Assignment A

Ans.1. BASIC STRUCTURE OF AN OPTICAL FIBER

The basic structure of an optical fiber consists of three parts; the core, the cladding, and the coating or buffer. The basic structure of an optical fiber is shown in figure 2-9. The core is a cylindrical rod of dielectric material. Dielectric material conducts no electricity. Light propagates mainly along the core of the fiber. The core is generally made of glass. The core is described as having a radius of (a) and an index of refraction n1. The core is surrounded by a layer of material called the cladding. Even though light will propagate along the fiber core without the layer of cladding material, the cladding does perform some necessary functions.

The cladding layer is made of a dielectric material with an index of refraction n2. The index of refraction of the cladding material is less than that of the core material. The cladding is generally made of glass or plastic. The cladding performs the following functions:

Reduces loss of light from the core into the surrounding air  Reduces scattering loss at the surface of the core Protects the fiber from absorbing surface contaminants Adds mechanical strength

For extra protection, the cladding is enclosed in an additional layer called the coating orbuffer. The coating or buffer is a layer of material used to protect an optical fiber from physical damage. The material used for a buffer is a type of plastic.

The buffer is elastic in nature and prevents abrasions. The buffer also prevents the optical fiber from scattering losses caused by microbends. Microbends occur when an optical fiber is placed on a rough and distorted surface. 

PROPAGATION OF LIGHT ALONG A FIBER

The concept of light propagation, the transmission of light along an optical fiber, can be described by two theories. According to the first theory, light is described as a simple ray. This theory is the ray theory, or geometrical optics, approach. The advantage of the ray approach is that you get a clearer picture of the propagation of light along a fiber. The ray theory is used to approximate the light acceptance and guiding properties of optical fibers. According to the second theory, light is described as an electromagnetic wave. This theory is the mode theory, or wave representation, approach. The mode theory describes the behavior of light within an optical fiber. The mode theory is useful in describing the optical fiber properties of absorption, attenuation, and dispersion. 

Ans2. Attenuation

Attenuation in an optical fiber is caused by absorption, scattering, and bending losses. Attenuation is the loss of optical power as light travels along the fiber. Signal attenuation is defined as the ratio of optical input power (Pi) to the optical output power (Po). Optical input power is the power injected into the fiber from an optical source. Optical output power is the power received at the fiber end or optical detector. The following equation defines signal attenuation as a unit of length:

Signal attenuation is a log relationship. Length (L) is expressed in kilometers. Therefore, the unit of attenuation is decibels/kilometer (dB/km). As previously stated, attenuation is caused by absorption, scattering, and bending losses. Each mechanism of loss is influenced by fiber-material properties and fiber structure. However, loss is also present at fiber connections.

Ans.3. Lasers are monochromatic (single color wavelength), collimated (non-divergent) and coherent (wavelengths in- phase) in contrast, LED's are neither coherent nor collimated and generate a broader band of wavelengths (multiple). In addition, a significant difference between the two is the power output. The peak power output of lasers is measured in watts, while that of LED's, is measured in milliwatts. Also, LED's usually have a 50% duty cycle, meaning that they are "on" 50% of the time and "off" 50% of the time regardless of what frequency (pulses per second) setting is used.

There are many light emitting products on the market today, claiming to be lasers that do not meet scientifically defined attributes for being a true laser. For

example, products that use Light Emitting Diodes or LEDs as they are more commonly known, do in fact produce light, however the light is not intense,

producing very little energy and is non-coherent, similar to light produced by common household light bulbs. Non-coherent or non-culminated light is the

result of photons moving in random directions at random times, generating random frequencies. The most common use of LEDs is in electronic equipment,

such as cell phones and VCRs, to inform the users that the item is ON. LEDs are cheap and easy to reproduce (Pontinen 1992). Obviously, these devices are

NOT lasers. This misconception is in large part a by-product of marketing. Some sales professional use the word "laser" in order to describe a process such

as in "laser pointers" which refers more to mankind's collective imagination than scientific comprehension.

LED Diode vs LASER Diode

LED Diode

Full form of LED- light emitting diode.

LED's are small in size, longer life, reliable and require little power.

Here generation photon by spontaneous emittion.

LED's produce a divergent and incohrent light beam.

