Question: 6 -

A hetero-structure laser is better than a diode laser (injection laser) because of its

Low cost

Low threshold current

Non-linear operation

Long wavelength emission

Answer:

Low threshold current

Solution:

Hetero-structure is better because of its low threshold current need

Question: 7 -

Losses in optical fibres can be caused by which of the following ?

(i) Impuritues

(ii) Micro bending

(iii) Stepped index operation

Select the correct answer using the code given below :-

ii and iii

only iii

iii and i

ii and i

Answer:

ii and i

Solution:

Losses in optical fibre occur due to impurities and micro bending

Question: 8 -

In an optical fibre , the light beam propagates due to which one of the following ?

Simple reflection of light at a boundary between two media

Total internal reflection at the boundary of the fibre

Scattering of light in the medium

Refraction of light in the medium

Answer:

Total internal reflection at the boundary of the fibre

Solution:

Due to total internal reflection at the boundary of fibre , the light beam propagates

Question: 9 -

An extrinsic semiconductor with energy gap 1 eV has a carrier concentration N at temperature 200 K . Another intrinsic semiconductor has the same value of carrier concentration N at temperature 600 K . What is the energy gap value for the second semiconductor ?

3 eV

9 eV

(3/2) eV

(1/3) eV

Answer:

(1/3) eV

Solution not available.

Question: 10 -

Consider the following statements :-

A semiconductor to be used in optoelectronic devices should have

(i) Direct energy band gap

(ii) Indirect energy band gap

(iii) Any value of forbidden energy band gap

(iv) Right value of band gap corrresponding to light wavelength

Which of these statements is/are correct ?

only i

ii and iii

ii and iv

iv and i

Answer:

iv and i

Solution:

It should be direct band gap material and emitted light photons wavelength will depend on the energy band gap