                 # Relation Between Wavelength and Transmission Distance of Optical Transceiver Jason Data Center Architect Jan 17, 2023

Optical transceiver wavelength and transmission distance are important parameters of optical transceiver, they are related to how far the network signal can be transmitted. As we all know, different wavelengths of optical transceivers have different transmission distances, so what is the relationship between wavelength and transmission distance? Is wavelength a factor that affects the transmission distance of an optical transceiver? You can read this article to find the answer to these questions. ## Relation Between Wavelength and Transmission Distance of Optical Transceiver

Optical transceiver wavelength refers to the optical wavelength band used for optical signal transmission, and its unit is nanometer (nm). The commonly used wavelengths are 850nm, 1310nm and 1550nm, as well as CWDM wavelengths of 1270~1610nm and DWDM wavelengths of 1525~1565nm or 1570~1610nm. 850nm wavelength optical transceivers are usually used with multimode fiber and are mostly used for short distance transmission; 1310nm and other wavelengths are usually used with single-mode It should be noted that earlier, low-rate optical transceivers with wavelength of 1310nm (i.e. SFP optical transceivers below gigabit) can also be used with multimode fiber, and the longest transmission distance is 2km.

The transmission distance of optical transceiver can be divided into short, medium and long distance, and the transmission distance of 2km and below is generally considered as short distance, the transmission distance between 10~20km is medium distance, and the transmission distance above 30km is long distance. The following table shows the transmission distances corresponding to different wavelength optical transceivers with different optical fibers. From the above table, we can see that the same wavelength of optical transceiver with different fiber types, the transmission distance will also be different. Then why will the same wavelength of optical transceiver transmission distance be different? This is because the optical signal will produce dispersion and loss during transmission, and dispersion and loss are the main factors affecting the transmission distance of optical transceivers.

Dispersion: In general, single-mode transmission does not produce inter-mode dispersion, while multimode transmission supports multiple transmission modes, light will be refracted several times, which will produce inter-mode dispersion. The greater the dispersion, the shorter the transmission distance of the optical transceiver.

Loss: Different wavelengths of light transmission loss, from large to small 850nm> 1310nm> 1550nm, the smaller the loss, the longer the transmission distance of the optical transceiver. It can be seen that there is no direct correlation between optical transceiver wavelength and transmission distance, but it is because the transmission characteristics of different wavelengths are different, so they correspond to different transmission distance applications.

## How to Check the Transmission Distance of Optical Transceiver?

We mentioned above that the transmission distance of optical transceivers varies, so some people must ask, when we get an optical transceiver, how do we know what its transmission distance is? Usually, we can check the optical transceiver label naming and optical transceiver DDM information to get its transmission distance, see "How to see the optical transceiver rate? How to choose?

In addition, we can also calculate the transmission distance of the optical transceiver through the formula. The formula for calculating the transmission distance of optical transceiver is (Receiving sensitivity - transmitting optical power) / wavelength optical attenuation coefficient. 【The calculated value is the ideal value】.

Take a NADDOD 10G optical transceiver with a wavelength of 1310nm as an example.
Optical transceiver transmit optical power of -8.2 ~ 0.5dBm, receive sensitivity of <-14.4dBm, query the spectrum table can be seen, 1310nm wavelength optical attenuation coefficient of 0.4 ~ 0.45dBm/km. That is, the ideal transmission distance of the optical transceiver = [(-14.4dBm) - (-8.2dBm)]/(0.45dBm/km) ≈ 13km
However, in actual application, there are also external losses in the transmission process of the optical transceiver, such as bending loss, connector loss, etc., so the actual transmission distance of the optical transceiver will be shorter than the calculated transmission distance.

## Conclusion

The above is all the content of this article, I believe you should be clear about the relationship between optical transceiver wavelength and transmission distance. The wavelength of the optical transceiver does not directly affect the transmission distance, but the dispersion and loss in the transmission process are the main factors affecting the transmission distance.