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Communications MCQ Set 1

1. Which of the following is not a technique for fabrication of glass fibers?
a) Vapor phase oxidation method
b) Direct melt method
c) Lave ring method
d) Chemical vapor deposition technique

View Answer

Answer: c [Reason:] Lave ring method refers to the deposition of a crystalline layer on a substrate. All the other methods, except lave ring method, refer to the optical fiber fabrication.

2. _____________ technique is method of preparing extremely pure optical glasses.
a) Liquid phase (melting)
b) Radio frequency induction
c) Optical attenuation
d) Vapor Phase Deposition (VPD)

View Answer

Answer: d [Reason:] Vapor Phase Deposition techniques are used to prepare silica-rich glasses. These glasses exhibit highest transparency and optimal optical properties.

3. Which of the following materials is not used as a starting material in vapor-phase deposition technique?
a) SiCl4
b) GeCl4
c) O2
d) B2O3

View Answer

Answer: d [Reason:] In vapor-phase deposition technique, starting materials are volatile organic compounds. These materials are distilled to reduce the concentration of transition metal impurities. B2O3 is used as a dopant.

4. P2O5 is used as a _____________
a) Dopant
b) Starting material
c) Cladding glass
d) Core glass

View Answer

Answer: a [Reason:] P2O5 is a non silica material. Dopants are formed from non silica materials so that refractive index modification is achieved. Other dopants include Ti O2, Ge O2etc.

5. How many types of vapor-phase deposition techniques are present?
a) One
b) Two
c) Three
d) Four

View Answer

Answer: b [Reason:] Vapor-phase deposition techniques are divided into two types. The two types are flame hydrolysis and chemical vapor deposition (CVD). Further, these two types are subdivided into two more sections.

6.___________ uses flame hydrolysis stems from work on soot processes which were used to prepare the fiber with losses below 20 dB/km.
a) Outside vapor phase oxidation
b) Chemical vapor deposition
c) Liquid phase melting
d) Crystallization

View Answer

Answer: a [Reason:] Outside vapor phase oxidation is a type of vapor flame hydrolysis. It was originally developed by Hyde. In this process, the glass composition is deposited from a ‘soot’ generated by hydrolyzing the halide vapors in an oxygen-hydrogen flame.

7. Complete the given reaction
SiCl4+ 2H2O→ SiO2+ ______
a) 2HCl
b) 4HCl
c) 2Cl2
d) 4Cl2

View Answer

Answer: b [Reason:] SiCl4is a starting material used in vapour-phase deposition technique. Dopants are added to the starting material in presence of heat to give glass compound. In the above reaction SiO2 (solid compound) along with 4HCl(gas) is obtained.

8. In modified chemical vapor deposition, vapor phase reactant such as _________ pass through a hot zone.
a) Halide and oxygen
b) Halide and hydrogen
c) Halide and silica
d) Hydroxides and oxygen

View Answer

Answer: a [Reason:] Halide and oxygen are passed through the hot zone during chemical vapor deposition. Glass particles formed during this travel are deposited on the walls of silica tube which are moved back and forth allowing the particles to deposit layer by layer.

9. _________ is the stimulation of oxide formation by means of non-isothermal plasma maintained at low pressure in a microwave cavity surrounding the tube.
a) Outside Vapor Phase Oxidation (OVPO)
b) Vapor Axial Deposition (VAD)
c) Modified Chemical Vapor Deposition (MCVD)
d) Plasma-activated Chemical Vapor Deposition (PCVD)

View Answer

Answer: d [Reason:] PCVD method was first developed by Cuppers and Koenig’s. It involves a plasma-induced chemical vapor deposition inside a silica tube. It is different from MCVD process as it involves stimulation of oxide formation by means of non-isothermal plasma.

10. Only graded index fibers are made with the help of vapor-phase deposition techniques. State whether true or false.
a) True
b) False

View Answer

Answer: b [Reason:] Vapor phase deposition techniques are used for preparation of both step-index and graded index fibers. These techniques provide fibers with low attenuation losses. Also, it gives similar performance for the fabrication of both single mode and multimode fibers.