Types of LED 1> surface emitter and 2> Edge emitter.

Their response is fast.

A wide range of wavelengths is available.

The cost of LED would be less.

An intensity of generating light is less.

Coupling efficiency of LED with fiber is less.

LED's use with the multimode fibers.

Bandwidth of led is moderate.

In led have require no extra circuit because of its simple circuit.

Here require drive current is 50 to 100mA.

LASER Diode

Full form of LASER - light amplification by stimulated emmition of radiation.

Laser's are bigger in size, longer life, less reliable and require more power then LED.

Here generating photon by stimulated emission.

Laser produce q monochromatic and coherent light beam.

Types of Laser (a) semiconductor laser and (b) Gas laser.

Their response is faster than LED.

A small range of wavelength is available.

The cost of Laser would be higher.

Coupling efficiency of Laser with fiber is higher.

Laser use with both single mode and multi mode fibers.

-Bandwidth of laser is higher.

In laser have require extra circuit for isolation of temperature reaction.

Here require drive current is Therashold current 5 to 40mA.

Ans.4. In a typical fiber optic network, the data signal is transmitted using single light pulse at either 1310 nm or 1550 nm wavelengths.  Historically, the way to increase the capacity of a single fiber is to increase the bit rate of the signal (1 Mbps to 10 Mbps to 100 Mbps).  Throughout the last 30 years, optical systems have increased their capacity regularly, allowing for bandwidth upgrades that outpaced the growth in bandwidth demands.Primarily driven by Ethernet and packet-based services, the need for bandwidth has exploded. Even mid-sized network operators are demanding multiple 10 Gbps pipes to accommodate large increases for growing and diverse applications such as surveillance, ITV, and data-center connections. This growth requires transport that is flexible and scalable.Wavelength division multiplexing (WDM) is now a cost-effective, flexible and scalable technology for increasing capacity of a fiber network. WDM architecture is based a simple concept – instead of transmitting a single signal on a single wavelength, transmit multiple signals, each with a different wavelength. Each remains a separate data signal, at any bit rate with any protocol, unaffected by other signal on the fiber.

Wave Division Multiplexing

CWDM and DWDM

There are two types of WDM: Coarse and Dense Wavelength Division Multiplexing (CWDM and DWDM).CWDM uses a wide spectrum and accommodates eight channels.  This wide spacing of channels allows for the use of moderately priced optics, but limits capacity.  CWDM is typically used for lower-cost, lower-capacity, shorter-distance applications where cost is the paramount decision criteria.DWDM systems pack 16 or more channels into a narrow spectrum window very near the 1550 nm local attenuation minimum.  Decreasing channel spacing requires the use of more precise and costly optics, but allows for significantly more scalability.  Typical DWDM systems provide 1-44 channels of capacity, with some new systems, offering up to 80-160 channels. DWDM is typically used where high capacity is needed over a limited fiber resource or where it is cost prohibitive to deploy more fiber.ROADM and FOADM

As with most transport systems, there are requirements to add and drop traffic along ring and tapered networks.  WDM systems support two types of add/drop Fixed and Reconfigurable Optical Add/Drop Multiplexers (FOADM and ROADM).FOADMs are based on simple static fibers that permit add/drop of predefined wavelengths. These systems are fully integrated and manageable and provide a fine balance of features and cost.

ROADMs add the ability to remotely switch traffic from a WDM system at the wavelength layer. While more expensive than FOADMs, ROADMs are used in application where traffic patterns are not fully known or change frequently.The key features and benefits of WDM include:

Protocol and Bit Rate Agnostic – wavelengths can accept virtually any services Fiber Capacity Expansion – WDM adds up to 160X bandwidth to a single fiber Hi Cap/Long Haul and Lo Cap/Short Haul Applications – CWDM and DWDM provide price performance for virtually any network Remotely Provisionable – ROADMs provide the flexibility to change with changing network requirements

WDM Network

Ans.5. An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. Optical amplifiers are important in optical communication and laser physics. With the demand for longer transmission lengths, optical amplifiers have become an essential component in long-haul fiber optic systems. Semiconductor optical amplifiers (SOAs), erbium doped fiber amplifiers (EDFAs), and Raman optical amplifiers lessen the effects of dispersion and attenuation allowing improved performance of long-haul optical systems. 

