2. A Report by,
Harish.R
Final year (UG) B.E,
ECE- Dept, JJCET, Trichy-09
Contact Mail: harishshaheb@gmail.com
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3. INTRODUCTION
Lasers have been considered for space communications since their realization in 1960.
It was soon recognized that, although the laser had potential for the transfer of data at
extremely high rates, specific advancements were needed in component performance
and systems engineering, particularly for space-qualified hardware.
Advances in system architecture, data formatting, and component technology over the
past three decades have made laser communications in space not only a viable but also
a attractive approach to inter satellite link applications.
The high data rate and large information throughput available with laser
communications are many times greater than in radio frequency (RF) systems.
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5. The extremely high antenna gain made
possible by the narrow beams enables small
telescope apertures to be used.
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6. OPERATION
Free space laser communications systems are wireless connections through the
atmosphere.
They work similar to fiber optic cable systems except the beam is transmitted through
open space
The carrier used for the transmission of this signal is generated by either a high power
LED or a laser diode
The laser systems operate in the near infrared region of the spectrum. The laser light
across the link is at a wavelength of between 780 – 920 nm.
Two parallel beams are used, one for transmission and one for reception.
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9. Modulation Techniques
Modulation is simply a process of super imposing the modulating or low frequency
signal into the high frequency carrier signal.
The optical laser light here act as the carrier wave .It does not contain any data with it.
Here normally we employ Pulse Position Modulation or On-Off keying techniques for
modulating the carrier wave.
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10. Radiation Pattern ( A comparison)
The antenna radiation pattern is the display of the radiation properties of the antenna
as a function of spherical co ordinates.
A typically radiation pattern is characterized by a main beam with 3 db beam width and
side lobes at different levels.
For an effective communication the minor lobes that is side lobe levels must be
minimized.
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11. R.P of RF antenna vs R.P of optical
antenna
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12. Optical antenna produce non ionizing
radiation
Ionizing radiations : These are the radiations which has enough ability to ionize an atom or
a molecule when passing through matter where as non ionizing radiation do not.
Even though the optical antennas operating frequency range is in the range of few Hz ,the
wavelength is reduced.
Since here laser is used for communication which falls under non ionizing radiation which is
reflected from the body surface.
A question might arise that higher frequency component cause more harmless. But this is
not actually the case
Each particle has its own absorbing and radiating properties. Human and animals body skin
have tendency to reflect the incident light or optical energy where as plants absorbs most of
the light energy.
Thus we clear that laser energy is no more harmful as RF.
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13. OPTICAL ANTENNA
An optical antenna is a device that efficiently couples the energy of free-space radiation
to a confined region of sub wavelength size.
While antennas are widespread in the radio wave and microwave regimes they are
basically unexplored at optical frequencies.
Because nano scale devices need to interface with optical radiation it is likely that
optical antennas will have a broad impact on future technology.
The light beam from an optical antenna is highly directed in nature since it uses
coherent light form(Laser) for its transmission. Whereas the Electro-Magnetic waves
from a RF antenna takes multiple path to reach its destination antenna.
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16. APPLICATIONS
Temporary network installation for events or other purpose as disaster recovery
For communications between spacecraft, including elements of satellite constellation
Security applications
Military application: (its potential for low electromagnetic emanation when
transferring sensitive data for air forces)
Enterprise connectivity: FSO links can be installed makes them for interconnecting local
area network segments that are housed in buildings separated by public streets.
Telecommunication and computer networking
Point-to-point LOS links
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17. ADVANTAGES AND DISADVANTAGES
High Directivity & Gain achieved.
Larger Bandwidth of operation.
High Information throughput is available.
Increased Data rate.
No need of trenching & digging lands.
Minor lobe level reduced
Data is highly secured.
No E-M interference.
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19. CONCLUSION
The implementation of any of these systems in an inter-satellite link will require a
substantial development effort.
Most of the recent large effort of digging up the ground and laying down new fiber has
been directed towards extending the fiber optic backbone to new central offices, and
not laying fiber directly to the customer
The growing requirements for the efficient and secure communications has led to an
increased interest in the operational deployment of laser cross-links for commercial and
military satellite systems in both low earth and geo-synchronous orbits.
With the dramatic increase in the data handling requirements for satellite
communication services, laser inter satellite links offer an attractive alternative to RF
with virtually unlimited potential and an unregulated spectrum.
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20. REFERENCES
IEEE communications Magazine. August 2000, free space laser communications: Laser
cross-link systems and technology by: David L. Begley, Ball Aerospace & technologies
corporation
Free Space Optics or Laser Communication through the Air BY: Dennis Killinger Optics &
Photonics News
High data-rate laser transmitters for free-space laser Communications. BY:A. Biswas, H.
Hemmati and J. R. Lesh Optical Communications Group Jet Propulsion Laboratory.
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