Fibers that carry more than one mode are called multimode fibers. Multimode fiber has a bigger diameter. The range is around 50 to 100 microns but 62.5 micrometers is usually used.
In most of the applications, two fibers are used in multimode fibers and Wavelength Division Multiplexing is not normally used on multi-mode fibers. Plastic optic fibers promise performances similar
A multi-mode cable has a larger core than a single-mode fiber. This core allows light to flow on multiple paths along with the core, allowing a small impulse light pulse to be smeared into a wide out- put pulse. This dispersion degrades the rate at which light pulses can be transmitted.
2. Wavelength Division Multiplexing is not normally used in ________
Single Mode Fiber
Multimode Fiber
Both 1 and 2
None of the above
Answer:2. Multimode Fiber
Explanation:
In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology that multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light.
This technique enables bidirectional communications over a single strand of fiber, also called wavelength-division duplexing, as well as multiplication of capacity.
Wavelength Division Multiplexing is not normally used in Multimode Fiber. Most WDM systems operate on single-mode fiber optic cables which have a core diameter of 9 µm.
3. The diameter range of Multimode fiber is _____
10 to 20 micron
20 to 30 micron
40 to 50 micron
50 to 100 micron
Answer:4. 50 to 100 micron
Explanation:
Fibers that carry more than one mode are called multimode fibers. Multimode fiber has a bigger diameter. The range is around 50 to 100 microns but 62.5 micrometers is usually used.
In most applications, two fibers are used | in multimode fibers and Wavelength Division Multiplexing is not normally used on multi-mode fibers.
4. Multimode fiber is commonly used in ______
Short Distance
Long Distance
Medium Distance
All of the above
Answer:1. Short Distance
Explanation:
Multimode fiber is commonly used in short-distance (usually less than 2 km) communication applications. Because signal quality drops as distance increases, multimode fiber is generally used for short-distance communications across local area networks (LANs).
5. The core size of Multimode fiber is _____ as compared to single-mode Fiber.
Small
Large
Equal
None of the above
Answer:2. Large
Explanation:
Multimode fiber’s core size is larger than single-mode fiber and is, therefore, easier to connect, with greater tolerance of components with less precision.
Multimode fibers can propagate over 100 modes. The number of modes propagated depends on the core size and numerical aperture (NA). As the core size and NA increase. the number of modes increases. Typical values of fiber core size and NA are 50 to 100 um and 0.20 to 0.29. respectively.
6. Which of the following are the types of Multimode Fiber?
Step Index Multimode Fiber
Graded Step Index Multimode Fiber
Both 1 and 2
None of the above
Answer:3. Both 1 and 2
Explanation:
There are two types of multimode fibers:
(I) step-index fiber
(ii) graded-index fiber.
They differ by the index of refraction profiles of their core and cladding.
Step Index Fiber:- A step-index fiber is an optical fiber that has a core and cladding with different but uniform refractive indexes.
Graded Index Fiber:- Graded index multimode fiber is a type of optical fiber where the refractive index is higher at the axis of the core and then it decreases gradually towards the core-cladding interface. That is to say, the refractive index of a graded-index fiber gradually decreases from its center, and eventually decreases to the same value as the cladding at the core edge.
7. The number of modes that multimode step-index fibers propagate depends on
Relative Refractive Index Difference
Core Radius
Wavelength
All of the above
Answer: 4. All of the above
Explanation:
The number of modes that multimode step-index fibers propagate depends on the Relative Refractive Index Difference and core radius of the fiber. The number of propagating modes also depends on the wavelength of the transmitted light.
In a typical multimode step-index fiber, there are hundreds of propagating modes. Most modes in multimode step-index fibers propagate far from the cutoff.
8. In multimode step-index fibers propagate far from _____
Threshold
Cutoff
Core
Cladding
Answer: 2. Cutoff
Explanation:
Most modes in multimode step-index fibers propagate far from the cutoff.
