optical communication

1. R V COLLEGE ENGINEERING.
DEPARTMENT OF TELECOMMUNICAION ENGINEERING
BY
SANTHOSHKUMAR (1RV14TE410 ).
Prashnat m angadi(1RV14TE407)
smitha (1RV14TE411)
Topic-
FREE SPACE OPTICS COMMUNICATION(FSO).

2. CONTENTS
• INTRODUCTION
• HISTORY OF FSO
• HOW FSO WORKS
• ARCHITECTURE
• FSO SECURITY
• APPLICATIONS
• MERIT
• DEMERIT
• CONCLUSION
• REFERENCES.

3. FREE SPACE OPTICS COMMUNICATIPON

4. INTRODUCTION
• Free Space Optics (FSO) communications, also called Free
Space Photonics (FSP) or Optical Wireless, refers to the
transmission of modulated visible or infrared (IR) beams
through the atmosphere to obtain optical communications.
Free-space optical communication-
(FSO) is an optical
communication technology that uses
light propagating in free space to
wirelessly transmit data
for telecommunications or computer
networking.

5. HOW FREE SPACE OPTICS WORKS
• Free Space Optics (FSO) transmits invisible, eye-safe light beams
from one "telescope" to another using low power infrared laser in
the teraHertz spectrum.
• The beams of light in Free Space Optics (FSO) systems are
transmitted by laser light focused on highly sensitive photon
detector receivers.
• These receivers are telescopic lenses able to collect the photon
stream and transmit digital data containing a mix of Internet
messages, video images, radio signals or computer files.

6. *
FSO systems use optical wireless link heads each having:
• a transceiver with a laser or LED transmitter, a lens or telescope (can have
more that one) .shaping overcomes building movement
• a receiver usually a semiconductor May also employ servo motors, voice
coils, mirrors, CCD arrays, and even liquid crystals and micro-
electromechanical systems (MEMS) for tracking and acquisition.
• FSO operates in the infrared (IR) range around 850 and 1550 nm (frequencies
around 200 THz).
• FSO can use Power Over Ethernet (PoE).

7. 7
1010
1010
DATA
IN
LED/LD
DRIVER
PHOTO
DETECTOR
SIGNAL
PROCESSO
R
DATA
OUT
ATMOSPHERIC CHANNEL
TRANSMITTER RECEIVER
FSO Block-Diagram
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
1.Both parties can communicate with each
Other simultaneously.

8. Better Modulation Techniques
Classic systems use a relatively simple modulation
• Called “Non-Return to Zero” (NRZ).
(Allow the medium to flow in only one direction.)
• Each symbol encodes 1 bit worth of data.
But there are other more efficient modulations
• If we can’t signal faster, carry more data in each signal.
• Some modulation schemes currently being adopted are:
• Duo-binary
• DPSK (Differential Phase Shift Keying)
• DQPSK (Differential Quaternary Phase-Shift Keying)

9. 9
Modulation Method

10. Architecture

11. Free space Optical Amplifiers.

12. Free space Optical Amplifiers.
 FSO Optical amplifiers increase the intensity of a signal
• There are different types, for different spectrums of light.
• The most common is the Erbium Doped Fiber Amplifier(EDFA).
• Another method is Raman Amplification, typically for ultra
long-haul.
 In an EDFA, a piece of fiber is “doped” with Erbium ions.
 Additional laser power at 980nm and/or 1480nm is pumped in via
a coupler.
 The interaction between the Erbium and the pump laser causes the
emission of light in the C-band spectrum, amplifying the signal.

13. Free space Optic Transmission Bands.
 There are several frequency “windows” available:
• 850nm – The First Window
• Highest attenuation, only used for short reach applications today.
 1310nm – The Second Window (O-band)
• The point of zero dispersion on classic SMF, but high attenuation.
• Primarily used for medium-reach applications (up to 10km) today.
 1550nm – Third Window (C-band)
• Stands for “conventional band”, covers 1525nm – 1565nm.
• Has the lowest rate of attenuation over SMF.
• Used for almost all long-reach and DWDM applications today.
• Also called the “Erbium Band”, the frequencies which support EDFAs.
 Forth Window (L-band)
• Stands for “long band”, covers 1570nm – 1610nm.

