![PN = PTC[(1−δ )(1−C)]N−1
where ,
PT is the transmitted power
C is the fraction of power coupled out at each tap
δ accounts for insertion losses, assumed to be the
same at each tap
N should not exceed 60.](https://image.slidesharecdn.com/light-wave-system-3855513-130118082800-phpapp01/85/Light-wave-system-3855513-11-320.jpg)
![• 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) =V0[1−exp(−t/RC)]](https://image.slidesharecdn.com/light-wave-system-3855513-130118082800-phpapp01/85/Light-wave-system-3855513-25-320.jpg)
Light wave-system-3855513
- 3. From an architectural standpoint, it is classified as,… POINT TO POINT LINKS DISTRIBUTION NETWORKS LOCAL AREA NETWORKS
- 4. • They transport information, available in the form of a digital bit stream • The link length can vary from less than a kilometer to 1000’s 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, 1. Transmission Distance 2. Data Rate for a given BER
- 6. o Attenuation o Distance Bandwidth Product o Cost of the connectors o Splicing Then decide, • single or multimode fiber • step or graded index fiber
- 7. Large number of users within a local area
- 10. PN = (PT /N)(1−δ )log2N where , δ is the insertion loss of each directional coupler. δ = 0.05 PT =1 Mw PN = 0.1 μW N can be as large as 500
- 11. PN = PTC[(1−δ )(1−C)]N−1 where , PT is the transmitted power C is the fraction of power coupled out at each tap δ accounts for insertion losses, assumed to be the same at each tap N should not exceed 60.
- 15. 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
- 18. •Emission wavelength •Spectral line width (FWHM) and number of modes •Output power •Stability •Emission pattern •Effective radiating area
- 19. 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. Wavelength LED Systems LASER Systems. 800-900 nm 150 Mb/s.km 2500 Mb/s.km (Typically Multimode Fiber) 1300 nm (Lowest 1500 Mb/s.km 25 Gb/s.km dispersion) (InGaAsP Laser) 1550 nm (Lowest 1200 Mb/s.km Up to 500 Attenuation) Gb/s.km (Best demo)
- 21. 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 < 10−9.
- 22. • When the dispersion-limited transmission distance is shorter than the loss-limited distance of the system is said to be dispersion limited. BL ≤ (4|D|σλ )−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. o 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 o The minimum average power required by the receiver is the receiver sensitivity o It is expressed in dBm
- 24. • 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) =V0[1−exp(−t/RC)]
- 27. 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
- 29. 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, 1. Modal noise 2. Dispersion broadening 3. Intersymbol interference 4. Mode-partition noise 5. Frequency chirp 6. Reflection feedback.