oscillators have no the required level of the short-term frequency instability in the
frequency range of 1–100 GHz.
Oscillators with the dielectric resonator (cavity) on ceramic alloys have the
evident limitations on the phase noise level. At the expense of the relatively low
Q-factor of such a cavity, which equals approximately 1000 (on the 10GHz generation frequency), the typical phase noise level of commercially available oscillators
could not, as a rule, be less than À90 to À115 dBm/Hz at 1-kHz frequency offset
from the nominal generation frequency 8–20 GHz.
Microwave oscillators with frequency stabilization by the solid-state leuco-sapphire dielectric cavity [12–17] have at present the most low registered phase noise
level of À167 dBm/Hz at 1–10-kHz offsets. The operating frequency range of such
oscillators is from 6 to 35 GHz and has, as a rule, the discrete range of frequency
tuning. The leuco-sapphire cavity of such an oscillator has relatively large overall
dimensions (a diameter is 30–100 mm) and a big weight (150–400 g). Due to large
overall dimensions and a weight of a cavity in such oscillators, the oscillation
frequency strongly depends upon mechanical loads. The serious disadvantage of
an oscillator with leuco-sapphire cavity is the fact that in such oscillators, at the
expense of relatively high dependence of material permittivity upon a temperature
(10
À4 1/deg), systems of frequency heat-setting are complicate and expensive.
Recently, an developers’ attention in the field of the high-stable oscillation
sources is attracted to the new type of a source called an optoelectronic oscillator
(OEO), which contains besides traditional elements of RF section (a nonlinear active
element, high-Q frequency-selective element, the circuit of the positive feedback,
auxiliary circuit for control and stabilization) the optical section (a laser as the source
of optical oscillations, FODL in the optical section, auxiliary optical elements, for
example, a modulator and a demodulator). At definite configurations of optical and
RF sections and their parameters (see further chapters in this book), both optical and
RF oscillations are excited, which interact in complicate manner and give to OEO
some unique properties, which will be analyzed later in this book. These properties
will be considered in detail later in this Introduction with the purpose of the first
acquaintance of readers with OEO features.
One of the alternative approaches to creation of reliable compact and low-cost
low-noise oscillators in the frequency range 1–100 GHz is an application in OEO of
the stabilized low-noise fiber-optical delay line on the base of the fast-acting
quantum-well laser diode, a photodiode, as well as at the expense of special
low-dispersion optical fibers. These FODLs have a large delay for harmonic microwave oscillations. The delay time in these FODLs is from 1 ns to 50 μs (for a
bandwidth of transmitted frequencies up to 100 GHz). At that, the power losses in
these FODLs (at the expense of scattering and the optoelectronic conversion) are
10–18 dB and more in microwave and mm-wave ranges.
In the best samples of the microwave optoelectronic oscillators, which have a
similar FODL in the feedback loop, a low power spectral density of the phase noise
is already achieved equaled to À130 to À153 dBc/Hz at frequency offsets of
1–10 kHz [18–20]. The short-term frequency instability of this OEO is about
10
À10 . The ultralow phase noise of this OEO is achieved at the expense of creation
2
1 Introduction
frequency range of 1–100 GHz.
Oscillators with the dielectric resonator (cavity) on ceramic alloys have the
evident limitations on the phase noise level. At the expense of the relatively low
Q-factor of such a cavity, which equals approximately 1000 (on the 10GHz generation frequency), the typical phase noise level of commercially available oscillators
could not, as a rule, be less than À90 to À115 dBm/Hz at 1-kHz frequency offset
from the nominal generation frequency 8–20 GHz.
Microwave oscillators with frequency stabilization by the solid-state leuco-sapphire dielectric cavity [12–17] have at present the most low registered phase noise
level of À167 dBm/Hz at 1–10-kHz offsets. The operating frequency range of such
oscillators is from 6 to 35 GHz and has, as a rule, the discrete range of frequency
tuning. The leuco-sapphire cavity of such an oscillator has relatively large overall
dimensions (a diameter is 30–100 mm) and a big weight (150–400 g). Due to large
overall dimensions and a weight of a cavity in such oscillators, the oscillation
frequency strongly depends upon mechanical loads. The serious disadvantage of
an oscillator with leuco-sapphire cavity is the fact that in such oscillators, at the
expense of relatively high dependence of material permittivity upon a temperature
(10
À4 1/deg), systems of frequency heat-setting are complicate and expensive.
Recently, an developers’ attention in the field of the high-stable oscillation
sources is attracted to the new type of a source called an optoelectronic oscillator
(OEO), which contains besides traditional elements of RF section (a nonlinear active
element, high-Q frequency-selective element, the circuit of the positive feedback,
auxiliary circuit for control and stabilization) the optical section (a laser as the source
of optical oscillations, FODL in the optical section, auxiliary optical elements, for
example, a modulator and a demodulator). At definite configurations of optical and
RF sections and their parameters (see further chapters in this book), both optical and
RF oscillations are excited, which interact in complicate manner and give to OEO
some unique properties, which will be analyzed later in this book. These properties
will be considered in detail later in this Introduction with the purpose of the first
acquaintance of readers with OEO features.
One of the alternative approaches to creation of reliable compact and low-cost
low-noise oscillators in the frequency range 1–100 GHz is an application in OEO of
the stabilized low-noise fiber-optical delay line on the base of the fast-acting
quantum-well laser diode, a photodiode, as well as at the expense of special
low-dispersion optical fibers. These FODLs have a large delay for harmonic microwave oscillations. The delay time in these FODLs is from 1 ns to 50 μs (for a
bandwidth of transmitted frequencies up to 100 GHz). At that, the power losses in
these FODLs (at the expense of scattering and the optoelectronic conversion) are
10–18 dB and more in microwave and mm-wave ranges.
In the best samples of the microwave optoelectronic oscillators, which have a
similar FODL in the feedback loop, a low power spectral density of the phase noise
is already achieved equaled to À130 to À153 dBc/Hz at frequency offsets of
1–10 kHz [18–20]. The short-term frequency instability of this OEO is about
10
À10 . The ultralow phase noise of this OEO is achieved at the expense of creation
2
1 Introduction