light wave system - PowerPoint PPT Presentation

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light wave system

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introduction to light wave system – PowerPoint PPT presentation

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Updated: 22 January 2014
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Title: light wave system


1
LIGHT WAVE SYSTEMS
BY, A.POOJA SHUKLA, ECE - B,
190912066, SAVEETHA UNIVERSITY.
2
SYSTEM ARCHITECTURE
3
SYSTEM ARCHITECTURE
  • From an architectural standpoint, it is
    classified as,
  • POINT TO POINT LINKS
  • DISTRIBUTION NETWORKS
  • LOCAL AREA NETWORKS

4
POINT TO POINT LINK
  • They transport information, available in the
    form of a digital bit stream
  • The link length can vary from less than a
    kilometer to 1000s of kilometer
  • They are used for high speed transmission
  • Optical regenerators should perform,
  • 1. Re-amplification
  • 2. Re-shaping
  • 3. Re-timing

5
  • System Requirements,
  • Transmission Distance
  • Data Rate for a given BER

6
Other factors are,
  • Attenuation
  • Distance Bandwidth Product
  • Cost of the connectors
  • Splicing
  • Then decide,
  • single or multimode fiber
  • step or graded index fiber

7
LOCAL AREA NETWORKS
Large number of users within a local area
8
RING TOPOLOGY
9
STAR TOPOLOGY
10
PN (PT /N)(1-d )log2N
where , d is the insertion loss of each
directional coupler. d 0.05 PT 1 Mw PN
0.1 µW N can be as large as 500
11
DISTRIBUTION NETWORK
PN PTC(1-d )(1-C)N-1
where , PT is the transmitted power C is the
fraction of power coupled out at each tap d
accounts for insertion losses, assumed to be the
same at each tap N should not exceed 60.
12
HUB TOPOLOGY
13
BUS TOPOLOGY
14
DESIGN CONSIDERATION
15
Design Considerations
  • Link Power Budget
  • There is enough power margin in the system to
    meet the given BER
  • Rise Time Budget
  • Each element of the link is fast enough to meet
    the given bit rate

16
Receiver sensitivities Vs bit rate
17
BASIC CONSIDERATION
18
Selection of optical source,
  • Emission wavelength
  • Spectral line width (FWHM) and number of modes
  • Output power
  • Stability
  • Emission pattern
  • Effective radiating area

19
Selecting the detector,
  • Type of detector
  • APD High sensitivity but complex, high bias
    voltage (40V or more) and expensive
  • PIN Simpler, thermally stable, low bias voltage
    (5V or less) and less expensive
  • Responsivity (that depends on the avalanche gain
    quantum efficiency)
  • Operating wavelength and spectral selectivity
  • Speed (capacitance) and photosensitive area
  • Sensitivity (depends on noise and gain)

20
Typical bit rates at different wavelengths
Wavelength LED Systems LASER Systems.
800-900 nm (Typically Multimode Fiber) 150 Mb/s.km 2500 Mb/s.km
1300 nm (Lowest dispersion) 1500 Mb/s.km 25 Gb/s.km (InGaAsP Laser)
1550 nm (Lowest Attenuation) 1200 Mb/s.km Up to 500 Gb/s.km (Best demo)
21
LOSS LIMITED LIGHT WAVE SYSTEMS
  • If the signal is detected by a receiver that
    requires a minimum average power at the bit rate
    B, the maximum transmission distance is limited
  • The system requirements typically specified in
    advance are the bit rate B and the
  • transmission distance L
  • The performance criterion is specified through
    the bit-error rate (BER), a typical requirement
    being BER lt 10-9.

22
DISPERSION LIMITED LIGHT WAVE SYSTEM
  • When the dispersion-limited transmission
    distance is shorter than the loss-limited
    distance of the system is said to be dispersion
    limited.

BL (4Ds? )-1
  • A solution to the dispersion problem is offered
    by dispersion-shifted fibers for
  • which dispersion and loss both are minimum near
    1.55 µm.

23
POWER BUDGET
  • The purpose of the power budget is to ensure
    that enough power will reach the receiver to
    maintain reliable performance during the entire
    system lifetime
  • The minimum average power required by the
    receiver is the receiver sensitivity
  • It is expressed in dBm

24
RISE TIME BUDGET
  • Used to ensure that the system is able to
    operate properly at the intended bit rate
  • Even if the bandwidth of the individual system
    components exceeds the bit rate, it is still
    possible that the total system may not be able to
    operate at
  • that bit rate
  • It is used to allocate the bandwidth among
    various components

25
  • The rise time Tr of a linear system is defined
    as the time during which the response increases
    from 10 to 90 of its final output value when the
    input is changed abruptly.
  • When the input voltage across an RC circuit
    changes instantaneously from 0 to V0, the output
    voltage changes as,
  • Vout(t) V01-exp(-t/RC)

26
LONG HAUL SYSTEM
27
LONG HAUL SYSTEM
  • Here we focus on the factors that limit the
    performance of amplified fiber links
  • It depends on following factors,
  • 1. Performance - limiting
    factor
  • 2. Terrestrial light wave
    systems
  • 3. Undersea light wave
    systems

28
SOURCES OF POWER PENALTY
29
SOURCES OF POWER PENALTY
The sensitivity of the optical receiver in a
realistic lightwave system is affected by several
physical phenomena which, in combination with
fiber dispersion, degrade the SNR at the decision
circuit
30
  • Among the phenomena that degrade the receiver
    sensitivity are,
  • Modal noise
  • Dispersion broadening
  • Intersymbol interference
  • Mode-partition noise
  • Frequency chirp
  • Reflection feedback.

31
FREQUENCY CHIRPING
32
THANK YOU
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