Class 11 Telecom Chapter 1 Fundamentals of Optical Fiber Technology

Class 11 Telecom Chapter 1 Fundamentals of Optical Fiber Technology Solutions English Medium As Per AHSEC New Syllabus to each chapter is provided in the list so that you can easily browse through different chapters Class 11 Telecom Chapter 1 Fundamentals of Optical Fiber Technology Question Answer and select need one. Class 11 Telecom Chapter 1 Fundamentals of Optical Fiber Technology Notes Download PDF. AHSEC Class 11 Elective Telecom Question Answer English Medium.

Class 11 Telecom Chapter 1 Fundamentals of Optical Fiber Technology

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Fundamentals of Optical Fiber Technology

Chapter: 1

A. Multiple Choice Questions:

1. Which of the following is the innermost layer in optical fiber?

(a) Cladding.

(b) Jacket.

(c) Buffer.

(d) Core.

Ans: (d) Core.

2. Aramid yarn is used in which of the following layers?

(a) Buffer.

(b) Strength material.

(c) Jacket.

(d) Cladding.

Ans: (b) Strength material.

3. Which of the following cables have both optical fiber and metal conductor for transmission of light and electrical signal?

(a) Armoured cable.

(b) Ribbon cable.

(c) Composite cable.

(d) Messenger cable.

Ans: (c) Composite cable.

4. In which cable optical fibers are arranged side by side in one row?

(a) Ribbon cable.

(b) Composite cable.

(c) Messenger cable.

(d) Armoured cable.

Ans: (a) Ribbon cable.

5. Strength member is also known as __________.

(a) Polyester elastomer.

(b) Kevlar.

(c) Polymer.

(d) Polyethylene.

Ans: (b) Kevlar.

6. The component in the optical fiber communication system that converts light energy into electrical energy is the _____________.

(a) Transmitter.

(b) Receiver.

(c) Optical fiber.

(d) Coupler.

Ans: (b) Receiver.

7. What was one of the earliest advantages that light held over other forms of communication?

(a) Ability to communicate complex ideas.

(b) Ability to carry messages quickly.

(c) Ability to carry messages privately.

(d) Ability to carry coded messages.

Ans: (b) Ability to carry messages quickly.

8. Optical optics fiber will play a critical role in realizing the dream of _____________ India.

(a) Analog India.

(b) Digital India.

(c) Modern India.

(d) Traditional India.

Ans: (b) Digital India.

9. Which of the following is not the element of communication?

(a) Sender.

(b) Receiver.

(c) Medium.

(d) Node.

Ans: (d) Node.

10. Which of the following is the diameter of single mode optical fiber?

(a) 8.5–9 µm.

(b) 9–10 µm.

(c) 86 µm.

(d) 10–11 µm.

Ans: (a) 8.5–9 µm.

B. Fill in the blanks

1. Signal is ___________ representation of data.

Ans: Electrical.

2. Alexander Graham Bell invented a device called ___________.

Ans: Telephone.

3. Optical fibers are simple threads like ___________.

Ans: Glass.

4. LASER or LED is the ___________ for optical fiber transmission.

Ans: Light source.

5. Receiver stage consists of ___________, ___________ and ___________.

Ans: Photodetector, amplifier and demodulator.

6. The basic structure of an optical fiber consists of four parts, ___________, ___________ ___________ and ___________.

Ans: Core, cladding, strength member and jacket.

7. In single mode operation the diameter of cladding is ___________.

Ans: 125 µm.

8. In multi-mode mode operation the diameter of cladding is ___________.

Ans: 125 µm.

9. Optical fiber cable transmits encoded ___________ signal.

Ans: Light.

10. Core is made up of ___________.

Ans: Glass.

C. True or False:

1. Noise is the desired signal.

Ans: False.

2. A photon is a discrete quantity of light energy.

Ans: True.

3. Glass is opaque material.

Ans: False.

4. Light is confined in the core of an optical fiber cable.

Ans: True.

5. The fiber optic cable is a small and compact cable, and it is highly susceptible to cuts or damages during installation or construction activities.

Ans: True.

