on the entry power of laser emission into the optical fiber, as well as on the spectral
line width of QWLD emission and parameters of effective section of the fiber
[6]. The multi-photon nonlinear effects arising due to direct and inverse Brillouin
scattering [7, 8] are the most extensively studied. We can increase the threshold
power of nonlinear optical effects by 10–20 times by means of use in RF FODL of
specific micro-structured optical fibers, which transverse sections are represented in
Fig. 2.13 (see later). In the optical disk resonators (ODR) with the diameter
1–10 mm, their nonlinearity is clearly demonstrated at entry powers 10–100 μW
of optical emission. At that, nonlinear effects not only cause the spectral stochastic
noises of oscillations, but lead to the high temperature instability of the natural ODR
frequency. Unfortunately, this does not give a possibility to use ODR in OEO as the
passive high-Q resonators and filters in RF FODL.
2.6.3 Dispersion RF FODL in OEO
In the general case, RF FODL is characterized by dispersion properties, i.e., its delay
depends on the optical oscillation frequency generated by a laser. The modern smalldispersion optical fibers are characterized by the spectral linear delay of order
(1–10) ps/(nm/km). On the other hand, there are specific dispersive optical fibers
permitting to implement both negative and positive dispersion of 100–1000 ps/
(nm/km).
The delay line dispersion leads to distortions of the generated signal spectrum, an
appearance of additional spurious components in the RF signal spectrum (due to
combination with nonlinear effects in FOS), which is accompanied by spreading of
the laser spectral line. Nevertheless, as we show in Chap. 7, their level is demonstrated in small-dispersive optical fibers at the spectral line width of the modulated
light sources more than 500 MHz and for fiber lengths more than 10 km.
2.6.4 Types of Optoelectronic Oscillators by the Composition
of Modulated Light Source
Utilization of different types of the modulated light sources in OEO depends on the
oscillator destination. For instance, in OEO of RF range (in the measuring fiberoptical systems), it is expedient to apply the laser diode (or the light-emitting diode)
with low-frequency internal modulation. In OEO of microwave range (in devices for
signal formation, say, for communication systems or for radar systems), the efficient
QWLD with internal modulation or QWLD with the external absorption modulator
are more promising. In low-noise microwave and mm-wave oscillators (8–30 GHz),
QWLD with MZ modulator can be used.
36
2 Nanostructural Optoelectronic Oscillators with the Fiber-Optical Delay Line
line width of QWLD emission and parameters of effective section of the fiber
[6]. The multi-photon nonlinear effects arising due to direct and inverse Brillouin
scattering [7, 8] are the most extensively studied. We can increase the threshold
power of nonlinear optical effects by 10–20 times by means of use in RF FODL of
specific micro-structured optical fibers, which transverse sections are represented in
Fig. 2.13 (see later). In the optical disk resonators (ODR) with the diameter
1–10 mm, their nonlinearity is clearly demonstrated at entry powers 10–100 μW
of optical emission. At that, nonlinear effects not only cause the spectral stochastic
noises of oscillations, but lead to the high temperature instability of the natural ODR
frequency. Unfortunately, this does not give a possibility to use ODR in OEO as the
passive high-Q resonators and filters in RF FODL.
2.6.3 Dispersion RF FODL in OEO
In the general case, RF FODL is characterized by dispersion properties, i.e., its delay
depends on the optical oscillation frequency generated by a laser. The modern smalldispersion optical fibers are characterized by the spectral linear delay of order
(1–10) ps/(nm/km). On the other hand, there are specific dispersive optical fibers
permitting to implement both negative and positive dispersion of 100–1000 ps/
(nm/km).
The delay line dispersion leads to distortions of the generated signal spectrum, an
appearance of additional spurious components in the RF signal spectrum (due to
combination with nonlinear effects in FOS), which is accompanied by spreading of
the laser spectral line. Nevertheless, as we show in Chap. 7, their level is demonstrated in small-dispersive optical fibers at the spectral line width of the modulated
light sources more than 500 MHz and for fiber lengths more than 10 km.
2.6.4 Types of Optoelectronic Oscillators by the Composition
of Modulated Light Source
Utilization of different types of the modulated light sources in OEO depends on the
oscillator destination. For instance, in OEO of RF range (in the measuring fiberoptical systems), it is expedient to apply the laser diode (or the light-emitting diode)
with low-frequency internal modulation. In OEO of microwave range (in devices for
signal formation, say, for communication systems or for radar systems), the efficient
QWLD with internal modulation or QWLD with the external absorption modulator
are more promising. In low-noise microwave and mm-wave oscillators (8–30 GHz),
QWLD with MZ modulator can be used.
36
2 Nanostructural Optoelectronic Oscillators with the Fiber-Optical Delay Line