10 Gigabit Multimode And DMD Testing Technology

Posted on by FS.COM

As we all know, the optical fiber cable system in the transmission of the optical signal, can not do without optical transceivers and fiber. There are two major types of optical transceivers categories: light-emitting diode (LED) and Laser light emitting device. Although in performance, the laser light is far supperior to the light-emitting diode, the vast majority of LAN users, but due to the manufacturing cost of the problem has been difficult to afford the high prices of laser emitters. Until recently, a new type of light emitting device of the vertical cavity surface emitting VCSELs (Vertical cavity surface emitting lasers) emergence, to solve this problem. VCSELs absorption of the laser light-emitting device performance advantages, such as high-speed response, the transmission spectrum is narrow, and the advantages of the light-emitting diode, such as coupling, high efficiency and low cost. Therefore, the use of low-cost, high-performance VCSELs emitting devices with the multi-mode fiber optic cable can transmit signals up to 10Gb / s.

However, another problem appeared in front of the user, that is, the transmission distance. In addition to the transfer rate using fiber optic cable, transmission distance requirements. Experimental results show that the traditional multimode fiber optic cable, either 50μm or 62.5μm can support 10Gb / s network transmission, but its support distances are less than 100 meters, this network backbone can not be met.

Multimode fiber transmission bottlenecks – DMD

Why can support 100Mbps when 2000m of multimode fiber at 1 Gbps only supports 550 meters? its main reason is due to the phenomenon of multi-mode fiber of the DMD. Tested, we found that the multi-mode optical fiber in the transmission of the optical pulse, the optical pulse in the transmission process will diverge broadening When this divergence is severe to a certain extent between the front and rear pulse superimposed on each other, so that the receiving end does not accurately distinguish between each of the optical pulse signal, a phenomenon we called DMD (Differential Mode Delay). The main reason is that the multimode optical fiber with a optical pulse includes a plurality of modal components, from the angle of view of the optical transmission, each modal component type go in the optical fiber transmission path, for example, a straight line along the center of the fiber transmissionthe light component transmitted through the fiber cladding reflection light component having a different path. From electromagnetic point of view, contained within the three-dimensional space in the multimode fiber diameter the many modal (300-1100) component, their composition is very complex.

A new classification of multimode fiber in the ISO standard, at present OM1 refers to the traditional 62.5μm multimode fiber, OM2 refers to the traditional 50 μm multimode fiber, OM3 is the new 10 Gigabit optical fiber . Note that the two modes of the bandwidth of optic fiber indicators., Overfilled Launch Bandwidth the of the matching indicators of was is for a a LED the light emitting device, while the the LASER bandwidth is the against the of the matching indicators of of the Novel laser the light emitting device. The OM3 optic fiber cable at the same time in two modes under the have carried out a optimized. Another should be noted that the choice of transmission wavelength, 850nm or 1300nm. Although the longer the wavelength, the performance will be better, but the cost of the light-emitting device will be doubled, therefore, if possible, try to choose a short-wavelength applications to reduce costs. In In For example, the the new type of VCSELs light-emitting device is to Application environment for the in order to short-wave long, instead of the standard Laser light-emitting device is mainly used for the environment of the long-wavelength.

The OM3 fiber of test problems

DMD test steps are: using a 5μm single-mode probe with OM3 fiber under test is connected by single mode probe optical pulse to keep the fiber under test, at the same time, the probe scanning move from the fiber axis edge to move every time, every time it moves around 1μm. At the receiving end, for each position of the optical pulse will be recorded and the DMD indicator to form superimposed on with a time-domain diagram. Reach the light pulse will due to the different path generated time difference, at the same time In due to to optical pulse itself will to divergence, the difference of will in these two areas added together, According to the comparison of standards, FOR USE IN THE judgment OM3 fiber-optic from whether to to meet the standard.

OM3 fiber performance advantages

User network applications in the face of pressure to upgrade from the 1Gb / s to the future 10Gb / s for the application and future smooth upgrade the excessive Each user needs to be carefully considered.

In the current 1Gb/s network era, the traditional multi-mode fiber support distance not more than 550 meters, while the use of single mode fiber and mean at the same time the use of expensive laser light-emitting device, cabling system, both of which cost almost the same, but in thenetwork device, the two options means that the price difference is at least doubled. In many cases, when the user transmission over a distance of 500 meters and 1000 meters but had to use laser devices. New OM3 multimode fiber allows for the support of Gigabit Ethernet Distance extended to 1000 meters, without the need to use expensive laser device. So at this stage, the user can bring significant performance advantages.

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