This is the summary notes of the important terms and concepts in Chapter 13 of the book "Electronic Communications System" by Wayne Tomasi. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Uses light as a carrier of information.
Electronic communications system is directly proportional to
Bandwidth of an analog communications system as a percentage
of its carrier frequency.
bandwidth utilization ratio
Device constructed from mirrors and selenium detectors that
transmitted sound waves over a beam of light.
Experimented with an apparatus called photophone.
Alexander Graham Bell
Used extensively in medical field.
Invented in 1960.
Laser (light amplification by stimulated
emission of radiation)
Advantages of Optical Fiber cables.
1. wider bandwidth and greater information Capacity
2.immunity to crosstalk
3. immunity to statistic Interference
5. safety and convenience
6. lower transmission loss
8. durability and reliability
Disadvantages of Optical Fiber cables.
1. interfacing cost
3. remote electrical Power
4. optical fiber cables are more
susceptible to losses introduced by bending the cable
5. specialized tools, equipment, and
Reduces the possibility of the occurrence of a detrimental
One wire is at the ground potential, whereas the other is at
Single-ended or unbalanced
Increases the tensile strength of the overall cable assembly.
Process of decaying from one energy level to another energy
Spontaneous decay or spontaneous emission
Science of measuring only light waves that are visible to
Measures the rate at which electromagnetic waves transfer
Spectral separation of white light.
Simply the ratio of velocity of propagation of a light ray in
free space to the velocity of propagation of a light ray in a given material.
Angle at which the propagating ray strikes the interface with
respect to the normal.
Angle of incidence
Angle formed between the propagating ray and the normal after the
ray has entered the second medium.
Angle of refraction
Closely related to acceptance angle and is the figure of merit
commonly used to measure the magnitude of the acceptance angle.
Simply means path.
More than one path.
Probably the most important characteristic of the cable.
Three factors that contribute to the absorption losses in
1. ultra violet absorption
2. infrared absorption
3. ion resonance absorption
Caused mainly by small bends and kinks in the fiber.
Caused by excessive pressure and tension and generally occur
when fibers are bent during handling or installation.
Caused by the difference in the propagation times of light
rays that take different path down a fiber.
A p-n junction made from two different mixtures of the same
types of atom.
Generally constructed of silicon-doped gallium-arsenide.
Homojunction LED’s output approximately 500 µ at a wavelength
of 900 nm.
Advantages of heterojunction devices over homojunction
1. increase in current density generates a
more brilliant light spot.
2. smaller emitting area makes it easier to
couple its emitted light into a fiber.
3. small effective area has a smaller
capacitance, which allows the planar heterojunction LED to be used at a
Depletion-layer photo diode and is probably the most common
device used as a light detector in fiber optic communications system.
Characteristic of a light detector.
2. dark currents
3. transit time
5. light sensitivity