1

Electro-optic microdisk RF receiver

Mani Hossein-Zadeh

Advanced Network Technology Lab.(www.usc.edu/alevi)

4th photonic seminar University of Southern California

August 20th , 2004

2

Outline

n Introduction

n Microwave-photonics

n Microdisk resonant optical modulators

n LiNbO3 microdisk modulator

n LiNbO3 microdisk photonic RF receiver

n Integrated photonic RF receiver

3

Definitions

Baseband (Digital data, video, voice, …..)

Optical frequencies ( ~ 200 THz)

Baseband (0 – 1 GHz)

RF and mm-wave frequencies (5 GHz – 100 GHz)

Frequency

E-field or voltage amplitude

Frequency

E-field, voltage or current amplitude

Frequency

E-field or voltage amplitude

Optical carrier

RF carrier

≈

Data modulated RF carrier (suppressed carrier)Data modulated RF carrier ( transmitted carrier)

Baseband modulated optical carrier RF subcarrier modulated optical carrier

4

Conventional and photonic RF receiver architecture

n Conventional electronic homodynereceiver architecturew High-speed electronics² local oscillator at carrier

frequency ( fRF )² low-noise amplifier²RF mixer

w RF filters

n Photonic RF receiver architecturew Photonic components²Microdisk optical modulator²Optical filter²Low power DFB laser²Low-speed photoreceiver

w No high-speed electronicsw No conventional local oscillatorw No RF mixerw Reduced size and power consumptionw Insensitive to RF carrier frequencyw Optical isolation

LO ( fRF )antenna ( fRF )

bandpassfilter mixer

lowpassfilter`

low-noiseamplifier

basebandantenna

microdiskmodulator

bandpassoptical filter

low-speedphotoreceiver

lase

r

baseband

fRF

f

f

5

Applications areas

n Microdisk photonic RF receiverw Indoor wirelessw Fiber feed backbone networksw Space communication² Technology transfer

– Our 8.7 GHz LiNbO3 microdisk modulator shipped to NASA

Mars exploration requires new, efficient Ka-band receivers for surface to surface, surface to relay, and surface to Earth communications.

Photonic RF receiver

Indoor wireless LAN

Base stations

Central office

Customer units

Fiber feed backbone networks

Photonic RF receiver

60 GHz

6

Microwave photonics

n Microwave-photonics

w RF modulation of optical carrier

w High-speed optical detection

w Photonic generation of RF signals

w Photonic RF signal processing

200THz

≈

GHz

OM ODOSP

OpticalElectrical (RF)

ν1 −ν2

200THz

≈

200THz

≈GHz

OM

GHz200THz

≈ OD

OD

≈ν1

≈

ν2

ff

f

f f

f

ff

f

f

f

7

n External optical modulator applications:

w High-speed optical links (10 Gb/s-40 Gb/s)

w mm-wave/RF-optical links

w mm-wave/RF optical receiver

RF over fiber (RoF)

broad band Mach-Zehnder modulator

Resonant modulators

Microdisk modulator(Traveling wave)

Fabry-Perot modulator(Standing wave)

Small optical modulator withhigh sensitivity around a highfrequency carrier

OM

Base band signal

OD

? ? ?

L

OMOD

GHz

L

GHz

GHz

ff

f

f

8

n Resonant optical modulatorw Long photon lifetime (τp = Q/ωres) ⇒ long interaction length ⇒ high sensitivity

w Limited modulation bandwidth ( BW ≤ ∆νFWHM = νres /Q), centered

around integer multiples of the optical free-spectral-range (FSR)

Resonant optical modulators

RF frequency

Optical amplitude modulation

∆νFSR∆νFSR ∆νFSR

∆νFWHM∆νFWHM /2

--- Traveling wave MZ modulatorOptically resonant modulator

0

0.2

0.4

0.6

0.8

1

50 100 150 200

Disk diameter( µm)

