Appendix: Optical Connector and Fiber Cable

MMA2L20-AR 25GbE SFP28 LR Transceiver Product Specifications

The optical port in the transceiver is a pair of LC connectors which mate with fiber-optic cables with duplex LC connector.

Optical LC Receptacle (transceiver, front view)

image2021-10-4_12-44-42.png

TX RX

Reference: IEC specification IEC 61754-20.

The fiber which connects transceiver A’s lane 1 must end at transceiver B’s lane 2 at the other end of the link. This calls for a crossed cable, also referred to as ‘Type B’. The fiber is standard single mode fiber. The maximum length is specified in

LC to LC Cable Fiber Connections

Connector A
Duplex LC

Connection

Connector B
Duplex LC

1

--->

2

2

<---

1

Multiple LC patch cables can be connected in series, but each added connector pair adds reflections and modal dispersion in the link which again impairs performance. An odd number of ‘crosses’ must be used between transceivers at the two ends.

Typical Look of a Single Mode LC Fiber Patch Cable

image2021-10-4_12-46-45.png

Remember to clean the connectors with a fiber cleaner before plugging the cable in.

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