| 单词 | MMF (MultiMode Fiber) |
| 释义 | MMF (MultiMode Fiber) aperture supports many fewer modes of light.The latter example is preferable.There are two general categories of modes: • Low-order modes are relatively straight paths that signals or signal elements travel as they propagate. As low-order modes are relatively direct, the signals encounter and interact with relatively little physical matter and attenuate relatively little. Such signals also reach a distant point in the fiber circuit relatively soon as they have traveled a short distance. • High-order modes are relatively transverse paths signals or signal elements travel as they propagate through the fiber. As these paths are highly indirect, the signals encounter and interact with considerable physical matter and, therefore, attenuate to a greater extent than those propagating along low-order modes. Such signals also reach a distant point in the fiber circuit relatively late, as they have traveled a long distance. Most MMF also is graded-index fiber, rather than step-index. Graded-index fiber compensates for high order modes by accepting errant light rays into the cladding, which comprises a great many layers of glass of slightly and progressively lower refractive index, or index of refraction (IOR). As a result, the errant signal components gradually increase in velocity and refract, or bend, back towards the core, where they rejoin other signal elements that propagated along other modes, i.e., took more or less direct paths. To some extent, graded-index fiber mitigates issues of pulse dispersion, a type of inter-symbol interference that occurs when various signal elements of various strengths overrun each other and that is especially prob-lematic in high-bandwidth applications, as bit times (pulse lengths) are very short and pulses must be very close together. Issues of attenuation and pulse dispersion combine to limit MMF to relatively short-haul, low-speed applications such as local area networks (LANs) running at 1 Gbps or less. See also cladding, core, graded-index fiber, IOR, LED, MMF, mode, numerical aperture, pulse dispersion, reflection, refraction, SMF, step-index fiber, VCSEL, and wavelength. Coating OD: 250 µ |