When the light launched into the core strikes the cladding, the light is reflected from the core-to-cladding interface. The cladding is designed so that the light launched into the core is contained in the core. The cladding is a layer of material that surrounds the core. The optical fiber guides the light launched into the fiber core (Figure 1). This is significant because a fiber’s bandwidth determines its information carrying capacity, i.e., how far a transmission system can operate at a specified bit error rate. Intermodal dispersion limits multimode fiber bandwidth. The difference in the time delay between the modes is called Differential Mode Delay (DMD). In multimode fiber, the time it takes for light to travel through a fiber is different for each mode resulting in a spreading of the pulse at the output of the fiber referred to as intermodal dispersion. A multimode fiber allows many light propagation paths, while a single mode fiber allows only one light path. The “mode” is an allowable path for the light to travel down a fiber. The distinguishing difference, and the basis for the naming of the fibers, is in the number of modes allowed to propagate in the core of a fiber. These fiber types have dominated the commercial fiber market since the 1970’s. Both are used in a broad range of telecommunications and data networking applications. There are two different types of fiber optic cable: multimode and single mode fiber type (MMF and SMF). The differences among the different transmission fiber types result in variations in the range and the number of different wavelengths or channels at which the light is transmitted or received, the distances those signals can travel without being regenerated or amplified, and the speeds at which those signals can travel. Specialty fiber designs, such as dispersion compensating fibers and erbium doped fibers, perform functions that complement the transmission fibers. These new fiber designs – used primarily for the transmission of communication signals – include Non-Zero Dispersion Fiber (NZDF), Zero Water Peak Fiber (ZWPF), 10-Gbps laser optimized multimode fiber, and fibers designed specifically for submarine applications. Since Bell Laboratories invented the concept of application-specific fibers in the mid-1990s, fiber designs for specific network applications have been introduced. Early fiber designs that are still used today include single mode fiber type and multimode fiber. Depending on the type of application and the reach to be achieved, various types of fiber may be considered and deployed, such as single mode fiber type and multimode duplex fiber.įiber optic cables come in several different configurations, each ideally suited to a different use or application. Fiber optic cables are the medium of choice in telecommunications infrastructure, enabling the transmission of high-speed voice, video, and data traffic in enterprise and service provider networks.
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