6.5 Connectors
6.5.1 Connectors Types
GPON networks typically use SC type connectors. The preferred connector polish is the angled polish, SC/APC (Green), but the
ultra-polished SC/UPC (Blue) can also be used.
SC Connector
SC officially stands for Subscriber Connector; however, some people believe that “Square Connector,” is the correct name. It is a
general purpose push/pull style connector. It was developed by NTT, which has an advantage in LAN/enterprise networks where
duplex cabling to support TX/RX channels are commonly used.
SC connector end face
SC Connectors are frequently used in network applications. The connector is square and keyed with push-pull mating, 2.5mm
ferrule, and molded housing for protection. The SC is a snap-in connector that is widely used in single mode systems due in part for
its performance; it latches with a simple push-pull motion.
6.5.2 Connector Performance and Polishing
Polishing of fiber optic connectors is the process of polishing the end-face of the ceramic ferrule within the fiber optic connector. The
purpose is to improve the light transfer between the mating of connectors, in order to minimize optical losses and reducing
reflections. This is an important aspect of fiber optic communications as losses affect the quality of the light signals.
There are two main types of losses that are affected by the style and quality of polishing, which dictate the optical performance level
of terminated fiber optic connectors:
Insertion Loss (IL)
- The most important performance indicator of a fiber optic connection. This is the loss of light signal,
measured in decibels (dB), during the insertion of a fiber optic connector.
Return Loss (RL)
- Also known as back reflection, is the portion of the light signal that is reflected back to the original light
source. This occurs as the light is reflected off the connector and travels back along the fiber to the light source. This indicator
is measured in negative decibels (dB). When reading return loss figures, the higher the absolute value of the decibel unit
means the better the performance of the interconnection.
The amount of insertion loss is affected by fiber alignment, and/or the quality of the finishing on the end of ferrule, while reflectance
is affected by the style of polishing on the ceramic ferrule in a connector. There are two different styles of polishing, reflected by the
shape of their finish:
Ultra Physical Contact (UPC)
- The UPC style ferrule has the shape of the PC style, except they are polished with several
grades of polishing film that allows for an ultra-smooth surface. The main difference between UPC and PC is that the former
have lower return loss.
Angled Physical Contact (APC)
- The APC style produces the lowest return loss when
compared to other styles. The ferrule is polished to an angle of 8 degrees. The angle is calculated so that it is less than the
critical angle, which ensures light is not propagated back along the fiber.
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