Almost all optical module specifications have a column for "center wavelength". Common values are 850nm, 1310nm, and 1550nm. These three numbers are not taken randomly. They correspond to the three low-loss working windows of quartz fiber, and each is bound to different fiber types and transmission distances. If the wavelength is wrongly selected, the module itself is not damaged, but the link may only run a few tens of meters or may not work at all.
850nm: equipped with multi-mode optical fiber for short distance
The 850nm window uses multi-mode optical fiber (OM3/OM4). The light source is cheap and the power consumption is low. It is an economical solution for hundreds of meters of interconnection in the computer room, with typical coverage of 300 meters to 550 meters, such asSFP Gigabit Multimode Dual Fiber Optical ModuleIt falls into this category. However, multimode optical fiber has large inter-mode dispersion, and the signal is seriously broadened beyond one kilometer, so 850nm is never used for long distances, and cross-building interconnection must be replaced by a single-mode solution.
1310nm: the mainstay of single-mode mid-range
1310nm is the zero-dispersion window of single-mode fiber. It takes into account both cost and distance under 0dB/km level dispersion. It conventionally covers 10km to 40km. It is the most commonly used wavelength for interconnection between campus buildings and access layers. According to experience, 1310nm dual-fiber is the most cost-effective in a 10km scenario. The link loss is generally estimated at 0.35dB/km, leaving an additional 1dB to 2dB for patch panels and connectors.
1550nm: the first choice for long distance and low loss
1550nm is the window with the lowest optical fiber loss (about 0.2dB/km). It is mostly used in long-distance 60km, 80km modules and links that require relay or amplification, such asSFP 2.5G single mode dual fiber 80KM optical moduleJust works at 1550nm. Single-fiber bidirectional modules also often use the two wavelengths of 1310/1550 to transmit in different directions on one fiber.
A practical judgment method: measure the distance first, and then determine the fiber. Multi-mode 850 is the most economical within 500 meters, 1310 is sufficient within dozens of kilometers, and 1550 is used when approaching or exceeding 60km. Please refer to the transformation of the all-optical network in the parkCampus network and FTTH integrated cabling solution, allocate wavelengths according to sections, so you don't have to use expensive ones for the whole process; when you need to confirm the combination of wavelengths and optical fibers for each section, you can find EB-LINK technical support to check the parameters.