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LASER Communication
Post: #1

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Laser communications offer a viable alternative to RF communications for inter satellite links and other applications where high-performance links are a necessity. High data rate, small antenna size, narrow beam divergence, and a narrow field of view are characteristics of laser communications that offer a number of potential advantages for system design.

Lasers have been considered for space communications since their realization in 1960. Specific advancements were needed in component performance and system 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 viable but also an attractive approach into inter satellite link applications.

Information transfer is driving the requirements to higher data rates, laser cross -link technology explosions, global development activity, increased hardware, and design maturity. Most important in space laser communications has been the development of a reliable, high power, single mode laser diode as a directly modulable laser source. This technology advance offers the space laser communication system designer the flexibility to design very lightweight, high bandwidth, low-cost communication payloads for satellites whose launch costs are a very strong function of launch weigh. This feature substantially reduces blockage of fields of view of most desirable areas on satellites. The smaller antennas with diameter typically less than 30 centimeters create less momentum disturbance to any sensitive satellite sensors. Fewer on board consumables are required over the long lifetime because there are fewer disturbances to the satellite compared with heavier and larger RF systems. The narrow beam divergence affords interference free and secure operation.
Post: #2
Post: #3

Free Space Laser Communications


¢ Free space laser communications
“ a.k.a. Free Space Optics, Optical

Presented By

Phillip Dykstra
WareOnEarth Communications Inc.


¢ Basically a laser and a telescope
¢ Most are protocol independent
¢ Typical range < 4 km (.5, 1, 2, 4,

¢ Typical bandwidths: 10, 100, 1000

“ Lucent 10 Gbps DWDM (TeraBeam)


¢ LED (single or multiple)
“ 1 mW typical
¢ Laser (single or multiple)
“ 10-20 mW typical, up to 100 mW
¢ Usually 785 or 850 nm, some 1310

¢ Eye safety limit: 1.5 mW/cm^2 at

785 nm
¢ Multiple transmitters boost power,

may also reduce scintillation fades


¢ PIN Diodes
-43 dBm typical
¢ Avalanche Photo Diodes (APD)
-53 dBm typical (also greater dynamic

¢ Single or multiple detectors
¢ Larger aperture increases receive

power, reduces scintillation fades
¢ Design goal: BER < 10^-9 typical
Post: #4

:Light Amplification by Stimulated Emission of Radiation

A device produces a coherent beam of optical radiation by stimulating electronic, ionic, or molecular transitions to higher energy levels
When they return to lower energy levels by stimulated emission, they emit energy.

Concentrate in a narrow range of wavelengths (one specific colour).

All the emitted photons bear a constant phase relationship with each other in both time and phase

A very tight beam which is very strong and concentrated.
Post: #5
please make a look on these page for more about LASER Communication i am sure you never miss a second for reading this report
Post: #6
Laser Communications
Laser Classes

 Class I – Sealed systems
 Class II – Output <1mW
 Class IIIa – Output 1mW - 5mW
 Class IIIb – Output 5mW – 500mW
 Harmful to eyes, diffuse viewing OK
 Class IV – Output >500mW
 Harmful to skin and eyes, diffuse viewing hazardous
Diode Lasers
 Laser diodes emit an elliptical beam with astigmatism
 Better units will include corrective lenses for astigmatism and to make the dot appear round
 Neither of these problems are inherently bad for DX purposes but correcting them also improves divergence, a big win (more gain).
Human Spectral Response
 Perceived Intensities
 Laser Diode
 Pointer Design
 Pointer Innards
 AM
 Easy with gas lasers, hard with diodes
 PWM (Pulse Width Modulation)
 Used by Ramsey in their kit
 PFM (Pulsed FM)
 Potentially the highest bandwidth (>100kHz)
Gain Systems
 Transmitter
 Maximum output power
 Minimum divergence
 Receiver
 Maximum lens area
 Clarity
 Tight focus on
 Sun shade over detector
 Shade in front of lens
 Detector spectral response
 Colored filters
 Absorb ~50% of available light
 Difficult to find exact frequency
Mounting Systems
 Mounts and stands need only be as accurate as beam divergence
 Good laser diodes will be 1-2mR (milliRadian)
 A 32 pitch screw at the end of a 2' mount will yield 1mR per revolution. Since quarter turns (even eighth turns) are possible, this is more than accurate enough
 Higher thread pitches allow shorter mounts which may be more stable (against wind, vibration, wires)
 1mR is 1.5' of divergence every 1000', 3' at 2000 ', etc.
 GPS and Compass
 Scopes and Binoculars
 Strobe lights, large handheld floods, headlights
 HTs to yell when laser light is seen at remote location
Weak Signal Modes
Laser DX

 Transmit voice for miles line-of-sight
 Use weak signal modes for “cloud scatter”
 Transmit video with cheap pens
 Transmit high speed data without WEP
 Blind flies for easy extermination
Post: #7
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Post: #8
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Post: #9
to get information about the topic "space laser communications" full report ppt and related topic refer the link bellow

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