carrier). In Fig. 7.20 the following designation are introduced: DBF is the laser diode
with the Bragg resonator, FOL is the fiber-optical laser, LN FOL is the low-noise
fiber-optical laser with different half-widths of the optical emission spectrum.
Now we can make the following conclusions from this comparison. On the one
hand, we have the commercially available QWLD with low PSD of the phase noise
and the high output power of emission (more than 10 mW), which can play the role
of modulated and non-modulated narrowband sources in the low-noise OEO. On the
other hand, experimental dependences of PSD of the phase noise of QWLD
presented in Fig. 7.20, cannot be modeled by the presented in previous part of this
chapter kinetic differential equations for QWLD (Eq. 7.46) because the important
parameter—the optical phase of the laser emission is not included in these equations.
For analysis of PSD of the phase noise and the influence on the PSD of phase noises
in RF range, we must present the form and analyze of the semiclassical differential
equations of QWLD, in which the phase of optical emission is included. This is done
in Sect. 7.6 of this book.
7.3.7 Brief Conclusions
Thus, as the result of theoretical investigation of the laser diode performed in this
part of this chapter, we can make the following conclusions:
On the base of velocity equations for the mesa-strip QWLD, the analysis is
performed of its electro-optical and electrical characteristics in the microwave
range (1–12 GHz), and the QWLD transfer functions are also obtained for the first
time, and their PFC and AFC for different pumping currents. On the base of
calculation of AFC and PFC of QWLD, we see that the influence on the PFC
slope of the pumping current is various in the whole frequency range:
• At small exceeds of the pumping current (1.2–2.0) at variations of the pumping
current of 1 mA, the maximal slope of PFC is 30–70
/mA (0.6–1.3 rad/mA or
1–2 ps/mA) on the fixed radio frequency in the range 1–5 GHz.
• At large exceeds of the pumping current above the threshold value (5–8), the
maximal slope of PFC is 1–5
/mA on the fixed frequency in the range 5–10 GHz.
Experimentally measurements of PFC qualitatively and quantitatively coincide
with calculated values obtained on the base of velocity equations.
Revealed functions of QWLD AFC and PFC give us the possibility to estimate
the range of possible detuning of the OEO generation frequency (at the singlefrequency generation mode of OEO) in the microwave range at variation of the
pumping current, and also to estimate the function slope of the generation frequency
versus the pumping current in the microwave range. At that, the relative range of
detuning of OEO frequency in the microwave range (8–12 GHz) at small exceeds of
the pumping current above the threshold value (1.5–3) is (20–60) (ps/T FOS ).
The relative range of detuning in OEO in the microwave range (8–12 GHz) at
large exceeds above the threshold values (5–8) is about (2–6) ps/T FOS . For example,
408
7 Optoelectronic oscillator (OEO) as the Time and Spatial Correlator of Random. . .
with the Bragg resonator, FOL is the fiber-optical laser, LN FOL is the low-noise
fiber-optical laser with different half-widths of the optical emission spectrum.
Now we can make the following conclusions from this comparison. On the one
hand, we have the commercially available QWLD with low PSD of the phase noise
and the high output power of emission (more than 10 mW), which can play the role
of modulated and non-modulated narrowband sources in the low-noise OEO. On the
other hand, experimental dependences of PSD of the phase noise of QWLD
presented in Fig. 7.20, cannot be modeled by the presented in previous part of this
chapter kinetic differential equations for QWLD (Eq. 7.46) because the important
parameter—the optical phase of the laser emission is not included in these equations.
For analysis of PSD of the phase noise and the influence on the PSD of phase noises
in RF range, we must present the form and analyze of the semiclassical differential
equations of QWLD, in which the phase of optical emission is included. This is done
in Sect. 7.6 of this book.
7.3.7 Brief Conclusions
Thus, as the result of theoretical investigation of the laser diode performed in this
part of this chapter, we can make the following conclusions:
On the base of velocity equations for the mesa-strip QWLD, the analysis is
performed of its electro-optical and electrical characteristics in the microwave
range (1–12 GHz), and the QWLD transfer functions are also obtained for the first
time, and their PFC and AFC for different pumping currents. On the base of
calculation of AFC and PFC of QWLD, we see that the influence on the PFC
slope of the pumping current is various in the whole frequency range:
• At small exceeds of the pumping current (1.2–2.0) at variations of the pumping
current of 1 mA, the maximal slope of PFC is 30–70
/mA (0.6–1.3 rad/mA or
1–2 ps/mA) on the fixed radio frequency in the range 1–5 GHz.
• At large exceeds of the pumping current above the threshold value (5–8), the
maximal slope of PFC is 1–5
/mA on the fixed frequency in the range 5–10 GHz.
Experimentally measurements of PFC qualitatively and quantitatively coincide
with calculated values obtained on the base of velocity equations.
Revealed functions of QWLD AFC and PFC give us the possibility to estimate
the range of possible detuning of the OEO generation frequency (at the singlefrequency generation mode of OEO) in the microwave range at variation of the
pumping current, and also to estimate the function slope of the generation frequency
versus the pumping current in the microwave range. At that, the relative range of
detuning of OEO frequency in the microwave range (8–12 GHz) at small exceeds of
the pumping current above the threshold value (1.5–3) is (20–60) (ps/T FOS ).
The relative range of detuning in OEO in the microwave range (8–12 GHz) at
large exceeds above the threshold values (5–8) is about (2–6) ps/T FOS . For example,
408
7 Optoelectronic oscillator (OEO) as the Time and Spatial Correlator of Random. . .