From the analysis of plots in Figs. 7.34b and 7.35, we can deduce some remarkable conclusions: PSD of phase noises in OEO exceed the amplitude noises by
10–25 dB/Hz on the frequency offset of 10 kHz, with pumping current growth, PSD
of the phase noise significantly decreases, namely, at frequency offset from the RF
carrier of 10 kHz, PSD is by 35–40 dB/Hz less, which is caused, on the one hand, by
the decrease of laser PSD by 25 dB/Hz, but on the other hand, by the decrease of
PSD of the OEO phase noise by 10–15 dB/Hz owing to the growth of the Q-factor of
RF FODL with the optical fiber of the length 1000 m with the total delay of 5 μs.
Comparison of PSD of the phase noise in OEO DM (Figs. 7.34b and 7.35) and
OEO MZ (Figs. 6.27b and 6.34) permit to make the important conclusion. The main
difference of OEO DM from OEO MZ is a choice of a laser or the low-noise source
of the coherent emission. For OEO DM, the bandwidth of the laser (or QWLD) RF
modulation must be approximately equal to the OEO operation RF generation. The
bandwidth of the laser RF modulation is approximately equal to the natural frequency of the relaxation photon–electron resonance. Phase noises of a laser are
smaller for narrow bands of the RF modulation.
In OEO MZ, in which the external modulation is used, the laser can have the
bandwidth of the RF modulation, which is several hundred times less than the
operation frequency of generation. So, for example, at the operation frequency of
10 GHz, in OEO DM, the laser with the bandwidth of the RF modulation of 12 GHz
must be used. In OEO MZ, at the operation frequency of 10 GHz, the laser with the
extremely narrow RF modulation bandwidth is chosen, as a rule, 0.1–10 MHz. Such
lasers, as it shown in Chaps. 2, 3, 4 and 7 of this book, has the ultralow natural phase
noises (about À100 dB/Hz at the 10 kHz-offset from the carrier). Of course, the
utilization of lasers with the ultralow phase noises in OEO MZ is more effective,
from the point of view of the oscillator low RF phase noise obtaining.
But, application in OEO of the statistical averaging schemes with extraction of
two optical harmonic (as shown in Chaps. 3–7 and experimentally confirmed, for
instance, in [26]), makes OEO DM (which is 3–5 times cheaper than OEO MZ) as
the promising source of the RF oscillations with the ultralow noises in microwave
and mm-wave ranges.
7.7 Systems of Frequency and Phase Automatic Control
in OEO
In this section, we give the description and the conception of systems of frequency
and phase automatic control with the fiber-optical delay line for application in radio
systems and devices for stable oscillations formation including OEO.
7.7 Systems of Frequency and Phase Automatic Control in OEO
449
10–25 dB/Hz on the frequency offset of 10 kHz, with pumping current growth, PSD
of the phase noise significantly decreases, namely, at frequency offset from the RF
carrier of 10 kHz, PSD is by 35–40 dB/Hz less, which is caused, on the one hand, by
the decrease of laser PSD by 25 dB/Hz, but on the other hand, by the decrease of
PSD of the OEO phase noise by 10–15 dB/Hz owing to the growth of the Q-factor of
RF FODL with the optical fiber of the length 1000 m with the total delay of 5 μs.
Comparison of PSD of the phase noise in OEO DM (Figs. 7.34b and 7.35) and
OEO MZ (Figs. 6.27b and 6.34) permit to make the important conclusion. The main
difference of OEO DM from OEO MZ is a choice of a laser or the low-noise source
of the coherent emission. For OEO DM, the bandwidth of the laser (or QWLD) RF
modulation must be approximately equal to the OEO operation RF generation. The
bandwidth of the laser RF modulation is approximately equal to the natural frequency of the relaxation photon–electron resonance. Phase noises of a laser are
smaller for narrow bands of the RF modulation.
In OEO MZ, in which the external modulation is used, the laser can have the
bandwidth of the RF modulation, which is several hundred times less than the
operation frequency of generation. So, for example, at the operation frequency of
10 GHz, in OEO DM, the laser with the bandwidth of the RF modulation of 12 GHz
must be used. In OEO MZ, at the operation frequency of 10 GHz, the laser with the
extremely narrow RF modulation bandwidth is chosen, as a rule, 0.1–10 MHz. Such
lasers, as it shown in Chaps. 2, 3, 4 and 7 of this book, has the ultralow natural phase
noises (about À100 dB/Hz at the 10 kHz-offset from the carrier). Of course, the
utilization of lasers with the ultralow phase noises in OEO MZ is more effective,
from the point of view of the oscillator low RF phase noise obtaining.
But, application in OEO of the statistical averaging schemes with extraction of
two optical harmonic (as shown in Chaps. 3–7 and experimentally confirmed, for
instance, in [26]), makes OEO DM (which is 3–5 times cheaper than OEO MZ) as
the promising source of the RF oscillations with the ultralow noises in microwave
and mm-wave ranges.
7.7 Systems of Frequency and Phase Automatic Control
in OEO
In this section, we give the description and the conception of systems of frequency
and phase automatic control with the fiber-optical delay line for application in radio
systems and devices for stable oscillations formation including OEO.
7.7 Systems of Frequency and Phase Automatic Control in OEO
449