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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