Optical Fiber Type – Transmission Mode And Standards

September 28, 2021

What Is Optical Fiber

Optical fiber is made of silica glass through a complicated process. It is a highly transparent glass filament as thin as hair. The optical fiber transmit optical signal instead of electrical signal, so it is also called light-guide fiber.

As the transmission medium for optical communications, optical fiber has high efficiency, great capacity and strong anti-interference for long distance communications.

Optical Fiber Type

Optical fiber is divided into SM fiber (Single Mode Fiber) and MM fiber (Multi Mode Fiber) according to the transmission mode.

Single Mode Fiber (SMF)

After the light enters the fiber at a specific angle of incidence, and full emission occurs between the fiber and the cladding. When the diameter is small, the light is only allowed to pass through one direction. This type of transmission mode is single mode.

The central glass core of the SMF is very thin, it corresponds to the single mode ferrule. The core diameter is generally 8.5 or 9.5μm, and it works at 1310 and 1550nm wavelengths.

Multimode Fiber (MMF)

Multimode fiber (MMF) is a fiber that allows multiple guided mode transmission. The core diameter of a multimode fiber is generally 50μm/62.5μm, which corresponds to a multimode ferrule. Since the core diameter of a multimode fiber is larger, it can allow different modes of light to be transmitted on a single fiber. The standard wavelengths of multimode are 850nm and 1300nm respectively.

There is also a new multimode fiber standard called WBMMF (Wideband Multimode Fiber), which uses wavelengths between 850nm and 953nm. Both single-mode fiber and multi-mode fiber have a cladding diameter of 125μm.

ITU Standard

According to the ITU, there are 7 kinds of fibers: G651, G652, G653, G654, G655, G656, G657. Among which G652 and G657 are commonly used.


G652 fiber is the most widely used optical fiber in the metropolitan area network. It is a standard single mode fiber with a zero-point dispersion of 1300nm. G652 fiber is subdivided into 4 types: G652A, G652B, G652C and G652D. The main difference lies in PMD (Polarization Mode Dispersion). Among them, G652D is more commonly used. Because of its low fiber dispersion at 1300nm operating wavelength, the transmission distance of the system is only limited by loss.


G657 is a bending loss-insensitive fiber, and is the most commonly used fiber optic cable for FTTH home network access. It is widely used because of its better performance, but the cost is higher than G652D.

G651 is a multi-mode fiber, mainly used in multi-tenant, residential buildings, and enterprise networks in FTTH networks. Its most advantage is that it has bending radius that is half that of G652 fiber. It is suitable for indoor laying and is generally used in FTTH environments.

ANSI/TIA Standard

In ANSI/TIA-568.3-D, TIA adopts the optical fiber nomenclature in the international standard ISO/IEC 11801. Multimode fiber has the prefix “OM”, and single mode fiber has the prefix “OS”.

OS1 and OS2

Both OS1 and OS2 are single-mode fibers. OS1 is the normal single-mode fiber used earlier and OS2 are the common single mode optical fiber currently in use. OS2 is a low-water peak optical fiber.

OM1, OM2, OM3, OM4, OM5

OM1 is 62.5/125μm and OM2 is 50/125μm. OM3 is a 50μm core diameter multimode fiber optimized by 850nm laser. Using 850nm VCSEL, the fiber transmission distance can reach 300m in 10Gb/s Ethernet.

OM4 is an upgraded version of OM3. OM4 multimode fiber optimizes the differential mode delay (DMD) generated by OM3 multimode fiber during high-speed transmission. So the transmission distance is greatly improved, and the fiber transmission distance can reach 550m;

OM5 fiber patch cord is a new standard for fiber patch cords defined by TIA and IEC. The fiber diameter is 50/125μm. Compared with OM3 and OM4 fiber patch cords, OM5 fiber patch cords can be used for higher bandwidth applications. The bandwidth and maximum distance for different levels of transmission are different.

Fiber Optic Cable

The optical fiber is drawn from pure quartz with a special process into a glass tube thinner than a hair with a few dielectrics in the middle. Its texture is brittle and fragile, so an additional protective layer is needed. Fiber optic cable is optical fiber combined with plastic protective tube, strength member and a cable sheath.

Fiber Optic Cable Types

There are many types of fiber optic cables, and there are many categories. They are mainly classified as follows:

  • Sheath material: LSZH, PVC, PE, TPU
  • Cable outer diameter: φ0.9, φ2.0, φ3.0……
  • Fiber mode field: single mode (9/125μm), multimode (50/125μm, 62.5/125μm)
  • Cable color: single mode is generally yellow, multimode is generally orange (OM1/OM2), light blue (OM3), OM4 (violet), OM5 (lime green).
  • Cable structure: Simplex fiber optic cable, Duplex fiber optic cable, central loose tube and stranded multi loose tube core, double sheath, mini multi-core, breakout optical cable, FTTH cable and so on
  • Optical fiber: Corning, YOFC, Fujikura, Sumitomo, OFS, etc.

Optical Fiber or Fiber Optic Cable

Fiber optic cable include optical fibers, and optical fibers are glass fibers in fiber optic cable. Broadly speaking, optical fibers and fiber cable are all transmission media. But in a strict sense, the two are different products.

The difference between optical fiber and fiber optic cable is that optical fiber is a thin and soft medium that transmits light beams. Most optical fibers must be covered by several layers of protective structures before put into application. And the covered cables are called fiber optic cables. Therefore, the optical fiber is the core part of the fiber optic cable, and the optical fiber constitutes the fiber cable through the protection of some components and the auxiliary protective layer.

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Tony Lau is technical manager and co-founder at HOC. He loves writing about content optical fiber communications, specializes in fiber optic cables, FTTH turnkey solutions, ADSS cable, and ODN networks.

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