Frequently Asked Questions
While single-mode fibers can only support one mode, multimode fibers can propagate thousands of modes due to the larger size of the core. The number of modes supported by an optical fiber is dependent on the radius of the core, the wavelength, and the index of refraction of the core and the cladding materials.
Step index optical fibers are characterized by a uniform distribution of the core refractive index. This means that the refractive index is the same everywhere inside the core. On the other hand, graded index optical fibers are characterized by a core whose refractive index varies with radial position. For a graded index fiber, the refractive index of the core tends to be higher near the center and smaller radially outward.
There are many ways to think about optical modes. One way is to think of a mode as one possible solution of the wave equation in a waveguide, fiber, or free space. It is the spatiotemporal distribution/propagation of the optical (electromagnetic) wave inside the fiber. A single mode corresponds to one such solution with a defined periodicity (wavelength) and phase velocity. Multimode optical fibers are designed in such a way that multiple optical modes can simultaneously be propagated inside the fiber without deterioration.
Multimode fibers are characterized by a wide core and an overall bigger cross-section than single-mode fibers. This makes them easier to align with other devices like lasers and less likely to suffer from breakage. Additionally, connectors and attachments to multimode fiber are cheaper as they are easier to fabricate. Multimode fibers are also ideal for short-distance communication networks.
Yes, a change in temperature can induce small variations in the index of refraction of multimode temperature which could cause undesired effects such as power loss or birefringence. However, many multimode fibers are designed to operate at temperatures as high as 700 degrees Celsius.
The core diameters of multimode fibers can range from 50 µm to 500 µm or more. In general, multimode fibers with larger core diameters can sustain higher number of modes.
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