How to Choose the Right Wavelength for Your SFP Module

1. Module Description

2. The difference between single-mode optical modules and multi-mode optical modules

3. Selection of SFP modules

1. Module Description

Optical module, also known as fiber module, is a hot-swappable module that integrates optical transceiver. Through optical fiber connection, the signal electrical/optical-optical/electrical conversion is completed. It can support transmission at different distances and different rates.

BiDi optical module: Data transmission can be achieved with only one optical fiber. The single-fiber bidirectional optical module is different from the general optical module with two ports (TX transmitter and RX receiver port). It has only one optical fiber port. It uses WDM technology to send and receive different central wavelengths in two directions, thereby realizing bidirectional transmission of optical signals in optical fiber. BiDi optical modules must be used in pairs.

Colored light: The laser emitted by the optical module fluctuates in a very small range near a certain central wavelength, can be directly connected to the multiplexing device, and has a standard wavelength. This type of optical module is called a colored light module.

Wavelength: refers to the distance that the wave propagates in one vibration period. That is, along the propagation direction of the wave, the distance between two adjacent points with a vibration phase difference of 2π. The wavelength λ is equal to the product of the wave speed u and the period T, that is, λ=uT. Waves of the same frequency propagate at different speeds in different media, so the wavelengths are also different.

2. The difference between single-mode optical modules and multi-mode optical modules

Optical modules are divided into single-mode optical modules and multi-mode optical modules according to the different types of applicable optical fibers. The optical fiber wavelength of single-mode optical modules is 1310nm, 1550nm and WDM wavelength, while the optical fiber wavelength of multi-mode optical modules is 850nm or 1310nm. Currently, the main wavelength is 850nm. Single-mode and multi-mode in single-mode optical modules and multi-mode optical modules refer to the transmission mode of optical fiber in optical modules, so they need to be used with single-mode optical fiber and multi-mode optical fiber respectively. The line diameter of single-mode optical fiber is 9/125μm, and the line diameter of multi-mode optical fiber is 50/125μm or 62.5/125μm.

3. Selection of SFP modules

The wavelength of an optical module refers to the optical band used for optical signal transmission, and its unit is nanometer (nm). Currently, 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. Optical modules with a wavelength of 850nm are usually used with multimode optical fibers and are mostly used for short-distance transmission; optical modules with wavelengths of 1310nm and other wavelengths are usually used with single-mode optical fibers and are mostly used for medium and long-distance transmission. It should be noted that the earlier low-speed optical modules with a wavelength of 1310nm (i.e., SFP optical modules below 1000M) can also be used with multimode optical fibers, with a maximum transmission distance of 2km.