GATE 2026 IN – Question 64
For a fiber Bragg grating-based sensor, the shift in the Bragg wavelength gives information about the value of the measurand. For a Bragg wavelength of 1550 nm and effective index of 1.44, the grating period is ________ nm. (Rounded off to two decimal places.)
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Correct answer: 537.00 to 539.00
Explanation
The first-order Bragg condition is $\lambda_B=2n_{eff}\Lambda$. Therefore $\Lambda=1550/(2\times1.44)=538.1944\ \mathrm{nm}$.
To two decimal places, the grating period is **538.19 nm**.