A proposed method of stabilizing microwave and millimeter-wave oscillators calls for the use of feedback in optoelectronic delay lines characterized by high values of the resonance quality factor (Q). The method would extend the applicability of optoelectronic feedback beyond the previously reported class of optoelectronic oscillators that comprise two-port electronic amplifiers in closed loops with high-Q feedback circuits

Iltchenko, Vladimir

Maleki, Lute

NASA Technical Reports Server

10 NASA Tech Briefs, November 2009
used as an address in a lookup table.
Each processing element has a lookup
table, unique for its position in the win-
dow, containing the weight coefficients
for the Gaussian function for that posi-
tion. The pixel value is multiplied by
the weight, and the outputs of the pro-
cessing element are the weight and
pixel-value·weight product. The prod-
ucts and weights are fed to the adder
tree. The sum of the products and the
sum of the weights are fed to the di-
vider, which computes the sum of prod-
ucts ÷ the sum of weights. The output
of the divider is denoted the bilateral
smoothed image.
The smoothing function is a simple
weighted average computed over a 3×3
subwindow centered in the 9×9 window.
After smoothing, the image is delayed by
an additional amount of time needed to
match the processing time for comput-
ing the bilateral smoothed image. The
bilateral smoothed image is then sub-
tracted from the 3×3 smoothed image to
produce the final output.
The prototype filter as implemented in
a commercially available FPGA processes
one pixel per clock cycle. Operation at a
clock speed of 66 MHz has been demon-
strated, and results of a static timing
analysis have been interpreted as suggest-
ing that the clock speed could be in-
creased to as much as 100 MHz.
This work was done by Andres Huertas,
Robert Watson, and Carlos Villalpando of
Caltech and Steven Goldberg of Indelible Sys-
tems for NASA’s Jet Propulsion Laboratory.
Further information is contained in a TSP
(see page 1). NPO-45906
A Bilateral Subtraction Filter is implemented in an FPGA that performs parallel pipeline computations
in a moving 9×9-pixel window.
Line Buffer Row Processing
Element
Weights
Products
Line Buffer Row Processing
Element
Line Buffer
Line Buffer
Subtraction
Unit
Output
Divider
Sum of
Products
Sum of
Weights
Center-Pixel Delay and
3x3 Center-Biased
Smoother
Weights
Products
Adder
Tree
Row Processing
Element
Weights
Products
Row Processing
Element
Weights
Products
Pixel
Values In
Simple Optoelectronic Feedback in Microwave Oscillators
Phase and frequency stability would be enhanced greatly.
NASA’s Jet Propulsion Laboratory, Pasadena, California
A proposed method of stabilizing mi-
crowave and millimeter-wave oscillators
calls for the use of feedback in optoelec-
tronic delay lines characterized by high
values of the resonance quality factor
(Q). The method would extend the ap-
plicability of optoelectronic feedback
beyond the previously reported class of
optoelectronic oscillators that comprise
two-port electronic amplifiers in closed
loops with high-Q feedback circuits.
The upper part of the figure illustrates
the example of a typical free-running oscil-
lator in a conventional form stabilized
with an external metal radio-frequency
(RF) resonant cavity. The oscillator could
be of any of a variety of types, including
those based on Gunn diodes, impact ava-
lanche transit-time (IMPATT) diodes, kly-
strons, backward-wave tubes, and others.
The maximum Q of a typical resonant
metal cavity ranges from about 104 at an
oscillation frequency of 10 GHz down to
A High-Q Optoelectronic Delay Line would be substituted for the RF resonant cavity of a conventional
free-running oscillator stabilized with an external resonator.
RF Oscillator
To Be
Stabilized
Phase
Shifter
Laser
Electro-Optical
 Modulator 
High-Q Opto-Electronic
Feedback Loop
Photodetector
Fiber-Optic
Delay Line
RF Oscillator
To Be
Stabilized
Phase
Shifter
RF Resonant
Cavity
CONVENTIONAL
PROPOSED
https://ntrs.nasa.gov/search.jsp?R=20090040059 2019-08-30T08:12:10+00:00Z
NASA Tech Briefs, November 2009 11
103 at a frequency of 100 GHz and to even
