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Views: 399 Author: Addams Publish Time: 2025-03-27 Origin: Site
1. Detailed explanation of fiber loss
2. Detailed explanation of loss at different wavelengths
3. Detailed explanation of link budget of optical module
3.1 Key factors affecting link budget
3.2 Solution to insufficient link budget
As the core component of optical communication system, the performance of optical module is directly related to the reliability and distance of data transmission. In practical applications, optical signals will experience various losses from the transmitter to the receiver. These losses need to be reasonably designed and arranged to meet the link budget of optical module. This article will analyze in detail the fiber loss, the influence of different wavelengths and the key elements of link budget of optical module.
Fiber loss is the energy attenuation caused by material, structure and environmental factors during the transmission of optical signals, mainly including the following categories:
Impurities (such as hydroxide ions) in optical fiber materials absorb light energy, especially forming a "water peak" near 1380nm. Modern low water peak optical fiber (such as G.652.D) has significantly reduced this loss.
The optical fiber is excessively bent during use, resulting in changes in the total reflection path of light and optical power loss. When using it, avoid excessive bending of the optical fiber, and use bend-insensitive optical fiber when wiring in a narrow environment.
Caused by poor fusion of fiber optic connectors (such as LC, SC) or fusion points. The loss of fiber optic connectors is about 0.3dB, and the loss of fiber optic fusion points is about 0.1dB. In wiring, the number of fiber optic connectors and fusion points should be reduced as much as possible, which can significantly reduce the connection loss of optical fibers.
The working wavelength of the optical module directly affects the fiber loss and transmission distance. The following are the loss characteristics of common wavelengths:
Wavelength（nm） | Applicable fiber type | Typical loss（dB/km） | Main application scenarios |
850 | Multimode Fiber（OM1-OM5） | 2.5-3.5 | Short-distance data center (within 100m, such as 100G SR4) |
1310 | Single mode fiber（G.652） | 0.3-0.4 | Metropolitan area network, enterprise network (10-40km) |
1550 | Single mode fiber（G.652/G.655） | 0.2-0.25 | Long-distance backbone network (over 100 km, with EDFA) |
850nm wavelength: mainly used for multimode fiber, high loss, low optical module hardware cost, suitable for short-distance transmission, can tolerate high loss disadvantages during short-distance transmission. (Such as inside the computer room).
1310nm wavelength: Close to the zero dispersion point of G.652 optical fiber, suitable for medium and short distance transmission of uncompensated 10G/25G systems, low cost, and the first choice for 40KM transmission.
1550nm wavelength: Lower loss and compatible with EDFA (erbium-doped fiber amplifier), it is the first choice for long-distance DWDM systems, but there is a dispersion problem, and dispersion compensation should be considered during transmission.
Link budget is the core indicator for evaluating whether the optical module can meet the transmission requirements. The calculation formula is:
Link budget = P transmission − P reception − system margin
Where: P transmission: optical module transmission power (dBm)
Preception: optical module receiving sensitivity (dBm)
System margin: 3~5 dB is usually reserved to deal with uncertain factors such as aging and temperature fluctuations. It needs to be considered in DWDM systems and can be omitted in conventional systems.
Fiber quality and type: Because the nominal transmission distance of optical modules is measured under laboratory conditions and standard optical fibers. However, in the actual working environment, the quality of optical fiber varies, and the link loss will not be consistent with the nominal value. The actual transmission distance depends on the value of the optical fiber test report.
Number of connectors and splicing points: For each additional connector, the loss increases by 0.2dB-0.3 dB, and for each additional splicing point, the loss increases by 0.1dB-0.3dB. The number of connectors and splicing points also directly affects the link budget of the optical fiber.
Upgrade optical modules: Choose high sensitivity (such as Coherent reception) or high power modules.
Reduce connection points: Use pre-terminated optical cables to reduce the number of connectors.
Add optical amplifiers: Insert EDFA in long-distance links
The link loss calculation of optical modules is the most important task in the design of optical communication systems. It directly determines whether the optical modules can be used normally. It needs to be judged comprehensively based on multiple parameters to maximize the performance of optical modules and ensure the efficient and stable operation of the network.
