Summary
Highlights
Fiber optic connectors join fibers together or connect them to transmission equipment. They are designed to be demountable, requiring low loss, low reflectance, repeatability, and durability under repeated use.
The most crucial specification is low loss, primarily due to fiber misalignment. Repeatability in termination and reconnection is also vital. Low reflectance is important for laser sources to prevent issues and optical noise. Connectors must also perform well under environmental changes, be easy to terminate, and cost-effective.
The video traces four generations of connectors, showing a reduction in size. Modern popular connectors include the ST, SC (using a 2.5 mm ceramic ferrule), LC (small ceramic ferrule, favored for high-speed systems), and MTP (for prefabricated cable systems, not easily field-terminated).
Connectors align fiber ends accurately, typically using a cylindrical ceramic ferrule with a precisely sized hole. Most are male-style with a protruding ferrule that needs polishing and require mating adapters. Keyed ferrules allow for physical contact (PC) connections, while convex ferrules improve performance. For single-mode systems sensitive to reflections, angled physical contact (APC) connectors are used to absorb reflected light.
Common methods include adhesive polish types (epoxy, anaerobic, hot melt) for reliable, low-loss, and cost-effective connections. Crimp polish and crimp cleave connectors use crimping and sometimes avoid polishing, but have poorer performance. Pre-polished splice connectors have a factory-polished stub fiber, allowing for quick but more expensive and higher-loss installation.
The termination process involves preparing the cable (stripping jacket, trimming strength members, removing buffer, cleaning fiber), mixing and injecting epoxy into the connector, ensuring a proper epoxy bead, and slowly inserting the fiber. For single fiber cables, the connector is crimped to the strength members. The adhesive must then cure, ideally with a curing oven.
After curing, the protruding glass fiber is cleaved using a scribe, and the fragment is safely discarded. Polishing involves multiple stages: air polishing with 12 Micron film, followed by final polishing on finer grades, typically in a figure-8 pattern. Over-polishing should be avoided. The polished end is then inspected with a microscope (100-400x magnification) to ensure a smooth, clean, and scratch-free surface.
Anaerobic adhesives offer quicker termination (30 seconds to minutes) and can be accelerated. 3M Hot Melt connectors use pre-loaded adhesive, requiring heating to liquefy, inserting the fiber, allowing it to cool, and then cleaving and polishing. Pre-polished splice connectors, which have a factory-polished stub fiber, are terminated by cleaving and inserting a fiber, often using mechanical or fusion splices, and can be verified with a visual fault locator.
Field termination may be unnecessary with prefabricated cabling systems, which can be designed using CAD and directly installed and tested. These systems are cost-effective for both premises and outside plant installations. The FOA (Fiber Optic Association) offers additional YouTube videos on splicing and termination, and detailed technical information on their website.