Tag Archives: MPO connectors

MPO Cables Testing Method

As the migration to 40G/100G Ethernet using parallel array transmission systems, the high-density MPO cables are widely used in the data centre. In the connection, contamination even as small as 0.001 mm can cause the optical loss. Mating a contaminated connector to a clean connector will lead to poor performance and can damage the connection. So it’s important to test the link segments consisting of MPO array cabling and keep the cable clean. However, MPO cable testing and cleaning is full of challenges.

Why MPO cable testing and cleaning is not easy? First, MPO connectors are very sensitive to dirt and contamination. The ferrules are large and hard to clean and inspect. Most microscopes don’t have adapters for MPO connectors. Those microscopes with adapters for MPO connectors can only see a small section of the ferrule because they are adapted from single fibre microscopes. So you have to inspect the entire ferrule and every fibre. Second, cleaning is also a problem because of the designs of MPO connectors with pins and holes. Most dry cleaners can only clean the place between the pins. However, dirt may accumulate around the pins or in the holes, which cause alignment problems. So remember to keep MPO connectors well covered and protected when not in use.

Calculate the Acceptable Attenuation

Calculate the acceptable total loss of the entire optical link so that you can find if the test result is good or bad. Do as the following steps with your link loss calculator:

  • 1. Select the fibre type and test wavelength combination;
  • 2. Select the unit of length in feet or meters;
  • 3. Enter the total link length under test;
  • 4. Enter the number of connections of each type (a pair of connectors counts as one connection);
  • 5. Enter the number of splices (each connection counts as a connection plus a splice).
MPO Trunk Cable Testing Procedures

In this case, MPO connectors can be directly connect to the test equipment. That requires 12 output sources and either 12 input ports or an MPO port with a detector which can accept the light from 12 or 24 fibres. But at present this is not available. In the laboratory or factory settings, there are test equipment that can achieve this. Then, engineers use an MPO to LC fan-out cord to separate the trunk into single fibre channels for testing.

There are five basic steps for an MPO trunk cable testing (see figure 1):

MPO testing

Figure 1. set reference (three pictures above) and test MPO cable (two pictures below)

  • 1. Find a test equipment where the input port can be changed to an LC connector or has an LC already.
  • 2. Set a reference and there are three methods. Insert the known good cords into relative input ports and run an autotest (the above three pictures). If the loss is fewer than 0.1 dB (usually the maximum loss of LC connection is 0.2 dB), then the reference cords are good. This is critical to the test.
Reference Method Reference Cable Connectors Included in Measurement Estimated Reduction in Measured Loss Estimated Increase in Errors
1-Cable Method(test equipment compatible with connectors being tested) 1, launch 0 0 dB 0 dB
2-Cable Method(single fibre ferrule connectors, test equipment not compatible with connectors being tested) 2, launch and receive 1 0.2-1 dB +/-0.2 dB
3-Cable Method(male/female or plug and jack connectors, test equipment compatible with connectors being tested) 3, launch, receive and “golden cable” 2 0.3-1.5 dB +/-0.25 dB


  • 3. After setting the reference, remove the middle test reference cords and connect fan-out cables with an MPO trunk cable.
  • 4. Measure and record the loss every pair of LC connectors at the left side.
  • 5. Measure and record the loss every pair of LC connectors at the right side.

Compare the test result with calculated acceptable attenuation, If the test result is not ideal, that may be caused by the contamination, defects in the cable plant, or improper test equipment usage. Then you should better check connector end-faces for dirt and defects, and check link segment for broken fibre, poor splices and tight bends. MPO connectors are very likely to be contaminated because of fibres, number of connections and tight loss budgets. To keep MPO cabling system perform well, frequent cleaning and inspection with one-push cleaner are required.

MPO/MTP Polarity in Data Centres

Today, data centres are being built to support 40G/100G transmissions. MPO/MTP interface patch cables are created to support 40G/100G data rates. Different from traditional 2–fibre configurations, with one send and one receive, 40G & 100G Ethernet implementations over MPO/MTP fibres use multiple parallel 10G connections that are aggregated. 40G uses four 10G fibres to send and four 10G fibres to receive, while 100G uses ten 10G fibres in each direction. To ensure the systems work well, it’s important to better know MPO/MTP polarity to keep the right fibre connections.

Understanding the Polarity

Maintaining the correct polarity across a fibre network ensures that a transmit signal from any type of active equipment will be directed to the receive port of a second piece of active equipment–and vice versa. The polarity means that once the signal is received, the electronics will sort out and organize the stream of data. Transmits will be connected to receives. Every send needs its own receive just like the ball players with pitchers & catchers. For 10G transmission, Pitcher 1 needs to throw to Catcher 1, Pitcher 2 to Catcher 2 and so on. For 40/100G, any pitcher can throw to any catcher. But if you’ve got two catchers looking at each other – the play can’t go on.

Three Connecting Methods

According to the TIA 568 standard, there are three methods for configuring systems to make proper connections, Methods A, B & C for multi‐fibre arrays using MPO/MTP connectors. Each of these methods handle the transition from a transmit position to a receive position in a slightly different manner, and each employs a backbone cable that is constructed in a specific manner.

Before looking at each method in detail, it’s necessary to know MPO/MTP connectors. The following will introduce MTP connector. Each MTP connector has a key on one side of the connector body. When the key sits on top, it means the key up position. In this orientation, each of the fibre holes in the connector is numbered in sequence from left to right. We will refer to these connector holes as positions, or P1, P2, etc. There is also a white dot marked on the right connector body to designate the position P1 of the connector when it’s plugged in.


MTP adaptor is designed to hold the two MTPs. As each MTP has a key, there are two types of MTP adaptors (as shown in the following figure):

Type A—key-up to key-down. Here the key is up on one side and down on the other. The two connectors are connected turned 180° in relation to each other;

Type A

Type B—key-up to key-up. Here both keys are up. The two connectors are connected while in the same position in relation to each other.

Type B

  • Method A—The transmit‐receive flip must happen in the patch cords, and the trunk cable is a straight through transmission, with the key up on one end, and the key down on the opposite end. This means that the fibre at Position 1 (P1) of the connector on the left will arrive at P1 of other connector.
  • Method B—The keys are in an up position at both ends of the trunk cable, but the fibre at P1 in one connector end is at P12 at the opposite end, and the fibre at P12 at the originating end is at position 1 at the opposing end. The fibre positions of Type B cable are reversed at each end.
  • Method C—This method uses key up to key down adapters to connect array connector. Each adjacent pair of fibres at one end are flipped at the other end.
40G/100G Transmission Connectivity

40G needs an MPO 12 fibre connector. Only 8 fibres of the 12 are applied with other 4 remaining dark. Four positions are used to transmit, the other four positions are used to receive. 100G requires the use of an MPO 24 fibre connector. The 100G is split into 10 x 10G channels, 10 for transmitting and 10 for receiving.

To upgrade to 40G/100G data transmissions, network designers should better understand well the MPO/MTP polarity. Select the right types of MPO cables, MPO connectors, MPO cassette and patch cables, the proper solution for data centres would be achieved with high density and flexibility and reliability.