modeling and experimental investigation of OEO MZ samples on the operation
frequencies 8–10 GHz show the well-comparison of calculated and experimental
static dependences of amplitude and frequency of OEO MZ taking into account the
stabilization effect at large pumping currents of QWLD and FOS lengths of 1–5 km.
In this chapter, we proved that OEO MZ can be used as the measuring system of
the width of the laser spectral line. Performed analysis shows that the RF spectrum is
determined by detected phase noises of laser optical emission. The value of PSD of
the phase noise is proportional to the square of the natural width of laser optical
emission spectral line. It is shown that in OEO MZ the various variants of the PLL
system structure are possible with laser control basing on the reference RF oscillator
and with RF oscillator control basing on the reference laser. We prove that the PLL
system in OEO MZ significantly decreases requirements to the spectral line width of
the laser generation and to the length of the optical fiber. At introduction of PLL loop
in OEO MZ, the essential (more than by 15 dB/Hz) decrease of PSD level of phases
noises on the generation frequencies 8–10 GHz. The theoretical and experimental
studying of the low-noise laser generator (OEO MZ) with the PLL system is
performed. We considered theoretical problems of oscillation generation with low
level of phase noises in the system of OEO MZ with PLL as a function of the laser
spectral line width.
It is shown that OEO MZ with PLL system is the RF oscillator with the ultralow
level of PSD of the phase noise. The value of single-side PSD of the phase noise may
achieve À120 Ä À 150 dB/Hz at frequency offsets 1–10 kHz from the nominal
generation frequency 10 GHz when using the high-coherent lasers with the line
width 1–10 kHz. Development and analysis of the theoretical model of OEO MZ
revealed that the power spectral density of the phase noise of microwave oscillations
is determined by the laser phase noise and by the line width of the laser optical
emission, by the laser power, by delay in the optical fiber. The decrease of PSD of
the phase noise by more than 10 dB/Hz is provided by equalization of the optical
power in MZ channels.
As the result of investigations, the conclusion is derived that to provide the PSD
level of the OEO phase noise less than À130 dB/Hz on frequency 10 GHz at offset of
1 kHz, the spectral line width of optical emission of commercially available lasers
(at the output power not less than 10 mW) should be less than 1–10 kHz.
The different types of low-noise oscillators are developed and experimentally
implemented with RF FODL with the stabilized electrical circuits of laser diode’s
bias current, or the bias voltage of the operation point of the electro-optical modulator and the bias current of the photodiode.
The optoelectronic oscillators were developed for centimeter wave range on the
base of QWLD, stabilized by RF FODL and by self-heterodyning, provide the phase
noise at the room temperature with the offset 1 kHz from the carrier at the following
level:
– Approximately À120 dB/Hz in the simplest variants with lasers with the optical
emission line width of 1 MHz and at application of optical fibers with delay
6.8 Conclusions
365
frequencies 8–10 GHz show the well-comparison of calculated and experimental
static dependences of amplitude and frequency of OEO MZ taking into account the
stabilization effect at large pumping currents of QWLD and FOS lengths of 1–5 km.
In this chapter, we proved that OEO MZ can be used as the measuring system of
the width of the laser spectral line. Performed analysis shows that the RF spectrum is
determined by detected phase noises of laser optical emission. The value of PSD of
the phase noise is proportional to the square of the natural width of laser optical
emission spectral line. It is shown that in OEO MZ the various variants of the PLL
system structure are possible with laser control basing on the reference RF oscillator
and with RF oscillator control basing on the reference laser. We prove that the PLL
system in OEO MZ significantly decreases requirements to the spectral line width of
the laser generation and to the length of the optical fiber. At introduction of PLL loop
in OEO MZ, the essential (more than by 15 dB/Hz) decrease of PSD level of phases
noises on the generation frequencies 8–10 GHz. The theoretical and experimental
studying of the low-noise laser generator (OEO MZ) with the PLL system is
performed. We considered theoretical problems of oscillation generation with low
level of phase noises in the system of OEO MZ with PLL as a function of the laser
spectral line width.
It is shown that OEO MZ with PLL system is the RF oscillator with the ultralow
level of PSD of the phase noise. The value of single-side PSD of the phase noise may
achieve À120 Ä À 150 dB/Hz at frequency offsets 1–10 kHz from the nominal
generation frequency 10 GHz when using the high-coherent lasers with the line
width 1–10 kHz. Development and analysis of the theoretical model of OEO MZ
revealed that the power spectral density of the phase noise of microwave oscillations
is determined by the laser phase noise and by the line width of the laser optical
emission, by the laser power, by delay in the optical fiber. The decrease of PSD of
the phase noise by more than 10 dB/Hz is provided by equalization of the optical
power in MZ channels.
As the result of investigations, the conclusion is derived that to provide the PSD
level of the OEO phase noise less than À130 dB/Hz on frequency 10 GHz at offset of
1 kHz, the spectral line width of optical emission of commercially available lasers
(at the output power not less than 10 mW) should be less than 1–10 kHz.
The different types of low-noise oscillators are developed and experimentally
implemented with RF FODL with the stabilized electrical circuits of laser diode’s
bias current, or the bias voltage of the operation point of the electro-optical modulator and the bias current of the photodiode.
The optoelectronic oscillators were developed for centimeter wave range on the
base of QWLD, stabilized by RF FODL and by self-heterodyning, provide the phase
noise at the room temperature with the offset 1 kHz from the carrier at the following
level:
– Approximately À120 dB/Hz in the simplest variants with lasers with the optical
emission line width of 1 MHz and at application of optical fibers with delay
6.8 Conclusions
365