Optic Patch
Fibre Optic single mode vs multi mode compatibility?
Can I use single mode fibre media converters with a multi-mode fibre? I know I'm not supposed to, but could it still work since the cable is only 300m long? Will the signal loss be too much to let it work?
I have a 62.5/125um multi-mode cable running about 300m between two buildings.
My single modemedia convertors have a link loss budget of 16dB and use 1300nm wavelength.
I'd like to know how likely this is to work before I buy expensive patch cables.
Maybe.
In my example we had several building in a corporate campus, all connected with multi-mode fiber. Our original network was an ATM fiber backbone on Cisco Catalyst 5000 switches with multi-mode GBICs. After the company changed hands, this was replaced with a gigabit ethernet backbone and newer Cisco hardware. The network architect specified an odd-ball solution for two pairs of fiber connections between two buildings that were farthest apart (between 300 and 400 meters, I believe).
This wasn't a straight shot, either. Each end had one or two fiber patch panels, and there was a patch bay in one of the intermediate buildings between the far ends with multi-mode fiber jumpers in the bay.
--Single-mode GBICs on the Cisco Catalyst 6500 and 4000 switches at either end.
--Special 'conditioning' fiber Patch Cable that allowed the single-mode GBIC to connect to a Multimode Fiber. These patch cords were about $200/each.
And get the right connectors. In our case, the purchased conditioning cables were SC-to-SC, but our existing fiber plant had ST connectors. Each end had additional SC-to-ST adapters, which added loss and made the connection drop whenever someone monkeyed with the pile of fiber jumpers.
I do not have any of the technical info anymore to remember the link loss budget end-to-end in our cable plant. I no longer support that infrastructure, and most of the buildings are now occupied by Nike, who demolished the existing infrastructure (including the Verizon local fiber ring that went through the ceiling in one of the buildings).
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Everything You Need to Know About Fiber Optic Testing - Fiber Optic Technology Tutorial Series
Overview of Fiber Optic Testing
There are mandatory tests for every stage of the design, manufacture, and installation of the fiber optic components, link, cable plant, and network.
Most fiber optic test procedures have been thoroughly tested and codified as industry standards. These standards are part of EIA/TIA RS455 and are being adapted into IEC standards.
Most of these standards refer to tests of individual components under a variety of environmental conditions; therefore, only a few related to testing the performance of the installed cable plant.
With data communication networks, we are primarily concerned with three fiber optic test procedures: FOTP-95 for measurements of optical power, FOTP-171 for testing patch cables and OFSTP-14 for testing the loss of the installed cable plant.
Optical Fiber Testing
A great many tests must be performed on optical fibers. A fiber manufacturer must test a fiber to determine the characteristics by which the fiber will be specified. As a quality control measure during manufacture of fibers, the manufacturer must constantly test the fibers to ensure that they meet the specifications. Among the tests are the following: core diameter, cladding diameter, numerical aperture (NA), attenuation, refractive index profile and tensile strength.
Other tests performed on fibers or on fiber optic cables concern their mechanical and environment characteristics. Mechanical tests such as impact resistance, tensile loading, and crush resistance test the cable's ability to withstand physical and mechanical stresses. Environmental tests evaluate the changes in attenuation under extremes of temperature, repeated changes of temperature, and humidity.
Fiber Optic Cable Plant Testing
There are some testing concerns in a premises-cabling application based on the recommendations found in TIA/EIA-568A for generic cabling systems and TSB-67 on testing.
An important concept in testing is distinguishing between the link and the channel. The channel is the end-to-end system, including any patch cables at the equipment or work area. The link is the "behind-the-walls" cabling from the equipment-side patch panel to the work-area-side outlet.
Testing can be done on either a link level or a channel level. Installers of a building cabling system are usually concerned with the link. The link forms the basic infrastructure for the building cabling.
Fiber Optic Component Testing
Fiber optic data links are composed of three components: a transmitter, a receiver and the interconnection cable plant. These components must be compatible with the parameters of the intended application.
The loss budget must be adequate for the expected loss in the cable plant and the dynamic characteristics must meet the bandwidth requirements set by the network data transmission rate.
The loss budget is set by the output power of the transmitter and the sensitivity of the receiver. On a static basis, this is determined by the difference in optical power levels, but in reality the issue is a dynamic one, determined by the performance of the components at the data transmission rate of interest.
Continuity Testing
Simple continuity testing can be achieved by a flashlight: Does the light come through the fiber? Fancy flashlights - called visual continuity testers - are available specifically for fiber optic testing. A read light is easiest to see.
About the Author
Colin Yao is an expert on fiber optic communication technologies and products. Learn more about
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