The impact of optical module operating temperature on 5G

Since the 4G/5G RRU/AAU is usually installed outdoors, the operating temperature range of the optical module is relatively strict.

However, the BBU/DU is usually installed in the equipment room, and it is obviously not necessary if pre-transmitted optical modules are required to meet the above operating temperature requirements. In YD/T1351-2019, the operating temperature of optical modules is divided into commercial grade: 0 degrees to 70 degrees and industrial grade: -40 degrees to 85 degrees. For optical modules used in engine compartments, the operating temperature meets commercial grade requirements.

The transmission performance of low-speed optical modules is not affected by the operating temperature. For example, the color optical modules currently used for 4G forward transmission mostly have an operating temperature range of 0-70°C. There are no reports of network failures caused by operating temperature changes. However, the dispersion cost of the 5g forward color optical module (see "Discussion on the impact of dispersion in the 5g forward passive WDM scheme") is higher than normal temperature (15°C to 35°C). The dispersion cost of optical modules with wavelengths of 1351nm and 1371nm increases even as high as 2-3dB.

When passive wavelength division is used for 4G pre-transmission, each optical module usually uses an adjacent wavelength. For example, a 6-in-1 system uses 1271 nm and 1291 nm, 1311 nm and 1331 nm, and 1351 and 1371 nm, as shown below.

Optical module temperature

However, if the 5G forward transmission wavelength is allocated according to the above method, an optical module with a wavelength of 1371nm will be installed on the AAU side, which may cause a large dispersion cost due to the influence of temperature.

The optical modules used in the fronthaul are designed to be integrated transceiver management modules, and each optical module includes two different ports for information sending and receiving capabilities. The receiving of the optical module is not very sensitive to the wavelength range, so when using it, we only need to pay attention to the sending wavelength of the optical module. For example, an optical module with a transmission wavelength of 1271nm can be used in pairs with an optical module with a transmission wavelength of 1291nm, and can also be used in pairs with an optical module with a transmission wavelength of 1331nm.

optical module

Therefore, for 5G forward, it is recommended to install optical modules with the transmission wavelengths of the last three waves (1331 nm, 1351 nm, 1371 nm) in the computer room, and use commercial optical modules; install optical modules with the transmission wavelengths of the first three waves (1271 nm, 1291 nm, 1331 nm) on the AAU side. For optical modules, industrial-grade optical modules are required.