Semiconductor Optical AmplifiersSemiconductor optical amplifiers (SOAs) are essentially laser diodes, without end mirrors, which have fiber attached to both ends. They amplify any optical signal that comes from either fiber and transmit an amplified version of the signal out of the second fiber. SOAs are typically constructed in a small package, and they work for 1310 nm and 1550 nm systems. In addition, they transmit bidirectionally, making the reduced size of the device an advantage over regenerators of EDFAs. However, the drawbacks to SOAs include high-coupling loss, polarization dependence, and a higher noise figure. Figure 1 illustrates the basics of a Semiconductor optical amplifier.

Figure 1 - Semiconductor Optical Amplifier

Modern optical networks utilize SOAs in the follow ways: Power Boosters: Many tunable laser designs output low optical power levels and must be immediately followed by an optical amplifier. ( A power booster can use either an SOA or EDFA.) In-Line Amplifier: Allows signals to be amplified within the signal path. Wavelength Conversion: Involves changing the wavelength of an optical signal. Receiver Preamplifier: SOAs can be placed in front of detectors to enhance sensitivity.

EDFAsThe explosion of dense wavelength-division multiplexing (DWDM) applications make these optical amplifiers an essential fiber optic system building block. EDFAs allow information to be transmitted over longer distances without the need for conventional repeaters. The fiber is doped with erbium, a rare earth element, that has the appropriate energy levels in their atomic structures for amplifying light. EDFAs are designed to amplify light at 1550 nm. The device utilizes a 980 nm or 1480nm pump laser to inject energy into the doped fiber. When a weak signal at 1310 nm or 1550 nm enters the fiber, the light stimulates the rare earth atoms to release their stored energy as additional 1550 nm or 1310 nm light. This process continues as the signal passes down the fiber, growing stronger and stronger as it goes. Figure 2 shows a fully featured, dual pump EDFA that includes all of the common components of a modern EDFA. 

Figure 2 - Block Diagram of an EDFA

The input coupler, Coupler #1, allows the microcontroller to monitor the input light via detector #1. The input isolator, isolator #1 is almost always present. WDM #1 is always present, and provides a means of injecting the 980 nm pump wavelength into the length of erbium-doped fiber. WDM #1 also allows the optical input signal to be coupled into the erbium-doped fiber with minimal optical loss. The erbium-doped optical fiber is usually tens of meters long. The 980 nm energy pumps the erbium atom into a slowly decaying, excited state. When energy in the 1550 nm band travels through the fiber it causes stimulated emission of radiation, much like in a laser, allowing the 1550 nm signal to gain strength. The erbium fiber has relatively high optical loss, so its length is optimized to provide maximum power output in the desired 1550 nm band. WDM #2 is present only in dual pumped EDFAs. It couples additional 980 nm energy from Pump Laser #2 into the other end of the erbium-doped fiber, increasing gain and output power. Isolator #3 is almost always present. Coupler #2 is optional and may have only one of the two ports shown or may be omitted altogether. The tap that goes to Detector #3 is used to monitor the optical output

power. The tap that goes to Detector #2 is used to monitor reflections back into the EDFA. This feature can be used to detect if the connector on the optical output has been disconnected. This increases the backreflected signal, and the microcontrolled can set to disable the pump lasers in this event, providing a measure of safety for technicians working with EDFAs. Figure 3 shows a two-stage EDFA with mid-stage access. In this case, two single-stage EDFAs are packaged together. The output of the first stage EDFA and the input of the second stage EDFA are brought out the user. Mid-stage access is important in high performance fiber optic systems. To reduce the overall dispersion of the system, dispersion compensating fiber (DCF) can be used periodically. However, problems can arise from using the DCF, mostly the insertion loss reaching 10 dB. Placing the DCF at the mid-stage access point of the two-stage EDFA reduces detrimental effects on the system, and allows the users noticeable gain.