FSR

(TH

z) LiNbO3

Polymer

InP, GaAs

0

20

40

60

80

0.5 1.5 2.5 3.5 4.5 5.5

Disk diameter (mm)

FSR

(G

Hz)

0

2

4

6

8

10

5 15 25 35 45

Disk diameter( µm)

FSR

(TH

z) LiNbO3

Polymer

InP, GaAs

LiNbO3

9

n Microdisk modulators

w Semiconductor

²InP

²InGaAsP

w Polymer

²APC/CPW

²CLD1/APC

w Electro-optic crystals

²LiNbO3

²SBN

²KTN

Bandwidth and optical quality factor

0

50

100

150

200

250

1.5E+06 3.5E+06 5.5E+06 7.5E+06 9.5E+06Optical quality factor (Q)

Dat

a ra

te (M

b/s)

Baseband modulation

FSR modulationLiNbO3 microdisk

02

4

6

8

10

2.0E+04 7.0E+04 1.2E+05 1.7E+05 2.2E+05 2.7E+05

Optical quality factor (Q)D

ata

rate

(Gb/

s) Baseband modulationFSR modulation

Polymerand all-buried InP/InGaAsPmicrodisk

1

21

41

5000 13000 21000 29000 37000 45000

Optical quality factor (Q)

Dat

a ra

te (G

b/s)

BasebandmodulationFSR modulation

semiconductormicrodisk (InP)

BW ≤ ∆νFWHM = νres /Q

10

0

20

40

60

80

0 0.02 0.04 0.06 0.08 0.1Wavelength ( 1550.05+...nm)

Opt

ical

pow

er (

W

)

Average size LiNbO3 microdisk optical resonator

n Optically polished electro-optic microdisk (LiNbO3) withcurved sidewall for high optical Q (>106)w Measured sidewall roughness

² Root mean square = 0.846 nm² Peak-peak height = 5.1 nm

Diameter = 2.82 mm

Thickness = 0.4 mm

12.5 µm13.

7 µm

2 - 6 mm

FSR: 7 – 22 GHz

nm

100-700 µm

Interferometric surface profiler

FSR

Whispering Gallery (WG) modes

nm

11

n LiNbO3 microdisk modulator w Small volume: 3 mm3 = π×3×0.4 mm3w large electro-optical coefficient

(r33 = 30.8×10-12 m/V)w High-Q optical whispering-gallery

(WG) resonance:2×106- 6×106 (loaded), 1.2×107 (unloaded)

w Long photon life time : 1.6 – 5 ns (loaded), 9.5 ns (unloaded)

w Long interaction length: 0.2-0.7 m (loaded), 1.3 m (unloaded)

w High-Q RF resonator :70 – 90 (loaded), Gv ∝ vQRF

n RF-photonic applicationw Optical modulation

² low power optical amplitude modulation

w RF signal processing in optical domain² high-frequency operation

– low loss in optical domain ² reduced power consumption

– laser diode local oscillator² optical isolation

RF-photonic LiNbO3 microdisk technology

Simultaneous electrical and optical resonance

Combination of microdisk and RF-photonictechnology demonstrated in LiNbO3 microdisk receiver

1 mm1 mm

12

LiNbO3 microdisk modulator

c-axis

R

TE TM RF resonator

optical mode

E-field

n LiNbO3 microdisk modulatorw Increased RF sensitivity and low power² RF and optical signal in simultaneous resonance² RF resonance provides voltage gain² high-Q (> 106 ) whispering gallery(WG) mode provide long RF-photon interaction time² photons highly confined at edge allowing high RF-photon spatial overlap

w Modulation only occurs at fRF = m ×∆νFSR with a bandwidth of ∆ν = ν0 /Q(νFSR= optical free spectral range, m : integer)

gmicrostripline

dielectric LiNbO3 microdisk

incident beam

microprism

FSR

Optical inputOptical inputOptical outputOptical output

wavelength

output

RF inputRF output

13

RF ring resonator

n Ring resonator controls the E-field inside the LiNbO3disk

w Proper spatial distributionw Synchronizing the RF and the optical waves

– fRF = m ×∆νFSR (m = 1, 2, …)w E-field amplification ( ∝√QRF)

