Fibre-optic and Spectroscopic Instrumentation - Communication and Optical Instrumentation - Instrumentation Engineering Previous Year Questions

1

2010 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2010

Light coming out of an optical fiber is incident on a plane perpendicular to the fiber axis and 50 mm away from the end of the fiber. The light coming out creates a circular spot that can at most be of 20 mm diameter. Neglecting the diameter of the fiber, the numerical aperture of the fiber is, approximately,

A

0.14

B

0.20

C

0.34

D

0.40

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2

2011 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2011

The core/cladding index difference of a single-mode optical fiber cable is 0.01. The refractive index of the material of the core is 1.5. The maximum angle of acceptance of the fiber is approximately equal to

A

17.5°

B

12.1°

C

8.6°

D

2.0°

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3

2014 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2014

Monochromatic light from a step index (\(n_1 = 1.500; n_2 = 1.485\)), multimode optical fiber of core diameter 100 \(\mu m\) is incident (through air (\(n = 1.000\)) onto a linear photo-detector array placed at 1 mm distance from the tip of the fiber. The tip of the fiber is polished and its exit plane is perpendicular to the axis of the fiber. The detector array is oriented parallel to the exit plane of the tip. The array consists of photo-detector elements each of 5 \(\mu m\) diameter. The distance between the edges of two adjacent elements can be assumed to be zero. The number of elements illuminated by the light coming out of the fiber is _________.

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4

2007 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2007

The angle of acceptance when the fiber is used in water (refractive index = 1.33) is closest to

A

15°

B

16°

C

17°

D

18°

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5

2007 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2007

Two experiments are conducted in which light is launched into the fiber from a uniformly distributed planar source kept 5 mm away from the tip. In the first experiment (E₁) both the source and the fiber are in air. In the second experiment (E₂) both the source and the fiber are in water. Neglecting absorption in the medium between the source and the tip, the ratio of the amount of light coupled into the fiber in E₁ to the amount of light coupled into the fiber in E₂ is closest to

A

0.5

B

1.0

C

1.4

D

1.9

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6

2008 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2008

A 5 MHz acoustic pulse travels from a transducer through a 2 cm thick fat tissue before it encounters an interface with a liver tissue at normal incidence. The amplitude attenuation factors of fat and liver are \(0.075\,Npcm^{-1}MHz^{-1}\) and \(0.1\,Npcm^{-1}MHz^{-1}\) respectively. The amplitude reflectivity coefficient of fat-liver interface is 0.1. Taking both attenuation and reflection losses into account, the amplitude loss (in dB) of echo pulse when it returns to the transducer is

A

0.74

B

-2.6

C

-6

D

-33

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7

2018 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2018

A multi-mode optical fiber with a large core diameter has a core refractive index \(n_1 = 1.5\) and cladding refractive index \(n_2 = 1.4142\). The maximum value of \(\theta_A\) (in degrees) for which the incident light from air will be guided in the optical fiber is ±______.

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8

2019 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2019

In a single-mode optical fiber, the zero-dispersion wavelength refers to the wavelength at which the

A

material dispersion is zero.

B

waveguide dispersion is zero.

C

sum of material dispersion and waveguide dispersion is zero.

D

material dispersion and waveguide dispersion are simultaneously zero.

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9

2021 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2021

In the figure shown, a large multimode fiber with \( n_{core} = 1.5 \) and \( n_{clad} = 1.2 \) is used for sensing. A portion with the cladding removed passes through a liquid with refractive index \( n_{liquid} \). An LED is used to illuminate the fiber from one end and a paper is placed on the other end, 1 cm from the end of the fiber. The paper shows a spot with radius 1 cm. The refractive index \( n_{liquid} \) of the liquid (rounded off to two decimal places) is ________.

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10

2023 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2023

A silica-glass fiber has a core refractive index of 1.47 and a cladding refractive index of 1.44. If the cladding is completely stripped out and the core is dipped in water having a refractive index of 1.33, the numerical aperture of the modified fiber is______ (rounded off to three decimal places).

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11

2026 · Instrumentation Engineering · Communication and Optical Instrumentation · Fibre-optic and Spectroscopic Instrumentation

Instrumentation Engineering (IN) 2026

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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