6. Data rate is much lower in a fiber hence more information can be carried fiber than copper cables.

Ans: False.

7. Fiber optic cables cannot be used in the fields of medicine and research.

Ans: False.

8. Radiation may either be “electromagnetic,” which is usually considered to travel in the form of waves, or “particles”.

Ans: True.

9. Non-wired media means communication is established without material as a medium.

Ans: True.

10. LASER or LED is the light source for optical fiber transmission.

Ans: True.

D. Short Answer Question. 

1. List down the features of optical fiber cables.

Ans: The features of optical fiber cables are as under: 

(i) Small in size and lighter weight.

(ii) Greater bandwidth.

(iii) High data rate.

(iv) Less attenuation.

(v) Ruggedness and flexibility.

(vi) Less electromagnetic interference.

(vii) Metal free.

(viii) Electrical isolation.

2. How does the optical fiber communication system work?

Ans: In optical fiber communication, major elements are transmitter, receiver and optical fiber as a propagation medium as shown in Figure 1.22. The transmitter stage consists of drive circuitry and light source such as Light Emitting Diode or LASER. The receiver stage consists of a photo-detector such as photo-diode or PIN Diode, an amplifier and a signal restorer. Now, we will discuss in detail the stages of the optical fiber communication system.

(i) Transmitter: The transmitter transmits optical signal to the fiber cable. A 

The transmitter consists of an interface circuit, a driver circuit and an optical source.

(ii) Interface circuit: It makes an interface between the input and transmitter circuitry. 

(iii) Driver circuit: It processes the input electrical signal, which contains information and feeds to the light source. 

(iv) Optical source: It produces the light signal for the optical fiber. It can be LED or LASER.

(v) Transmission Channel: It consists of an optical fiber cable, between transmitter and receiver. This transmission channel transmits optical signals from one end to another. 

(vi) Receiver: Optical signal is used as input to the optical receiver. Receiver stage 

consist of a photo detector, signal amplifier and signal restorer. 

(vi) Photo-detector: It converts optical signal into electrical signal.

(vii) Signal amplifier: It is used to improve signal quality by removing the noise to achieve better quality of the signal. 

(viii) Signal restorer: It converts amplified signals for restoring.

3. Why is communication necessary? What is the importance of communication?

Ans: Communication is the process of transferring data or information from one end to another end. Communication must include three basic elements i.e. Transmitter, Receiver and Medium.

In this digital era, we are living in a fast growing world. Today technology is upgrading day by day. One of the developing sectors is the telecom sector on which the whole communication system depends. Telecom sector includes mobile communication, satellite communication, TV and broadcasting, Optical fiber communication, cellular communication. Advanced technologies boosting the data transfer capacity of the network. With the invention of a high data transfer medium one can see the match, which is played in different parts of the world. This live streaming is possible because of the high data transfer capability of the medium. Innovation in carrying the data at high speed is greatly benefiting the telecommunication industry. Optical fiber is the fastest way to transfer the data. This is possible as data is transferred in the form of light and we know that speed of light is the fastest possible speed on the global scale. 

4. Name the elements of optical fiber communication. 

Ans: In optical fiber communication, major elements are transmitter, receiver and optical fiber as a propagation medium.

5. How optical fibers are used in medical treatment? 

Ans: Optical fiber cables are widely used in the fields of medicine and research. Optical communication is an important part of surgical methods, popularly known as endoscopy.

6. Write features of each element used in optical fiber communication in one sentence.

Ans: (i) Transmitter: The transmitter transmits optical signal to the fiber cable.

(ii) Interface circuit: It makes an interface between the input and transmitter circuitry.

(iii) Driver circuit: It processes the input electrical signal, which contains information and feeds to the light source.

(iv) Optical source: It produces the light signal for the optical fiber.

(v) Transmission Channel: This transmission channel transmits optical signal from one end to another.

(vi) Optical Splitter: Optical fiber splitter directs the beam of light from main fiber to two or more fibers.

(vii) Optical Connector: It is for temporary joints between two individual optical fibers that are broken or to be joined for communication.

(viii) Optical Splice: It is used to permanently join optical fibers which are broken.

