Q:
In the design of a single mode step index optical fiber close to upper cut off, the single mode operation is NOT preserved if
Answer & Explanation
Answer: D) Radius is doubled and operating wavelength is halved
Explanation: The cut off frequency is given by f = 2?a sin ?/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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