Optical Communication Set 7

Electrical Engineering

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This set of Optical Communication Multiple Choice Questions & Answers (MCQs) focuses on Optical Communication Set 7

Q1 | It is a device that distributes light from a main fiber into one or more branch fibers.
  • optical fiber coupler
  • optical fiber splice
  • optical fiber connector
  • optical isolator
Answer: optical fiber coupler
Explaination:
nowadays, requirements to divide combined optical signals for applications are increasing. optical fiber coupler is one such device that is used for dividing and combining optical signals. it is generally used in lans, computer networks etc.
Q2 | Optical fiber couplers are also called as
  • isolators
  • circulators
  • directional couplers
  • attenuators
Answer: directional couplers
Explaination:
optical fiber couplers are
Q3 | How many types of multiport optical fiber couplers are available at present?
  • two
  • one
  • four
  • three
Answer: three
Explaination:
multiport optical fiber couplers are subdivided into three types. these are three and four port couplers, star couplers and wavelength division multiplexing (wdm) couplers. these couplers distribute light among the branch fibers with no scattering loss.
Q4 | The optical power coupled from one fiber to another is limited by                          
  • numerical apertures of fibers
  • varying refractive index of fibers
  • angular power distribution at source
  • number of modes propagating in each fiber
Answer: number of modes propagating in each fiber
Explaination:
when two fibers are coupled to each other, the optical power is limited by number of modes propagating in each fiber. for example, when a fiber propagating with 500 modes is connected to a fiber that propagates only 400 modes, then at maximum, only 80% of power is coupled into the other fiber.
Q5 |                  couplers combine the different wavelength optical signal onto the fiber or separate the different wavelength optical signal output from the fiber.
  • 3-port
  • 2*2-star
  • wdm
  • directional
Answer: wdm
Explaination:
wdm coupler is abbreviated as wavelength division multiplexing coupler. it is a category of multiport optical fiber couplers. it is designed to permit a number of different peak wavelength optical signals to be transmitted in parallel on a single fiber.
Q6 | How many fabrication techniques are used for 3 port fiber couplers?
  • one
  • two
  • three
  • four
Answer: two
Explaination:
there are two fabrication techniques available for three port couplers. first is a lateral offset method which relies on the overlapping of the fiber end faces and the other is the semi-transparent mirror method. using these techniques, three port couplers with both multimode and single-mode fibers can be fabricated.
Q7 | Which is the most common method for manufacturing couplers?
  • wavelength division multiplexing
  • lateral offset method
  • semitransparent mirror method
  • fused bi-conical taper (fbt) technique
Answer: fused bi-conical taper (fbt) technique
Explaination:
the fbt technique is basic and simple. in this technique, the fibers are generally twisted together and then spot fused under tension such that the fused section is elongated to form a bi-conical taper structure. a three port coupler can be obtained by removing one of the input fibers.
Q8 | Couplers insertion loss is same as that of excess loss.
  • true
  • false
Answer: false
Explaination:
excess loss is defined as the ratio of input power to output power. the insertion loss is defined as the loss obtained for a particular port-to-port optical path.
Q9 | The measured output power at ports 2,3 and 4 are 0.003, 23.0 and 24.5 μW respectively. Determine the excess loss.
  • 0.22 db
  • 0.33 db
  • 0.45 db
  • 0.12 db
Answer: 0.22 db
Explaination:
excess loss is a ratio of power input to power output of the fiber and it is given by excess loss = 10log10 p1/(p3+p4) wherep1, p3, p4 = output power at ports 1,3 and 4 resp.
Q10 | How many manufacturing methods are used for producing multimode fiber star couplers?
  • two
  • one
  • three
  • five
Answer: two
Explaination:
the manufacturing methods of star couplers are mixer-rod technique and fbt technique. in the mixer-rod method, a thin platelet of glass is employed, which mixes light from one fiber, dividing it among the outgoing fibers. fbt method involves twisting, heating and pulling of fiber.
Q11 | Calculate the splitting loss if a 30×30 port multimode fiber star coupler has 1 mW of optical power launched into an input port.
  • 13 db
  • 15 db
  • 14.77 db
  • 16.02 db
Answer: 14.77 db
Explaination:
the splitting loss is related to the number of output ports n of a coupler. it is given by-
Q12 | A                            coupler comprises a number of cascaded stages, each incorporating three or four-port FBT couplers to obtain a multiport output.
  • star
  • ladder
  • wdm
  • three-port
Answer: star
Explaination:
a star coupler can be realized by constructing a ladder coupler. it consists of many cascaded stages. if a three-port coupler is used, then a ladder coupler does not form symmetrical star coupler. it is a useful device to achieve a multiport output with low insertion loss.
