I. system of 16 channels in Opti-system software.



There is an increasing demand of transmission bandwidth for long haul
wavelength division multiplexed optical fibre communication systems. Bandwidth
is well used by using broadband and gain flattened amplifiers. Broadband
amplification is done by combining many amplifiers having totally different
gain bandwidths. Totally different gain flattening techniques are offered for
gain flattening functions to scale back gain variation like gain flattening
filters as fiber Bragg gratings, improvement of fabric composition of fiber
amplifiers, using rare earth doped ions, hybrid amplifiers, wavelength

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The hybrid optical amplifier composed of single erbium doped fiber
amplifier and a Raman amplifier is proposed for wavelength division multiplexed
system and also investigates the impact of reduced channel spacing. The
performance has been evaluated in terms of gain and noise figure. Gain and
noise figure are important characteristics of the optical amplifier to evaluate
the performance. There are various parameters on which the gain spectrum of
EDFA and Raman amplifier depends. The effort has been made to optimize these
parameters by simulating the system of 16 channels in Opti-system software. In
this paper the length, pumping wavelength, pumping power of EDFA/Raman is
optimized. After the analysis the reduction in gain is about 2.7dB and the
noise figure is about6.86dB.




The gain flattening of Erbium-doped fibre amplifiers (EDFA) has been a
research issue in recent years, with the development of high capability
wavelength division multiplexing (WDM) optical communication systems. For
single channel systems, the gain variation isn’t a problem. However, because
the variety of channels will increase, the transmission downside arises as a
result of a traditional EDFA has intrinsic non-uniform gain. They usually gift
gain peaking at concerning 1530 nm and therefore the helpful gain information
measure could also be reduced to but ten nm. The gain of EDFAs depends on
several device parameters like erbium-ion concentration, amplifier length, and
core radius and pump power. To extend the gain-bandwidth of an amplified light
wave system many ways is used, however equalising optical filters operating as
spectrally selective loss elements seem to be the most effective candidates.
This paper primarily focuses on totally different ways used for gain flattening
in EDFA.

EDFAs are widely
used in comparison to other similar amplifiers and optical devices for larger
wavelength optical communication system because of its advantages of high gain,
large bandwidth, less noise figure (NF), polarization insensitivity, low pump powers
and better performance. One difficulty in implementing a WDM system including
EDFA’s is that the EDFA gain spectrum is wavelength dependent and it doesn’t
necessarily amplify the wavelength of the channels equally. Bandwidth of EDFA
can be increased to more than 30nm with appropriate gain flattening in the
third transmission window for future development of WDM long-haul optical fiber
communication systems. Moreover, the noise performance of EDFA is characterized
by its NF which is signal to noise ratio reduction ratio of input to output of
the amplifier and should have a low value. Gain is the main characteristic to
evaluate the performance of an optical amplifier. The gain spectrum must be
uniform for the long distance transmission, but EDFA cannot amplify all the
wavelengths equally 4. Hence the gain flatness is important for EDFA’s
wavelength division multiplexing (WDM) which is important technique for long
haul optical transmission link system. Different compensation methods were
studied in past and based on these methods efforts were made to increase the
gain flatness of EDFA. Methods such as hybrid Al-co doped &Al/P co doped
EDFAs 1, hybrid EDFA/RFA amplifiers, erbium doped waveguide amplifiers
(EDWA) having gain flattened and gain clamped functions simultaneously 4, the
usage of the gain flattening filters (GFF) such as, thin film dielectric
filters, sinusoidal filters 4, chirped fiber brag gratings 5, acousto-optic
tunable filter 6. The combination of distributed Raman amplifier and EDFA
present better performance than conventional EDFA 1.




Wideband and gain flattened optical amplifiers are crucial for long haul
optical communication systems. Gain flattening of EDFA is done by numerous
techniques. In initial approach, 2 stages of EDFA are used. a brief fiber
length C-band EDFA produces ASE that, in turn, with pump power enters the
second stage to extend the output gain in long length L-band EDFA. 2 fiber brag
gratings (FBG) are placed within the second section at each ends of long fiber
to form fabric part cavity. The gain in L-band is flattened by the compressed
gain below the matched wavelength of FBG In another approach, hybrid amplifiers
are used. Fiber to amplifier couplers will work severally of others and needed variety
of amplifiers is added in step with the demand. A double pass assembly of EDFA
with hybrid gain medium- silicon and oxide is employed in parallel
configuration. Chirp fiber brag grating is employed in each stage to realize
the desired gain in Cband and L- band regions it causes the double propagation
of the signal leading to overall enhanced gain however noise figure
additionally will increase that is that the major downside. Hybrid electronic
equipment is EDFA–Raman amplifier. Raman amplifier is distributed and distinct.
The distinct Raman electronic equipment is employed in spite of style of
transmission fiber and its main purpose is to expand the usable bandwidth of
the fiber. Then again, the distributed Raman amplifier (DRA) improves the reach
of fiber span. The impact of DRA is that it decreases the noise similarly
because the non linearities. EDFA + DRA is wont to increase the gain similarly
as decrease the noise figure. EDFA includes a larger gain variation with
relevance the wavelength. Raman amplifier includes a smaller gain variation
compared to EDFA. This property is wont to kind a hybrid optical amplifier
(HOA). By increasing the quantity of pumps, the gain of HOA is enhanced .But
there’s a limit to the rise in variety of pumps otherwise gain can decrease. By
adjusting the pump wavelengths, pump power and length of fiber, amplification
and gain flattening is drained totally different wavelength regions. Erbium and
ytterbium co-doped phosphate (Er/ Yb–EDFA) and Raman phosphate fiber amplifier
is used as hybrid amplifier and has the advantage of upper transmission
capability than silicon based mostly fiber amplifiers. Phosphate glass has
larger phonon energy, greater solubility to rare earth ions, massive emission
cross section and better energy transfer efficiency. This hybrid amplifier is
used for higher transmission capability on dense wavelength division
multiplexed systems.

In another technique, Er doped wave guide Amplifier (EDWA) and Er doped
fiber amplifier is connected asynchronous to realize the gain flatness within
the C- band. EDWA is a smaller amount economical than EDFA due to higher erbium
concentration. Higher erbium concentration needs a lot of pumping power .There
is loss of wave guide within the fiber. EDWA provides high gain briefly optical
path. High gain and gain flatness is obtained by this technique however
broadband amplification can’t be obtained.



Current scenario

doped fibre amplifiers have had a significant impact within the field of light
wave communications. Optical amplifiers have contributed to the expansion of a
fifth generation of optical communication systems. However because the demands
on the networks accrued techniques like Dense Wavelength Division Multiplexing
(DWDM) were developed. The performance of DWDM in ultra-long haul networks
improved as a result of amplifiers were accessible that might amplify the
wavelengths utilized in the network while not requiring any conversion of the
optical signal to the electrical signal. The importance of EDFA’s is because of
their compatibility with the fibre network, low insertion loss, polarization
unfitness, high gain levels and close to quantum restricted noise performance.
In DWDM transmission systems and their connected optical networks, one in all
the key technological problems is that the achievement of broad and flat gain
bandwidth for erbium Doped Fiber Amplifiers (EDFA’s). Gain variations occur
between optical channels having massive wavelength spacing (e.g. ??> 1nm).
In long electronic equipment chains, even little spectral gain variations (e.g.