Fiber Optics Flashcards
is essentially a waveguide for light
Optical Fiber
index of refraction of the cladding is ___ that of the core, causing rays of light leaving the core to be refracted back into the core
Less Than
LASER meaning:
Light Amplification by Stimulated Emission of Radiation
Advantages of optical fiber include:
- Greater bandwidth than copper
- Lower loss
- Immunity to crosstalk
- No electrical hazard
Optical fibers work on the principle of
Total Internal Reflection
is closely related to the critical angle and is often used in the specification for optical fiber and the components that work with it
Numerical Aperture
is twice that given by the numerical aperture
Angle of Acceptance
Multimode propagation will cause ____, which results in the spreading of pulses and limits the usable bandwidth
Dispersion
Types of index profiles:
- Step-Index
- Graded-Index
the index of refraction changes radically between the core and the cladding
Step-Index
is a compromise multimode fiber, but the index of refraction gradually decreases away from the center of the core
Graded-Index
increases with the bandwidth of the light source
Dispersion
Basic types of fiber-optic cables: (2)
- loose tube cable
- tight-buffer cable
all the stress of cable pulling is taken up by the cable’s strength members and the fiber is free to expand and contract with temperature
loose tube cable
are cheaper and generally easier to use
tight-buffer cable
Splice & Connector Losses:
- Axial or angular misalignment
- Air gaps between the fibers
- Rough surfaces at the ends of the fibers
is a permanent connection
Splice
is a removable connection
Connector
Coupler Construction (2)
- transmissive coupler
- reflective coupler
Optical emitters operate on the idea that electromagnetic energy can only appear in a discrete amount known as a ___
Quantum
is form of junction diode that is operated with forward bias
LED
generate coherent, intense light of a very narrow bandwidth
Laser Diode
The most common optical detector used with fiber-optic systems is the ___
PIN diode
PIN diode is operated in ___
Reverse bias mode
The creation of electron-hole pairs due to the absorption of a photon of incoming light may set off avalanche breakdown, creating up to 100 more pairs
Avalanche Photodiode (APD)
band of light frequencies that is too high to be seen by the human eye with wavelengths ranging between 770nm and 10^6 nm
Infrared
band of light frequencies to which the human eye will respond with wavelengths ranging between 390 nm and 770 nm
Visible
band of light frequencies that are too low to be seen by the human eye with wavelengths ranging between 10 nm and 390 nm
Ultraviolet
The coating helps protect the fiber from moisture, which reduces the possibility of occurrence of a detrimental phenomenon called ___ or static fatigue cause by high humidity
Stress Corrosion
Types of optical fibers commonly used today: (3)
- plastic core and cladding
- glass core, plastic cladding (or PCS - plastic-clad-silica)
- glass core, glass cladding (or SCS - silica-clad-silica)
Process of decaying from one energy level to another energy level is called ___
Spontaneous decay or spontaneous emission
Is the science of measuring only light waves that are visible to the human eye
Photometry
Measures light throughout the entire electromagnetic spectrum
Radiometry
How a light ray reacts when it meets the interface of two transmissive materials that have different indexes of refraction
Snell’s Law
Defined as the minimum angle of incidence at which a light ray may strike the interface of two media and result in an angle of refraction of 90 degrees or greater
Critical Angle
Defined as the maximum angle in which external light rays may strike the air/glass interface and still propagate down the fiber
Acceptance angle or Acceptance cone half-angle
Closely related to acceptance angle and is the figure of merit commonly used to measure the magnitude of the acceptance angle
Numerical Aperture (N.A.)
Simply means path
Mode
has a central core with a uniform refractive index
Step-index Fiber
Has no cladding and the refractive index of the core is nonuniform, it is highest in the center of the core and decreases gradually with distance toward the outer edge
Graded-index Fiber
Type of optical fiber configurations: (3)
- single-mode step index optical fiber
- multimode step-index optical fiber
- multimode graded-index optical fiber
Predominant losses in optical fiber cables: (6)
- absorption loss
- material or Rayleigh scattering loss
- chromatic or wavelength dispersion
- radiation loss
- modal dispersion
- coupling loss
The light rays that escape represent loss in light power called __
Rayleigh scattering loss
Occurs as a result of differences in the thermal contraction rates between the core and cladding material
Microbending
Is caused by the differences in the propagation times of light rays that take different paths down a fiber
Modal dispersion OR Pulse spreading
Characteristics of Light Detectors: (4)
- responsivity
- dark current
- transit time
- spectral response
- light sensitivity
A measure of the conversion efficiency of a photodetector; Its the ratio of the output current of a photodiode to th input optical power and has the unit of A/W
Responsivity
The leakage current that flows through a photodiode with no light input
dark current
The time it takes a light-induced carrier to travel across the depletion region of a seminconductor
transit time
range of wavelength values that a given photodiode will respond
spectral response
The minimum optical power a light detector can receive and still produce a usable electrical output signal
Light Sensitivity
bandwidth of an analog communications system as a percentage of its carrier frequency
bandwidth utilization ratio
Materials commonly used for the buffer jacket include: (6)
- steel
- fiberglass
- plastic
- flame-retardant polyninyl chloride (FR-PVC)
- Kevlar Yarn
- Paper
Wavelengths that are refracted the most
Violet
Wavelengths that are refracted the least
Red
indicates what signal frequency can be propagated down through a given distance of fiber cable and is expressed mathematically as the product of distance and bandwidth
Bandwidth length product (BLP) or Bandwidth distance product (BDP)
Losses caused by imperfect physical connections
Coupling Loss
Lateral or axial displacement between two pieces of adjoining fiber cables
Lateral Displacement
Sometimes called END SEPARATION; When splices are made, the fibers should actually touch
Gap Displacement/Misalignment
Loss that if less than 2deg, will be 0.5 dB
Angular Displacement/Misalignment
Loss incurred if the ends of 2 adjoining fibers are not polished and fit together squarely
Imperfect Surface Finish
Type of laser that use a mixture of helium and neon enclosed in a glass tube
Gas Lasers
Type of laser that uses organic dyes enclosed in a glass tube for an active medium
Liquid Lasers
Type of laser that uses a solid, cylindrical crystal such as ruby for the active medium
Solid Laser
Type of laser that ae made from semiconductore p-n junctions and are commonly called ILDs
Semiconductor Laser
