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Free Space Laser Communications

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Free Space Laser Communications. Phillip Dykstra. WareOnEarth ... Laser and Weather stats. Links to laser company web sites. phil_at_sd.wareonearth.com ... – PowerPoint PPT presentation

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Title: Free Space Laser Communications


1
Free Space Laser Communications
25 June 2001
  • Phillip Dykstra
  • WareOnEarth Communications Inc.
  • phil_at_sd.wareonearth.com

2
Introduction
  • Free space laser communications
  • a.k.a. Free Space Optics, Optical Wireless
  • Basically a laser and a telescope
  • Most are protocol independent
  • Typical range lt 4 km (.5, 1, 2, 4, 8km)
  • Typical bandwidths 10, 100, 1000 Mbps
  • Lucent 10 Gbps DWDM (TeraBeam)

3
Example Systems
LightPointe Flight series
ICS Sky series
LSA Supraconnect
4
Transmitters
  • 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 nm
  • Eye safety limit 1.5 mW/cm2 at 785 nm
  • Multiple transmitters boost power, may also
    reduce scintillation fades

5
Detectors
  • PIN Diodes
  • -43 dBm typical
  • Avalanche Photo Diodes (APD)
  • -53 dBm typical (also greater dynamic range)
  • Single or multiple detectors
  • Larger aperture increases receive power, reduces
    scintillation fades
  • Design goal BER lt 10-9 typical

6
Laser Link GeometryCritical Design Parameters
Receive area 200 cm2
Receiver sensitivity
Beam Divergence 3 mrad
Distance 1km
Transmit Power
Diameter 3 m Beam area 70686 cm2
Adapted from a LightPointe Technology slide
7
System Comparison(OC3 1km products)

OpticalAccess ICS
LightPointe Transmit Power (mW) 10 (10 dBm)
100 (20 dBm) 4 (6 dBm) Beam Diverg (mrad)
2.5 11
3 Receive Area (cm2) 52
232 200 Min
Recv Power (nW) 100 (-40 dBm) 32 (-45 dBm)
50 (-43 dBm) Price
19.5k 25k
24k
8
Example Loss BudgetOptical Access T1000X
10 dBm
Tx Power (dBm) 10.00 Distance 686
meters Beam Diameter 1.72 meters Beam Area
2.31 meters2 Geometric loss -26.65 dB Rx
Max (dBm) -16.65 Rx Min (dBm)
-40.00 Margin (dBm) 23.35
-3 dB mispointing
- 10 dB scintillation
10 dB for atmospheric attenuation
-17 dBm
-20 dBm
-30 dBm
-40 dBm
9
Equipment Delivery
10
T1000X Interface Box
11
T1000X Full View
12
Platform Mount
13
Eastward View
14
Westward View
15
Concrete Pedestal Base
16
Front of T1000X
17
(No Transcript)
18
Fog Event (19 June 01)
19
Fog Event (cont)
20
Packet Loss
21
Availability
  • Availability Prob (Visibility gt Vmin)

V gt 1.5km V gt
0.5km San Diego 98
99.1 Las Vegas 99.9 100
  • 99.999 is nearly impossible, except in the
    desert
  • Some products add backup microwave (lower speed)

22
For More Info
  • http//wcisd.hpc.mil/
  • Served by the laser link
  • Laser and Weather stats
  • Links to laser company web sites
  • phil_at_sd.wareonearth.com
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