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Single-mode Fiber VS Multi-mode Fiber

Views: 132     Author: Site Editor     Publish Time: 2020-05-07      Origin: Site


Earlier we learned about the use and purchase points of fiber cords. In this article, we will be familiar with two categories of fiber cords: single-mode fiber and multi-mode fiber. Optical fiber cords can be divided into common single-mode and multi-mode cords for silicon-based optical fibers according to different transmission media, as well as other optical fiber cords that use plastic as a transmission medium.

 

Single-mode Fiber: The general fiber cord is indicated by yellow, the connector and protective sleeve are blue; the transmission distance is longer.

 

Multi-mode Fiber: The general fiber cord is indicated in orange, some are indicated in gray, and connectors and protective sleeves are beige or black; transmission distance is short.

 

In short, fiber optic cabling is divided into two types multi-mode and single-mode. The following mainly describes the differences between the two in different aspects.



Mode difference

 

In the field of optical fiber data transmission, the term "mode" is used to describe the propagation of optical signals within the fiber optic glass core. That is, the mode is the propagation path of light. Therefore, in single-mode light, light travels along one path; in multi-mode fiber, light travels in multiple paths. In a single-mode fiber, light travels in a straight line, because the core size of a single-mode fiber is small (about one-tenth of the core of a multi-mode fiber), and light does not bounce.

 


Bandwidth limit delay

 

Why does single-mode fiber support higher bandwidth and longer distance? Sending light in a single mode can eliminate differential mode delay (DMD), which is the main factor limiting the bandwidth of multi-mode fiber. When propagating in multiple modes in a multi-mode fiber, some light moves along the center of the fiber, while other light moves along a path near the core cladding. The propagation mode at the outer edge is called a high-order mode, and the propagation mode near the center of the core is called a low-order mode. High-order and low-order modes have different propagation speeds, and DMD is the difference in propagation time.

 

If the DMD is smaller, the light pulse will spread less over time and the bandwidth will be higher. The greater the time difference between pulses, the receiver may not be able to distinguish the pulses correctly. DMD is directly related to distance—increasing as the fiber length increases. This is why the distance requirement of multi-mode fiber is much shorter than that of single mode fiber. Multi-mode fiber has a maximum length of 500 meters, while the length of single mode fiber can reach 10 kilometers. Fiber defects are also one of the causes of DMD. Fiber manufacturers have mastered the limitation of DMD by carefully optimizing the refractive index distribution of the fiber.

 


Cable color, light source and test differences

 

Single mode is almost all yellow, while multi-mode is usually light green. Different types of multi-mode may also have different colors. For example, OM3 is almost all light green. OM4 multi-mode sometimes uses a pink called Erika Violet to help distinguish it from OM3, while the new generation of multi-mode fiber OM5 is gray green.

 

Another key difference is the cost associated with light sources and transmission equipment. Single-mode fiber requires a laser light source with a narrow spectral width, so the cost of the receiver is higher. Compared with multi-mode optical cables, the price of single-mode optical cables is lower, but the cost of single-mode optical fiber receivers is 1.5 to 4 times that of multi-mode optical receivers.

 

For multi-mode and single-mode test methods, it is important to understand that these two fiber types cannot be mixed, and the access line must match the type of fiber being tested. Testing multi-mode fiber also requires an annular flux (EF) test to indicate how much light is being injected into the cable under test. EF testing limits the number of launch modes to reduce variability and achieve accurate and repeatable test results.

 

In summary, theoptical fiber wiring is divided into two types multi-mode and single-mode. The significant difference between the two is in mode, bandwidth limit delay and cable color, light source and test differences.

 

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