EC6702-Optical Communication and NetworksI - INTRODUCTION TO OPTICAL FIBERS
What is Numerical Aperture of a step index fiber
Define critical angle
What is total internal reflection in a fiber?
State Snell’s Law
Why do we prefer step index single mode fiber for long distance communications?
State the necessity of cladding for an optical fiber.
Relate the meridional rays from skew rays
Outline any four advantages of an optical communication system
What is meant by Conical Half angle?
Relate a formula for the normalized frequency and NA. Hence, find the Numerical aperture for a step index fiber that has normalized frequency V=26.6 at a 1300nm wavelength and core radius of 25µm.
Apply the ray transmission theory to find the critical incident angle for a glass rod of refractive index 1.5, surrounded by air.
With the knowledge of the total internal reflection, calculate the critical angle of incidence between two substances with different refractive indices where n1 = 1.5 and n2 = 1.46.
A manufacturing Engineer wants to make an optical fiber that has a core index of 1.480 and cladding index of 1.478. What should be the core size for single mode operation at 1550nm?
List out the advantages of the multimode fiber.
Distinguish Step index fibers and Graded index fiber
Evaluate the critical angle with the relative refractive index difference of 1% for an optical fiber. Given the core refractive index is 1.46.
Determine the cutoff wavelength of a single mode fiber with core radius of 4µm and ? = 0.003.
A graded index optical fiber has a core with a parabolic index profile which has a diameter of 50µm.the fiber has a numerical aperture of 0.2.calculate the total number of guided modes in the fiber when its operating at a wavelength of 1µm.
Formulate the normalized frequency at 820 nm for a step index fiber having a 25µm radius. The refractive indexes of the cladding and the core are 1.45 and 1.47 respectively. Solve to find the number of modes that propagate in this fiber at 820 nm?
Draw a neat diagram and explain the ray theory behind the optical fiber communication with a special mention about the total internal reflection, Acceptance angle and Numerical aperture.
What is numerical aperture of an optical fiber? Deduce an expression for the same.
Draw the block diagram of a optical fiber link transmission and explain the different components.
(i) What is Numerical Aperture of a fiber? Deduce an expression for the same with neat figure showing all the details.
(ii) Draw and explain the refractive index profile and ray transmission in multimode step index & single mode step index fibers. (i) Demonstrate about the transmission of light through graded index fiber with neat diagrams. (8)
(ii) Show that linearly polarized modes in optical fibers is related to the V number by obtaining proper equations and expressions. (i) Explain the phenomenon of total internal reflection using Snell's law with figures and calculations.
(ii) Classify fibers and explain them.Show that numerical aperture is dependent on the refractive indices of core and cladding through proper derivation.
(i) Apply the basic Maxwells equation to derive the mode equations for the circular fiber. With the derived results for a single mode step index fiber, estimate the shortest wavelength of light which allows single mode operation when the relative
(i) Choose the proper core size and cladding refractive index for a Si fiber using proper equations. The silica core refractive index is 1.458, v = 75 and NA = 0.3 and is operated at 820nm. Calculate the total number of modes entering this fiber.
(ii) Identify the proper angle of incidence so that the total internal reflection takes place within the optical fiber. (i) Calculate NA of silica fiber with its core refractive index (n1) of 1.48 and cladding refractive index of 1.46. Analyze and find out what should be the new value of ‘n1’ in order to change the NA to 0.23.
(ii) Distinguish step-index from graded index fibers.(i) Compare the optical link with that of the satellite link.
(ii) Contrast the advantage and disadvantage of step index, graded index, single mode propagation and multimode propagation. (i) Explain the ray propagation into and down an optical fiber cable. Also derive the expression for the acceptance angle.
Determine the fraction of average optical power residing in the cladding of a step index fiber having core radius of 25µm. The fiber operates at 1300nm and has a numerical aperture of 0.22.
(ii) A fiber has core radius of 25mm, core refractive index of 1.48 and relative refractive index difference (?) is 0.01.If the operating wavelength is 0.84mm, find the value of normalized frequency and the number of guided modes. Evaluate the number of(i) A step index fiber has a core diameter of 7µm and core refractive index of 1.49. Estimate the shortest wavelength of light which allows single mode of operation when the relative refractive index difference for the fiber is 1%.