E-field intensity distribution in the middle of the disk

Second-harmonic

w R

g

h

gPin = 1 W

(Vpp = 20 V)

400 µm

5.13 mm

Simulated fundamental RF resonance

magnetic coupling

E-f

ield

mag

nitu

de (

V/m

)

0

0.5

11.2 ×10

5

fRF (GHz)5.3 5.55.4 5.6 5.7

Emax

GE

Fundamental

+ - +-

- +

14

Third harmonic modulation

n Third harmonic modulation

w Disk diameter = 5.13 mmw Disk thickness = 0.4 mmw ∆νFSR = 8.7 GHzw f RF = 3× ∆νFSR =26.1GHzw Optical Q = 3.5 ×106w Modulation bandwidth ≈ 50 MHz

26 26.1 26.2 26.3

Frequency (GHz)

Mod

ulat

ed o

ptic

al p

ower

(nor

mal

ized

)

1

0 -30

-20

-10

0

7 12 17 22 27

Frequency(GHz)

S11

(dB

)

26.15 GHz

LiNbO3microdisk

RF ring resonator

Optical output

5 mm

150 µm magnetic coupling gap

RF input

Optical input

15

14.6 GHz LiNbO3 microdisk modulator

n 14.6 GHz LiNbO3 microdisk modulatorw 3 mm diameter LiNbO3 microdisk

² D = 3 mm, h = 400 µm² Q = 4 – 8 × 106, FSR = 14.6 GHz

w Single prism optical couplingw Improved RF coupling

² fine tuning of the ring-microstripline coupling coefficient: Critical coupling with 350 µm gap.

Tuning RF coupling

RF outputRF input

Optical mode

Sharp edge

Ring resonator

Ground plane

-10

-8

-6

-4

-2

14.4 14.5 14.6 14.7 14.8 14.9 15

Frequency (GHz)

S-pa

ram

eter

(dB

) g=250 µmg=350 µmg=450 µm

-10

-8

-6

-4

-2

14.4 14.5 14.6 14.7 14.8 14.9 15

Frequency (GHz)

S-pa

ram

eter

(dB

) g=250 µmg=350 µmg=450 µm

g=250 µmg=350 µmg=450 µm

wModified E-field distribution

² cylindrical symmetric E-field distribution

² enhanced E-field intensity

16

0

1

2

3

4

5

6

7

8

9

0 0.2 0.4 0.6 0.8 1 1.2Vpp,in (V)

Mod

ulat

ed o

ptic

al p

ower

at 1

4.5

GH

z(

µW )

Linear modulation at 14.6 GHz

Microstripline

Microring resonator

Microprism

3 mm

Output fiber

LiNbO3 microdisk

02468

1012

0.0044 0.0049 0.0054

Wavelength 1550+… (nm)

Tran

smitt

ed o

ptic

al p

ower

( W

)

Q = 4×106

n 14.6 GHz LiNbO3 microdisk modulator

w Disk diameter = 3 mmw Disk thickness = 0.4 mmw ∆νFSR = 14.6 GHzw f RF = 14.6 GHzw Optical Q = 4 ×106w Modulation bandwidth ≈ 45 MHz

0.7 V

17

0

50

100

13 14 15 16 17 18 19Wavelength detuning (pm)

Tra

nsm

itted

opt

ical

po

wer

( µ

W )

-80-70-60-50-40-30-20-10

0

-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10

Input RF power (dBm)

Dem

odul

ated

RF

pow

er

(dB

m )

Power sensitivity of single-frequency linear modulation at 14.6 GHz

n Linear modulation sensitivityw Dynamic range : > 70 dB

w SNR of 10 dB at -70 dBm (100 pW)

