oscillator of microwave or mm-wave ranges. Utilization of the quantum-well laser
diodes in OEO with the low phase noise level; the active low-noise delay line on the
base of the optical fiber; the phase noise heterodyning on the phase-detector area;
application the modulation methods with the single sideband optical frequency at
suppression of the optical carrier in the optical channel can be attributed to these
methods.
In this chapter beginning, the OEO functional diagrams with direct and external
modulation of optical emission are presented, the mathematical description of
components including in OEO is given: a laser, the optical fiber, the photodetector,
the RF amplifier, the RF filter. Furthermore, to widen knowledge about OEO
functional possibilities, the various OEO variants, which improve its operation
characteristics, are presented.
The variant with direct modulation of the laser pumping current and the external
photodetector; the variant with external electro-optical Mach–Zehnder modulator for
laser emission; the variant with laser emission modulation in both MZ optical
channels; the variant of OEO without the RF amplifier but with optical amplifier
located in the OEO fiber optical system and with the external photodetector can be
attributed to these variants of improvement. It is proved that the special interest can
be demonstrated by variants with the external photodetector, since requirements to
elements of electrical matching essentially decrease, and the same situation with the
variants with double modulation in both MZ optical channels.
The special role in this chapter is derived to the laser representation in OEO as the
main source of fluctuations which have the quantum nature. It is shown that the
dispersion on the laser phase noise is defined by the carrier noise dispersion and
depends on the lifetime at the excited level. The level of the OEO phase noise is
defined by the laser phase noise, which depends on the lifetime.
The OEO model is considered taking into account of the correlator of the laser
phase noise, which is formed by the laser, the optical MZ modulator and the
photodetector. It is shown that at the closed feedback loop in OEO MZ, the spectrum
at the photodetector output has the Lorentzian shape, is defined by the laser phase
noises, while its maximal value depends on the ratio of time constants. Effectiveness
of noise suppression in OEO is not only defined by the fiber length, but also depends
on the ratio of the laser coherence time and the delay line in the optical fiber.
At consideration of the modulation methods in OEO, we showed that the transfer
mode in realized (from the laser and the modulator to the photodetector area) of two
optical harmonics of laser emission with optical frequencies of ν 0 and ν 0 À f 0 . The
transmission mode with the single sideband optical frequency, which is shifted from
the optical carrier, is examined. In this mode, the ultralow phase noise level of RF
oscillations in microwave and mm-wave ranges and the high short-term frequency
stability are provided, owing to the interference of two rigidly correlated optical
oscillations on the light-sensitivity photodetector area. Another important conclusion is the fact that in OEO DM and OEO MZ, the mode of radio-frequency doubling
is possible. In this mode, the significant possibility of DC optical component
suppression of laser emission is provided; the essential level of this component
degrades the OEO phase noises. In this case, we must introduce in OEO DM the
3.5 Conclusions
129
diodes in OEO with the low phase noise level; the active low-noise delay line on the
base of the optical fiber; the phase noise heterodyning on the phase-detector area;
application the modulation methods with the single sideband optical frequency at
suppression of the optical carrier in the optical channel can be attributed to these
methods.
In this chapter beginning, the OEO functional diagrams with direct and external
modulation of optical emission are presented, the mathematical description of
components including in OEO is given: a laser, the optical fiber, the photodetector,
the RF amplifier, the RF filter. Furthermore, to widen knowledge about OEO
functional possibilities, the various OEO variants, which improve its operation
characteristics, are presented.
The variant with direct modulation of the laser pumping current and the external
photodetector; the variant with external electro-optical Mach–Zehnder modulator for
laser emission; the variant with laser emission modulation in both MZ optical
channels; the variant of OEO without the RF amplifier but with optical amplifier
located in the OEO fiber optical system and with the external photodetector can be
attributed to these variants of improvement. It is proved that the special interest can
be demonstrated by variants with the external photodetector, since requirements to
elements of electrical matching essentially decrease, and the same situation with the
variants with double modulation in both MZ optical channels.
The special role in this chapter is derived to the laser representation in OEO as the
main source of fluctuations which have the quantum nature. It is shown that the
dispersion on the laser phase noise is defined by the carrier noise dispersion and
depends on the lifetime at the excited level. The level of the OEO phase noise is
defined by the laser phase noise, which depends on the lifetime.
The OEO model is considered taking into account of the correlator of the laser
phase noise, which is formed by the laser, the optical MZ modulator and the
photodetector. It is shown that at the closed feedback loop in OEO MZ, the spectrum
at the photodetector output has the Lorentzian shape, is defined by the laser phase
noises, while its maximal value depends on the ratio of time constants. Effectiveness
of noise suppression in OEO is not only defined by the fiber length, but also depends
on the ratio of the laser coherence time and the delay line in the optical fiber.
At consideration of the modulation methods in OEO, we showed that the transfer
mode in realized (from the laser and the modulator to the photodetector area) of two
optical harmonics of laser emission with optical frequencies of ν 0 and ν 0 À f 0 . The
transmission mode with the single sideband optical frequency, which is shifted from
the optical carrier, is examined. In this mode, the ultralow phase noise level of RF
oscillations in microwave and mm-wave ranges and the high short-term frequency
stability are provided, owing to the interference of two rigidly correlated optical
oscillations on the light-sensitivity photodetector area. Another important conclusion is the fact that in OEO DM and OEO MZ, the mode of radio-frequency doubling
is possible. In this mode, the significant possibility of DC optical component
suppression of laser emission is provided; the essential level of this component
degrades the OEO phase noises. In this case, we must introduce in OEO DM the
3.5 Conclusions
129