Integrated electro-optical waveguide based devices with liquid crystals on a silicon backplane Florenta Costache Group manager Smart Micro-Optics SMO/AMS Fraunhofer Institute for Photonic Microsystems, Dresden, Germany
Fraunhofer IPMS, Dresden Customized devices based on MEMS - silicon and CMOS technology From demonstrator to pilot fabrication IP of technology, devices and applications; licensing Surface MEMS Technology MEMS on CMOS- Backplanes Application: Spatial Light Modulator R&D - Smart Micro-Optics MEMS/MOEMS Bulk MEMS Technology - dim. Structures in Silicon Applications: MEMS Scanner Pressure Sensor CMOS HV- CMOS- Process Application: Backplane for Spatial Light Modulator Source: IPMS Organic on silicon technology platform Electroactive materials Device design and fabrication Active waveguides Tunable micro-optics Electroactive material research Polymers, liquid crystals, blends Applications: Waveguides, actuators, sensors Tunable micro-optics Polymer actuators Applications: Variable focus micro-lenses EO waveguides EO materials Applications: switches, power splitter, VOA
Introduction Current trends for photonic applications (i.e. telecommunication, sensing ) Migration from electrical to photonic circuits and interfaces Higher integration capability Reduced complexity and simplified devices Re-configurability of circuits and devices Reduction of the number of conversions The existing technologies meet some of these demands The search for new solutions continues!!! IPMS new concept of liquid crystal waveguides opens the way to new reconfigurable devices
Outline Electro-optically induced waveguides (EOIW) Liquid crystals for EOIW switching LC-EOIW based devices fabrication On chip characteristic functions of LC-EOIW devices Conclusions and outlook
Electro-optically induced waveguides... ), ( 2 1 ), ( 2 1 ), ( 2 0 0 0 + + + = y x E R n y x E r n n y x n k k k linear Pockels effect quadratic EO Kerr effect EO effects : refractive index change due to applied electric field EO material layer placed in between stripe electrodes EOIW EOIW devices: switching, splitting, attenuation, modulation EOIW manufacturable using planar silicon wafer technology E off E on... ), ( 2 1 ), ( 2 1 ), ( 2 0 0 0 + + + = y x E R n y x E r n n y x n k k k
EOIW Materials Requirements EO materials low optical loss fast switching speed low power consumption low cost Effect Material EO coeff. Bandwidth Fabrication Pockels LiNbO 0pm/V > GHz Growth, Cutting EO Kerr Polymer-Dye >100pm/V > GHz Poling Optoceramics (PLZT) high GHz High pressure sintering Isotropic phase liquid crystals Moderate > MHz EASILY INTEGRABLE In LC cells Our choice!!! Isotropic phase liquid crystals (LC) Large EO Kerr constants Refractive index close to SiO 2 Low absorption ( < 0.5 db/cm) Transmission: 400-1600nm Long-time stability Low permittivity Easy-to-handle; Inexpensive temperature and mobility cristalline nematic isotropic degree of order
Electro-optically induced waveguides EOIW based on liquid crystals Liquid crystals Liquid crystal Electrode on/off Cladding EOIW switch by planar silicon wafer technology processes 1 Free-space coupled EOIW chip demonstrator 2 Bending EOIW Wafer with various electrode configurations 1 2
EOIW - Coupling efficiency Multimode operation: Measurements in good agreement with simulation Similar behavior of coupling efficiency for LC-blends based waveguides
LC-EOIW for various functionalities Waveguide pathway given by the electrode pathway Switching 1x2 (free space coupling) ITO or Al cladding i cladding ii insulation i) 1x2 LC switch: electrode geometry; ii) EOIW on a chip Switching 1x1 OFF Attenuation 2 cm ON beam direction
Characteristic parameters LC-EOIW: functions on the same chip Fiber In Fiber Out 1x1 Switching IL < 4dB Attenuation 0-0 db Transmission: Optimized @ 1550 nm; SM TM Straight waveguide Temperature: 5 C
Fiber-coupled LC-EOIW chip Wavelength range: 400 1600 nm Optimized for 1550 nm Configuration: SM/MM Optimized for SM Multiple functions on the same chip 1x2 Switching Ins. Loss < 5dB (for TM pol.) IL possible < 2dB Possible PDL < 1dB Response time: ~0.5 µs Splitting Ins. Loss < 7dB (50/50) Attenuation At. Range: 0-0 db Modulation f db LC-Chip > 2MHz Switching / Attenuation Modulation Power splitting
1x2 Fiber-coupled LC-EOIW switch Distinctive chip features: On-chip fiber-to-waveguide coupling (V-grooves) Small footprint More channels possible (Re)configurable design and functions Scalable, integrable with other devices Reliable no mechanical parts LC used: non-degradable In In Out 2 Out 1 Out 2 Out 1 Switching from the input port to an output port Power splitting from the input to two output ports
LC-EOIW technology Configurable for applications: Fiber optic sensor networks Fast channel switching Signal monitoring Optical telecom networks Based on LC-EOIW concept: N x M Switching Polarization diversity Interconnection VOA Variable power splitting 1x2 switch ( 1550nm, SM, PM, bidirectional ) Fiber 2 Fiber 1 Fiber 10 cm Modulator ( 1550nm, 5MHz ) Fiber 2 Fiber 1 Modulation for laser technology
Further possible EO waveguide devices Devices for fiber optic networks Switch & VOA & PS In Router & Switch Wavelength selection = λ λ n n Out In Directional coupler Ring resonator Fiber to chip coupling Out In Out In Out In with structured electrode configuration
Summary: LC-EOIW LC-EOIW switch specifications: Wavelength: currently optimized for 1550 nm Channel number: 1x2 Switching time: ~0.5 µs (2MHz) Insertion loss: < 4dB; under development < 2 db Polarization: Polarization sensitive (TM) Possible PDL < 1dB Configuration: SM (MM possible) LC EOIW technology - parameters which can be configured Number channels/ports Wavelength (between 400-1600 nm) SM or MM Function: switching, VOA, modulation, power-splitting
Conclusions EO induced waveguides in liquid crystals Free-space 1x2 switching with LC waveguides Fiber-coupled 1x2 switching with LC waveguides Fabrication using planar silicon technology Versatile design for switching, connection, attenuation, modulation, power splitting Projects: Fraunhofer Attract Grant # 69212 BMBF - Photonics Research Germany, Contract # 1N12441