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Explanation of Optical Module Parameters
Knowledge Base + 2024.01.30

When we receive an optical module, we can observe some basic parameters of the optical module from the label, such as the encapsulation form, rate, wavelength, and transmission distance. Considering that some newcomers to optical modules may not understand the letters on the optical module or the specific meanings of the parameters on the optical module, the following is a brief introduction to these contents and some issues regarding how to choose optical modules. The core technical parameters of optical modules include: transmission rate, encapsulation, transmit optical power, receive sensitivity, transmission distance, center wavelength, optical interface type, operating temperature, maximum power consumption, etc. Let's introduce them one by one.

Transmission Rate: The transmission rate of the optical module refers to the number of bits transmitted per second, expressed in Mb/s or Gb/s. Optical modules can be divided into:

100Mbps optical modules: Usually labeled as 155M, 100Base, FE, etc.

       ▶ 1Gbps optical modules: Common representations include 1G, 1.25G, 1000Base, GE, etc.

        10Gbps optical modules: Represented as 10G, 10GBase, XG, etc.

        25Gbps optical modules: Represented as 25G, 25GBase.

        40Gbps optical modules: Represented as 40G, 40GBase.

        100Gbps optical modules: Represented as 100G, 100GBase.

        400Gbps optical modules: Represented as 400G, 400GBase.

Encapsulation: Encapsulation of optical modules refers to a standard, also understood as the physical form of the optical module. The most common encapsulations for 100Mbps and 1Gbps optical modules are SFP. For 10Gbps modules, the encapsulation is usually SFP+, while for 25Gbps/40Gbps/100Gbps/400Gbps, the encapsulations are SFP28/QSFP/QSFP28/QSFP-DD respectively.

Transmit Optical Power and Receive Sensitivity: Transmit optical power refers to the output optical power of the light source at the transmission end of the optical module. Receive sensitivity refers to the minimum received optical power of the optical module under certain rates and bit error rate conditions. The units for transmit optical power and receive sensitivity are both dBm. Generally, the higher the rate, the poorer the receive sensitivity, meaning a larger minimum received optical power requirement and higher demands for the receiving end devices of optical modules.

Transmission Distance: Transmission distance of optical modules is categorized into short, medium, and long ranges. Short-distance transmission usually refers to distances below 2km, medium distances range from 10-20km, and distances greater than or equal to 30km are considered long-distance transmissions.

Center Wavelength: The center wavelength of optical modules refers to the range of light waves utilized during the transmission of optical signals, measured in nanometers (nm). Commonly used wavelengths include 850nm, 1310nm, and 1550nm, as well as the CWDM wavelengths ranging from 1270nm to 1610nm and the DWDM wavelengths ranging from 1525nm to 1565nm or 1570nm to 1610nm. Typically, for short-distance transmissions within 500m, the 850nm wavelength is commonly used. For distances ranging from 500m to 20km, the 1310nm wavelength is often employed. For distances between 20km and 40km, either 1310nm or 1550nm wavelengths can be selected. Distances greater than or equal to 40km typically utilize the 1550nm wavelength.

Optical Interface Type: Common optical module interface types include dual LC interface, single LC interface, SC interface, and MPO interface. Dual LC interfaces are suitable for dual-fiber optical modules, while single LC interfaces and SC interfaces are commonly used for single-fiber bidirectional optical modules. MPO interfaces are often used for 40Gbps, 100Gbps, and other dual-fiber optical modules. There is also the issue of distinguishing between the transmit and receive optical ports of optical modules. For dual-fiber optical modules, the module generally indicates: Rx/Tx, or arrows indicating the direction (▼/▲), where Rx&▼ represents the receiving end, and Tx&▲ represents the transmitting end. One end's Tx must connect to the other end's Rx, otherwise, the two ends cannot communicate. For single-mode single-fiber optical modules, they are typically labeled as A-end and B-end (must be used in pairs), as they both transmit and receive signals over one fiber.

Operating Temperature Range: The operating temperature of optical modules significantly affects their performance. If the operating temperature of the optical module is too high or too low, it may affect the normal use of the module or even its lifespan. The operating temperature ranges of optical modules are divided into three types: commercial grade temperature (0-70°C), extended temperature range (-20-85°C), and industrial grade temperature (-40-85°C). Industrial-grade optical modules are suitable for use in outdoor, remote mountainous areas, tunnels, and other environments where temperatures vary greatly. Industrial-grade optical modules incorporate temperature compensation software to ensure stable power supply to the module. When the temperature changes, the temperature compensation software adjusts accordingly.

Maximum Power Consumption: The maximum power consumption refers to the maximum electrical power consumed by the optical module per second during operation. In the current context of energy conservation, carbon neutrality, and green environmental protection, as one of the important communication components, optical modules are widely used, and low-power optical modules can effectively reduce data center costs.

In summary, we should select the appropriate optical module based on the actual usage scenario, including the operating environment, power consumption, parameters of the opposite-end optical module, and performance of the optical module. Some users may struggle with whether to use original equipment manufacturer (OEM) modules or compatible modules. In fact, there is no need to worry too much. If the budget is sufficient, OEM modules can be chosen, but if cost considerations are important, compatible optical modules are a good option. Currently, compatible manufacturers can very well adapt to various brands of optical modules, and the prices are much cheaper compared to OEM modules, with assured quality.

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