Electro-Optic Sensors for RF Electric Fields: a Diagnostic Tool for Microwave

Circuits and Antennas

If any of the enclosed materials are to be cited in other publications, the users are responsible for referencing the authors of this tutorial as the source of such material.

Reproductions of any of the enclosed materials, either partial or whole, and including the extraction of individual graphs or figures, is not allowed without permission from the copyright holder and appropriate citation of the source.

Specific copyright information is included on each slide as appropriate.

Electro-Optic Sensors for RF Electric Fields: a Diagnostic Tool for Microwave

Circuits and Antennas

John F. Whitaker, Kyoung Yang*, Ron Reano, and Linda P.B. Katehi#

Center For Ultrafast Optical Science & Radiation LaboratoryDept. of Electrical Engineering & Computer ScienceUniversity of Michigan, Ann Arbor

* Currently at EMAG Technologies, Inc.# Currently at Purdue University

Outline

• Motivation & Background

• Fundamental Concepts of Electro-Optic Probing

• System Configuration & Attributes

• Diagnostic Measurement Examples

• Thermal & Magnetic-Field Imaging

Motivation• Near-field measurements – radiating structures

– High spatial resolution at h << λ– Observation of nonradiating waves– Near-to-far-field transformation

• Near-field measurements – guided-wave structures– Internal-node characterization

• Near-field diagnostics - fault isolation – Detect malfunctioning components– Determine relative phase of sources

• Design/performance verification• Model Validation

Electro-Optic Sampling Probe Embodimentsinput beamoutput beam

optical fiber

integrated type

fiber-based EO probingexternal (free-space)EO probing

substrate probing

1st Generation 2nd Generation 3rd Generation

Additional field-mapping concept & applications references:

• U. Colorado – Boulder• U. Duisberg

• U. Maryland• Brunel Univ.• U. Tokyo

• U. Aachen• NTT (x2)• NPL

"This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder."

Principle – Electro-optic Effect

•RF electric-field measurements based on electro-optic (Pockels) effect.

•External polarizers are cross-polarized.

•Change in polarization state due to electric field induced linear birefringence.

"(c) 2002 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Electro-Optic Equivalent-Time Sampling for High-Bandwidth Measurements

microwave signal f m

Principle:Harmonic Mixing

f = f - n fm rep.IF

timereplocal oscillator (laser pulse train) f

f Iintermediate frequency Ftime

time

Fiber-Based EO Field-Mapping System

Lock-inAmplifier

opticalisolator

mirror

polarization dependantbeam splitter

fiber coupler

fiber polarizationcontroller (λ/2,λ/4)

computer-controlledtranslation stage

10 M

Hz

com

mon

refe

renc

e

single-modeoptical fiber

GRIN Lens

GaAs Tip

λ/2 wave plate

input (detection) beam

reflected (signal) beam

photo diode

RF-Synthesizer

Ti:Sapphire Laser

RF-Synthesizer

"(c) 2001 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Polarization Control in an Electro-Optic Probing System IN2 IN4IN1 IN3

optical isolatorλ/2 WP BS

photo diode

OUT1

OUT3

H

V90o

67.5o

0o 0o

0o

(45+δ)o

λ/2 loop λ/4 loop

(22.5+δ)o

o22.5

IN7(22.5+θ)o

(22.5+θ+δ)o

(45+δ)o

90o

OUT4

IN5

fiber couplerOUT2

OUT5

IN6

GaAs tip

single-mode optical fiber GRIN Lens

"This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder."

1-D Electro-Optic Field MappingCoplanar Waveguide Transmission Line cross Section

zcrosssection

x

-200 -100 0 100 2000.0

0.2

0.4

0.6

0.8

1.0

position (µm)

norm

. am

plitu

de

-100

-50

0

50

100

Normal field component

-200 -100 0 100 200

0.0

0.2

0.4

0.6

0.8

1.0

-200

-100

0

100

norm

. am

plitu

de

position (µm)

Tangential field component

rel.

phas

e (d

eg.)

rel.

phas

e (d

eg.)

"(c) 1998 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Electro-Optic Electric-Field-Sensing Capabilities

• Extract both amplitude and phase of electric fields• Isolate X, Y, and Z vectorial components

– (110) GaAs probe tip for tangential fields– (100) GaAs probe tip for normal field

• Near-field measurement (range < 100 µm)• Low invasiveness

– probe much smaller than wavelength– no metal near field to be measured– finite difference simulations indicate small changes

in Zc for typical probe heights• High positioning flexibility with fiber coupling

Electro-Optic Electric-Field Sensing: System Performance

• Bandwidth: >100 GHz

• Spatial Resolution: < 8 µm• Phase stability: +/- 3°/hour

• Cross Polarization Suppression: > 30 dB

• Time for Measurement: 15-60 min.

• Area of measurement: micrometers to meters• Sensitivity: < 1 V/m/(Hz)1/2

Electro-Optic Field Mapping of a Microstrip Patch- Measurement vs. FEM Simulation

amplitude (height :0 mm)

x component

y component

z component

simulationmeasurement measurement simulation

phase (height :0 mm)

180

100

0

-100

-180

1.00

0.80

0.60

0.40

0.20

0.00

x component

y component

z component

xy

"(c) 2000 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Electro-Optic Electric-Field Sensing:S11 Measurement on Microstrip Patch Antenna

0 10 20 30 40-250

-200

-150

-100

-50

0

50

100

150

200

feeding line antenna

3.523 GHz 4.011 GHz 4.563 GHz

E.O

. sig

nal p

hase

[deg

.]

distance [mm]

0 10 20 30 40-1

0

1

2

3

4

5

6

feeding line antenna

3.523 GHz 4.011 GHz 4.563 GHz

E.O

. sig

nal a

mpl

itude

[ a.

u. ]

distance [mm]

3.0 3.5 4.0 4.5 5.0-40

-30

-20

-10

0

E.O. measurement HP 8510 measurement

l S11

l [d

B]

frequency [GHz]

"(c) 2000 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Field-Sensing-Probe Invasiveness• Return loss from CPW measured and calculated with and without

EO probe in position.

