Q1. Define fiber optics.

Q2. Describe the basic functions of a fiber optic data link.

Q3. List the three parts of a fiber optic data link.

Q4. What mechanisms in the fiber waveguides weaken and distort the optical signal?

Q5. What effect does noise have on the fiber optic signal?

Q6. Define loss.

Q7. In 1969, what did several scientists conclude about optical fiber loss?

Q8. How can loss be reduced during construction (or fabrication) of optical fibers?

Q9. What are the two basic types of optical fibers?

Q10. Which type of optical fiber (multimode or single mode) tends to have lower loss and produces lesssignal distortion?

Q11. What optical fiber properties reduce connection loss in short-distance systems?

Q12. In fiber optic systems, designers consider what trade-offs?

Q13. List seven advantages of fiber optics over electrical systems

Q1. Quantum physics successfully explained the photoelectric effect in terms of fundamental particlesof energy called quanta. What are the fundamental particles of energy (quanta) known as whenreferring to light energy?

Q2. What type of wave motion is represented by the motion of water?

Q3. When light waves encounter any substance, what four things can happen?

Q4. A substance that transmits almost all of the light waves falling upon it is known as what type ofsubstance?

Q5. A substance that is unable to transmit any light waves is known as what type of substance?

Q6. What is the law of reflection?

Q7. When a wave is reflected from a surface, energy is reflected. When is the reflection of energy thegreatest?

Q8. When is the reflection energy the least?

Q9. Light waves obey what law?

Q10. A refracted wave occurs when a wave passes from one medium into another medium. Whatdetermines the angle of refraction?

Q11. A light wave enters a sheet of glass at a perfect right angle to the surface. Is the majority of thewave reflected, refracted, transmitted, or absorbed?

Q12. When light strikes a piece of white paper, the light is reflected in all directions. What do we callthis scattering of light?

Q13. Two methods describe how light propagates along an optical fiber. These methods define twotheories of light propagation. What do we call these two theories?

Q14. What is the basic optical-material property relevant to optical fiber light transmission?

Q15. The index of refraction measures the speed of light in an optical fiber. Will light travel faster inan optically dense material or in one that is less dense?

Q16. Assume light is traveling through glass, what happens when this light strikes the glass-airboundary?

Q17. What condition causes a light ray to be totally reflected back into its medium of propagation?

Q18. What name is given to the angle where total internal reflection occurs?

Q19. List the three parts of an optical fiber.

Q20. Which fiber material, core or cladding, has a higher index of refraction?

Q21. Light transmission along an optical fiber is described by two theories. Which theory is used toapproximate the light acceptance and guiding properties of an optical fiber?

Q22. Meridional rays are classified as either bound or unbound rays. Bound rays propagate throughthe fiber according to what property?

Q23. A light ray incident on the optical fiber core is propagated along the fiber. Is the angle ofincidence of the light ray entering the fiber larger or smaller than the acceptance angle (ÿa

Q24. What fiber property does numerical aperture (NA) measure?

Q25. Skew rays and meridional rays define different acceptance angles. Which acceptance angle islarger, the skew ray angle or the meridional ray angle?

Q26. The mode theory uses electromagnetic wave behavior to describe the propagation of the lightalong the fiber. What is a set of guided electromagnetic waves called?

Q27. A light wave can be represented as a plane wave. What three properties of light propagationdescribe a plane wave?

Q28. A wavefront undergoes a phase change as it travels along the fiber. If the wavefront transversesthe fiber twice and is reflected twice and the total phase change is equal to 1/2p, will thewavefront disappear? If yes, why?

Q29. Modes that are bound at one wavelength may not exist at longer wavelengths. What is thewavelength at which a mode ceases to be bound called?

Q30. What type of optical fiber operates below the cutoff wavelength?

Q31. Low-order and high-order modes propagate along an optical fiber. How are modes determinedto be low-order or high-order modes?

Q32. As the core and cladding modes travel along the fiber, mode coupling occurs. What is modecoupling?

Q33. The fiber's normalized frequency (V) determines how many modes a fiber can support. As thevalue of V increases, will the number of modes supported by the fiber increase or decrease?

Q34. The value of the normalized frequency parameter (V) relates the core size with modepropagation. When single mode fibers propagate only the fundamental mode, what is the value ofV?

Q35. The number of modes propagated in a multimode fiber depends on core size and numericalaperture (NA). If the core size and the NA decrease, will the number of modes propagatedincrease or decrease?