Figure 3 - Two-stage EDFA with Mid-stage Access

The optical input first passes through optical Isolator #1. Next the light passes through WDM #1, which provides a means of injecting the 980 nm pump wavelength into the first length of erbium-doped fiber. WDM #1 also allows the optical input signal to be coupled into the erbium-doped fiber with minimal optical loss. The erbium-doped optical fiber is usually tens of meters long. Like the fully feature, dual pumped EDFA, the 980 nm energy pumps the erbium atoms into an excited state that decays slowly. When light in the 1550 nm band travels through the erbium-doped fiber it causes stimulated emission of radiation. As the optical signal gains strength, output of the erbium-doped fiber then goes into the optical isolator #2, the output of which is available to the user. Typically, a dispersion compensating device will be connected at the mid-stage access point. The light then travels through isolator #3 and WDM #2,

which couples additional 980 nm energy from a second pump laser into the other end of a second length of erbium-doped fiber, increasing gain and output power. Finally, the light travels through isolator #4. Photons amplify the signal avoiding almost all active components, a benefit of EDFAs. Since the output power of an EDFA can be large, any given system design can require fewer amplifiers. Yet another benefit of EDFAs is the data rate independence means that system upgrades only require changing the launch/receive terminals. The most basic EDFA design amplifies light over a narrow, 12 nm, band. Adding gain equalization filters can increase the band to more than 25 nm. Other exotic doped fibers increase the amplification band to 40 nm. Because EDFAs greatly enhance system performance, they find use in long-haul, high data rate fiber optic communication systems and CATV delivery systems. Long-haul systems need amplifiers because of the lengths of fiber used. CATV applications often need to split a signal to several fibers, and EDFAs boost the signal before and after the fiber splits. There are four major applications that generally require optical fiber amplifiers: power amplifier/booster, in-line amplifier, preamplifier or loss compensation for optical networks. Below are detailed description of each application. Power Amplifier/Booster Figure 4 illustrates the first three application for optical amplifiers. Power amplifiers (also referred to as booster amplifiers) are placed directly after the optical transmitter. This application requires the EDFA to take a large signal input and provide the maximum output level. Small signal response is not as important because the direct transmitter output is usually -10 dBm or higher. The noise added by the amplifier at this point is also not as critical because the incoming signal has a large signal-to-noise ratio (SNR). 

Figure 4 - Three Applications for an EDFA

In-Line Amplifiers In-line amplifiers or in-line repeaters, modify a small input signal and boost it for retransmission down the fiber. Controlling the small signal performance and noise added by the EDFA reduces the risk of limiting a system's length due to the noise produced by the amplifying components. Preamplifiers Past receiver sensitivity of -30 dBm at 622 Mb/s was acceptable; however, presently, the demands require sensitivity of -40 dBm or -45 dBm. This performance can be achieved by placing an optical amplifier prior to the receiver. Boosting the signal at this point presents a much larger signal into the receiver, thus easing the demands of the receiver design. This application requires careful attention to the noise added by the EDFA; the noise added by the amplifier must be minimal to maximize the received SNR. Compensating for Loss in Optical Networks Inserting an EDFA before an 8 x 1 optical splitter increases the power to almost +19 dBm allowing each of the eight output legs to provide +9 dBm, making the output almost equal to the original transmitter power. The optical splitter alone has a nominal optical insertion loss of 10 dB. The transmitter has an optical output of +10 dBm, meaning that the optical splitter outputs without an EDFA would be 0 dBm. This output power would be acceptable for most digital applications; however, in analog CATV

applications this is the minimal acceptable received power. Therefore, inserting the EDFA before the optical splitter greatly increases the output power.

Figure 5 - Loss Compensation in Optical Networks

Wideband EDFAs Optical communication systems carrying 100 or more optical wavelengths require and increase in the bandwidth of the optical amplifier to nearly 80 nm. Normally employing a hybrid optical amplifier, consisting of two separate optical amplifiers, allows for separate amplification, one for the lower 40 nm band and the second for the upper 40 nm band. Figure 6 exemplifies the optical gain spectrum of a hybrid optical amplifier. The solid lines illustrate the response of two individual amplifier sections. The dotted line, which has been increased by 1 dB for clarity, shows the response of the combined hybrid amplifier.

Figure 6 - Optical Gain Spectrum of a Hybrid Optical Amplifier

Raman Optical AmplifiersRaman optical amplifiers differ in principle from EDFAs or conventional lasers in that they utilize stimulated Raman scattering (SRS) to create optical gain. Initially, SRS was considered too detrimental to high channel count DWDM systems. Figure 7 shows the typical transmit spectrum of a six channel DWDM system in the 1550 nm window. Notice that all six wavelengths have approximately the same amplitude. 

