Title: Introduction to Fibre Optic Communication
1Introduction to Fibre Optic Communication
Mid Sweden University
2Outline
- Optical Fibres (Magnus)
- Fibre Amplifiers (Magnus)
- Pump Sources (Magnus, Kent)
- Optical Devices (Kent)
- Optical Soliton Systems (Kent)
3Optical Communication Systems
- Terrestial
- Long haul
- Metropolitan
- Office
- Submarine
4Properties of Optical Fibres
5Transmission Wavelengths
- Loss mechanisms
- Material absorption
- Rayleigh scattering
- lt 0.25 dB/km loss _at_ 1.5 ?m
- lt 0.5 dB/km loss _at_ 1.2 - 1.6 ?m
6Dispersion
- Modal dispersion
- Chromatic dispersion
- material dispersion
- waveguide dispersion
7Optical Fibre types
- Multi-mode fibres
- Core size 50 - 100?m
- Advantages
- Large NA
- LED signal light source can be used
- Inexpensive
- Disadvantages
- Large modal dispersion
- Small bandwidth
- Single-mode fibres
- Core size 3 - 10 ?m
- Advantages
- No modal dispersion
- Large bandwidth
- Disadvantages
- Small NA
- Laser signal light source must be used
- Expensive
8Single-Mode Fibre Types
- Standard single-mode fibre (SMF)
- ?0 _at_ 1310 nm
- Dcromlt 20 ps/nm-km _at_ 1550 nm
- Dispersion-shifted fibre (DSF)
- ?0 _at_ 1550 nm
- Nonzero dispersion fibre (NDF)
- Small chromatic dispersion _at_ 1550 nm to reduce
penalties from FWM and other nonlinearities
9Limiting factors for high bit-rate and
transmission distance
- Pulse broadening
- Modal dispersion 10 ns/km
- Chromatic dispersion 0.1 ns/km
- Nonlinear optical effects
- Stimulated Brillouin scattering (SBS), PT 1-3
mW - Stimulated Raman scattering (SRS), PT 1-2 W
- Self phase modulation (SPM)
- Four wave mixing (FWM) (multi-channel systems)
10Optical Amplifiers
- Rare-earth doped fibre amplifiers
- EDFA
- TDFA
- PDFA
- NDFA
- Raman Fibre amplifiers
- Semiconductor optical amplifiers (SOA)
11Application of Optical Amplifiers
- In-line amplifiers
- replaces regenerators
- Power amplifiers
- boost signals to compensate fibre losses
- Preamplifiers
- boost the recieved signals
- LAN amplifiers
- compensate distribution losses in local-area
networks
12Erbium Doped Fibre Amplifier (EDFA)
- Very few components
- High reliability
13Optical Amplifier
- Characteristics of an ideal amplifier
- High pump absorption
- Large spectral bandwidth
- Gain flatness
- High QE
- Low noise
- High gain
- High reliability (submarine systems)
14Origin of Noise in Fibre Amplifiers
15Noise Mechanisms
- Signal hetrodynes with ASE signal - spontanous
beat noise - ASE heterodynes with itself Spontanous -
spontanous beat noise - Amplified signal shot noise - negligible
16Noise Figure
- NF SNRin / SNRout
- NF will always be greater than one, due to added
ASE noise - The NF-value is usually given in dB
- Noise figures close to 3 dB have been obtained in
EDFAs (ideal amplifier)
17Erbium Doped Fibre Amplifier
- Spectroscopic properties
- Long upper level life time 10 ms
- No ESA for 980 and 1480 nm pump
- Best GE _at_ 980 nm
- 100 QE
- NF close to 3 dB
18Erbium Doped Fibre Amplifier
- Optical properties for different glass hosts
- Wider stimulated emission
- Wider amplification bandwidth
19Erbium Doped Fibre Amplifier
- Gain spectrum
- Gain peak _at_ 1535 nm
- Broad spectral BW 40 nm
20EDFA Input/Output Characteristics
- Fibre NA 0.16
- Fibre length 9 m
- 200 mW of pump power _at_ 980 nm
21Erbium Doped Fibre Amplifier
22Gain Efficiency vs Pump Wavelength
- 980 nm 11 dB/mw
- 1480 nm 5 dB/mw
