laser emission passes through optical fibers to photodetectors PD0, PD1, PD2,. . .
PDN, and after amplification, it is registered. The amplified electrical sinusoidal
oscillation with the voltage amplitude 0.1 V with the frequency 1 GHz (from outputs
of two different photodetectors, for example, PD1 and PD2) passes to the phase
difference meter. The feature of this structure (see Fig. 8.11) is that at the switch Sw
closing in the last right position, the electrical oscillations pass to AOM, which are
created by OEO. In this case, OEO is formed by the LTI-501 laser and by (closed in
the feedback loop) the АОМ modulator, the optical fiber FO0, the photodetector
FD0, the RF nonlinear amplifier NA, and the filter F. From the filter F output
(at satisfying of excitation conditions in OEO), oscillation with the 1 GHz-frequency
pass to the АОМ modulator. At that, the gain in power of the NA amplifier is
50–60 dB. The total gain for the OEO open loop depends on the electrical power
acting on AOM (1 W), on the optical power passing on the light-sensitive area of the
PD0 photodetector (0.01–0.1 mW), the conversion slope of PD (0.5) and optical
losses in the channel.
During experiment according to Fig. 8.11, we investigate: the spatial structure of
the laser emission for various powers from 1 to 28 W (Fig. 8.12); the watt–ampere
laser characteristic; different methods for excitation of optical fibers by the infrared
emission with the wavelength 1.06 μm. Functions of OEO oscillation frequency and
differential phase incursions in channels are experimentally studied at temperature
variations from 0 to 40
C.
The normal operation of OEO with RF FODL was provided in the single-mode
laser generation. During experiments, offsets of the interchannel phase difference are
2–3
at the fixed temperature of optical fibers. So, we prove the perspectiveness of
this structure for the active phased antenna array with FOS.
The average modulation frequency of power optical emission is approximately
1 GHz at the entry optical power in the light guide from 1 to 20 W. Intensity
distributions at output of the powerful laser in the cross-section and photo-pictures
of emission “spots” at different output power values for the wavelength 1.06 μm are
presented in Fig. 8.12. Such a structure of the phase-generator method with OEO is
experimentally examined for application in modulated signal layout in channels of
the phased antenna array.
As the result of this part of experimental investigations, the working capacity and
availability are proved for the microwave fiber-optical system on the base of the
powerful laser for the active phased antenna array. The measured phase difference
drifts in channels on the generation frequency 1 GHz for the single-mode powerful
laser are not more than 1
. Recommendations are developed on reduction of phase
difference drifts by means of the optical frequency and the laser power stabilization
as well as by means of the thermal AOM and fiber-optical channel compensation.
480
8 Experimental Investigations and Practical Circuits of Optoelectronic. . .
PDN, and after amplification, it is registered. The amplified electrical sinusoidal
oscillation with the voltage amplitude 0.1 V with the frequency 1 GHz (from outputs
of two different photodetectors, for example, PD1 and PD2) passes to the phase
difference meter. The feature of this structure (see Fig. 8.11) is that at the switch Sw
closing in the last right position, the electrical oscillations pass to AOM, which are
created by OEO. In this case, OEO is formed by the LTI-501 laser and by (closed in
the feedback loop) the АОМ modulator, the optical fiber FO0, the photodetector
FD0, the RF nonlinear amplifier NA, and the filter F. From the filter F output
(at satisfying of excitation conditions in OEO), oscillation with the 1 GHz-frequency
pass to the АОМ modulator. At that, the gain in power of the NA amplifier is
50–60 dB. The total gain for the OEO open loop depends on the electrical power
acting on AOM (1 W), on the optical power passing on the light-sensitive area of the
PD0 photodetector (0.01–0.1 mW), the conversion slope of PD (0.5) and optical
losses in the channel.
During experiment according to Fig. 8.11, we investigate: the spatial structure of
the laser emission for various powers from 1 to 28 W (Fig. 8.12); the watt–ampere
laser characteristic; different methods for excitation of optical fibers by the infrared
emission with the wavelength 1.06 μm. Functions of OEO oscillation frequency and
differential phase incursions in channels are experimentally studied at temperature
variations from 0 to 40
C.
The normal operation of OEO with RF FODL was provided in the single-mode
laser generation. During experiments, offsets of the interchannel phase difference are
2–3
at the fixed temperature of optical fibers. So, we prove the perspectiveness of
this structure for the active phased antenna array with FOS.
The average modulation frequency of power optical emission is approximately
1 GHz at the entry optical power in the light guide from 1 to 20 W. Intensity
distributions at output of the powerful laser in the cross-section and photo-pictures
of emission “spots” at different output power values for the wavelength 1.06 μm are
presented in Fig. 8.12. Such a structure of the phase-generator method with OEO is
experimentally examined for application in modulated signal layout in channels of
the phased antenna array.
As the result of this part of experimental investigations, the working capacity and
availability are proved for the microwave fiber-optical system on the base of the
powerful laser for the active phased antenna array. The measured phase difference
drifts in channels on the generation frequency 1 GHz for the single-mode powerful
laser are not more than 1
. Recommendations are developed on reduction of phase
difference drifts by means of the optical frequency and the laser power stabilization
as well as by means of the thermal AOM and fiber-optical channel compensation.
480
8 Experimental Investigations and Practical Circuits of Optoelectronic. . .