Question

In the design of a single mode step index optical fiber 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 The question was asked during an interview. Query is from Advanced and Tricky Questions topic in portion Advanced and Tricky Questions of Electromagnetic Theory Select the correct answer from above options Electromagnetic Theory questions and answers, Electromagnetic Theory questions pdf, Electromagnetic Theory question bank, Electromagnetic Theory questions and answers pdf, mcq on Electromagnetic Theory pdf,electromagnetic theory book pdf,electromagnetic theory pdf notes,electromagnetic theory lecture notes,electromagnetic theory of light,maxwell electromagnetic theory,electromagnetic theory proposed by,electromagnetic theory engineering physics,electromagnetic theory nptel

Answer 1

The correct option is (d) Radius is doubled and operating wavelength is halved Explanation: 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.