1.3 μm. Experimental investigations of the optical spectrum, the watt–ampere
characteristics, amplitude and phase responses of the given QWLD sample are
conducted on the special experimental workbench and described in Chap. 4.
The maximal QWLD output power of the optical emission is about 10 mW at the
wavelength 1310 nm. The width of the laser generation spectral line is about 3 nm.
In the experimental breadboard, the wideband (up to 12 GHz) intensity modulation of laser emission occurs by the QWLD bias current. The photodiode on the base
of InGaAsР with the spectral bandwidth of 0.8–1.5 μm is used as the photodetector.
The reverse light reflection from the photodiode butt is À40 to À50 dB.
The experimental QWLD used in the experimental sample of microwave OEO
with RF FODL combines the following functions:
• The semiconductor optical emission source with the high temporal coherence and
the large quantum effectiveness (S LD % 0.5–0.6 W/A) of the microwave oscillation conversion for the QWLD bias current into oscillations of the output laser
emission intensity.
• The ultra-wideband microwave modulator of this emission intensity, which has
the large enough (of the order S OM % 0.5–0.6 W/A) slope of the modulation
characteristic.
• The active electro-optical quasi-resonance microwave filter having a capacity to
wide frequency electronic tuning by the QWLD bias current.
On these wavelengths, the chromatic dispersion and optical losses in the singlemode fiber light guide from the allotted quartz glass are ps/(nm km) and
0.15–0.25 dB/km, relatively, for the QWLD optical emission with the wavelength
of 1.3 μm.
In the OEO structure in Fig. 8.13, an energy of highly coherent optical oscillations (the optical carrier) passes to the photoreceiver (PR) from the QWLD output.
Radio-frequency oscillations (subcarrier) obtained in the photoreceiver pass through
an amplifier (A), the frequency-selective radio-frequency filter (RFF) (which is the
frequency-defining element in the whole range of spectral OEO tuning) and are
directed to the QWLD microwave input through the microwave directional coupler
(DC) in this closed loop. All functional units of the OEO breadboard, mentioned in
Fig. 8.13, are successively and in coordination connected each other into the closed
loop of the positive feedback. If excitation conditions in this structure are satisfied,
then at microwave output, oscillations occur in the microwave range. Oscillation
observation is performed with the help of the C-4-27 spectrum analyzer.
The radio-frequency filter (RFF) represents the dielectric microwave resonator
(DR) made on ceramics with the Q-factor Q % 1000 at average frequency of 8 GHz,
which has the high permittivity and low losses in the microwave range. This RFF is
tuned on the one of its natural resonance frequencies which is equal to about
8.2 GHz. The narrow RFF bandwidth of about 7 MHz allows obtaining of the
single-frequency generation mode of OEO with suppression of the side components
better than 49 dB for different light guide lengths from 1 to 4640 m. To ensure the
single-frequency generation mode with suppression of side components, the special
measures are used. The soft excitation condition is satisfied in the oscillator and the
8.4 Implementation of OEO in the Microwave Range and Its Experimental. . .
483
characteristics, amplitude and phase responses of the given QWLD sample are
conducted on the special experimental workbench and described in Chap. 4.
The maximal QWLD output power of the optical emission is about 10 mW at the
wavelength 1310 nm. The width of the laser generation spectral line is about 3 nm.
In the experimental breadboard, the wideband (up to 12 GHz) intensity modulation of laser emission occurs by the QWLD bias current. The photodiode on the base
of InGaAsР with the spectral bandwidth of 0.8–1.5 μm is used as the photodetector.
The reverse light reflection from the photodiode butt is À40 to À50 dB.
The experimental QWLD used in the experimental sample of microwave OEO
with RF FODL combines the following functions:
• The semiconductor optical emission source with the high temporal coherence and
the large quantum effectiveness (S LD % 0.5–0.6 W/A) of the microwave oscillation conversion for the QWLD bias current into oscillations of the output laser
emission intensity.
• The ultra-wideband microwave modulator of this emission intensity, which has
the large enough (of the order S OM % 0.5–0.6 W/A) slope of the modulation
characteristic.
• The active electro-optical quasi-resonance microwave filter having a capacity to
wide frequency electronic tuning by the QWLD bias current.
On these wavelengths, the chromatic dispersion and optical losses in the singlemode fiber light guide from the allotted quartz glass are ps/(nm km) and
0.15–0.25 dB/km, relatively, for the QWLD optical emission with the wavelength
of 1.3 μm.
In the OEO structure in Fig. 8.13, an energy of highly coherent optical oscillations (the optical carrier) passes to the photoreceiver (PR) from the QWLD output.
Radio-frequency oscillations (subcarrier) obtained in the photoreceiver pass through
an amplifier (A), the frequency-selective radio-frequency filter (RFF) (which is the
frequency-defining element in the whole range of spectral OEO tuning) and are
directed to the QWLD microwave input through the microwave directional coupler
(DC) in this closed loop. All functional units of the OEO breadboard, mentioned in
Fig. 8.13, are successively and in coordination connected each other into the closed
loop of the positive feedback. If excitation conditions in this structure are satisfied,
then at microwave output, oscillations occur in the microwave range. Oscillation
observation is performed with the help of the C-4-27 spectrum analyzer.
The radio-frequency filter (RFF) represents the dielectric microwave resonator
(DR) made on ceramics with the Q-factor Q % 1000 at average frequency of 8 GHz,
which has the high permittivity and low losses in the microwave range. This RFF is
tuned on the one of its natural resonance frequencies which is equal to about
8.2 GHz. The narrow RFF bandwidth of about 7 MHz allows obtaining of the
single-frequency generation mode of OEO with suppression of the side components
better than 49 dB for different light guide lengths from 1 to 4640 m. To ensure the
single-frequency generation mode with suppression of side components, the special
measures are used. The soft excitation condition is satisfied in the oscillator and the
8.4 Implementation of OEO in the Microwave Range and Its Experimental. . .
483