Modes that are cut off cease to be bound to the core of the fiber.
Modes that are farther away from the cutoff wavelength concentrate most of their light energy into the fiber core.
Modes that propagate close to cutoff have a greater percentage of their light energy propagate in the cladding.
Since most modes propagate far from the cutoff, the majority of light propagates in the fiber core.
9. Multimode step-index fiber has ________
Large core diameter & large numerical aperture
Large core diameter and small numerical aperture
Small core diameter and large numerical aperture
Small core diameter & small numerical aperture
Answer: 1. Large core diameter & large numerical aperture
Explanation:
Multimode step-index fibers have relatively large core diameters and large numerical apertures. Large core size and a large numerical aperture make it easier to couple light from a light-emitting diode (LED) into the fiber.
Multimode step-index fiber core size is typically 50 pm or 100 pm. Unfortunately, multimode step-index fibers have limited bandwidth capabilities.
10. Which of the following are advantages of Multimode step-index fiber?
Easy to couple Light
Simple in manufacturing
Inexpensive
All of the above
Answer: 4. All of the above
Explanation:
Advantages of Multimode Step-index Fibers
Due to the relatively large source-to-fiber aperture of a multimode step-index fiber, it becomes quite easy to couple light into and out of it.
The manufacturing process of multimode step-index fibers is relatively simple.
Multimode step-index fibers are inexpensive.
Because of their large core diameters, these fibers are the best choice for illumination, collection, and use in bundles as light guides.
12. Which of the following are disadvantages of Multimode step-index fiber?
High distortion
Low Bandwidth
Smearing
All of the above
Answer: 4. All of the above
Explanation:
Disadvantages of Multimode Step-index Fibers
In multimode step-index fibers, light rays traverse several paths, different from each other within the optical fiber cable. Consequently, there is a large difference in their propagation times which results in spreading out of the transmitted optical pulse by the time it arrives at the receiving end. This amounts to higher distortion as compared to other types of optical fibers.
The transmission bandwidth and achievable rate of information are quite less than those that are possible with other types of optical fiber cables.
Multimode Step-index Fiber has a border acceptance angle. However, the broader the acceptance angle, the longer the light path for a given ray. The existence of many different paths through the fiber causes “smearing” of signal pulses, making this type of fiber unsuitable for telecommunications.
13. The diameter range of Multimode graded-index fiber is
10 to 20 micron
20 to 30 micron
40 to 50 micron
50 to 100 micron
Answer: 4. 50 to 100 micron
Explanation:
Disadvantages of Multimode Step-index Fibers
These fibers have the second largest range of core size after Multi-mode step-index fiber. The diameter range of Multimode graded-index fiber is 50 to 100 microns. The graded-index core has a tendency to bend rays from wider incoming angles through a sharper curve.
14. What are the advantages of multimode fiber?
Can use LEDs
Easy to couple optical source
Easy to connect
All of the above
Answer: 4. All of the above
Explanation:
Multimode fibers offer several advantages for lower bandwidth applications.
(a) Spectrally incoherent optical sources such as LEDs can be efficiently coupled to non-metallic fibers.
(b) For large values of fiber core diameter and numerical aperture, it is relatively easier to couple them 1 to external optical sources.
(c) Fiber connectors can have a lower tolerance for making connections with the fibers.
15. Light propagates in multimode graded-index fibers according to ______ and ________
Reflection and refraction
Refraction and Total Internal Reflection
Reflection and Total internal Reflection
None of the above
Answer: 4. Refraction and Total Internal Reflection
Explanation:
Light propagates in multimode graded-index fibers according to refraction and total internal reflection.
The gradual decrease in the core’s refractive index from the center of the fiber causes the light rays to be refracted many times. The light rays become refracted or curved, which increases the angle of incidence at the next point of refraction. Total internal reflection occurs when the angle of incidence becomes larger than the critical angle of incidence.
