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Optical module TX/RX concept

Optical module TX/RX concept

TX and RX optical power is critical to ensure the normal communication of the sfp module receivers. But how much do you know about TX/RX optical power? And how to test the optical power of fiber optic transmitter and receiver? You will find the answers in this article.

What is the TX/RX optical power of the transmitter and receiver?

TX optical power (transmission power) refers to the output optical power of the optical receiver (sfp) in the transmitter, and RX optical power (receive) means the input optical power in the receiver. Both of them are important parameters that affect the signal transmission distance. In general, only when the transmitted and received optical power is in the threshold, the transmission distance or the quality of the module can be ensured. However, optical modules with different wavelengths, transmission speeds, and transmission distances have different transmitted and received optical power. For example, the table below shows the TX/RX optical power of 1G SFP modules with different transmission distances and wavelengths.

parameterdistanceWavelengthTX Optical PowerRX Optical Power
1G SFP Transceiver500m850nm-9.5 dBm~-2.5 dBm-17 .0dBm~0 dBm
10km1310nm-9.5 dBm~-3.0 dBm-9.5 dBm~-3.0 dBm
40km1310nm-4.5 dBm~3.0 dBm-22.5dBm~-3.0dBm
40km1550nm-4.0 dBm~1.0 dBm-21.0dBm~-3.0dBm
80km1550nm-2.0 dBm~5.0 dBm-23.0dBm~-3.0dBm
100km1550nm0dBm~5.0 dBm-30.0dBm~-9.0dBm

How to measure the TX/RX optical power of the module?

For a receiver part optical module with high availability and reliability, the transmitted and received optical power should be in a normal range. But how to test whether the optical power transmitted and received by the receiver is within the normal range?

In general, customers can directly control the TX/RX optical power of the module through the DDM (Digital Diagnostic Monitoring) function. However, if there is a problem with DDM information or if DDM is not supported by the system, it is recommended to first troubleshoot the optical module and then solve the problems. After that, you can get the TX/RX optical power of the modules. For more information on troubleshooting DDM errors and solutions, please refer to the Fiber Optic Receiver Troubleshooting section.

In addition, using a fiber optic power meter is another way to measure the TX/RX optical power of the transmitter and receiver. Using the +10GBASE-LR SFP module as an example, the test steps are as follows:

First, insert the 10GBASE-LR SFP module into the SFP port of the 10G switch.

Then, connect the optical transmitter and receiver to the fiber optic power meter using LC-FC fiber optic cables.

Finally, press the optical power parameter key and press the “λ” key to select the wavelength of +10GBASE-LR SFP optical module (that is, to select the wavelength at 1310nm). After completion, the number displayed on the screen is the transmitted optical power of the modules. Also, the transmitted optical power is equal to the optical power received by the transmitter-receiver on the other side through the short circuit.

پاورمتر فیبر نوری

Fiber optic power meter

How to diagnose the optical power of the modules?

When there is a problem in the power of fiber optic modules, such as high or low power, unstable optical power, etc., which affects the performance and transmission distance of the modules. So why do these undesirable phenomena occur? The hardware of the fiber optic receivers must have a problem and the following are provided:

The transmitted component of TOSA (laser optics) has a bad performance.

TOSA PD and PIN components are not solidified.

LD+ and LD- TOSA pins are not soldered firmly.

The connecting pins of the optical module are not correctly placed in the sfp slot of the switch or device.

Components (such as capacitors, resistors, inductors) are missing or not properly soldered and placed under IC pins.

All optical modules produced in Erionet are fully tested by the quality control unit.

In a word, the transmitted and received optical power is one of the important parameters to ensure the communication quality of fiber optic receivers. It is very important to note that the optical power is within the normal range. Optical power is not the only parameter that needs to be considered, and to know more about transceiver tests, refer to the article What Kind of Tests Are Required for Transceivers and Transceivers? do.