To the matters of keyway and connector, the rules are fairly simple.
Three factors impact choosing the correct MPO cable for transceivers, keyway orientation, connector ‘gender’, and polarity. MPO transceivers have alignment pins built into the transceiver, therefore MPO connectors installed in transceiver must be ‘female.’ Additionally, MPO transceivers are also designed with the keyway on top, therefore any MPO cables plugged into transceivers must be the keyway up to ensure proper fiber handling and continuity.
MPO cable polarity is critical to connecting network elements. However, with three polarity options, choosing the correct MPO cable can be confusing to even the most seasoned of network professionals. These guidelines will assist in choosing the correct cable for the application.
Type or Method A
Application: Transceiver to MPO Adapter Panel
Method A, or Straight Through, cables are configured in a keyway up to keyway down orientation so that each fiber (1, up to 24) from the transceiver will arrive at position 1, up to 24 on the other end.
Type or Method B
Application: Transceiver to Transceiver (8-fiber parallel transceivers 40G/100G, SR4, PSM)
When directly connecting two transceivers to one another a Type or Method B polarity MPO Cable is required. Type or Method B cables cross over the fibers within the cable to ensure the Transceiver Tx and Rx are properly connected. Method B cables are configured keyway up to keyway up.
Type or Method C
Application: Transceiver to MPO Panel (100G SR10, ER10, ZR10 only)
Method C, or pairs flipped, cables will align the top Tx fiber with the bottom Rx fiber of a 24 fiber MPO cable by flipping the Tx and Rx pairs. This polarity configuration is not compatible with 8-fiber parallel 40G and 100G transceivers. These cables are keyway up to keyway down and are thus in-compatible with transceiver to transceiver connections. Transceiver to MPO panels and breakout cassettes are suitable applications for Method C MPO cables.
See our assortment of MPO and other cables here.