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