BY

K.BABU AYYAPPA REDDY - IV B TECH ECE

REG NO: 07691A0407

MADANAPALLE INSTITUTE OF TECHNOLOGY AND SCIENCES

ANGALLU,

MADANAPALLI,

CHITTOOR DISTRICT.

UNDER THE ESTEEMED GUIDANCE OF:

B.D.VENKATARAMANA M.Tech, (PhD),

Professor,

Department of ECE.

A TECHNICAL REPORT ON

CERTIFICATE

This is to certify that Mr. K.BABU AYYAPPA REDDY is a student

of IV B.Tech ECE, with registration number 07691A0407 in the batch 2007-2011

has taken active interest in preparing report on “FREE SPACE OPTICS”.

This is in potential fulfillment of requirement for the Bachelor of

Technology degree in Electronics and Communication Engineering, under

Madanapalli Institute of Technology and Science.

This report is verified by:

Dr.A.R.REDDY Ph.D, B.D.VENKATARAMANA M.Tech, (Ph.D)

Head Of Department, Seminar Guide,

ECE, MITS Dept. of ECE.

ACKNOWLEDGEMENT

I extend my sincere gratitude towards Prof. A.R.Reddy Head of

Department, ECE for giving us his invaluable knowledge and wonderful technical

guidance.

I express my thanks to Mr. B.D.VENKATARAMANA (Professor, Dept.

of ECE) our project guide and also to our staff advisor Ms.TRIVENI (Assistant

Professor Dept. of ECE) for their kind co-operation and guidance for preparing and

presenting this seminar.

I also thank all the other faculty members of ECE department and my

friends for their help and support.

ABSTRACT:

Free space optics (FSO) is a line-of-sight technology that

currently enables optical transmission up to 2.5 Gbps of data, voice, and video

communications through the air, allowing optical connectivity without deploying

fiber optic cables or securing spectrum licenses.

FSO system can carry full duplex data at giga bits per second

rates over Metropolitan distances of a few city blocks of few kms. FSO, also

known as optical wireless, overcomes this last-mile access bottleneck by sending

high bit rate signals through the air using laser transmission.

FSO can be the ultimate solution for high-speed access.

Instead of hybrid fiber-coax system, hybrid fiber-laser system may turn out to be

the best way to deliver the high capacity last-mile access. FSO provide higher

security, and throughput. FSO is capable to fulfill the increasing demand of

bandwidth.

CONTENTS

1. INTRODUCTION

2. FSO! FREE SPACE OPTICS

3. RELEVANCE OF FSO IN PRESENT DAY COMMUNICATION

4. ORIGIN OF FSO

5. THE TECHNOLOGY OF FSO

6. WORKING OF FSO SYSTEMS

7. WHY FSO?

8. APPLICATIONS OF FSO

9. MARKET

10. MERITS OF FSO

11. LIMITATIONS OF FSO

12. FSO! AS A FUTURE TECHNOLOGY

13. CONCLUSION

14. BIBLIOGRAPHY

(1).INTRODUCTION:

Communication, as it has always been relied and simply depended upon speed.

The faster the means! the more popular, the more effective the communication is ! Presently in

the twenty-first century wireless networking is gaining because of speed and ease of deployment

and relatively high network robustness. Modern era of optical communication originated with the

invention of LASER in 1958 and fabrication of low-loss optical fiber in 1970.

When we hear of optical communications we all think of optical fibers, what I

have for u today is AN OPTICAL COMMUNICATION SYSTEM WITHOUT FIBERS or in

other words WIRE FREE OPTICS.

Free space optics or FSO –Although it only recently and rather suddenly sprang in

to public awareness, free space optics is not a new idea. It has roots that 90 back over 30 years-to

the era before fiber optic cable became the preferred transport medium for high speed

communication. FSO technology has been revived to offer high band width last mile

connectivity for today’s converged network requirements.

(2). FSO! FREE SPACE OPTICS:

Free space optics or FSO, free space photonics or optical wireless, refers to the

transmission of modulated visible or infrared beams through the atmosphere to obtain optical

communication. FSO systems can function over distances of several kilometers.