Q13 | 2 dB along with a splice loss of 0.1 dB at the interconnection of each stage. Determine the excess loss.
  • 1.9 db
  • 1.4 db
  • 0.9 db
  • 1.1 db
Answer: 1.1 db
Explaination:
the number of stages m within the ladder design is given by 2m=16. hence m=4.
Q14 | A permanent joint formed between two different optical fibers in the field is known as a                          
  • fiber splice
  • fiber connector
  • fiber attenuator
  • fiber dispersion
Answer: fiber splice
Explaination:
the jointing of two individual fibers is called as fiber splicing. it is used to establish long-haul optical fiber links by joining two small length fibers.
Q15 | The insertion losses of the fiber splices are much less than the Fresnel reflection loss at a butted fiber joint.
  • true
  • false
Answer: true
Explaination:
the fresnel reflection loss is usually more because there is no large step change in refractive index with the fusion splice as it forms a continuous fiber connection. also, some method of index matching tends to be utilized with mechanical splices.
Q16 | What is the main requirement with the fibers that are intended for splicing?
  • smooth and oval end faces
  • smooth and square end faces
  • rough edge faces
  • large core diameter
Answer: smooth and square end faces
Explaination:
a curved mandrel is used which cleaves the fiber to achieve end preparation. the edges must be smooth and have square face at the end for splicing purpose.
Q17 | In score and break process, which of the following is not used as a cutting tool?
  • diamond
  • sapphire
  • tungsten carbide
  • copper
Answer: copper
Explaination:
the score and break process is also called as scribe and break. it involves the
Q18 | The heating of the two prepared fiber ends to their fusing point with the application of required axial pressure between the two optical fibers is called as                          
  • mechanical splicing
  • fusion splicing
  • melting
  • diffusion
Answer: fusion splicing
Explaination:
fusion splicing is also called as welding. it refers to the welding of two fiber ends. it is essential for fusion splicing that the fiber ends are adequately positioned and aligned in order to achieve good continuity of the transmission medium at the junction point.
Q19 | Which of the following is not used as a flame heating source in fusion splicing?
  • microprocessor torches
  • ox hydric burners
  • electric arc
  • gas burner
Answer: gas burner
Explaination:
micro-plasma torches uses argon and hydrogen and alcohol vapor. the most widely used heating source is an electric arc. thus, gas burner is not used in fusion splicing.
Q20 | The rounding of the fiber ends with a low energy discharge before pressing the fibers together and fusing with a stronger arc is called as                          
  • pre-fusion
  • diffusion
  • crystallization
  • alignment
Answer: pre-fusion
Explaination:
pre-fusion involves rounding of fiber ends. it removes the requirement for
Q21 |                            is caused by surface tension effects between the two fiber ends during fusing.
  • pre-fusion
  • diffusion
  • self-alignment
  • splicing
Answer: self-alignment
Explaination:
the two fiber ends are close but not aligned before fusion. during fusion, the surface tension affects the fiber ends to get aligned. after fusion, they are aligned in such a way that a transmission medium can get a good continuity.
Q22 | Mean splice insertion losses of 0.05 dB are obtained using multimode graded index fibers with the Springroove splice.
  • true
  • false
Answer: true
Explaination:
springroove utilizes a bracket containing two cylindrical pins which act as alignment guide for two fiber ends. an elastic element is used to press the fibers into a groove. the assembly is secured with a drop of epoxy resin. it provides a loss of 0.05 db and has found a practical use in italy.
Q23 |                      is the unique property of the glass fiber.
  • transmission
  • opaque property
  • ductile
  • malleable
Answer: transmission
Explaination:
glass fibres have a unique property as a transmission medium which enables their use in the communication. the major transmission characteristics are dispersion and attenuation.
Q24 |                      limits the maximum distance between the optical fiber transmitter and receiver.
  • attenuation
  • transmission
  • equipment
  • fiber length
Answer: attenuation
Explaination:
attenuation along with dispersion and the conductor size are some of the factors that limit the maximum distance between the optical transmitter and the receiver. the associated constraints within the equipment also affect the distance.
Q25 | The                        incorporates a line receiver in order to convert the optical signal into the electrical regime.
  • attenuator
  • transmitter
  • repeater
  • designator
Answer: repeater
Explaination:
repeaters are a mediator between transmitter and receiver. the weak
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