Volume 4, Number 18
There are two types of glass fiber optic cables, multimode and singlemode. The word mode (ray of light) refers to the fact that either several (multi), or just one mode (single), will pass through the cable at the same time. Singlemode cable can transmit voice, video and data over a longer distance (up to 100 Kilometers!) than multimode fiber cable and is typically used with laser driven transceivers at each end of the cable. These laser transceivers are sometimes four times the cost of multimode transceivers. Multimode cable is generally used for distances less than two kilometers and can be used with less expensive LED driven transceivers.
Fiber: Is made up of the core which is the glass that the light travels through and the Cladding which is a glass coating over the core that keeps light in.
Buffer Coating: Protective cover (typically plastic) over Cladding
Strength Member: Usually Kevlar strands that add strength to the cable
Both Glass and Plastic optical cable experience attenuation, or loss of light. Over distance, the effectiveness of the light pulse decreases causing errors in the data being transmitted. The physical properties of singlemode fiber offer very low attenuation over distance, which is why singlemode fiber is used to connect cities, campuses and wide area telephone and data networks. Multimode fiber cables experience more attenuation, or loss, per the same distance than singlemode fiber.
Typically Multimode fiber is used within buildings and to connect buildings together in a campus environment. Lastly, plastic optical fiber has the highest attenuation, or loss of light per distance compared to the glass fiber cable types mentioned above. For many applications the maximum distance for plastic fiber cable is less than 10 meters.
Glass Fiber specifications list the core and cladding diameters as a ratio. The example below details the core to cladding ratio for the three most common types of glass fiber cable. Multimode fiber is commonly 62.5/125 or 50/125 micron, singlemode fiber is commonly 9/125 micron.
Types of Polishes on Glass Fiber ConnectorsThe polish on a fiber connector dictates the amount of back reflection. Back reflection is a measure of the light reflected off the polished end of a fiber connector measured in negative dB. In some singlemode fiber applications the amount of back reflection on the connectors can be critical.
Typical Applications for Glass Fiber Optic Cables
Plastic Optical Fiber Cables
Plastic optical fiber cables experience high loss or attenuation and are used on short distance applications such as in cars, in airplanes and with high-end audio equipment such as DVD players, CD players and MP3 and DAT recorders. The low cost and ease of connectorization make plastic optical fiber the logical choice for these short distance applications.
Plastic optical fiber, like glass fiber is immune to lightning, and EMI and RFI. Using plastic fiber on high-end audio systems eliminates the distortion caused by capacitance and resistance of traditional wire audio cables, guaranteeing a "pure" sound.
Anatomy of a Plastic Optical Cable
Typical applications for Plastic fiber optic cables
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