Optical Fiber Waveguides MCQ || Types of Optical fiber Waveguides Questions and Answers

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.

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.

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.

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.

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.

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.

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.

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.

Answer:4. All of the above

Explanation: 

In selecting materials for optical fibers, a number of requirements must be satisfied.

• It must be possible to make long, thin fibers from the material.
• The material must be transparent at a particular optical wavelength in order for the fiber to guide light efficiently.
• Physically compatible materials that have slightly different refractive indices for the core and cladding must be available.

Materials that satisfy these requirements are gasses and plastic.

Answer: 4. All of the above

Explanation: 

An optical fiber is a flexible, transparent fiber made by drawing glass (silic or plastic.

Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (data transfer rates) than electrical cables.

The types of optical fiber cable are

1. Glass fiber
2. Halide Glass fiber
3. Active Glass fiber
4. Chalgenide glass fiber
5. Plastic optical fiber
6. Photonic Crystal Fiber