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DON BOSCO INSTITUTE OF TECHNOLOGY, (DBIT), MUMBAI, 400070. Date of Assignment : 21 st March, 2011. Date of Submission: 4 th April,2011.
1. Describe Describe the structur structuree of different different types types of optical optical fibers fibers with with ray paths. paths. What is the approximate core and cladding diameter of an optical fiber in each case. Sketch their refractive index profile. 2. Describe Describe a simple simple block diagra diagram m of an optical optical fiber fiber transmiss transmission ion link and and explain explain the function of each element in the link. 3. Explain Explain the principl principlee of light transm transmissi ission on down the step step index index and graded index index fiber 4. Using simpl simplee ray theory, theory, describe describe the the mechanism mechanism for the the transmiss transmission ion of light light within an optical fiber. Briefly with the aid of suitable diagram w hat is meant by the acceptance angle for an optical fiber. Show how this is related to numerical aperture and the refractive indices for the fiber core and cladding. 5. An optical optical fiber fiber has a numerical numerical apertur aperturee of 0.20 and a cladding cladding refract refractive ive index of 1.59. Determine : (a) The acceptance angle for the the fiber in water which has a refractive index index of 1.33; (b) The critical critical angle at the core cladding cladding interface interface 6. The velocity velocity of light light in the the core of a step index fiber fiber is 2.01x 108 m/s, and the critical angle at the core cladding interface is 800. Determine the numerical aperture and the acceptance angle for the fiber in air, assuming it has h as a core diameter suitable for consideration by ray analysis. The velocity of light in a vacuum is is 2.998 x 103 m/s. 7. Determine Determine the relat relative ive refractiv refractivee index differen difference ce for an optical optical fiber fiber and show show how it may be related to the numerical aperture. A step index fiber with a large core diameter compared with the wavelength of the transmitted light has an acceptance angle in air of 220 and a relative refractive index difference of 3%. Estimate the numerical aperture and the critical angle at the core-cladding interface for the fiber. 8. A step index fiber has a solid acceptance angle in air of 0.115 radians and a relative refractive index difference of 0.9%. Estimate the speed of light in the fiber core. 9. Briefly indicate with the aid of suitable diagrams the difference between meridional and skew ray paths in step index fibers. 10. Describe with the aid of simple ray diagram: (a) the multimode multimode step index fiber (b) the single-mode step index fiber Comapre the advantages and disadvantages of these two types of fiber for use a s an optical channel. 11. A multimode step index fiber has a relative refractive index difference of 1% and a core refractive index of 1.5. The number of modes propogating at a wavelength of 1.3µm is 1100. Estimate the diameter of o f the fiber core. 12. Explain what is meant by a graded index fiber, giving an expression for the
possible refractive index profile. Using simple ray theory concepts, discuss the transmission of light through the fiber. Indicate the major advantage of this type of fiber with regard to multimode propagation 13. A graded index fiber with a parabolic index profile supports the propagation of 742 guided modes. The fiber has a numerical aperture in air of 0.3 and a core diameter of 70µm. Determine the wavelength of the light propogating in the fiber. Further estimate the maximum diameter of the fiber which gives single mode operation at the same wavelength. 14. A single mode step index fiber has a core diameter of 7µm and a core refractive index of 1.49. Estimate the shortest wavelength of light which allows single-mode operation when the relative refractive index difference for the fiber is 1%. 15. In problem 14 it is required to increase the core diameter to 10µm whilst maintaining single mode operation at the same wavelength. Estimate the maximum possible relative index for the fiber. What do you mean by attenuation property of a fiber? Why does the attenuation of a signal take place in an optical fiber What are the typical wavelengths used in fiber communication Draw any two structure each for LED and LD. Compare the properties of LED and LD and comment on their suitability for optical communication What are the various factors contributing to the attenuation in optical fibers Explain intramodal and intermodal dispersion in optical fibers. How does dispersion effect the bandwidth of optical fibers What are the desirable properties of the source of optical communication What do you mean by splicing of fiber? What is the name of the similar term in metallic system? What is the basic difference between the two. Explain the various steps involved in splicing procedure Compare different splicing techniques? What are the advantages of placing an optical matching cement List the important point-to-point link design used in optical communication. Explain