Several advances have been made in applying industrial automation to the assembly process for fiber optic terminations used in harsh environments.
An automated work cell has been developed and qualified for use for a variety of military and aerospace programs. The work cell automates all of the essential assembly steps that control performance and reliability of the final fiber termination.
The development of the automated processes has forced an in-depth study of the design of terminations in order to determine the effectiveness of the automation itself. This knowledge should be considered in the development of future fiber optic terminations and field repair processes.
The termination of optical fiber requires many discrete steps, all of which are very critical in governing the performance and reliability of the final fiber optic assembly.
Throughout the mil/ aero industry where reliability is so crucial, the termination process is performed manually. As with any manual process, the accuracy, consistency, and overall quality are dictated by the skill level of the operator performing the functions and is limited.
The automated workcell is comprised of 3 primary pieces of equipment, Terminus Attachment Workstation, Epoxy Cure Workstation, and Polish Workstation. These workstations together automatically perform all of the critical assembly tasks for terminating an optical cable.
- The Terminus Attachment Workstation: Processes the end of an optical fiber to accept a terminus. This consists of stripping and cutting the various protective layers of the fiber cable to the required lengths. Once the fiber end is prepared, a terminus is automatically loaded.
- The Epoxy Cure Workstation: Accepts the assembled cable and precisely heats the termini to cure the epoxy. This system uses forced convection to heat the terminus and employs a sophisticated computer control system that calibrates offsets for different terminus types by inferring temperature with the terminus itself – where the epoxy resides.
- The Polish Workstation: Once the terminus is assembled to the fiber cable end and cured, it will undergo polishing. The Polish Workstation will automatically polish the terminus end face with a process consisting of a series of films with a successively finer abrasive.
High quality and reliability of fiber optic terminations are governed not only by the constituent components, but to a much larger extent, the termination process itself.
By automating this process and controlling its consistency, the key characteristics for a highly reliable assembly can now be attained.
The key assembly characteristcis for high reliability are:
- Terminus Assembly Contribution: In examining the cross section of a properly assembled terminus, there are 2 main attributes that are critical for high reliability; epoxy voids and proper insertion depth. Inadequacies in either can result in lower optical performance when exposed to the stresses of a harsh environment or in outright failure of the terminus through a fiber fracture.
- Curing Contributions: In curing the epoxy, the objective is to achieve a glass transition temperature, Tg, that is higher than the most extreme operating temperature that the termination will experience to ensure the utmost mechanical integrity. The automated Epoxy Cure Workstation allows for precise cure control to meet the needs of a harsh environment termination.
- Polishing Contributions: All optical connectors must be polished to a set of specifications that address Geometry, Surface quality, and Optical Performance. However termini that fall outside of the geometric tolerance window can affect the long-term reliability, optical performance, and intermateability between connectors which make it the most critical polishing criteria.
Overall, by deploying automated manufacturing for fiber optic cable assemblies, significant benefits can be realized in both quality and reliability.
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