noises the best microwave oscillators with the leuco-sapphire resonator. Measured
time jitter (time incursions of the pulse front edge due to fluctuations) is 0.8 fs. FSS
represents the optoelectronic converter of optical emission frequency of 456 THz
into RF oscillations of 10 GHz, This converter uses the scheme of photodetection of
double-frequency optical oscillations using self-heterodyne mixing on the photodetector area. Exactly as a result self-heterodyne mixing, the record level of phase noise
PSD is obtained in the FSS.
We should note that, thanks to utilization of a laser with low phase noise with the
high-stability optical resonator, the record ultralow phase noises of RF oscillation are
obtained in FSS. On 10-GHz frequency, at offset 0.001 kHz from RF carrier, its
levels is less than À110 dB/Hz. Such extremely low low-frequency phase noises are
explained not only by extremely low susceptibility of the optical resonator in the
femtosecond laser to the low-frequency noises due to small geometrical sizes.
2.9.3 A Synthesizer with the Optical Micro-Resonator
In the synthesizer with the optical micro-resonator (SOMR), which block diagram is
shown in Fig. 2.20a the synthesis of RF oscillations of 10 and 89 GHz occur [76–78].
The main formation principle, as in FSS, is double-frequency optical conversion
with self-heterodyne emission mixing on the photodetector into microwave oscillations. Exactly due to self-heterodyne mixing, in the SOMR, one obtains the relatively low level (although not record) of PSD of the phase noise and good short-term
10 GHz-frequency instability.
The distinctive feature of SOMR is utilization of the nonlinear optical conversion
in the optical micro-resonator (shown in Fig. 2.20b) for formation of two optical
frequencies. The optical emission enter in the micro-resonator input at relatively
high power of 200 mW from the narrowband laser with ultralow laser optical phase
noises (with wavelength 1.55 μm and the spectral line width of 3 kHz). At that, the
optical Q-factor of the micro-resonator (i.e., the ratio of the own natural optical
frequency to the resonance peak width on 0.7-level) is 10
9 .
Thanks to the large optical power of 200 mW and the narrow spectral line of
optical emission of 3 kHz, the multifrequency oscillations are formed at the microtoroid output, which spectrum is shown in Fig. 2.20d. In this system, on the
frequency 8.57 GHz, the short-term frequency stability 10
À12 is obtained. The
laser pumping block consists of the high-coherent laser with the line width of
3 kHz synchronized by the more powerful laser with the optical amplifier with
automatic frequency control. SOMR, as we see from description of its functional
diagram, is also concerned to optoelectronic devices of RF oscillation formation, and
the conversion of optical frequencies of 200 THz into oscillations of 10 GHzfrequency occurs. Phase noises of RF oscillation in this system are determined by
the laser phase noises. We also see in this device much similar with OEO with RF
FODL, for instance, extraction of subcarrier oscillation in the photocurrent of the
photodetector.
2.9 Modern Optoelectronic Methods for Precision RF Oscillation Formation
61
time jitter (time incursions of the pulse front edge due to fluctuations) is 0.8 fs. FSS
represents the optoelectronic converter of optical emission frequency of 456 THz
into RF oscillations of 10 GHz, This converter uses the scheme of photodetection of
double-frequency optical oscillations using self-heterodyne mixing on the photodetector area. Exactly as a result self-heterodyne mixing, the record level of phase noise
PSD is obtained in the FSS.
We should note that, thanks to utilization of a laser with low phase noise with the
high-stability optical resonator, the record ultralow phase noises of RF oscillation are
obtained in FSS. On 10-GHz frequency, at offset 0.001 kHz from RF carrier, its
levels is less than À110 dB/Hz. Such extremely low low-frequency phase noises are
explained not only by extremely low susceptibility of the optical resonator in the
femtosecond laser to the low-frequency noises due to small geometrical sizes.
2.9.3 A Synthesizer with the Optical Micro-Resonator
In the synthesizer with the optical micro-resonator (SOMR), which block diagram is
shown in Fig. 2.20a the synthesis of RF oscillations of 10 and 89 GHz occur [76–78].
The main formation principle, as in FSS, is double-frequency optical conversion
with self-heterodyne emission mixing on the photodetector into microwave oscillations. Exactly due to self-heterodyne mixing, in the SOMR, one obtains the relatively low level (although not record) of PSD of the phase noise and good short-term
10 GHz-frequency instability.
The distinctive feature of SOMR is utilization of the nonlinear optical conversion
in the optical micro-resonator (shown in Fig. 2.20b) for formation of two optical
frequencies. The optical emission enter in the micro-resonator input at relatively
high power of 200 mW from the narrowband laser with ultralow laser optical phase
noises (with wavelength 1.55 μm and the spectral line width of 3 kHz). At that, the
optical Q-factor of the micro-resonator (i.e., the ratio of the own natural optical
frequency to the resonance peak width on 0.7-level) is 10
9 .
Thanks to the large optical power of 200 mW and the narrow spectral line of
optical emission of 3 kHz, the multifrequency oscillations are formed at the microtoroid output, which spectrum is shown in Fig. 2.20d. In this system, on the
frequency 8.57 GHz, the short-term frequency stability 10
À12 is obtained. The
laser pumping block consists of the high-coherent laser with the line width of
3 kHz synchronized by the more powerful laser with the optical amplifier with
automatic frequency control. SOMR, as we see from description of its functional
diagram, is also concerned to optoelectronic devices of RF oscillation formation, and
the conversion of optical frequencies of 200 THz into oscillations of 10 GHzfrequency occurs. Phase noises of RF oscillation in this system are determined by
the laser phase noises. We also see in this device much similar with OEO with RF
FODL, for instance, extraction of subcarrier oscillation in the photocurrent of the
photodetector.
2.9 Modern Optoelectronic Methods for Precision RF Oscillation Formation
61