14. Free space Optic Transmission Bands

15. 15
Noise in FSO Systems
 Background Radiation (e.g. sun light)
 Shot Noise (Poisson distributed)
 Thermal Noise (Gaussian distributed)
 Scintillation Noise

16. Building Motion – Thermal
Expansion
Results from Seattle
Deployment:
• 15% of buildings move
more than 4mrad
• 5% of buildings move
more than 6mrad
• 1% of buildings move
more than 10mrad

17. SERVICE TYPES AND NETEORK TRANSMISSION OF FSO.
Two basic service types (switching technologies)
 Connection-oriented
 Connectionless
Connection-oriented
Based on circuit switching (setup, connect, tear-
down)
Example: Public Switching Telephone Network
(PSTN)
Originally only supported voice
Not good for bursty traffic
Connectionless
Based on sending datagrams
Examples: Packet, massage, burst switching
Improves bandwidth and network utilization

18. *
*1.Physical layer methods.
•Free space optical terminal –Field proven adaptive optics
system reduces beam spread, increases collection efficiency.
•Optical Automatic Gain Control system – Field proven system
substantially reduces receive power variations. 60 dB dynamic
range, < 1 ms response time
•Optical modem and FEC with near theoretical sensitivity
2.Network layer methods.
•Packet retransmission systems (link or network) –Assures
delivery of packets lost during deep fades.
•Deep queues at the nodes (link or network)
•Network re-routing or re-pointing (network only)

19. *
*Unguided media transport electromagnetic waves without using
a physical conductor. This type of communication is often
referred to as wireless communication. Signals are normally
broadcast through free space and thus are available to anyone
who has a device capable of receiving them.
*Microwaves
* Radio Waves
*Infrared

20. MAC Sublayer
• In Standard Ethernet, the MAC sublayer governs the operation
of the access method. It also frames data received from the upper
layer and passes them to the physical layer.
Frame Format
• The Ethernet frame contains seven fields: preamble, SFD, DA,
SA, length or type of protocol data unit (PDU), upper-layer data,
and the CRC
• Ethernet does not provide any mechanism for acknowledging
received frames, making it what is known as an unreliable
medium. Acknowledgments must be implemented at the higher
layers.

21. IEEE Project 802 has created a sublayer called media access
control that defines the specific access method for each LAN. For
example,
it defines CSMA/CD as the media access method for Ethernet
LANs and the tokenpassing-method for Token Ring and Token
Bus LANs. A part of the framing function is also handled by the
MAC layer.

22. Ethernet frame

23.  Preamble - The first field of the 802.3 frame contains 7 bytes
(56 bits) of alternating Os and 1s that alerts the receiving
system to the coming frame and enables it to synchronize its
input timing.The pattern provides only an alert and a timing pulse.
 Start frame delimiter (SFD) -The second field (l byte: 10101011)
signals the beginning of the frame. The SFD warns the station or
stations that this is the last chance for synchronization. The last 2
bits is 11 and alerts the receiver that the next field is the
destination address.
 Destination address (DA)- The DA field is 6 bytes and
contains the physical address of the destination station or
stations to receive the packet.
 Data- This field carries data encapsulated from the upper-
layer protocols. It is a minimum of 46 and a maximum of
1500 bytes,

24.  CRC- The last field contains error detection information.CRC is
calculated over the address, types and data field.
 If the receiver calculates the CRC and finds that it is not
zero(corruption transmission),it discards the frame.

25. Applications
• Metro Area Networks (MAN)
• Last Mile Access
• Enterprise connectivity
• Fiber backup
• Backhaul
• Service acceleration

26. Merits
• Flexible network solution over conventional broadband
services.
• Straight forward deployment- no licenses required
• Low initial investment
• Ease of installation
• Re-deployability
• High bit rates and low error rates

27. Demerits
• Fog
• Physical obstructions
• Scintillation
• Solar interference
• Scattering
• Absorption
• Building sway / Seismic activity

28. [1] .V. W. S. Chan, “Coherent optical space communications system: Architecture and
technology issues,” in SPIE Control Communication Technol. Laser Syst., vol. 295, 1981,
pp. 10–17.
[2]. V. W. S. Chan, “Space coherent optical communication systems—An introduction,”
IEEE J. Lightwave Technol., vol. LT-5, pp. 633–637, Apr. 1987.
[3]. Couch, L. Digital and Analog Communication Systems. Upper Saddle River, NJ:
Prentice Hall, 2000
[4]. Garcia, A. and Widjaja, I, Communication Networks. New York, NY: McGraw-Hill,
2003
[5]. Keshav, S. An Engineering Approach to Computer Networking. Reading,MA: Addison-
Wesley, 1997.
[6]. Kumar A., Manjunath, D., and Kuri, 1. Communication Networking. San Francisco,
CA: Morgan, Kaufmans, 2004.
[7].Data communication and networking.Behrouz A.Forouzan.
REFERENCES.