(ii) A graded index fiber has a core with a parabolic refractive index profile which has a diameter of 50 µm. The fiber has a numerical aperture of 0.2.Estimate the total number of guided modes propagating in the fiber when it is operating at a wavelengtConclude whether TEM waves exist in as optical fiber. If not what type of mode will propagate in a practical optical fiber?
Summarize phase shift with total internal reflection and evanescent field. Construct the Wave front propagation along an optical fiber.
A graded index fiber with a parabolic index profile core has a refractive index at the core axis of 1.5 and a relative index difference of 1%.Solve the maximum possible core diameter which allows single mode operation at a wavelength of 1.3µm.
With schematic diagram, explain the blocks and their functions of the major elements of an optical fiber transmission link.
Interpret attenuation coefficient of a fiber?
List the factors that cause intrinsic joint losses in a fiber.
Define attenuation.
What is meant by Stimulated Raman Scattering?
Express group delay in optical fiber.
What are bending losses? Name its types.
What are the factors that cause Rayleigh scattering in optical fibers?
Discuss the significance of group velocity.
Give the measure of information capacity in optical wave guide
Classify the fiber losses which are given per unit distance.
Construct an expression for the effective number of modes guided by a curved multimode fiber of radius 'a'.
Identify the cause of intra modal dispersion.
State the impact of fiber birefringence.
Inspect the effects of dispersion in multimode fibers.
Compare intramodal and intermodal dispersions.
Define chromatic dispersion & what are the causes for the same?
What is Polarization Mode Dispersion (PMD)?
A manufacturers data sheet lists the material dispersion Dmat=110ps/nm.km at a wavelength of 860nm.find the rms pulse broadening per km due to material dispersion if the optical source has a spectral width =40nm at b an output wavelength of 860nm
A fiber has an attenuation of 0.5 dB/km at 1500nm. Tf 0.5mW of optical power is initially launched into the fiber, estimate the power level after 25km.
A continuous 12 kms long optical fiber link has a loss of 1.5dB/km. Propose a proper solution to find the minimum optical power that must be launched into the fiber to maintain the optical power level of 0.3 µWatt at the receiving end?
Describe the linear scattering losses in optical fibers. Also explain the loss or signal attenuation mechanisms in a fiber.
(i) Identify how the attenuation is encountered in optical fiber communication due to: (a) Bending (b) Absorption.
(ii) Solve the maximum transmission distance for a fiber link with an attenuation of 0.2 dB/Km if the power launched in 1mW and the receiver sensitivity is 50 µV. Calculate the attenuation for another link with same parameters and distance of 26Kms. (i) What is meant by critical bending radius of optical fibers? Explain.
(ii) Define signal distortion? How does Signal distortion in single mode fibers? Examine the effects of nonlinear scattering losses in optical fiber. Also bring out the differences between Absorption losses and Scattering losses.
Based on the behavior of the optical fiber, bring out the note about Information Capacity determination and group delay, explain how a signal distortion occurs in Optical wave guides.
Discuss about the Scattering losses. Imagine a scenario where the energy from the light travelling through the core is transferred to the cladding. Present the concept behind this to justify that it leads to the attenuation of the light signal.
Show that the Scattering losses are caused by the interaction of light. Explain (a) Intrinsic Absorption losses and
(b) Extrinsic Absorption losses.Illustrate the modal noise due to intermodal dispersion that occurs in a multimode fibers. Explain how the bandwidth of an optical fiber is affected.
(i) With diagram derive the expression for intramodal dispersion.
(ii) Explain how the refractive index profile and cut off wavelength of a single mode fiber affects the performance a single mode fiber.
(i) What do you mean by pulse broadening? Explain its effect on information carrying capacity of a fiber.
(ii) How a waveguide dispersion affects the performance of the transmission in an optical fiber? Explain. (i) Solve the maximum bitrate for the fiber link of 5kms. The numerical aperture is 0.25 and the refractive index is 1.48.
(ii) With the knowledge on dispersion, explain the following in single mode fiber: mode birefringence and beat length. (i) Analyse and present how the refractive index profile and the cutoff wavelength affects the design of a single mode fiber.