Figure 7 - DWDM Transmit Spectrum with Six Wavelengths

By applying SRS the wavelengths, it is obvious that the noise background has increased, making the amplitudes of the six wavelengths different. The lower wavelengths have a smaller amplitude than the upper wavelengths. The SRS effectively robbed energy from the lower wavelength and fed that energy to the upper wavelength.

Figure 8 - Received Spectrum After SRS is on a Long Fiber

A Raman optical amplifier is little more that a high-power pump laser, and a WDM or directional coupler. The optical amplification occurs in the transmission fiber itself, distributed along the transmission path. Optical signals are amplified up to 10 dB in the network optical fiber. The Raman optical amplifiers have a wide gain bandwidth (up to 10 nm). They can use any installed transmission optical fiber. Consequently, they reduce the effective span loss to improve noise performance by boosting the optical signal in transit. They can be combined with EDFAs to expand optical gain flattened bandwidth. Figure 9 shows the topology of a typical Raman optical amplifier. The pump laser and circulator comprise the two key elements of the Raman optical amplifier. The pump laser, in this case, has a wavelength of 1535 nm. The circulator provides a convenient means of injecting light backwards in to the transmission path with minimal optical loss.

Figure 9 - Typical Raman Amplifier Configuration

Figure 10 illustrates the optical spectrum of a forward-pumped Raman optical amplifier. The pump laser is injected at the transmit end rather than the receive end as shown in Figure 9. The pump laser has a wavelength of 1535 nm; the amplitude is much larger than the data signals.

Figure 10 - Example of Raman Amplifier -- Transmitted Spectrum

As before, applying SRS makes the amplitude of the six data signals much stronger. The energy from the 1535 nm pump laser is redistributed to the six data

signals.

Figure 11 - Example of Raman Amplifier -- Received Spectrum

Assignment B

Ans.1. Synchronous Optic Network (SONET) and Synchronous Digital Hierarchy (SDH) are standards used in fiber optic networks that power large telephone and Internet networks. SONET networks are deployed in North America; SDH networks are deployed everywhere else.  Although the SONET standards were developed before SDH, it is considered a variation of SDH because of SDH's greater worldwide market penetration.The data communications industry uses the concept of “backbone” to refer to a large network capable of carrying heavy loads of traffic. SONET and SDH fiber optic networks, although expensive, are ideal backbone networks, offering high speeds and reliability. Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously overoptical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). At low transmission rates data can also be transferred via an electrical interface. 

SONET and SDH, which are essentially the same, were originally designed to transport circuit mode communications (e.g., Digital Signal1, Digital Signal3)

from a variety of different sources, but they were primarily designed to support real-time, uncompressed, circuit-switched voice encoded in Pluse-Code

Modulation format. The primary difficulty in doing this prior to SONET/SDH was that the synchronization sources of these various circuits were different.

This meant that each circuit was actually operating at a slightly different rate and with different phase. SONET/SDH allowed for the simultaneous transport of

many different circuits of differing origin within a single framing protocol. SONET/SDH is not a communications protocol in itself, but a transport protocol.

Due to SONET/SDH's essential protocol neutrality and transport-oriented features, SONET/SDH was the obvious choice for transporting the fixed

length Asynchronous Transfer Mode (ATM) frames also known as cells. It quickly evolved mapping structures and concatenated payload containers to

transport ATM connections. In other words, for ATM (and eventually other protocols such as Ethernet), the internal complex structure previously used to

transport circuit-oriented connections was removed and replaced with a large and concatenated frame (such as STS-3c) into which ATM cells, IP packets, or

Ethernet frames are placed.

In other words we can say that, Both SONET and SDH are based on a structure that has a basic frame format and speed. The frame format used by SONET is the Synchronous Transport Signal (STS), with STS-1 as the base-level signal at 51.84 Mbps. An STS-1 frame can be carried in an OC-1 signal. The frame format used by SDH is the Synchronous Transport Module (STM), with STM-1 as the base-level signal at 155.52Mbps. An STM-1 frame can be carried in an OC-3 signal. Both SONET and SDH have a hierarchy of signaling speeds. Multiple lower-level signals can be multiplexed to form higher-level signals. For example, three STS-1 signals can be multiplexed together to form an STS-3 signal, and four STM-1 signals multiplexed together to form an STM-4 signal.