lower values at higher frequencies. In con-
trast, the maximum Q attainable in a res-
onator based on an optoelectronic delay
line is of the order of 106 at a frequency of
10 GHz and increases with frequency.
The proposed method is partly similar
to two older patented methods that in-
volve the use of fiber-optic delay lines as
RF-phase-noise discriminators. However,
unlike those methods, the proposed
method does not call for the generation
of a low-frequency signal applied to a
control port of the oscillator to be stabi-
lized. Instead, the delayed RF signal
would simply be returned to the oscilla-
tor, as described below.
The lower part of the figure shows an
example of the same oscillator as before,
but this time stabilized by use of opto-
electronic feedback according to the
proposed method. The RF signal from
the oscillator would be fed through a cir-
culator to an electro-optical modulator,
which would modulate the RF signal
onto a laser beam. After traveling the
length of an optical fiber or other opti-
cal delay line, a photodetector would de-
modulate the signal. The RF output of
the photodetector would be returned via
the circulator to the oscillator.
The return of the delayed RF signal
would enforce a steady phase in an oth-
erwise noisy free-running oscillator,
thereby suppressing phase noise in the
oscillations. This stabilizing effect is ex-
pected as a consequence of the fre-
quency-pulling effect or self-injection
locking observed previously in oscilla-
tors equipped with high-Q external reso-
nant cavities.
The original tunability of the free-run-
ning oscillator would be substantially
preserved in the presence of optoelec-
tronic stabilization, except as described
next: Upon tuning of the oscillator, the
frequency of the oscillator would not
change continuously but would jump be-
tween successive resonances of the opto-
electronic feedback loop . Typical fre-
quency jumps would likely range from a
few tens of kilohertz for a kilometer-long
fiber-optic delay line up to a few giga-
hertz for an optical microresonator. 
This work was done by Lute Maleki and
Vladimir Iltchenko of Caltech for NASA’s Jet
Propulsion Laboratory. Further information is
contained in a TSP (see page 1).
In accordance with Public Law 96-517,
the contractor has elected to retain title to this
invention. Inquiries concerning rights for its
commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
(818) 354-2240
E-mail: iaoffice@jpl.nasa.gov
Refer to NPO-40144, volume and number
of this NASA Tech Briefs issue, and the
page number.
A small, segmented microstrip patch
antenna integrated with an X-band feed-
back oscillator on a high-permittivity
substrate has been built and tested (see
Figure 1). The oscillator antenna is pow-
ered by commercial solar photovoltaic
cells mounted nearby or on the same
substrate. This oscillator antenna is a
prototype for demonstrating the feasibil-
ity of such devices as compact, low-
power-consumption building blocks of
advanced, lightweight, phased antenna
arrays that would generate steerable
beams for communication and remote-
sensing applications.
The solar-powered oscillator antenna
includes a commercially available super-
low-noise, high-frequency field-effect
transistor integrated into the center of
the segmented microstrip-patch antenna.
Along with bias lines, a feedback loop,
and other conductors that are parts of
the oscillator antenna circuitry, the patch
antenna was formed by etching the corre-
sponding pattern out of a surface metal
layer on the substrate, which is a commer-
cial microwave laminate having a relative
permittivity of 10.2 and a thickness of
0.635 mm. The oscillator antenna occu-
pies an area of 5 by 6 mm on the sub-
strate. The oscillator feedback path ex-
Figure 1. A Schematic of Oscillator Antenna is shown with feedback loop. The dimensions are in mil-
limeters.
Small X-Band Oscillator Antennas 
In some applications, these compact units could be powered by solar cells. 
John H. Glenn Research Center, Cleveland, Ohio
4.88
Drain
E
H
Source
4.886.88
Gate
Capacitor
2.14
1.00


Simple Optoelectronic Feedback in Microwave Oscillators

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