Accordingly, with the pumping current growth, the optical frequency of the laser
emission central mode decreases as ν ¼ ν 0 [1 À S ν (I 0 /I thr À 1)], where S ν is a slope of
the function of emission optical frequency versus the pumping current, ν 0 is the
central mode frequency at the threshold pumping. At that, a slope of the central mode
wavelength equaled “on the threshold” to 1.3002 μm versus the DC QWLD
pumping current is 0.086 μm/mA or 0.086 mm/A, which corresponds to a slope of
the QWLD optical frequency function versus DC pumping current of
S v ¼ 0.75 THz/(50 mA) ¼ 0.015 THz/mA. Maximal relative deviations of the
optical frequency in the current range 20–70 mA are 0.75 THz/229 THz ¼ 0.0032.
The watt–ampere characteristics of QWLD ILPN-204 and 32DL-103 (Fig. 8.4b,
c) and LED of the transmitting module KEM (b) for different excitation conditions
1 and 2 are shown in Fig. 8.7b. Functions shown in Fig. 8.4 give a possibility to
observe the main difference in watt–ampere characteristics of light-emitting diodes
and laser diodes as well as QWLDs. For laser diodes, at exceed of the I bias threshold
value (I bias,thr ), the slope of the emission power function Р out (I bias ) sharply increases,
while at bias current values less than the threshold value I bias,thr , the watt–ampere
curve has a form of a parabola. This relates the fact that at bias currents less than
threshold one, a contribution into registered optical emission of spontaneous emission increases. Laser diodes used in breadboards differ in implementation construction of optical matching units of laser diodes with the fiber-optical light guider.
Modulation characteristics of the transition type are investigated for transmitting
and receiving modules connected in series through the short piece of the fiber-optical
light guider with a length of 2 m in the frequency ranges 0–10 MHz and 30–40 MHz.
These functions are shown in Fig. 8.5. Fulfilled measurements allow the correct
choice of operation current of emission source and provision of the optical coupling
from the output of the reception module KEM to the input of the transmitting module
KEM. The function of the output signal amplitude U out at the output of the KEM
reception module versus the LED bias current is presented in Fig. 8.5b. From this
figure, we see that at the “small” input signal U in 0.1 V (at the KEM transmitting
module input), the nonlinear function of the signal amplitude U out (I bias ) “repeats” the
watt–ampere characteristic of LED, while at the “large” input signal U in ¼ 1.0 V
characteristics U out (I bias ) are close to linear ones due to arising of “compensation”
effects.
Functions U out (U in ), in which U in , U out are voltage amplitudes of KEM, are
experimentally studied. The fiber-optical delay line consists in this experiment of
the KEM transmitting module, the optical fiber, and the KEM reception module. At
that, the LED bias current is 100 mA, while the frequencies of the sine signal applied
to the KEM transmitting module input are 4, 10, and 30 MHz.
The OEO nonlinear characteristic character was determined from functions
U out (U in ). In this case, at small U in signals, the total nonlinear characteristic of
KEM modules has a character close to parabolic (i.e., there is a “soft” nonlinearity
from the nonlinear oscillation theory point of view).
The average generation frequency of OEO was tuned by a variable capacitor of
the RF filter (a tuned circuit) and is equaled for the first breadboard approximately to
6.4 MHz, while for the second breadboard—30 MHz. For these breadboards, the
8.1 Characteristics of Modulated Emission Sources: The Laser Diode and the. . .
471
emission central mode decreases as ν ¼ ν 0 [1 À S ν (I 0 /I thr À 1)], where S ν is a slope of
the function of emission optical frequency versus the pumping current, ν 0 is the
central mode frequency at the threshold pumping. At that, a slope of the central mode
wavelength equaled “on the threshold” to 1.3002 μm versus the DC QWLD
pumping current is 0.086 μm/mA or 0.086 mm/A, which corresponds to a slope of
the QWLD optical frequency function versus DC pumping current of
S v ¼ 0.75 THz/(50 mA) ¼ 0.015 THz/mA. Maximal relative deviations of the
optical frequency in the current range 20–70 mA are 0.75 THz/229 THz ¼ 0.0032.
The watt–ampere characteristics of QWLD ILPN-204 and 32DL-103 (Fig. 8.4b,
c) and LED of the transmitting module KEM (b) for different excitation conditions
1 and 2 are shown in Fig. 8.7b. Functions shown in Fig. 8.4 give a possibility to
observe the main difference in watt–ampere characteristics of light-emitting diodes
and laser diodes as well as QWLDs. For laser diodes, at exceed of the I bias threshold
value (I bias,thr ), the slope of the emission power function Р out (I bias ) sharply increases,
while at bias current values less than the threshold value I bias,thr , the watt–ampere
curve has a form of a parabola. This relates the fact that at bias currents less than
threshold one, a contribution into registered optical emission of spontaneous emission increases. Laser diodes used in breadboards differ in implementation construction of optical matching units of laser diodes with the fiber-optical light guider.
Modulation characteristics of the transition type are investigated for transmitting
and receiving modules connected in series through the short piece of the fiber-optical
light guider with a length of 2 m in the frequency ranges 0–10 MHz and 30–40 MHz.
These functions are shown in Fig. 8.5. Fulfilled measurements allow the correct
choice of operation current of emission source and provision of the optical coupling
from the output of the reception module KEM to the input of the transmitting module
KEM. The function of the output signal amplitude U out at the output of the KEM
reception module versus the LED bias current is presented in Fig. 8.5b. From this
figure, we see that at the “small” input signal U in 0.1 V (at the KEM transmitting
module input), the nonlinear function of the signal amplitude U out (I bias ) “repeats” the
watt–ampere characteristic of LED, while at the “large” input signal U in ¼ 1.0 V
characteristics U out (I bias ) are close to linear ones due to arising of “compensation”
effects.
Functions U out (U in ), in which U in , U out are voltage amplitudes of KEM, are
experimentally studied. The fiber-optical delay line consists in this experiment of
the KEM transmitting module, the optical fiber, and the KEM reception module. At
that, the LED bias current is 100 mA, while the frequencies of the sine signal applied
to the KEM transmitting module input are 4, 10, and 30 MHz.
The OEO nonlinear characteristic character was determined from functions
U out (U in ). In this case, at small U in signals, the total nonlinear characteristic of
KEM modules has a character close to parabolic (i.e., there is a “soft” nonlinearity
from the nonlinear oscillation theory point of view).
The average generation frequency of OEO was tuned by a variable capacitor of
the RF filter (a tuned circuit) and is equaled for the first breadboard approximately to
6.4 MHz, while for the second breadboard—30 MHz. For these breadboards, the
8.1 Characteristics of Modulated Emission Sources: The Laser Diode and the. . .
471