fiber optic comm system
TRANSCRIPT
-
8/4/2019 Fiber Optic Comm System
1/26
Fiber Optic Communication System
Analysis and Design
-
8/4/2019 Fiber Optic Comm System
2/26
-Input which could either be analog or digital-Light Source (Laser or LED)-Modulator
-Fiber optic line-Amplifier-Detector
Applications:Cable TV Networks, Telephone Networks, Database Networks, LAN Networks
etc.
Fiber Optic Communication System
-
8/4/2019 Fiber Optic Comm System
3/26
Flowchart of the of the Analysis and Design
-
8/4/2019 Fiber Optic Comm System
4/26
The system designers must proceed through the
following five steps in order to develop a fiberoptic communication system:
1.Specify the system's operational
requirements.2.Describe the physical and environmental
requirements.
3.Compute the signal optical power
budget.
4.Perform a signal bandwidth analysis.
5.Review the system design.
-
8/4/2019 Fiber Optic Comm System
5/26
Define the application-Cable TV Broadcast, Telephone Network, Computer Network etc.
Determination of the signal-to-noise ratio-Depends on the bandwidth or data rate for an applicationThis implies a choice of signal types, either analog or digital.-The goal is to establish what optical power level will be required at theoptical detector inside the receiver unit.
STEP 1 (System Operational Requirements)
-
8/4/2019 Fiber Optic Comm System
6/26
Analog Signals-Video and audio can directly modulate optical output by causing the optical emitter tobrighten and dim.
Digital Signals-A digital pulse can be formed by turning the source "on" for a brief instant.
Bit error rate (BER)
-a parameter for system performance
-The majority of digital systems achieve a BER of 1 X 109.(1 error in 109 bits = 1 error in 1,000,000,000 bits).
-BER is a function of length because, the farther a pulse has to travel downa fiber the more distortion occurs.
-Amplifiers are used to build up weak signals.
-
8/4/2019 Fiber Optic Comm System
7/26
The resulting optical power level required at thedetector is a function of the data rate or bandwidth.
These levels for digital and analog signals are indicatedfor silicon detectors at 850 nm below.
-
8/4/2019 Fiber Optic Comm System
8/26
-To determine the components necessary to complete a fiberoptic system requires detailing run lengths and determining
system operating environments and components.
-Schematic drawing of the orientation and structure of the system
-The system designer should develop a layout schematic.
STEP 2 (System Layout)
-
8/4/2019 Fiber Optic Comm System
9/26
A fiber optic layout should detail distances between each fiber segment.
-
8/4/2019 Fiber Optic Comm System
10/26
STEP 3 (Signal Optical Power Budget)
-With the system layout and components known, it's now possible for the designer tocompute expected losses at each point in the system.
-
8/4/2019 Fiber Optic Comm System
11/26
-Every component including fiber has a range of optical loss due to variations inmanufacturer.
-An LED device, for example, will be specified with a minimum, average, and maximumoptical output power.
-Detectors also have sensitivity ranges. It is up to the system designer to determine theoptical power necessary at the detector surface from information supplied by themanufacturer.
-Once the receiver and transmitter power levels have been established it is possible toconsider the power transmitted by various cable lengths. This can be seen by plottingthe power on a diagram.
-
8/4/2019 Fiber Optic Comm System
12/26
-Taps, Splices and fiber length contributes to loss the system will have.- Use either peak or average optical power values for determining attenuationthroughout the system. Be consistent in your choice throughout the system
analysis.
Figure 28 - Typical optical power level in system with a tap and a splice.
-
8/4/2019 Fiber Optic Comm System
13/26
Figure 29 - Optical source-to-fiber power coupling chart for various emitters.
-Allow approximately 4 to 6 dB to account for thermal variations in the optical fiber,repair of damaged cables, and source degradation over time.
-Power coupled to various fiber types by a few typical source emitters is detailed inFigure 29.
-
8/4/2019 Fiber Optic Comm System
14/26
Fiber Selection
-Several Fiber Optics are available to suit the needs of different
communication system.
-
8/4/2019 Fiber Optic Comm System
15/26
-Choices for most LAN or data systems, for example, currently centers on the all-silicafibers.-Currently 3 sizes are most often considered:
-Video and CATV systems often employ 50/125 and single mode fibers because of theirhigh bandwidth and low loss performance characteristics.