each in brief What are the common LED structures used for optical fiber communications. Discuss the merits and drawbacks. Compare surface a nd edge emitting devices. Discuss the boundary conditions and the mode cutoff in case of an optical fiber. What is the significance of ‘V’ number. Get an expression for it in terms of NA Explain with neat sketches fiber splicing techniques also list the merits and demerits of each. Enlist the desirable requirements for a good fiber connector Explain the relation between bit rate and bandwidth in OFC Explain Modified chemical vapour deposition (MCVD) mthod of fiber fabricatiob in detail Explain the various lensing scheme for fiber coupling improvement Explain the various parameters required to find the performance if digital optical receiver How do you determine what portion of light entering the fiber will stay within the fiber What determines the cone of acceptance for a given fiber
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Explain the working of LED with a neat labeled diagram How does dispersion affect the transmission bandwidth of optical fibers? Explain any one technique to measure it Explain the various parameters essential in point-to-point link design How can OTDR meter be used as an optical demodulator Write a short note on APD Explain how RAPD can be used as an optical demodulator Explain how wavelength division multiplexing can be efficiently used to enhance communication. Explain and compare pin diodes with APD with the help of suitable electric field diagrams. What are the common LED structures used for optical fiber communications. Discuss their merits and drawbacks. Compare surface and edge devices Write short note on linearly polarized modes Discuss the operation of a silicon RAPD describing how it differs from pin photodiode. Outline the advantages and disadvantages with the use of RAPD as a detector. What are the general requirements of a good optical source? Describe the technique used to give both electrical and optical confinement in injection laser. Write short note on rise time budget Discuss a popular non-destructive technique for attenuation measurement Describe three methods of perform fabrication. Including starting materials, heat sources, fabrication temperatures used and the technique used to make the preform for each method. Define the rise time of pulse in a passive RC circuit and determine the relation between the rise time and bandwidth of the circuit. An optical fiber link is designed to operate 8 km length of the link without using a repeater. The rise time of different individual components are The rise time of LED source = 5ns The rise time of p-i-n photodetector = 8 ns Rise time due to modal dispersion =5ns/kn Rise time due to material dispersion = 1ns/km Calculate the system rise time and maximum bit rate that can be achieved in the link using (1) RZ format and (2) NRZ format Explain the significance of link power budget in optical fiber system design. What are the requirements and the parameters to be considered while designing a optical fiber communication system. Describe with necessary experimental arrangement the measurement of the signal attenuation in an optical fiber. Describe and explain the experimental setup used in optical Time Domain Reflectometer (OTDR) technique. How is the attenuation measured by this technique? Explain a typical curve obtained on the scope of an OTDR giving the results of the measurements done by an OTDR and also explain the limitations of this technique. Describe the arrangement for experimental setup for the time domain fiber
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dispersion measurement. Find the relation between the pulse b roadening and the widths of the input and output pulses with the assumption that the shapes of pulses are Guassian. How can you measure the numerical aperture of an optical fiber Describe the methods of measurement of diameter of the fiber core and cladding Describe with necessary experimental set up for measurement of attenuation of signal in a splice or connector. A multimode fiber of length 2 km is connected to an apparatus by cutback technique for the attenuation measurement. The measured output voltage from the photo detector using 2km length is found to be 2.1 volts at the wavelength of 0.85µm. The fiber is cutback to a length of 2 meters and the measured output voltage increased to 10.5 volts. Calculate the attenuation per kilometer in dB/km at the wavelength of 0. 85µm. Differentiate between spontaneous and simultaneous emission Derive the relation between LED current and optical output power. Coherent optical communication is preferred over non-coherent optical communication? Why? Explain the role of connectors in OFC Explain Linearly polarized modes Write short note on propagation of optical signal through GIF Explain in detail dispersion modified single mode fibers. Explain equilibrium Numerical Aperture. Explain the different modes that can be supported by an optical fiber Explain what are radiative losses in optical fiber Compare SMSI, MMSI and MMGI fibers in detail. Explain mode coupling in optical fiber and its effects
