process (determined by the spontaneous noise) and occurs with the time constant
(or the carrier lifetime on the upper energy level) of 10
À9 to 10
À8 s.
Description of excitation and oscillation propagation in the OEO RF part (in the
nonlinear amplifier, the filter and in electric circuits) is performed in this book by
traditional methods using the apparatus of the circuit theory and the nonlinear
oscillation theory. The time constant of OEO RF filter with the Q-factor of
100–1000 on the frequency, for example, of 10 GHz is about 10
À8 to 10
À7 s. At
that, this time constant is much more or congruent than the time constant of the laser
(or QWLD) optical, which is 10
À12 to 10
À6 s.
We may note that two oscillating processes are simultaneously developed and
observed in OEO in different ranges: optical and RF with frequency ratio approximately 1:2800. In other words, we may separate two different oscillating processes
in OEO on different frequencies or to say about different types of generators—the
optical quantum generator with generating frequency about ν 0 ¼ 128 THz and the
RF generator with generating frequency f 0 ¼ 1–100 GHz. At that, the optical
quantum generator in the OEO structure is as if the pumping source for the RF
generator. If the laser or QWLD can be separated in OEO in the single unit (Fig. 2.2),
then the RF generator includes the laser or QWLD. On the other hand, OEO may be
represented at mathematical modeling in specific cases by the equivalent circuit of
the traditional RF oscillator with laser presentation by various mathematical models,
including the simplest one: the linear or nonlinear element with the relatively simple
transfer function. For example, RF FODL in the OEO structure can be presented by
the linear two-port circuit, which is described by the Y-matrix with given input and
output admittance. In the further analysis in Chaps. 3 and 7, at OEO investigation,
we use mathematical models based on differential equations.
Spectra of two oscillating processes in OEO are formed by fluctuations of
different nature, and the final width of the OEO RF spectral line is determined by
parameters of two resonant systems—the optical laser cavity and the RF filter in the
OEO structure. The interesting OEO feature is that the RF oscillation spectrum is
formed by not only noises, which have an electronic nature, but the phase fluctuations of the laser optical emission, which have the quantum nature and are determined by spontaneous laser emission.
In the optical range, in low-noise microwave OEOs, transverse section sizes of
the photodetection area (or the emission “spot” on the light-sensitive area of the
photodetector) are commensurate with the laser wavelength. As a result of
interference on the photodetector area of two optical oscillations and photodetection,
the useful electric signal is extracted on the photodetector load. In contrast to the RF
range, in which transverse geometrical sizes of the detector chip (for instance, the
semiconductor diode) are 10–1000 times less than the wavelength of electromagnetic oscillations, which fall to this detector. In the optical range sizes of the
photodetector light-sensitive area (used in the low-noise OEOs, which operate on
frequencies above 0.3 GHz) are comparable with the laser emission wavelength and
are 1.5 μm. In this case, the model of the plane electromagnetic wave for the OEO
optical units and the photodetector area must be applied with a big prudence.
2.1 Operation Principle and Functional Diagram of OEO with RF FODL
23
(or the carrier lifetime on the upper energy level) of 10
À9 to 10
À8 s.
Description of excitation and oscillation propagation in the OEO RF part (in the
nonlinear amplifier, the filter and in electric circuits) is performed in this book by
traditional methods using the apparatus of the circuit theory and the nonlinear
oscillation theory. The time constant of OEO RF filter with the Q-factor of
100–1000 on the frequency, for example, of 10 GHz is about 10
À8 to 10
À7 s. At
that, this time constant is much more or congruent than the time constant of the laser
(or QWLD) optical, which is 10
À12 to 10
À6 s.
We may note that two oscillating processes are simultaneously developed and
observed in OEO in different ranges: optical and RF with frequency ratio approximately 1:2800. In other words, we may separate two different oscillating processes
in OEO on different frequencies or to say about different types of generators—the
optical quantum generator with generating frequency about ν 0 ¼ 128 THz and the
RF generator with generating frequency f 0 ¼ 1–100 GHz. At that, the optical
quantum generator in the OEO structure is as if the pumping source for the RF
generator. If the laser or QWLD can be separated in OEO in the single unit (Fig. 2.2),
then the RF generator includes the laser or QWLD. On the other hand, OEO may be
represented at mathematical modeling in specific cases by the equivalent circuit of
the traditional RF oscillator with laser presentation by various mathematical models,
including the simplest one: the linear or nonlinear element with the relatively simple
transfer function. For example, RF FODL in the OEO structure can be presented by
the linear two-port circuit, which is described by the Y-matrix with given input and
output admittance. In the further analysis in Chaps. 3 and 7, at OEO investigation,
we use mathematical models based on differential equations.
Spectra of two oscillating processes in OEO are formed by fluctuations of
different nature, and the final width of the OEO RF spectral line is determined by
parameters of two resonant systems—the optical laser cavity and the RF filter in the
OEO structure. The interesting OEO feature is that the RF oscillation spectrum is
formed by not only noises, which have an electronic nature, but the phase fluctuations of the laser optical emission, which have the quantum nature and are determined by spontaneous laser emission.
In the optical range, in low-noise microwave OEOs, transverse section sizes of
the photodetection area (or the emission “spot” on the light-sensitive area of the
photodetector) are commensurate with the laser wavelength. As a result of
interference on the photodetector area of two optical oscillations and photodetection,
the useful electric signal is extracted on the photodetector load. In contrast to the RF
range, in which transverse geometrical sizes of the detector chip (for instance, the
semiconductor diode) are 10–1000 times less than the wavelength of electromagnetic oscillations, which fall to this detector. In the optical range sizes of the
photodetector light-sensitive area (used in the low-noise OEOs, which operate on
frequencies above 0.3 GHz) are comparable with the laser emission wavelength and
are 1.5 μm. In this case, the model of the plane electromagnetic wave for the OEO
optical units and the photodetector area must be applied with a big prudence.
2.1 Operation Principle and Functional Diagram of OEO with RF FODL
23