Multimode fibers can propagate over 100 modes. Single Mode Fiber Multimode FibersĪs their name implies, multimode fibers propagate more than one mode. In general, single mode fibers are considered to be low-loss fibers, which increase system bandwidth and length. They lose power because light radiates into the cladding, which is lost at fiber bends. Single mode fibers operating at wavelengths larger than the cutoff wavelength lose more power at fiber bends. In single mode fibers, the wavelength can increase or decrease the losses caused by fiber bending. Signal loss depends on the operational wavelength (λ). Dispersion mechanisms in single mode fibers are discussed in more detail later in this chapter. Basically, dispersion is the spreading of light as light propagates along a fiber. Single mode fibers are capable of transferring higher amounts of data due to low fiber dispersion. Single mode fibers have a lower signal loss and a higher information capacity (bandwidth) than multimode fibers. The value of V should remain near the 2.405 level. Power transmitted by the cladding is easily lost at fiber bends.
![fibre cut off wavelength fibre cut off wavelength](https://slidetodoc.com/presentation_image_h/1a9b0a9e74ca6a431facbc02aa1d9994/image-37.jpg)
For low V values (-1.0), most of the power is propagated in the cladding material. When V -2.405, single mode fibers propagate the fundamental mode down the fiber core, while high-order modes are lost in the cladding. In single mode fibers, V is less than or equal to 2.405. The value of the normalized frequency parameter (V) relates core size with mode propagation. This is achieved by using a LASER as a light source. Single mode fibers propagate only one mode, because the core size approaches the operational wavelength (λ). A fiber core of this size allows only the fundamental or lowest order mode to propagate around a 1300 nanometer (nm) wavelength. The core size (diameter) is typically around 8 to 10 micrometers (m).
![fibre cut off wavelength fibre cut off wavelength](https://www.thorlabs.com/images/TabImages/ESM_Fiber_chart_4_tab.gif)
The core size of single mode fibers is small. Single mode fibers are also manufactured by following the same fabrication process as multimode fibers. Single mode fibers are manufactured with the same materials as multimode fibers. The basic structural difference is the core size. As previously explained, the structure of the fiber can permit or restrict modes from propagating in a fiber. As each name implies, optical fibers are classified by the number of modes that propagate along the fiber.
![fibre cut off wavelength fibre cut off wavelength](https://image5.slideserve.com/10683565/references-l.jpg)
Basically, optical fibers are classified into two types. Optical fibers are characterized by their structure and by their properties of transmission.