FSO is a line-of-sight technology, which enables optical transmission up to 2.5 Gbps

of data, voice and video communications, allowing optical connectivity without deploying fiber

optic cable or securing spectrum licenses. Free space optics require light, which can be focused

by using either light emitting diodes (LED) or LASERS(light amplification by stimulated

emission of radiation). The use of lasers is a simple concept similar to optical transmissions

using fiber-optic cables, the only difference being the medium.

As long as there is a clear line of sight between the source and the destination and

enough transmitter power, communication is possible virtually at the speed of light. Because

light travels through air faster than it does through glass, so it is fair to classify FSO as optical

communications at the speed of light. FSO works on the same basic principle as infrared

television remote controls, wireless keyboards or wireless palm devices.

FSO TRANSMITTER:

FSO RECEIVER:

(3). RELEVANCE OF FSO:

Presently we are faced with a burgeoning demand for high bandwidth and

differentiated data services. Network traffic doubles every 9-12 months forcing the bandwidth or

data storing capacity to grow and keep pare with this increase. The right solution for the pressing

demand is the untapped bandwidth potential of optical communications.

Optical communications are in the process of evolving Giga bits/sec to terabits/sec

and eventually to pentabits/sec. The explosion of internet and internet based applications has

fuelled the bandwidth requirements. Business applications have grown out of the physical

boundaries of the enterprise and gone wide area linking remote vendors, suppliers, and

Customers in a new web of business applications. Hence companies are looking for high

bandwidth last mile options. The high initial cost and vast time required for installation in case of

OFC speaks for a wireless technology for high bandwidth last mile connectivity there FSO finds

its place.

(4).ORIGIN OF FSO:

It is said that this mode of communication was first used in the 8th century by the

Greeks. They used fire as the light source, the atmosphere as the transmission medium and

human eye as receiver.

FSO or optical wireless communication by Alexander Graham Bell in the late 19th

century even before his telephone! Bells FSO experiment converted voice sounds to telephone

signals and transmitted them between receivers through free air space along a beam of light for a

distance of some 600 feet, - this was later called PHOTOPHONE. Although Bells photo phone

never became a commercial reality, it demonstrated the basic principle of optical

communications. Essentially all of the engineering of today’s FSO or free space optical

communication systems was done over the past 40 years or so mostly for defense applications.

(5). THE TECHNOLOGY OF FSO:

The concept behind FSO is simple. FSO uses a directed beam of light radiation

between two end points to transfer information (data, voice or even video). This is similar to

OFC (optical fiber cable) networks, except that light pulses are sent through free air instead of

OFC cores. An FSO unit consists of an optical transceiver with a laser transmitter and a receiver

to provide full duplex (bi-directional) capability.

Each FSO unit uses a high power optical source (laser) plus a lens that

transmits light through the atmosphere to another lens receiving information. The receiving lens

connects to a high sensitivity receiver via optical fiber. Two FSO units can take the optical

connectivity to a maximum of 4kms.

Figure shows the comparision of fso with other technologies

(6).WORKING OF FSO SYSTEM:

Optical systems work in the infrared or near infrared region of light and the

easiest way to visualize how the work is imagine, two points interconnected with fiber optic

cable and then remove the cable. The infrared carrier used for transmitting the signal is generated

either by a high power LED or a laser diode. Two parallel beams are used, one for transmission

and one for reception, taking a standard data, voice or video signal, converting it to a digital

format and transmitting it through free space .

Today’s modern laser system provide network connectivity at speed of 622 Mega

bits/sec and beyond with total reliability. The beams are kept very narrow to ensure that it does

not interfere with other FSO beams. The receiver detectors are either PIN diodes or avalanche

photodiodes. The FSO transmits invisible eye safe light beams from transmitter to the receiver

using low power infrared lasers in the tera hertz spectrum. FSO can function over kilometers.

WAVELENGTH:

Currently available FSO hardware are of two types based on the operating wavelength

– 800 nm and 1550 nm. 1550 FSO systems are selected because of more eye safety, reduced

solar background radiation and compatibility with existing technology infrastructure.

SUBSYSTEM:

In the transmitting section, the data is given to the modulator for modulating signal

and the driver is for activating the laser. In the receiver section the optical signal is detected and

it is converted to electrical signal, preamplifier is used to amplify the signal and then given to

demodulator for getting original signal. Tracking system which determines the path of the beam

and there is special detector (CCD, CMOS) for detecting the signal and given to pre amplifier.

