Expansion of the laser spectral line width (Fig. 6.32) leads to significant growth of
PSD level of the phase noise of OEO due to FOS dispersion. This is true even for
small laser emission spectral line compared to RF generation in OEO MZ. Owing to
FOS dispersion, the PSD spectrum of the phase noise has the remarkable feature: the
comb structure—the periodic dependence of the offset F from the nominal RF
frequency of oscillations. The period of this dependence is proportional to the
product of the dispersion time by laser emission bandwidth. Such the physical
property of PSD of the phase noise in OEO MZ is similar to the spectrum property
of laser diodes with high-dispersive active media [6–9], we obtain:
N FOS v
ð Þ ¼ N FOS v 0
ð Þ þ v À v 0
ð
Þ
dN FOS
dv
þ v À v 0
ð
Þ
2 d
2 N FOS
dv 2 :
ð6:94Þ
If dN FOS /dv 6 ¼ 0 and constant and d
2 N FOS /dv
2
¼ 0, the spectrum of oscillation
types in OEO remains equidistant. The dispersion effect on the mode spectrum in the
second order must be taken into consideration, if the first and the second derivatives
of the function of the optical frequency are not equal to zero, i.e., dN FOS /dv 6 ¼ 0 and
d
2 N FOS /dv
2 6 ¼ 0. At that, the equidistant property is disturbed or intervals between
adjacent spectrum oscillation types decreases.
We are speaking here about the single-frequency mode, but there are types of
oscillations, which cannot begin to generation, but they are present in the spectrum.
The value of the second derivative on the optical frequency d
2 N FOS /dv
2 of the FOS
refraction index may serve as the equidistant measure. At that, the expression for the
interval between the adjacent oscillation type can be written as S L ( f ):
Fig. 6.32 Calculated
functions of PSD of the
phase noise S( f ) in OEO
MZ with the high-dispersive
FOS in RF FODL with the
low-coherent laser versus
the frequency offset by
F from the nominal
operation frequency. The
curves on the graph
corresponds 1—Δv L ¼ 10
GHz, 2—Δv L ¼ 1 GHz,
3—Δv L ¼ 0.1 GHz
354
6 Operation Analysis of Optoelectronic oscillator (OEO) with External. . .
PSD level of the phase noise of OEO due to FOS dispersion. This is true even for
small laser emission spectral line compared to RF generation in OEO MZ. Owing to
FOS dispersion, the PSD spectrum of the phase noise has the remarkable feature: the
comb structure—the periodic dependence of the offset F from the nominal RF
frequency of oscillations. The period of this dependence is proportional to the
product of the dispersion time by laser emission bandwidth. Such the physical
property of PSD of the phase noise in OEO MZ is similar to the spectrum property
of laser diodes with high-dispersive active media [6–9], we obtain:
N FOS v
ð Þ ¼ N FOS v 0
ð Þ þ v À v 0
ð
Þ
dN FOS
dv
þ v À v 0
ð
Þ
2 d
2 N FOS
dv 2 :
ð6:94Þ
If dN FOS /dv 6 ¼ 0 and constant and d
2 N FOS /dv
2
¼ 0, the spectrum of oscillation
types in OEO remains equidistant. The dispersion effect on the mode spectrum in the
second order must be taken into consideration, if the first and the second derivatives
of the function of the optical frequency are not equal to zero, i.e., dN FOS /dv 6 ¼ 0 and
d
2 N FOS /dv
2 6 ¼ 0. At that, the equidistant property is disturbed or intervals between
adjacent spectrum oscillation types decreases.
We are speaking here about the single-frequency mode, but there are types of
oscillations, which cannot begin to generation, but they are present in the spectrum.
The value of the second derivative on the optical frequency d
2 N FOS /dv
2 of the FOS
refraction index may serve as the equidistant measure. At that, the expression for the
interval between the adjacent oscillation type can be written as S L ( f ):
Fig. 6.32 Calculated
functions of PSD of the
phase noise S( f ) in OEO
MZ with the high-dispersive
FOS in RF FODL with the
low-coherent laser versus
the frequency offset by
F from the nominal
operation frequency. The
curves on the graph
corresponds 1—Δv L ¼ 10
GHz, 2—Δv L ¼ 1 GHz,
3—Δv L ¼ 0.1 GHz
354
6 Operation Analysis of Optoelectronic oscillator (OEO) with External. . .