SM Fiber and MM Fiber

When the fiber core is so small that only light ray at 0° incident angle can stably pass through the length of fiber without much loss, this kind of 

fiber is called single mode fiber (SMF). The basic requirement for single mode fiber is that the core be small enough to restrict transmission to 

a single mode. This lowest-order mode can propagate in all fibers with smaller cores.

Multi mode fiber (MMF), is that that carry more than one mode are called multimode fibers.by comparison, is manufactured with core 

diameters as small as 50um and as large as hundreds of microns. And there are two types of multimode fibers. One type is step-index 

multimode fiber and the other type is graded-index multimode fiber.

The differences between single mode and multimode fiber mainly lies in fiber core diameter, wavelength & light source, bandwidth, color 

sheath, distance and cost.

Core Diameter

The most common type of single mode fiber has a core diameter of 8 to 10 μm and is designed for use in the near infrared (the most common 

are 1310nm and 1550nm). Please note that the mode structure depends on the wavelength of the light used, so that this fiber actually supports 

a small number of additional modes at visible wavelengths.

Multimode fiber core diameter is 50 µm and 62.5 µm typically, which enables it to have higher "light gathering" ability and simplify connections. 

The cladding diameter of single mode and multimode fiber is 125 µm.

Wavelength & Light Source

Due to the large core size of multimode fiber, some low-cost light sources like LEDs (light-emitting diodes) and VCSELs (vertical cavity surface-

emitting lasers) that works at the 850nm and 1300nm wavelength are used in multimode fiber cables. While the single mode fiber often uses a 

laser or laser diodes to produce light injected into the cable. And the commonly used single mode fiber wavelength is 1310 nm and 1550 nm.

Bandwidth

Multimode fiber bandwidth is limited by its light mode and the maximum bandwidth at present is 28000MHz*km of OM5 fiber. While single 

mode fiber bandwidth is unlimited theoretically because it allows only one light mode to pass through at a time.

Color

According to the TIA-598C standard definition, for non-military applications, single mode cable is coated with yellow outer sheath, and 

multimode fiber is coated with orange or aqua jacket.

Distance

Single mode fiber is suitable for long-distance applications, while multimode optical fiber is designed for short-distance runs.

Cost

Compared to single-mode transceivers, the price of multimode transceivers is nearly two or three times lower.