-Modern intercity telephone trunks also employ single mode fibers.
-Fibers may be selected in a variety of bandwidths and attenuation
- Attenuation of optical fibers will vary depending on the source wavelength of thetransmitter.
-
8/4/2019 Fiber Optic Comm System
16/26
* Values for 850nm wavelength.
-
8/4/2019 Fiber Optic Comm System
17/26
STEP 4 (Bandwidth Analysis)
-The System engineer must assure that a sufficient bandwidth is provided to
ensure the transmission of the signal.- Long-haul telephone systems employ large distances between repeaters andrequire the 100,000 MHz-km fiber bandwidths associated with single modefiber.
-The transmitter and optical fiber should then have bandwidths about 1.5 to 2 timesgreater than the receiver.
-For digital systems the system bandwidth will depend on the data rate and thecoding format according to:
BW system = R/Kwhere:
K equals 1.4 for (NRZ) coding format and 1.0 (RZ) format.R in bits per second
-The system bandwidth is limited by the lowest bandwidth component in the link.
-
8/4/2019 Fiber Optic Comm System
18/26
The approximate relationship between the total cable bandwidth (BWCo) and onekilometer section fiber bandwidth (BWf)
BWf= BWCo (L) x
where:
BWCo total cable bandwidthL is the fiber length in kilometers.x equals 1.0 for cable run lengths (L) of one kilometer or less and x equals 0.75 for fiber incable run lengths greater than 1 kilometer.
-
8/4/2019 Fiber Optic Comm System
19/26
-System designer to review all of the pieces to determine that all work together to deliverthe right signal to the right place at the right time.
-The number of fibers or a cable depends on the number of channels or signal carryingcapacity desired. Cables employing fibers with special high bandwidths are available ascustom products.
-Specific materials and multi-fiber construction have resulted in numerous cable designs
which incorporate a variety of fibers to meet specific applications.
STEP 5 (System Review)
-
8/4/2019 Fiber Optic Comm System
20/26
The complete cable structure can be established using the following criteria:
Cable Construction:Hybrid All Dielectric Metal Strength Members
Jacket Materials:PVC Polyurethane Polyethylene Other
Environmental Protection Flame RetardancySunlight Resistance
Water Resistance
Water Blocking (gel fill)
Rodent Protection (armor)Nuclear Radiation Resistance
Other
Chemical Resistance:To Oil Acid Alkali Solvents
Fiber Features:Number ofFibers
Fiber TypeCore Size
Wavelength
Attenuation
Bandwidth
NA (numerical aperture)
Double Window
Number and type of electrical conductors
-
8/4/2019 Fiber Optic Comm System
21/26
Design and Analysis of a Fiber Optic
Local Area Network1.Specify the system's operational requirements.
A typical LAN network consists of:-nodes, or computers
-a medium for connection, either wired ,wireless or fiber-special network equipment, such as routers or hubs-
Determine the use/primary function of the systemSingle mode or Multi Mode Fiber optic
LAN network usually shares-Data, applications, and resources, such as printers and computing poweretc.-Digital Modulation require 20 to 600 MHz-km
-
8/4/2019 Fiber Optic Comm System
22/26
-
8/4/2019 Fiber Optic Comm System
23/26
Determine the topology suited
2.Describe the physical and environmental requirements
(System Layout)
Linear bus topology
A star topology A tree topology
Mesh topology
-
8/4/2019 Fiber Optic Comm System
24/26
-
8/4/2019 Fiber Optic Comm System
25/26
4.Perform a signal bandwidth analysis
3.Compute the signal optical power budget.
-Local area networks (LAN) typically require 20 to 600 MHz-km fiber bandwidth-Consideration of the encoding to be used because, it affects the bandwidth ofthe system
Example of a Optical Link Budget
Typical: 20 dB loss. It may vary according to the length of the fiber optic cable used.
-
8/4/2019 Fiber Optic Comm System
26/26
5.Review the system design
- Final reassessment of the system design component, specifications chosen.
Typical: CAT5e and RJ45
Fiber optic mostly used: Multi-mode optical fiber is usually chosen for
LAN
1.25Gbit/sec multimode fiber