Characterizing fiber impairments

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International Journal of Electronics and Communication Engineering and Technology
(IJECET)
Volume 7, Issue 3, May–June 2016, pp. 87–102, Article ID: IJECET_07_03_011
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CHARACTERIZATION OF PHYSICAL
LAYER IMPAIRMENTS IMPACT ON
OPTICAL FIBER TRANSMISSION SYSTEMS
Suhail Al-Awis and Ali Y. Fattah
Department of Communications Engineering,
Faculty of Electrical Engineering
University of Technology, Baghdad, Iraq
ABSTRACT
In this paper the characterization of the impact of physical layer
impairments on quality of transmission of optical fiber transmission systems
had been demonstrated analytically and verified numerically with simulation
results. Linear and nonlinear impairments in optical links accurately
characterized with analytical modeling techniques but on the counterpart it is
cost efficient to characterize the impact of these impairments using empirical
techniques which provides real time information of these impairments to
digital signal processing algorithms used in their compensation to ensure high
throughput of the optical transmission systems.
Keyword: Optical Fiber, Characterization, Physical Layer Impairments and
Quality of Transmission.
Cite this Article: Suhail Al-Awis and Ali Y. Fattah, Characterization of
Physical Layer Impairments Impact on Optical Fiber Transmission Systems,
International Journal of Electronics and Communication Engineering &
Technology, 7(3), 2016, pp. 87–102.
http://www.iaeme.com/IJECET/issues.asp?JType=IJECET&VType=7&IType=3
1. INTRODUCTION
The quality of transmission of high speed optical fiber transmission systems is highly
affected by chromatic dispersion (CD), phase noise (PN), polarization mode
dispersion (PMD) and nonlinear effects. Coherent optical detection allows the
significant equalization of transmission system impairments in the electrical domain,
and has become one of the most promising techniques for the next generation
communication networks. With the full optical wave information, the fiber dispersion,
carrier phase noise and the nonlinear effects can be well compensated by the powerful
digital signal processing (DSP) [1].

Extensive addressing of the coherent optical transmission systems in the eighties
of the last century was resulted due to highly sensitive receivers [2,3]. However, 20
years later coherent technologies has been delayed [4-6]. Higher order modulation
formats detected by coherent detection like PDM-QPSK, PDM-8PSK, PDM-8QAM,
PDM-16QAM and PDM-36QAM use all possible degree of freedom of the optical
wave for information encoding via IQ-modulators to access in-phase and quadrature-
phase components for both polarizations to best utilize the available bandwidth more
than binary alternatives and boost the capacity without the installation of any extra
fibers [7-13]. Efficient modulation formats such PSK and QAM which are
implemented with the aid of DSP receivers attracted the interests of investigation until
2005 [14]. Electronic compensation of the transmission impairments as powerful as
traditional optical techniques was enabled by fully accessing the optical wave
information [6].
Canonical model of a multi span long haul optical fiber transmission system is
shown in Figure 1 (a). Before the invention of the optical amplifiers, optical-
electrical-optical (O-E-O) conversion take place to compensate the channel
impairments and the electrical signal is re-amplified, re-shaped, and re-timed (3R
regeneration) before converted back to optical format. O-E-O conversion is expensive
and requires priori knowledge of the transmitted signal such as its symbol rate at the
repeater in order to perform 3R regeneration [15].
Figure 1 (a) Canonical model of a multi-span long-haul fiber channel, (b) Multispan long-
haul fiber channel with inline amplification and dispersion compensation
Invention of the erbium doped fiber amplifier (EDFA) in the 1990s stalled the
development in coherent optical systems, which enabled repeaterless transmission
over long-haul distances. The combination of the C-band (1530–1570 nm) and L-band
(1570–1610 nm) spectrums resulted in 10 THz of bandwidth. Rapid growth of
internet applications traffic, such as multimedia sharing, made this bandwidth
becoming rapidly fully utilized. Thus, there is renewed interest in high-spectral-
efficiency transmission over long distances [16].
New challenges ahead the new channel configuration, in which optical signals are
propagated over thousands of kilometers of fiber, such as the need to compensate
chromatic dispersion (CD). A typical long-haul system model is shown in Figure 1
(b), with inline amplification and dispersion compensation fiber (DCF) after every
span. Furthermore, as the number of wavelength division multiplexed (WDM)
channels per fiber increase, and as the data rate per channel increase, fiber
nonlinearity, (PMD) and other impairments which were previously not important
became limiting factors [15]. Transmission impairments in optical fiber
communication can be categorized into linear and nonlinear impairments. Linear