Q36. Modal dispersion affects the bandwidth of multimode systems. It is essential to adjust what threefiber properties to maximize system bandwidth?

Q37. Attenuation is mainly a result of what three properties?

Q38. Define attenuation

Q39. What are the main causes of absorption in optical fiber?

Q40. Silica (pure glass) fibers are used because of their low intrinsic material absorption at thewavelengths of operation. This wavelength of operation is between two intrinsic absorptionregions. What are these two regions called? What are the wavelengths of operation for these tworegions?

Q41. Extrinsic (OH􀀀) absorption peaks define three regions or windows of preferred operation. List thethree windows of operation

Q42. What is the main loss mechanism between the ultraviolet and infrared absorption regions?

Q43. Scattering losses are caused by the interaction of light with density fluctuations within a fiber.What are the two scattering mechanisms called when the size of the density fluctuations is(a) greater than and (b) less than one-tenth of the operating wavelength?

Q44. Microbend loss is caused by microscopic bends of the fiber axis. List three sources of microbendloss.

Q45. How is fiber sensitivity to bending losses reduced?

Q46. Name the two types of intramodal, or chromatic, dispersion.

Q47. Which dispersion mechanism (material or waveguide) is a function of the size of the fiber's corerelative to the wavelength of operation?

Q48. Modes of a light pulse that enter the fiber at one time exit the fiber at different times. Thiscondition causes the light pulse to spread. What is this condition called?

Q1. Describe the term "refractive index profile."

Q2. The refractive index of a fiber core is uniform and undergoes an abrupt change at the corecladdingboundary. Is this fiber a step-index or graded-index fiber?

Q3. Multimode optical fibers can have a step-index or graded-index refractive index profile. Whichfiber, multimode step-index or multimode graded-index fiber, usually performs better?

Q4. List the standard core sizes for multimode step-index, multimode graded-index, and single modefibers.

Q5. Multimode step-index fibers have a core and cladding of constant refractive index n1 and n2,respectively. Which refractive index, the core or cladding, is lower?

Q6. In multimode step-index fibers, the majority of light propagates in the fiber core for what reason?

Q7. Multimode step-index fibers have relatively large core diameters and large numerical apertures.These provide what benefit?

Q8. The profile parameter (a) determines the shape of the multimode graded-index core's refractiveindex profile. As the value of the a increases, how does the core's profile change?

Q9. Light propagates in multimode graded-index fibers according to refraction and total internalreflection. When does total internal reflection occur?

Q10. What four fiber properties determine the number of modes propagating in a multimode gradedindexfiber?

Q11. Light travels faster in a material with a lower refractive index. Therefore, light rays that travel alonger distance in a lower refractive index travel at a greater average velocity. What effect doesthis have on multimode graded-index fiber modal dispersion and bandwidth?

Q12. What multimode graded-index fiber offers the best overall performance for most applications?

Q13. What are the most distinguishing characteristics of a multimode graded-index fiber?

Q14. How are source-to-fiber coupling and microbending and macrobending losses affected bychanges in core diameter and D?

Q15. While coupled power and bending loss favor a high D, whichD value, smaller or larger, improvesfiber bandwidth?

Q16. What are the two basic types of single mode step-index fibers?

Q17. Which fiber cladding, matched or depressed, consists of two regions?

Q18. In single mode operation, the value of the normalized frequency (V) should remain near the 2.405level. If the value of V is less than 1, do single mode fibers carry a majority of the power in thecore or cladding material?

Q19. What happens to the fundamental mode as the operating wavelength becomes longer than thesingle mode cutoff wavelength?

Q20. Give two reasons why the value of the normalized frequency (V) is varied in single mode stepindexfibers?

Q21. Give two reasons why optical fiber manufacturers depart from the traditional circular core andcladding, low-loss glass fiber design?

Q22. What five characteristics do applications using plastic clad silica (PCS) and all-plastic fiberstypically have?

Q23. List the types of materials used in fabricating low-loss, long wavelength optical fibers.

Q24. What are the two methods used by fiber manufacturers to fabricate multimode and single modeglass fibers?

Q25. Which method, vapor phase oxidation or direct-melt process, transforms deposited material intoa solid glass preform by heating the porous material without melting?

Q26. List three benefits that properly cabled optical fibers provide

Q27. In addition to a primary coating, manufacturers add a layer of buffer material for what reasons?

