this part of researches is experimental examination of OEO frequency f versus bias
current variations I bias of the modulated light source: the laser diode and the lightemitting diode. To solve this task, we use samples of OEO with RF FODL consisting
of laser diodes or light-emitting diodes. For the OEO sample with the laser diode the
breadboard No2 is used. This includes the following in series ring-connected: the
electronic photodetector, an amplifier, the RF filter, and the modulator, the laser
diode, the fiber-optical system. As the laser diode, we use the GaAs diode with the
double hetero-structure of the 32DL-103 model with the wavelength λ ¼ 0.85 μm,
and ILPN-204 with the wavelength λ ¼ 1.3 μm. The fiber-optical system in this
breadboard consists of the light guider mixer of modes and the interchangeable
single multimode light guider with lengths 20, 100, and 300 m. The OEO with RF
FODL has the generation frequency which approximately equal to the natural
frequency of the RF filter, and it is for various filters f osc % 8 MHz, and
f osc % 40 MHz.
At current values equaled to the threshold value, the frequency function f(I bias )
has a minimum. The hysteresis character of the f(I bias ) curve at increase or decrease
of the pumping current is explained by thermodynamic processes of heating or
cooling of the laser diode active area at small variations of an environment
temperature.
Theoretical dependences of delay time of RF oscillations for the system “the laser
diode–the photodiode” versus the normalized DC bias current are presented in
Fig. 8.8a. Figure 8.8b shows experimental functions of the relative frequencies f/f 0 ,
the generation voltage amplitude U of OEO with RF FODL, and the output power
P versus the bias current. The laser diode is ILPN-204 type. At that, the average
generation frequency f 0 of OEO is 30 MHz.
A gain of an electronic amplifier is K ampl ffi 10
3 . The p-i-n diode is used as the
photodetector. Experimental functions f(I bias ) of OEO with RF FODL are presented
in Fig. 8.9a. At that, the laser diode 32DL-103 and the light guider segment with the
length L ¼ 20 m is used in this OEO breadboard. The laser diode 32DL-103 has no
any special optical matching units, and it is joined with the optical fiber directly
tightly. At that, the spontaneous emission level (captured by the fiber-optical system)
was extremely low, and, as a consequence, RF OEO generation is appeared only for
the pumping currents more than the threshold value. At that, the function is monotonically increasing at the bias current growth.
Experimental functions of the OEO generation frequency f(I bias ) versus the bias
current are described in Chap. 4 for OEO using the laser diode of the ILPN-204 type
(in which construction the optical matching system in the form of the “micro-lens” is
included). At that, frequency functions f(I bias ) have the non-monotonic variation with
a change of function slope signs: for bias current increase from 0 to threshold current
values these functions are monotonically deceasing, while if the bias current is above
the threshold value, these functions are monotonically increasing. In contrast to the
previous case, a presence of the matching system in the laser diode allows the OEO
generation at currents less than the threshold value. An analysis of the slope polarity
change of the phase response at pumping current growth is described in Chap. 4 of
this book.
8.2 Influence of DC Bias Current Variations of the Laser Diode Upon the Generation. . .
475
current variations I bias of the modulated light source: the laser diode and the lightemitting diode. To solve this task, we use samples of OEO with RF FODL consisting
of laser diodes or light-emitting diodes. For the OEO sample with the laser diode the
breadboard No2 is used. This includes the following in series ring-connected: the
electronic photodetector, an amplifier, the RF filter, and the modulator, the laser
diode, the fiber-optical system. As the laser diode, we use the GaAs diode with the
double hetero-structure of the 32DL-103 model with the wavelength λ ¼ 0.85 μm,
and ILPN-204 with the wavelength λ ¼ 1.3 μm. The fiber-optical system in this
breadboard consists of the light guider mixer of modes and the interchangeable
single multimode light guider with lengths 20, 100, and 300 m. The OEO with RF
FODL has the generation frequency which approximately equal to the natural
frequency of the RF filter, and it is for various filters f osc % 8 MHz, and
f osc % 40 MHz.
At current values equaled to the threshold value, the frequency function f(I bias )
has a minimum. The hysteresis character of the f(I bias ) curve at increase or decrease
of the pumping current is explained by thermodynamic processes of heating or
cooling of the laser diode active area at small variations of an environment
temperature.
Theoretical dependences of delay time of RF oscillations for the system “the laser
diode–the photodiode” versus the normalized DC bias current are presented in
Fig. 8.8a. Figure 8.8b shows experimental functions of the relative frequencies f/f 0 ,
the generation voltage amplitude U of OEO with RF FODL, and the output power
P versus the bias current. The laser diode is ILPN-204 type. At that, the average
generation frequency f 0 of OEO is 30 MHz.
A gain of an electronic amplifier is K ampl ffi 10
3 . The p-i-n diode is used as the
photodetector. Experimental functions f(I bias ) of OEO with RF FODL are presented
in Fig. 8.9a. At that, the laser diode 32DL-103 and the light guider segment with the
length L ¼ 20 m is used in this OEO breadboard. The laser diode 32DL-103 has no
any special optical matching units, and it is joined with the optical fiber directly
tightly. At that, the spontaneous emission level (captured by the fiber-optical system)
was extremely low, and, as a consequence, RF OEO generation is appeared only for
the pumping currents more than the threshold value. At that, the function is monotonically increasing at the bias current growth.
Experimental functions of the OEO generation frequency f(I bias ) versus the bias
current are described in Chap. 4 for OEO using the laser diode of the ILPN-204 type
(in which construction the optical matching system in the form of the “micro-lens” is
included). At that, frequency functions f(I bias ) have the non-monotonic variation with
a change of function slope signs: for bias current increase from 0 to threshold current
values these functions are monotonically deceasing, while if the bias current is above
the threshold value, these functions are monotonically increasing. In contrast to the
previous case, a presence of the matching system in the laser diode allows the OEO
generation at currents less than the threshold value. An analysis of the slope polarity
change of the phase response at pumping current growth is described in Chap. 4 of
this book.
8.2 Influence of DC Bias Current Variations of the Laser Diode Upon the Generation. . .
475