Characterization of Physical Layer Impairments Impact on Optical Fiber Transmission
Systems
impairments include attenuation, amplified spontaneous emission (ASE) noise,
polarization mode dispersion (PMD), chromatic dispersion (CD) and linear crosstalk
in WDM systems from optical de-multiplexers/ filters and wavelength routers. On the
other hand self-phase modulation, cross-phase modulation, cross polarization
modulation classified as nonlinear impairments. To understand these impairments, the
propagation of a pulse in an optical fiber channel which is described by nonlinear
Schrödinger equation [17] should be understood clearly:
𝜕𝐴
𝜕𝑍
+
𝛼
2
𝐴 +
𝑖
2
𝛽2
𝜕2
𝐴
𝜕𝑇2
= 𝑖𝛾|𝐴|2
𝐴 (1)
Where is the signal amplitude, is the distance of the fiber, is the attenuation
coefficient, is group velocity dispersion parameter and is the Kerr nonlinear
coefficient.
2. THEORITECAL BACKGROUND
2.1 Linear Impairments
Modelling of single mode fiber in the absence of the nonlinearity can be
considered as linear time invariant (LTI) channel with dually polarized inputs and
output as shown in Figure 2 [15].
Figure 2 Dual-polarization linear channel modelling
The channel can be characterized by its impulse response matrix as shown in
equation 2.
ℎ(𝑡) = (
ℎ11(𝑡) ℎ12(𝑡)
ℎ21(𝑡) ℎ22(𝑡)
) 𝐇(𝛚) = (
𝐻11(𝜔) 𝐻12(𝜔)
𝐻21(𝜔) 𝐻22(𝜔)
) (2)
where hij(t) is the response of the i-th output polarization due to applied impulse at
the j-th input polarization of the fiber. H(ɷ) and h(t) are Jones matrices with
frequency-dependent and time-dependent elements, respectively. The matrix
description of the channel is sufficient for describing CD, polarization-dependent loss
(PDL), all PMD orders, optical filtering effects, sampling time error, and any other
linear impairment [18].
2.1.1 Fiber attenuation
Fiber loss parameter α(z), which describes the attenuation of the optical signal
power while propagating through the fiber channel as shown in equation (3).
𝛼(𝑧) = −
10
𝑧
𝑙𝑜𝑔10 (
𝑃𝑜𝑢𝑡
𝑃𝑖𝑛
) (3)
Where z is the length of the fiber channel, Pout and Pin are the output and input
optical powers of transmission fiber span respectively. It is mainly caused by material
absorption and Rayleigh scattering effects, but it is also a function of carrier signal
wavelength [19].
Etx(t) =
=Erx(t)
Erx,1(t)
Erx,2(t)
Etx,1(t)
Etx,2(t)
H=
h11 h12
h21 h22
Linear Channel

2.1.2 Chromatic dispersion
In [17] Linear Schrödinger Equation (LSE) described, where β can be expanded
around the carrier frequency into a Taylor series approximation, truncated at the 3rd
term as in equation (4):
𝜕𝐴
𝜕𝑧
+
𝛼
2
𝐴 + 𝛽1
𝜕𝐴
𝜕𝑡
+
i
2
𝛽2
𝜕2A
𝜕𝑡2 −
1
6
𝛽3
𝜕3 𝐴
𝜕𝑡3 = 0 (4)
Here the group velocity ʋG is related to β1 and therefore calculate the speed the
envelope of an optical signal propagates along the fiber:
𝛽1 =
1
𝑣 𝐺
=
1
𝑐
(𝑛 + 𝜔
𝑑𝑛
𝑑𝜔
) (5)
With c is the light speed in vacuum, n is the linear refractive index and ɷ is the
optical frequency. β2 is the group-velocity dispersion (GVD) parameter, which
broadens the travelling pulse:
𝛽2
1
𝑐
(2
𝑑𝑛
𝑑𝜔
+ 𝜔
𝑑2 𝑛
𝑑𝜔2) (6)
D is defined as the dispersion parameter of the first derivative of β1 with respect to
the optical wavelength λ:
𝐷 =
𝑑𝛽1
𝑑𝜆
= −
2𝜋𝑐
𝜆2 𝛽2 ≈
𝜆𝑑2 𝑛
𝑐𝑑𝜆2 (7)
β3=dβ2/dɷ is the GVD slope parameter, which relates to the dispersion slope
parameter S by:
𝑆 =
𝑑𝛽2
𝑑𝜆
= −
4𝜋𝑐2
𝜆3 𝛽2 + (
2𝜋𝑐
𝜆2 )
2
𝛽3 (8)
At the zero dispersion wavelength (β2 = 0) region, the GVD slope becomes
especially important for transmission. The retarded time frame T = t – z/ʋG is
introduced, which propagates with the signal at the group velocity dropping β1 from
the equation. Finally, the GVD slope influence can be neglected by considering
standard single-mode fibers (SMF) or other types with sufficiently high GVD:
𝜕𝐴
𝜕𝑧
+
𝛼
2
𝐴 +
𝑖
2
𝛽2
𝜕2 𝐴
𝜕𝑇2 = 0 (9)
The total dispersion profile of an optical fiber can be evaluated by material and
waveguide dispersion respectively (DM) and (DW). For the SSMF the summation of
these parameters resulted in a dispersion profile shown in Figure 3, with the zero
dispersion wavelength at 1324 nm and D=16ps/km/nm at 1550 nm [20].
Figure 3 Dispersion characteristic of a typical SMF as a function of wavelength and
frequency.