² SNR = 1 at – 85 dBm RF input power

w Modulation bandwidth: 80 MHz

w 0 dBm RF saturation power

w Fiber-to-Fiber insertion loss ~ 10 dB

w VHMM ~ 0.4 V

-88-85-82

-79-76-73

14.45 14.65 14.85Frequency(GHz)D

etec

ted

RF

pow

er (

dBm

)-70 dBm

Noise floor

310 µW/pm

-85 dBm sensitivity (SNR = 1)

Voltage

Optical output

VHMM

Quantifying the modulator sensitivity Q = 3.5×106

18

n Transmitted carrier RF format

w Nonlinear mixing of carrier and sidebands in the receiver

w No local oscillator required

n Photonic baseband down-conversion w Second-order nonlinear modulation with optical transfer function (Po ∝ VRF2 )

Self-homodyne RF-photonic receiver

f

ipNonlinear optical

modulation ( ) 2

Laser (194 THz)

Optical waveguide

fRF

E

f

Low speed photodiode+TIA

ff

22ffRFRFEE22

RF signal

Antenna

Optical

Electrical (baseband)Electrical (RF)

LO

Baseband

Antenna

f

V

19

),,,,,( ,0

20

2

2 hPQGfdVPd

N EinoVVRF RF

βκ===

Small signal regime (V0 < 0.1VHMM) and λ las = λ res :

GV: voltage gainQ: optical Q-factorPo,in: input optical power βΕ: E-field correction factorh: disk thicknessκ: optical coupling factorR: photodetector responsivity

...21

)( 220 ++= RFRFo VNNVP

ωb

2ωRF

2ωb

2ωRF± ωb2ωRF± 2ωb

222 RF

I VNm

RIb

≈ω

ω

I

DC term

Received signal: )cos())cos(1(0 RFbIRF mVV ωω+=

)2

()()( 220 RFRFoRF VNNRVRPVIγ

+==

Linear and nonlinear modulation with microdisk modulator

Tra

nsm

itte

d op

tica

l

pow

er (

Pt )

t Wavelength

t

t

Linear (Po ∝ VRF)

Nonlinear (Po ∝ VRF2)

VR

F

Linear output

Nonlinear output

Inpu

t

Optical transfer function

20

Optical input power = 50 µWOptical coupling factor (κ)= 0.114Distributed loss (/cm) = 0.0075 (Q = 1.2×107)DC shift = 0.135 pm/VVoltage gain factor (Volt) = 6Q = 3×106

Critical optical coupling and second-order nonlinear modulation with microdisk modulator

n Transmission dipsw Zero DC optical power (at λ laser = λ res )

with critical coupling

² reduction of optical noise generated by DC optical power

w Large second-order nonlinearity

λlaser = λres

VRF (Volt)

P o (W

)

2VHMM = 1.24 Volt

… First derivative (/10)--- Second derivative (/10)

05

10152025303540

85 90 95 100

Wavelength detuning (pm)

Det

ecte

d op

tical

pow

er(

W)

Critical coupling

Simulation

Measured transmitted powerQ = 2.8×106

×10-5

21

Experimental arrangement

Tunable laser:Tunable laser:linewidth < 0.5 MHzlinewidth < 0.5 MHzresolution < 0.3 pmresolution < 0.3 pm

isolator

polarizer

Baseband output

Low-speedPhotodetector

Tunable laserλlaser = 1550 nm

Signal generator (LO)

DC power supply

Signal/pattern generator

RF-filterBW = 1 GHz centered at 14.5 GHzRF mixer

Amplifier

Variableattenuator

Optical output

RF input

Baseband output

DC

Digital data output

22

Single tone down-conversion

n RF input signalw Carrier frequency = 14.6 GHzw Baseband frequency = 10 MHzw Transmitted carrier format

n Photodetector w Responsivity: 3 mV/µWw Bandwidth: 100 MHz

14.601 GHz

f

14.6 GHz

14.599 GHz

Voltage amplitude

)cos())cos(1( RFbIRF mV ωω+=

05

1015202530354045

0.40 0.60 0.80 1.00 1.20 1.40

RF modulation index (m I)

Sup

ress

ion

rati

o .