11. Modified Chemical Vapor Deposition (MCVD) process is also called as an inside vapor phase oxidation (IVPD) technique. State whether the given statement is true or false.
a) True
b) False

View Answer

Answer: a [Reason:] MCVD process was developed by Bell Telephone Laboratories and Southampton University, UK. It is called as inside vapor phase oxidation (IVPO) as it takes place inside the silica tube at the temperatures between 1400 and 1600 degree Celsius.

Communications MCQ Set 2

1. Which of the following is used to provide wavelength signal service among the nodes?
a) Regularization
b) Optical enhancing
c) Hopping
d) Pulse breakdown

View Answer

Answer: c [Reason:] The optical layer is dependent on wavelength. The entire physical interconnected network provides wavelength signal service among the nodes using hopping technique.

2. How many types of hopping are present?
a) Two
b) One
c) Three
d) Four

View Answer

Answer: a [Reason:] There are two types of hopping. They are single hop and multihop. These techniques provide wavelength dependent service for interconnected physical network among the nodes.

3. How many switching layers are possessed by MG-OXC?
a) Two
b) Three
c) One
d) Six

View Answer

Answer: b [Reason:] An MG-OXC has three switching layers. They are wavelength cross-connect (WXC), waveband cross-connects (BXC), and fiber cross-connects (FXC). These layers help to terminate the wavebands and individual wavelength channels.

4. _____________ supports a great number of wavelength channels and reduces the number of switches within the optical network.
a) Waveband switching
b) Optical remuneration
c) Optical genesis
d) Wavelength multiplexing

View Answer

Answer: a [Reason:] Waveband switching reduces the number of ports within the optical network. It reduces the complexity of numerous wavelength-driven channels and makes it efficient.

5. Individual wavelength channels and wavebands are terminated through________________ layers.
a) WXC and PXC
b) WXC and FXC
c) BXC and FXC
d) WXC and BXC

View Answer

Answer: d [Reason:] The individual wavelength channels are terminated and the terminated waveband is then de-multiplexed. The de-multiplexing is in the form of individual channels which are sent to WXC layer as inputs.

6. The routing and wavelength assignment problem addresses the core issue of _____________
a) Traffic patterns in a network
b) Wavelength adjustment
c) Wavelength continuity constraint
d) Design problem

View Answer

Answer: c [Reason:] The routing and wavelength assignment problem includes selecting a suitable path and allocating an available wavelength. These problems fall into two categories of sequential or combinational selections.

7. How many techniques of implementation are there for routing wavelength assignment (RWA)?
a) Two
b) Six
c) Three
d) Four

View Answer

Answer: a [Reason:] The implementation of RWA can be static and dynamic. This depends on the traffic patterns in the network. Static RWA techniques are semi-permanent and dynamic RWA techniques are random in nature.

8. ____________ deals with establishing the light path in frequently varying traffic patterns.
a) Wavelength routing
b) Wavelength multiplexing
c) Static RWA
d) Dynamic RWA

View Answer

Answer: d [Reason:] In dynamic RWA, the traffic patterns are not known. Thus, the connection requests are initiated in random fashion. Its random nature depends on the network state at the time of request.

9. Static RWA problem is also known as _____________
a) Routing problem
b) Virtual topology problem
c) Static wavelength problem
d) Light path problem

View Answer

Answer: b [Reason:] Static RWA problem refers to the connection problems which remain connected for a smaller duration of time. Thus, network resources are assigned to each connection. It is also called as virtual topology design problem.

10. The ___________ provides information about the physical path and wavelength assignment for all active light paths.
a) Network state
b) RWA
c) LAN topology
d) Secluded communication protocol

View Answer

Answer: a [Reason:] The physical path i.e. route is associated with the routing problem. Each connection is provided with network resources to reduce complexity in functioning. The network state is basically required to provide information related to routing and assignment problems.

