How to Check the Optical Signal Strength of SFP Modules?

As we all know, SFP optical modules support various applications such as Fiber Channel (FC) switches, SONET/SDH networks, Gigabit Ethernet, high-speed computer links, CWDM and DWDM interfaces. When the SFP optical module is connected to a switch, the optical signal strength is a key parameter to ensure the normal operation of the entire connection. This article introduces the optical signal measurement method of the SFP optical module and how to check the optical signal strength of the SFP optical module.

Optical signal strength of SFP optical module and its importance

Usually, the signal strength of the SFP optical module includes two parts: Tx power and Rx power, the former representing the transmission power signal, and the latter representing the reception power signal. For general SFP optical modules, the values of Tx and Rx power within a specific range indicate that the SFP optical module can operate normally. For instance, the tunable SFP+ optical module can operate effectively within a transmission power range of -9.5Bm to -3dBm, and a reception power range of 0~ -17dBm. If Tx or Rx is within the range of -30dBm or lower, it means that there is no signal sent or received.

The strength of the optical signal directly determines whether the network connection is normal. If the Rx power is not strong enough, there will be no signal in the optical link, which is why long-distance optical modules or optical amplifiers are needed for long-distance transmission. If the Rx power is too high, the SFP optical module will be damaged, so choosing a high-quality SFP optical module is a basic guarantee for ensuring the normal operation of the network connection.

Optical signal strength measurement of SFP optical module

Generally, there are two common methods for measuring optical signal strength: milliwatts and dBm. The former measures the optical signal strength by power measurement, while the latter measures the optical signal strength in decibels. Each SFP transceiver manufacturer may use one of them to measure the power of the optical signal, for example, switches may use dBm to measure it, and Brocade switches usually use mW to measure it. Note: the optical signal will attenuate during transmission, and network operators need to pay attention to this issue to ensure transmission quality.

Method for checking the optical signal strength of SFP optical module

To determine whether the SFP module is working at the appropriate signal level, you can check the status information of the SFP optical module, which is very critical and includes the fiber type, transmit optical power range, and optical receive power, etc.

In addition, switches like switches will provide CLI (command-line interface) references, which are useful for viewing detailed information about the SFP optical module, including rate, serial number, part number, and receive/transmit direction optical signal strength.

Although the methods for measuring optical signal strength are different, they all provide the current signal strength and the range of effective optical signal strength of the SFP module. As long as the signal strength of the SFP optical module is within the effective range, the SFP optical module can operate normally.

Optical signal strength is an important factor that affects the entire optical link. This article introduces the methods of measuring and checking the optical signal strength in the switch, hoping to help everyone use the SFP optical module correctly.