Systems
2.1.3 Polarization mode dispersion
Polarization of a light considers as a property of electromagnetic waves that
shows the transverse electric field orientation. X and Y are two orthogonal
polarization states exists in SMF. Stokes parameters can be used to describe the
representation of light polarization, which expressed straightforward by using
Poincaré sphere. This sphere consists of four parameters in terms of optical power as
shown in Figure 4 [21].
Figure 4 Poincaré sphere
SMF supports the transmission of two orthogonal polarization-modes, but
temperature fluctuations and random birefringence resulted from mechanical stress
changes the states-of-polarization (SOP) and, hence, the GVD to vary with time and
along the fiber length [22]. A typical fiber length ranges from hundreds of meters up
to few kilometers along which the SOP varies. Mathematically, the modal
birefringence, Bm described in equation (10):
𝐵 𝑚 =
|βx−βy|λ
2π
= |𝑛 𝑥 − 𝑛 𝑦| (10)
Where nx and ny as the effective refractive index of both modes. βx and βy are the
modes propagation constants. The axis with larger group velocity described as the fast
axis while the other with smaller group velocity denoted as the slow axis, referring to
Figure 5 for a linearly polarized optical pulse launched at 45o
into a fiber. The
difference between arrival times of the two pulses is referred to as differential group
delay ΔJ (DGD) which have Maxwellian distribution around mean DGD-value 〈ΔJ〉.
[20].
Figure 5 Random birefringence and resulting DGD for optical pulse launched into a fiber
at 45o
with respect to slow axis.
The PMD-induced pulse broadening can be evaluated from the DGD between the
two polarization components after averaging over random birefringence [23] as

Δ𝑇 = 𝐷 𝑃√𝐿 (11)
Where DP is the fiber PMD parameter measured in ps/√km. While in [24] PMD
power penalty can be estimated as,
𝑝𝑒𝑛 𝑃𝑀𝐷 = 10.2𝐵2
𝐷 𝑃
2
𝐿 (12)
Where B as the signal bit rate.
2.1.4 Linear cross talk in WDM systems
It arises in wavelength routers, optical filters and de-multiplexing devices. In
WDM systems a signal at a particular wavelength is de-multiplexed at the receiver by
means of an optical filter. Wavelength components outside the signal optical
bandwidth is not completely suppressed by the optical filters. Thus power from
adjacent channels in a WDM system leaks into the central channel causing what is
known as a cross talk penalty in the central channel. This penalty increases as the
number of multiplexed WDM channels is increasing. It is called out of band cross talk
since this crosstalk is generated by out of bandwidth of the central channel band.
Linear out of band crosstalk is shown in Figure 6 [25]. For a WDM system with N
channels the total generated photocurrent by the optical signal filtered at the receiver
is given by [20]
I = RmPm + ∑ RnTmnPn
N
n≠m ≡ Ich + IX (13)
where Pm is the power of the mth
channel or the filtered channel, Pn is the power of
the nth
neighboring channel, and R are the receiver photo responsitivities and T is the
receiver transmissivity of the nth
channel when the mth
channel is filtered. The
current due to the filtered channel power (Ich) and the current due to power of the
crosstalk from the neighboring channels is (IX). The current must be increases by to
keep the performance of the system in terms of eye opening.
Figure 6 Linear cross talk in WDM systems
The power penalty is thus given by
δX =
Ich+IX
IX
= 1 +
Ich
IX
(14)
δX is a measure of out of band crosstalk. Another source of crosstalk penalty in
WDM systems which is the wavelength routers based on AWGs. The operation of a
4x4 AWG router is depicted in Figure 7.

