Download to read offline
More Related Content
![Getting Started with Apache Spark: Big Data Made Simple [Free Meetup]](https://cdn.slidesharecdn.com/ss_thumbnails/apachesparkgettingstarted-260203175547-8361bcc3-thumbnail.jpg?width=640&height=640&fit=bounds)
Soliton systems
- 1.
- 2. 2 Contents • Introduction. • Featuresof Solitons. • Gordon-Haus Effect. • Soliton Transmission System. • Waveform / Timing Diagram. • Challenges.
- 3. 3 Solitons • First describedin 1834 by John Scott Russell. • Soliton or Solitary wave - self reinforcing wave packet, maintains shape, propagates at constant velocity. • Akira Hasegawa of AT&T Bell Labs - first to suggest that solitons could exist in optical fibers. • 1973 - Robin Bullough made the first mathematical report of existence of optical solitons.
- 4. 4 Solitons • Nonlinear ultrashortoptical pulses of pico- seconds width. • Maintains shape while propagating at a constant velocity, no distortion. • Caused by a cancellation of nonlinear and dispersive effects in the medium. • Potential to support very high optical transmission rates (Tb/s) over long distances. • Inherent stability facilitates long-distance transmission without using repeaters, could double transmission capacity.
- 5. 5 Solitons Fundamental Soliton Thirdorder Soliton
- 6. 6 Features of Solitons •Self maintaining - propagates without changing shape. • Overcomes dispersion limitation, avoids intersymbol interference. • Collision Invariant - soliton shape unaffected after collision with another soliton. • Collision invariance provides for efficient wavelength division multiplexing.
- 7. 7 Gordon–Haus Effect • Timingjitter - amplified spontaneous emission noise on optically amplified fiber link produce random variations of solitons’ central frequencies. • Chromatic dispersion within single-mode fiber converts variations in frequency to jitter in pulse arrival times. • Pulses move out of correct bit time slots, create errors in soliton transmission.
- 8. 8 Gordon–Haus Effect Timing jitterdue to Gordon–Haus effect shift soliton pulses into adjacent bit time slots.
- 9. 9 Gordon–Haus Effect • ASEnoise and Gordon–Haus jitter limit maximum permissible transmission distance for optical soliton transmission system. • Additive nature of the ASE noise - large SNR required to differentiate binary zeros from ones - necessites increasing optical signal power for longer transmission distances.
- 10. 10 Gordon–Haus Effect • Atsuch transmission distances, Gordon– Haus effect dominates, cause bit errors due to random displacements of pulses ending up in neighboring time slots. • Balance between effect of ASE noise and Gordon–Haus jitter required. • Use of in-line modulation or synchronous modulation schemes reduce unwanted noise sources, very long transmission distances (>10 000 km) achieved.
- 11. 11 Gordon–Haus Effect Acceptable rangeof values for ASE noise and Gordon–Haus jitter
- 12. 12 Optical Fiber SolitonTransmission
- 13. 13 Optical Fiber SolitonTransmission • Return-to-zero pulse generator - optical modulator & NRZ-to-RZ converter driven by DFB laser source. • Generation of optical soliton pulses crucial for soliton transmission, transmitter to produce ultrafast RZ pulses. • Mach–Zehnder modulator to modulate NRZ data at desired transmission rate. • Conversion back from RZ to NRZ, demultiplexer separates specific NRZ data for each channel.
- 14. 14 Soliton RZ Pulseusing Delay Line Interferometer • CW laser source generates optical signal, passed through phase modulator driven by encoded NRZ data signal. • DL interferometer provides constructive interference, converts NRZ phase modulation into RZ pulses, width corresponding to optical delay.
- 15. 15 Timing Diagram –RZ Pulse Generation Ideal binary on/off signal to be transmitted in RZ format Encoded version of NRZ signal Phases of two interfering signals at the output of the interferometer Phase difference Δφ between two interferometer arms gives RZ pulse |e(t)|2 – Amplitude of the envelope
- 16. 16 Soliton Propagation • Singlesoliton pulse propagating over a long transmission distance - pulse amplitude & timing maintained - pulse propagates within a bit pattern - no change in parameters. • Single pulse travels without emitting energy – non-linearities balanced. • Certain physical processes (i.e. amplifier noise and chromatic dispersion) remove the balance, deteriorates bit pattern when several soliton pulses propagate closely following each other.
- 17. 17 Soliton Propagation • Solitoninteraction cause one pulse shed energy to another, produces destructive interference. • Maintain safe distance between two consecutive soliton pulses to avoid any destructive interaction. • Strength of interaction - distance between two interacting soliton pulses. • Avoidance of interaction necessitates large bandwidth capacity.
- 18. 18 Soliton Propagation Soliton bitstream Soliton collision Safe separation distances T0 – Bit duration, τ – Soliton pulse width
- 19. 19 Soliton Propagation • Solitontransmission systems can be single-wavelength or multiwavelength channel. • Single-wavelength channel system - one transmitter used to launch the RZ pulses onto optical fiber. • Multiwavelength-channel systems - several transmitters simultaneously, data multiplexed using WDM.
- 20. 20 Soliton Propagation • Abilityto generate accurate ultrashort pulses declines with increasing transmission rate. • At high transmission rates over long distances, optical soliton pulses suffer from fiber attenuation & dispersive effects, low SNR, need for optical amplification & dispersion compensation – DMS systems. • Dispersion and polarization limit increase of transmission rates and distances.
- 21. 21 Soliton Transmission • Maximumallowable transmission bit rate for soliton pulses: • q0 - separation of soliton pulses over a bit period length is dimensionless, τ - soliton pulse width, T0 - duration of bit period.
- 22. 22 Soliton Transmission • q0determines pulse separation, provides value of separation between adjacent soliton pulses to avoid interaction. • T0/τ determines nature of nonlinear propagation for soliton pulses. • 0 < T0/τ < 1 for higher interaction strength, interaction decreases when T0/τ >>1. • Rule of thumb - T0/τ of 6 to 8 to ensure safe distance b/w adjacent soliton pulses.
- 23. 23 Dispersion Length • LengthLD of single-mode optical fiber over which the pulse width of soliton broadens significantly due to dispersion. β2 - second-order dispersion coefficient, τ - soliton pulse width, LA - optical amplifier spacing, LA<<LD.
- 24. 24 Dispersion Length • WhenLA >> LD, main factor affecting the pulse width and signal power is fiber attenuation. • α LD describes propagation of such soliton pulses more accurately. • When αLD ≥ 1, there will be large fiber attenuation, optical pulses cannot maintain their soliton nature. • αLD ≤ 1 to preserve soliton nature.
- 25.