Therefore, for mathematical modeling of QWLD, we use the semiclassical
theory. When using the method of laser balanced (kinetic) equations the phase
relationships are lost, which are the most important for analysis of laser phase
noise influence on the RF noises of OEO. It is necessary to note once more that
the most of OEO schemes under consideration with direct and external modulations can be attributed to schemes with phase or amplitude modulation of optical
emission, while in the process of photodetection with self-heterodyne mixing,
information about the subcarrier is contained in the phase of optical emission.
2. In this book, OEO is the main object under investigation. One of the tasks of this
investigation is the understanding of the basing operation mechanisms of the
complicate oscillating system, which determine the OEO phase noise. At that, the
main attention is attracted not so much to the OEO RF part (this is well-developed
in traditional RF oscillators) as to influence of laser emission characteristics on
the OEO frequency and amplitude, as well as to influence of amplitude and phase
noises of laser spontaneous emission on the OEO RF phase noise.
3. Solution of problem stated in this book on OEO investigation should be matched
with the specificity of the laser emission, which relates with the noise quantum
nature, the temporal and spatial coherence, the presence of the spatial distribution
on strength amplitude E 0 (R), on phase Ф 0 (R), and on fluctuations of amplitude m
(R) and phase Δφ(R), the adequacy with the laser wavelengths of overall dimensions of optical channels and the photodetector area in the microwave range.
4. Methods of direct and external modulation of the QWLD laser narrowband
emission (with additional suppression of optical harmonics), used in OEO,
potentially have the high degree of laser phase noise suppression, on the one
hand, due to utilization of lengthy low-dispersive optical fiber, the narrowband
QWLD laser emission, while, on the other hand, due to utilization of methods of
the phase noise compensation at self-heterodyne mixing on the photodetector, the
transmission of two optical harmonics (with suppression of the third optical
harmonic) through the optical channel and alignment of these harmonics in
amplitude.
5. An approach to OEO examination as to the system where two oscillating processes are developing in the optical and RF ranges with scattering, the energy
transformation, taking into consideration of spontaneous emission generation in
the laser, to our opinion, is new and effective. Such an approach enables to
analyze of laser element influence of OEO RF noises, to examine the RF
frequency control by the laser optical frequency (and vice versa), to provide the
control of the laser optical frequency varying the OEO RF frequency. In the
future, this permits to study the OEO synchronization by the external optical
emission source, to perform the analysis of PLL systems for OEO by modulated
laser oscillations, to investigate OEO as the master microwave oscillator for
different laser systems, for instance, the laser with synchronization of longitudinal modes with the pulse duration 1–10 ps with low jitter, etc.
6. As a result of the review fulfilled and the analysis of various oscillators in this
chapter, we can conclude that the phase noise level in OEO approaches to the
phase noise of the “best low-noise oscillator” on the leuco-sapphire. Difference in
2.10 Conclusions
65
theory. When using the method of laser balanced (kinetic) equations the phase
relationships are lost, which are the most important for analysis of laser phase
noise influence on the RF noises of OEO. It is necessary to note once more that
the most of OEO schemes under consideration with direct and external modulations can be attributed to schemes with phase or amplitude modulation of optical
emission, while in the process of photodetection with self-heterodyne mixing,
information about the subcarrier is contained in the phase of optical emission.
2. In this book, OEO is the main object under investigation. One of the tasks of this
investigation is the understanding of the basing operation mechanisms of the
complicate oscillating system, which determine the OEO phase noise. At that, the
main attention is attracted not so much to the OEO RF part (this is well-developed
in traditional RF oscillators) as to influence of laser emission characteristics on
the OEO frequency and amplitude, as well as to influence of amplitude and phase
noises of laser spontaneous emission on the OEO RF phase noise.
3. Solution of problem stated in this book on OEO investigation should be matched
with the specificity of the laser emission, which relates with the noise quantum
nature, the temporal and spatial coherence, the presence of the spatial distribution
on strength amplitude E 0 (R), on phase Ф 0 (R), and on fluctuations of amplitude m
(R) and phase Δφ(R), the adequacy with the laser wavelengths of overall dimensions of optical channels and the photodetector area in the microwave range.
4. Methods of direct and external modulation of the QWLD laser narrowband
emission (with additional suppression of optical harmonics), used in OEO,
potentially have the high degree of laser phase noise suppression, on the one
hand, due to utilization of lengthy low-dispersive optical fiber, the narrowband
QWLD laser emission, while, on the other hand, due to utilization of methods of
the phase noise compensation at self-heterodyne mixing on the photodetector, the
transmission of two optical harmonics (with suppression of the third optical
harmonic) through the optical channel and alignment of these harmonics in
amplitude.
5. An approach to OEO examination as to the system where two oscillating processes are developing in the optical and RF ranges with scattering, the energy
transformation, taking into consideration of spontaneous emission generation in
the laser, to our opinion, is new and effective. Such an approach enables to
analyze of laser element influence of OEO RF noises, to examine the RF
frequency control by the laser optical frequency (and vice versa), to provide the
control of the laser optical frequency varying the OEO RF frequency. In the
future, this permits to study the OEO synchronization by the external optical
emission source, to perform the analysis of PLL systems for OEO by modulated
laser oscillations, to investigate OEO as the master microwave oscillator for
different laser systems, for instance, the laser with synchronization of longitudinal modes with the pulse duration 1–10 ps with low jitter, etc.
6. As a result of the review fulfilled and the analysis of various oscillators in this
chapter, we can conclude that the phase noise level in OEO approaches to the
phase noise of the “best low-noise oscillator” on the leuco-sapphire. Difference in
2.10 Conclusions
65