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DISCLAIMER |
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on this page as is without any express or implied
warranties. Although, every effort has been taken
to ensure the accuracy of the information contained
in this page, the company assumes no responsibility
for errors or omissions, or for damages resulting
from the use of the information contained herein. |
| Q.1:
What is difference between single-mode & multimode fiber? |
A:
Singlemode fiber, which provides higher bandwidth
over longer distance, supports only single mode transmission
of light. While the multimode fiber, which has lower
bandwidth, supports multiple modes of light transmission
due to its large core diameter. Generally, multimode
fibers are used for LAN connectivity or the applications
where distances are smaller. Single mode fibers are
used for transmission of signal over the longer distances
such as trunk links or backbone links. |
|
| Q.2:
What is the relationship between bandwidth and distance? |
A:
In case of multimode fiber, this relationship is given
by the manufacturer as a MHz*km value. As the distance
increases, less bandwidth is realized. In this calculation
actual laser/LED bandwidth of the source must be used,
not just the data rate. Although a link will be limited
by the optical budget, but sometimes it can be limited
by this bandwidth value. For rough calculations multiplication
of bandwidth & distance is usually sufficient. However,
for detailed calculations other factors such as chromatic
dispersion, modal dispersion, source line width, etc.
must be considered. |
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| Q.3:
What do we mean by dB/Km loss and what are causes for
this loss? |
A.
As the light is guided through the core of optical
fiber, it experiences losses (attenuation) i.e. power
loss, which is expressed in dB/km. The attenuation
varies with wavelength and typically, it is 0.40 dB/km
@ 1310 nm and 0.30 dB/km @ 1550 nm. Following four
properties mainly cause attenuation:
1. Absorption: This occurs when light strikes impurities
in the core glass and is absorbed.
2. Scattering: This occurs when the light strikes
an area where the material density changes.
3. Macrobending: This is large-scale bending of the
fiber which exceeds the fiber bend radius and causes
light to leave the core and travel in the cladding
(usually an installation problem)
4. Microbending : This is microscopic distortion of
the fiber which causes light to leave the core and
travel in the cladding (created during manufacturing) |
|
| Q.4.
What do we mean by ITU G 652, G 653, G 655 compliant
fiber? |
A.
There are different types optical fibers. On a broader
scale, the optical fibers can be divided in two types
i.e. single mode and multimode. ITU, an international
standards body for telecommunication has defined the
standard specifications for various different types
of single mode fiber. The ITU G 652 defines the specification
for standard single mode optical fiber, while the
G 653 defines the specifications for dispersion shifted
single mode optical fiber and G 655 defines the specifications
for nonzero dispersion shifted fiber. The basic difference
between these three different fiber types is the chromatic
dispersion. The chromatic dispersion limits the maximum
bit rate transmission through a single mode fiber.
The ITU G 652 specification defines the maximum dispersion
of 3.5 ps/nm-km in 1310 nm region and generally this
type of fibers have maximum dispersion of 20 ps/nm-km
in 1550 nm region. The ITU G 653 represents the fibers
with zero dispersion wavelength close to 1550 nm.
The ITU G 655 represents the fibers with small but
non-zero dispersion in 1550 nm region. |
|
| Q.5.
What is the transmission capacity of single mode fiber? |
A.
The transmission capacity i.e. bit rate, of a optical
fiber is dependent upon dispersion characteristics
of an optical fiber. This parameter varies with wavelengths.
The dispersion is further divided in two type i.e.
chromatic dispersion and polarization mode dispersion.
The polarization mode dispersion is more prominent
for data rates above 10 Gbps. The chromatic dispersion,
which is defined in ps/nm-km, is further divided in
two different types i.e. material dispersion and waveguide
dispersion. The Chromatic dispersion causes broadening
of light pulse as it travels along the core of optical
fiber. Because of this Bit Error Rate (BER) is generated
in digital transmission systems. With the help of
linear imperical formula (with 1 dB power penalty),
it is possible to find out the maximum bit rate transmission
for a given repeater distance and dispersion. The
formula is as follows:
B2 L D < 104,000
Where,
B= Bit Rate in Gb/s
L= Distance in Km
D= Dispersion in ps/nm-km
From the above formula, it can be that with a dispersion
of 18 ps/nm-km, 2.5 Gbps signal can be transmitted
over a distance of 800 Km between the repeater station.
The polarization mode dispersion (PMD) also limits
the transmission capacity of fiber but more prominently
for data rates above 10 Gbps. The PMD of a fiber is
measured in ps/Ökm. As a rule of thumb, the total
PMD of a fiber link should be less than one tenth
of bit period of a given data rate. For example, a
fiber optic link with PMD of 0.5 ps/Ökm would be able
to transmit 10 Gbps signal over a distance of 400
Km comfortably. |
|
| Q.6.
What is splicing and which equipment are used for splicing? |
A.:
Optical
fibers are made of glass and these fibers are protected
f | | |