(dB

ele

ctri

cal)

f

10 MHz

20 MHz30 MHz

Input RF signal

Down-convertedsignal

Third harmonic

Second harmonic-20 dB

≈

-53

-51

-49

-47

-45

-43

-41

-39

-37

-20 -18 -16 -14 -12 -10 -8 -6Total RF power (dBm)

Dow

n co

nver

ted

optic

al p

ower

at

10

MH

z (

dBm

)

30

40

50

-0.4 -0.2 0 0.2 0.4Wavelength detuning (pm)

Rec

eive

d op

tical

po

wer

( W

)

SimulationMeasurement

Optical mode

mI = 0.7 (VLO/VBB = 2.8)

Voltage amplitude

23

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2Modulation index (m I)

Nor

mal

ized

det

ecte

d ba

seba

nd o

ptic

al p

ower

.

Optimizing modulation index for single frequency down-conversion efficiency

n RF modulation format effectw Total received RF power ≈ -15 dB

w Transmitted carrier format

² modulation index mI < 2

w Optimized modulation index

² measurement mI ≈ 0.7

² calculation (square law response) mI ≈ 0.8

Measurement Q = 4 × 106Q = 3.54 × 106

Q = 3.15 × 106

Calculated down-conversion efficiency and second-harmonic suppression ratio based on ideal square law response

0

10

20

30

40

50

0 0.5 1 1.5 2Modulation index (m I )

Seco

nd-h

arm

onic

sup

pres

sion

. (d

B e

lect

rical

)

0

10

20

30

40

0 0.5 1 1.5 2Modulation index (m I )

Pob

/Pom

(%

)

At small signal regime (PRF < -10dBm) a modulation index of mI = 0.7 results in 25% down-conversion efficiency and about 15 dB second-harmonic suppression ratio.

(Down-conversion efficiency,Pob/Pom, is defined as the ratio of modulated optical power at baseband frequency and the total modulated optical power)

Conclusion• 0.7< mI

24

n Time and frequency domain simulationw Input RF signal

² carrier frequency : 10 GHz

² baseband signal : 62.5 Mb/s NRZ PRBS data stream.

² modulation index : 0.6

w Detector band width = 100 MHz

Simulated signal flow in RF-photonic receiver

Time, t (ns)

Detected optical power (inverted)

Time, t (ns)

Input data

a.u.

a.u.

0

0 640

640

×10 ×10

)cos())cos(1( RFbIRF mV ωω+=

Optical output power, a.u.

0 180λlaser

RF input signal

Time, t (ns)

Po,max(2)

∆λRF

Time, t (ns)

0

180

Wavelength, λ

RF input spectrum Optical output intensity spectrum

25

Measured 10 Mb/s data down-conversion from 14.6 GHz carrier

n Ku-band photonic RF receiverw Carrier frequency : 14.6 GHzw Baseband: 10 Mb/s NRZ 27-1 PBRSw Received RF power measured within 100

MHz bandwidth centered at 14.6 GHz.w Digital photo receiver² sensitivity: -35 dBm² bandwidth: 100 MHz

-70-60-50-40-30-20-10

0

14.58 14.6 14.62 14.64 14.66Frequency (GHz)

RF

pow

er (d

Bm

)-70-60-50-40-30-20-10

0

0 10 20 30 40 50Frequency(MHz)

Bas

eban

d po

wer

(dB

m)

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

-22 -21 -20 -19 -18 -17 -16 -15 -14

Received RF power (dBm)

BER

Down-converted data

Input data

0

5

10

15

20

25

-0.6 -0.4 -0.2 0 0.2 0.4 0.6

Wavelength detuning (pm)

Rec

eive

d op

tica

l p

ower

( W

)

26

10 Mb/s, 50 Mb/s and 100 Mb/s data down-conversion from 14.6 GHz carrier

Original eye

Down-converted eye

Time, t (10 ns/div)Time, t (25 ns/div)

