1287 Forgewood Ave.
Sunnyvale, CA 94089
Tel: (408) 962-0895
Fax: (408) 743-5354
We welcome your custom requirements.
We have specialized in Low Phase Noise
Fixed Frequency Sources since 1998.
Nexyn offers the best performance and
reliability on the market.
Crystal reference phase noise to
- 130 dBc/Hz 100 Hz 100 MHz
Dual loop output
frequency resolution +/- 0.001 Hz
Internal reference stability
to +/- 10 ppb
5 - 1000 MHz External reference
Frequency: 10 MHz to 35 GHz
Power output: + 10 to + 24 dBm
Wide operating temperature
range: -55º to +85º
Spurious: < - 90 dBc
A plot of our new quieter PLDRO line.
1 10 100 1000 10000 100000 1000000
9GHz PLDRORESIDUAL PHASE NOISE (dBc)
high Q energy storage element may be
an optical resonator,
in which case its free
spectral range (FSR)
sets the frequency
of the oscillator. The
feedback loop consists of electronic
and optical components, which can be
interchanged in the
optical or electrical
segment of the loop. In its most common configuration the gain elements,
the filter and the phase shifter are included in the RF segment.
OEO is a versatile architecture
that allows for the interchange of
components in the optical loop with
their electronic counterparts, or vice
versa. For example, the needed gain
in the loop can be provided with either an electronic amplifier or an optical amplifier. The same is true for the
element that adjusts the phase in the
loop to keep the oscillator stable. Furthermore, since the center frequency
of the filter determines the operation
frequency, any desired frequency supported by the bandwidth of the modulator, the gain elements, and the PD
may be obtained. Conveniently, the
use of a tunable filter can produce a
tunable OEO with the unique feature
of same spectral purity for any frequency within the bandwidth. 3 More
importantly, even the light source can
be inside the loop. This may be accomplished by using an optical amplifier with its output connected to its
input, and by coupling it to the modulator as part of the optical segment of
the OEO. This latter scheme is known
as a coupled opto-electronic oscillator,
or COEO (see Figure 2 and Figure
3), and includes the benefit of an active element to multiply the Q of the
oscillator. 4 In the configuration shown
in Figure 2, the optical signal is produced in the upper loop with an optical gain. The optical loop and the RF
loop are coupled through the modulator.
Examples of OEOs with various
configurations are now numerous and
may be readily found in the literature. 5
OEOs with fiber delay lines as the en-
ergy storage elements that produce
signals with frequencies as high as
ement in conventional oscillators typi-
cally determines both the frequency
of operation and the achievable spec-
tral purity. Since a resonator’s size
(volume) decreases with increasing
frequency, high frequency electronic
resonators have lower Q, resulting in
lower oscillator spectral purity.
Photonic oscillators do not have
these inherent limitations. Since mi-
crowave, mm-wave and even THz sig-
nals are a fraction of the frequency of
light, the use of optical elements min-
imizes loss with increased frequency.
Furthermore, optical waveguides and
resonators can be produced with ex-
tremely low loss, providing very high
Q elements for photonic oscillators.
Finally, as described in this article,
the extremely high Q of certain opti-
cal resonators enables the emergence
of nonlinearities that can be put to ad-
vantage for generations of reference
The most widely known photonic
oscillator is the opto-electronic oscillator (OEO).2 The OEO is based on
a feedback loop that converts modulated light from a laser to RF (
micro-wave/mm-wave) frequency. In its generic form (see Figure 1), the modulated light is generated by direct modulation of the laser current, or by use
of an amplitude, or phase modulator.
The modulated light passes through
a high Q energy storage element, before it is detected by a high frequency photodetector (PD). The output
of the PD is amplified, adjusted for
phase, and fed back to the modulator to complete the loop. The high Q
element in the optical segment of the
loop can be a long fiber delay, in which
case the center frequency of a filter in
the electronic segment of the loop determines the frequency of operation.
Fig. 1 Schematic diagram of the generic Opto-Electronic Oscillator.