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A job description is a list that a person might use for general tasks, or functions, and responsibilities of a position. It may often include to whom the position reports, specifications such as the qualifications or skills needed by the person in the job, and a salary range. Job descriptions are usually narrative, but some may instead comprise a simple list of competencies; for instance, strategic human resource planning methodologies may be used to develop a competency architecture for an organization, from which job descriptions are built as a shortlist of competencies.

According to Torrington, a job description is usually developed by conducting a job analysis, which includes examining the tasks and sequences of tasks necessary to perform the job. The analysis considers the areas of knowledge and skills needed for the job. A job usually includes several roles. According to Hall, the job description might be broadened to form a person specification or may be known as "Terms Of Reference". The person/job specification can be presented as a stand-alone document, but in practice it is usually included within the job description. A job description is often used in recruitment.

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Expressions for acceptance angle (QA) & Numerical Aperture (NA)

Acceptance Angle (QA): All right rays falling on optical fiber are not transmitted through the
fiber. Only those light rays making i > c at the core-cladding interface are transmitted
through the fiber by undergoing T1R. For which angle of incidence, the refraction angle is
greater than 900 will be propagated through T1R. There by Acceptance Angle is defined as:
The maximum angle of incidence to the axis of optical fiber at which the light ray
may enter the fiber so that it can be propagated through T1R.

OPTICAL FIBRES

Optical fibers are the waveguides through which electromagnetic waves of optical
frequency range can be guided through them to travel long distances.

An optical fiber works on the principle of total internal reflection (71R).

 When light enters through one end of optical fiber it undergoes successive total internal
reflections and travel along the fiber in a “zig-zag” path.

 Optical fibers are made up of glass, plastic or SiO2 as thin as size of human heir.

 An optical fiber consists of three (3) co-axial regions.

The inner most region is the light-guiding region known as “Core”. It is surrounded by a
middle co-axial regional known as “cladding”. The outer most region which completely
covers the core & cladding regions is called “sheath or buffer jacket”.

Sheath protects the core & cladding regions from external contaminations, in addition to
providing mechanical strength to the fiber.

The refractive index of core (n1) is always greater than the refractive index of cladding
(n2) i.e., n1 > n2 to observe the light propagation structure of optical fiber.

Multi Mode Step Index Fibers:

These fibers have reasonably large core diameters and large NA to facilitate efficient
transmission to incoherent or coherent light sources.

These fibers allow finite number of modes.

 Normalized frequency (NF) is the cut off frequency, below which a particular mode
cannot exist. This is related to NA, Radius of the core, and wave length of light as

Graded index fibers

In case of graded index fibers, the refractive index of core is made to vary as a function of
radial distance from the centre of the optical fiber.

Refractive index increases from one end of core diameter to center and attains maximum
value at the centre. Again refractive index decreases as moving away from center to
towards the other end of the core diameter.

The refractive index variation is represented as …….

 The number of modes is given by the expression

OPTICAL FIBRES

Optical fibers are the waveguides through which electromagnetic waves of optical
frequency range can be guided through them to travel long distances.

An optical fiber works on the principle of total internal reflection (71R).

When light enters through one end of optical fiber it undergoes successive total internal
reflections and travel along the fiber in a “zig-zag” path.

 Optical fibers are made up of glass, plastic or SiO2 as thin as size of human heir.
 An optical fiber consists of three (3) co-axial regions.

The inner most region is the light-guiding region known as “Core”. It is surrounded by a
middle co-axial regional known as “cladding”. The outer most region which completely
covers the core & cladding regions is called “sheath or buffer jacket”.

Sheath protects the core & cladding regions from external contaminations, in addition to
providing mechanical strength to the fiber.


 The refractive index of core (n1) is always greater than the refractive index of cladding
(n2) i.e., n1 > n2 to observe the light propagation structure of optical fiber.

Advantages of optical fibers over metallic cables

1. Optical fibers allow light signals of frequencies over a wide range and hence greater
volume of information can be transmitted either in digital form or in analog form with in
a short time.
2. In metallic cables only 48 conversations can be made at once without cross talks where as
in optical fibers more than 15000 conversations can be made at once without cross talks.
3. Light cannot enter through the surface of the optical fiber except at the entry interface i.e.,
interference b/w different communication channels is absent. Hence purity of light signal
is protected.
4. Optical signal do not produce sparks like electrical signals and hence it is safe to use
optical fibers.
5. External disturbances from TV or Radio Stations power electronic systems and lightening
can not damage the signals as in case of metallic cables.
6. Materials used in the manufacture of optical fibers are SiO2, plastic, glasses which are
cheaper & available in plenty.