Optical waveguides – Accessories
Reexamination Certificate
2001-12-05
2003-11-18
Prasad, Chandrika (Department: 2839)
Optical waveguides
Accessories
C242S484600
Reexamination Certificate
active
06650820
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the general field of optical fiber accessories and is particularly concerned with an optical fiber winding tool.
BACKGROUND OF THE INVENTION
The use of optical fibers for telecommunication systems and other applications has become increasingly prevalent over the past few years. As is well known in the art, optical fibers are typically hair thin structures, capable of transmitting light signals at high rates and with low signal loss. They are ideally suited to the high requirements of digital transmission and, hence, are well matched to the evolving worldwide transmission network.
The most popular medium for light wave transmission through optical fibers is glass, a solid whose structure is amorphous. Commercial optical fibers are drawn from a pre-form, an elongated cylinder of glass having an inner core and an outer cladding, with the thickness of the core and the cladding typically being in the same ratio in the fiber as they are in the pre-form. During the drawing process, the pre-form is fed into a heated region where it necks down to the fiber size as the fiber is pulled from the heat zone. A coating is applied to the freshly drawn fiber before it touches any capstans or rollers. The coating protects the fiber from the environment and cushions it from external forces that induce micro-bending losses. The drawn fiber is taken up on spools in such a manner that the end portions of the fiber on each spool are available for testing. The spools of drawn, tested fibers are subsequently used to supply ribbon and cabling processes and apparatus.
The winding parameters during take up must be carefully controlled. Collection of the fiber at low tension is necessary in order to minimize damage to the fiber or coating thereon and to reduce the effect of micro-bending and macro-bending losses on the transmission media. The winding tension is minimized and the distribution of fiber across a spool is controlled to provide a desired package profile and to facilitate unwinding at a subsequent operation. Hence, great care is usually taken in order to minimize potential damages to the fiber during the initial winding step following the drawing of the fiber. Unfortunately, such concern with the possible damages resulting from improper handling of optical fibers, particularly during the critical winding steps, is often neglected once the fiber leaves the fiber-manufacturing site.
The specific handling requirements of optical fibers are directly linked to their inherent structure. Indeed, optical fibers being made of glass are characterized by their brittleness. A typical glass fiber will stretch elastically to about 7% strain and break abruptly without undergoing any permanent deformation. The actual breaking strengths between fibers will vary widely and depend on a variety of factors. The reason for this wide range is attributed to submicroscopic cracks in the fiber surface. These cracks can be inherent to the glass itself or a result of manufacturing processes and handling of the fiber.
The mere manipulation of the fiber, even by a skilled worker, may potentially lead to reduce mechanical and/or optical properties. Indeed, localized pressure on the fiber tends to deform the core, which is a softer glass than the cladding, causing radiated losses and mode coupling also referred to as micro-bending losses. Micro-bends consist of microscopic random deviations of a fiber around its straight nominal position. The amplitude of the deviation is typically a few microns or less and their period less than a millimeter. In multi-mode fibers, micro-bends cause light to be exchanged among the various guided modes, some of which have higher losses than others. In both multi-mode and single mode fibers, light can couple into modes that escape from the core. The small deflections usually result from fiber coating, cabling, packaging or other localized forces. They can also be created during the manual handling of the fiber by squeezing the fiber between the fingers of the intended user. Although micro-bending losses typically return to zero when the localized forces are removed, they may potentially create permanent losses.
Fibers exposed to active environments and under stress, weaken with time because existing cracks grow. Termed static fatigue, this crack-growth phenomenon limits the residual stress that a fiber can sustain over a period of time and imposes a minimum bend radius on fibers. Indeed, bending a fiber produces tensile stresses along its outer portion and compressive stresses along its inner portion. The minimum bend radius depends on various factors including specifications in given applications. For most applications, a 1″ minimum bend radius is usually recommended as being a comfortable minimum bend radius for an installed fiber, both to minimize bending induced loss and also to preserve fiber lifetime. A minimum bend radius also needs to be respected during winding operations. This tends to be difficult, especially with relatively short strips of optical fibers.
Hence, aside from breakage, optical fiber communication performance may be degraded by micro-cracks or micro-bends in the fiber generated by bending or other stresses imposed on the fiber. Such damage to an optical fiber not only reduces the fibers long-term durability, but it also causes losses in optical signal strength and content. As mentioned previously, great care is usually taken during initial handling and winding of the fibers at the manufacturing site. In order to reduce the risks of physically damaging the fiber, the control of fiber tension during initial winding immediately after the drawing of the fiber requires relatively sophisticated equipment.
In order to control fiber tension in the freshly drawn fiber, the latter is typically allowed to form a catenary between the capstan and the take up. As the spool fills, the catenary tends to decrease in length and it becomes necessary to decrease take up motor speed under controlled conditions. This is typically accomplished with an electro-optical system including a closed circuit television camera, which detects any change in the height of the fiber catenary and causes changes in the take up motor speed. Once initially wound, the fiber is shipped on a spool to other companies or clients that either use the fiber or further process the latter.
There exists a plurality of situations wherein an optical fiber needs to be re-wound into a coil after the initial winding on a spool at the manufacturing site. Some applications, such as the manufacturing of optic sensing devices, inherently require winding of the fiber. Other situations are related to general handling of the fiber. For example, it may be desirable to mount optical devices, such as multiplexers, demultiplexers, switches or the like, on relatively short strips of fibers, commonly referred to as “pigtails” that are eventually spliced to longer segments of optical fiber. The mounting of such optical components on strips of optical fiber requires handling and temporary storage of the fiber segments. The use of relatively sophisticated equipment and method conventionally used for initially winding the drawn fiber as herein above disclosed is not well suited to this type of application.
In assembly lines wherein optical components are attached to strips of optical fiber, the latter is wound at various stations. For example, once the optical component is attached to a pigtail, the pigtail is typically manually wound into a coil prior to shipment to an intended customer. The manual winding of pigtails presents numerous drawbacks. The operation is both tedious and time consuming. Furthermore, it involves repetitive and relatively unergonomical movements that may potentially lead to work related injuries such as tendonitis or the like.
Furthermore, as mentioned previously, manual winding of the pigtails may potentially lead to damages in the fiber with resulting loss of efficiency and reduced longevity. Accordingly, there exists a need for an optical fiber winding
Dufour Christian
Joubert Stéphane
Martineau Pierre
Moquin Jean-François
Ross Olivier
ITF Optical Technologies Inc.
Prasad Chandrika
Tessier Louis
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