Fibre-Optic Communications MCQ Quiz - Objective Question with Answer for Fibre-Optic Communications - Download Free PDF

Explanation:

The primary purpose of the metallic shield in a coaxial cable is to protect against electromagnetic interference (EMI). Understanding the role of the metallic shield involves delving into the construction, principles, and functionalities of co-axial cables as well as the nature of electromagnetic interference.

Co-axial Cable Construction:

A co-axial cable is designed to transmit electrical signals with high efficiency and minimal interference. It consists of several layers:

• Core Conductor: The innermost part of the cable, typically made of copper or aluminum, which carries the electrical signal.
• Dielectric Insulator: Surrounding the core conductor, this layer insulates the signal-carrying conductor from the outer layers and helps maintain the integrity of the signal.
• Metallic Shield: This layer, often made of braided copper or aluminum, surrounds the dielectric insulator. Its primary function is to shield the inner conductor from external electromagnetic fields and to prevent electromagnetic interference (EMI).
• Outer Jacket: The outermost protective layer that shields the cable from environmental factors such as moisture, physical damage, and wear.

Electromagnetic Interference (EMI):

Electromagnetic interference is the disturbance generated by external sources that affect an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. EMI can degrade the performance of electrical devices, cause data loss, or create noise in communication systems. In the context of co-axial cables, EMI can introduce unwanted signals that interfere with the transmission of the desired signal.

Function of the Metallic Shield:

The metallic shield in a co-axial cable serves several critical functions:

• EMI Protection: The metallic shield acts as a barrier to external electromagnetic fields, preventing them from penetrating the cable and causing interference with the transmitted signal. This ensures the integrity and clarity of the signal, which is especially important in high-frequency applications such as television broadcasting and internet data transmission.
• Signal Containment: It also prevents the electromagnetic fields generated by the signal within the cable from radiating outward and causing interference with other nearby electronic devices and cables.
• Grounding: The shield can serve as a grounding path, providing a reference point for the signal and improving overall signal stability and quality..

Explanation:

Which chemical is avoided for fiber optic cleaning?

Correct Option Analysis:

The correct option is:

Option 1: Acetone

Acetone is avoided for fiber optic cleaning due to several reasons. Acetone is a highly aggressive solvent and can cause damage to the delicate materials used in fiber optic components. The aggressive nature of acetone can lead to the dissolution or degradation of the plastic cladding or buffer material that surrounds the fiber optic glass core. This can compromise the integrity of the fiber optic cable, leading to signal loss or even complete failure of the communication link.

Moreover, acetone evaporates very quickly and can leave residues or streaks on the fiber optic surface. These residues can interfere with the transmission of light signals, causing signal attenuation and reducing the overall performance of the fiber optic system. The fast evaporation rate of acetone also makes it challenging to control during the cleaning process, increasing the risk of improper cleaning and potential damage.

In addition, acetone is highly flammable and presents a safety hazard in the workplace. The use of acetone in an environment with electrical equipment or open flames can lead to fire or explosion risks. Therefore, for safety and performance reasons, acetone is not recommended for cleaning fiber optic components.

Additional Information

Analysis of Other Options:

Option 2: Isopropyl alcohol

Isopropyl alcohol (IPA) is widely used for cleaning fiber optic components because it is effective at removing dust, oils, and other contaminants without damaging the fiber optic materials. IPA evaporates relatively quickly, leaving little to no residue, making it an excellent choice for maintaining the cleanliness and performance of fiber optic connections. It is important to use high-purity IPA (typically 99% or higher) to avoid introducing contaminants during the cleaning process.

Option 3: Ethyl alcohol

Ethyl alcohol (ethanol) is another solvent that can be used for cleaning fiber optic components. Like isopropyl alcohol, ethanol is effective at removing contaminants and evaporates quickly without leaving significant residues. However, isopropyl alcohol is generally preferred over ethanol because it is less hygroscopic (absorbs less moisture from the air), reducing the risk of moisture-related issues in the fiber optic system.