10 Mb/s 50 Mb/s

n Ku-band photonic RF receiverw RF carrier frequency : 14.6 GHzw Baseband: 10 Mb/s, 50 Mb/s, 100 Mb/s NRZ PBRS 27-1w m = 0.7w Received RF power : -15 dBm (integrated power measured within 100

MHz bandwidth centered at 14.6 GHz)

100 Mb/s

Time, t (5 ns/div)

27

-15

-10

-5

0

13.5 14.05 14.6 15.15 15.7

Frequency (GHz)

S11

(dB

)

Measurement of 14.6 GHz patch array performance

-30 dBm

-20 dBm

-40 dBm

-30 dBm

-20 dBm

-40 dBm

E-plane(x = 0,R = 5.5 ft)

H-plane(y = 0 ,R = 5.5 ft)

z

y

x

-30

-25

-20

-15

-10

-5

0 1 2 3 4 5 6 7Z (ft)

Receiv

ed

po

wer

(dB

m)

(x = 0, y = 0 , R = Z) input power to transmitting

antenna = 10 dBm

H-plane

E-plane

5.5 ft z

y

x

BW= 1 GHz

R

R

22 mm

n 2×2 patch antenna array at 14.6 GHzw εr = 2.94 , tan δ = 0.00119 w Efficient and directive radiationw Low return lossw Planar structure and small size

28

14.6 GHz wireless link with microdisk optical receiver

TransmitterReceiver

29

Wireless data communication with self-homodyne microdisk optical receiver

n Wireless self-homodyne microdisk RF-photonic receiverw 14.6 GHz 4-patch antenna array

w High sensitivity microdisk optical modulator

w RF-photonic nonlinear modulationw Carrier frequency : 14.6 GHzw Modulation index: m = 0.8w Baseband: 10 Mb/s NRZ PBRS 27-1w Input RF power to transmit antenna:

28 dBmTunable RFopen termination

RF coupling fine tuning

Original data

Down-converted data

Antenna

30

λ0

Future: photonic RF receiver

n Electrical stabilization and wavelength locking (dc bias on electrodes)wLocking the laser wavelength to a chosen optical transmitted power (Pol)

Wavelength (λ)

Po

Pol

∆λdc (0.13 pm/Volt)

sensitive low-speedphotodiodelaser

microstripline

optical waveguideRF signal

data

electro-optic microdisk

reference voltage

control circuit

n Higher carrier frequenciesw Harmonic modulationw Small disks

λ0

0

2

4

6

8

10

12

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Wavelength (1550+... nm)

Det

ecte

d op

tica

l po

wer

( µW

)

FSR = 340 pm (42.5 GHz)

Q = 1.3×106

1 mm

LiNbO3microdisk

31

Future: photonic RF receiver

n Optical filteringw Reduce noise by eliminating the photocurrent from high-frequency

components in the signal that are not used.

RF signal from antenna

Microdisk modulator

n Monolithic integration of photonic RF receiver

194 THz194 THzEE

////optical filter dataphotodetector

iipp

ff////

194 THz194 THz

22ffRFRF 22ffRFRFEE

ff f

laser

microstripline

optical waveguide

data

electro-optic microdisk

control circuit

passive ring resonators

photodetector DSP

32

Future: microdisk photonic RF receiver integration

n Electro-optic microdisk modulator for λ = 1550 nm laser lightw Electro-optic crystals

² LiNbO3– Electro-optic effect: r33 = 30.8 pm/V

² SBN– Electro-optic effect: r33 = 246 pm/V

² KTN– Electro-optic effect: r33 = 600 pm/V

w Polymer (CLD1/APC, APC/CPW)² Electro-optic effect: r 33= 36-65 pm/V

w InP/GaAs² Electro-optic effect: r41 ≈ 1.3-1.4 pm/V ² Depletion width modulation, electro-absorption (Frank- Keldish

effect), ……………….

