the microwave frequencies of the range 8–12 GHz is approximately 5–15 dB/Hz.
But, at that, OEO has the wider potential operating microwave range up to
70–100 GHz at keeping of low phase noises. The principal moment is that
OEO with RF FODL has potential possibilities of phase noise reduction due to
optimization of the laser and RF FODL as a whole.
Other important OEO advantages compared to the leuco-sapphire oscillator are
higher strength characteristics due to application of lengthy laid by rings RF
FODL structure, the potentially smaller weight and overall dimensions of the RF
FODL useful volume, in which laser emission propagates in the optical fiber. The
RF FODL useful volume is less than 1 cm
3 at application in RF FODL of 1 km of
the optical fiber length.
Other advantages of OEO are the weaker dependence on temperature (by two
orders) of the RF FODL phase-frequency response and stronger (by the order and
more) resistance to external mechanical influences and to accelerations due to
linear topology of laying of the quartz fiber thin thread in the RF FODL reel.
7. One of the analysis results of various optoelectronic structures for creation of
high-stable oscillations is the conclusion that modern optical micro-resonators
(Bragg, disks, etc.) can be used in OEO only as the optical discriminators in
systems on automatic phase control and the optical frequency due to low thresholds of the entry power of optical emission (5–20 μW), which is caused by
nonlinear optical effects.
8. The key moment at manufacture of stable oscillators in microwave and mm-wave
ranges is the reasonable transition from the completely RF oscillator and from the
completely optical oscillator to the hybrid structure of OEO containing both
optical and RF parts. Only in this case, the possibility appears of high-effective
selective suppression of spurious harmonics, spaced from the useful harmonic by
the interval less than 1–100 kHz by RF high-Q filters at increase of the geometric
length of RF FODL of the order 2–10 km. Fundamental reason of this restriction
is the fact that Q-factors of RF microwave and mm-wave filters are restricted by a
million (due to loss increase in the material at reduction of wavelength), while the
Q-factor of optical filters (without presence of nonlinear effects) is restricted by
10–1000 due to high power density owing to wavelength smallness, approximately, 1 μm. As a consequence of such a transition to the hybrid OEO structure,
the inevitable power losses arise, which are circulated in the oscillator loop. At
double optoelectronic conversion, the power decreases not less than by 10 times.
Moreover, the additional phase noises of spontaneous laser emission arise, which
are essentially higher of natural electronic noises, taking into account this conversion. Nevertheless, development of technology of quantum-dimension
low-noise laser diodes with optical phase adjustment, using high-Q microresonators (with line width less than 10 MHz on the optical carrier) (the phase
noise is less than À100 dB/Hz), and manufacture of commercially available
low-dispersive optical fibers with lengths of 2–10 km wounded into the compact
reels (with overall dimensions 5 Â 5 Â 5 cm) is guarantees the revolutionary
breakthrough in the field of stable microwave and mm-wave oscillators.
66
2 Nanostructural Optoelectronic Oscillators with the Fiber-Optical Delay Line
But, at that, OEO has the wider potential operating microwave range up to
70–100 GHz at keeping of low phase noises. The principal moment is that
OEO with RF FODL has potential possibilities of phase noise reduction due to
optimization of the laser and RF FODL as a whole.
Other important OEO advantages compared to the leuco-sapphire oscillator are
higher strength characteristics due to application of lengthy laid by rings RF
FODL structure, the potentially smaller weight and overall dimensions of the RF
FODL useful volume, in which laser emission propagates in the optical fiber. The
RF FODL useful volume is less than 1 cm
3 at application in RF FODL of 1 km of
the optical fiber length.
Other advantages of OEO are the weaker dependence on temperature (by two
orders) of the RF FODL phase-frequency response and stronger (by the order and
more) resistance to external mechanical influences and to accelerations due to
linear topology of laying of the quartz fiber thin thread in the RF FODL reel.
7. One of the analysis results of various optoelectronic structures for creation of
high-stable oscillations is the conclusion that modern optical micro-resonators
(Bragg, disks, etc.) can be used in OEO only as the optical discriminators in
systems on automatic phase control and the optical frequency due to low thresholds of the entry power of optical emission (5–20 μW), which is caused by
nonlinear optical effects.
8. The key moment at manufacture of stable oscillators in microwave and mm-wave
ranges is the reasonable transition from the completely RF oscillator and from the
completely optical oscillator to the hybrid structure of OEO containing both
optical and RF parts. Only in this case, the possibility appears of high-effective
selective suppression of spurious harmonics, spaced from the useful harmonic by
the interval less than 1–100 kHz by RF high-Q filters at increase of the geometric
length of RF FODL of the order 2–10 km. Fundamental reason of this restriction
is the fact that Q-factors of RF microwave and mm-wave filters are restricted by a
million (due to loss increase in the material at reduction of wavelength), while the
Q-factor of optical filters (without presence of nonlinear effects) is restricted by
10–1000 due to high power density owing to wavelength smallness, approximately, 1 μm. As a consequence of such a transition to the hybrid OEO structure,
the inevitable power losses arise, which are circulated in the oscillator loop. At
double optoelectronic conversion, the power decreases not less than by 10 times.
Moreover, the additional phase noises of spontaneous laser emission arise, which
are essentially higher of natural electronic noises, taking into account this conversion. Nevertheless, development of technology of quantum-dimension
low-noise laser diodes with optical phase adjustment, using high-Q microresonators (with line width less than 10 MHz on the optical carrier) (the phase
noise is less than À100 dB/Hz), and manufacture of commercially available
low-dispersive optical fibers with lengths of 2–10 km wounded into the compact
reels (with overall dimensions 5 Â 5 Â 5 cm) is guarantees the revolutionary
breakthrough in the field of stable microwave and mm-wave oscillators.
66
2 Nanostructural Optoelectronic Oscillators with the Fiber-Optical Delay Line