6.6.2 Analog Modeling of the Process Formation
of the Oscillation Spectrum in OEO MZ in Transients
An analysis of computer modeling results of Eqs. (5.60) and (6.28) shows that at
utilization in RF FODL of low-dispersed light guides with the dispersion of FOS less
than 10 ps/(nÁmÁkm) and the high-coherent lasers with the generation line width Δv
less than 10 MHz, the increase of PSD of the phase noise in OEO MZ at growth of
this width of the laser spectral line is mainly related to the conversion of phase noises
into the amplitude noises in the MZ modulator.
The most intensive effect of the laser line width Δv in OEO MZ is demonstrated
at utilization of the high-dispersed optical fibers with the slope τ D ¼ dT/dv ¼ 10
À2
1/GHz, which corresponds to FOS dispersion of 50 ns/(nmÁkm) and the
low-coherent lasers with the line width Δν L ¼ Δν and more than 30 GHz.
One of the results of computer modeling is presented in Fig. 6.32 in the form of
functions of PSD of the phase noise in OEO MZ for different values of the laser
generation line width, of the FOS dispersion: curve 1 in the Fig. 6.32 is the laser line
width Δv ¼ 10 MHz, the dispersion slope is equal to zero; curve 2 is the width
10 GHz, the dispersion slope τ D ¼ dT/dv ¼ 10
À2 1/GHz (which corresponds to the
FOS dispersion of 50 ns/(nmÁkm); curve 3 is the width 50 GHz, τ D ¼ dT/dv ¼ 10
À2
1/GHz. The average generation frequency of OEO MZ is 10 GHz. The delay time in
FOS is T FOS (v 0 ) ¼ 100 μs, which corresponds to the geometrical length of FOS of
L ¼ 20 km.
Figure 6.30 shows the one result of computer modeling. Here we see the scenario
of the spectrum formation of OEO MZ taking into consideration the laser phase
noise.
The scenario of spectrum formation of OEO MZ with the account of the laser
phase noises is shown in Fig. 6.31. Time-functions are normalized along the time
axis to the period of RF oscillations t/T 0 , where T 0 is the period of RF oscillations of
OEO MZ.
6.6.3 Influence of the Material’s Refraction Index Dispersion
of the Optical Fiber upon PSD of the Phase Noise
in OEO MZ
On the base of the analog model of OEO MZ (Fig. 6.29b), the investigation is
performed for the influence of dispersion of the refraction index upon spectrum
formation in OEO MZ.
Historically, the analysis of dispersion influence of the refraction index of the AE
material upon the laser generation spectrum was performed at examination of
semiconductor lasers in the middle of 1960s [6–9]. With the development of fiberoptical communication lines, the problems of dispersion influence of the optical fiber
upon the limit possibilities of the carrying capacity of the single-mode and multi6.6 Analog Modeling of OEO MZ
351
of the Oscillation Spectrum in OEO MZ in Transients
An analysis of computer modeling results of Eqs. (5.60) and (6.28) shows that at
utilization in RF FODL of low-dispersed light guides with the dispersion of FOS less
than 10 ps/(nÁmÁkm) and the high-coherent lasers with the generation line width Δv
less than 10 MHz, the increase of PSD of the phase noise in OEO MZ at growth of
this width of the laser spectral line is mainly related to the conversion of phase noises
into the amplitude noises in the MZ modulator.
The most intensive effect of the laser line width Δv in OEO MZ is demonstrated
at utilization of the high-dispersed optical fibers with the slope τ D ¼ dT/dv ¼ 10
À2
1/GHz, which corresponds to FOS dispersion of 50 ns/(nmÁkm) and the
low-coherent lasers with the line width Δν L ¼ Δν and more than 30 GHz.
One of the results of computer modeling is presented in Fig. 6.32 in the form of
functions of PSD of the phase noise in OEO MZ for different values of the laser
generation line width, of the FOS dispersion: curve 1 in the Fig. 6.32 is the laser line
width Δv ¼ 10 MHz, the dispersion slope is equal to zero; curve 2 is the width
10 GHz, the dispersion slope τ D ¼ dT/dv ¼ 10
À2 1/GHz (which corresponds to the
FOS dispersion of 50 ns/(nmÁkm); curve 3 is the width 50 GHz, τ D ¼ dT/dv ¼ 10
À2
1/GHz. The average generation frequency of OEO MZ is 10 GHz. The delay time in
FOS is T FOS (v 0 ) ¼ 100 μs, which corresponds to the geometrical length of FOS of
L ¼ 20 km.
Figure 6.30 shows the one result of computer modeling. Here we see the scenario
of the spectrum formation of OEO MZ taking into consideration the laser phase
noise.
The scenario of spectrum formation of OEO MZ with the account of the laser
phase noises is shown in Fig. 6.31. Time-functions are normalized along the time
axis to the period of RF oscillations t/T 0 , where T 0 is the period of RF oscillations of
OEO MZ.
6.6.3 Influence of the Material’s Refraction Index Dispersion
of the Optical Fiber upon PSD of the Phase Noise
in OEO MZ
On the base of the analog model of OEO MZ (Fig. 6.29b), the investigation is
performed for the influence of dispersion of the refraction index upon spectrum
formation in OEO MZ.
Historically, the analysis of dispersion influence of the refraction index of the AE
material upon the laser generation spectrum was performed at examination of
semiconductor lasers in the middle of 1960s [6–9]. With the development of fiberoptical communication lines, the problems of dispersion influence of the optical fiber
upon the limit possibilities of the carrying capacity of the single-mode and multi6.6 Analog Modeling of OEO MZ
351