(ii) Explain the mode coupling that occurs in a multimode step index fibers. Show that the intermodal dispersion that occurs in a multimode step index fiber causes signal degradation in fibers.
(i) Prove that, delay difference between axial ray and extreme meridional ray is dTs=L?n1/C.
(ii) List out the effects of the hydroxyl ions and transient impurities.Explain in detail about the scattering and the bending losses that occur in an optical fiber with relevant diagrams and expressions.
When the mean optical power launched into an 8 km length of fiber is the mean optical power at the fiber output is 3µm determine:
i) The overall signal attenuation or loss in decibels through the fiber assuming there are no connectors or splices; ii) The signal attenuation per kilometre for the fiber. iii) The overall signal attenuation for a 10km optical link using the same fiber Summarize in detail about material and waveguide dispersion mechanisms with mathematical expressions.
A multimode graded index fiber exhibits total pulse broadening of 0.1µs over a distance of 15km.estimate: a) The maximum possible bandwidth on the link assuming no Inter Symbol Interference;
b) The pulse dispersion per unit length; c) The bandwidth length product for the fiber. Define internal quantum efficiency of LED and Laser.
Describe about hetero junction structure.
State the drawbacks of Avalanche photodiode.
Write any four factors which affect the power launched into the fiber.
What is the minimum detectable optical power?
Cite responsivity and factors that determine the response time of the photodiode.
Summarize the advantage of PIN diode with APD diode.
A GaAs laser operating at 850 nm has a 500 µm length and a refractive index of n=3.7. Estimate the frequency and wavelength spacing.
Give the expression for fiber to fiber coupling efficiency and possible lensing schemes to improve optical source to fiber coupling efficiency.
Point out the relation between power launching and wavelength.
Calculate bandgap energy for an LED to emit 850nm.
Classify the different noises present in the avalanche photodiode.
Compute avalanche multiplication noise.
Compare the optical sources: LASER and LED.
Examine dark current noise, laser diode rate equation and why Silicon is not used to fabricate LED or LASER diode.
Categorize the types of mechanical misalignment.
Determine the different factors that determine the response time of photo detector.
Evaluate the lensing schemes to improve optical source to fiber coupling efficiency.
Construct mechanical splicing in optical fiber.
Elaborate on fiber to fiber coupling loss and significance of intrinsic layer in PIN diodes.
(i) What are direct band gap and indirect band, gap semiconductors?
(ii) Describe the characteristics required for an optical source.Write short note on, (i) Fiber connectors
(ii) Splices and couplers(i) What are the possible noise sources that contribute the photodetector noise?
(ii) What is meant by detector response time? Explain.Explain the different lensing schemes available to improve the power coupling efficiency of light emitting diode.
Draw and compare LED and Injection Laser Diode structures.
(i) Summarize coupled cavity semiconductor lasers and tunable semiconductor lasers.
(ii) Draw and explain the structure of Fabry Perot resonator cavity for a Laser diode. Derive Laser diode rate equation. (i) Explain in detail about source to Fiber power launching.
(ii) Draw the structures and electric fields in APD and explain its working.(i) Derive the expression for the quantum effiency of a double hetro structure LED.
(ii) Construct power launching and coupling in optical fiber amplifiers. (i) Illustrate the three factors that decides the response time of photodiodes. Explain them in detail with neat sketches.
(ii) Classify the three types of fiber misalignment that contribute to insertion loss at an optical fiber joint. With diagram, explain Surface Emitting LED, Edge Emitting LED.
(i) With neat sketch,explain the working of a light emitting diode.
(ii) Analyze about optical detection noise.(i) A double heterojunction InGaAsP LED emitting at a peak wavelength of 1310 nm has radiative and non-radiative recombination time of 25 ns and 90 ns respectively. The drive current is 35mA. Determine bulk recombination time, internal quantum efficiency
(ii) Compare the optical sources LED and ILD.(i) Determine the internal quantum efficiency and internal power level of LED.
(ii) Explain the term external quantum efficiency relating to LASER.(i) Elaborate in detail about various fiber splicing techniques. Discuss about fusion splicing and mechanical splicing with necessary diagrams.