The servo system is used for controlling system, the signal coming from the path to the processor

and compares with the environmental condition, if there is any change in the signal then the

servo system is used to correct the signal.

FSO: WIRELESS, AT THE SPEED OF LIGHT:

Unlike radio and microwave systems, Free Space Optics (FSO) is an optical

technology and no spectrum licensing or frequency coordination with other users is

required, interference from or to other systems or equipment is not a concern, and the

point-to-point laser signal is extremely difficult to intercept, and therefore secure.

Data rates comparable to optical fiber transmission can be carried by Free Space

Optics (FSO) systems with very low error rates, while the extremely narrow laser beam

widths ensure that there is almost no practical limit to the number of separate Free Space

Optics (FSO) links that can be installed in a given location.

Light Beam Used for FSO System:

Generally equipment works at one of the two wavelengths: 850 nm or 1550 nm.

Laser for 850 nm are much less expensive (around $30 versus more than $1000) and are favored

for applications over moderate distances. One question arises that why we use 1550 nm

wavelength.

The main reason revolves around power, distance, and eye safety. Infrared radiation

at 1550 nm tends not to reach the retina of the eye, being mostly absorbed by the cornea. 1550

nm beams operate at higher power than 850 nm, by about two orders of magnitude. That power

can boost link lengths by a factor of at least five while maintaining adequate strength for proper

link operation. So for high data rates, long distances, poor propagation conditions (like fog), or

combinations of those conditions, 1550 nm can become quite attractive.

(7).Why FSO Now? :

Substantial investments by carriers to augment the capacity of their core fiber

backbones have facilitated dramatic improvements in both price and performance, and they have

also increased the capacity of these large backbone networks. However, to generate the

communications traffic and revenue needed to fully utilize and pay for these backbone upgrades,

higher bandwidth connections must reach the end customers. This requires substantial bandwidth

upgrades at the network edge. Essentially, to fully leverage their backbone investments, service

providers will also need to expand and extend the reach of their metropolitan optical network to

the edge. FSO presents an opportunity that allows carriers to achieve that goal for one-fifth the

cost when compared to fiber (if even available) and at a fraction of the time.

Increased competition:

Regulation changes and significant investments by various funds have increased the

competitive climate in these metro networks. Each of the existing or new entrants is racing to

gain an advantage over their competition. FSO is one of the evolutionary technologies that

allows a carrier to acquire and retain new customers quickly and cost-effectively, thereby gaining

an entry point over competition. Metro optical networks are expected to see $57.3 billion

invested by 2005.

International growth:

Due to the growing number of Internet-based applications, most countries are

experiencing tremendous growth in bandwidth needs. In growing economies like Latin America

and China—where the ability to have high-bandwidth connectivity outweighs standards for

reliability—the lack of infrastructure and rising bandwidth demands offers a unique opportunity

for FSO.

Changing traffic patterns and protocol standards:

Multiple traffic types characterize metro networks. Where voice was once the dominant

traffic type, data has emerged as the winner. Moreover, these networks are also a mixture of

multiple protocols ranging from Ethernet, SONET, IP, ESCON, FICON, etc. As a Layer One

technology, FSO is protocol agnostic.

Wireless world:

With the rapid adoption and slow deployment of wireless technologies such as LMDS

and MMDS in response to high bandwidth communication needs in the metro area, many service

providers still find themselves short of bandwidth to satisfy their needs. To better understand this

growing need for FSO, it is important to understand the key drivers for FSO.

FSO: Optical or Wireless?

FSO is clearly an optical technology and not a wireless technology for two primary

reasons. One, FSO enables optical transmission at speeds of up to 2.5 Gbps and in the future 10

Gbps using WDM. This is not possible using any fixed wireless/RF technology existing today.

Two, FSO obviates the need to buy expensive spectrum (it requires no FCC or municipal license

approvals), which distinguishes it clearly from fixed wireless technologies. Thus, FSO should

not be classified as a wireless technology. Its similarity to conventional optical solutions will

enable a seamless integration of access networks with optical core networks and help to realize

the vision of an all-optical network.

Free-Space Optics (FSO) Security:

The common perception of wireless is that it offers less security than wire line connections.

