We examined how the choice of RF FODL component parameters (included in
OEO MZ) affects the operation. We found out that for providing of minimal level of
PSD of the phase noise (À120 dB/Hz at offset 1–10 kHz from the microwave
carrier), it is necessary to use the high-coherent lasers with the spectral line width
of 1–50 kHz with geometrical FOS length of 2–20 km. To suppress peaks of
oscillation types, which are not generated, we can use differential and combined
delay lines with two or three optical fibers of different length.
The further level reduction of PSD of the phase noise is possible at utilization of
PLL system in OEO MZ, as in the case of traditional RF oscillators. We shall
consider in detail the features of PLL system application in OEO in the next chapter.
Below we present results of numerical calculation of PSD of OEO MZ with the PLL
system.
The power spectral density of the phase noise of RF oscillations in OEO MZ is
presented in Chap. 7.
6.8 Conclusions
The OEO MZ analysis is performed as the system of two oscillators of the optical
and RF ranges, the differential equations with fluctuations are obtained and analyzed. The analytical functions for the power spectral densities of amplitude and
phase fluctuations of RF subcarrier (generated by OEO) are obtained. It is proved
that the power spectral density of phase noises in OEO MZ is determined by phase
fluctuations of the laser optical emission. The value of PSD of phase noises in OEO
MZ is proportional to the natural width of the laser spectral line, and inversely
proportional to the equivalent (taking into consideration the optical fiber an RF
FODL) Q-factor of the OEO oscillating system and inversely proportional of the
laser power.
Noises in OEO MZ are mainly defined by the laser phase fluctuations, which, in
turn, depend upon the spontaneous emission. The decrease of OEO phase noises can
be provided by a choice of the high-coherent sources of optical emission with the
relatively high power of optical emission (20–40 mW). The other methods of PSD
decrease of phase noises in OEO MZ are: the growth of delay time of the optical
carrier in FOS optical fibers, the control of MZ operation point and application of
combined modulators (which use the more than two parallel optical channels), MZ
with increased dynamic range (on the value of a ratio of optical phase increments at
variation of the control voltage).
It is stated than at utilization of standard low-dispersive optical fibers in MZ, the
dispersion of fibers has no serious influence on PSD of the phase noises at widths of
the laser line less than 10 MHz. At application of the high-dispersive optical fibers
(with the dispersion level 50 ns/nm km) or the low-coherent laser (with the line
width more than 1000 MHz), ripples on the offset frequency are observed, which
period is determined by dispersion on FOS and by the natural width of the laser
generation line, in the spectral line of OEO MZ generation. Fulfilled computer
364
6 Operation Analysis of Optoelectronic oscillator (OEO) with External. . .
OEO MZ) affects the operation. We found out that for providing of minimal level of
PSD of the phase noise (À120 dB/Hz at offset 1–10 kHz from the microwave
carrier), it is necessary to use the high-coherent lasers with the spectral line width
of 1–50 kHz with geometrical FOS length of 2–20 km. To suppress peaks of
oscillation types, which are not generated, we can use differential and combined
delay lines with two or three optical fibers of different length.
The further level reduction of PSD of the phase noise is possible at utilization of
PLL system in OEO MZ, as in the case of traditional RF oscillators. We shall
consider in detail the features of PLL system application in OEO in the next chapter.
Below we present results of numerical calculation of PSD of OEO MZ with the PLL
system.
The power spectral density of the phase noise of RF oscillations in OEO MZ is
presented in Chap. 7.
6.8 Conclusions
The OEO MZ analysis is performed as the system of two oscillators of the optical
and RF ranges, the differential equations with fluctuations are obtained and analyzed. The analytical functions for the power spectral densities of amplitude and
phase fluctuations of RF subcarrier (generated by OEO) are obtained. It is proved
that the power spectral density of phase noises in OEO MZ is determined by phase
fluctuations of the laser optical emission. The value of PSD of phase noises in OEO
MZ is proportional to the natural width of the laser spectral line, and inversely
proportional to the equivalent (taking into consideration the optical fiber an RF
FODL) Q-factor of the OEO oscillating system and inversely proportional of the
laser power.
Noises in OEO MZ are mainly defined by the laser phase fluctuations, which, in
turn, depend upon the spontaneous emission. The decrease of OEO phase noises can
be provided by a choice of the high-coherent sources of optical emission with the
relatively high power of optical emission (20–40 mW). The other methods of PSD
decrease of phase noises in OEO MZ are: the growth of delay time of the optical
carrier in FOS optical fibers, the control of MZ operation point and application of
combined modulators (which use the more than two parallel optical channels), MZ
with increased dynamic range (on the value of a ratio of optical phase increments at
variation of the control voltage).
It is stated than at utilization of standard low-dispersive optical fibers in MZ, the
dispersion of fibers has no serious influence on PSD of the phase noises at widths of
the laser line less than 10 MHz. At application of the high-dispersive optical fibers
(with the dispersion level 50 ns/nm km) or the low-coherent laser (with the line
width more than 1000 MHz), ripples on the offset frequency are observed, which
period is determined by dispersion on FOS and by the natural width of the laser
generation line, in the spectral line of OEO MZ generation. Fulfilled computer
364
6 Operation Analysis of Optoelectronic oscillator (OEO) with External. . .