What is Single Mode fiber? What is Multimode fiber?

Today, the development of 4.0 technology is more and more widely applied, along with the necessity of various types of connection services such as fiber optic network, fiber optic internet, cable TV ..., which significantly increases the ability storage capacity and speed of network bandwidth.

Fiber optic network system divides into 2 types: Single Mode fiber (SM) and Multimode fiber (MM).

1. First, we find out what the word “Mode” is?

Mode is a term in network fiber cables, used in fiber optic, which means light rays. When light rays are transmitted in optical fibers, they will transmit 3 lines, corresponding to 3 different light rays.

• High Order Mode: light rays propagate in fiber optic cables with a large number of reflections. The time that light rays spread in fiber from A to B is longer than Low Order Mode light rays.

• Low Order Mode: light rays spread in fiber optic cable with a small number of reflections.

• Axial Mode: light rays spread along the central axis of the fiber optic cable. The time it takes for light to propagate in fiber from A to B is the fastest.

These 3 types of light rays have different distances when transmitted in optical fiber. At the same time, the time is different when being transmitted at the same speed to the end of the fiber. The difference in time among light rays in optical fiber is called dispersion.

2. Single Mode fiber

Single Mode fiber is the fiber in which only one type of light is spread as Axial rays, which means there is no dispersion phenomenon.

Data transmission speed with SM will be fast, far with large bandwidth.

SM works effectively on 2 wavelengths of 1310nm and 1550nm.

2.1. Characteristics of SM

• Optical transmission: a light-emitting diode or laser transmits light pulse data into fiber optic.

• Receiving: using optical sensors to turn back light pulses into data.

• Optical fiber only transmits light waves so it is not disturbed and eavesdropped during transmission.

• The attenuation is lower than that of copper cables, so it can load signals away thousands of kilometers and is chosen by many businesses.

• Installation requires certain expertise.

• Fiber optic cables and attached devices are expensive

• Used for distances more than thousands of kilometers, popular in telephone networks, cable television networks. Transmission is far away without signal amplification.

2.2. Technical characteristics of SM

• Maximum length of 5000m

• Minimum curvature radius when setting up: 20 times the outer radius of the cable

• Minimum curvature radius after setting up: 10 times the outer diameter of the cable

• Maximum traction force when installing: 2700N

• Largest traction when working: 1300N

• Maximum compression force when installing: 2000N / 100mm

• Storage temperature ranges from -30 to 60 degrees

• The temperature range for installation ranges from -5 to 50 degrees

• The working temperature range ranges from -30 to 60 degrees

2.3. Advantages of SM

• Designed optical cable with a smaller diameter than copper cable. Therefore, fiber optic cable is usually lighter than copper cable, so it is easier to transport.

• Higher load capacity, this allows you to transfer more channels through the cable.

• Low signal attenuation, less signal loss in optical fiber in copper cable.

• The light signal from the fiber does not interfere with other fibers in the same cable, making the signal quality better.

• Digital signal suitable for downloading digital information that is especially useful in computer networks.

• No fire and no electricity through, so there is no risk of fire from optical fiber.

• Use less electricity.

2.4. Application of Fiber Optic Single Mode

SM transmits signals far away with high bandwidth, so it is suitable for flexible use both outdoors and indoors.

SM is very flexible in the construction of indoor cable trays or under the drain, hanging electric poles, buried underground directly ...

This type of fiber optic cable is also suitable for installation of internal LAN network.

Currently, telecom services are widely used by people, so service providers must continuously expand their optical transmission systems to meet customers' needs.

3. Optical cable Multimode

Unlike optical cable Single Mode only transmits one type of Axial light, this Multimode optical cable can transmits all 3 types of light rays (High Order, Low Order and Axial).

Therefore, MM is influenced by dispersion phenomenon. Suitable for use in many media.

MM enables users to easily convert signals running on copper cable to optical signals and vice versa.

3.1. There are 2 types of MM

- Fiber Optic Multimode order of refractive index: This is a homogeneous core fiber, having a refractive index of n1 and a layer reflecting light around the core with n2 extract. Optical fiber Multimode order extraction rate is greatly affected by dispersion phenomenon. Therefore, bandwidth is not high and not used in network systems.

 - Optical fiber Multimode variable refractive index: Optical fiber core is combined from multiple layers of glass with different refractive index n1, n2, n3 .... The inner glass layer has a higher extract than the outer layer. The light rays will spread more slowly when the extract is high and will be faster when having a low extract.

3.2. Characteristics of optical cable Multimode

As SM, MM also has the following characteristics:

• Transmit: A light-emitting diode (LED) or laser transmits the pulsed light data into an optical cable.

• Receiving: using optical sensors to turn back light pulses into data.

• Fiber optic cable only transmits light waves (no electrical signal transmission) so it is fast, free from interference and eavesdropping.

• The attenuation is lower than that of copper cables, so it is possible to load signals away thousands of kilometers.

• Installation requires certain expertise.

• Optical fiber and attached devices are expensive compared to copper cables

3.3. Technical characteristics of optical cable Multimode

MM optical cable is currently divided into 4 categories:

OM1: 62.5 μm core diameter, using Overfilled Launch (OFL) measurement method, reaching 200/500 MHz-km bandwidth at wavelength of 850/1300 nm.

OM2: 50 μm core diameter, using Overfilled Launch (OFL) measurement method, reaching 500/500 MHz-km bandwidth at wavelength of 850/1300 nm.

OM3: 50 μm core diameter, using Effective Modal Bandwidth (EMB) measurement method, the laser source helps increase bandwidth to 2000 MHz-km, supporting 10 GE application.

OM4: 50 μm fiber core diameter, operating bandwidth more than 2 times compared to OM3, reaching 4700 MHz-km (EMB), specially designed for 10, 40 and 100 GE applications.

3.4. Application of optical cable Multimode

Due to the characteristic of light transmission according to dispersion phenomenon, MM is suitable for deploying data transmission system on fiber-optic platform.

In addition, MM ensures internal network system on fiber-optic cable used in enterprises, factories, enterprises ... effectively operated, can transmit video signals, audios, images with high speed and long distance without reducing signal quality.

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