Download PTU B.Tech 2020 March ECE 7th and 8th Sem BTEC 702 Optical Communication Question Paper

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Total No. of Pages : 02

Total No. of Questions : 09

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B.Tech.(ECE) (2012 to 2017) (Sem.-7,8)

OPTICAL COMMUNICATION

Subject Code : BTEC-702

M.Code : 71911

Time : 3 Hrs. Max. Marks : 60

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INSTRUCTION TO CANDIDATES :

1. SECTION-A is COMPULSORY consisting of TEN questions carrying TWO marks each.
2. SECTION-B contains FIVE questions carrying FIVE marks each and students have to attempt any FOUR questions.
3. SECTION-C contains THREE questions carrying TEN marks each and students have to attempt any TWO questions.

SECTION-A

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Q1) Write briefly :

1. What are the kinds of modulation formats used in optical communications?
2. A certain fiber has an attenuation loss of 1.5 dB/km at 1300 nm. If 0.5 mW of optical power is initially launched into the fiber, what is the power level in microwatts after 8 km?
3. Define Bitrate (BR) and Bit Error Rate (BER).
4. Explain the concept of cavity in the lasers.

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5. What are the possible principal requirements in optical connectors? List them.
6. Distinguish between line width and bandwidth.
7. Give the sources of noise in optical receivers.
8. Calculate Line width (Frequency Spread) of two Fabry-Perot lasers operating on :
   1. Wavelength 1300 nm at 3 nm spectral width
   2. Wavelength 1550 nm at 4 nm spectral width.

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9. How are LED structures different from their counterpart LASERs?
10. Draw Speckle / Model noise pattern that is produced when coherent laser light is launched into multimode fiber.

SECTION-B

Q2) Establish the necessary threshold condition for Laser diode. Discuss Injection laser characteristics, Mode Hopping, Frequency chirp.

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Q3) Write and apply Maxwell equations for optical fiber communication. Derive the standard wave equation using them.

Q4) Explain the design and working principle of APD. What are its advantages and disadvantages? Discuss compromises to improve its performances.

Q5) Estimate the CW operating lifetime for an AlGaAs LED with an activation energy of 0.6 eV and a constant of proportionality (Bo) of 2.3 x 10° h™" when the junction temperature of device is constant at 50°C. It may be assumed that the LED is no longer useful when its optical power is 0.8 of its value.

Q6) Discuss in short Linear and Stimulated Scattering, Frequency chirping.

SECTION-C

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Q7) How does light propagate through optical fibers? What is its basic principle? Establish the condition for light ray transmission through a step indexed fiber on the basis of ray theory. Distinguish the fibers types on the basis of light propagation and bandwidth : SI-MMF, GI-MMF, and SMF.

Q8) Explain in detail the multiplexing technique: WDM, OTDM, Subscriber Multiplexing and Code Division Multiplexing used in optical communication.

Q9)

1. Write short note on : DFB lasers; Responsivity.
2. A multimode step index fiber is operating at a wavelength of 0.85 um with a core diameter of 80 um and a relative index difference 1.5%. If the refractive index of core is 1.48. Determine::
   1. Normalized frequency for the fiber.

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   2. The number of guided modes.

NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any page of Answer Sheet will lead to UMC against the Student.

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