As the investigation results of frequency and amplitude oscillations functions in
OEO at variations of FOS parameters, we obtain the new earlier unknown mechanisms of frequency control in OEO:
• The linear at using of DC of Y-type and variations of excitations coefficients in
the single optical channel.
• The quasi-linear at using of DC of Y-type and variations of excitation coefficients
in two optical channels.
• The periodic at using of DC of Х-type by means of longitudinal optical coupling.
Considered methods of OEO frequency control are new and not-studied in
publications and they expand the application areas of OEO. New devices, which
use in its base the described methods of OEO frequency control, are protected by
Russian patents.
We show that the OEO long-term frequency instability with utilization of “specific” optical fibers can achieve 10
À8 . To provide the high-stability generation, we
can use relatively low-Q tuned RF filter (which is nonexpensive) and the stable RF
FODL with the large delay time (10–25 μs), for example, on the base of the single
light guide. At that, the benefit in frequency stability is determined by the ratio of the
signal delay in the optical part of OEO with RF FODL to the time constant of the
RF part.
This benefit is 20–300. There is a possibility to improve the indices of RF highstable low-noise microwave oscillators, which operate at room temperatures on the
principle of frequency pulling by the high-Q external resonators owing to the
structure of OEO with RF FODL. This approach does not resort of the complicate
and expensive methods of PLL systems in the microwave range. The decrease of
weight coefficients till values 10
À2 by reduction of the thickness of the protective
polymer envelope to 1–2 μm (or without formation of the polymer envelope of the
optical fiber at the technological cycle of the OF manufacture) provides that the OEO
temperature frequency instability is as in any quartz systems (10
À5 ), i.e., it is
determined by the refraction index of the quartz light-guiding thread. The temperature stabilization of the optical fiber to values ΔT OF /T OF ¼ 10
À3 leads the OEO
instability Δf/f ¼ 10
À8 . It recommended to provide the decrease of OEO temperature
instability using methods of the temperature compensation of the optical fiber by the
choice of weight coefficients a thr and a pol of the quartz thread and the polymer
envelope, relatively. This provides the decrease of the temperature coefficient of the
thread refraction index to values Δn OF = n OF ΔT
0
OF
À
Á ¼ 10
À6 to 10
À7 , for example,
during the process of the optical fiber manufacture owing to addition into the quartz
thread of boron and germanium dopes and their oxides, by selection of mutually
compensating dopes into the thread and the envelope of the optical fiber. The
utilization in OEO of differential RF FODL on the base of two or several optical
fibers of the different length is the variant of the temperature compensation.
In previous sections of this chapter, we show that at utilization in OEO of optical
fibers produced according to authors recommendations for the new technology [25]
for manufacturing of the optical fibers with complicate micro-structural thread and
the envelope with application of the high-accuracy method for regulation of plasma
438
7 Optoelectronic oscillator (OEO) as the Time and Spatial Correlator of Random. . .
OEO at variations of FOS parameters, we obtain the new earlier unknown mechanisms of frequency control in OEO:
• The linear at using of DC of Y-type and variations of excitations coefficients in
the single optical channel.
• The quasi-linear at using of DC of Y-type and variations of excitation coefficients
in two optical channels.
• The periodic at using of DC of Х-type by means of longitudinal optical coupling.
Considered methods of OEO frequency control are new and not-studied in
publications and they expand the application areas of OEO. New devices, which
use in its base the described methods of OEO frequency control, are protected by
Russian patents.
We show that the OEO long-term frequency instability with utilization of “specific” optical fibers can achieve 10
À8 . To provide the high-stability generation, we
can use relatively low-Q tuned RF filter (which is nonexpensive) and the stable RF
FODL with the large delay time (10–25 μs), for example, on the base of the single
light guide. At that, the benefit in frequency stability is determined by the ratio of the
signal delay in the optical part of OEO with RF FODL to the time constant of the
RF part.
This benefit is 20–300. There is a possibility to improve the indices of RF highstable low-noise microwave oscillators, which operate at room temperatures on the
principle of frequency pulling by the high-Q external resonators owing to the
structure of OEO with RF FODL. This approach does not resort of the complicate
and expensive methods of PLL systems in the microwave range. The decrease of
weight coefficients till values 10
À2 by reduction of the thickness of the protective
polymer envelope to 1–2 μm (or without formation of the polymer envelope of the
optical fiber at the technological cycle of the OF manufacture) provides that the OEO
temperature frequency instability is as in any quartz systems (10
À5 ), i.e., it is
determined by the refraction index of the quartz light-guiding thread. The temperature stabilization of the optical fiber to values ΔT OF /T OF ¼ 10
À3 leads the OEO
instability Δf/f ¼ 10
À8 . It recommended to provide the decrease of OEO temperature
instability using methods of the temperature compensation of the optical fiber by the
choice of weight coefficients a thr and a pol of the quartz thread and the polymer
envelope, relatively. This provides the decrease of the temperature coefficient of the
thread refraction index to values Δn OF = n OF ΔT
0
OF
À
Á ¼ 10
À6 to 10
À7 , for example,
during the process of the optical fiber manufacture owing to addition into the quartz
thread of boron and germanium dopes and their oxides, by selection of mutually
compensating dopes into the thread and the envelope of the optical fiber. The
utilization in OEO of differential RF FODL on the base of two or several optical
fibers of the different length is the variant of the temperature compensation.
In previous sections of this chapter, we show that at utilization in OEO of optical
fibers produced according to authors recommendations for the new technology [25]
for manufacturing of the optical fibers with complicate micro-structural thread and
the envelope with application of the high-accuracy method for regulation of plasma
438
7 Optoelectronic oscillator (OEO) as the Time and Spatial Correlator of Random. . .