Option 4: Fiber cleaner

Fiber cleaners are specialized cleaning solutions specifically formulated for cleaning fiber optic components. These cleaners are designed to effectively remove contaminants without damaging the fiber optic materials or leaving residues. Fiber cleaners are typically available in convenient packaging, such as pre-moistened wipes or spray bottles, making them easy to use in the field or in a laboratory setting. They are considered the best choice for fiber optic cleaning due to their effectiveness and safety.

Explanation:

Cleaning the Core of an Optical Fiber Cable (OFC)

Definition: Optical Fiber Cable (OFC) is a type of cable that uses light to transmit data at high speeds. The core of the optical fiber is the central part of the fiber where the light travels. To ensure optimal performance, it is crucial to clean the core of the optical fiber properly before use.

Cleaning Process: Before cleaning the core of an optical fiber cable, several layers of the cable must be removed. These layers include the jacket, buffer coating, and Kevlar. Let’s understand each of these layers:

1. Jacket: The outermost layer of the optical fiber cable is the jacket. It provides protection against physical damage and environmental factors. The jacket is typically made of durable materials like polyethylene or PVC.

2. Buffer Coating: Beneath the jacket, the buffer coating is applied directly over the optical fiber. This layer protects the fiber from moisture and mechanical damage. The buffer coating is generally made of plastic or acrylate materials.

3. Kevlar: Kevlar is a synthetic fiber known for its high tensile strength. It is used as a reinforcing layer in optical fiber cables to provide additional strength and durability. Kevlar helps prevent the fiber from breaking when the cable is bent or pulled.

To clean the core of the optical fiber, all these layers must be removed carefully. Here is a step-by-step process for removing these layers and cleaning the core:

1. Remove the Jacket: Use a cable stripping tool to remove the outer jacket of the optical fiber cable. Be careful not to damage the inner layers while stripping the jacket.
2. Remove the Kevlar: After removing the jacket, you will see the Kevlar strands. Use scissors or a Kevlar cutter to trim the Kevlar strands. Ensure that you cut the strands close to the edge of the buffer coating.
3. Remove the Buffer Coating: Use a fiber stripping tool to remove the buffer coating. This tool is designed to strip the coating without damaging the fiber. Carefully place the fiber into the stripping tool and pull the tool along the length of the fiber to remove the coating.
4. Clean the Core: Once the core is exposed, use a lint-free wipe and an appropriate cleaning solution (usually isopropyl alcohol) to clean the core. Gently wipe the core to remove any dirt, dust, or residues.

This thorough cleaning process ensures that the optical fiber core is free from any contaminants that could interfere with data transmission.

Correct Option Analysis:

The correct option is:

Option 4: All of these

This option correctly states that all the layers (jacket, buffer coating, and Kevlar) need to be removed before cleaning the core of the optical fiber cable.

Additional Information

Understanding the importance of each layer in the optical fiber cable helps in appreciating the careful process required for cleaning the core. The jacket provides overall protection, the Kevlar adds strength, and the buffer coating protects against moisture and mechanical damage. Removing all these layers ensures that the core is exposed and can be thoroughly cleaned to maintain the cable’s performance and reliability.

Explanation:

• The primary reason for applying resin over a copper conductor before taping is to insulate the conductor.
• Insulation is crucial in preventing short circuits, electrical leaks, and ensuring the safety and efficiency of the electrical system.
• Resin also provides a protective barrier against moisture, dust, and other environmental factors that can cause corrosion or degradation of the copper conductor.

Fibre light source

A fiber light source is used to inject light into a fiber optic cable for the purpose of testing it.

In fiber optics, Laser and LED are used as a light source to emit electromagnetic radiation.