Systems
Figure 7 4x4 AWG Router
Where letters a,b,c and d refer to the port and the subscripts 1,2,3 and 4 refer to
the wavelength number. For ideal conditions the wavelengths at the input ports are
routed to the output ports according to the scheme shown in Figure 7. However due to
imperfections in the AWG structure each wavelength in the output port suffers from
in band crosstalk which appears due to power leaking from other ports at the same
wavelength and the out of band crosstalk which appears from the wavelength
channels in the same port [25]. The in-band crosstalk penalty for a WDM system with
N channels is given by [26] as shown in equation (15).
𝛿 𝑋 = −10 log10(1 − 𝑟𝑋
2
𝑄2) (15)
Where
𝑟𝑋
2
= 𝑋(𝑁 − 1)
N is the number of channels and -value is the measure of eye opening of the
receiver.
2.2. Non-Linear Impairments
Any dielectric subjected to light have nonlinear response for intense electromagnetic
fields, and hence the optical fibers. Although the silica is intrinsic and not a highly
nonlinear material, but the waveguide geometry that confines light into a small cross
sectional area over long haul fiber makes nonlinear effects very important in the
design step of modern lightwave systems [27].
Fiber nonlinearities classified either to nonlinear refractive index (Kerr effect) or
to nonlinear optical scattering .The Kerr effect take place in response to the
dependence of the index of refraction on light intensity. Fiber nonlinearities of this
type are self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave
mixing (FWM).The stimulated scattering effects are caused by parametric interaction
between the light and materials.
There are two types of stimulated scattering effects: Stimulated Raman Scattering
(SRS) and stimulated Brillouin scattering (SBS). One difference between the
scattering effect and the Kerr effect is that, stimulated scattering has threshold power
level at which the nonlinear effects manifest themselves while Kerr effect does not
have such threshold [28].
Assuming that the SOP of the transmitted light is not maintained, it may be shown
that the threshold power PB due to Stimulated Brillouin scattering (SBS) is given as
in equation (16). While that resulted from the Stimulated Raman scattering (SRS) is
given in equation (17) [30].
𝑃𝐵 = 4.4 × 10−3
𝑑2
𝜆2
𝛼 𝑑𝐵 𝑣 (𝑤𝑎𝑡𝑡𝑠) (16)

Where 𝑑 as the ﬁber core diameter and λ as the operating wavelength, both are
measured in µm, 𝛼 𝑑𝐵 is the ﬁber attenuation in dB per kilometer and ν is the source
bandwidth in GHz.
𝑃𝑅 = 5.9 × 10−2
𝑑2
𝜆𝛼 𝑑𝐵 (𝑤𝑎𝑡𝑡𝑠) (17)
Where 𝑑, 𝜆 and 𝛼 𝑑𝐵 are defined as in equation (16) above.
Decomposing the optical field A in equation (9) into three field components
interacting with each other A0, A1 and A2, each describes different WDM channel with
Δβ as the phase relationship between them. To highlight the influence of nonlinearity
restricted to small-signal distortions, equation (9) can be separated into three coupled
equations for WDM channel A0 [29]:
𝜕𝐴 𝑜
𝜕𝑧
+
𝛼
2
𝐴 𝑜 +
𝑖
2
𝛽2
𝜕2
𝐴 𝑜
𝜕𝑇2
= 𝑖𝛾|𝐴 𝑜|2
𝐴 𝑜 + 2𝑖𝛾(|𝐴1|2
+ |𝐴2|2)𝐴 𝑜 + 𝑖𝛾 ∑ 𝐴𝑙 𝐴 𝑚 𝐴𝑙+𝑚
∗
𝑒 𝑖∆𝛽𝑧
𝑙,𝑚≠0
3. SYSTEM MODEL AND SIMULATION RESULTS
3.1. Linear Impairments Characterization
3.1.1 Chromatic dispersion penalty measurements
The system model depicted in Figure 8, was developed in VPITransmission maker to
measure the impact of fiber dispersion for different alfa values of MZM on the BER
OSNR and OSNR penalty, which is defined as the difference in optical SNR that is
required to reach a certain target BER for the case of propagation over the system of 1
km under test and the back-to-back one. Linear interpolation is used to find the
correct OSNR values. The OSNR is varied by adjusting the signal power and keeping
the noise power constant. For this approach to work accurately enough, it is critical to
set the two attenuation values of the variable optical attenuator in front of the receiver
such that the target BER lays in between the two calculated BER values as shown in
figure. Simulation results that shows the effect of the OSNR on the BER for different
valued of MZM alfa factor which described the chirping behavior of the modulator
and the OSNR penalty for different values of dispersion is shown in Figure 9 (a) and
(b) respectively.
NRZ MZM
Modulator
GW Opt.
Noise
OOK
Rx
OSNR
OSNR
BER vs OSNR
Opt. Amp
Att. Mux
Only Disp.
accounted
After the Fiber
Link
Without Disp.
effect
Figure 8 System model for OSNR penalty measurements due to fiber dispersion
SPM XPM
FWM

