Dispersion And Types of Multimode Fiber

Multimode optical fiber dispersion is the time of the different modes in a multimode optical fiber transmission difference generated, because there are many mode of multimode fiber, the resulting dispersion is more complicated. So multi-mode optical fiber is not used as a dispersion single-mode fiber to characterize the dispersion properties of the coefficient. Multimode Fiber Cables with dispersion characteristic pattern "Bandwidth " to indicate that the " bandwidth" of the multi-mode fiber, it means the ability of a transmission signal in units of MHz * Km, refers to the product of speed and distance , low rate the transmission distance and high- speed transmission distance is near . With a "Bandwidth " associated with the type of light source used for multimode fiber. Different types of light sources with the same optical fibers obtained by the test "Bandwidth " is different, the bandwidth of a multimode optical fiber with the general terms of use. Different types of light emission characteristics of the injection for reasons multimode fiber mode excitation type : LED can excite all modes, this light is called test OFL (overfilled launch) testing. FP and VCSEL lasers with multi-mode fiber can stimulate injection -mode optical fiber portion , such tests are called UFL (underfilled launch) Test This test out several light sources "bandwidth " is different .

Species historically commercialization of multimode fiber is very large, there are different classification methods, the current standard is more popular in the beginning of 2002 classification ISO / IEC 11801 enacted.

ISO / IEC standard classification simplifies multi-mode fiber. The old 62.5um fiber referred to as OM1 fiber, 50um fiber referred to as OM2 fiber. Emerging mode dispersion optimized fiber were divided by the bandwidth of the OM3 and OM4 fiber. Both fiber bandwidth in the EMB (Effective Modal Bandwidth) conditions were greater than 2000MHz * K and 4700MHz * Km, corresponding to the conditions of use that source using 850nm VCSEL.

Common 62.5/125μm graded-index OM1 Multimode Fiber is the iec-60793-2 fiber optic products specification alb type. It was born in the late -index multimode fiber 50/125μm gradient. As the core diameter and a numerical aperture of the fiber 62.5/125μm larger , with a strong light gathering capability and bending characteristics , especially in the 20th century, before the mid-1990s , the lower the rate of the LAN , less demanding on the fiber bandwidth thus making this fiber to obtain the most widely used, becomes 20 years between the mid- 1980s to the mid -1990s mainstream products in most countries data communications fiber market. 62.5/125μm graded-index multimode fiber is the first to be adopted as the United States a number of industry standard multimode fiber , such as interior wiring systems standards at & t 's ; American Electronics Industry Association (eta) LAN standards ; American National Standards institute (ansi) of 100 mb / s token Ring standards ; ibm token ring standards. Typically 62.5/125μm graded-index multimode fiber bandwidth is for 200 ~ 400 mhz · km, at 1 gb / s rate , 850 nm wavelength transmission 300 m, 1 300 nm wavelength transmission 550m. Full power injection (OFL) bandwidth of 200/500 MHz.km @ 850/1300 nm.

Common 50/125μm graded-index OM2 Multimode Fiber is the iec-60793-2 fiber optic products specification ala type. Historically, in order to reduce system costs as much as possible LAN, commonly used inexpensive led as the light source, rather than expensive ld. Because of the low output power led, ld much larger than the divergence angle connector loss, and 50/125μm multimode fiber core diameter and numerical aperture are relatively small, it is not conducive to the efficient coupling and led, as the core diameter and numerical aperture the 62.5/125μm (class alb) fiber enables more light power coupled into the fiber link to, therefore, 50/125μm graded-index multimode fiber in the mid-1990s, had not been widely used, and is mainly used as a data communication standard in Japan and Germany.

At a rate of 10Gbps, 850nm VCSEL can only guarantee the transmission distance of about 30m in the worst OM1 fiber, in the latest OM4 fiber transmission distance of 550m of guarantees. 850nm VCSEL have a high luminous efficiency, low threshold, high modulation rates can be easily coupled and so on. The main source is the use of multimode optical fiber, OM3, OM4 fiber is mainly optimized for 850nm VCSEL mode dispersion.

Each VCSEL coupled into the modes of the multimode fiber are not identical, therefore, a multi-mode Fiber Optic Patch Cables with a difference of each VCSEL "bandwidth", the performance is often much longer than the transmission distance of the optical fiber shown in a nominal bandwidth. In multimode fiber using FP or DFB guaranteed transmission distance is not as 850nm VCSEL, but does not exclude an individual can transmit very far situation.