(ii) Develop the operation of an injection laser & PIN photodiode.(i) Generalize the resonant frequencies of laser diodes.
(ii) A planar LED is fabricated from gallium arsenide which has a refractive index of 3.6, Estimate the optical power emitted into air as a percentage of the internal optical power for the device when the transmission factor at the crystal-air i(i) Assess with neat diagram about the structure of LASER diode and its radiation pattern.
(ii) A GaAs optical source with refractive index of 3.6 is coupled to a silica fiber that has refractive index of 1.48. Estimate the power loss between source and the fiber.
(i) Evaluate about fusion splicing and mechanical splicing.
(ii) Summarize the threshold current densities at 32oC and 100oC for a AlGaAs injection laser with To=160 K and the similar ratio for an InGaAIP device with To=55 k. (i) Compose the different types of noise affecting the performance of a photodetector and derive an expression for the signal to noise ratio.
(ii) A photodiode is constructed GaAs which has a band gap energy of 1.43 eV at 300 K. Solve the long wavelength cut-off. List the advantages of using transimpedance front end receiver configuration and error sources associated with it.
What is the cut back method?
Define responsivity, bit-error rate and receiver sensitivity.
Write any two advantages of trans impedance amplifiers with generic structure.
A digital fiber optic link operating at 1310 nm, requires a maximum BER of 10-8. Identify the average photons per pulse.
The photo detector output in a cutback-attenuation set up is 3.3 V at the far end of the fiber. After cutting the fiber at the near end, 5m from the far end photo detector output read was 9.2 V. Find the attenuation of the fiber in dB/Km.
Generalize the error sources of receiver.
Interpret the idea about quantum limit.
Express dark current and detector response time.
Summarize the different methods for measuring the attenuation of a fiber.
Justify the use of silicon is preferred to make optical receivers.
Interpret Modal Noise and Mode partition Noise.
Calculate the mean of (1/f) noise corner frequency.
Point out the advantages of preamplifiers.
Categorize the types of preamplifiers.
Examine the standard fiber measurement techniques.
Determine Bend attenuation.
Why the attenuation limit curve slopes towards to the right and significance of maintaining the fiber outer diameter constant.
Develop the measures to avoid modal noise.
Propose the range of system margin in link power budget.
Draw the configuration of the fundamental optical receiver. Write about each block and the source of error during transmission.
With diagrams describe the following: (i) Measurement of NA of a fiber,
(ii) Measurement of refractive index profile.Explain in detail about the methods used for measuring the intermodal dispersion and chromatic dispersion.
(i) A digital fiber optic link operating at 850 nm requires a maximum BER of 10-9.Cite the quantum limit in terms of the quantum efficiency of the detector and the energy of the incident photon.
(ii) Define the attenuation and explain any method to measure the attenuation in an optical fiber in detail. (i) Explain any two types of pre amplifiers used in a receiver.
(ii) Estimate the terms-Quantum limit and Probability of Error with respect to a receiver with typical values. (i) Give main idea about ‘Insertion-Loss method’ used for attenuation measurement.
(ii) Express the technique used in Frequency-Domain intermodal Dispersion measurement. List the various types of pre amplifiers available for optical networks and explain any three of them with their circuit diagrams.
Demonstrate the following in detail: (i) Fiber refractive index profile measurement.
(ii) Fiber cutoff wavelength measurement.Exhibit various performance measures of a digital receiver? Derive an expression for the Bit Error Rate of a digital receiver.
Examine the dispersion and numerical aperture measurements of fiber.
(i) Explain in detail about the front end optical amplifiers.
(ii) Considering the probability distributions for received logic 0 and 1 signal pulses, derive the expressions for BER and error function. Analyze the following: (i) Fiber refractive index profile measurement.
(ii) Fiber cut-off wavelength measurement.Evaluate the error sources of fundamental receiver operations. Discuss the performance of digital receiver by defining the probability of error.
(i) Develop the schematics of pin photodiode and APD and explain.
(ii) Design the fundamental receiver operation in optical communication.(i) Elaborate the numerical aperture measurements methods in optical fiber.
