The basic structure of the optical
fiber bare fiber is generally divided into three layers: a core, a cladding, and a coating layer.
Fiber core and cladding are made of glass of different refractive indexes, the center of a high refractive index glass core (germanium-doped silica), a low refractive index silica glass intermediate cladding (pure silica). Light at a particular angle of incidence of the incident optical fiber, total reflection (due to slightly lower than that of the cladding of the core), which can propagate in the fiber occurs between the fiber and the cladding.
The main effect of the coating layer is to protect the optical fiber from outside damage, while increasing the flexibility of the optical fiber. As previously mentioned, the core and cladding are made of glass, friable not bend, using a coating layer protects the optical fibers and the life prolonged action.
Outside the fiber will increase the non-naked outer fiber sheath layer, in addition to protect the outer sheath may be of different colors to distinguish the various fibers.
Fiber according to a transmission mode into a single mode fiber (Single Mode Fiber) and multimode fiber (Multi Mode Fiber). Light at a particular angle of incidence of the incident optical fiber, total reflection occurs between the fiber and the cladding, when the diameter is small, only one direction passes through, that is, single-mode fiber; when larger diameter optical fiber, the light may be allowed to and an incident angle incident to a plurality of propagation, this time is called a multimode fiber.
Transmission characteristics of the fiber
optical transmission has two main characteristics: loss and dispersion. Refers to loss in optical fibers is attenuation of the fiber per unit length, in units of dB / km. Fiber loss level directly affects the distance optical fiber communication system, the transmission distance or the distance relay. Fiber dispersion is due to the signal transmitted by the optical fiber component and a different frequency components carried by different modes, the different frequency components and different transmission speeds of the different pattern component, thereby causing signal distortion.
Fiber dispersion into the material dispersion, waveguide dispersion and mode dispersion. The first two signals are not due to the dispersion caused by a single frequency, since the latter signal instead of a single mode dispersion caused. Not a single mode signal causes mode dispersion. Flyer only a single mode fiber the fundamental mode, so only the material dispersion and waveguide dispersion, no modal dispersion. The multimode fiber there intermodal dispersion. Fiber dispersion not only affect the transmission capacity of a fiber, but also limits the distance relay optical fiber communication systems.
Single-mode fiber (SM Fiber)
single-mode fiber (Single Mode Fiber), light in a specific incident angle is incident on the optical fiber, total reflection occurs between the fiber and the cladding, when the diameter is small, only allows light to pass through in one direction, that is, single-mode fiber; center of the glass is very small core single mode fiber core diameter is typically 8.5 or 9.5 m, and operates at a wavelength of 1310 and 1550nm.
Multimode fiber (MM Fiber)
multimode fiber (Multi Mode Fiber), is to allow a plurality of optical fiber transmission of guided modes. Core diameter multi-mode fiber is generally 50μm / 62.5μm, since the core diameter of the multimode optical fiber is larger, may allow different modes of light transmitted on an optical fiber. Standard multimode wavelength 1300nm and 850nm, respectively, to. There is also a new standard multimode optical fiber, called WBMMF (broadband multimode optical fiber), it uses a wavelength between 850nm to 953nm.
Single-mode fiber and multimode fiber, the clad diameter are both 125μm.
Single-mode fiber or multimode fiber?
Transmission distance
smaller the diameter of a single mode fiber closer reflection, allows only one mode of light propagation so that the optical signal propagates further. Reducing the number of light reflection as the light passes through the core is generated, and generating the reduced signal attenuation further spread. Since it has no inter-modal dispersion or the dispersion is small, single-mode fiber can transmit between mold 40 km or longer distances without affecting the signal, so single-mode fiber generally used for long-distance data transmission, widely used in telecommunications companies, cable TV providers and universities and so on.
Multimode optical fiber having a large core diameter, can spread light in multiple modes. In the multi-mode transmission due to the large core size, inter-modal dispersion is large, i.e., an optical signal "diffusion" faster. When the long-distance signal transmission quality may be reduced, thus multimode fiber commonly used for short-distance, audio / video applications and local area networks (LANs), and OM3 / OM4 / OM5 multimode optical fiber may support high-speed data transmission.
Bandwidth, capacity,
bandwidth is defined as the ability to carry information. The main factors affecting the optical fiber transmission bandwidth of various degrees of dispersion, of which the most important mode dispersion, low dispersion single mode fiber, it can light a wide band transmission over long distances. Since the multi-mode fiber will have complicated problems of interference, interference, etc., so the bandwidth capacity of a single mode fiber are not as good. The latest generation of multimode fiber bandwidth OM5 to 28000MHz / km, while the single-mode fiber will have a bandwidth much larger.
Costs
if single-mode fiber has higher bandwidth and transmission distance farther, then why need multimode fiber? Cost is perhaps the key to this problem. Since single-mode fiber core diameter is too small, difficult to control the beam delivery, we need a laser as a light source thereof. Optical very expensive because, so the cost of single mode fiber will be higher than the cost of a multi-mode fiber optic cable. The fact that most data centers to promote the use of multimode fiber to save costs.
Select which mode fiber, more depends on the application needs. HYC can provide various types of fiber jumpers. HYC (HYC) is a national high-tech enterprises a focus on the basis of passive optical communication device development, manufacturing, sales and service in one. Main products: the three core optical fiber connector (High Density Data Center optical connector), wavelength division multiplexer, an optical splitter and other optical passive elemental device, widely used in fiber to the home, 4G / 5G mobile communications, Internet data centers, defense and communications.