In fact, Free Space Optics (FSO) is far more secure than RF or other wireless-based

transmission technologies for several reasons:

Free Space Optics (FSO) laser beams cannot be detected with spectrum

analyzers or RF meters

Free Space Optics (FSO) laser transmissions are optical and travel along

a line of sight path that cannot be intercepted easily. It requires a matching Free Space

Optics (FSO) transceiver carefully aligned to complete the transmission. Interception is

very difficult and extremely unlikely.

The laser beams generated by Free Space Optics (FSO) systems are

narrow and invisible, making them harder to find and even harder to intercept and crack

Data can be transmitted over an encrypted connection adding to the

degree of security available in Free Space Optics (FSO) network transmissions

(8).APPLICATIONS OF FSO:

Optical communication systems are becoming more and more popular as the

interest and requirement in high capacity and long distance space communications grow. FSO

overcomes the last mile access bottleneck by sending high bit rate signals through the air using

laser transmission. Applications of FSO system are many and varied but a few can be listed.

1. Metro Area Network (MAN): FSO network can close the gap between the last mile

customers, thereby providing access to new customers to high speed MAN’s resulting to Metro

Network extension.

2. Last Mile Access: End users can be connected to high speed links using FSO. It can also be

used to bypass local loop systems to provide business with high speed connections.

3. Enterprise connectivity: As FSO links can be installed with ease, they provide a natural

method of interconnecting LAN segments that are housed in buildings separated by public streets

or other right-of-way property.

4. Fiber backup: FSO can also be deployed in redundant links to backup fiber in place of a

second fiber link.

5. Backhaul: FSO can be used to carry cellular telephone traffic from antenna towers back to

facilities wired into the public switched telephone network.

6. Service acceleration: instant services to the customers before fiber being layered.

(9).MARKET:

Telecommunication has seen massive expansion over the last few years. First came

the tremendous growth of the optical fiber. Long-haul Wide Area Network (WAN) followed by

more recent emphasis on Metropolitan Area Networks (MAN). Meanwhile LAN giga bit

Ethernet ports are being deployed with a comparable growth rate. Even then there is pressing

demand for speed and high bandwidth.

The ‘connectivity bottleneck’ which refer the imbalance between the increasing demand

for high bandwidth by end users and inability to reach them is still an unsolved puzzle. Of the

several modes employed to combat this ‘last mile bottleneck’, the huge investment is trenching,

and the non- redeploy ability of the fiber has made it uneconomical and nonsatisfying. Other

alternatives like LMDS, a RF technology has its own limitations like higher initial investment,

need for roof rights, frequencies,

rainfall fading, complex set and high deployment time.

In the United States the telecommunication industries 5 percent of buildings are

connected to OFC. Yet 75 percent are within one mile of fiber. Thus FSO offers to the service

providers, a compelling alternative for optical connectivity and a complement to fiber optics.

(10).MERITS OF FSO:

1. Free space optics offers a flexible networking solution that delivers on the promise of

broadband.

2. Straight forward deployment-as it requires no licenses.

3. Rapid time of deployment.

4. Low initial investment.

5. Ease of installation even indoors in less than 30 minutes.

6. Security and freedom from irksome regulations like roof top rights and spectral licenses.

7. Re-deployability

Unlike radio and microwave systems FSO is an optical technology and no spectrum

licensing or frequency co ordination with other users is required. Interference from or to other

system or equipment is not a concern and the point to point laser signal is extremely difficult to

intercept and therefore secure. Data rate comparable to OFC can be obtained with very low error

rate and the extremely narrow laser beam which enables unlimited number of separate FSO links

to be installed in a given location.

(11).LIMITATIONS OF FSO:

The advantages of free space optics come without some cost. As the medium is

air and the light pass through it, some environmental challenges are inevitable.

1. FOG AND FSO:

Fog substantially attenuates visible radiation, and it has a similar affect on the near-

infrared wavelengths that are employed in FSO systems. Rain and snow have little affect on

FSO. Fog being microns in diameter, it hinder the passage of light by absorption, scattering and

reflection. Dealing with fog – which is known as Mie scattering, is largely a matter of boosting

the transmitted power. In areas of heavy fogs 1550nm lasers can be of more are. Fog can be

countered by a network design with short FSO link distances. FSO installations in foggy cities

like SanFrancisco have successfully achieved carrier-class reliability.