• Frequency domain measurements (2 - 40 GHz): |S11| < -30 dB with and without probe

"(c) 2001 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Electric Field Sensing in a 1 X 4 Power Distribution Network: Operation and Fault Isolation

IN

OUT OUT OUT OUT

short point3.7

mm

Wilkinsonpower divider

y

z-component, frequency: 15 GHz

xz8.3 mm

-0

--25

--50matched circuit, amplitude (dB)

-0

--30

--60partially shorted circuit, amplitude (dB)

shorted air-bridge fault

"(c) 1998 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Field Sensing in an Antenna ArrayDiagnosis of Malfunction in a Ka-Band Quasi-Optical Amplifier Patch Array

patch antenna

input horn

output horn

input polarizeroutput polarizer

QO array

Ampl

itude

(nor

m.)

coup

ler

MM

IC a

mpl

ifierBasic operating principle

Array provided by Lockheed-Martin

"(c) 2001 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Field Sensing in an Antenna ArrayKa-Band Quasi-Optical Amplifier Slot Array:Observation of parasitic coupling

ampl

itude

(nor

m.)

DC bias point

0.00

0.20

0.40

0.60

0.80

1.00

-180 100 0 180100phase (degree)

0.00 0.20 0.40 0.60 0.80 1.00amplitude (norm.)

Array provided by Zoya PopovicUniv. of Colorado - Boulder

"(c) 2001 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Field Sensing Inside Microwave PackagesShielded Microstrip at f = 8 GHz

sliding top metal plate

short termination

glass tube (supporter)

GRIN lensGaAs EO tip

input port

optical fiber

side metal wall

microstrip substrate

Shielded Microstrip (open side view)

"(c) 2001 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Field Sensing Inside Microwave Packages: Shielded Microstrip Measurements

E h = 1 mm

shielded microstripexposed microstrip

amplitude [norm.] phase [degree] amplitude [norm.] phase [degree]

"This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder."

Thermal Calibration, Sensing, and Imaging• Temperature measurements based on optical absorption due to the

temperature dependence of the band-edge in GaAs.

"(c) 2001 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

•Relationship between optical power (P) and temperature (T)

System Implementation for Simultaneous Electric Field and Temperature Sensing

*Absorption Temperature &E-field

*Polarization-state E-Field

• E-fields and thermal distributions can be measured at the same time with a single probe.

"(c) 2001 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Electro/Thermal Measurements on a Quasi-Optical Amplifier via Optical Sensor

• Corrupted electric-field data corrected via:

Temperature Corrected Data

Cor

r. E-

Fiel

d D

ata

[µV]

Cor

r. E-

Fiel

d D

ata

[µV]

Power M

eter Data [V]

Measured Tem

p [ oC]

Simultaneous Measurements

Time [min] Time [min]• Simultaneous measurements show an increase of 7oC in 11

min during which the output E-field is essentially constant."(c) 2001 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Magnetic-Field Mapping via Magneto-Optic Sampling• RF magnetic-field measurements based on Faraday effect

• External polarizers are oriented at 45 degrees.

T = −12

12

2sin( )αo H V Lα µ=α = µοHVL

•Rotation of optical linear polarization due to magnetic field induced circular birefringence.

"This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder."

Magneto-Optic Magnetic-Field-Sensing System Schematic and Probe

Terbium Gallium Garnet (TGG) magneto-optic material

"This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder."

Magnetic-Field Sensing• Magnetic-field phasor vs. position of horn antenna aperture

obtained at 60 GHz

- Probe length tuned to device frequency to create resonant cavityand provide 10-dB sensitivity enhancement.

- B-field can be combined with E-field to determine impedance at internal measurement locations

"This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder."

Combined Electric/Magnetic-Field Sensor• Utilizing a Hybrid Electro-Optic Magneto-Optic Probe

TGG (εr=12.4)Diameter: 2 mmLength: 2.3 mm

V = 61 rad T-1 m-1

GaAs (εr=13.2)Edge: 2 mm

Length: 0.1 mmr41 = 1.1 pm V-1

"(c) 2002 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Hybrid EO/MO Sensor Measurements•Device-under-test: Shorted microstrip transmission line

•RF: 4.003 GHz @ 17.7 dBm

• Demonstrated 22 dB of isolation• Isolation between electric and magnetic field sensitivity:

- limited by degree to which electrooptic effect can be minimized- minimization driven by optical linear polarization purity

"(c) 2002 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

Electric-Field, Magnetic-Field, and ThermalSensing in a High-Power Microstrip Patch

x

x

x|Hx| |Hx|

"(c) 2002 IEEE. Personal and classroom use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE."

ConclusionA fiber-optic-based field-sensing system offers:

• high spatial-resolution, broad-bandwidth, and low invasiveness

• detailed performance verification and diagnosis in the near-field region

• high measurement flexibility• detection of electric field distributions inside

of microwave enclosures and packages• expanded capability with thermal and

magnetic-field sensing