Systems
(a) (b)
Figure 9 Simulation results for OSNR penalty measurements (a) BER vs OSNR for different
values of MZM’s alfa factor (b) OSNR penalty due to fiber dispersion
3.1.2 Polarization mode dispersion penalty measurements
To characterize the effect of the PMD on the optical fiber transmission link, the
system model depicted in Figure 10 which is developed with VPITrasmission maker
is used for this purpose. It is shown how the SOP of a CW probe signal is changed by
the SOP of a CW or modulated pump signal along the fiber. To simplify the
simulation, dispersion-less and loss-less fiber with constant birefringence is used with
the following settings:
Loops = 20, Fiber Span = 5 km, Attenuation = 0 dB/m, Dispersion = 0 s/m^2.
SOP
Monitoring
Pump
Att. = 0
Disp. = 0
SPM = No
XPM = Yes
Birefringence = Constant
Mux
Probe
CW
CW
Poincare
NRZ
Figure 10 Three channels WDM system model to identify PMD effects
The Poincare SOP graph is shown in Figure 11 (a) for azimuth 15o
and ellipticity
of 10o
of the CW pump signal. A modification to the SOP of the CW pump signal was
made to observe the impact on the probe. Pump SOP changed to azimuth 25o
,
ellipticity 15o
as shown in Figure 11 (b). While in Figure 11 (c) the probe and CW
pump have same SOP at azimuth 25o
, Ellipticity 15o
.

(a) (b) (c)
Figure 11 SOP of the probe and the pump signals (a) SOP at pump polarization az =15o
, Elp
= 10o
(b) SOP at pump polarization az = 25o
, Elp = 15o
(c) SOP at probe and pump
polarizations az = 25o
, Elp = 15o
If the CW pump is deactivated and the modulated (10G NRZ) pump is activated,
the depolarization of the probe is clearly observed as shown in Figure 12.
Figure 12 SOP of the Received Signals impacted by SOP of the NRZ-OOK Pump Signal.
3.1.3 Linear cross talk in WDM systems penalty measurements
To illustrate the impact of non-adjacent crosstalk in the NxN AWG on the BER
level in such NxN optical interconnection systems. Following the experimental setup
in [31], the beat crosstalk for only a single wavelength had been simulated with VPI
photonics simulator, using a single signal source divided into 16 paths by 1x16 power
splitter as shown in Figure 13 (a). Then one path is used as a source of the main
signal, while all the remaining paths are used as sources of same-wavelength
crosstalk. All sources are de-correlated from each other by using delay lines with
subsequently increasing time delays. After this the rest paths are connected to the
AWG's input ports, and the BER is measured for the main signal directed to the
AWG's first output port. Eye penalty diagrams for different values of cross talk
attenuations are shown in Figure 13 (b-d). Importantly, as is shown in [31], the
probability density distribution of the signal-crosstalk beat noise becomes Gaussian at
large number of crosstalk sources, N. This allows to employ in the simulation the
Gauss method for the BER estimation as shown in Figure 13 (e).

