Important Short Questions and Answers: Optical Networks

OPTICAL NETWORKS

1.  What are the techniques to reduce optical feedback?

·        Fiber end faces with a curved surface to the laser emitting facet.

·        Index matching oil or gel at air glass interfaces.

·        PC connectors

·        Optical isolators within the transmitter module.

2.     What are the basic performances of the WDM?

•         Insertion loss

•         Channel width

•         Cross talk

3.     What is WDM? Define.

WDM is wave length division multiplexing. The optical beam consists of different wavelengths and several channel information is transmitted over a single channel.

4.  What is meant as bidirectional WDM?

A single WDM which operates as both multiplexing and De multiplexing Devices is said as the bidirectional WDM.

5.  Define Radiance.

Radiance (or brightness) is a measure, in Watts, of the optical power radiated into a unit solid angle per unit area of the emitting surface.

6.  What is meant by ‘population inversion’?

In thermal equilibrium, the density of excited electrons is very small. Most photons incident on the system will therefore be absorbed, so that stimulated emission is essentially negligible. Stimulated emission will exceed absorption only if the population of the excited states is greater than that of the ground state. This condition is known as population inversion.

7.     What are the factors to be considered in link power budget?

The factors to be considered in link power budget are:

•         Transmission speed

•         Optical sources & detectors

•         Optical fiber

8.     What are the causes of absorption?

Normally, the system is in the ground state. When a photon of energy hγ12 impinges on the system, an electron in state E1 can absorb the photon energy & be excited to state E2.

9.  What is meant by hetero junction?

In hetero junction, two different alloy layers are on each side of the active region. Because of the sandwich structure of differently composed alloy layers, both the carriers & optical field are confined in the central active layer.

10. What is meant by indirect band gap semiconductor material?

For indirect band gap materials, the conduction-band minimum & the valence- band maximum energy levels occur at different values of momentum. Here, band-to- band recombination must involve a third particle to conserve momentum, since the photon momentum is very small. Phonons serve this purpose.

11. What is meant by ‘modal noise’?

It arises when light from a laser is coupled into the multimode fiber.

12. .What is the necessity of cladding for an optical fiber?

a)     To provide proper light guidance inside the core

b)    To avoid leakage of light from the fiber

c)     To avoid mechanical strength for the fiber

d)    To protect the core from scratches and other mechanical damages

GLOSSARY

1. Techniques to reduce optical feedback.

Fiber end faces with a curved surface to the laser emitting facet.

Index matching oil or gel at air glass interfaces.

PC connectors

Optical isolators within the transmitter module.

2. Performances of the WDM.

• Insertion loss

• Channel width

• Cross talk

3. WDM.   

 WDM is wave length division multiplexing.  The  optical beam consists  of different  wavelengths  and  several channel information  is  transmitted over a  single channel.

4. Bidirectional WDM.    

A single WDM which operates as both multiplexing and De multiplexing Devices is said as the bidirectional WDM.

5.  Radiance.

Radiance (or brightness) is a measure, in Watts, of the optical power radiated into a unit solid angle per unit area of the emitting surface.

6.  Population inversion

In thermal equilibrium, the density of excited electrons is very small. Most photons incident on the system will therefore be absorbed, so that stimulated emission is essentially negligible. Stimulated emission will exceed absorption only if the population of the excited states is greater than that of the ground state. This condition is known as population inversion.

7.  Causes of absorption

Normally, the system is in the ground state. When a photon of energy hγ12 impinges on the system, an electron in state E1 can absorb the photon energy & be excited to state E2.

8.  Hetero junction

In hetero junction, two different alloy layers are on each side of the active region. Because of the sandwich structure of differently composed alloy layers, both the carriers & optical field are confined in the central active layer.

9.  Indirect band gap semiconductor material

For indirect band gap materials, the conduction-band minimum & the valence- band maximum energy levels occur at different values of momentum. Here, band-to- band recombination must involve a third particle to conserve momentum, since the photon momentum is very small. Phonons serve this purpose.

10. PON.

A system that brings optical fiber cabling and signals all or most of the way to the end user. Depending on where the PON terminates, the system can be described as fiber-to-the-curb (FTTC), fiber-tothe- building (FTTB), or fiber-to-the-home (FTTH).