Polymer-based optical interconnects using nano-imprint lithography Arjen Boersma,Sjoukje Wiegersma Bert Jan Offrein, Jeroen Duis, Jos Delis, Markus Ortsiefer, Geert van Steenberge, MikkoKarppinen, Alfons van Blaaderen, Brian Corbett www.fp7-firefly.eu Contents Motivation General concept Low optical loss polymers Polymer waveguides Nano Imprint Lithography (NIL) Laser Direct Imaging (LDI) Photonic Crystals Integration Conclusion and Outlook 2 1
Introduction Firefly is a European project of 9 partners in 6 countries The main goal is the development of polymer based optical interconnects 3 Motivation In the information and communication industry the performance of microprocessors continues to increase. Consequently, the data flow to and from the processors has to increase. Introduction of opticaldata transmission as a replacement of electronicdata transmission in most transmission applications longer than 10 meters. A need remains for optical data transmission for shorter distances Source: IBM Source: IBM 4 2
Video 5 General concept and objectives Development of polymeric, single mode waveguides and photonic crystal structures for optical data transfer based on 3D structured nano-materials manufactured using new cost effective production processes suitable for large scale manufacturing. Development of new optical components Waveguide-fibre coupling VCELS The target application: the manipulation of light in, for example, optical interconnects for data communication in, for example, computing systems 6 3
Low optical loss polymers (1/4) - Requirements Requirements: Optical loss in optical windows 1310 and 1550 nm < 0.2 db/cm Tunablerefractive index: n/n CORE = 0.3-1.0 % There is a trade of. Low index steps result in more tolerant coupling to glass fibersand VCSELs, and lower scattering loss due to sidewall roughness. High index steps make compact waveguide bends possible Photodefineable by UV curing: Nano Imprint Lithography Laser Direct Imaging Curing in air (i.e. no oxygen inhibition) Viscosity at room temperature for photolithographic process: < 2000 cps. Good adhesion to substrates Resistant to solder reflow at 260 C 7 Low optical loss polymers (2/4) State-of-the-art Many optical polymer solution for wavelengths below 1310 nm Type ~1300 nm Fluorinated acrylates ~1550 nm Photopatternable In air NIL 0.2 0.7 Yes (1 hour) No No Cytop/Teflon AF 0.02 0.1 No (RIE) No No BCB 0.2 1.5 No (RIE) No No Ormocer 0.25 0.5 Yes Yes Yes Lightlink(POSS) <0.1 <0.2 Yes Yes No Siloxanes 0.1 1.5 Yes Yes Yes 8 4
Low optical loss polymers (3/4) - Approach Siloxane based polymers : Reduced amount of CH bonds UV curable in air by use of epoxy functionality High temperature resistant Refractive index easy adjustable Suitable viscosity for processing pure Component 1 0.65 pure Component 2 9 Low optical loss polymers (4/4) - Results The Si-CH 3 groups in the siloxanepolymer cause high absorption in 1550 nm range Amount of SiCH 3 reduced by: Fluor groups Phenyl groups Deuterium groups Loss at 1310 nm can be reduced to < 0.1 db/cm Introduction of deuterated moieties shifts absorption peak from lower wavelength exactlyto 1550 nm Best results were obtained with fluoro-phenyl groups (~0.5 db/cm) 10 5
Polymer waveguides (1/4) - Modelling Results: Imprint process leads to a residual layer of ~ 0.5 µm which influences modes n CLADDING =1.41 and core material derived from this; Index contrast < 1% Calculate modes for 0.85% index contrast between core and clad 4.5 µm core waveguide leads to mode size of 6 µm Between MFD of VCSEL (6 µm) and optical fibre (9 µm) 2 µm square waveguide MFD = 8 x 12 µm 4.5 µm square waveguide MFD = 6 µm 9 µm square waveguide MFD = 9 µm 11 Polymer waveguides (2/4) Nano Imprint Lithography Attractive manufacturing process for multilayer waveguide networks 12 6