2. PHYSICAL OBSTRUCTIONS:

Flying birds can temporarily block a single beam, but this tends to cause only short

interruptions and transmissions are easily and automatically re-assumed. Multi-beam systems are

used for better performance.

3. SCINTILLATION:

Scintillation refers the variations in light intensity caused by atmospheric turbulence. Such

turbulence may be caused by wind and temperature gradients which results in air pockets of

varying diversity act as prisms or lenses with time varying properties. This scintillation affects

on FSO can be tackled by multi beam approach exploiting multiple regions of space- this

approach is called spatial diversity.

4. SOLAR INTERFERENCE:

This can be combated in two ways –

The first is a long pass optical filter window used to block all wavelengths below 850nm from

entering the system.

The second is an optical narrow band filter proceeding the receive detector used to filter all but

the wavelength actually used for intersystem communications.

5. SCATTERING:

Scattering is caused when the wavelength collides with the scatterer. The physical size of

the scatterer determines the type of scattering.

When the scatterer is smaller than the wavelength-Rayleigh scattering.

When the scatterer is of comparable size to the wavelength –Mie scattering.

When the scatterer is much larger than the wavelength -Non-selective Scattering

In scattering there is no loss of energy, only a directional redistribution of energy which

may cause reduction in beam intensity for longer distance.

6. ABSORPTION:

Absorption occurs when suspended water molecules in the terrestrial atmosphere extinguish

photons. This causes a decrease in the power density of the FSO beam and directly affects the

availability of a system. Absorption occurs more readily at some wavelengths than others.

However, the use of appropriate power, based on atmospheric conditions, and use of spatial

diversity helps to maintain the required level of network availability.

7. BUILDING SWAY / SEISMIC ACTIVITY:

One of the most common difficulties that arises when deploying FSO links on tall

buildings or towers is sway due to wind or seismic activity Both storms and earthquakes can

cause buildings to move enough to affect beam aiming. The problem can be dealt with in two

complementary ways: through beam divergence and active tracking

A. With beam divergence, the transmitted beam spread, forming optical cones which can take

many perturbations.

B. Active tracking is based on movable mirrors that control the direction in which beams are

launched.

(12).FSO! AS A FUTURE TECHNOLOGY:

Infrared technology is as secure or cable applications and can be more reliable than

wired technology as it obviates wear and tear on the connector hardware. In the future it is

forecast that this technology will be implemented in copiers, fax machines, overhead projectors,

bank ATMs, credit cards, game consoles and head sets.

All these have local applications and it is really here where this technology is best suited, owing

to the inherent difficulties in its technological process for interconnecting over distances.

Outdoors two its use is bound to grow as communications companies, broadcasters and

end users discovers how crowded the radio spectrum has become. Once infrared’s image issue

has been overcome and its profile raised, the medium will truly have a bright, if invisible, future!

(13).CONCLUSION:

We have discussed in detail how FSO technology can be rapidly deployed to

provide immediate service to the customers at a low initial investment, without any licensing

hurdle making high speed, high bandwidth communication possible. Though not very popular in

India at the moment, FSO has a tremendous scope for deployment companies like CISCO,

LIGHT POIN few other have made huge investment to promote this technology in the market. It

is only a matter of time before the customers realized, the benefits of FSO and the technology

deployed in large scale.

(14).BIBLIOGRAPHY: 1. Free-Space Optics: Enabling Optical Connectivity in Today's Networks by

Heinz Willebrand, Ph.D., Baksheesh S. Ghuman Sams Publishing 2001/12/21

2. “Free Space Optics (FSO), Optical Wireless, Infrared Fixed Wireless Access, Wireless

Broadband, Laser”. Copyright 2000 Cable Free Solutions Limited. Retrieved from

http://www.cablefreesolutions.com/

3. Isaac I. Kim and Eric Korevaar, “Availability of Free Space Optics (FSO) and hybrid FSO/RF

systems”

4. Rowe, Schuf. Computer Networking. (2005). Pearson Education, Inc

5. Vikrant kaulgnd, “Free space optics Bridges the last mile’’, Electronics for u, June 2003 pp.

38-40.

6. Andy Emerson, “Fibreless Optics ’’, Everyday practical electronics, April 2003 pp . 248.

7. www.fsona.com

8. www.freespaceoptics.com

9. www.freespaceoptic.com

10. www.fsocentral.com