As we know, there are 2 MTP connector types: MTP male connector and MTP female connector. And for fiber optic patch cords with MTP connectors on both ends, we must also pay attention to the polarity of the fiber.
There are 3 main types of fiber polarity: A, B, and C. How can we distinguish them when there is no mark on the MTP patch cord?
The Methods To Identify Fiber Polarity
Based on the design and production principles of MTP patch cord itself, we can use the direction of the alignment key and the fiber line sequence to identify, as following table:
| Polarity Type | Line Sequence | Positioning Key Direction |
| Type A | Straight-through type: 1→1, 12→12 (the fiber sequence at both ends is completely the same) | The key positions are opposite, one end is KEY UP, the other end is KEY DOWN) |
| Type B | Cross-over type: 1→12, 12→1 (the fiber sequence is completely reversed) | The key positions are the same, both are KEY UP or KEY DOWN |
| Type C | Paired cross-over: 1→2, 2→1, 3→4, 4→3 (adjacent fiber cores are interchanged) | The key positions are opposite, one end is KEY UP, the other end is KEY DOWN) |
Note:
Above is an example of MTP 12 fiber connector, the actual rule needs to be expanded according to the number of cores.
The white dot on the side of the MTP connector indicates the insertion direction.
Practical Inspection Method
- Visual inspection with a red light pen:
Output red light on a single channel and observe the fiber sequence matching at the other end.
For example, input red light on a single channel with fiber sequence number 1 at one end and observe which fiber sequence number will be the red light coming out of at the other end. If it is Type A polarity, it should come out from 1 at the other end. If not, the line sequence is wrong.
2. Special tester:
- Select the corresponding polarity mode (such as 12A/24B), and the instrument will automatically display the wrong channel (red mark).
- Support custom line sequence verification to cope with non-standard design.
All Yingda MPO/MTP connectors are strictly tested for line sequence, and only qualified ones can enter the next production process.
3. Link verification:
After inserting the optical module, test the link continuity, reverse polarity error.
Application Scenario Difference
When using MTP jumper, we will also find that different polarities have very different usage scenarios:
Type A MTP to MTP Patch Cord
Mostly used for MTP patch panel trunk links (such as pre terminated fiber cable), and requires A→B MPO jumpers to flip polarity.
Type B MTP MPO Patch Cord
Preferred for direct device connection (such as switch interconnection), the fiber sequence at both ends of the MPO fiber jumper automatically completes Tx/Rx matching.
Type C MTP Patch Cord
Special crossover scenarios, less used.
Purchase and Use Precautions
- No mixing: The same fiber optic link must have the same polarity type.
- Cleanliness and maintenance: Interface contamination can lead to test misjudgment.
- New technology application: Variable polarity MPO patch cables can switch A/B polarity through a mechanical switch to reduce deployment errors.
Conclusion
Through 3 verification of key direction, fiber sequence mapping, and application scenarios, combined with professional tool testing, MPO polarity can be accurately managed. Before construction, the equipment interface requirements (such as optical module Tx/Rx definition) must be clarified to avoid link failure.
MPO Polarity FAQ
How many MTP connector types?
MTP connectors can be 8, 12, 16, 24, 32 or more like 72, 144 cores, with male and female difference.
How to determine if the MPO fiber is connected reversely?
The simplest solution is to observe the direction of the keyway (protrusion/groove) of the MPO connector:
The key positions at both ends of Type A/C MPO patch cord should be opposite (one end is key up and the other end is key down), and the key positions at both ends of Type B MPO patch cord should be the same, both key up or both key down. If the key direction does not meet the above rules, the polarity is wrong.
In addition, you can confirm the position of the white dot mark on the side of the MPO fiber connector (indicating the first core fiber). The white dots at both ends should be on the same side (Type A/C) or diagonally symmetrical (Type B).
What is the lifespan of an MTP connector?
600 Times. Most traditional MPO connectors are 500 plugging and unplugging cycles. While, the MTP connector (an upgraded version of the MPO) has an optimized spring structure and floating ferrule design. The rear end remains intact after 600 insertions and removals, extending its life by 20%.
