FIbras ótica

Question 1

Optical Fibers definition

Answer 1

-Fiber-optic lines are strands of optically pure glass as thin as a human hair that carry digital information over long distances.
-Fiber Optics are cables that are made of optical fibers that can transmit large amounts of information at the speed of light.
-An optical fiber is essentially a waveguide for light

Question 2

Optical Fibers structure

Answer 2

Core: -Glass or plastic with a higher
index of refraction than the
cladding
-Carries the signal
Cladding: – Glass or plastic with a
lower index of refraction
than the core
Buffer: – Protects the fiber from
damage and moisture
Jacket: – Holds one or more fibers in
a cable

Question 3

Características das fibras oticas

Answer 3

• It has little mechanical strength, so it must be enclosed in a
  protective jacket
• Often, two or more fibers are enclosed in the same cable for
  increased bandwidth and redundancy in case one of the
  fibers breaks
• It is also easier to build a full-duplex system using two fibers,
  one for transmission in each direction

Question 4

Light transmisson principle

Answer 4

–The index of refraction of the cladding is less than that of the core, causing rays of light leaving the core to be refracted back into the core
–Because the cladding does not absorb any light from the core, the light wave can travel great distances.
–However, some of the light signal degrades within the fiber, mostly due to impurities in the glass. The extent that the signal degrades
depends on the purity of the glass and the wavelength of the transmitted light

Question 5

Acceptance angle

Answer 5

-The maximum angle of incidence at the end face of an optical fiber for which the light ray can be propagated along Core-Cladding interface is known as Maximum
Acceptance Angle. It is also called Acceptance cone half angle

Question 6

Acceptance cone

Answer 6

• Rotating the Acceptance angle about the fiber axis describes the Acceptance Cone of the fiber.
• Light launched at the fiber end within this Acceptance Cone alone will be accepted and propagated to the other end of the fiber by total internal reflection.

Question 7

Numerical aperture

Answer 7

– Numerical Aperture is the light gathering capacity of an optical fiber and it is proportional to Acceptance Angle.

– It is numerically equal to sine of minimum Acceptance Angle.

–It is the measure of the amount of light that can be accepted by a fiber.

– It depends only on Refractive indices of core and cladding and not on fiber dimensions.

– It is always <1 and ranges from 0.13 to 0.50.

– A larger numerical aperture implies that a fiber will accept a large amount of light
from the source.

Question 8

Transmission modes

Answer 8

– Since optical fiber is a waveguide, light can propagate in a number of modes

– If a fiber is of large diameter, light entering at different angles will excite different modes while narrow fiber may only excite one mode

– Multimode propagation will cause dispersion, which results in the spreading of pulses and limits the usable bandwidth

–Single-mode fiber has much less dispersion but is more expensive to produce. Its small size, together with the fact that its numerical aperture is smaller than that of
multimode fiber, makes it more difficult to couple to light sources