Practical optical fiber systems, both multimode and single mode, require connectors for terminating components, system configuration, testing, and maintenance. And in all types of system, from the long-haul large-capacity single-mode fiber systems to the large-core multimode fiber systems used in local area networks, the connectors must exhibit low insertion loss while also being cost effective. With the long-haul single-mode fiber systems, where fiber attenuation may be as low as 0.2 dB/km, it is obvious that the connector’s insertion loss can severely limit the distance between repeaters. Besides the connector's coupling efficiency other factors can also limit the span length. Reflections from connectors close to the transmitter may affect the longitudinal mode spectrum and noise characteristics of some laser transmitters and thereby cause system degradation. Also, high-loss connectors may cause higher-order modes to propagate, in short jumper cables, resulting in modal noise and its associated power penalty. Although these single-mode fiber systems usually employ a small number of connectors, for low insertion losses their 5–10-μm core diameters require fiber alignments of submicron accuracy. In contrast to these single-mode systems local area networks are being designed using large-core multimode fibers (at least today). These networks can be very connector intensive with as many as twenty or more connectors being used between transmitters and receivers. In addition, other optical components such as couplers, taps, and switches may also be used, and the combined losses of the components and connectors must be accommodated by the relatively low system gain provided by low-cost LED transmitters and PIN receivers. In these applications the connector’s performance and cost-effectiveness again must be balanced to achieve a practical resolution. A further consideration is that in all practical systems, both single mode and multimode, there exist applications that require both factory and field-installed versions of these connectors. It Is, therefore, important that field-Installable versions are available for all practical connector designs, Including those designed for single-mode fibers.

© 1985 Optical Society of America

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