Q28. List the three techniques used by manufacturers to buffer optical fibers.

Q29. List seven properties cable jackets should have.

Q30. List the three types of cable designs being considered by the Navy

Q31. Describe an optical fiber cable component (OFCC).

Q32. Two layers of arimid yarn strength members encase the OFCC units. Why are these strengthmembers stranded in opposing directions?

Q33. Why do cable manufacturers introduce a controlled twist to the stacked ribbons during thecabling process?

Q34. OFCC, stranded, and ribbon cables have different fiber capacities. What is the approximatenumber of fibers that each cable can accommodate in a 0.5-inch cable?

Q35. Which fiber optic cable (OFCC, stranded, or ribbon) has the worst bend performance?

Q1. Which fiber optic component (splice, connector, or coupler) makes a permanent connection in adistributed system?

Q2. What are the main causes of coupling loss?

Q3. Define the loss in optical power through a connection

Q4. Fiber-to-fiber coupling loss is affected by intrinsic and extrinsic coupling losses. Can intrinsiccoupling losses be limited by limiting fiber mismatches?

Q5. In fiber-to-fiber connections, Fresnel reflection is one source of coupling losses. Light is reflectedback into the source fiber and is lost. What causes Fresnel reflection?

Q6. Reduction of Fresnel reflection is possible by reducing the step change in the refractive index atthe fiber interface. What material reduces the step change in refractive index at a fiber interface?

Q7. List the three basic errors that occur during fiber alignment

Q8. When the axes of two connected fibers are no longer in parallel, the two connected fibers are inwhat kind of misalignment?

Q9. How does index matching gel affect the amount of coupling loss caused by (a) fiber separation,(b) lateral misalignment, and (c) angular misalignment?

Q10. Which are more sensitive to alignment errors, single mode or multimode fibers?

Q11. Quality fiber-end preparation is essential for proper system operation. What properties must anoptical fiber-end face have to ensure proper fiber connection?

Q12. What is the basic fiber cleaving technique for preparing optical fibers for coupling?

Q13. Using a standard microscope to inspect a fiber-end face, you observe that all parts of the fiberendface are in focus at the same time. Is the fiber-end face flat, concave, or convex?

Q14. List six types of fiber mismatches

Q15. Does coupling loss from refractive index profile difference result when the receiving fiber has alarger profile parameter (a) than the transmitting fiber?

Q16. Define a fiber optic splice.

Q17. Fiber splicing is divided into two broad categories that describe the techniques used for fibersplicing. What are they?

Q18. Describe a transparent adhesive

Q19. The Navy recommends using the rotary splice for what two reasons?

Q20. What fiber property directly affects splice loss in fusion splicing?

Q21. List two reasons why fusion splicing is one of the most popular splicing techniques in commercialapplications.

Q22. What is a short discharge of electric current that prepares the fiber ends for fusion called?

Q23. Do small core distortions formed by arc fusion's self-alignment mechanism have more of an affecton light propagating through multimode or single mode fibers?

Q24. What connection properties result in fiber optic connector coupling loss?

Q25. Which is the more critical parameter in maintaining total insertion loss below the required level,fiber alignment or fiber mismatch?

Q26. Fiber optic connectors can reduce system performance by increasing what two types of noise?

Q27. Which type of fiber optic connector (butt-jointed or expanded beam) brings the prepared ends oftwo optical fibers into close contact?

Q28. Is coupling loss from fiber separation and lateral misalignment more critical in expanded-beamor butt-jointed connectors?

Q29. Is coupling loss from angular misalignment more critical in expanded beam or butt-jointedconnectors?

Q30. The Navy classifies fiber optic connectors in what two ways?

Q31. What is the difference between passive and active fiber optic couplers?

Q32. Which type of optical splitter (Y-coupler or T-coupler) splits only a small amount of power fromthe input fiber to one of the output fibers?

Q33. Describe a directional coupler.

Q1. List the fiber geometrical measurements performed in the laboratory.

Q2. End users measure the total attenuation of a fiber at the operating wavelength (l). Write theequation for total attenuation (A), between an arbitrary point X and point Y located on an opticalfiber.

Q3. Will an optical fiber's attenuation coefficient vary with changes in wavelength?

Q4. What two properties of the launch condition may affect multimode fiber attenuationmeasurements?

Q5. Does underfilling a multimode optical fiber excite mainly high-order or low-order modes?

