Multimode fiber Profiles: Step Index vs. Graded. What are the difference, advantages, and applications in Industry.
Slideshow Tutorial Transcript
- Graded Index Fiber vs. Step Index Fiber: Why use graded index fiber?
- There are mainly two types of multimode fibers: Step Index and Graded Index fibers • The core on a step index fiber has the same refractive index throughout. • The refractive index on a graded index fiber gradually changes from the center of the core, to where the core meets the cladding. MM Fiber Profiles: Step Index vs Graded
- Step Index vs Graded Step Index Fiber Shows a clear distinction between the core and cladding. Graded Index Fiber Shows a gradual change from the core to the cladding.
- Issue with Step Index Fiber • Light rays travel somewhat uncontrolled inside a step index fiber. • The blue ray travels directly down the center of the fiber, meaning it travels a shorter distance than the red, green or black ray. • Rays that travel a longer distance will take more time to get to the end of the fiber than rays that travel a shorter distance. • The result is that some of the signal arrives before the rest of the signal. The signal becomes smeared. • This is bad for communication.
- Advantage of Graded Index Fiber • Light rays are controlled well within a graded index fiber. • Just as with the step index fiber, certain rays will travel shorter distances than other rays. • However, in a graded index profile fiber the rays will reach the end of the fiber at the same time… • How does this happen?
- The speed of light depends on the refractive index of whatever the light is traveling in. – When traveling in space (air, refractive index is 1.0) light travels at 300,000km/s – When traveling in glass, where the refractive index is 1.5, it travels at 200,000km/s – Changing the refractive index changes the speed of light!!! Since the refractive index of the core in a step index fiber is the same, the light rays will all travel the same speed. (Rays that travel a shorter distance will arrive sooner than rays that travel a longer distance.) However, the refractive index of the core in a graded index fiber changes, which means light rays inside the core will travel a different speeds. Optics of Step and Graded Index Fiber
- Graded Index Fiber • In a graded index fiber, the refractive index at the center of the fiber is the highest. This means that the light traveling at the center of the fiber travels slower. • Rays that don’t travel in the center will travel faster. As the rays move farther from center, they will travel faster. • The result is that all of the rays in the core will arrive at the end of the fiber at the same time. This is ideal for communication.
- Long distance applications • Higher Cost • Less prone to attenuation • Over longer distances, the benefits of the graded fiber are worth the added cost • Short distance applications • Lower cost • More prone to attenuation • Over shorter distances, the disadvantages of step fiber are outweighed by the lower cost of deployment Step vs Graded in the Industry Step Graded
- OP1021 Launch Condition Analyzer – Nearfield Scanner profiles the optical power density of the fiber – Farfield Scanner produces plots to determine numerical aperture (NA) and mode field diameter (MFD) – Measure the profile of Step Index and Graded Index fiber
- OP940 Insertion Loss & Return Loss. Fastest IL & RL testing. 3 seconds, using the front panel in Dual ILRL mode – Simultaneous, dual wavelength IL & RL – Easy front panel maintenance – It can be expanded using an external optical switch or the switch can be integrated for multifiber connector testing.