(ix) Receiver: Optical signal is used as input to the optical receiver.

(x) Photo-detector (in Receiver): It converts optical signal into electrical signal.

(xi) Signal amplifier (in Receiver): It is used to improve signal quality by removing the noise to achieve better quality of the signal.

(xii) Signal restorer (in Receiver): It converts amplified signals for restoring.

A. Multiple Choice Questions:

1. In which of the following patterns are electric and magnetic components of EM waves oriented?

(a) They are parallel to one another.

(b) They are at right angles to one another.

(c) They are randomly oriented to one another.

(d) They are unrelated.

Ans: (b) They are at right angles to one another.

2. Which of the following natural lights possess________.

(a) Be neither a wave nor a particle.

(b) Be primarily a wave.

(c) Have characteristics of both a wave and a particle.

(d) Be primarily a particle.

Ans: (c) Have characteristics of both a wave and a particle.

3. Which of the following forms of electromagnetic wave has a lower frequency than the other three?

(a) Infrared light.

(b) Visible light.

(c) Gamma rays.

(d) Microwaves.

Ans: (d) Microwaves.

4. Refraction of light is characterised by change in its________.

(a) Colour as it passes from one medium into another.

(b) Speed as it passes from one medium into another.

(c) Frequency as it passes from one medium into another.

(d) Direction within a single medium.

Ans: (b) Speed as it passes from one medium into another.

5. If a beam of light passing from medium A to medium B bends toward normal what can we say?

(a) Medium A is denser than medium B.

(b) Medium A has a higher refractive index than medium B.

(c) Medium A has a lower refractive index than medium B.

(d) Both medium A and medium B have the same refractive index.

Ans: (c) Medium A has a lower refractive index than medium B.

6. The critical angle is that angle of incidence for which the angle of refraction is________.

(a) 180°.

(b) 0°.

(c) 45°.

(d) 90°.

Ans: (d) 90°.

B. Fill in the blanks: 

1. The speed of light from coming from the sun to earth is________________. 

Ans: 1. 3 × 10^8 m/s.

2. Refraction at the air – water interface leads to_____________ of light. 

Ans: Bending.

3. If light is passed through the glass to air and angle of transmitted light is greater than the critical angle then it leads to____________________. 

Ans: Total internal reflection.

4. White light coming from the sun is composed of________ colours. 

Ans: Seven.

5. Phenomena of Total Internal Reflection takes place in____________ cable. 

Ans: Optical.

6. Light through the optical fiber propagates inside the core at a speed of ____________. 

Ans: 2 × 10^8 m/s. 

C. True and False:

1. If white light is passed through the prism the light splits into seven colours. 

Ans: True. 

2. Total internal reflection is a method which allows the light to pass through the cladding part of the fiber.

Ans: False.

3. The diameter of the core is larger than the cladding.

Ans: False.

4. Buffer-coating is made up of steel. 

Ans: False.

5. Buffering to the core- cladding provides protection of the fiber. 

Ans: True.

6. Speed of light becomes larger when it travels from rarer medium to denser medium. 

Ans: False.

7. Speed of light becomes lesser when it travels from denser medium to rarer medium. 

Ans: False.

D. Answer in short:

1. Why is the optical fiber core and cladding covered with buffer-coating?

Ans: It is necessary to provide protection to the core and cladding from external and environmental damage. Buffer is one such layer, which provides this protection. It is made up of hard-plastic coating.

2. List the seven colours of the rainbow and draw them in your notebook.

Ans: Seven colours of the rainbow (VIBGYOR):

(i) Violet.

(ii) Indigo.

(iii) Blue.

(iv) Green.

(v) Yellow.

(vi) Orange.

(vii) Red.

Students draw it by yourself.

3. What is the electromagnetic spectrum? 

Ans: The electromagnetic spectrum is the term used to describe the entire range of waves.Spectrum include infrared radiation, visible region, ultraviolet radiation, microwaves,radio waves, X-Rays, gamma rays. Light is also known as visible light or visible spectrum.