(ii) A He-Ne laser operating at a wavelength of 0.63 µm was used with a solar cell cube to measure the scattering loss in a multimode fiber sample.With a constant optical power the radiating from the solar cell cube was 6.14 nV. The optical power measurem(i) Generalize with a typical experimental arrangement, brief the measurement process of diameter of the fiber.
(ii) The photo detector output in a cutback attenuation set up is 3.3 V at the far end of the fiber. After cutting the fiber at the near end, 5 m from the far end, photo detector output read was 3.92 V. Invent the attenuation of the fiber in dB/km. (i) Assess the different structures of receiver in the optical fiber communication with neat diagram.
(ii) A trigonometrical measurement is performed in order to determine the numerical of a step index fiber. The screen is positioned 10.0 cm from the fiber end face. When illuminated from a wide-angled visible source the measured output pattern size is(i) Summarize the dispersion measurement methods in optical fiber.
(ii) Measurements are made using a calorimeter and thermocouple experimental arrangement. Initially a high absorption fiber is utilized to obtain a plot of (T8 - Tt) on a logarithmic scale against t. It is found from the plot that the readings of State the concept of WDM.
Mention any two nonlinear effects present in optical fiber.
Identify the drawbacks of broadcast and select networks for wide area network applications.
Summarize the transmission bit rate of the basic SONET frame in Mbps.
Outline interchannel cross talk that occurs in a WDM system.
Examine about the Power Penalty in non-linear effects on network performance.
List the benefits of SONET over PDH networks.
Give the significance of solitons.
Illustrate the problems associated with PDH networks.
Draw the basic structure of STS-1 SONET frame.
Predict the function of EDFA.
Illustrate the key parameters required for analyzing the optical link.
Manipulate the difference between fundamental and higher order soliton.
Express the various SONET/SDH layers.
Analyze how the speckle pattern can form?
Classify the important features of time-slotted optical TDM network.
Justify the features in DWDM.
Conclude the advantages of using soliton signals through fiber.
Develop the basic performance parameters of the WDM system.
Propose the three topologies used for fiber optic network.
Write about intrachannel and interchannel crosstalk that occur in WDM systems.
Draw the architecture of 12 × 12 optical cross connect and explain.
(i) Define the principle of WDM networks.
(ii) State the principles used in SONET.Explain in brief the blocks and their functions of an optical receiver with schematic diagrams.
Discuss about protection mechanism in UPSR and BLSR ring architecture and point to point architecture with neat sketch.
(i) Illustrate the effects of noise in optical networks.
(ii) Extend the perceptions of ultrahigh capacity networks.(i) Summarize the basic concepts of Optical Networks.
(ii) Express the non-linear effects on network performance.(i) Model the Layered architecture of SONET/SDH with neat diagram.
(ii) Illustrate the detailed notes on optical CDMA and its applications.(i) Demonstrate SONET frame structure with appropriate diagram.
(ii) Build the SONET Network topology.With suitable example, analyze the conditions and constraints in the formulation and solution of routing and wavelength assignment problem in an optimal way.
Compare and analyze optical switching Methods.
(i) Inspect about the optical power budgeting.
(ii) Analyze the optical power budget for the below system and hence determine its viability. Components are chosen for a digital optical fiber link of overall length 7Km and operating at 20Mbit s-1 using an RZ code. It is decided that an LED emitting aSummarize the amplification mechanism, architecture, gain, ?, amplifier noise in EDFA.
Discuss the performance improvement of WDM + EDFA systems.
Estimate the following requirements for the design of an optically amplified WDM link:
(a) Link Bandwidth (b) Optical power requirements for a specific BER. An engineer has the following components available:
a) GaAlAs laser diode, operating at 850 nm,fiber coupled power 0dbm b) Ten sections of cable each of which is 500 m long, has 4dB/km attenuation has connectors at both ends c) 2dB/connector connector loss d) A PIN photodiode receiver, -45 dBm sensitivitEvaluate the salient feature of solitons using relevant expressions and diagrams.
A 90 Mb/s NRZ data transmission system that sends two DS3 channels uses a GaAlAs laser diode that has a spectral width of 1 nm. The rise time of the laser transmitter output is 2 ns. The transmission distance is 7 km over a graded index fiber that has 800

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