1.) Light emitting diode (LED)

• LEDs are low cost, slower speed, easy to use, multimode-only, and have a wide output pattern.
• Because LEDs produce less concentrated light than lasers and have a much lower power output than lasers, they’re difficult to couple into fibers, limiting them to multimode fibers.
• LEDs have less bandwidth than lasers and can achieve a maximum throughput of 1 Gbps.

2.) Laser diode

• Laser diodes are higher cost and faster speed, allow single-mode or multimode and have a narrow output pattern.
• Lasers can achieve throughput up to and beyond 10 Gbps.

Single mode fiber cables are used in home installations.

Types of Fiber cables

1.) Single mode fiber

• It has a much smaller core size of 9 microns and has a single light path and can travel much longer distances of up to 100km.
• Single-mode fiber features only one transmission mode.
• Compared with multi-mode fiber, it can carry higher bandwidths; however, it needs to have a light source having a narrow spectral width.
• These require more expensive electronics which operate in the 1310 and 1550nm windows and are typically used in longer distance LAN’s, Cable TV and telephony applications.

​2.) Multimode fiber

• It can carry multiple light rays (modes) at the same time by having varying optical properties at the core; essentially light travelling the shortest path (down the middle) travels the slowest.
• The larger core simplifies connections and takes advantage of the lower cost LED & VCSEL technologies which operate in the 850nm window.
• Due to dispersion the range is limited so it tends to be used as premises cabling when less than a kilometer..
• It comes in two core sizes, 62.5 and 50 microns.

Flat Ribbon Cable (FRC)

• FRC (Flat Ribbon Cable) is the most widely used type in electronics for interconnections for power and signals from 6 to 64 pins.
• These are used to interconnect internal peripherals in computers, such as hard drives, CD drives, and floppy drives. 
• They consist of highly stranded, individually-insulated conductors that are laid parallel and then fused in a flat, flexible ribbon form, hence are known as flat ribbon cables.
• To reduce the risk of reversed connections one edge of the cable is usually marked with a red stripe. By convention, the edge with the stripe is connected to pin 1 on the connector. 

CONCEPT:

• Optical fibers are transparent fibers and act as a light pipe to transmit light between its two ends. They are made up of silicon dioxide.

• The total internal reflection occurs when the angle of incidence is greater than the critical angle.
• In optical fiber glasses of a high and lower index are assembled in the precise order.
• The light comes in from one end of the fibre and after thousands of successive internal reflections, the light reaches the opposite end of the fiber with almost zero loss. 

EXPLANATION:

• The refractive index of the material of the core (μ1) is higher than that of the cladding (μ2).
• When the light is incident on one end of the fiber at a small angle, the light passes inside, undergoes repeated total internal reflections along with the fiber, and finally comes out.
• Hence, the function of the cladding is to provide a lower refractive index at the core interface in order to cause reflection within the core so that light waves are transmitted through the fiber.
• Thus, cladding and core are used in the optical fiber in order to cause Total internal reflection. Therefore option 2 is correct.

The advantages of optical fiber are:

1. High Bandwidth and hence High speed

2. Low Signal loss 

3. Immunity against electromagnetic interference 

4. Small Size

5.Small Weight

6. High flexibility

The correct answer is Total internal reflection of light.

• Optical fibers work on the principle of total internal reflection.
• When light ray strikes at the internal surface of optical fiber cable called such the incidence angle is greater than the critical angle, then incident light ray reflects in the same medium, and this phenomenon repeats.
  Additional Information
•  The phenomenon in which the angle of incidence is more than the critical angle is known as total internal reflection.

• Characteristics of optical fiber:

  • The bandwidth of the optical fiber is large with a frequency of 2 × 10¹⁴Hz.
  • The transmission losses in an optical fiber are near 0.1db/km.
  • They are flexible with high tensile strength.
  • Communication using optical fibers are free from electromagnetic interference

The correct answer is option 3.