4. For what range of electromagnetic spectrum optical fiber are used.

Ans: However, in optical fiber technology, the wavelength range, which is going to use infrared, visible, and ultraviolet.Most fiber optic systems use infrared light between 800 and 1550 nanometers. This region is referred to as the near infrared (near-IR).

5. How light is injected into optical fiber?

Ans: Coupling is the act of joining two things together. In this case, two things are light source and optical fiber. The coupling efficiency is primarily dependent on the core diameter and numerical aperture (NA) of the fiber. Secondly, coupling depends upon the output of light source, which we are using i.e. light emitting diode or laser diode.The optical signal is then coupled into the optical fiber cable.Laser light sources couple light efficiently into the core of optical fiber cable.

6. What type of information is carried by light i.e. analog or digital and state the reason? 

Ans: A typical metal wire carries the data in the form of an electrical signal. However, optical fiber cable carries data in the form of digitally encoded signals.

7. If a signal gets weakened, then what measure is taken to restore it?

Ans: Hence, to rectify this problem of attenuation a device known as amplifier or repeater are required to regain the strength of the signal.

A. Multiple Choice Questions:

1. LEDs emit photons that are out of phase; this is referred to as light ___________.

(a) Coherent.

(b) Incoherent.

(c) Stimulated.

(d) Spontaneous.

Ans: (b) Incoherent.

2. Lasers emit photons that are in phase, this is referred to as light  _____________.

(a) Coherent.

(b) Incoherent.

(c) Stimulated.

(d) Spontaneous.

Ans: (a) Coherent.

3. The photons emitted from a laser have the same wavelength and are in phase; this is referred to as light.

(a) Coherent.

(b) Incoherent.

(c) Stimulated.

(d) Spontaneous.

Ans: (a) Coherent.

4. LEDs have an output pattern when compared to the output pattern of a laser.

(a) Narrow.

(b) Wide.

(c) Coherent.

(d) Stimulated.

Ans: (b) Wide.

5. LEDs with visible wavelengths are typically used for ________ distance fiber optic communication systems.

(a) Long.

(b) Short.

(c) Both short and long.

(d) Sometimes long, sometimes short.

Ans: (b) Short.

6. Long wavelength 1300 nm LEDs are suited for _______ transmission distance, then short wavelength 850 nm LEDs.

(a) Long.

(b) Short.

(c) Both short and long.

(d) Sometimes long, sometimes short.

Ans: (a) Long.

7. The optical output power of a laser ____________ than the optical output power of an LED.

(a) Wider.

(b) Greater.

(c) Narrower.

(d) Less.

Ans: (b) Greater.

B. Fill in the Blanks:

1. The amount of light energy coupled into the core of an optical fiber depends on the _______ and ___ of the optical fiber. 

Ans: Diameter and Numerical Aperture.

2. LED radiation should not degrade more than __________over its lifetime. 

Ans: 20%.

3. Laser light sources have a modulation speed __________than LEDs. 

Ans: Greater.

4. LED transmitters are designed to support only ____________modulation. 

Ans: On-Off.

5. Bandwidth of LED is____________ and bandwidth of LAERS is____________. 

Ans: Lower and Higher.

6. LEDs are suitable for use with _______________ mode fiber. 

Ans: Multi.

7. LASER s is suitable for use with _______________ mode fiber. 

Ans: Single.

8. Edge-emitting LEDs have ______ hetero-junction structure. 

Ans: A

C. Short Answers Questions:

1. Make a comparison between LED and LASER diodes? 

Ans:

2. Explain the working of the LASER diodes? 

Ans:  In simple electric bulbs, light is produced by converting electricity into thermal energy. But, semiconductor lasers generate light, directly from electric power.

Light bulb→ Electrical energy → Thermal energy → Light

Semiconductor laser → Electrical energy → Light

As we know, that atom has different energy levels. Each energy level has their own energies, for example, the first orbit of an atom energy level is E1, second orbit has an energy level E2 and so on. In general, when an electron jumps from a higher energy level to a lower energy level, it emits light or photons. The energy of the emitted photon is equal to the energy difference between the energy levels. This emitted energy from each photon is collected in a space called a cavity in the laser. Energy which is collected in the form of photons is used to produce a high intensity, directional, coherent, monochromatic beam of light.

