November 7, 2016

How to Choose Suitable Patch Cable for Optical Transceiver?

People are always amazed by the fast development of optical communication. Fiber optic transceiver, a small-size but important component, can best represent the advancing of the optical communication industry. The form factor of optical transceiver has changed from GBIC for Gigabit Ethernet to SFP+ for 10GbE, QSFP+ for 40GbE and CFP or QSFP28 for 100GbE. It is not difficult to tell the differences among these transceivers. However, users may feel confused about the patch cable which is used to connect optical transceiver to the telecommunication network. This post will introduce how to choose the suitable patch cable for optical transceiver from the aspects of transmission media, transmission distance & rate, and interface.

Optical Transceiver and Patch Cable Overview

Optical transceiver or optical transmitter and receiver (shown in the following picture) is a device that uses fiber optics technology to send and receive data. The transceiver has electronic components to condition and encode/decode data into light pulses and then send them to the other end as electrical signals. To send data as light, it makes use of a light source, which is controlled by the electronic parts, and to receive light pulses, it makes use of a photodiode semiconductor. There are different types of transceivers for different Ethernet networks, such as 1G GBIC, 10G SFP+, 40G QSFP+, etc.

Fiber-Optic-Transceiver

A patch cable or patch cord is an electrical or optical cable used to connect one electronic or optical device to another for signal routing. It is composed of electrical or optical cable terminated with connectors at each end. Optical patch cable is the most popular cable widely applied in data center and telecommunication networks. They can be differ from different connector types (see in the image below), like LC, SC, ST and FC, etc, different core diameters, like single-mode optical patch cable, multimode optical patch cable, and different fiber cable structure, like simplex optical patch cable and duplex optical patch cable.

Optical-connectors

Factors to Consider When Choosing patch cable for Optical Transceiver
Transmission Media

As we all know, there are two kinds of transmission medias in the network—fiber optic and copper. Therefore, based on these two media types, transceivers can be divided into fiber optic based transceiver and copper based transceiver. Copper based transceiver, such as 1000Base-T SFP and 10GBase-SFP+, which usually has a RJ45 interface, can achieve connection to the network with the use of cat5/6/7 patch cables.

Compared to copper based transceiver, patch cable choices for fiber optic based cable are more complicated. Generally, fiber optic patch cable comes in two types: single-mode fiber patch cable and multimode fiber patch cable, and each type can be used in different applications. Single-mode fiber patch cable can be further classified into OS1 and OS2, while multimode fiber patch cable can be further divided into OM1. OM2, OM3 and OM4. Single-mode fiber optic cable has a small diameter core that allows only one mode of light to propagate, so it is suitable for long distances data transmission. On the contrary, multimode fiber optic cable has a large diameter core that allows multiple modes of light to propagate, thus it is available for short distance data transmission. Typically, if the transmission distance is shorter than 500 meters, multimode fiber optic cable is suggested, otherwise, the single-mode fiber patch cable is a better choice.

Transmission Distance and Rate

It is known that the transmission rate will decrease as the transmission distance increases. Single-mode fiber patch cable can provide higher performance for different rates in both short and long distances, but it will cost more. When it comes to short transmission distance, it’s better to choose multimode fiber patch cable. As we have mentioned above, multimode fiber patch cable can be classified into OM1, OM2, OM3 and OM4.

OM1 patch cable supports 10 Gigabit Ethernet applications at 33 m, but is usually used for 100 Megabit Ethernet applications, while OM2 patch cable is standardized to support 10 Gigabit Ethernet applications at 82 m, but is usually applied for 1 Gigabit Ethernet applications. OM3 patch cable is commonly used to run 10 Gigabit Ethernet applications at 300 m, though it has been improved to work with 40G and 100G Ethernet applications if using a MPO connector. OM4 patch cable is optimized to support 10 Gigabit Ethernet at length up to 550 m, and 100 Gigabit Ethernet at 150 m with MPO connectors. The different performances of multimode fiber patch cable types are shown in the table below.

Multimode fiber types

Transceiver Interface

Transceiver interface is also an important factor when selecting patch cable for transceiver. Most optical transceivers have two ports, one port for transmitting and one port for receiving, so duplex SC and LC interfaces are usually employed. However, for BiDi transceiver which has only one port for both transmitting and receiving, simplex fiber patch cords will be used. For 40G QSFP+ transceivers, which often use MPO/MTP interfaces, multimode fiber patch cords attached with MPO/MTP connectors will be deployed.

Conclusion

Optical transceiver and patch cable are both vital components in telecommunication networks. Without any of these two devices, the network connection can be achieved. Only matched optical transceivers and patch cables can provide better performance. Through the information that we have mentioned above, hope you can choose the suitable patch cable for your optical transceiver.

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