Chp 3 Physical Layer Cabling Fiber Optics Flashcards
Fiber Optic Network
- A fiber optic transmission strand can carry the signal (in from a modulated light beam) a few feet or even hundreds or thousands of miles. A cable may contain three or four hair-like fibers or a bundle of hundreds of fibers.
- A source of invisiable infared radiation, usually a light emitting diode (LED) or a solid-state laser - that can be modulated to impress digital data or an analog signal on the light beam
- A photsenitive detector to convert the optical signal back into a electrical signal at the receiver.
- Efficient optical connectors at the light source-to-cable interface and at the cable-to-photo detector interface. These connectors are also critical when splicing teh optical cable due to excessive loss that can occur at connections.
ADAVANTAGES
OF
OPTICAL COMMUNICATION LINKS
COMPARED TO COPPER CONDUCTORS
- EXTREMELY WIDE SYSTEM BANDWITH
- IMMUNITY TO ELECTROSTATIC INTERFERENCE
- ELIMINATION OF CROSS TALK
- LOWER SIGNAL ATTENUATION THAN OTHER PROPAGATION SYSTEMS
- LOWER COST
- SAFETY
- CORROSION
- SECURITY
EXTREMELY WIDE SYSTEM BANDWTIH
AS AN ADVANTAGE OF
OPTICAL COMMUNICATION LINKS
THE INTELLIGENCE IS IMPRESSED ON TEH LIGHT BY VERING THE LIGHT’S AMLITUDE. BECAUSE THE BEST LEDs HAVE A 5 NS RESPONSE TIME, THEY PROVIDE A MAXIMUM BANDWITH OF ABOUT 100MHZ. WITH LASER LIGHT SOURCES HOWEVER, DATA RATES ARE OVER 10GBPS ARE POSSIBLE WITH A SINGLE MODE FIBER. THE AMOUNT OF INFORMATION MUTIPLEXED ON SUCH A SYSTEM IN THE HUNDREDS OF GBPS, IS INDEED STAGGERING.
IMMUNITY OF THE ELECTROSTATIC INTERFERENCE
AS AN ADVANTAGE TO OPTICAL COMMUNICATION
EXTERNAL ELECTRICAL NOISE AND LIGHTING DO NOT EFFECT ENERGY IN A FIBER OPTIC STRAND.
HOWEVER, THIS IS TRUE ONLY FOR THE OPTICAL STRANDS, NOT THE METALLIC CABLE COMPONENTS OR CONNECTING ELECTONICS.
ELIMINATION OF CROSSTALK
AS AN ADVANTAGE OF
OPTICAL COMMUNICATION
The light in one glass fiber does not interfere with, nor is it suscepptible to, the light in an adjacent fiber. Recall that crosstalk results from the electromagnetic coupling between two adjacent copper wires.
LOWER SIGNAL ATTENUATION THAN OTHER PROPAGATION SYSTEMS
BEING AN ADVANTAGE OF OPTICAL COMMUNICATION
Typical attenuation of 1GHz bandwith signal for optical fibers is 0.03db per 100ft compared to 4.0 dB for RG-58U coaxial
LOWER COST
AS AN ADVANTAGE
OF OPTICAL COMMUNICATION
Optical fiber cost are continuing to decline. The cost of many systems are declining with the use of fiber, and that trend is accelerating.
SAFETY
AS AN ADVANTAGE OF OPTIACL COMMUNICATION
In many wired systems, the potential hazard of short circuits requires precautionary designs. Additionaly, the dielectric nature of optic fibers elimnates the spark hazzard.
- CORROSION*
- AS AN ADVANTAGE OF OPTICAL COMMUNICATION*
Given that glass is basically inert, the corrosive effects of certain environments are not a problem
SECURITY
AS AN ADVANTAGE OF OPTICAL COMMUNICATION.
due to its immunity to and from electromagnetic coupling and radiation, optical fiber can be used in most secure environments. Although it can be intercepted or tapped, it is very difficult to do so.
