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In the design of a single mode step index optical fibre close to upper cut-off, the single-mode operation is not preserved if
- a)radius as well as operating wavelength are halved
- b)radius as well as operating wavelength are doubled
- c)radius is halved and operating wavelength is doubled
- d)radius is doubled and operating wavelength is halved
Correct answer is option 'D'. Can you explain this answer?
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In the design of a single mode step index optical fibre close to uppe...
Answer:
Introduction:
In the design of a single-mode step index optical fiber, the single-mode operation is preserved when the fiber is operated close to its upper cut-off frequency. The upper cut-off frequency is the highest frequency that can propagate in the fiber as a single mode.
Explanation:
When the radius of the fiber is doubled and the operating wavelength is halved, the single-mode operation is preserved. This can be explained using the concept of the normalized frequency (V-number) of the fiber.
Normalized Frequency (V-number):
The V-number of an optical fiber is a dimensionless parameter that determines the mode of propagation in the fiber. It is given by the formula:
V = (2π/λ) * a * (n1^2 - n2^2)^0.5
Where λ is the operating wavelength, a is the radius of the fiber, and n1 and n2 are the refractive indices of the core and cladding, respectively.
Effect of Doubling the Radius:
When the radius of the fiber is doubled, the V-number is also doubled. This is because the V-number is directly proportional to the radius. As a result, the V-number becomes larger than the critical V-number required for single-mode operation. This means that higher-order modes start to propagate in the fiber, leading to multimode operation.
Effect of Halving the Operating Wavelength:
When the operating wavelength is halved, the V-number is also halved. This is because the V-number is inversely proportional to the operating wavelength. As a result, the V-number becomes smaller than the critical V-number required for single-mode operation. This means that the fiber cannot support single-mode propagation and higher-order modes start to propagate.
Conclusion:
In the given options, when the radius is doubled and the operating wavelength is halved, the single-mode operation is not preserved. This is because both of these changes lead to an increase in the V-number, which results in the propagation of higher-order modes. Therefore, option 'D' is the correct answer.
Introduction:
In the design of a single-mode step index optical fiber, the single-mode operation is preserved when the fiber is operated close to its upper cut-off frequency. The upper cut-off frequency is the highest frequency that can propagate in the fiber as a single mode.
Explanation:
When the radius of the fiber is doubled and the operating wavelength is halved, the single-mode operation is preserved. This can be explained using the concept of the normalized frequency (V-number) of the fiber.
Normalized Frequency (V-number):
The V-number of an optical fiber is a dimensionless parameter that determines the mode of propagation in the fiber. It is given by the formula:
V = (2π/λ) * a * (n1^2 - n2^2)^0.5
Where λ is the operating wavelength, a is the radius of the fiber, and n1 and n2 are the refractive indices of the core and cladding, respectively.
Effect of Doubling the Radius:
When the radius of the fiber is doubled, the V-number is also doubled. This is because the V-number is directly proportional to the radius. As a result, the V-number becomes larger than the critical V-number required for single-mode operation. This means that higher-order modes start to propagate in the fiber, leading to multimode operation.
Effect of Halving the Operating Wavelength:
When the operating wavelength is halved, the V-number is also halved. This is because the V-number is inversely proportional to the operating wavelength. As a result, the V-number becomes smaller than the critical V-number required for single-mode operation. This means that the fiber cannot support single-mode propagation and higher-order modes start to propagate.
Conclusion:
In the given options, when the radius is doubled and the operating wavelength is halved, the single-mode operation is not preserved. This is because both of these changes lead to an increase in the V-number, which results in the propagation of higher-order modes. Therefore, option 'D' is the correct answer.
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In the design of a single mode step index optical fibre close to uppe...
The cut off frequency is given by f = 2πa sin α/wavelength, where a is the radius of core. For a single mode step index fiber, f must lie between 0 and 2.405. Thus to get f below 2.405, the radius must be doubled and wavelength must be halved.
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In the design of a single mode step index optical fibre close to upper cut-off, the single-mode operation is not preserved ifa)radius as well as operating wavelength are halvedb)radius as well as operating wavelength are doubledc)radius is halved and operating wavelength is doubledd)radius is doubled and operating wavelength is halvedCorrect answer is option 'D'. Can you explain this answer?
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In the design of a single mode step index optical fibre close to upper cut-off, the single-mode operation is not preserved ifa)radius as well as operating wavelength are halvedb)radius as well as operating wavelength are doubledc)radius is halved and operating wavelength is doubledd)radius is doubled and operating wavelength is halvedCorrect answer is option 'D'. Can you explain this answer? for Electronics and Communication Engineering (ECE) 2024 is part of Electronics and Communication Engineering (ECE) preparation. The Question and answers have been prepared according to the Electronics and Communication Engineering (ECE) exam syllabus. Information about In the design of a single mode step index optical fibre close to upper cut-off, the single-mode operation is not preserved ifa)radius as well as operating wavelength are halvedb)radius as well as operating wavelength are doubledc)radius is halved and operating wavelength is doubledd)radius is doubled and operating wavelength is halvedCorrect answer is option 'D'. Can you explain this answer? covers all topics & solutions for Electronics and Communication Engineering (ECE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for In the design of a single mode step index optical fibre close to upper cut-off, the single-mode operation is not preserved ifa)radius as well as operating wavelength are halvedb)radius as well as operating wavelength are doubledc)radius is halved and operating wavelength is doubledd)radius is doubled and operating wavelength is halvedCorrect answer is option 'D'. Can you explain this answer?.
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