OPTICAL FIBER COMMUNICATION SYSTEM
SEM-VII, 2012-13
B.TECH EXAMINATION
UTTARAKHAND TECHNICAL UNIVERSITY
(UTU)
Time: 3 Hours
Total
Marks:100
Attempt any four parts:
- Discuss Dispersion mechanism with respect to single
mode fiber indicating the dominating effects and then show how inter-modal
dispersion may be minimize within the single mode region.
- Briefly discuss with the aid of a suitable diagram what
is meant by the acceptance angle for an optical fiber. Show how this is
related to the fiber numerical aperture and the refractive indexes for the
fiber core and cladding?
- A step index with a large core diameter compared with
the wavelength of the transmitted light has an acceptance angle in air of
22 degree and a relative refractive index difference of 3%. Estimate the
numerical aperture and the critical angle at the core-cladding interface
of the fiber.
- What are the modes in optical fiber? Calculate number
of modes for a graded index optical fiber if core diameter (d = 62.5 μ m),
NA =0.275 and Operating wavelength = 1300 nm.
- Two polarization maintaining fibers operating at the
wavelength of 1.3 micrometer have beat length of 0.7 mm and 0.8 mm. Determine
the briefringence in each case and comment the result.
- Derive an expression for the acceptance angle for skew rays which changes direction by an angle of 2γ at each reflection in step index fiber in terms of NA and γ.
