One of the features of the structure shown in Fig. 3.9b is a presence of the fiber
optical system of the differential type. It is formed by two optical fibers having the
different delay time T 1 and T 2 . The presence of such FOS allows, as it is shown
below and in Chap. 6, not only performing the selection of optical harmonics and
execution of the mode with the single sideband frequency, but the essential reduction
of the phase noise of RF oscillations.
The promising OEO structure with the direct modulation by the pumping current
without RF amplifier is presented in Fig. 3.9c. Oscillation amplification is performed
in the optical OEO part by the optical amplifier A2 in FOS. The output RF oscillation
is formed in the output by the external photodetector PD2. Such a structure has a
series of advantages, which will be discussed in Chap. 6. The potentially possible
reduction of the phase noise owing to elimination of the RF amplifier noises can be
attributed to the one from these advantages. The absence of RF matching blocks,
compactness, and manufacturability are concerned to another advantages.
Mentioned OEO structures are integrated into the single class—they contain the
main OEO element—the optical quantum generator with external or internal modulator (installed in the laser resonator) and the optoelectronic network of the positive
feedback, which covers the modulated source of the laser emission. The given
optoelectronic network contains the optical fiber, the photodetector, the RF amplifier
and the RF filter. The different elements operating in the radio-frequency and optical
frequency ranges can be included into the optoelectronic section.
Let us analyze the operation of mentioned OEO structures (Fig. 3.1). The primary
analysis consists in formation of equations of amplitude and phase balance, formation of symbolic and abbreviated differential equations of OEO. For this, it is
necessary, as usual in any dynamic systems, to offer a description of modulation
methods of laser emission and to determine the transfer functions for components
included in OEO. Because the OEO under consideration represents the device with
low phase noise, we shall at once pay attention to noise when providing description
of modulation methods.
3.2 Methods of Modulation and Heterodyning of Laser
Emissions at DM and MZ Modulations
Let us consider structures with direct internal modulation of the quantum-well laser
diode (QWLD). The intensity modulation of QWLD is performed by variation of the
pumping current. In OEO MZ structures, the emission modulation of QWLD is
performed by the external Mach–Zehnder modulator.
⁄
ä
Fig. 3.9 (continued) optical system of OEO and external photodetector PD2. OF2 is the optical
filter 2, OC2 is the optical coupler 2, PD1 is the photodetector 1, PD2 is the photodetector 2
3.2 Methods of Modulation and Heterodyning of Laser Emissions at DM and MZ. . .
93
optical system of the differential type. It is formed by two optical fibers having the
different delay time T 1 and T 2 . The presence of such FOS allows, as it is shown
below and in Chap. 6, not only performing the selection of optical harmonics and
execution of the mode with the single sideband frequency, but the essential reduction
of the phase noise of RF oscillations.
The promising OEO structure with the direct modulation by the pumping current
without RF amplifier is presented in Fig. 3.9c. Oscillation amplification is performed
in the optical OEO part by the optical amplifier A2 in FOS. The output RF oscillation
is formed in the output by the external photodetector PD2. Such a structure has a
series of advantages, which will be discussed in Chap. 6. The potentially possible
reduction of the phase noise owing to elimination of the RF amplifier noises can be
attributed to the one from these advantages. The absence of RF matching blocks,
compactness, and manufacturability are concerned to another advantages.
Mentioned OEO structures are integrated into the single class—they contain the
main OEO element—the optical quantum generator with external or internal modulator (installed in the laser resonator) and the optoelectronic network of the positive
feedback, which covers the modulated source of the laser emission. The given
optoelectronic network contains the optical fiber, the photodetector, the RF amplifier
and the RF filter. The different elements operating in the radio-frequency and optical
frequency ranges can be included into the optoelectronic section.
Let us analyze the operation of mentioned OEO structures (Fig. 3.1). The primary
analysis consists in formation of equations of amplitude and phase balance, formation of symbolic and abbreviated differential equations of OEO. For this, it is
necessary, as usual in any dynamic systems, to offer a description of modulation
methods of laser emission and to determine the transfer functions for components
included in OEO. Because the OEO under consideration represents the device with
low phase noise, we shall at once pay attention to noise when providing description
of modulation methods.
3.2 Methods of Modulation and Heterodyning of Laser
Emissions at DM and MZ Modulations
Let us consider structures with direct internal modulation of the quantum-well laser
diode (QWLD). The intensity modulation of QWLD is performed by variation of the
pumping current. In OEO MZ structures, the emission modulation of QWLD is
performed by the external Mach–Zehnder modulator.
⁄
ä
Fig. 3.9 (continued) optical system of OEO and external photodetector PD2. OF2 is the optical
filter 2, OC2 is the optical coupler 2, PD1 is the photodetector 1, PD2 is the photodetector 2
3.2 Methods of Modulation and Heterodyning of Laser Emissions at DM and MZ. . .
93