Optical fiber is the most popular ways for transmitting light at both ends, and it is widely used in telecommunications. Optical fiber is a flexible transparent fiber which is made of extruded glass or plastic. Optical fiber has longer transmission distance and higher bandwidth than wired cable. An optical fiber is usually composed of three components: a transparent core, a transparent cladding material and a coating layer.

 

Optical fibers can be divided into two kinds generally, they are MMF (multi-mode fiber) which can support multiple propagation paths or horizontal modes and SMF (single mode fiber) which supports a single mode. Both multi-mode fiber and single mode fiber are can be support to MPO Cable. And AOC cables usually use Multi-mode fiber. 

The main differences between SMF and MMF are as below:

1. Transmission Distance

SMF is used for long-distance transmission. SMF (single-mode fiber) is an optical fiber that directly transmits optical signals in the horizontal. Single-mode fiber runs at a movement rate of 100M/s or 1 G/s, and the transmission distance can reach at least 5 kilometers. 

Multimode fiber (MMF) is mainly used for short-distance telecommunication, such as in buildings or data center. Transmission speed is 100M/s, the transmission distance can reach 2km (100BASE-FX), 1 G/s can reach 1000m, and 10 G/s can reach 550m. 

 

2. Core Diameter

Typical single-mode fibers have core diameters of 8~10 µm, while multi-mode fibers has a larger diameter, usually 50 or 62.5 µm core diameter. The layer diameters are all 125 µm.

 

3. Light source

Usually lasers and LEDs are used as light sources. The laser light source is obviously more expensive than the LED light source because the laser light produces a near-single mode of light, which can be precisely controlled and has a high power. Laser light source is usually used for single-mode. LED light which are mostly used in multi-mode fiber is more scattered and in many mode.

 

4. Bandwidth

Single-mode fiber also exhibits modal dispersion caused by multiple spatial modes, but the modal dispersion is smaller than that of multi-mode fiber. Single-mode fiber has a higher bandwidth than multi-mode fiber.

5. Modal dispersion

LED light sources are used in multi-mode fibers to create a series of wavelengths that propagate at different speeds. This will cause mode dispersion, which limits the effective transmission distance of multi-mode fiber. In contrast, a laser light which is used to drive a single-mode fiber produces a single wavelength of light. Therefore, its modal dispersion is much smaller than that of multi-mode fiber.

6. Wavelength

Single-mode fiber is an optical fiber with only one strand (two strands in most applications) of glass fiber, with a core diameter of 8μm~10μm, and only one transmission mode. Due to the relatively narrow core diameter, single-mode fibers can only transmit optical signals with a wavelength of 1310nm or 1550nm. Multi-mode fiber work with wavelength of 850nm. 

7. Price

MMF can support multiple optical modes, and its price is higher than SMF. But in terms of equipment, since single-mode fiber usually uses laser light, single-mode fiber equipment is more expensive than multi-mode fiber equipment. Therefore, the cost of using multi-mode fiber is much less than the cost of using single-mode fiber. MMF is usually used in LAN. While transmission distance is over 5km, SMF will be the better way.