• Owing to the fiber-optical delay line with the geometrical length more than
1000 m (the suppression coefficient due to the length, which was analyzed in
Chap. 6).
• Owing to utilization in OEO of QWLD with ultralow phase noises (relatively,
PSD of the phase noise of QWLD is equal À95 to À120 dBm/Hz at the offset
1–10 kHz from the optical carrier).
• Owing to suppression of the DC component of the laser emission passed to the
photodetector and, accordingly, the suppression coefficient is equal to 0.01–0.1.
• Owing to the statistical correlation of noises at combination of the side optical
harmonics in the photodetector (accordingly, the suppression coefficient is equal
to 0.001–0.1).
The process of spectra convolution of the detected laser phase noise with the
spectrum of the total electronic noise has the new character from the point of view of
oscillations theory and the statistical communication theory. We know that the
spectrum of the electronic noise is well described (to the accuracy of constants
C 1E , C 2E ) by the formula S EPN F
ð Þ %
C 1E
F
2 þ
C 2E
F
3
. The convolution of detected laser
phase S LPN (F), the view of which can be characterized by the Lorentzian curve with
the spectrum of the electronic noise S EPN (F), gives the new type compared to the
Lorentzian curve.
The joint suppression factor of the own electronic noises S PNE (F) in OEO varies
and takes values K 1Γ (F) Á K 2Γ (F) Á K 3Γ (F) ¼ 0.1 – 0.001.
Besides other, the laser coherence time, the irregularity of excitation coefficient of
MZ optical channel effect on the level of PSD of the phase noise in OEO. Limitation
in equalization of excitation coefficients of MZ optical channels leads to the limit
values of the DC laser emission suppression, which introduce the significant contribution into the level of PSD of the phase noise owing to the nonlinear conversion of
phase noises in the photodetector.
The described theory of passive and active waveguides (taking into account of
nonsymmetry of optical channels) allows development of the mathematic apparatus
for waveguide modeling in modulators and differential delay lines, which are used in
OEO MZ and in OEO DM.
The structure of OEO MZ can be treated as the coherent optical processor or the
spatial correlator with utilization of spatial filtering. The convolution operations not
only in optical and RF ranges, but the spectra convolution operation on the spatial
frequencies may be executed in OEO. As spatial filters, we can use the miniature
circular and sector spatial filters, which are well-studied in publications on the
Fourier optics.
Obtained calculated and experimental variations of PFC and the time constant of
QWLD (or the value of PFC on the modulation frequency f m divided by the value of
the given frequency) T LD ¼ φ LD /(2πf m ) give a possibility to perform measurements
of the light time delays (with application of given types of QWLDs as the modulated
light source) in FOS and in fiber-optical light guides with the help of self-oscillation
methods [30] not worse than 2 Â 10
À3 ns, which is equivalent, for instance, to
7.8 Conclusions
461
1000 m (the suppression coefficient due to the length, which was analyzed in
Chap. 6).
• Owing to utilization in OEO of QWLD with ultralow phase noises (relatively,
PSD of the phase noise of QWLD is equal À95 to À120 dBm/Hz at the offset
1–10 kHz from the optical carrier).
• Owing to suppression of the DC component of the laser emission passed to the
photodetector and, accordingly, the suppression coefficient is equal to 0.01–0.1.
• Owing to the statistical correlation of noises at combination of the side optical
harmonics in the photodetector (accordingly, the suppression coefficient is equal
to 0.001–0.1).
The process of spectra convolution of the detected laser phase noise with the
spectrum of the total electronic noise has the new character from the point of view of
oscillations theory and the statistical communication theory. We know that the
spectrum of the electronic noise is well described (to the accuracy of constants
C 1E , C 2E ) by the formula S EPN F
ð Þ %
C 1E
F
2 þ
C 2E
F
3
. The convolution of detected laser
phase S LPN (F), the view of which can be characterized by the Lorentzian curve with
the spectrum of the electronic noise S EPN (F), gives the new type compared to the
Lorentzian curve.
The joint suppression factor of the own electronic noises S PNE (F) in OEO varies
and takes values K 1Γ (F) Á K 2Γ (F) Á K 3Γ (F) ¼ 0.1 – 0.001.
Besides other, the laser coherence time, the irregularity of excitation coefficient of
MZ optical channel effect on the level of PSD of the phase noise in OEO. Limitation
in equalization of excitation coefficients of MZ optical channels leads to the limit
values of the DC laser emission suppression, which introduce the significant contribution into the level of PSD of the phase noise owing to the nonlinear conversion of
phase noises in the photodetector.
The described theory of passive and active waveguides (taking into account of
nonsymmetry of optical channels) allows development of the mathematic apparatus
for waveguide modeling in modulators and differential delay lines, which are used in
OEO MZ and in OEO DM.
The structure of OEO MZ can be treated as the coherent optical processor or the
spatial correlator with utilization of spatial filtering. The convolution operations not
only in optical and RF ranges, but the spectra convolution operation on the spatial
frequencies may be executed in OEO. As spatial filters, we can use the miniature
circular and sector spatial filters, which are well-studied in publications on the
Fourier optics.
Obtained calculated and experimental variations of PFC and the time constant of
QWLD (or the value of PFC on the modulation frequency f m divided by the value of
the given frequency) T LD ¼ φ LD /(2πf m ) give a possibility to perform measurements
of the light time delays (with application of given types of QWLDs as the modulated
light source) in FOS and in fiber-optical light guides with the help of self-oscillation
methods [30] not worse than 2 Â 10
À3 ns, which is equivalent, for instance, to
7.8 Conclusions
461