- 830 nm 1.3 dB/mw
23980 nm vs 1480 nm pumping EDFAs
- 1480 nm pumps
- Higher noise
- Need higher drive current - heat dissipation
required - expensive - Smaller GE
- Large tolerance in pump wavelength 20 nm
- 980 nm pump
- Low noise
- Wasted energy because electrons must relax
unproductively - Higher GE
- Narrow absorption band 2 nm
24Tm-Doped Fibre Amplifier (TDFA)
- Gain _at_ 1470 nm (S-band)
- Pumping _at_ 1060 nm
- Low QE 4
- Measured lifetime _at_ 3H4 0.6 ms
25Pr-doped Fibre Amplifiers (PDFA)
- Resonance _at_ 1.32 ?m
- Low QE 4
- GE lt 0.2 dB/mW
- Two pumping wavelengths
- InGaAs laser _at_ 1017 nm (lt 50 mW output)
- NdYLF crystal laser _at_ 1047 nm (ineffective
expensive)
26Pr-doped Fibre Amplifiers (PDFA)
- Results so far
- QE of 5 in ZBLAN glass
- QE of 19 in GLS glass (University of
Southampton, 1998) - Small signal gains 38 dB
- Saturated output powers of up to 200 mW
- NF 15 dB
- Problem
- Require glass compositions with low phonon
energies - Non-silica based splicing difficulties
27Nd-doped Fibre Amplifiers (NDFA)
- Gain _at_ 1310 1360 nm if doped in ZBLAN
- Gain _at_ 1360 1400 nm if doped in Silica.
- Strong ESA at signal wavelength
- NF good, but not as good as in EDFAs
- Limited performance due to competing radiative
transitions - Splicing difficulties
28Raman Amplifiers
- Characteristics
- Uses SRS in intrinsic silica fibres
- Require high pump powers
- Broad gain spectrum
- Max. gain _at_ 60 - 100 nm above pump wavelength
29Raman Amplifiers
- 9 km gain fibre
- Gain peak 60 - 100 nm above pump wavelength
- Low NF 5 dB
- Peak gain is 18 dB
- Pump wavelength 1455 nm
30Multi-Wavelength pumping
- Dual Wavelength Pumping
- Pump wavelengths 1420 nm and 1450 nm
- Large spectral BW 50 nm
- Low NF 5 dB
31Raman Amplifier
- Advantages
- SRS effect is present in all fibres
- Gain at any wavelength
- Low NF due to low ASE
- Disadvantages
- Fast response time
- High pump powers required
- High power pumps are expensive at the wavelengths
of interest
32Pumping
- Core pumping
- Low NF 3.5 dB
- High cost
- High complexity
- Cladding pumping
- NF 6 dB
- Low cost
- Low complexity
33Dubble Clad Optical Fibre
- Core size 10 15 ?m
- Core NA 0.12 0.2
- Pump cladding size 100 400 ?m
- Pump cladding NA 0.4
- Effective pump absorption coefficient ?eff
?core(Acore/Acladding)
- Increase pump absorption by co-doping with Yb
34Fibre Design
- Problem Pump absorption low, rays will miss
doped core - Solution break symmetry
- a) Offset core, hard to splice
- b) Difficult to make
- c) Not difficult to make
35Launching schemes
- Straightforward, but inconvenient to use
- Looks simple, but is difficult to make
- Possible problem fibre damage fibre gets hot
and may brake - Typical launching efficiency 70 80
36Fibre Lasers
- Simple design with very few components
- Very narrow line width (10 kHz)
- For use as a signal source, some external
modulator must be used - High power output are obtainable in cw- mode 4W,
10 W in pulsed mode
37Yb-doped Fibre Laser
- Strong absorption and emission band _at_ 976 nm
- High power pumps is required 3 W
- Absorption _at_ 915 - 940 is weaker but wider
- Results so far
- 500 mW (J. Minelly, Corning)
- 800 mW (A. Kurkow, GPI, Moscow)
38The future of Fibre Amplifiers
- Increase in spectral bandwidth 140 nm (hybrid
solutions)
39Prototype for a large BW - amplifier
- Hybrid solution EDFA TDFA
40Latest Developments
41END OF PART I