We should note that small proper phase noises at RF FODL output are from À110
to À40 dB/Hz, which are determined by the laser phase noise. Phase noises of
QWLD for the offset (1/10) kHz are À100 to À120 dB/Hz and hence, the coherence
length is up to 50 km.
A possibility to achieve the high-accurate relative alignment (up to 10
À1 to 10
À3 )
of the optical power in the channel of MZ modulator interferometer and in RF FODL
directional optical couplers permits reduction of laser phase noises to values of
electronic noises. This possibility can be granted by optical attenuators at selfheterodyne mixing on the photodetector. In QWLD OEO with the direct and external
modulation, there is a possibility to reduce the OEO phase noises, which are
determined by the quantum nature of spontaneous emission, more than an order
thanks to self-heterodyne mixing.
From the analysis of above formulas, it follows that for phase noise reduction due
to self-heterodyne mixing, it is necessary to suppress the “third” or the one from the
“sideband optical harmonics”, i.e., to provide the narrowband laser. Phase noise
reduction at self-heterodyne mixing depends in this case on not only temporal but on
the spatial source coherence in the transverse section.
Self-heterodyne mixing in OEO with application of the MZ modulator (Fig. 2.1),
thanks to laser noises correlation, as is shown in Chap. 7, gives a possibility to
suppress the OEO phase noise caused by detected laser noises by 10–15 dB/Hz.
2.6 Integration in Future Optical and Optoelectronic
Systems
OEO has potentially two and more different input/output terminals: optical and
electrical (in microwave range). A presence of two outputs broadens the functional
possibilities of OEO application in optoelectronic systems of future generation of
devices for high-stable precision oscillation formation. Oscillations on the microwave carrier pass from the electric microwave output to inputs of signal consumers—frequency multipliers, amplifiers, modulators, and the recording devices
(the spectrum analyzer, frequency-meters etc.). From the optical output, the microwave-modulated/non-modulated optical emission of QWLD is applied (if necessary)
to optical channel of data transmission, to systems of optical data processing, etc.
When using the optical output, we can provide the full galvanic and microwave
decoupling of OEO with its output load. For example, we must transmit the signal
from OEO optical output to the external (outside the OEO structure) second photodetector of another device, and from the second photodetector output, the signal may
pass to the output amplifier. Such a galvanic optical decoupling essentially
(by 10–20 dB) reduces the OEO noise level, which are caused by external noise
sources and be a signal reflected from the load.
34
2 Nanostructural Optoelectronic Oscillators with the Fiber-Optical Delay Line
to À40 dB/Hz, which are determined by the laser phase noise. Phase noises of
QWLD for the offset (1/10) kHz are À100 to À120 dB/Hz and hence, the coherence
length is up to 50 km.
A possibility to achieve the high-accurate relative alignment (up to 10
À1 to 10
À3 )
of the optical power in the channel of MZ modulator interferometer and in RF FODL
directional optical couplers permits reduction of laser phase noises to values of
electronic noises. This possibility can be granted by optical attenuators at selfheterodyne mixing on the photodetector. In QWLD OEO with the direct and external
modulation, there is a possibility to reduce the OEO phase noises, which are
determined by the quantum nature of spontaneous emission, more than an order
thanks to self-heterodyne mixing.
From the analysis of above formulas, it follows that for phase noise reduction due
to self-heterodyne mixing, it is necessary to suppress the “third” or the one from the
“sideband optical harmonics”, i.e., to provide the narrowband laser. Phase noise
reduction at self-heterodyne mixing depends in this case on not only temporal but on
the spatial source coherence in the transverse section.
Self-heterodyne mixing in OEO with application of the MZ modulator (Fig. 2.1),
thanks to laser noises correlation, as is shown in Chap. 7, gives a possibility to
suppress the OEO phase noise caused by detected laser noises by 10–15 dB/Hz.
2.6 Integration in Future Optical and Optoelectronic
Systems
OEO has potentially two and more different input/output terminals: optical and
electrical (in microwave range). A presence of two outputs broadens the functional
possibilities of OEO application in optoelectronic systems of future generation of
devices for high-stable precision oscillation formation. Oscillations on the microwave carrier pass from the electric microwave output to inputs of signal consumers—frequency multipliers, amplifiers, modulators, and the recording devices
(the spectrum analyzer, frequency-meters etc.). From the optical output, the microwave-modulated/non-modulated optical emission of QWLD is applied (if necessary)
to optical channel of data transmission, to systems of optical data processing, etc.
When using the optical output, we can provide the full galvanic and microwave
decoupling of OEO with its output load. For example, we must transmit the signal
from OEO optical output to the external (outside the OEO structure) second photodetector of another device, and from the second photodetector output, the signal may
pass to the output amplifier. Such a galvanic optical decoupling essentially
(by 10–20 dB) reduces the OEO noise level, which are caused by external noise
sources and be a signal reflected from the load.
34
2 Nanostructural Optoelectronic Oscillators with the Fiber-Optical Delay Line