Wireless Optical Transmission at
10 Gbps and Beyond
Connectivity Unlimited TM
Table of Contents
PART I – CURRENT TECHNOLOGY OVERVIEW
•Bandwidth Blowout (RF vs. IR)
•Trade-offs
•Comparison with Fiber Optics
•The atmosphere
Attenuation
Scattering
•Equipment Fade Margins
PART II – The PHOTONIC AIR LINK
•Basic concept
•Fiber limitations are dominant
•RF plus IR
•WDM extends bandwidth
•Optical Transformers
•Our wish list for the future
Slide No. 2
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Wireless Spectrum Carrier Frequencies
Fig. 1
Wireless Spectrum
Carrier Frequencies
RF
IR Beams
Frequency
350THz
No restrictions
0.8-1.5 m
Mm and sumbmillimeter
18-90 GHz
wave
Spread
Spectrum
10 GHz
900-5500
100
MHz
MHz
Unlicensed bands
Licence required
5-10 mm
3 cm
10-30 cm
TV
carriers
3m
Wavelength
Slide No. 3
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Trade-offs between RF and IR
Slide No. 4
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Wireless Infrared Principles
Slide No. 5
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Comparison of Fiber Optics & FSO (Virtual Fiber)
Yyyyyyyyy
yyyyyyy
<50 dB
Slide No. 6
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Atmospheric Transmission at Sea Level
Slide No. 7
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Definition of types of ray path
Slide No. 8
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Polar diagram of scattering of red light
Slide No. 9
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Visibility & Losses
The Visibility (or visual range) is defined as that distance where the
radiance of a visible light source is reduced to 1/50 of its initial
value:
V(in km) = ln 50/ (in km-1)
In FSO, scattering and absorption losses are represented in dB/km(S)
so:
S(dB/km) ≈ 17/V(km)
Slide No. 10
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Scattering Attenuation of Optical Beams
Weather Condition
Attenuation
Visibility (km)
(dB/km) at 850 nm
Clear weather, light
haze
0 to 3
50 to 6
Light rain
3 to 6
6 to 3
Heavy rain
6 to 17
3 to 1
Snow
10 to 35
1.5 to 0.5
Light fog
17 to 70
1 to 0.25
Heavy fog
80 to 200
0.2 to 0.08
Clouds
300 to 500
0.06 to 0.03
Slide No. 11
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Neither snow nor sleet…
UWIN802 installed in Riga,
Latvia by “Erseta” in
September, 1996.
Ethernet 10 Mbps, ~200 m
“….it works quite well and
we have no problems”.
Slide No. 12
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Fade Margin Calculation
Fade Margin calculation
AB
• Loss Factor = L.F. = 10 log AB/AR [dB]
AR
-AB = Beam area; AR = Receiver area
-AB ~ R2HV where
-H = azimuth angle
AB
-V = elevation angle, R = distance
 Loss Budget = L.B. = 10 log PB/Pt [dB]
H
AR
-PB = Power in the beam
-Pt = Threshold power
R
 Fade Margin = F.M. = L.F. - L.B. [dB]
Slide No. 13
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Today, the Photonic Air Link has a
special niche in a niche technology
Tomorrow, it may become the key
commodity in a mainstream market
Slide No. 14
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Wireless Interconnection without Electronics
Slide No. 15
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Current MMF Fibers Used in FSO
Fiber type
Core diam.
(microns)
NA
Bandwidth
MHz.km
Max length
at Gigabit
ETH
(meters)
Graded Index
62.5
100
125
0.28
0.29
0.30
400
100
100
200
50
50
200
400
600
0.37
0.39
0.39
100
10
8
50
10
5
Graded Index
Semi GI
Semi GI
Step Index
Step Index
Note: Gradium lens 50 mm diam. has focal length 80 mm (NA ≈ 0.3)
Slide No. 16
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Key Components of High Bandwidth
Transmission System
connectors
TX
Network
switch,
PABX, etc
TX
f.o cable
NIU
Up to 50
m
RX
Network Interface
Unit
(in or near the
equipment closet)
Slide No. 17
Duplex f.o.
cable
RX
Optical Antenna Module
(OAM)
(on Roof or Tower)
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Media Converter Designs
Fig 2.2
Media Converter Designs
All λ MC
or APD RCVR
TX
f.o. RX at 1550
O
To PAL TX
850 nm
S
W
850,1310,1550
8 dBm
VCSEL at 850
RX
200 or 400
micron fiber
f.o. TX at 850
Si Pin or APD RCVR
Protocol – independent
Wavelength – independent
Frequency independent
Slide No. 18
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Media Converter Designs
Fig.2.3
Media Converter Designs
(For 1550 nm switches only)
Protocol-independent Media Converter
To PAL TX
TX
O
Any
EDFA
SMF
10-20 dBm
Switch
S
W
From PAL RX
200 micron fiber
RX
SMF (or
MMF)
f.o. 1550 TX
InGaAs pin or APD RSVR
(200 µ)
Slide No. 19
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RFIR 100 System
Fig. 2.1
RFIR 100 System
On the roof or
tower
NIU
RF antenna
FSRF
duplex coax
RADIO
lenses
f.o. XcVR
&MC
To & from the network
Patch cable
duplex f.o.
FSIR
RFIR 100
The Optical Antenna (IR)
Slide No. 20
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MUX/DeMUX with MMF
1549 nm
Slide No. 21
1557 nm
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Optical Wireless WDM
Experimental Arrangement
Slide No. 22
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Experimental test under FSO conditions of
Nanonics OPT XF
MMF
PAL
RCVR.
SOURCE
(Note 1) Plano-convex
f = 80 mm
collimator
1.5 meters
FC/PC
22 μW
MMF
NANONICS
DEVICE
OPT
XF
POWER METER
Nanonics Taper
(62.5 to 9 microns)
SMF
9μ
400 nW
17 dB loss
Experimental test under FSO conditions of Nanonics OPT XF
Note: Same experiment repeated with taper from 200 to 70 microns and 75 micron photodiode 10 microns
distant, 1 dB loss.
Slide No. 23
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Future Research
• Large core broadband fiber with high N.A.
(BW>200 MHz-km for d>150 microns)
• CWDM demux with large core common input fiber
• Large core EDFA
•Low capacitance, large area photodiodes (MSM?)
(BW ≈10 GHz, d≥80 microns)
•Migration to 10 micron wavelength
Slide No. 24
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