Q6. Multimode optical fiber launch conditions are typically characterized as being overfilled orunderfilled. Which of these optical launch conditions exists if the launch spot size and angulardistribution are larger than that of the fiber core?

Q7. A mode filter is a device that attenuates specific modes propagating in the core of an opticalfiber. What mode propagating along single mode fibers do mode filters eliminate?

Q8. What are the two most common types of mode filters?

Q9. The cutoff wavelength of matched-clad and depressed-clad single mode fibers varies according tothe fiber's radius of curvature and length. The cutoff wavelength of which single mode fiber typeis more sensitive to length?

Q10. Will the cutoff wavelength of uncabled fibers (lcf) generally have a value higher or lower than thecutoff wavelength of cabled fibers (lcc)?

Q11. Describe the -3 decibel (dB) optical power frequency (f3dB).

Q12. Delay differences between the source wavelengths occur as the optical signal propagates alongthe fiber. What is this called?

Q13. What determines the range of wavelengths over which meaningful data is obtained forcalculating the chromatic dispersion?

Q14. Why do end users perform fiber geometry measurements in the laboratory?

Q15. Define cladding diameter

Q16. Explain the difference between multimode and single mode core-cladding concentricity errors

Q17. Near-field power distributions describe the emitted power per unit area in the near-field region.Describe the near-field region

Q18. How is the core diameter defined?

Q19. Far-field power distributions describe the emitted power per unit area as a function of angle ÿ inthe far-field region. Describe the far-field region

Q20. Will fiber coupling loss generally increase or decrease if the mode field diameter of a singlemode fiber is decreased?

Q21. In multimode fibers, how do fiber joints increase fiber attenuation following the joint?

Q22. List two effects that reflections can have on a fiber optic data link.

Q23. Reflectance is given as what ratio?

Q24. Does return loss include power that is transmitted, absorbed, and/or scattered?

Q25. Is it essential for end users to remeasure optical fiber geometrical properties after installation inthe field?

Q26. When is an OTDR recommended for conducting field measurements on installed optical fibers orlinks?

Q27. An OTDR measures the fraction of light that is reflected back from the fiber or link under test.What causes light to be reflected back into the OTDR?

Q28. List the types of fiber optic components considered part of a fiber optic cable plant.

Q29. What is a temporary or permanent local deviation of the OTDR signal in the upward ordownward direction called?

Q30. Why is a dead-zone fiber placed between the test fiber and OTDR when conducting attenuationmeasurements?

Q31. The amount of backscattered optical power at each point depends on what two properties?

Q32. How can test personnel eliminate the effects of backscatter variations?

Q33. If the length of the fiber point defect changes with pulse duration, is the OTDR signal deviation apoint defect or a region of high fiber attenuation?

Q34. Give the type of fault (reflective or nonreflective) normally produced by: (a) fiber breaks, (b)fiber cracks, and (c) fiber microbends.

Q35. Explain how a point defect may exhibit an apparent gain

Q36. A point defect exhibiting an apparent gain in one direction will exhibit what, when measured inthe opposite direction?

Q37. When is an optical power meter measurement recommended for conducting field measurementson installed optical fiber cables or cable plants?

Q38. If an installed optical fiber cable does not have connectors or terminations on both ends, howshould the cable be tested?

Q1. What are the three parts of a fiber optic transmitter?

Q2. Which part of a fiber optic transmitter converts the processed electrical signal to an opticalsignal?

Q3. LEDs operating at 850 nm provide sufficient optical power for short-distance, low-bandwidthmultimode systems. List three conditions that prevent the use of LEDs in longer distance, higherbandwidth multimode systems.

Q4. Why can multimode graded-index fiber 1300-nm systems using LEDs operate over longerdistances and at higher bandwidths than 850-nm systems?

Q5. Semiconductor LEDs emit incoherent light. Define incoherent light

Q6. Which semiconductor sources (LD or LED) emit more focused light and are capable of launchingsufficient optical power into both single mode and multimode fibers?

Q7. The amount of optical power coupled into an optical fiber depends on what four factors?

Q8. What are the two most common semiconductor materials used in electronic and electro-opticdevices?

Q9. What is a laser?

Q10. .Describe stimulated emission.

Q11. What are the three basic LED types?

Q12. Which types of LEDs are the preferred optical sources for short-distance, low-data-rate fiberoptic systems?

Q13. What are facets?

Q14. What is lowest current at which stimulated emission exceeds spontaneous emission in asemiconductor laser called?