11. ________________ plays an important role in determining the blocking probability of a network.
a) CGA algorithm
b) Semi-pristine environment
c) RWA algorithm
d) Pass key protocol

View Answer

Answer: c [Reason:] RWA algorithm’s efficiency is calculated on the basis of no blocking or lowest blocking probability. It also provides the information about the availability of the path between the source and destination.

12. Wavelength assignment in RWA is independent on the network topology. State whether the given statement is true or false.
a) True
b) False

View Answer

Answer: b [Reason:] RWA algorithm deals with the wavelength assignment, physical path and blocking probability. Network topology plays a crucial role in the wavelength assignment. The network state and topology enables the RWA algorithm to function smoothly.

13. Static RWA technique is semi-permanent. State whether the given statement is true or false.
a) True
b) False

View Answer

Answer: a [Reason:] The connections employs in static RWA are semi-permanent but remain active for a relatively longer period of time. The traffic patterns are known in advance and thus the optimization can be done by assigning network resources to each connection.

Communications MCQ Set 3

1. Monolithic integration for optical sources are confined to the use of __________ semiconductors.
a) Ⅲ-Ⅴ
b) Ⅱ-Ⅲ
c) Ⅰ-Ⅱ
d) Ⅶ-Ⅷ

View Answer

Answer: a [Reason:] Ⅲ-Ⅴsemiconductor compounds are much useful. They possess both optical and electronic properties. These properties can be exploited to produce high performance devices.

2. Circuits fabricated from GaAs or AlGaAs operate in wavelength region of __________
a) 0.1 and 0.2 μm
b) 0.8 and 0.9 μm
c) 0.4 and 0.6 μm
d) 0.6 and 0.7 μm

View Answer

Answer: b [Reason:] Circuits fabricated from GaAs use injection laser which is fabricated on GaAs with a MESFET. This is used to bias and modulate the laser.

3. The OEICs realization __________ as compared to the other developments in IO.
a) Scripted
b) Decreased
c) Lagged behind
d) Increased

View Answer

Answer: c [Reason:] IO devices use dielectric materials such as lithium niobate. This lagging behind is caused by inherent difficulties in fabrication of OEICs even if Ⅲ-Ⅴ semiconductors are used.

4. Compositional and structural differences between photonic and electronic devices __________
a) Provide high efficiency
b) Provide low efficiency
c) Highly used
d) Create problems

View Answer

Answer: d [Reason:] Compositional and structural differences cause epitaxial crystal growth, planarization for lithography, electrical interconnections. They also cause thermal and chemical stability of materials, electric matching and heat dissipation.

5. To avoid large chip, ________ devices are used.
a) InGaAsP
b) InGa
c) GaAs
d) InGaAs

View Answer

Answer: a [Reason:] To avoid large chip, InGaAsP devices are used with directly modulated semiconductor lasers. This gives good dynamic characteristics at 40 Gbit/s at 1.55 μmwavelength.

6. Devices operating at transmission rates greater than 40 Gb/s are _________
a) GaAs and InP
b) GaAs
c) InGa
d) InGaAs

View Answer

Answer: a [Reason:] Optoelectronic integrated circuits are based on heterojunction bipolar transistor and electron mobility transistor use GaAs and InP. These are capable of operating at transmission rates higher than 40 Gb/s.

7. HEMT based __________ have a spot-size convertor with a photodiode.
a) p-n junction diode
b) p-i-n photoreceiver
c) IGBT
d) BJT

View Answer

Answer: b [Reason:] P-I-N photoreceiver comprises of spot-size convertor with a photodiode. Spot-size convertor increases fiber alignment tolerances by one order of magnitude. This enables use of cleaved instead of lensed fiber.

