Transcript Fiber-Optic Communications

Fiber-Optic Communications
James N. Downing
Chapter 1
Introduction to Fiber-Optic
Communications
Chapter 1 Introduction
• Objectives
– Be familiar with major historical developments in
telecommunications and in fiber optics
– Understand the reasons for regulation,
deregulation and standardization
– Identify the parts of a basic telecommunication
system
– Calculate component and system gain or loss by
the transfer function and using decibels
Chapter 1 Introduction
• Objectives
– Define analog and digital
– Describe the modulation and multiplexing
processes
– Understand the relationship between frequency,
bandwidth, and bit rate
– Understand the basic operation of the PSTN,
CATV, and data networks
Chapter 1 Introduction
• Objectives
– Identify the various classifications for data
networks
– Define convergence
– Describe the reasons why fiber-optic systems are
critical to the future of telecommunications
Chapter 1 Introduction
1.1
Telecommunications
– Milestones
• Telegraph in 1837 by S.B. Morse
• Telephone in 1876 by A.G. Bell
• Electromagnetic waves in late 1800’s by Hertz and
Marconi
• Wireless telegraphy and radio in 1906
• Practical televisions in 1940
Chapter 1 Introduction
1.1 Milestones in Telecommunications
– Digital computer in 1939
– First digitized message in 1941
– Transistors in 1947 by Shockley, Bardeen, and
Brittain
– Mainframe computers in 1980s
– Personal computers in 1990s
Chapter 1 Introduction
1.1 Milestones in Telecommunications
– LANs, PSTN, and internet
– CATV
– Mobile radio and phones
Chapter 1 Introduction
1.1 Regulation and Deregulation
– Prior to the early 1900s, there was no regulation of
the telecommunications industry.
– The ICC was selected to be the watchdog of the
fledgling industry. (At this time, AT&T was the
dominant industry.)
– In 1934, the Communications Act established the
FCC and charged it with regulation of the
telephone and radio broadcasting networks.
Chapter 1 Introduction
1.1 Regulation and Deregulation
– By 1968, private mobile radio systems were
allowed to connect to PSTNs.
– By 1976, long-distance services were allowed to
be delivered by industries other than AT&T.
– In 1984, AT&T was ordered to get rid of the socalled Baby Bells.
Chapter 1 Introduction
1.1 Regulation and Deregulation
– The Telecommunications Act of 1996 lifted many
of the restrictions that had been imposed on the
industry and contributed toward the tremendous
growth in the telecommunications industry.
– The FCC contributes to the implementation of all
types of communications, which not only include
terminal equipment and connections but also
determine the regions over which the industry can
provide services.
Chapter 1 Introduction
1.1 Telecommunications Standards
– Developed by
• International: ISO, ITU, IEEE
• United States: FCC, TIA, ANSI
• Europe: CEPT, ETSI
Chapter 1 Introduction
1.2 Communications Basics
– Basic System Analysis
• Consists of an information source, a
transmitter, a channel, a receiver, and an
output.
• The transfer function of a system is defined as
the output divided by the input.
• See Figure 1.1.
Chapter 1 Introduction
1.2 Communications Basics
– Basic System Analysis
• If the system is composed of several smaller
systems, then the overall transfer function is
the product of the transfer functions of the
smaller systems.
• See Fig 1.2.
Chapter 1 Introduction
• Figure 1.1
xout
T
xin
• Figure 1.2
T  T1 *T2 *T3
Chapter 1 Introduction
1.2 Communications Basics
– Analog and Digital Signals
• An analog signal is continuous—all values
between any two points are all allowed.
• A digital signal is discrete—only certain values
are allowed.
Chapter 1 Introduction
1.2 Communications Basics
– Frequency and Bandwidth
• Frequency is defined as the number of cycles
per second. The units are Hertz.
• Period is defined as the time needed to
complete one cycle.
• Frequency and period are reciprocals.
Chapter 1 Introduction
1.2 Communications Basics
– Frequency and Bandwidth
• Bandwidth (BW) describes the range of
frequencies over which the system works.
• A filter controls the frequencies to be passed by
a system.
• Aggregate bandwidth or data rate is the total
transmission capability of a system.
Chapter 1 Introduction
1.2 Communications Basics
– Modulation: The means by which
information is encoded on a carrier signal
•
•
•
•
Amplitude modulation
Frequency modulation or phase modulation
Amplitude-shift keying
Frequency-shift keying
Chapter 1 Introduction
1.2 Communications Basics
– Modulation: The means by which
information is encoded on a carrier signal
• Frequency-shift keying
• Pulse code modulation
– Nyquist’s Theorem
– Quantization noise
• On-off keying