photonic at the end of twentieth century and in beginning of twenty-first century. For
effectiveness increase of modern microwave modulators, the bias electrodes in them
and the microwave electrodes are sprayed “from the top” of optical channels
(Fig. 6.7), and the transverse distance between these channels is reduced to 20 μm.
At that, the channel length is about 2000 μm, and the length of electrodes is about
1000 μm (Fig. 6.7). Electrodes which provide the constant bias, are sprayed directly
near the Y directional coupler (Fig. 6.8). In some MZ modulator models, in order to
increase the modulation effectiveness, the special “thin electron-holes p-n junction”
is formed between the substrate and optical channel. In the simplified structure of the
MZ modulator (Figs. 6.8, 6.10a), in the transverse section, the capacitance C pn of the
p-n junction is shown to be formed between optical channels OC1 and OC2 and the
substrate, and the inter-electrode capacitance С срs is formed between electrodes,
which are connected to channels OC1 and OC2, and the resistor R pn .
For operation of MZ modulator of the microwave range, the polarized emission of
the high-coherent single-frequency laser is required. Quantum-well laser diodes with
the polarizer are such a type of the emission sources.
Output emissions E 1L and E 2L of the first and second channels of the MZ
modulator, in general case, may pass to the photodetector input through the different
light guiders FOS1 and FOS2, and then the delay difference is:
ΔT M ¼ T 2M À T 1M + T FOS2 À T FOS1 .
Figure 6.8a, b show transverse sections of the MZ modulator for different variants
of signal electrodes’ location. The equivalent electrical circuit for connection of the
RF signal and DC bias voltage for the AM 1550 modulator electrodes from
JENOPTIK is presented in Fig. 6.8c.
In the case, when the FOS is formed by the single lengthy optical fiber, the delay
difference is defined as:ΔT M ¼ T 2M À T 1M .
It is necessary to emphasize that the fiber-optical delay line (RF FODL) in ОЕО
MZ is the low-dispersed, i.e., the delay time in FOS is the function of the optical
frequency: T FOS ¼ T FOS (ν). OЕО MZ represents the closed self-oscillating system
with dissipation, in which structure the low-dispersed delay line is included. Specific
MZ construction permits to provide not only the control of the MZ operation point,
but to control of the optical powers in channels OC1 and OC2. Not only temporal
laser coherence affects the MZ modulation effectiveness, but the spatial coherence
as well.
6.3 Mathematical Model of OEO MZ
6.3.1 The Laser in OEO MZ
Below, for the analysis of the QWLD phase noises, we give the fluctuation equations
for the laser deducted with the help of the semiclassical theory, which elements was
demonstrated in Chap. 4. Dynamic character of laser noise characteristics can be
294
6 Operation Analysis of Optoelectronic oscillator (OEO) with External. . .
effectiveness increase of modern microwave modulators, the bias electrodes in them
and the microwave electrodes are sprayed “from the top” of optical channels
(Fig. 6.7), and the transverse distance between these channels is reduced to 20 μm.
At that, the channel length is about 2000 μm, and the length of electrodes is about
1000 μm (Fig. 6.7). Electrodes which provide the constant bias, are sprayed directly
near the Y directional coupler (Fig. 6.8). In some MZ modulator models, in order to
increase the modulation effectiveness, the special “thin electron-holes p-n junction”
is formed between the substrate and optical channel. In the simplified structure of the
MZ modulator (Figs. 6.8, 6.10a), in the transverse section, the capacitance C pn of the
p-n junction is shown to be formed between optical channels OC1 and OC2 and the
substrate, and the inter-electrode capacitance С срs is formed between electrodes,
which are connected to channels OC1 and OC2, and the resistor R pn .
For operation of MZ modulator of the microwave range, the polarized emission of
the high-coherent single-frequency laser is required. Quantum-well laser diodes with
the polarizer are such a type of the emission sources.
Output emissions E 1L and E 2L of the first and second channels of the MZ
modulator, in general case, may pass to the photodetector input through the different
light guiders FOS1 and FOS2, and then the delay difference is:
ΔT M ¼ T 2M À T 1M + T FOS2 À T FOS1 .
Figure 6.8a, b show transverse sections of the MZ modulator for different variants
of signal electrodes’ location. The equivalent electrical circuit for connection of the
RF signal and DC bias voltage for the AM 1550 modulator electrodes from
JENOPTIK is presented in Fig. 6.8c.
In the case, when the FOS is formed by the single lengthy optical fiber, the delay
difference is defined as:ΔT M ¼ T 2M À T 1M .
It is necessary to emphasize that the fiber-optical delay line (RF FODL) in ОЕО
MZ is the low-dispersed, i.e., the delay time in FOS is the function of the optical
frequency: T FOS ¼ T FOS (ν). OЕО MZ represents the closed self-oscillating system
with dissipation, in which structure the low-dispersed delay line is included. Specific
MZ construction permits to provide not only the control of the MZ operation point,
but to control of the optical powers in channels OC1 and OC2. Not only temporal
laser coherence affects the MZ modulation effectiveness, but the spatial coherence
as well.
6.3 Mathematical Model of OEO MZ
6.3.1 The Laser in OEO MZ
Below, for the analysis of the QWLD phase noises, we give the fluctuation equations
for the laser deducted with the help of the semiclassical theory, which elements was
demonstrated in Chap. 4. Dynamic character of laser noise characteristics can be
294
6 Operation Analysis of Optoelectronic oscillator (OEO) with External. . .