Components and Operational Considerations regarding Fiber Polarity

Posted on Aug 9, 2022

The various components play distinctly different roles in cable connectivity. When connecting these components, how they interact requires attention to achieve proper polarity. This article focuses on how these components interact with each other and operational considerations regarding polarity methods to build a viable cabling system.

Connectivity Methods of Cable Assemblies

Cable assemblies come in a variety of options and make use of different connectivity methods, such as simplex, duplex, or MPO connectivity. In particular, connectors for fiber optic cables have different genders and alignment methods. It is critical to ensure the right connectivity between connectors, which protects the connectors and devices, as well as to maintain the correct polarity.

Simple and Duplex Connectors

Simplex fiber optic connectors (LC, SC, etc.) are always male. Duplex connectors are just simple connectors joined together, so duplex connectors are also male. Couplers are always female. Simplex or duplex connectors can be plugged into similar connectors without risk of damage.

MPO Connectors

Both male MPO connectors and female MPO connectors are available. Parallel optic couplers are genderless and can accept MPO connectors of either gender. MPO equipment ports are always male, requiring a female cord. Female-female fiber patch cords can be used in any direction, making them a good choice. Male-female trunk cables are also recommended. However, if it is necessary to extend a trunk assembly, female-to-male fiber patch cords should be adopted to ensure that the connectors match correctly. And the combined assembly will operate as male-to-male.

The Usage of Couplers

Couplers can have two fundamental configurations: Key Up to Key Up (KU/KU) and Key Up to Key Down (KU/KD). For the right polarity, different connections are used depending on the coupler type.

Simplex & Duplex Couplers

When couplers with simplex or duplex connectors are used, the angled polish is sideways. The components only pair correctly when the couplers are Key Up to Key Up. And if KU/KD couplers are used with APC connectors, they may be damaged because they do not fit correctly. Therefore, simplex and duplex couplers are usually of the KU/KU type. From the perspective of polarity, with KU/KU simplex and duplex couplers, an odd number of flips in the channel can be achieved, no matter how many links you connect. In this way, the polarity will always be in effect.

Key Up to Key Up

MPO Couplers

MPO couplers are usually Key Up to Key Down. Due to the wide face of the MPO connector, the angled polish is in the vertical plane. When using MPO APC connectors, the KU/KU will not mate properly and may cause damage. Therefore, the KU/KD MPO coupler allows no changes to be required when using the APC connector.

Key Up to Key Down

Special Cases

To ensure the right polarity, there are a few special cases that require attention, as follows.

Port Inversion—When using type B components, fibers and ports are transposed correctly (1-12, 2-11, 3-10, etc.). If the ports are not inverted, port 1 will plug into port 6.

APC Connectors—Remember Key Up to Key Up for duplex and Key Up to Key Down for MPO connectors.

Multi-Row Optics—A longitudinal flip is required while maintaining the same vertical orientation.

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