The attached narrated power point presentation explains the working principle of Thulium Doped Fiber Amplifiers based on their energy level diagrams. The material also attempts to explain the different types, advantages, disadvantages and applications of Thulium Doped Fiber Amplifiers, apart from comparison between different optical amplifier types. The material will be of interest to KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
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Thulium Doped Fiber Amplifiers
• Thulium-doped fiber amplifier (TDFA)
provides high-power optical amplification in
S+ (1450–1480 nm) and S-bands (1480–1530
nm).
• TDFA to complement C- (1530–1560 nm) and
L-band (1560–1580 nm) amplification based
on EDFAs in high-capacity dense wavelength
division multiplexed (DWDM) systems.
• TDFA length and pump power determine
achievable gain and noise figure.
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Thulium Doped Fiber Amplifiers
• Additional bandwidth, modularity, inherent
higher pumping efficiency, and lower
nonlinear signal degradation compared
with alternatives such as S-band Raman
amplification.
• Light amplification in the Near Infra-Red
(NIR).
• Applications like coarse wavelength
division multiplexing (CWDM) and fiber to
the home (FTTH).
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Thulium Doped Fiber Amplifiers
(TDFA)
• Broad emission centered at 1.47 μm.
• Amplification in 1460 nm band based on
four level transition from 3H4 to 3F4 level.
• Spectral range covers the S-band.
• Used in S-band optical communications.
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Energy Level Diagram of Tm3+
• 4 Level Transition from 3H4 to 3F4 levels.
GSA – Ground State Absorption.
ESA – Excited State Absorption.
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TDFA Amplification 1.4 μm Pump
• Self terminating – limited amplification,
lifetime of 3H4 level (1.23 ms) shorter than
that of 3F4 lower level (10.8 ms).
• Difficult to create population inversion
between 3H4 and 3F4 levels using only one
pump wavelength.
• Lower level to be depopulated, auxiliary
pump needed.
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TDFA Amplification
• Main pump wavelengths are 800, 1050
and 1400 nm.
• Additional 1050 and 1400 nm laser diodes
used as auxiliary pump source.
• Main pump wavelength absorbed by
thulium ions through ground state
absorption (GSA).
• Population inversion achieved through
excited state absorption (ESA).
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TDFA Amplification
• Amplification through stimulated emission.
• Amplified spontaneous emission acts as
amplifier main noise source.
• Non-radiative losses caused by interaction
with phonons.
• Use of low phonon energy fluoride glasses as
host material for thulium ions.
• Ensure longer lifetime of higher amplification
level, reduce non-radiative energy transfer.
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TDFA Amplification 1.05 μm Pump
• High-power amplification than 1.4 μm
pumping.
• Yb - doped fiber lasers available at 1.05 μm
range.
• Larger the energy difference between the
pump and the signal.
- Excess heat.
- Heat radiation due to multiphonon
relaxation, no photon emission.)
- Lower Efficiency.
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Choice of Host Glass
• Silica glass – poor emission efficiency due
to large phonon energy.
• Silica glass - Tm3+ ion excited at the 3H4
level rapidly relaxes to 3H5 level by
multiphonon relaxation, no photon
emission.
• Fluoride fiber or tellurite fiber – low phonon
energy, efficient amplification in S-band.
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Bidirectional Single-Colour Pumped
TDFA
• Two pump diodes emit 1056 nm pumping
radiation.
• Pump radiation combined with signal using
the left WDM coupler, then both photon flows
travel through thulium doped fluorozirconate
fiber, amplification occurs.
• Second WDM coupler used to incorporate
pumping photon flow from the counter-
propagating direction.
• Amplified signal measured with an optical
spectrum analyzer.
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Properties of SiO2 and ZBLAN
Glasses
• Connection between thulium doped fiber
and standard fiber difficult.
• Difference in optical, mechanical and
thermal properties.
• Glueing technique to connect both fibers
due to processing temperature difference.
• Difference in refractive indices, angle
cleaved fibers to avoid reflections to the
fiber core on the connection interface.
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TDFA Spectra
• To avoid laser
oscillation for
higher
amplification,
ensure connection
between SiO2 and
ZBLAN fiber with
lower losses and
lower reflection.
Fiber: 5000ppm Tm3+ NA=0.16, length 1.9 m
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Bidirectional Double-Colour
Pumped TDFA
• Second pump source used, 790 nm pumping
power using Ti:Saphire laser pumped by
argon-ion-laser, connected with amplifier
using a special 790/1470 nm WDM coupler.
• Resonant ground state absorption to upper
amplification level using 790 nm pump.
• Population inversion between 3H4 and 3F4
can be varied, influences amplification profile.
• Low pump power at 790 nm from just one
side, only very small gain shift observed.
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Bidirectional Double-Colour
Pumped TDFA
• Careful design for WDM couplers
(1050/1470 nm) for small losses and a
proper coupling ratio for all three
wavelengths.
• If 1050/1470 WDM couplers not optimized
for 790 nm, relatively large losses at this
wavelength.
• To shift gain spectrum more towards longer
wavelengths apply more pump power at
790 nm, carefully control population
inversion along the active fiber.
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Gain Spectrum - Bidirectional
Double-Colour Pumped TDFA
Gain Shifted TDFA
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Device Merits Demerits [2]
EDFA High Power Efficiency
( >50%)
Less Wavelength
Range (1500 – 1600
nm), Amplified
Spontaneous Emission
Raman Amplifier GBW pump dependent Low Gain ( 20 – 25 dB)
Semiconductor
Optical Amplifier
Compact, Output
Saturation Power (5 –
10 dBm)
High Noise Factor (~ 8
dBm), High Coupling
Losses
YDFA High Output Power Incompatibility with
other types
EYCDFA
(co-doped)
High and flat gain (30 –
34 dB)
High Noise Factor (~ 10
dB)
TDFA Low Fiber Loss, Low
Noise
Amplified Spontaneous
Emission
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References
• Your Standard Text Books.
• M. M. Kozak, R. Caspary & W. Kowalsky,
“Thulium-doped Fiber Amplifier for the S-
Band” Conference Paper, July 2004.
• Prince Jain & Neena Gupta, ”Comparative
Study of all Optical Amplifiers”,
International Journal of Scientific and
Engineering Research, Volume 5, Issue
11, November 2014, ISSN 2229-5518.
