Free space optics

Copyright © 2002 Terabeam Corporation. All rights reserved. 1

Free Space Optics (FSO)Free Space Optics (FSO)

BY,

YASH


Presentation OverviewPresentation Overview

• Idea behind Free Space Optics?

• Evolution of Free Space Optics?

• Why Free Space Optics?

• Challenges

• Applications

• Advantages of FSO


In the late nineteenth century, Alexander Bell expanded his "phone-phone" communication which was modulated by sunlight.

In the late nineteenth century, Alexander Bell expanded his "phone-phone" communication which was modulated by sunlight.


In the mid-1960's NASA initiated experiments to utilize the laser as a means of communication between the ground and space.

In the mid-1960's NASA initiated experiments to utilize the laser as a means of communication between the ground and space.


Evolution of Free Space Optics Evolution of Free Space Optics


Every thing was destroyed including normal fiber linkEvery thing was destroyed including normal fiber link

Wall street stock market was closed because the communication was

destroyed


• FSO communication between Merrill Lynch Brokerage and Wall Street in New York following the terrorist attack that destroyed normal fiber optic link


Why Free Space Optics?Why Not Just Bury More Fiber?Why Free Space Optics?Why Not Just Bury More Fiber?

• Cost• Rights of Way• Permits• Trenching(digging)• Time

With FSO, especially through the window,

no permits, no digging, no fees


Why Free Space Optics?How Fiber Optic Cable WorksWhy Free Space Optics?How Fiber Optic Cable Works

Light Source

Glass Fiber Strands

Detector

NetworkDevice

• Pulses of light communicate the data• “ON” = 1• “OFF = 0

• Capable of more than 40 Gbps

Light Source

Detector

NetworkDevice


Why Free Space Optics?How FSO WorksWhy Free Space Optics?How FSO Works

1 Network traffic converted into pulses of invisible light representing 1’s and 0’s

2 Transmitter projects the carefully aimed light pulses into the air

5 Reverse direction data transported the same way.

• Full duplex

3 A receiver at the other end of the link collects the light using lenses and/or mirrors

4 Received signal converted back into fiber or copper and connected to the network

Anything that can be done in fiber can be done with FSO


• Beams only a few meters in diameter at a kilometer• Allows VERY close spacing of links without interference• No side lobes• Highly secure• Efficient use of energy• Ranges of 20m to more than 8km possible

Why Free Space Optics?Very Narrow and Directional Beams

Why Free Space Optics?Very Narrow and Directional Beams


Why Free Space Optics?Deployment Behind WindowsWhy Free Space Optics?Deployment Behind Windows

• Rapid installations without trenching and permitting

• Direct connection to the end user

• Bypasses the building owner– No roof rights– No riser rights


Why Free Space Optics?The FSO “Value Proposition”Why Free Space Optics?The FSO “Value Proposition”

• No interference• Unlicensed• Easy to install• Through the window

(or from the rooftop)• No trenching, no permits• Fiber-like data rates• Many deployment options• Fungible equipment


ChallengesEnvironmental factorsChallengesEnvironmental factors

Sunlight

Building Motion

Alignment

WindowAttenuation

Fog

Each of these factors can “attenuate” (reduce) the signal. However, there are ways to mitigate each environmental factor.

Scintillation

RangeObstructions

Low Clouds


ChallengesLow Clouds, Rain, Snow and Dust

ChallengesLow Clouds, Rain, Snow and Dust • Low Clouds

– Very similar to fog– May accompany rain and snow

• Rain– Drop sizes larger than fog and

wavelength of light– Extremely heavy rain (can’t see

through it) can take a link down– Water sheeting on windows

• Heavy Snow– May cause ice build-up on windows– Whiteout conditions

• Sand Storms– Likely only in desert areas; rare in

the urban core


• Beam spreading and wandering due to propagation through air pockets of varying temperature, density, and index of refraction.

• Almost mutually exclusive with fog attenuation.• Results in increased error rate but not complete outage.

ChallengesScintillationChallengesScintillation


Application of Free Space Optics

1. Satellite Laser Communication

Application of Free Space Optics

1. Satellite Laser Communication

a)Space-to-Ground Lasercom Link

b)2000 km Link Distance

c)1 Gbps Transmission Rate


2. Military application of FSO2. Military application of FSO

Air Force

Its potential for low electromagnetic emanation when transferring sensitive

data

Navy

Secure communication with submerged submarines.


Advantages Advantages

• Wireless communicate from A to B

• Low costs ($10K to $20K)

• High bit rate (10 Mbps to 2.5 Gbps)

• Set up a link in a few days

• The lasers used are eye safe, so even a butterfly can fly unscathed through a beam


Conclusion Conclusion

• FSO is just starting to be applied to solve the Internet “last-mile” interconnectivity problem.

• Some believe that it may be the unlimited

bandwidth solution for the metro urban core of downtown building-to-building communication, as well as the optimal technology for home-to-home and office-to-office connectivity


ReferenceReference

• http://www.lightpointe.com/

• http://www.freespaceoptic.com/

• http://www.fsonews.com/

• http://www.cablefreesolutions.com/

• http://www.thefoa.org/

• http://www.free-space-optics.org/

• http://www.freespaceoptics.com/

• http://www.opticsreport.com/

http://www.lightpointe.com/

http://www.freespaceoptic.com/

http://www.fsonews.com/

http://www.cablefreesolutions.com/

http://www.thefoa.org/

http://www.free-space-optics.org/

http://www.freespaceoptics.com/

http://www.opticsreport.com/


Education

Free space optics