2.6.1 New Methods of Optical and Optoelectronic Frequency
Control of the RF Oscillators
One of the important OEO advantages is a possibility of generated frequency control
with the help of optical and optoelectronic methods using the differential RF FODL
and the fiber-optical discriminators. Authors of this book patented [3, 20, 21] and
theoretically and experimentally investigated new types of OEO radio-frequency
control including the variation of the pumping current and of the laser optical
frequency. The OEO RF frequency control is performed at variation of the RF
FODL phase-frequency response. One of the methods of OEO frequency control
is the approach developed by authors and using RF FODL with various geometric
lengths. Variations of the entry optical power into fibers with different lengths lead to
the OEO microwave frequency variations. One of the important achievements of
OEO revealed by authors is broadening of the RF frequency control possibilities by
the purely optical and optoelectronic methods using for this of differential RF FODL
and different fiber-optical discriminators.
2.6.2 Nonlinearities in OEO
OEO represents the oscillating system with various types of nonlinearities. Besides
the “traditional” nonlinearity of the electronic amplifier in the OEO feedback loop, at
studying of oscillation passing through the feedback loop, we need to keep in mind
that potentially there are additional and enough complicate for investigations the
nonlinearities of the photodiode, the laser, the modulator as well as nonlinearity of
the fiber-optical light guider. In OEO, there are also the various versions of nonlinear
laws: quadratic and cubic (the laser diode with internal modulation by the pumping
current, and the photodiode), the cosine nonlinearity (the Mach–Zehnder modulator), and others. For instance, the cosine nonlinearity of the MZ modulator can be
used for multiplication by the even number of times of the subcarrier frequency of
optical oscillations [4].
The analysis and experimental results of the signal transmission system with the
ultralow noise level (À100 dB/Hz at 1-Hz offset) are presented in [5]. Authors of this
paper describe an expression for the transfer function of the MZ modulator for large
oscillation amplitude on the electric MZ input. The transfer function in this paper is
presented as a sum of terms of even and odd harmonics of Bessel functions. At that,
the nonlinear function of the oscillation amplitude of the first harmonic is determined
by the even and odd Bessel functions.
Nonlinearity in lengthy quartz single-mode optical fibers with the geometric
length from 1 to 12 km is manifested at development of large power densities in
the optical thread at the level of 20–500 mW/1 μ
2 at average continuous powers
20–200 mW of QWLD emission. The threshold power level, at which nonlinear
effects begin to become apparent, depends on a type and a length of the optical fiber,
2.6 Integration in Future Optical and Optoelectronic Systems
35
Control of the RF Oscillators
One of the important OEO advantages is a possibility of generated frequency control
with the help of optical and optoelectronic methods using the differential RF FODL
and the fiber-optical discriminators. Authors of this book patented [3, 20, 21] and
theoretically and experimentally investigated new types of OEO radio-frequency
control including the variation of the pumping current and of the laser optical
frequency. The OEO RF frequency control is performed at variation of the RF
FODL phase-frequency response. One of the methods of OEO frequency control
is the approach developed by authors and using RF FODL with various geometric
lengths. Variations of the entry optical power into fibers with different lengths lead to
the OEO microwave frequency variations. One of the important achievements of
OEO revealed by authors is broadening of the RF frequency control possibilities by
the purely optical and optoelectronic methods using for this of differential RF FODL
and different fiber-optical discriminators.
2.6.2 Nonlinearities in OEO
OEO represents the oscillating system with various types of nonlinearities. Besides
the “traditional” nonlinearity of the electronic amplifier in the OEO feedback loop, at
studying of oscillation passing through the feedback loop, we need to keep in mind
that potentially there are additional and enough complicate for investigations the
nonlinearities of the photodiode, the laser, the modulator as well as nonlinearity of
the fiber-optical light guider. In OEO, there are also the various versions of nonlinear
laws: quadratic and cubic (the laser diode with internal modulation by the pumping
current, and the photodiode), the cosine nonlinearity (the Mach–Zehnder modulator), and others. For instance, the cosine nonlinearity of the MZ modulator can be
used for multiplication by the even number of times of the subcarrier frequency of
optical oscillations [4].
The analysis and experimental results of the signal transmission system with the
ultralow noise level (À100 dB/Hz at 1-Hz offset) are presented in [5]. Authors of this
paper describe an expression for the transfer function of the MZ modulator for large
oscillation amplitude on the electric MZ input. The transfer function in this paper is
presented as a sum of terms of even and odd harmonics of Bessel functions. At that,
the nonlinear function of the oscillation amplitude of the first harmonic is determined
by the even and odd Bessel functions.
Nonlinearity in lengthy quartz single-mode optical fibers with the geometric
length from 1 to 12 km is manifested at development of large power densities in
the optical thread at the level of 20–500 mW/1 μ
2 at average continuous powers
20–200 mW of QWLD emission. The threshold power level, at which nonlinear
effects begin to become apparent, depends on a type and a length of the optical fiber,
2.6 Integration in Future Optical and Optoelectronic Systems
35