Q15. Describe the output of a laser diode.

Q16. Which type of optical source usually lacks reflective facets and in some cases are designed tosuppress reflections back into the active region?

Q17. Which type of optical source tends to operate at higher drive currents to produce light?

Q18. Are the effects of temperature changes on LDs more or less significant than for LEDs?

Q19. Specify the mechanism that SLDs lack that is required by laser diodes to achieve lasing.

Q20. How does the source drive circuit intensity modulate the source?

Q21. What is a prebias?

Q22. Is the drive circuitry generally more complex for an LED or a laser diode? Why?

Q23. What are the two types of output interfaces for fiber optic transmitters?

Q24. List five common fiber optic transmitter packages.

Q25. What type of source is typically used in low-data-rate digital applications?

Q26. Why would a laser diode be used in a low-data-rate digital application?

Q27. What type of source is generally used in high-data-rate digital applications?

Q28. Why are LEDs preferred over laser diodes for low- and moderate-frequency analog applications?

Q1. What is a fiber optic receiver?

Q2. Which part of the receiver amplifies the electrical signal to a level suitable for further signalprocessing?

Q3. Which performance parameter is the minimum amount of optical power required to achieve aspecific bit-error rate (BER) in digital systems or a given signal-to-noise ratio (SNR) in analogsystems?

Q4. Define receiver dynamic range.

Q5. Describe the operation of an optical detector.

Q6. For efficient operation, should a detector have a high or low responsivity at the operatingwavelength?

Q7. List the two principal optical detectors used in fiber optic systems.

Q8. What are the four most common materials used in semiconductor detector fabrication?

Q9. What is a photocurrent?

Q10. Define responsivity

Q11. How are PIN photodiodes usually biased?

Q12. What is the dark current?

Q13. Will dark current increase or decrease as the temperature of the photodiode increases?

Q14. Should the capacitance of the photodetector be kept small or large to prevent the RC timeconstant from limiting the response time?

Q15. Trade-offs between competing effects are necessary for high speed response. Which competingeffect (fast transit time, low capacitance, or high quantum efficiency) requires a thin active area?

Q16. Why is detector saturation not generally a problem in fiber optic communications systems?

Q17. Describe avalanche multiplication

Q18. How can the gain of an APD be increased?

Q19. Which amplifier stage (the preamplifier or the postamplifier) is a dominant contributor of noiseand significantly influences the sensitivity of the receiver?

Q20. List the key operational parameters used to define receiver performance.

Q21. List the main types of receiver noise.

Q22. What is the main factor that determines receiver sensitivity?

Q23. For a reduction in thermal noise, should the value of the detector's load resistor be increased ordecreased?

Q24. What are two types of noise that manifest themselves as shot noise?

Q25. What are the two basic types of preamplifiers used in fiber optic receivers?

Q26. Which preamplifier design (high-impedance or transimpedance) provides improvements inbandwidth and greater dynamic range with some degradation in sensitivity from an increase innoise?

Q27. For what types of applications are APDs generally used?

Q28. Why is a low-pass filter generally part of a digital fiber optic receiver?

Q1. List four system topologies that can be constructed using point-to-point fiber optic links

Q2. Which topology (linear bus, ring, star, or tree) consists of equipments attached to one another ina closed loop?

Q3. Which topology (bus, ring, star, or tree) has a center hub interconnecting the equipments?

Q4. Define modulation.

Q5. What is a digital signal?

Q6. In NRZ code, does the presence of a high-light level in the bit duration represent a binary 1 or abinary 0?

Q7. How can the loss of timing occur in NRZ line coding?

Q8. How is a binary 1 encoded in RZ line coding?

Q9. In Manchester encoding, does a low-to-high light level transition occurring in the middle of thebit duration represent a binary 1 or a binary 0?

Q10. What is an analog signal?

Q11. What type of modulation do most analog fiber optic communications systems use?

Q12. Why has the transmission of video using analog techniques been very popular, especially forshorter distances?

Q13. Why is it generally only necessary to refer to point-to-point data links when discussing theprocess of fiber optic system design?

Q14. List five system design parameters considered when system designers choose the systemoperational wavelength and link components.

Q15. What two analyses are performed to determine if a link design is viable?

Q16. Optical fibers or cables should never be bent at a radius of curvature smaller than a certainvalue. Identify this radius of curvature

Q17. List five precautions to take when installing fiber optic systems on board naval ships.