SAW resonators), electromagnetic (YIG, DDR, CR, and DDRLS) and optoelectronic (RF FODL and ODR) according to mechanisms of oscillation delay and
energy accumulating. With radio-frequency growth, acoustic losses increases in
the “acoustic-electronic” quartz and SAW resonators, and this leads to reduction
of their Q-factor in microwave frequencies. Among “electromagnetic” resonators, in
which the conversion of electrical oscillations into the microwave electromagnetic
field occurs, the disk dielectric resonator from the leuco-sapphire has the maximal Qfactor.
The main shortcoming of the dielectric resonator from the leuco-sapphire is its
strong dependence of the resonance frequency and its phase-frequency response
upon temperature (the temperature instability of the resonance frequency of the
leuco-sapphire resonator is about 10
À4 1/
C). The alternative approach for Q-factor
increase is application mechanisms of optoelectronic conversion and usage of RF
FODL and optical disk resonators. The Q-factor of RF FODL on frequencies
5–100 GHz is about Q ¼ 10
5 to 10
6 .
At present, the Q-factor value (which can be estimate approximately by the ratio
of the own filter natural frequency on the laser generation frequency to the resonance
peak width on the 0.7 level) of optical disk resonators, at which nonlinear optical
effects are not manifested, is Q ¼ 10
4 to 10
7 . The overall dimensions of resonators, at
which the transmission of one transverse optical mode is provided, approach to
dimensions of several tens of optical wavelengths or several tens of microns.
Nonlinear optical effects such as three- and four-photon interaction, the Brillouin
scattering, etc. have a threshold character, and are manifested in the disk optical
resonators due to high power density in the cross-section (of the order more than
50 mW/(μm)
2 ) in the ultralow micro-volumes of the resonator. Owing to high power
density in ODR, the material temperature sharply increases due to emission absorption in the quartz or the paratellurite, which leads to complicate temperature compensation of such a resonator.
2.8.3 Dimensions of Oscillator Resonance Systems
At first, we would like to note that in RF FODL with geometric length of the optical
fiber of 1–5 km, the useful volume (in which emission propagates in the regime of
one transverse mode) is not more than 1 cm
3 .
Figure 2.15a shows maximal overall dimensions of resonators and delay lines
used in the modern high-stable OEOs and microwave and mm-wave oscillators.
Here we see that the optical disk resonator (ODR) is a leader of minimal dimensions.
Its linear dimensions with input/output emission devices are less than 1 mm. The plot
of maximal overall dimensions of the optical fiber reel with the length 5–10 km is
presented in Fig. 2.15b over years. The empiric function of the reel size reduction,
and appearance of nano-dimension fibers in the market with minimal losses of
0.001 dB per one bend of radius of 2–3 mm guarantees appearance in the market
2.8 Comparison of OEO Characteristics with Other Traditional Oscillators
53
energy accumulating. With radio-frequency growth, acoustic losses increases in
the “acoustic-electronic” quartz and SAW resonators, and this leads to reduction
of their Q-factor in microwave frequencies. Among “electromagnetic” resonators, in
which the conversion of electrical oscillations into the microwave electromagnetic
field occurs, the disk dielectric resonator from the leuco-sapphire has the maximal Qfactor.
The main shortcoming of the dielectric resonator from the leuco-sapphire is its
strong dependence of the resonance frequency and its phase-frequency response
upon temperature (the temperature instability of the resonance frequency of the
leuco-sapphire resonator is about 10
À4 1/
C). The alternative approach for Q-factor
increase is application mechanisms of optoelectronic conversion and usage of RF
FODL and optical disk resonators. The Q-factor of RF FODL on frequencies
5–100 GHz is about Q ¼ 10
5 to 10
6 .
At present, the Q-factor value (which can be estimate approximately by the ratio
of the own filter natural frequency on the laser generation frequency to the resonance
peak width on the 0.7 level) of optical disk resonators, at which nonlinear optical
effects are not manifested, is Q ¼ 10
4 to 10
7 . The overall dimensions of resonators, at
which the transmission of one transverse optical mode is provided, approach to
dimensions of several tens of optical wavelengths or several tens of microns.
Nonlinear optical effects such as three- and four-photon interaction, the Brillouin
scattering, etc. have a threshold character, and are manifested in the disk optical
resonators due to high power density in the cross-section (of the order more than
50 mW/(μm)
2 ) in the ultralow micro-volumes of the resonator. Owing to high power
density in ODR, the material temperature sharply increases due to emission absorption in the quartz or the paratellurite, which leads to complicate temperature compensation of such a resonator.
2.8.3 Dimensions of Oscillator Resonance Systems
At first, we would like to note that in RF FODL with geometric length of the optical
fiber of 1–5 km, the useful volume (in which emission propagates in the regime of
one transverse mode) is not more than 1 cm
3 .
Figure 2.15a shows maximal overall dimensions of resonators and delay lines
used in the modern high-stable OEOs and microwave and mm-wave oscillators.
Here we see that the optical disk resonator (ODR) is a leader of minimal dimensions.
Its linear dimensions with input/output emission devices are less than 1 mm. The plot
of maximal overall dimensions of the optical fiber reel with the length 5–10 km is
presented in Fig. 2.15b over years. The empiric function of the reel size reduction,
and appearance of nano-dimension fibers in the market with minimal losses of
0.001 dB per one bend of radius of 2–3 mm guarantees appearance in the market
2.8 Comparison of OEO Characteristics with Other Traditional Oscillators
53