Si WDM Modulator Array for FWH-OCDMA

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Si WDM Modulator Arrayfor FWH-OCDMA
OCDMA Review April 6th, 2005

• Sagi Mathai, Xin SunProf. Tsu-Jae King, Prof.
  Ming C. Wu
• EECS DepartmentUniversity of California, Berkeley

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FWH-OCDMA All Si Transmitter
Wavelength Selective Microring Modulator Array
Encoded Output
Multi-Wavelength Source Input
Drop Ports for Feedback Control
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Free-Carrier Plasma Effect
Absorption Coefficient Change
Refractive Index Change
Holes
Holes
?? (cm-1)
-?n
Electrons
Electrons
Carrier Concentration (cm-3)
Carrier Concentration (cm-3)
Ref Irace, et.al., Silicon Photonics, Topics in
Appl Phys, vol 94, pp 361-392, 2004.
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Modulation Mechanism
OPTICAL FREQUENCY RESPONSE
SCHEMATIC (TOP VIEW)
si
st
Modulated Output
st/si2
?n?0
?n0
?
?0
sd

• 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

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Wavelength Channel Distribution
FREE SPECTRAL RANGE
4 WAVELENGTH CHANNELS
100 GHz
FSR (GHz)
FSR 500 GHz
Radius (µm)
FSR 500 GHz corresponds to R 24 µm
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Quality Factor and RC Parasitic Limits
QUALITY FACTOR LIMITED BANDWIDTH
RC LIMITED BANDWIDTH
f3dB (GHz)
f3dB (GHz)
RL50 ?
?01.55 µm
Radius (µm)
Quality Factor
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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Transfer Function at Resonance
POWER TRANSMISSION
si
st
?2 0.063 ? 0.54 cm-1
sd
Carrier Density (cm-3)
Target 10 dB Extinction Ratio
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Carrier Transport Simulation
SWITCHING DYNAMICS
CARRIER CONCENTRATION
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Previous Results on Passive Si Microdisk
Resonators

• Microdisk resonators have been fabricated on Si
• Optical performance characterized
• Optical Q gt 100,000 was demonstrated

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Si Microring Modulator Schematic
P-type Regions
Input Port
Drop Port
Transmit Port
SOI
N-type Region
Add Port
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Cross Section
TOP VIEW
C
D
B
A
A-B CROSS SECTION
C-D CROSS SECTION
N-type Doping
P-type Doping
C
D
BOX
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BPM Waveguide Simulations
STRAIGHT WAVEGUIDE
CURVED WAVEGUIDE
Oxide
Oxide
Si
Si
Oxide
Oxide
Width 0.45 ?m Rib height 0.2 ?m Slab height
0.05 ?m
Radius 24 ?m
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Mask Layout
RF and DC Biasing Pads
Input Port
Transmit Port
Microring Resonator
250 microns
Drop Port
Add Port
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Fabrication Process
(1) Waveguide Dry Etching
(2) Hydrogen Anneal
(3) P Implant
(4) N Implant
(5) Recrystallization/Dopant Activation Anneal
(6) Ni-Silicide
(7) Passivation/Via
(7) Contact Pads/Interconnect
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Berkeley 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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Si-Modulator Testbed
RF Source
DC Voltage Source
Bias-T
IR Camera
DUT
ECTL
PC
?/2 Plate
Polarizer
EDFA
VOA
Free-Space Optical Bench
ESA
OSA
RF Amp
BERT
PD
Oscilloscope
Electrical Characterization
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Summary

• 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)