SPEED OF LIGHT IN FREE SPACE
3 X 108 m / s
** is reduced in other media, including fiber optic cables
MULTI MODE FIBER
850 AND 1310 nm
nano meters
Fibers that support many wave guide modes
SINGLE MODE FIBER
1310 AND 1550 nm
nano meters
Fiber cable with core diameters of about 7 - 10 nm, light follows a sigle path
AKA mono mode
used to minimize pulse depression effects is to make the core extremely small
Typically used with higher power, highly directional modualated light sources such as a laser.
CLADDING
Meterial surrounding the core, which must have a lower index of refraction to keep the light in the core.
Almost always glass sometimes plastic
2 KEY DISTANCE LIMITING PARAMETERS IN FIBER OPTIC TRANSMISSION
Attenuation
and
Dispersion
ATTENUATION
The loss of power introduced by the fiber.
This loss accumualtes as the light is propagated through the fiber strand
The loss is expressed in dB/km *decibals per kilometer
The loss or attenuation of a signal is due to a combination of 4 factors Scattering. Absorption, Macrobending, Microbending.
SCATTERING
Primary loss factor over the three wavelength ranges.
Accounts for 96% of the loss and is the basis of the attenuation curves and values.
AKA Rayleigh scattering
Caused by refractive index fluctuations
Decreses as wavelength increases
ABSORPTION
Second loss factor, a composite of light interaction with the atomic structure of glass.
Involves the conversion of optical power to heat
MACROBENDING
LOSS DUE TO LIGHT BREAKING UP AND ESCAPING INTO THE CLADDING
MICRO BENDING
LOSS CAUSED BY VERY SMALL MECHANICAL DEFLECTIONS AND STRESS ON THE FIBER
TOO MUCH FORCE BEING APLLIED TO THE CABLE
TOO TIGHT TIE WRAPS
DISPERSION
OR
PULSE BROADENING
Broading of a light pulse as it propagates through the fiber strand
ISOLATOR
AN INLINE PASSIVE DEVICE THAT ALLOWS OPTICAL POWER TO FLOW ONLY IN ONE DIRECTION
ATTENUATORS
USED TO REDUCE TEH RECEIVED SIGNAL LEVEL
AVAILABLE IN FIXED AND VARIABLE CONFIGS
BRANCHING DEVICESTS
USED IN SIMPLEX SYSTEMS WHER A SINGLE OPTICAL SIGNAL IS DIVIDED AND SENT TO SEVERAL RECIEVERS SUCH AS POINT TO MULTIPOINT DATA DISTRIBUTION SYS
SPLITTERS
USED TO SPLIT OR DIVIDE TEH OPTICAL SIGNAL FOR DISTRIBUTION TO ANY NUMBER OF PLACES
WAVELENGTH DIVISION MULTIPLEXERS
COMBINE
OR DIVIDE TWO OR MORE OPTICAL SIGNALS EACH HAVING A DIFFERENT WAVELENGTH
AKA OPTIACL BEAM SPLITTERS
OPTICAL LINE AMPLIFIRES
ANALOG AMPLIFIERS. PLACEMENT CAN BE AT THE OPTICAL TRANSMITTER OUTPUT MIDSPAN OR NEAR RECIEVER
FUSION SPLICING
A LONG TERM
METHOD WHERE TWO FIBERS ARE FUSED OR WELDED TOGETHER
MECHANICAL SPLICES
TWO FIBERS JOINED TOGETHER WITH AN AIR GAP, THEREBY REQUIRING AN INDEX MATCHING GEL TO PROVIDE A GOOD SPLICE
FTTC
FIBER TO THE CURB
PROVIDES HIGH BANDWITH TOA LOCATION PROXIMITY TO THE HOME AND PROVIDES A HIGH SPEED DATA LINK VIA COPPER TWISTED PAIR USING VDSL
COST EFFECTIVE WAY TO PROVIDE LARGE BANDWITH AT HOME
FFTH
FIBER TO THE HOME
PROVIDES UNLIMITED BANDWITH TO THE HOME HOWEVER THE KEY TO ITS SUCCESS IS THE DEVELOPMENT OF LOW COST OPTICAL TO ELECTRONIC CONVERTER
BACKBONE
MAIN FIBER DISTRIBUTION
BULD OF DATA TRANSFERS HERE
