What are the differences between single-mode fiber and multimode fiber? There are two types of fiber optic cabling—multimode and single-mode. Multimode cabling is shorter in length than singlemode cabling, so singlemode is suitable for outdoor long-distance fiber optic applications, while multimode is the main choice for data center and interior building applications.
However, due to the inherent high bandwidth capabilities of single-mode fiber and its growing popularity for shorter distance applications, more and more technicians are faced with the problem of installing both single-mode and multimode fiber. But we found that not everyone understands the technical differences between the two fiber types. Let's take a deeper look next.
Single Mode Fiber and Multimode Fiber
What is the pattern?
In the field of fiber optic data transmission, the term "mode" is used to describe the way light signals propagate within the glass core of an optical fiber—that is, a mode is the path that light travels. Therefore, in single-mode fiber, light travels along one path; in multimode fiber, light travels in multiple paths.
You can imagine this: when you slide down from the top of the water slide, you are constantly bouncing and sliding between the baffles on both sides of the slide. Every angle on the way down is a pattern. Light propagates within the core of a multimode fiber in the same manner as described above. Light hits the glass at an angle and is reflected back while traveling the length of the core. Why isn't light coming out of the core? First, the light hits the glass at a small angle, causing the glass to reflect the light like a mirror. Second, there is a cladding outside the core. To keep the light inside the core, the cladding has different refractive index properties, a technical parameter that determines how much light is reflected or refracted when it hits the material.
In single-mode fiber, by contrast, light travels in a straight line, and because the core size of single-mode fiber is smaller (about one-tenth the size of the core of multimode fiber), the light does not bounce around.
Bandwidth Limit Latency
Why does single-mode fiber support higher bandwidth and longer distances? Sending light in a single mode eliminates differential mode delay (DMD), which is the main factor limiting the bandwidth of multimode fiber.
When propagating in multiple modes in a multimode fiber, some light travels along the center of the fiber, while other light travels along a path closer to the cladding of the core. The propagating modes at the outer edges are called higher-order modes, and the propagating modes closer to the center of the core are called lower-order modes. The propagation speeds of the high-order and low-order modes are different, and DMD is the difference in propagation time.
The smaller the DMD, the less the light pulse spreads over time and the higher the bandwidth. The greater the difference in timing between pulses, the receiver may not be able to correctly distinguish between pulses. DMD is directly related to distance—it increases with fiber length. This is why multimode fiber has much shorter distance requirements than single-mode fiber, which can be up to 500 meters long, while single-mode fiber can be up to 10 kilometers long.
Fiber defects are also a cause of DMD, and fiber manufacturers have learned to limit DMD by carefully optimizing the fiber refractive index profile. Mode refraction not only occurs at the junction of the core and the cladding, the multimode fiber adopts a graded refractive index distribution, and the refractive index from the center of the core to the boundary between the core and the cladding changes continuously. This creates a parabolic (i.e., symmetrical curve) path, causing lower-order modes to travel slower over shorter distances closer to the fiber core, and higher-order modes to travel faster over longer distances closer to the edge of the core. This minimizes the time delay between pulses, resulting in lower DMD and higher bandwidth.
more significant difference
More notable differences between multimode and singlemode include cable color, light source, and testing. Singlemode is almost always yellow, while multimode is usually light green. Different types of multimodes may also have different colors - OM3 is almost always light green, OM4 multimode sometimes comes in a pink called Erika Violet (Erika Violet) to help distinguish it from OM3, while the latest generation of multimode Mode fiber OM5 is gray-green.
Another key point of difference is the cost associated with the light source and delivery equipment. Single-mode fiber requires a laser source with a narrow spectral width, so the cost of the receiver is higher. Compared with multimode fiber optic cable, the price of single mode fiber optic cable itself is lower, but the cost of single mode fiber optic receiver is 1.5 to 4 times that of multimode receiver.
