Multimode fiber has bandwidth limitations. The current local area network is mostly composed of 90% multimode fiber. As the fiber optic cable factory upgrades to single-mode fiber optic cables, we must also provide a transfer path to continue to use the installed multi-mode fiber optic cable equipment as far as possible. However, if single-mode equipment is used on existing multi-mode optical cable equipment, there are some technical problems. The biggest problem is the Modular Delay Difference (DMD). This means that when a fast-increasing time laser pulse acts on a multimode fiber, the difference in the propagation time of different modes in the light causes a significant pulse broadening.
To solve this problem, a mode conversion jumper was developed to solve the Gigabit Ethernet network application method that uses a laser-based transmitter. In the application field beyond the design purpose of the installed fiber optic equipment, the mode conversion jumper is a method to realize the driving distance of the equipment. This enables customers to upgrade their hardware technology without incurring the cost of upgrading fiber optic equipment. In addition, the mode switch jumper significantly improves the quality of the data signal while increasing the transmission distance.
What is the mode adjustment jumper?
Mode conversion patch cord, also known as mode conversion plug-in line (MCP), is a double multi-mode patch cord with a small section of single-mode fiber at the beginning of the transmission length. This optical cable is designed to adjust the laser emission and obtain the effective bandwidth, so that the effective bandwidth is close to the bandwidth measured by the overflow emission method. MCP allows the laser transmitter to operate at a gigabit rate when using multimode fiber. Will not be limited by the difference in modulus delay. The key point is to excite a larger number of modes in the fiber, and weigh the mode system. The overflow emission condition highly excites the mode system, which can avoid the large-scale excitation of individual mode systems with the same power level. The laser can be launched into a single-mode fiber and then connected to a multi-mode fiber. The access point is off-center with respect to the fiber core of the single-mode fiber. This method achieves the above purpose.
Tip: Different offsets are required for 50µm and 62.5µm multimode fibers. Engineers found that an offset of 17~23µm can achieve a bandwidth equivalent to the effective mode of the 62.5µm multimode fiber overflow launch method. The offset of 10~16µm is better for 50µm multimode fiber.
The basic principle of this approach is that the optical cable will launch laser light into a small part of the single-mode fiber. The other end of the single-mode optical fiber is connected to the multi-mode part of the optical cable and is offset from the center of the multi-mode optical fiber. Transceivers that use both single-mode and multi-mode fibers (such as 1000BASE-LX/LH, 10GBASE-LX4, and 10GBASE-LRM) need to use this jumper. When launching the laser into a multi-mode fiber, the transceiver can generate a complex signal, which may cause a mode delay difference, which will severely limit the transmission distance. MCP cleared these multiple signals and solved the problem on the receiver side. Here is a picture showing the MCP and the typical method of connecting to the transceiver module. If necessary, it can be inserted between the transceiver module and the multi-mode optical cable equipment.
Requirements for using MCP in laser-based transmission systems
The requirements for MCP are only specified for 1000BASE-LX/LH transceivers that use 1300nm window transmission and are applied on multimode fiber. It is forbidden to use MCP in the 850nm window of 1000BASE-SX link. For 1000BASE-LX/LH applications on FDDI-level, OM1 and OM2 fiber types, MCP is required. It is forbidden to use MCP on OM3 called "optimized laser fiber". Remarks:
1. In some cases, customers may have such experience that the link works well on OM1 or OM2 fiber types above FDDI-level and without MCP. However, it should be noted that this does not guarantee that the link can maintain a good state in multiple runs, so MCP is still recommended.
2. If MCP is not used in non-standard applications, there may be danger, especially when the jumper cable is FDDI-class or OM1 type. In such an example, the power is directly connected to the 62.5µm fiber, which may be as high as a few dBm, and the nearest receiver will saturate. This will lead to a higher bit error rate, link oscillations, link state degradation, and ultimately irreversible damage to the device.
3. When the customer is still unwilling to use the MCP fiber optic cable, and the customer uses the OM3 fiber optic cable, please measure the power level before inserting the fiber optic cable into the adjacent receiver. When the measured power is greater than -3dBm, a 1300nm, 5dB attenuator should be used and plugged into the source of the optical module transmitter on both sides of the link.
4. For simplicity, another alternative method is to use single-mode jumpers in the same place. There is no saturation problem on single-mode fiber.
The MCP requirements are only specified for the transmission of 10GBASE-LX4 and 10GBASE-LRM transceivers in the 1300nm window and their applications on multimode optical fibers. It is forbidden to use MCP in the 850nm window on the 10GBASE-SR link. For the application of GBASE-LX4 and 10GBASE-LRM on FDDI-level, OM1 and OM2 fiber types, MCP is required. It is forbidden to use MCP on OM3 called "optimized laser fiber".
Remarks of 10GBASE-LX4:
1. In some cases, customers may have such experience that the link works well on the OM2 fiber type without MCP. But if MCP is not used on FDDI-level or OM1 fiber type, the probability of good link operation is very low.
2. When the customer is still unwilling to use MCP fiber optic cable on OM2, and for customers who use OM3 fiber optic cable, it is necessary to use a 5dB attenuator of 1300nm and place it at the source of the transmitter of the optical module on both sides of the link to avoid saturation , It may cause link oscillation and damage the device.
3. For simplicity, another alternative method is to use single-mode jumpers in the same place. There is no saturation problem on single-mode fiber. It should be noted that when 10GBASE-LX4 equipment uses IEEE-compliant single-mode fiber, the transmission distance can reach more than 10km.
Remarks of 10GBASE-LRM:
1. For customers who use OM3 fiber type, MCP should not be used. It is strongly recommended to measure the power level before inserting the fiber into the adjacent receiver. When the received power measurement exceeds 0.5dBm, a 5dB attenuator of 1300nm should be used and installed at the transmitter source of the optical modules on both sides of the link.
2. For simplicity, another alternative method is to use single-mode jumpers in the same place. There is no saturation problem on single-mode fiber. It should be noted that the transmission distance of 10GBASE-LRM devices can reach 300 meters when using single-mode fiber.
Points to note when installing MCP
When using 1000BASE-LX/LH, 10GBASE-LX4, and 10GBASE-LRM transceivers with traditional 62.5 or 50µm multimode fiber, MCP must be installed between the transceiver and the multimode fiber optic cable at both ends of the link. For all links on FDDI-level, OM1 and OM2 fiber types, MCP is required, but it is prohibited to use MCP on OM3 and the latest fiber type applications.
Remarks: It is not recommended to use 1000BASE-LX/LH, 10GBASE-LX4 and 10GBASE-LRM transceivers with multimode fiber and non-patch cables to achieve very short link transmission (tens of meters). The result of doing this is to increase the bit error rate (BER) and damage the receiver.
The MCP is installed between the receiver transmitter and the wiring board. For each installation device, two MCPs are required. When installing the jumper, perform the following steps:
Step 1: Insert the single-mode optical fiber connector into the transmitting hole of the transceiver;
Step 2: Insert the other half of the dual connector into the receiving hole of the transceiver;
Step 3: At the other end of the jumper, insert two multi-mode connectors into the wiring board;
Step 4: Repeat the operations from Step 1 to Step 3 to locate the second transceiver on the other end of the network link.