# Physical Optics-Polarisation and Modern Optics [Optionals IAS Mains Physics]: Questions 1 - 5 of 14

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## Question 1

Polarisation and Modern Optics
Principles of Fibre Optics Attenuation

Appeared in Year: 2012 (IFS)

### Describe in Detail

Essay▾

A step – index silica fiber consists of core of refractive index 1.450 and diameter . If the numerical aperture of the fiber is 0.16, calculate:

(i) the acceptance angle of the fiber,

(ii) refractive index of the cladding, and

(iii) if the fiber is immersed in water of refractive index 1.33, how does the acceptance angle change? (paper -1) (Section – A)

### Explanation

• Here, from question, we can say,

• The numerical aperture of the optical fiber is given as,

• where, is acceptance angle of the fiber. is the refracting medium of surrounding of optical fiber. And are the refracting indexes of core and cladding of the optical fiber, respectively.

(i) The acceptance angle of the fiber is calculated from equation (1) as,

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## Question 2

Polarisation and Modern Optics
Principles of Fibre Optics Attenuation

Appeared in Year: 2010 (IFS)

### Describe in Detail

Essay▾

With a suitable diagram, deduce an expression for numerical aperture (NA) for ab optical fiber having refractive indices of core and cladding and , respectively and being placed in a medium of index . (Section – A)

### Explanation

• As shown in figure an optical fiber having refractive indices of core and cladding and , respectively. And is the refractive index of outside medium. A light beam incident at angle with core axis, and then it refracted at an angle and fall on the core – cladding interface at angle . Where,

• From Snell՚s Law, at point of e…

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## Question 3

Polarisation and Modern Optics
Principles of Fibre Optics Attenuation
Edit

Appeared in Year: 2010 (IFS)

### Write in Short

Between multimode and single mode fibers, explain critically how and why single mode fiber is chosen for communication. (Section – A)

## Question 4

Polarisation and Modern Optics
Single Mode Fibres

Appeared in Year: 2010 (IFS)

### Write in Short

Why are the two wavelengths and important in single – mode fiber – optical communication system? (Section – A)

## Question 5

Polarisation and Modern Optics
Ruby and He-Ne Lasers

Appeared in Year: 2013 (IFS)

### Describe in Detail

Essay▾

Explain the lasing action of laser using energy level diagram and describe the operation of laser experimental setup. (Section A)

### Explanation

• The light is produced in He – Ne laser by atomic transitions in the Neon atom. The Helium acts as a buffer gas in it. That means Helium doesn՚t directly produce laser light, it only helps the atom of the Neon gas to produce lasing in as manner.
• Helium absorbed some energy, when energy applied to the He – Ne gas mixture, and it achieve an excited sta…

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