8. P-I-N photoreceiver based on HEMT is integrated with _________ guiding layers.
a) GaAs and InP
b) GaAs
c) InGa
d) InGaAsP

View Answer

Answer: d [Reason:] P-I-N photoreceiver is integrated with InGaAsP guiding layers. In this HEMT based technology, InGaAsP provides more confinement.

9. An optical power splitter integrated with optical waveguide amplifier is more useful. State whether the given statement is true or false.
a) True
b) False

View Answer

Answer: a [Reason:] The aim of optical waveguide amplifier is to reduce the number of amplifiers in system. Alongwith, it also reaches maximum number of nodes.

10. The use of intelligent optical switches is necessary. State whether the given statement is true or false.
a) False
b) True

View Answer

Answer: b [Reason:] Most applications of OEICs in optical networks require large switching capacity to support a large number of WDM channels. This also provides control of both optical signal wavelength and signal power.

11. The wafer scale replication technology uses ____________
a) SOL gel
b) GaAs
c) InGa
d) InGaAsP

View Answer

Answer: a [Reason:] Replication technology employs hot embossing, molding and ultraviolet lithography. Ultraviolet curable SOL gel enables refractive and diffractive micro-optical elements to be replicated directly on glass substrates.

12. ___________ is useful for production of both planar micro-optical elements and stacked optical microsystems.
a) Wavelength amplifier
b) Wavelength convertor
c) Replication technology
d) Optical switching matrix

View Answer

Answer: c [Reason:] SOL gel materials used in replication technology allows combination of replication with lithography. This leaves selected areas material-free for sawing and bunding.

13. Optical interconnection between optoelectronic device is achieved in _________
a) Wavelength amplifier
b) Wavelength convertor
c) Replication technology
d) Chip-to-chip interconnection

View Answer

Answer: d [Reason:] The chip-to-chip interconnection of optical components have a vertical cavity surface-emitting laser. These are assembled in micro-trenches in which embedded electrodes are connected through passive junction of poliver waveguide on alignment pits.

14. Multilevel interconnections are incorporated in _______
a) PIC
b) AWG based coupler
c) Convertors
d) OEIC technologies

View Answer

Answer: a [Reason:] PIC reduces the overall size of optical functions. This causes interconnection of several modules growing on same substrate.

15. When there is M number of WDM channels present at N input ports, then the output port 1 produces a _________
a) CW signal
b) WDM signal
c) Amplified signal
d) Distorted signal

View Answer

Answer: b [Reason:] The reconstituted spectrum of WDM signal at any output port consists of a different set of wavelength channels with at least one wavelength channel from each input port producing a WDM signal having wavelength signal from each of input ports.

Communications MCQ Set 4

1. The fraction of incident photons generated by photodiode of electrons generated collected at detector is known as
a) Quantum efficiency
b) Absorption coefficient
c) Responsivity
d) Anger recombination

View Answer

Answer: a [Reason:] Efficiency of a particular device is obtained by ratio of input given to that of output obtained. Thus, similarly, in photodiode, input i.e. incident photon and output generated electrons and their ratio is quantum efficiency.

2. In photo detectors, energy of incident photons must be ________________ band gap energy
a) Lesser than
b) Greater than
c) Same as
d) Negligible

View Answer

Answer: b [Reason:] While considering intrinsic absorption process, the energy of incident photon must be greater than band gap energy of material fabricating photo detector.

3. GaAs has band gap energy of 1.93 eV at 300 K. Determine wavelength above which material will cease to operate
a) 2.431*10-5
b) 6.424*10-7
c) 6.023*103
d) 7.234*10-7

View Answer

Answer: b [Reason:] The long wavelength cutoff is given by λc= hc/Eg = 6.6268*10-34*2.998*108/1.93*1.602*10-19 = 6.424*10-7μm.

4. The long cutoff wavelength of GaAs is 0.923 μm. Determine bandgap energy
a) 1.478*10-7
b) 4.265*10-14
c) 2.784*10-9
d) 2.152*10-19

View Answer

Answer: d [Reason:] Long wavelength cutoff of photo detector is given by λc= hc/Eg Eg = hc/λc= 6.6268*10-34*2.998*108/0.923*10-6 = 2.152*10-19eV.