Systems
(a) (b)
(C) (D)
(E)
Figure 13 Impact of Crosstalk in an Arrayed-Waveguide Grating Router (AWGR) on NxN
Optical Interconnection (a) System Model (b) Eye diag. at 25 dB XT att. (c) Eye diag. at 30
dB XT att. (e) Eye diag. at 35 dB XT att. (d) BER vs ROP for different values of XT att.
Another simulation for a WDM system modelled as in Figure 14 (a) to make a
comparison of BER degradations due to intraband and interband crosstalk of the same
attenuation level as shown in Figure 14 (b).

(A) (B)
Figure 15 Comparison of BER degradation due to intraband and interband crosstalk of the
same level (a) System model (b) BER vs XT attenuation for different cases
3.1.3 Nonlinear impairments penalty measurements
The performance degradation due to Rayleigh and Brillouin scattering can be
reduced by separating the frequencies of the counter-propagating channels. In the
simulation setup of Figure 16 (a), the crosstalk is represented by the Rayleigh and
Brillouin distortions produced in the Universal Fiber. The system performance for
different input powers and channels separations is estimated with the Rx_OOK_BER
module as shown in Figure 16 (b).
(a)
(b)
Figure 16 Performance degradation due to Rayleigh and Brillouin scattering (a) Simulation
Setup (b) BER vs Channel Spacing for Different Channel Power Levels
BER vs Ch.
Separation
Opt. Mux
110 km Fiber
NRZ
NRZ
OOK
Rx
Universal
Fiber
Tx 1
8x10 Gbps
Tx 2
8x10 Gbps
In_Fw
Bus
Out_Fw
In_Bw
Out_Bw
Opt. Filter
BER vs XT Att.
Opt. Att. to
Control XT
Opt. Att.
Mux
Desired Signal
λ1
NRZ
NRZ
NRZ
OOK
Rx
OOK
Rx
OOK
Rx
Intraband
Crosstalk Signal
(λ2 = λ1)
Interband Crosstalk Signal (λ3 ≠ λ1)
100GHz away from desired signal
Opt. Att. to
Control XT Mux
No Crosstalk
B-B

Systems
When pulse collision take place as shown in Figure 17 (b), one pulse walking
through a pulse on a different WDM channels the pulses will interact because they
both affect the index of the fiber along which they propagated causing XPM
impairment as shown in Figure 17 (c). The effect of the fiber's nonlinearity combined
with the dispersion of the fiber also causes shaping of a pulse, by its own effect on the
fiber's index. This is SPM which will compress a strong pulse, increasing its peak
amplitude refer to Figure 17 (d).
Finally the FWM impairment penalty characterization can be clearly observed
using VPITransmission maker simulation setup in Figure 18, which consist of 4 x 10
Gbit/s WDM transmission system over Dispersion Shifted Fiber (DSF). The
emergence of the FWM products outside the WDM signal bandwidths can be clearly
observed in terms of eye penalty and optical spectrum as shown in Figure 19 (a-b).
The WDM signal attenuation due to FWM penalty is shown in Figure 19 (c).
Figure 17 SPM and XPM Measurement (a) Simulation setup (b) Pulse collision of strong and
weak pulse (c) Strong pulse impact on weak pulse XPM (d) Weak pulse impact on strong
pulse SPM
Figure 18 Simulation Setup of a 4 x 10 Gbit/s WDM transmission system over DSF fiber to
characterize the FWM effect
(a)(b)
(d)(c)
ROP (dBm)
Vs
L (km)
NRZ
NRZ
NRZ
NRZ
Power
Meter
Power
Meter
Power
Meter
Power
Meter
1 km of DSF
Attenuation=0.2 dB/km
Opt. MUXOpt. MUX

Figure 19 Emergence of FWM products (a) Eye penalty of the multiplexed signals (b)
Optical spectrums of the multiplexed signals (c) Power level of the received signals.
4. CONCLUSIONS
In this paper the physical layer impairments of the optical fiber transmission link
had been characterized using analytical modelling and verified using numerical
simulations. It is shown that linear impairments are deterministic and have
controllable impact on the performance of the transmission links in terms of BER,
OSNR and Eye penalty. But nonlinear impairments have nondeterministic and
partially controllable impact of the quality of transmission QoT of optical fiber
transmission links. Besides the analytical modeling techniques an empirical modelling
one which are based on numerical simulations or experimental results seems more
promising especially for online impairment measurement and impairment
compensation algorithms since empirical techniques will save more computational
cost.
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