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Sagi Mathai 1
Si WDM Modulator ArraySi WDM Modulator Arrayfor FWH-OCDMAfor FWH-OCDMA
Sagi Mathai, Xin SunProf. Tsu-Jae King, Prof. Ming C. Wu
EECS DepartmentUniversity of California, Berkeley
OCDMA ReviewApril 6th, 2005
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Sagi Mathai 2
FWH-OCDMA All Si TransmitterFWH-OCDMA All Si Transmitter
EncodedOutput
Multi-WavelengthSource Input
Drop Ports for Feedback Control
Wavelength Selective Microring Modulator
Array
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Sagi Mathai 3
Free-Carrier Plasma EffectFree-Carrier Plasma Effect
Carrier Concentration (cm-3) Carrier Concentration (cm-3)
PNPN 1818 100.6105.8,
8.01822 105.8108.8, PNPNn
Ref: Irace, et.al., Silicon Photonics, Topics in Appl Phys, vol 94, pp 361-392, 2004.
1012 1013 1014 1015 1016 1017 101810-6
10-5
10-4
10-3
10-2
10-1
100
101
102
1012 1013 1014 1015 1016 1017 101810-9
10-8
10-7
10-6
10-5
10-4
10-3
Absorption Coefficient Change Refractive Index Change
(
cm-1)
-n
Electrons
Holes
Electrons
Holes
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Sagi Mathai 4
Modulation MechanismModulation Mechanism
• Index of refraction can be tuned by injecting or depleting carriers in the microring optical waveguide
• Shifting the index of refraction will shift the microring resonant frequency and thus its transfer curve
• The resulting modulation in resonant frequency will cause intensity modulation on the optical carrier
si
sd
n0
n=0
OPTICAL FREQUENCYRESPONSE
SCHEMATIC(TOP VIEW)
Modulated Output
st
|st/si|2
0
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Sagi Mathai 5
Wavelength Channel DistributionWavelength Channel Distribution
100 GHz
FSR = 500 GHz0 5 10 15 20 25 30
0
200
400
600
800
1000
Radius (µm)
FS
R (
GH
z)
4 WAVELENGTH CHANNELS
FSR = 500 GHz corresponds to R = 24 µm
FREE SPECTRAL RANGE
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Sagi Mathai 6
Quality Factor and RC Parasitic LimitsQuality Factor and RC Parasitic Limits
5 10 15 20 25 30200
250
300
350
400
450
500
Radius (µm)
f 3d
B (
GH
z)
103 104 1050
5
10
15
20
25
30
Quality Factor
f 3d
B (
GH
z)
QUALITY FACTORLIMITED BANDWIDTH
RC LIMITEDBANDWIDTH
RL=50 0=1.55 µm
RC Parasitics do not limited the bandwidth
2.5 Gb/s switching speed requires Q = 80,000
10 Gh/s switching speed requires Q = 20,000
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Sagi Mathai 7
Transfer Function at ResonanceTransfer Function at Resonance
1013 1014 1015 1016 1017-25
-20
-15
-10
-5
0si
sd
st
i
t
s
slog20
Carrier Density (cm-3)
POWER TRANSMISSION
2 = 0.063 = 0.54 cm-1
Target 10 dB Extinction Ratio
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Sagi Mathai 8
Carrier Transport SimulationCarrier Transport Simulation
0.0 0.5 1.0 1.5 2.0 2.5 3.0-7.0x10-6
-6.0x10-6
-5.0x10-6
-4.0x10-6
-3.0x10-6
-2.0x10-6
-1.0x10-6
0.0
tOFF
=0.042nstON
=0.051ns
n
Time (ns)
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.01E10
1E11
1E12
1E13
1E14
1E15
1E16
Ho
le C
on
cen
trat
ion
(cm
-3)
Driving Voltage (V)
SWITCHING DYNAMICS CARRIER CONCENTRATION
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Sagi Mathai 9
Previous Results on Passive Si Microdisk Previous Results on Passive Si Microdisk ResonatorsResonators
• Microdisk resonators have been fabricated on Si
• Optical performance characterized
• Optical Q > 100,000 was demonstrated
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Sagi Mathai 10
Si Microring Modulator SchematicSi Microring Modulator Schematic
InputPort
DropPort
TransmitPort
AddPort
P-typeRegions
N-typeRegion
SOI
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Sagi Mathai 11
Cross SectionCross Section
B
A
C D
TOP VIEW
A-B CROSS SECTION C-D CROSS SECTION
N-typeDoping
C D
BOX
0.45 m
0.45 m
P-typeDoping
A B
0.2 m
0.05 m
BOX
N-typeDoping P-type
Doping
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Sagi Mathai 12
BPM Waveguide SimulationsBPM Waveguide Simulations
Width = 0.45 mRib height = 0.2 m
Slab height = 0.05 m
Radius = 24 m
STRAIGHT WAVEGUIDE CURVED WAVEGUIDE
Oxide Oxide
Oxide Oxide
SiSi
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Sagi Mathai 13
Mask LayoutMask Layout
Input Port
Drop Port
Transmit Port
Add Port
RF and DC Biasing Pads
MicroringResonator
250 microns
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Sagi Mathai 14
(1) Waveguide Dry Etching (2) Hydrogen Anneal (3) P+ Implant
Fabrication ProcessFabrication Process
(4) N+ Implant(5) Recrystallization/DopantActivation Anneal
(6) Ni-Silicide
(7) Passivation/Via (7) Contact Pads/Interconnect
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Sagi Mathai 15
Berkeley Microlab CapabilityBerkeley Microlab Capability
• Complete 0.35μm CMOS on 6” wafers
• 0.35μm Deep UV Lithography: ASML 5500/90 Stepper
• Device group demonstrated FIN FET with 60 nm gate length (King, Hu, Bokor)
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Sagi Mathai 16
ECTL PC /2 Plate Polarizer
Bias-TDC Voltage
SourceRF
Source
EDFA
Free-SpaceOptical Bench
Oscilloscope
ESA
BERT
IR CameraVOA
ElectricalCharacterization
OSA
DUT
RFAmp
PD
Si-Modulator TestbedSi-Modulator Testbed
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Sagi Mathai 17
SummarySummary
• Reviewed preliminary study on an all Si based microring modulator array
• Exploit SOI technology and CMOS compatible fabrication process
• Built testbed for device characterization
• 1st generation device target– 2.5 Gb/s
– Single wavelength channel
– Free spectral range ~ 0.5 THz
• Next generation device– 10 Gb/s
– Q = 20,000
– 4 wavelength channels (100 GHz spacing)
– Low power (~µW)