5. Quantum efficiency is a function of photon wavelength. Determine the given statement is true or false.
a) True
b) False

View Answer

Answer: a [Reason:] Quantum efficiency is less than unity as all of incident photons are not absorbed to create electrons holes pairs. For example quantum efficiency of 60% is equivalent to 60% of electrons collected per 100 photons. Thus efficiency is a function of photon wavelength and must be determined at a particular wavelength.

6. Determine quantum efficiency if incident photons on photodiodes is 4*1011 and electrons collected at terminals is 1.5*1011
a) 50%
b) 37.5%
c) 25%
d) 30%

View Answer

Answer: b [Reason:] Quantum efficiency is given by Quantum Efficiency = No. of electrons collected/No. of incident photons = 1.5*1011 /4*1011 = 0.375 * 100 = 37.5%.

7. A photodiode has quantum efficiency of 45% and incident photons are 3*1011 . Determine electrons collected at terminals of device.
a) 2.456*109
b) 1.35*1011
c) 5.245*10-7
d) 4.21*10-3

View Answer

Answer: b [Reason:] Quantum efficiency is given by Quantum efficiency = No. of electrons collected/No. of incident photons Electrons collected = Quantum efficiency * number of incident photons = 45/100 * 3*1011 = 1.35*1011 .

8. The quantum efficiency of photodiode is 40% with wavelength of 0.90*10-6. Determine the responsivity of photodiodes
a) 0.20
b) 0.52
c) 0.29
d) 0.55

View Answer

Answer: c [Reason:] Responsivity of photodiodes is given by R = ηe λ/hc = 0.4*1.602*10-19* 0.90*10-6/ 6.626*10-34* 3*108 = 0.29 AW-1.

9. The Responsivity of photodiode is 0.294 AW-1at wavelength of 0.90 μm. Determine quantum efficiency.
a) 0.405
b) 0.914
c) 0.654
d) 0.249

View Answer

Answer: a [Reason:] Responsivity of photodiode is R = ηe λ/hc η= RXhc/eλ = 0.294*6.626*10-34* 3*108/ 1.602*10-19* 0.90 *108 = 0.405 AW-1.

10. Determine wavelength of photodiode having quantum efficiency of 40% and Responsivity of 0.304 AW-1
a) 0.87 μm
b) 0.91 μm
c) 0.88 μm
d) 0.94 μm

View Answer

Answer: d [Reason:] The Responsivity of photodiode is R = ηe λ/hc λ = Rhc/ηe = 0.304*6.626*10-34*3*108/ 0.4*1.602*10-19 = 0.94 μm.

11. Determine wavelength at which photodiode is operating if energy of photons is 1.9*10-19J
a) 2.33
b) 1.48
c) 1.04
d) 3.91

View Answer

Answer: c [Reason:] To determine wavelength, λ = hc/t = 6.626*10-34*3*108/ 1.9*10-19 = 1.04 μm.

12. Determine the energy of photons incident on a photodiode if it operates at a wavelength of 1.36 μm
a) 1.22*10-34J
b) 1.46*10-19J
c) 6.45*10-34J
d) 3.12*109J

View Answer

Answer: b [Reason:] The wavelength of photodiode is given by λ = hc/t E = hc / λ = 6.626*10-34*3*108/ 1.36*10-6 = 1.46*10-19J.

13. Determine Responsivity of photodiode having o/p power of 3.55 μmand photo current of 2.9 μm.
a) 0.451
b) 0.367
c) 0.982
d) 0.816

View Answer

Answer: d [Reason:] The Responsivity of photodiode is R = Ip/Po = 2.9*10-6/ 3.55*10-6 = 0.816 A/W.

