(with accuracy of 20%) with calculated functions obtained on the base of the
theoretical model of OEO with RF FODL developed in Chaps. 3–7 of this book.
As the result of the experimental data analysis, it is proved that excitation of OEO
with RF FODL happens at the bias current about 35 mA, while the QWLD threshold
bias current is 12 mA. This is one of features of OEO of the microwave range.
Inequality of the QWLD threshold bias current and the bias current, for which the
microwave generation arises, is explained by the fact that at small bias currents, the
conditions of amplitude and phase balance are not satisfied. At small bias currents
(less than 35 mA), the natural frequency of the QWLD resonance peak is 1–6 GHz
(Fig. 7.18). At that, for the natural RFF frequency of 8.2 GHz, the amplitude balance
condition is not satisfied because the QWLD has in this case the small transfer factor.
At the average generation frequency of 8.201 GHz, we obtained the relative frequency instability in the experimental breadboard of OEO not worse than in the time
interval of 10 min at room temperature. In OEO of the microwave range, at large
delay time from 1 to 25 μs, the stabilization effect arises in the RF FODL of the
microwave-modulated optical emission path.
Thus, we considered the specific implementations of fiber-optical systems,
QWLD amplitude and phase responses and we described methods of frequency
control of the microwave oscillations in OEO by variations of QWLD DC pumping
(bias) current because the phase response of the laser diode insignificantly varies
with the pumping current.
Theoretically studied and experimentally implemented results of frequency
tuning ranges versus the QWLD pumping current in the microwave range on
frequency 8.2 GHz were examined. At small pumping current excesses over the
threshold value by 1–2 times, the frequency tuning slope is 0.2 MHz/mA, while for
excesses by 5–8 times, relatively, the slope is less than 0.01 MHz/mA for the average
generation frequency of 8.2 GHz.
Experimental functions of the frequency and amplitude shown in Fig. 8.13, at
variations of QWLD DC pumping current, have 10–20%-coincidence with calculated functions, which means that we have the correct choice of QWLD and OEO
mathematical models.
Thus, for the first time in Russia, we realized microwave generation in OEO with
RF FODL in the microwave range on frequency 8.2 GHz. We proved the possibility
of utilization of the native QWLD as the modulated light source with the ultrawideband modulation frequency as well as the native ultra-wideband photodiode.
Measured experimental function of the generation frequency for various bias currents is close to the calculated one and well described by the parabolic function.
At small bias currents, the slope of generation frequency variations versus the
bias current is 0.3 MHz/mA. At large QWLD bias currents (by 5–8 times), the slope
is 0.003 MHz/mA. Fulfilled examinations allow optimization of QWLD bias current
choice. The optimal QWLD bias current for single-frequency mode of the steadystate OEO generation is 60 mA. The general conclusion made about availability of
QWLD utilization as the modulated light source in OEO of microwave range on
frequencies 8–15 GHz.
486
8 Experimental Investigations and Practical Circuits of Optoelectronic. . .
theoretical model of OEO with RF FODL developed in Chaps. 3–7 of this book.
As the result of the experimental data analysis, it is proved that excitation of OEO
with RF FODL happens at the bias current about 35 mA, while the QWLD threshold
bias current is 12 mA. This is one of features of OEO of the microwave range.
Inequality of the QWLD threshold bias current and the bias current, for which the
microwave generation arises, is explained by the fact that at small bias currents, the
conditions of amplitude and phase balance are not satisfied. At small bias currents
(less than 35 mA), the natural frequency of the QWLD resonance peak is 1–6 GHz
(Fig. 7.18). At that, for the natural RFF frequency of 8.2 GHz, the amplitude balance
condition is not satisfied because the QWLD has in this case the small transfer factor.
At the average generation frequency of 8.201 GHz, we obtained the relative frequency instability in the experimental breadboard of OEO not worse than in the time
interval of 10 min at room temperature. In OEO of the microwave range, at large
delay time from 1 to 25 μs, the stabilization effect arises in the RF FODL of the
microwave-modulated optical emission path.
Thus, we considered the specific implementations of fiber-optical systems,
QWLD amplitude and phase responses and we described methods of frequency
control of the microwave oscillations in OEO by variations of QWLD DC pumping
(bias) current because the phase response of the laser diode insignificantly varies
with the pumping current.
Theoretically studied and experimentally implemented results of frequency
tuning ranges versus the QWLD pumping current in the microwave range on
frequency 8.2 GHz were examined. At small pumping current excesses over the
threshold value by 1–2 times, the frequency tuning slope is 0.2 MHz/mA, while for
excesses by 5–8 times, relatively, the slope is less than 0.01 MHz/mA for the average
generation frequency of 8.2 GHz.
Experimental functions of the frequency and amplitude shown in Fig. 8.13, at
variations of QWLD DC pumping current, have 10–20%-coincidence with calculated functions, which means that we have the correct choice of QWLD and OEO
mathematical models.
Thus, for the first time in Russia, we realized microwave generation in OEO with
RF FODL in the microwave range on frequency 8.2 GHz. We proved the possibility
of utilization of the native QWLD as the modulated light source with the ultrawideband modulation frequency as well as the native ultra-wideband photodiode.
Measured experimental function of the generation frequency for various bias currents is close to the calculated one and well described by the parabolic function.
At small bias currents, the slope of generation frequency variations versus the
bias current is 0.3 MHz/mA. At large QWLD bias currents (by 5–8 times), the slope
is 0.003 MHz/mA. Fulfilled examinations allow optimization of QWLD bias current
choice. The optimal QWLD bias current for single-frequency mode of the steadystate OEO generation is 60 mA. The general conclusion made about availability of
QWLD utilization as the modulated light source in OEO of microwave range on
frequencies 8–15 GHz.
486
8 Experimental Investigations and Practical Circuits of Optoelectronic. . .