitoring of cleanroom techniques in order to achieve maximum benefits of the new environment.
Training
An updated training program is also instrumental in achieving new levels of performance. A thorough training program emphasizes proper techniques and procedures for cable assembly. All technicians should be required to complete a basic training course prior to handling fibers. Technicians also should be retrained at a minimum frequency of once a quarter to ensure they are exposed to the latest techniques for high-performance assembly. In addition, specialized training courses can certify technicians in polishing, testing or other procedures.
 Visual inspection machine. |
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Quality Control
Quality control continues to be vital to the cable assembly process with in-process inspections and audits used to ensure that proper procedures are being followed throughout. In-process checks and requalification procedures ensure consistent and ongoing adherence to proper procedures. These checks should look at both procedural-based and performance-based criteria. This not only ensures that the cable assemblies are manufactured according to plan, but that they are being manufactured to performance standards defined by the customer. The checks can be done in parallel to minimize rework, reduce the overall cost and improve manufacturing throughput.
Certification
Customers expect their fiber optic cable assemblies to perform consistently throughout a rigorous installation and service life. One level of prediction of the product's ability to serve in the intended application is its ability to stand up under the performance and environmental tests found in Telcordia GR326-CORE. Therefore, fiber optic cable assembly suppliers strive to satisfy this standard through independent testing. The goal is to provide customers with independent test data showing conformance to the requirements, thus certifying to customers that products will meet requirements throughout their intended service life.
Conclusion
With the improved cable assembly process, FONS Corp. has satisfied the certification requirements and additionally achieved higher performance levels for almost all of the objectives set by Telcordia in GR-326-CORE, Issue 3. The success is largely due to consistency in the connector ferrule endface geometry and robustness of the mechanical design.
RANDY REAGAN, FONS Corp., 30 Forbes Rd., Northboro, MA 01532; (508) 393-4268; Fax: (508) 393-3657; Web site: www.fons.com.