Sensitive low-speedphotodiode

Microlensesmicroprism

laser

Microstripline

V-groove

Optical waveguide

RF signal

data

LiNbO3 mounted on Si optical bench

Sensitive low-speedphotodiode

laser

Microstripline

Optical waveguide

RF signal

data

Semiconductor or polymer(photonic integrated chip)

LiNbO3microdisk

Semiconductor/polymer microdisk

Hybrid integration (NASA) Monolithic integration

Microphotonic receiver

Integrated planarantenna

Digital signal processing

33

Power efficiency

n 60 GHz monolithic electronic receiver (LNA+LO+MX)(Ref: K. Ohata et al, IEEE MTT, Vol. 44, Dec 1996 ) w 0.15 µm N-AlGaAs/InGaAs HJFET MMIC technologyw Power consumption = 400 mWw Volume: 900 mm3

n 60 GHz photonic receiverw No high-speed electronic devicesw Less power consumption ( 0.05 dB/pm Baseband output

Power ≈ 6 mW Power < 50 mW (BiCMOS)Power ≈ 56 mW

34

Conclusion

n Microwave photonic technology can provide solutions to current challenges in mm-wave electronic wireless design.

n Nonlinear optical modulation and transmitted carrier RF modulation format may be combined in a self-homodyne architecture to realize a low-power and low-cost photonic RF receiver.

n Microdisk resonant optical modulator is one of the best candidates for self-homodyne photonic RF receiver design

n Proof of concept experiments with LiNbO3 microdisk modulator demonstrate the feasibility of electro-optic microdisk wireless receiver for short distance applications.

n By employing alternative electro-optical materials such as semiconductors and polymers, the photonic RF receiver can be integrated in a single chip.

35

END

ELECTROMAGNETIC WORLD!ELECTROMAGNETIC WORLD!in which DCin which DC--toto--light is used for communicationlight is used for communication

Optical

Electrical (baseband)Electrical (RF)

Electrical (DC)

36

-10

-8

-6

-4

-2

0

8.5 8.7 8.9 9.1 9.3 9.5 9.7 9.9

Frequency(GHz)

S21(d

B)

RF resonant frequency tuning

n Mechanical tuning of resonant frequency (compatible with MEMS technology)w Resonant frequency of the ring resonator can be tuned by

varying the height of an air cylinder under the LiNbO3 disk.w Accurate tuning of fRF to optical FSR

240MHz

h

4.17 mm

5.98 mm

LiNbO3

Air

Brass

Copper ring

RF input RF output

99.05

9.19.15

9.29.25

9.39.35

0 1000 2000 3000 4000

h (mm)

Res

onan

t fre

quen

cy (G

Hz)

37

Feedback loop stabilization

n Microdisk modulatorw LiNbO3 disk (D = 5.13 mm , h = 400µm)w RF ring electrodew Feedback loop stabilization

² Tuning the resonant wavelengthsby DC voltage.

² Locking to maximum slopeby feedback loop.

High-speedphotodetector

Laser light in

Low-speed photodetector

Reference voltage

10%

90%

RF output

RF input

Ring

LiNbO3 disk

Splitter

∆ ≈ 0.13 pm/V

Time(sec)

10 %

det

ecte

d op

tical

po

wer

(µW

)

Feed back on

Feed back off

Laser light out

Gold wire

1.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

3772.1 604.2 1000.0 1500.0 2000.0 2500.0 3000.0 3500.0

Time(sec)

10 %

det

ecte

d op

tical

po

wer

(µW

)

0.026 0.0265 0.027 0.0275 0.028Wavelength (1550+...nm)

Optical mode spectrum

38

Magnetic coupling

Second harmonic modulation

Photons in resonance with even second harmonic moden Photon in resonance with E-field

w fRF = 2× fFSR

RF input

Dielectric

Dielectric

Ring resonator

Cut plane In the middle of the disk

microstripline

c-axis

Air

t = T/2= 1/(2fFSR)

Optical traveling wave

RF standing-wave

RF input