A plane mirror is used to reflect generated photons repeatedly within the cavity of a laser. This will enhance the intensity of light. High intense, phase-aligned laser light is emitted by stimulated emission. This process continues as external voltage is applied to energize the photons. This will result in continuous laser light emission. 

3. Discuss the principle of LASER diodes? 

Ans: The term LASER stands for ‘Light Amplification by Stimulated Emission of radiation’. A laser is a device that amplifies or increases the intensity of light. It produces directional light beams. Lasers not only amplify or increase the intensity of light but also generates the light. Lasers emit light through a process called stimulated emission of radiation.

Stimulated emission– Stimulated means to encourage development. So in this type of emission electrons are used to encourage or excite other electrons to produce light energy.

As we are discussing optical fiber communication. For this reason, we are focusing on lasers which are used in optical fiber communication. Semiconductor lasers are widely used in optical fiber communication. They are also known as laser diodes. These laser diodes are made up of extrinsic and intrinsic semiconductor as shown in Figure 3.14. These semiconductor devices emit light in the form of a laser, when voltage is applied to the P-N junction of compound semiconductor.

A plane mirror is used to reflect generated photons repeatedly within the cavity of a laser. This will enhance the intensity of light. High intense, phase-aligned laser light is emitted by stimulated emission. This process continues as external voltage is applied to energize the photons. This will result in continuous laser light emission.

4. What is diode? 

Ans: When two semiconductors i.e. P-type and N-type semiconductors are combined to form a new component known as diode. ‘Di’ defines two, thus diodes have two terminals electronic components.

5. What are advantages and disadvantages of LED and LASER diodes?

Ans: Advantages of LED:

(i) LEDs are preferred light sources for short distances.

(ii) LEDs are used in optical fiber networks because of the following reasons–Inexpensive.

(iii) LEDs can be switched on and off at high speeds.

Disadvantages of LED:

(i) The maximum light output of an LED is typically very low, about 100 microwatts.

(ii) LEDs produce photons of different wavelengths, which is undesired in case of optical fiber communication.

(iii) The light produced is neither directional nor coherent. Therefore, it is difficult to couple the LEDs output to the single-mode fiber.

(iv) It is too hard to get the light into the narrow core. 

Advantages of Laser Diodes:

(i) High-Speed Modulation: Excellent for high-speed data transmission. 

(ii) Collimated Beam: Produce a narrow, concentrated beam that can be focused to a small spot. 

(iii) Monochromatic Light: Generate a narrow band of wavelengths (color). 

(iv) Precision: Allows for precision targeting in industrial and medical applications. 

Disadvantages of Laser Diodes:

(i) High Cost: More expensive to produce and purchase than LEDs. 

(ii) Eye Hazard: The concentrated light can be harmful to the eyes. 

(iii) Complex Coupling: Can be difficult to couple into small optical fibers. 

(iv) Higher Power: Generally require more complex driving electronics. 

6. What is a p-n junction? 

Ans: Photons emitted from the junction, where the p-type and n-type regions meet.

7. Explain S-LED and E-LED. 

Ans: Based on the amount of light emitted by the LED, structure of LEDs is classified as – S-LED and E-LED:

(i) S-LED: S-LED is the surface emitter LED. As the name suggests, in this type of LED, emission of photons is from the surface area. It is confined to the small circular area of the LED. The diameter of the circular area is around 20 to 50 micrometres (10-6 m). Structural layout of surface emitter LED.

(ii) E-LED: E-LED is the edge emitter LED. As the name suggests, in this type of LED, emission of photons is from the edge of the LED. In this type of LED numbers of layers of semiconducting material are used. The area through which light can be emitting out is 8 to 10 micrometer (10-6 m) in thickness and up to 150 micrometer (10-6 m) in width.

8. Name some of the commonly used LASER.

Ans: Lasers are classified into various types based on the medium used to emit laser light.

(i) Semiconductor laser.

(ii) Solid-state laser.

(iii) Gas laser.

9. Comparison between LASER light and white light. 

Ans: 

10. Differentiate spontaneous and stimulated emission. 

Ans: 

Parimol

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