Sagi Mathai 1 Si WDM Modulator Array for FWH-OCDMA Sagi Mathai, Xin Sun Prof. Tsu-Jae King, Prof. Ming C. Wu EECS Department University of California, Berkeley OCDMA Review April 6 th, 2005

Sagi Mathai 2 FWH-OCDMA All Si Transmitter Encoded Output Multi-Wavelength Source Input Drop Ports for Feedback Control Wavelength Selective Microring Modulator Array

Sagi Mathai 3 Free-Carrier Plasma Effect Carrier Concentration (cm -3 ) Ref: Irace, et.al., Silicon Photonics, Topics in Appl Phys, vol 94, pp , Absorption Coefficient ChangeRefractive Index Change  (cm -1 ) -n-n Electrons Holes Electrons Holes

Sagi Mathai 4 Modulation 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 sisi sdsd n0n0  n=0 OPTICAL FREQUENCY RESPONSE SCHEMATIC (TOP VIEW) Modulated Output stst |s t /s i | 2 0

Sagi Mathai 5 Wavelength Channel Distribution 100 GHz FSR = 500 GHz Radius (µm) FSR (GHz) 4 WAVELENGTH CHANNELS FSR = 500 GHz corresponds to R = 24 µm FREE SPECTRAL RANGE

Sagi Mathai 6 Quality Factor and RC Parasitic Limits Radius (µm) f 3dB (GHz) Quality Factor f 3dB (GHz) QUALITY FACTOR LIMITED BANDWIDTH RC LIMITED BANDWIDTH R L =50  0 =1.55 µm RC Parasitics do not limited the bandwidth 2.5 Gb/s switching speed requires Q = 80, Gh/s switching speed requires Q = 20,000

Sagi Mathai 7 Transfer Function at Resonance sisi sdsd stst Carrier Density (cm -3 ) POWER TRANSMISSION  2 =  = 0.54 cm -1 Target 10 dB Extinction Ratio

Sagi Mathai 8 Carrier Transport Simulation SWITCHING DYNAMICSCARRIER CONCENTRATION

Sagi Mathai 9 Previous Results on Passive Si Microdisk Resonators Microdisk resonators have been fabricated on Si Optical performance characterized Optical Q > 100,000 was demonstrated

Sagi Mathai 10 Si Microring Modulator Schematic Input Port Drop Port Transmit Port Add Port P-type Regions N-type Region SOI

Sagi Mathai 11 Cross Section B A CD TOP VIEW A-B CROSS SECTIONC-D CROSS SECTION N-type Doping CD BOX 0.45  m P-type Doping AB 0.2  m 0.05  m BOX N-type Doping P-type Doping

Sagi Mathai 12 BPM Waveguide Simulations Width = 0.45  m Rib height = 0.2  m Slab height = 0.05  m Radius = 24  m STRAIGHT WAVEGUIDECURVED WAVEGUIDE Oxide Si

Sagi Mathai 13 Mask Layout Input Port Drop Port Transmit Port Add Port RF and DC Biasing Pads Microring Resonator 250 microns

Sagi Mathai 14 (1) Waveguide Dry Etching(2) Hydrogen Anneal(3) P+ Implant Fabrication Process (4) N+ Implant(5) Recrystallization/Dopant Activation Anneal (6) Ni-Silicide (7) Passivation/Via(7) Contact Pads/Interconnect

Sagi Mathai 15 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)

Sagi Mathai 16 ECTL PC /2 Plate Polarizer Bias-T DC Voltage Source RF Source EDFA Free-Space Optical Bench Oscilloscope ESA BERT IR Camera VOA Electrical Characterization OSA DUT RF Amp PD Si-Modulator Testbed

Sagi Mathai 17 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 1 st 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)