Baghsiahi, H.

Fernández, F.A.

Papakonstantinou, I.

Selviah, D.R.

Wang, K.

Yu, G.

English

UCL Discovery

Photolithographically Manufactured Acrylate Polymer Multimode Optical Waveguide Loss Design Rules Kai Wang1,David R. Selviah1, Ioannis Papakonstantinou2, Guoyu Yu3, Hadi Baghsiahi1, F. Anibal Fernández11Optical Devices & Systems, Department of Electronic & Electrical Engineering, University College London (UCL)2Sharp Laboratories of Europe Ltd (formerly at UCL)3Technium OpTIC (formerly at UCL) 2nd Electronics System-Integration Technology Conference, ESTC, 1st-4thSeptember 2008, Greenwich, UKCopyright © 2008 UCL21. Motivation:1. Optical versus Electronic interconnect2. Waveguide design rules2. Photolithographic fabrication of acrylate polymer waveguides3. Measurement technique4. Loss measurement of waveguide components design rules1. Straight waveguides2. Crossings3. Bends4. Tapers5. Tapered bends5. Optical system design2 Copyright © 2008 UCLOutline3Optical versus Electronic Interconnect Copper tracks become inefficient as data rates rise above 10 Gb/s• Skin effects in the conductors,• Cross-talk,• Electromagnetic Interference (EMI),• Reflection,• Signal loss and manufacture cost increases. Optical interconnect has potential benefits• Less delay due to no RC components,• High speed travel in optical materials,• Low propagation loss 0.03 ~ 0.06 dB/cm at 850 nm wavelength inwaveguide < 50 50 m in cross-section,• Do not require impedance matching,• Wavelength division multiplexing is achievable.4 The optical loss depends on several factors: Material, Fabrication Measurement Technique Photolithographically fabricated by Exxelis Ltd. using e-beam mask Truemode® acrylate polymer formulation Core refractive index 1.5560 Cladding refractiveindex 1.5264 NA = 0.302 Cross sections typically 50 μm 50 μm and 70 μm 70 μm square4 Copyright © 2008 UCLFabrication Parameters5 Copyright © 2008 UCLElectrical System with Optical InterconnectOptical and ElectronicInterconnectsBackplaneMezzanine Board (DaughterBoard, Line Card)Optical Connector61. Motivation:1. Optical versus Electronic interconnect2. Waveguide design rules2. Photolithographic fabrication of acrylate polymer waveguides3. Measurement technique4. Loss measurement of waveguide components design rules1. Straight waveguides2. Crossings3. Bends4. Tapers5. Tapered bends5. Optical system design6 Copyright © 2008 UCLOutline7Photolithographic fabrication of waveguides, 50 µm × 50 µm Core Copyright © 2008 UCL8Waveguides Samples – Top View Copyright © 2008 UCLStraight waveguides Bends90° Crossings 50° Crossings9VCSEL illuminated Photolithographicly fabricated by Exxelis, 50 μm × 50 μm waveguide Cut with a dicing saw, unpolishedCopyright © 2008 UCLWaveguide Output Facet PhotographsUnder nomarski microscope 101. Motivation:1. Optical versus Electronic interconnect2. Waveguide design rules2. Photolithographic fabrication of acrylate polymer waveguides3. Measurement technique4. Loss measurement of waveguide components design rules1. Straight waveguides2. Crossings3. Bends4. Tapers5. Tapered bends5. Optical system design10 Copyright © 2008 UCLOutline11 Copyright © 2008 UCLOptical Loss Measurement850 nm VCSEL-5.2 dBmIntegrating sphere photodetector70/150 μm pinholenW Power Meter50/125 μm step index fibremode scrambler RIndex matching fluid -5.2 dBm0 dBm121. Motivation:1. Optical versus Electronic interconnect2. Waveguide design rules2. Photolithographic fabrication of acrylate polymer waveguides3. Measurement technique4. Loss measurement of waveguide components design rules1. Straight waveguides2. Crossings3. Bends4. Tapers5. Tapered bends5. Optical system design12 Copyright © 2008 UCLOutline13 13 70 μm × 70 μm waveguide cross sections and 10 cm long Waveguide end facets diced but unpolished scatters light into cladding In the cladding power drops linearly at a rate of 0.011 dB/µm Crosstalk reduced to -30 dB for waveguides 1 mm apartCopyright © 2008 UCLDesign Rules for Inter-waveguide Cross Talk1 mm141. Motivation:1. Optical versus Electronic interconnect2. Waveguide design rules2. Photolithographic fabrication of acrylate polymer waveguides3. Measurement technique4. Loss measurement of waveguide components design rules1. Straight waveguides2. Crossings3. Bends4. Tapers5. Tapered bends5. Optical system design14 Copyright © 2008 UCLOutline15 Copyright © 2008 UCLSchematic Diagram Of Waveguide Crossings at 90° and at an Arbitrary Angle, θ16 16 Loss of 0.023 dB per 90° crossing consistent with other reports The output power dropped by 0.5% at each 90° crossing The loss per crossing (Lc) depends on crossing angle (θ),  Lc=1.0779 · θ -0.8727.Copyright © 2008 UCLDesign Rules for Arbitrary Angle CrossingsMean Loss Per Crossing00.020.040.060.080.10.120.140.160.180 20 40 60 80 100Crossing Angle (Degree)Loss Per Crossing (dB)0.023Transmitted mean power per crossing (dB)Crossing angle (degree)Power drops 1.8% at 20°171. Motivation:1. Optical versus Electronic interconnect2. Waveguide design rules2. Photolithographic fabrication of acrylate polymer waveguides3. Measurement technique4. Loss measurement of waveguide components design rules1. Straight waveguides2. Crossings3. Bends4. Tapers5. Tapered bends5. Optical system design17 Copyright © 2008 UCLOutline18wlinloutRsRs+ΔRRf  = Rs + NΔRABIOutputInputOSchematic diagram of one set of curved waveguides. Light through a bent waveguide of R = 5.5 mm – 34.5 mm• Radius R, varied between 5.5 mm < R < 35 mm, ΔR = 1 mm• Light lost due to scattering, mode miss-match loss, radiation loss, reflection and back-scattering • Illuminated by a MM fibre with a red-laser.Copyright © 2008 UCLOptical Power Loss in 90° Waveguide Bends19Width (μm) Optimum Radius (mm) Minimum Loss (dB)50 13.5 0.7475 15.3 0.91100 17.7 1.18Copyright © 2008 UCLLoss of Waveguide Bends50 µm × 50 µm 70 µm × 50 µm 100 µm × 50 µm Bend radius (mm)Power transmission (dB)201. Motivation:1. Optical versus Electronic interconnect2. Waveguide design rules2. Photolithographic fabrication of acrylate polymer waveguides3. Measurement technique4. Loss measurement of waveguide components design rules1. Straight waveguides2. Crossings3. Bends4. Tapers5. Tapered bends5. Optical system design20 Copyright © 2008 UCLOutline21 21 The input section win = 50 μm, and its length lin = 11.5 mm The tapered bend transforms the waveguide width from win, to wout The width of the tapered bends varies linearly along its length Output straight waveguide length lout = 24.5 mm. Output widths wout = 10 μm, 20 μm, 25 μm, 30 μm and 40 μmCopyright © 2008 UCLDesign Rules for Tapered Bends22 22 Dashed lines correspond to the boundaries of the win = 50 μm taperedbend Dotted lines correspond to the boundaries of the 25 μm bend Tapered bend has more misalignment tolerance for a slight losspenaltyCopyright © 2008 UCLMisalignment Tolerance of a Tapered BendTaper ratio, TRTransmitted power (TP)and misalignment tolerance (MT)23 23The product of transmission and misalignment tolerance is a constantwhich increases linearly with TR such that the product = 0.650TR - 0.09 This product is independent of the bend radius as experimental pointsalmost coincide.Copyright © 2008 UCLProduct of Maximum Transmission And Misalignment ToleranceMT > TP TP > MT241. Motivation:1. Optical versus Electronic interconnect2. Waveguide design rules2. Photolithographic fabrication of acrylate polymer waveguides3. Measurement technique4. Loss measurement of waveguide components design rules1. Straight waveguides2. Crossings3. Bends4. Tapers5. Tapered bends5. Optical system design24 Copyright © 2008 UCLOutline25 Copyright © 2008 UCLElectrical System with Optical InterconnectOptical and ElectronicInterconnectsBackplaneMezzanine Board (DaughterBoard, Line Card)Optical Connector26 26Copyright © 2008 UCLSystem DemonstratorFully connected waveguide layout using design rules27Conclusions and Acknowledgement  Characterised photolithographically manufactured acrylate polymermultimode waveguide by measuring the optical loss of key waveguidecomponents. Design rules derived from the experimental measurement to assistoptical system designers to optimise OPCB layout. The authors thank EPSRC via IeMRC for funding and Dave Milward, formanaging the project, Ken Hopkins, and Richard Pitwon, XyratexTechnology Ltd, for helpful discussions. Navin Suyal and Habib Rehman,Exxelis for preparation of the Truemode® polymer and photolithographicfabrication of the waveguides, Gary Hinde, Cadence for technical support.Thanks for Your Attention

Photolithographically manufactured acrylate multimode optical waveguide loss design rules

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