SONET and SDH are technically comparable standards. The term SONET is often used to refer to either.

Ans.2. Intersymbol Interference

In a digital transmission system, distortion of the received signal, manifested in the temporal spreading and consequent overlap of individual pulses to the degree that the receiver cannot reliably distinguish between changes of state, i.e., between individual signal elements. At a certain threshold, intersymbol interference will compromise the integrity of the received data. Intersymbol interference may be measured by eye patterns.

In telecommunication, Intersymbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable. ISI is usually caused by multipath propagation or the inherent non-linear frequency response of a channel causing successive symbols to "blur" together. The presence of ISI in the system introduces errors in the decision device at the receiver output. Therefore, in the design of the transmitting and receiving filters, the objective is to minimize the effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate possible. Ways to fight intersymbol interference include adaptive equalization and error correcting codes.

Crosstalk in Optical –Fibers

The crosstalk in fiber optics, the undesired optical power that is transferred from, i.e., that leaks from, one optical fiber to another.The crosstalk is often a measure of the optical power picked up by an optical fiber from an adjacent energized fiber.  The crosstalk, (XT), is always negative. The negative sign is

commonly ignored. The crosstalk may be given simply in dB (decibels), such as 90dB. The crosstalk is undesired capacitive, inductive or conductive coupling from one electrical circuit, part of a circuit or channel to another.

Ans.3. Fiber optic joints or terminations are made two ways: 1)  splices which create a permanent joint between the two fibers or 2) connectors that mate two fibers to create a temporary joint and/or connect the fiber to a piece of network gear. 

Splices are considered permanent joints and are used for joining most outside plant cables. Fusion splicing is most widely used as it provides for the lowest loss and least reflectance, as well as providing the most reliable joint. Virtually all singlemode splices are fusion. Mechanical splicing is used for temporary restoration and for most multimode splicing.Connectors are used for terminations, that is the ends of the fibers where they connect to equipment or to patch panels where fiber routing can be changed by patching different fibers together. Different connectors and termination procedures are used for multimode and singlemode fibers. Multimode fibers are relatively easy to terminate, so field termination is generally done by installing connectors directly on tight buffered fibers using the procedures outlined below. Most field singlemode terminations are made by splicing a factory-made pigtail onto the installed cable rather than terminating the fiber directly as is commonly done with multimode fiber. Singlemode terminations require extreme care in assembly, especially polishing, to get good performance (low loss and reflectance), so they are usually done in a clean manufacturing facility using heat-cured epoxy and machine polishing.

Assignment c

1. The 3-D shape of an Optical Fiber is

a. A cylinder rod

b. Rectangular

c. Square

d. Circle

Ans: a

2. The waves that travels through the fiber is

a. Electrical Wanes

b. Radio Waves

c. Light Waves

d. None of the above

Ans: C

3. Optical fiber are made up of

a. Sand & Glass

b. Conductor

c. Glass and Plastic

d. None of the Above

Ans: C

4. “Bare fibers” are having protection Sheath

a. Yes

b. No

c. Not sure

d. There is no such term

Ans: B

5. Can fibers be bent at right angles?

a. Yes

b. No

c. Not sure

d. There is no such term

Ans: B

6. The principle on which the optical fiber works is:

a. Total Internal Reflection

b. Critical Angle of Incidence

c. Angle of Inciddence

d. None of the Above

Ans: A

7. Transmission media are usually categorized as _______.

A) fixed or unfixed

B) guided or unguided

C) determinate or indeterminate

D) metallic or nonmetallic

8.

Transmission media lie below the _______ layer.

A) physical

B) network

C) transport

D) application

9. _______ cable consists of an inner copper core and a second conducting outer

sheath.

A) Twisted-pair

B) Coaxial

C) Fiber-optic

D) Shielded twisted-pair

10. 4. In fiber optics, the signal is _______ waves.

