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fiber optic communication basics and terminologies
1. UNIT I: OVERVIEW OF
OPTICAL FIBER
COMMUNICATIONS
By DR. Saiyma Fatima Raza
2. Introduction
• Fiber-Optic Communication is the most modern and advanced
mode of data communication (not more than 60 years ago).
• Fiber optics has revolutionized the way we receive information
and communicate with one another, and it has played a major
role in leading in the Information Age. Since the communication
scientists were in an incessant search of a wideband and low-
loss medium of data communication which
3. HISTORY
• The first revolution in the communication came when Sir Alexander
Graham Bell successfully converted voice signals into electrical signals
which were transmitted on electrical wires and then converted back to
voice signals.
• Both the telegraph and the analog voice signals were sent using a baseband
transmission mode.
• Motivation for better links:
• Improve transmission fidelity
• Increase data rates
• Reduce in-line repeaters
4. Fig.: Region of EM spectrum used for Radio and optic communication
5. Contd…
• Main parameter focused was increase in link capacity
• Primary trend was use of high frequency carrier wave
• Radio technology increased from HF toVHF & UHF
• Research showed that optical frequency are several order of magnitude higher
than those used in electrical communication
• Invention of laser aroused the curiosity about use of optical region of EM for
information transmission
• Near IR region was preferred
• First installation of optic fibre occurred in late 1970
6. Advantages of Optical Fibers
The advantages of optical fibers compared to copper wires include the following:
• Long DistanceTransmission
• Large Information Capacity
• Small Size and Low Weight
• Immunity to Electrical Interference
• Enhanced Safety
• Increased Signal Security
8. Optical Spectral Bands
• Electromagnetic energy is a combination of electrical and magnetic fields and
includes power, radio waves, microwaves, infrared light, visible light, ultraviolet
light, X rays, and gamma rays.
• The fundamental nature of all radiation within this spectrum is that it can be
viewed as electromagnetic waves that travel at the speed of light, which is about c
= 3 x 10^8 m/s in a vacuum.
• Physical properties of the waves in different parts of the spectrum can be
measured in several interrelated ways.
• length of one period of the wave
• energy contained in the wave
• oscillating frequency of the wave.
9. Contd…
• Optical communication generally uses wavelength to designate the spectral
operating region and photon energy or optical power.
• Relation of different physical parameters of wave:
1. c = λν
2. E = hν (Planck’s Law)
[h = 6.63 x 10^–34 J-s = 4.14 x 10^–15 eV-s is Planck’s constant]
E(eV) =
1.2406
λ(μ𝑚)
10. Contd…
• Optical spectrum range - 5 nm in the ultraviolet region to 1 mm for far infrared
radiation.
• Optical fiber communication uses the near-infrared spectral band ranging from
nominally 770 to 1675 nm.
• The InternationalTelecommunications Union (ITU) has designated six spectral
bands for use in optical fiber communications within the 1260-to-1675-nm region.
• The 770-to-910 nm band is used for shorter-wavelength multimode fiber systems.
Thus this region is designated as the short-wavelength or multimode fiber band
12. Windows and Spectral Bands
Fig.: Characteristics and operating ranges of the four key optical fiber link components
13. Contd…
• Late 1970s made exclusive use of the 770-to-910-nm wavelength band where there was a low-
loss window and GaAlAs optical sources and silicon photodetectors operating at these
wavelengths were available
• This region was referred to as the first window because around 1000 nm there was a large
attenuation spike due to absorption by water molecules. As a result of this spike, early fibers
exhibited a local minimum in the attenuation curve around 850 nm
• In the 1980s manufacturers could fabricate optical fibers with very low losses in the 1260-to-
1675-nm region.
• This spectral band is called the long-wavelength region.
• Optical fibers doped with rare-earth elements such as Pr,Th, and Er creates optical fiber
amplifiers (called PDFA,TDFA, and EDFA devices, respectively)
• Presence of water molecules, a third-order absorption spike remained around 1400 nm.This
spike defined two low-loss windows, these being the second window centered at 1310 nm and
the third window centered at 1550 nm.These two windows now are called the O-band and C-
band.
14. Contd…
• Special material-purification processes can eliminate almost all water molecules
from the glass fiber material, thereby dramatically reducing the water-attenuation
peak around 1400 nm.
• This process opens the E-band (1360-to-1460 nm) transmission region to provide
around 100 nm more spectral bandwidth in these specially fabricated fibers than in
conventional single-mode fibers.
• Systems operating at 1550 nm provide the lowest attenuation but has signal
dispersion
• This has led to S and C band systems for high capacity long span terrestrial and
undersea transmission links
15. Decibel Units
• Measure of optical signal for link
• Measure of attenuation and loss
• Measuring attenuation through a link or a device ---> reference the output signal
level to the input level.
• Decay of signal strength is exponential hence use of logarithmic power ration
measured in decibels is convenient.
Power ration in dB = 10log
𝑃2
𝑃1
• Decibels is relative measure for absolute power measure:
Power level (in dBm) = 10log
𝑃 𝑖𝑛 𝑚𝑊
1 𝑚𝑊
16. Network Information Rates
1. Telecom Signal Multiplexing:
Type of service Data rate
Video on demand/interactive TV 1.5 to 6 Mb/s
Video games 1 to 2 Mb/s
Remote education 1.5 to 3 Mb/s
Electronic shopping 1.5 to 6 Mb/s
Data transfer or telecommuting 1 to 3 Mb/s
Video conferencing 0.384 to 2 Mb/s
Voice (single telephone channel) 33.6 to 56 kb/s
17. Contd…
• Network providers combine the signals from many different users and send the
aggregate signal over a single transmission line.
Fig.: Digital transmission hierarchy used in the North American telephone network
18. Contd…
2. SONET/SDH Multiplexing Hierarchy:
• These standards define a synchronous frame structure for sending multiplexed digital
traffic over optical fibre trunk lines.
• Basic building block SynchronousTransport Signal - Level 1 (STS-1), bit rate of 51.84
Mb/s
• Higher-rate SONET signals are obtained by byte-interleaving N of these STS-1 frames,
which then are scrambled and converted to an OpticalCarrier - Level N (OC-N) signal.
19. Key Elements of Optical Fiber Systems
Fig.: Main constituents of an optical fibre communications link
22. Standards for Optical Fiber
Communications
1. Primary standards:
• Refer to measuring and characterizing fundamental physical parameters such as
attenuation, bandwidth, operational characteristics of fibers, and optical power levels
and spectral widths.
• National Institute of Standards andTechnology - (NIST)
• Other national organizations include the National Physical Laboratory (NPL) in the
United Kingdom
• The Physikalisch-Technische Bundesanstalt (PTB) in Germany.
23. Component testing standards
• Define tests for fiber-optic component performance and establish equipment-
calibration procedures.
• Telecommunications Industry Association (TIA) group of organization for
testing standards.
• The Electronics Industries Alliance (EIA), theTelecommunication Sector of the
InternationalTelecommunication Union (ITU-T) are testing organisations.
24. System standards
• It refers to measurement methods for links and networks.
• The major organizations are the American National Standards Institute (ANSI), the
Institute for Electrical and Electronic Engineers (IEEE), the ITU-T, andTelcordia
Technologies.
