August 20, 2023
There are many types of optical modules on market
Depending on package type: SFP, XFP, SFP+...
Speed classification: 155M, 1.25G, 10G, 40G...
Wavelength classification: 850nm, 1310nm, 1550nm, CWDM...
Depending on mode: singlemode, multimode...
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How to choose an optical module?
In order to understand optical module more clearly, editor visited company's transmission bosses, and finally figured out easiest method for choosing an optical module for everyone. It only takes two steps to select the right optical module!
Before choosing an optical module, we must first know what it is used for.
The role of optical module is photoelectric conversion, which is used as a transmission medium between switch and device. The transmitting side converts electrical signal into an optical signal. After transmission over optical fiber, receiving side converts optical signal into an electrical signal.
Since optical module is related to transmission of optical signals, we must think about what kind of interference will occur when transmitting optical signals. I don't know if you still remember something from school knowledge in physics. The famous double-slit interference experiment in history of physics has been confirmedWhen monochromatic light passes through a double slit, light and shadow interference of a strip on the screen occurs.
▲Interference experiment with two slits in history of physics
The experiment shows that light is also a kind of electromagnetic wave, having character of a wave, because it is a wave, there will be a problem of coincident frequency interference. , in a broader sense, if we are in physical world. Using same wavelength of light in a channel to receive and send signals will result in inevitable co-channel interference that will seriously affect communications.
To solve problem of interference of same frequency of same light wave in same channel, we have two methods:
1. Transmission of two different wavelengths of light in one channel
One is used to send signals and other is used to receive, which solves problem of co-channel interference. The optical module using one optical fiber bi-directional transmission technology is bi-directional over a single fiber. This module must be used in pairs. The biggest advantage is saving of optical fiber resources.
2. Transmission of light of one wavelength in two channels
One physical channel is used to send signals and one physical channel is used to receive signals, which can also solve problem of co-channel interference. The optical module using this technology is bi-directional with dual fiber. The optical module has two ports: TX is a transmitting port and RX is a receiving port. Compared to a single fiber module, it should occupy one more fiber resource.
Understanding difference between single-fiber and dual-fiber connections, let's understand differences between single-mode and multi-mode.
●Single Mode Fiber (SMF)
The transmission distance is long, more than 100 km, and bandwidth is high. It is mainly used for outdoor long distance transmission.
Multimode Fiber (MMF)
The transmission distance is short, and multimode fiber can support transmission distance up to 2km (at 155M speed), which is mainly used for short distance transmission.
Do you understand above knowledge? !
It is very easy to choose an optical module after understanding above knowledge~
It only takes two steps to select an optical module!
1. Singlemode/Multimode
1. In scenario where distance between front and rear ends is more than 2 km, only single-mode optical modules can be used, since maximum transmission distance of multi-mode optical modules is 2 km (at 155M speed).
2. There is no clear difference between singlemode and multimode, it is better to choose most suitable for scene.
Distance is most direct reference standard for selecting singlemode and dualmode!
2. Single/double fiber
1. Single fiber models (whether multimode or single mode) must be used in pairs, and front and rear models cannot be same because transmit and receive wavelengths are different;
2. The model of dual fiber (whether it is multimode or single mode) does not need to distinguish between model of front end and back end, and model is same. However, dual fiber optical module must be cross-connected during use!
3. By default, dual fiber optical module is preferred. The dual fiber model is not easy to make a mistake in implementation of project, and external and internal models are consistent for easy management and maintenance.
It is recommended to use dual-fiber optical modules when fiber resources are sufficient,
Single fiber optical modules are used when fiber resources are limited and economic considerations are taken into account.
1. Single-fiber and dual-fiber optical modules have nothing to do with single-mode or multi-mode. types of single fiber and dual fiber. The fundamental purpose of single fiber is to solve problem of bidirectional transmission and reception of data in one channel. A popular point is to save optical fiber.
2. Single fiber optical modules must be used in pairs, and front and rear models cannot be same.
3. The optical module type must match optical fiber type. Single-mode optical fiber must be equipped with a single-mode optical module, and multi-mode optical fiber must be equipped with a multi-mode optical module.
4.SFP stands for hot-swappable small optical transceiver module with a standard transmission rate of 155M/1.25G; SFP+ stands for high-speed SFP module with a standard 10 G transmission rate. The difference between two modules is fundamental difference in transmission speed.