A) light

B) radio

C) infrared

D) very low-frequency

11. Which of the following primarily uses guided media?

A) cellular telephone system

B) local telephone system

C) satellite communications

D) radio broadcasting

12. Which of the following is not a guided medium?

A) twisted-pair cable

B) coaxial cable

C) fiber-optic cable

D) atmosphere

13. What is the major factor that makes coaxial cable less susceptible to noise than

twisted-pair cable?

A) inner conductor

B) diameter of cable

C) outer conductor

D) insulating material

14. In an optical fiber, the inner core is _______ the cladding.

A) denser than

B) less dense than

C) the same density as

D) another name for

15. The inner core of an optical fiber is _______ in composition.

A) glass or plastic

B) copper

C) bimetallic

D) liquid

16. When a beam of light travels through media of two different densities, if the angle of

incidence is greater than the critical angle, _______ occurs.

A) reflection

B) refraction

C) incidence

D) criticism

17. When the angle of incidence is _______ the critical angle, the light beam bends along

the interface.

A) more than

B) less than

C) equal to

D) none of the above

18. Signals with a frequency below 2 MHz use _______ propagation.

A) ground

B) sky

C) line-of-sight

D) none of the above

19.

________ cable consists of two insulated copper wires twisted together.

A) Coaxial

B) Fiber-optic

C) Twisted-pair

D) none of the above

20. _______ cable is used for voice and data communications.

A) Coaxial

B) Fiber-optic

C) Twisted-pair

D) none of the above

21. _____ cable can carry signals of higher frequency ranges than _____ cable.

A) Twisted-pair; fiber-optic

B) Coaxial; fiber-optic

C) Coaxial; twisted-pair

D) none of the above

22. ______ cables are composed of a glass or plastic inner core surrounded by cladding,

all encased in an outside jacket.

A) Coaxial

B) Fiber-optic

C) Twisted-pair

D) none of the above

23. ______ cables carry data signals in the form of light.

A) Coaxial

B) Fiber-optic

C) Twisted-pair

D) none of the above.

24. Transmission media are usually categorized as

a. Fixed or unfixed

b, Guided or unguided

c. Determinate or indeterminate

d. Metallic or nonmetallic

25. Transmission media are closest to the ________ layer.

a. Physical

b. Network

c. Transport

d. Application

26. Category 1 UTP cable is most often used in _______ networks.

a. Fast Ethernet

b. Traditional Ethernet

c. Infrared

d. Telephone

27. BNC connectors are used by ________ cables.

a. UTP

b. STP

c. Coaxial

d. Fiber-optic

28. _______ cable consists of an inner copper core and a second conducting outer

sheath.

a. Twisted-pair

b Coaxial

c. Fiber-optic

d. Shielded twisted-pair Dr. Gihan NAGUIB 2

29. In fiber optics, the signal source is ______waves.

a. Light

b. Radio

c. Infrared

d. Very low-frequency

30. Smoke signals are an example of communication through_____

a. A guided medium

b. An unguided medium

c. A refractive medium

d. A small or large medium

31.Which of the following primarily uses guided media?

a. Cellular telephone system

b. Local telephone system

c. Satellite communications

d. Radio broadcasting

32. Which of the following is not a guided medium?

a. Twisted-pair cable

b. Coaxial cable

c. Fiber-optic cable

d. Atmosphere

33.. In an environment with many high-voltage devices, the best transmission medium

would be _________

a. Twisted-pair cable

b. Coaxial cable

c. Optical fiber

d. The atmosphere

34. . What is the major factor that makes coaxial cable less susceptible to noise than

twisted-pair cable?

a. Inner conductor

b. Diameter of cable

c. Outer conductor

d. Insulating material

35. The RG number gives us information about

a. Twisted pairs

b. Coaxial cables

c. Optical fibers

d. All the above

36. In an optical fiber, the inner core is ___________ the cladding.

a. Denser than

b. Less dense than

c. The same density as

d. Another name for

37. The inner core of an optical fiber is in composition.

a. Glass or plastic

b. Copper

c. Bimetallic

d. Liquid

39. Optical fibers, unlike wire media, are highly resistant to

a. High-frequency transmission

b. Low-frequency transmission

c. Electromagnetic interference

d. Refraction

40. When the angle of incidence is __________ the critical angle, the light beam

bends along the interface.

a. More than

b. Less than

c. Equal to

d. None of the above