Fiber Optic Receivers

• Fiber optic receivers convert light signals into electrical signals for use by equipment such as computer networks.
• These electro-optical devices consist of an optical detector, a low-noise amplifier, and signal conditioning circuitry.
• After the optical detector converts the incoming optical signal into an electrical signal, the amplifier increases it to a level suitable for additional signal processing. 
• Two types of semiconductors are used in fiber optic receivers i.e. silicon semiconductor such as photo diode and indium gallium arsenide semiconductors.
• Silicon semiconductors are used in short-wavelength receivers with a range of 400 nm to 1100 nm.
• Indium gallium arsenide semiconductors are used in long-wavelength receivers with a range of 900 nm to 1700 nm.

Communicating data from one location to another requires some form of pathway or medium.

These pathways are called communication channels.

Different types of communicating media are as shown below:

Optical fiber is used by many telecommunications companies to transmit telephone signals, internet communication, cable television signals, etc. 

Broadcasting by fiber optic cables consumes a lot of bandwidth. Hence it is not suitable for broadcasting. 

Fibre light source

A fiber light source is used to inject light into a fiber optic cable for the purpose of testing it.

In fiber optics, Laser and LED are used as a light source to emit electromagnetic radiation.

1.) Light emitting diode (LED)

• LEDs are low cost, slower speed, easy to use, multimode-only, and have a wide output pattern.
• Because LEDs produce less concentrated light than lasers and have a much lower power output than lasers, they’re difficult to couple into fibers, limiting them to multimode fibers.
• LEDs have less bandwidth than lasers and can achieve a maximum throughput of 1 Gbps.

2.) Laser diode

• Laser diodes are higher cost and faster speed, allow single-mode or multimode and have a narrow output pattern.
• Lasers can achieve throughput up to and beyond 10 Gbps.

Optical Fibre:

• It is a very thin fiber made of glass and plastic having a radius of the order of a micrometer (10^-6 m).
• It works on the principle of Total Internal Reflection.
• It is lightweight, fast, and useful for long-distance data and light transmission with very few losses.
• Optical fiber mostly used for communication purposes with negligible loss of energy.
• A bundle of such thin fibers forms a light pipe.

Explanation:

• The working principle of optical fibers is Total Internal Reflection. So option 3 is correct. 
• Each fiber consists of a core and cladding.
• The refractive index of the material of the core (μ₁) is higher than that of the cladding (μ₂).
• When the light is incident on one end of the fiber at a small angle, the light passes inside, undergoes repeated total internal reflections along with the fiber, and finally comes out.
• The angle of incidence is always larger than the critical angle of the core material with respect to its cladding.
• Even if the fiber is bent, the light can easily travel through along the fiber.

​

Fiber optic cable

A fiber optic cable consists of five main components: core, cladding, coating, strengthening fibers, and cable jacket.

1.) Core

• The core of the fiber cable is made up of glass.
• This is the physical medium that transports optical signals from an attached light source to a receiving device.
• The core is a single continuous strand of high-purity glass or plastic whose diameter is measured in microns. 
• The larger the core, the more light the cable can carry, which correlates to a higher data transfer rate.

2.) Cladding

• This is a thin layer that is extruded over the core and serves as the boundary that contains the light waves, enabling data to travel through the length of the fiber.

3.) Coating

• This is a plastic coating over the cladding to reinforce the fiber core, help absorb shocks, and provide extra protection against excessive cable bends.
• It does not have any effect on the optical waveguide properties.

4.) Strengthening fibers 

• These components help protect the core against crushing forces and excessive tension during installation.
• The materials can range from Kevlar, to wire strands, to gel-filled sleeves.
• Sometimes light-absorbing (“dark”) glass is added between the fibers, to prevent light that leaks out of one fiber from entering another. This reduces cross-talk between the fibers.

5.) Cable jacket

• This is the outer layer, or sheathing, of the cable.
• Its purpose is to protect the cable from environmental hazards, such as construction work, fishing gear, and even sharks, which are often attracted to the electrical fields created by signal conductors to repeaters.