Further Understanding of Fiber Transceiver’s Tx Power and Rx Power

Once you choose a fiber transceiver, it is common for you to hear the introduction of something such as fiber transceiver’s Tx (transmit) power and Rx (receive) power. Do you know what do the two represent? For the appropriate fiber transceiver, is there any high demand on its Tx power and Rx power? In reality, the two are significant parameters of the fiber transceiver by which the fiber transceiver’s transmission reach is determined. For more information about fiber transceiver’s Tx power and Rx power, just take the two in 10GBASE SRSFP and 10GBASE LR SFP transceivers as reference.

Generally, the optical Tx power means the signal level which leaves from the equipment within the scope of transmitter power, while the optical Rx power means the incoming signal level received by the far terminal equipment falling within the scope of receiving power. Both of the two parameters are very significant elements which have an influence on the fiber transceiver’s transmission distance. Next, let’s have a detailed study about the 2 elements in 10GBASE SR and 10GBASE LR SFP transceivers.

10GBASE SR SFP+ transceiver is a type of multi-mode fiber transceiver with support of the distance of 300 meters over OM3 multi-mode fiber jumper cable. 10GBASE LR SFP transceiver, a single-mode mode of fiber transceiver, can achieve the 10G network at the maximum length of 10 kilometers on the single-mode fiber jumper cable. What’s the reason for the two transceivers in different transmission distances with the support of the same signal? In addition to the differences of fiber jumper cables the 2 transceivers always operate with, their Tx power and Rx power parameters are also the reasons.

From the following image, it can be learned diverse Tx power and Rx power between 10GBASE SR and 10GBASE LR SFP transceivers. For the former, Tx power is from -7.3 dBm to -1 dBm and the maximum Rx power is less than -11.1 dBm. For the latter, Tx power is between -8.2 and 0.5 dBm and the Rx power can be up to -14.4 dBm. Therefore, once you choose 10GBASE fiber transceiver, it is advised that the information about the 2 transceivers should be obtained for further knowledge about the transceiver’s performance.

10GBASE SR and 10GBASE LR SFP Transceivers’ Optical Power Budget 

As mentioned before, Tx power and Rx power have an influence on the fiber transceiver’s transmission distance. How does the impact occur? In reality, the fiber transceiver’s optical power budget (maximum allowable loss) is determined by the Tx power and Rx power, which directly influences the transmission reach. In brief, the larger optical power budget determines the longer time for the transmission of the signal in the fiber transceiver. How do you calculate the fiber transceiver’s optical power budget? The formula is: Optical power budget = Min Tx power – Max Rx power

You can calculate SFP-10G-SR and SFP-10G-LR transceivers’ optical power budgets based on the formula. The optical power budgets of the two transceivers are 3.8 dBm and 6.2 dBm respectively. Therefore, the latter can have the support of longer transmission distance compared to the former.

As 2 primary elements of the fiber transceiver, Tx power and Rx power can primarily decide the transmission reach. Once you choose a fiber transceiver, use the minimum Tx power to minus the maximum Rx power, and then the transceiver’s optical power budget would be obtained. The larger optical power budget determines the better performance of transceiver.

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