14. Determine incident optical power on a photodiode if it has photocurrent of 2.1 μAand responsivity of 0.55 A/W
a) 4.15
b) 1.75
c) 3.81
d) 8.47

View Answer

Answer: c [Reason:] The Responsivity of photodiode is R = Ip/Po Po = Ip/R = 2.1*10-6/0.55 = 3.81 μm.

15. If a photodiode requires incident optical power of 0.70 A/W. Determine photocurrent.
a) 1.482
b) 2.457
c) 4.124
d) 3.199

View Answer

Answer: b [Reason:] The Responsivity of photodiode is given by R = Ip/Po Ip = R*Po = 0.70*3.51*10-6 = 2.457μm.

Communications MCQ Set 5

1. The detailed knowledge of the refractive index profile predicts the __________ of the fiber.
a) Nodal response
b) Variation in frequency
c) Impulse response
d) Amplitude

View Answer

Answer: c [Reason:] Refractive index profile plays an important role in characterizing the properties of optical fibers. These properties include numerical aperture, intermodal response and number of modes propagating in the fiber. This makes the impulse response of the fiber.

2. ______________ of the fiber is strongly dependent on the refractive index profile.
a) Amplitude
b) Tuning frequency
c) Diameter
d) Information carrying capacity

View Answer

Answer: d [Reason:] Information carrying capacity is strongly dependent on the refractive index profile same as that of the impulse response of the fiber. These characteristics predict the dispersion in the fiber.

3. ______________ is required in case of graded index fibers.
a) High amplitude
b) High frequency
c) High impulse response
d) Optimum profile

View Answer

Answer: d [Reason:] In case of graded index fibers, it is essential that the fiber manufacturer is able to produce particular profiles with higher accuracy. This profile is known as optimum profile as it minimizes the dispersion rate.

4. _______________ have been widely used to determine the refractive index profiles of optical fibers.
a) Interference microscopes
b) Gyro meters
c) Mode-diameter device
d) Tunable microscopes

View Answer

Answer: a [Reason:] Interference microscopes are used to determine the refractive index profiles of the fibers. These microscopes use an index matching technique to determine the index profiles.

5. Which of the following is not an interference microscope?
a) Gerry Buzynski
b) Michelson
c) Mach-Zehnder
d) L.G. Cohen

View Answer

Answer: a [Reason:] Mach-Zehnder and Michelson are the widely used interference microscopes. L.G.Cohen reused a modification of the Mach-Zehnder.

6. What stands for x in the given equation?
δn=qλ/x
a) Displacement
b) Thickness
c) Constant
d) Coefficient of refraction

View Answer

Answer: b [Reason:] The given equation is an equation for the difference in the refractive index which is denoted byδn. q is the fringe shift, λ is the the wavelength and x is the thickness of the fiber slab.

7. The ________ method gives an accurate measurement of the refractive index profile.
a) Slab
b) Biometric
c) GSLB
d) Tuning

View Answer

Answer: a [Reason:] The slab method gives an accurate measurement of the refractive index profile. Also, there are some drawbacks to it. The computation of individual points is somewhat tedious unless an automated technique is used.

8. Which of the following is the main drawback of the slab technique?
a) Efficiency
b) Amplitude
c) Time
d) Accuracy

View Answer

Answer: c [Reason:] The main drawback of the slab method is the time required to prepare the fiber slab. There are some interferometry methods which requires no sample preparation.

9. ________________ method is used to measure the nonlinear refractive index of the silica fiber.
a) Grating
b) Non-linear
c) Silica-refraction
d) IGA

View Answer

Answer: IGA is abbreviated as induced-grating autocorrelation. This method requires no slab preparation and involves electro-optic effect where measuring the electric field autocorrelation function determines the refractive index of the optical fiber.

10. Near field scanning method provides a rapid method for acquiring the refractive index profile. State whether the given statement is true or false.
a) True
b) False

View Answer

Answer: a [Reason:] The near field scanning method provides no time lag for slab preparation, thus it is not time bound. Hence, it is accurate and rapid mode of measuring refractive index profile.