Polymer waveguides (3/4) -NIL Single mode waveguides by NIL shown for Ormocer and Siloxanes Ormocer waveguide loss ~0.1-0.2 db/cm Inverted waveguides imprinted in the siloxane polymer 13 Polymer waveguides (4/4) Laser Direct Imaging Channel waveguide-like microstructures with very low sidewall roughness were fabricated using laser direct write photolithography Direct UV exposure using a frequency-tripled Nd:YAG laser, followed by development A broad range of width (6-13 μm)was obtained by scanning the laser writing speed Tapered waveguide for nonoptimized polymer SEM image of a waveguide defined by laser direct write photolithography Waveguide width versus laser writing speed Laser beam diameter: ~8.3 µm 14 7
Photonic Crystals (1/5) - Concept Bends in low index contrast waveguides must be large to reduce loss Aim is to reduce sizes of bends in waveguides Photonic crystal from high refractive index nanoparticles Band-gap and angle of incidence determine reflection on/in colloidal crystal 15 Photonic Crystals (2/5) modelling 3D Sphere Structure Same result as without shell Lattice Constant 700nm TiO2 Core Core Radius 215 nm SiO2 Shell Shell Radius 350 nm 16 8
Photonic Crystals (3/5) - Manufacturing Patterned deposition of monodisperse nanoparticles in templates Monodisperse 500 nm silica spheres Si Mould for manufacturing nanostructured templates Convective and capillary filling of templates Core-shell TiO 2 -SiO 2 spheres SPIE-OPTO M12 Technical San Francisco, meeting 5 February Oct 20122013 17 Photonic Crystals (4/5) Colloidal stacking Depth of template determines amount and stacking of nanoparticles SEM picture of particles deposited without template SEM picture of particles deposited with template 18 9
Photonic Crystals (5/5) Results 19 Integration (1/3) Additional components For integration some additional components are required VCSELs are tuned to meet the integration requirements, with respect to: Sizes (thickness, width) Wavelengths Processability Size of Array Optical Fibres will be aligned with waveguides: U-groove or V-groove CTE mismatch End facet processing 20 10
Integration (2/3) First integration steps use gold mirror in stead of photonic crystal cladding core cladding mirror VCSEL Silicon substrate fibre VCSEL waveguide Fibre waveguide Mirror waveguide Photonic crystal -waveguide 21 Integration (3/3) - Tolerances Insertion Loss (db) VCSEL waveguide coupling using a 45 degree mirror Find coupling loss as a function of VCSEL and waveguide mode size As a function of polymer planarization thickness, misalignment, tilt 0-2 -4-6 -8-5 -4-3 -2-1 0 1 2 3 4 5 Vertical Height Error (µm) Waveguide(wo=2 µm) Waveguide(wo=3 µm) Waveguide(wo=4 µm) Waveguide(wo=5 µm) Waveguide(wo=6 µm) Insertion Loss (db) Insertion Loss (db) 0-2 -4-6 -8 0 20 40 VCSEL-Mirror Distance (µm) 0-1 -2-3 -4-5 -6-7 -8-7,5-5 -2,5 0 2,5 5 7,5 Mirror Tilt Error ( ) 22 11
Conclusions and Outlook Nano Imprint Lithography enables integration of waveguides and templates for photonic crystals First results obtained for individual components Siloxane polymer defined that seems suitable for NIL Optical loss must be improved Photonic crystals for light reflection will be challenging Integration of components needs major effort to show feasibility of concept First demonstrators build in Q2 2013 23 Thank you for your attention For more information please contact: Dr. Arjen Boersma TNO De Rondom 1 PO Box 6235 5600 HE Eindhoven The Netherlands E-mail: arjen.boersma@tno.nl Office: +31 (0)88 866 57 13 General: +31 (0)6 533 843 20 www.tno.nl 24 12