Nghiên cứu tính toán và thiết kế mạch tích hợp quang băng rộng chuyển đổi và tách ghép mode (design and simulation of wideband photonic integrated circuits for multi mode (de)multiplexing and conversion)

MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY -0 TRAN TUAN ANH DESIGN AND SIMULATION OF WIDEBAND PHOTONIC INTEGRATED CIRCUITS FOR MULTI-MODE (DE)MULTIPLEXING AND CONVERSION DOCTORAL DISSERTATION IN TELECOMMUNICATIONS ENGINEERING HANOI – 2020 MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY -0 TRAN TUAN ANH DESIGN AND SIMULATION OF WIDEBAND PHOTONIC INTEGRATED CIRCUITS FOR MULTI-MODE (DE)MULTIPLEXING AND CONVERSION Major: Telecommunications Engineering Code: 9520208 DOCTORAL DISSERTATION IN TELECOMMUNICATIONS ENGINEERING SUPERVISORS: PROF DR TRAN DUC HAN DR TRUONG CAO DUNG HANOI – 2020 DECLARATION OF AUTHORSHIP I, Tran Tuan Anh, declare that this dissertation entitled, "Design and simulation of wideband photonic integrated circuits for multi-mode (de)multiplexing and conversion", and the work presented in it is my own I confirm that: - This work was done wholly or mainly while in candidature for a Ph.D research degree at Hanoi University of Science and Technology - Where any part of this dissertation has previously been submitted for a degree or any other qualification at Hanoi University of Science and Technology or any other institution, this has been clearly stated - Where I have consulted the published work of others, this is always clearly attributed -Where I have quoted from the work of others, the source is always given - With the exception of such quotations, this dissertation is entirely my own work - I have acknowledged all main sources of help Where the dissertation is based on work done by myself jointly with others, I have made exactly what was done by others and what I have contributed myself Hanoi, October, 2020 Postgraduate Student Tran Tuan Anh SUPERVISORS SUPERVISOR SUPERVISOR i Acknowledgment First and foremost, I would like to thank my supervisor Prof Dr Tran Duc Han for his support and advice throughout my research time in Hanoi University of Science and Technology (HUST) His encouragement and full support led me to every success of my study I have been able to learn a lot from him about being a good teacher and researcher I would like to express my gratitude to my supervisor, Dr Truong Cao Dung, for guiding and motivating me since I was an undergraduate student at HUST He has given me the very first guidance until I finished my doctoral dissertation I special thanks to Prof Dr Vu Van Yem for his constant help during my study postgraduate courses and sincere advices for my future career I am also thankful to my research team, Ms Nguyen Thi Hang Duy, Mr Ta Duy Hai, Ms Tran Thi Thanh Thuy and Mr Hoang Do Khoi Nguyen in Posts and Telecommunications Institute of Technology They gave me a lot of help during my last two years Finally, I would like to express my grateful thanks to my parents, Mr Tran Quoc Hung and Mrs Tran Thi Huong, and my uncle, Mr Tran Quoc Dung, for their support and encouragement TRAN TUAN ANH ii Table of Contents INTRODUCTION CHAPTER SOI WAVEGUIDE STRUCTURE, ANALYSIS AND FABRICATION 1.1 Shapes and functions of silicon-on-insulator waveguide _8 1.2 Optical waveguide analysis and simulation methods 12 1.2.1 Wave equations _ 12 1.2.2 Effective index method _ 15 1.2.3 Finite difference method 17 1.2.4 Beam propagation method _ 18 1.2.5 Finite difference beam propagation method _ 19 1.3 Silicon-on-insulator waveguide fabrication 21 1.3.1 Separation by implanted oxygen (SIMOX) 21 1.3.2 Bond and Etch-back SOI (BESOI) 23 1.3.3 Wafer Splitting _ 24 1.3.4 Silicon Epitaxial Growth 25 1.3.5 Fabrication of surface etched features 25 1.4 Silicon-on-insulator waveguide structure used for MDM functionality _28 1.4.1 Directional coupler 28 1.4.2 Multimode interference _ 32 1.4.3 Asymmetric Y-junction waveguide _ 41 1.5 Conclusion _43 CHAPTER MODE DIVISION MULTIPLEXER BASED ON ASYMMETRIC DIRECTIONAL COUPLER _ 44 2.1 Two mode division (De)multiplexer based on an MZI asymmetric silicon waveguide _45 2.1.1 Design and structural optimization 45 2.1.2 Simulation and performance analysis 49 2.2 Conclusion _52 3.1 Cascaded N x N general interference MMI analysis _54 3.2 Three-mode division (De)multiplexer based on a trident coupler and two cascaded 3×3 MMI silicon waveguides _56 3.2.1 Design and structural optimization 56 3.2.2 Simulation and performance analysis 64 3.3 Conclusion _68 CHAPTER MODE DIVISION MULTIPLEXER BASED ON TILT BRANCHED BUS STRUCTURE SILICON WAVEGUIDE 70 4.1 Three-mode multiplexed device based on tilt branched bus structure using silicon waveguide 70 4.1.1 Design and structural optimization 70 4.1.2 Simulation and performance analysis 74 iii 4.2 Four-mode multiplexed device based on tilt branched bus structure using silicon waveguide 78 4.2.1 Design and structural optimization 78 4.2.2 Simulation and performance analysis 83 4.2.3 Proposal of experimental diagram _ 85 4.3 Conclusion _89 DISSERTATION CONCLUSION AND FUTURE WORKS _ 92 PUBLICATIONS DURING PHD COURSE 94 UNDER REVIEW PAPER 94 PUBLICATIONS BEFORE PHD COURSE 94 REFERENCE 95 iv Abbreviation ADC Asymmetric Directional Coupler AON All Optical Network BESOI Bond and Etch-back SOI BER Bit Error Rate BPM Beam Propagation Method CMOS Complementary Metal Oxide Semiconductor Cr.T Cross talk CMP Chemical Mechanical Polishing CVD Chemical Vapor Deposition CWDM Coarse Wavelength Division Multiplexing DC Directional Coupler DWDM Dense Wavelength Division Multiplexing DUT Device Under Test DUV Deep Ultra Violet EBL Electron Beam Lithography EDFA Erbium Doped Fiber Amplifier EIM Effective Index Method EME Eigenmode Expansion EMS Eigenvalue Mode Solver FD-BPM Finite Difference Beam Propagation Method FDM Finite Difference Method FDTD Finite Difference Time Domain FFT-BPM Fast Fourier Transform Beam Propagation Method FTTH Fiber to the Home GI General Interference I.L Insertion Loss v LER MDM MMI Line Edge Roughness MPA Mode Division Multiplexing MZI Multimode Interference OEICs Mode Propagation Analysis ONU Mach-Zehnder Interferometer OOK Opto-electronic Integrated Circuits PDM Optical Network Unit PECVD On-off Keying Signals PICs Polarization Division Multiplexing PMMA Plasma-enhanced chemical vapor deposition PLCs Planar Integrated Circuits PON Polymethyl Methacrylate RI Planar Lightwave Circuits SI Passive Optical Network SDM Restricted Interference SIMOX Symmetric Interference SOI Spatial Mode Division Multiplexing TBC Separation by Implanted Oxygen TE Silicon on Insulator TEM Transparent Boundary Condition TM Transverse Electric WDM Transverse Electromagnetic XPM Transverse Magnetic Wavelength Division Multiplexing Cross Phase Modulation vi List of Tables Table 1.4.1 Summary of different MMI types’ properties 41 Table 2.2.1 Comparison of our proposed designs based on ADC with others designs having similar structure 53 Table 3.3.1 Comparison of our proposed designs based on MMI with others designs having similar structure 69 Table 4.3.1 Comparison of our proposed designs based on branch bus structure with others designs having similar structure 90 vii List of Figures Fig Set up initial parameters of SOI waveguide and simulation method in RSoft Fig Pathway monitoring power at each output port of a design Fig 1.1.1 Schematic of non-planar optical waveguides High index is indicated by darker color Fig 1.1.2 Schematic of SOI waveguide 10 Fig 1.1.3 Schematic of SOI Rib waveguide 10 Fig 1.2.1 Scheme of the effective index method for solving the propagation constant of a step-index channel waveguide Starting from a 2D waveguide, the problem is split into two step-index planar waveguides 16 Fig 1.2.2 The cross-section of the waveguide is made discrete with a rectangular grid of points which have identical spacing 18 Fig 1.2.3 Comparison between FD-BPM (left) and FFT-BPM (right) simulation FD-BPM under TBC gives better simulation result as the simulated wave is smoother 20 Fig 1.2.4 Comparison between FD-BPM simulation time depending on computed step of grid size 0.05μm (a) verse grid size 0.01μm (b) 21 Fig 1.3.1 Variation of the oxygen profile during the SIMOX process (a) Low-dose; (b) high-dose (peak is at the stoichiometric limit for SiO2); and (c) after o implantation and annealing at 1300 C for several hours 22 Fig 1.3.2 The bond and etch-back process to form BESOI: (a) oxidation; (b) bonding; and (c) thinning 23 Fig 1.3.3 (a) Thermally oxidized wafer is implanted with a high dose 17 (approximately 10 cm−2) of hydrogen (b) A second wafer is bonded to the first as in the BESOI process (c) Thermal processing splits the implanted wafer at a point consistent with the range of the hydrogen ions 24 Fig 1.3.4 (a) Schematic of a silicon rib waveguide (b) Electron micrograph of a silicon rib waveguide Reproduced by permission of Intel Corporation 26 Fig 1.3.5 Schematic of a confined AC-generated plasma suitable for silicon processing The processed wafer in placed on the lower, grounded electrode .27 Fig 1.4.1 Directional coupler consisting of slab optical waveguide 29 Fig 1.4.2 Periodic exchange of power between waveguide and .30 Fig 1.4.3 Simulation of periodic exchange of power between waveguide and using BPM 30 31 Fig 1.4.5 The schematic configuration of MMI waveguide 33 Fig 1.4.6 Two-dimensional representation of a MMI waveguide 34 Fig 1.4.7 Power distribution of GI-MMI with 38 Fig 1.4.4 Power transfer ratio verse phase mismatch parameter ∆ =3 =3 (left), =3 /2 (middle), /3 (right) using FD-BPM simulation viii Both devices are designed numerically and only support TE modes operation, not TM modes, because SOI waveguides have a large difference of mode indices between TE polarization states and TM polarization states at the same order Commonly, as typical SOI-based devices are designed to use either TE or TM polarized light, a mixture of TE and TM polarization in the input signal will significantly degrade the optical performance of the device, which in turns limits the applications of SOI-based photonic circuits in optical communications To overcome this drawback, many structures for realizing polarization diversity schemes have been used, including polarization splitters [110], [111], polarization rotators [112], polarization-insensitive waveguides [113], TE/TM-passing polarizers [114]–[118], in order to achieve a transparent photonic integrated circuit Therefore, to enhance optical performances of proposed device, TEpass polarizers need to be used before and after connecting with the device to refine TM polarization Compared to recent works such as Chunlei Sun et al [119] and Yunhong Ding et al [120], the proposed devices have the same performance and fabrication tolerance but their structure is less complex On the other hand, it is also the first time that designs, which can couple and convert some specific high-order modes from bus waveguide into non-fundamental mode in the branched waveguide following particular phase matching conditions, are introduced Criteria Number of mode Our (de)Mux proposed modes design (de)Mux Ref [34] modes (de)Mux Ref [36] modes (de)Mux Ref [89] modes *FP – Footprint, **M – Material, ***BW – Bandwidth Table 4.3.1 Comparison of our proposed designs based on branch bus structure with others designs having similar structure 90 It can be a foundation of further development of universal design principles for arbitrary mode selection and arbitrary mode conversion as well as increasing number of modes can be coupled and converted in a single branch waveguide from the bus waveguide Compared to designs proposed in chapter and 3, those devices are more potential in (de)multiplexing multi-mode due to its simple structure and working principles Table 4.3.1 shows some comparison between our proposed designs with similar structures However, one of the drawbacks of asymmetric Yjunction waveguide mode (de)MUXer is its relatively large footprint Both devices are suitable to be applied in constructing the high speed computing systems, intrachip communication systems and DWDM-MDM communication systems The content of this chapter has been published in the papers below: H D T Nguyen, T A Tran, D H Ta, T P Bui, Q N Le, T M Nguyen, D C Truong, “A low loss mode division (de)multiplexing device based on soi waveguide in the form of a branched bus,” Journal of Science and Technology – University of Danang, vol 132, no 11, pp 25-28, 2018 T A Tran, H D T Nguyen, D C Truong, H T Nguyen, Y V Vu and D H Tran, “Three-mode multiplexed device based on tilted- branch bus structure using silicon waveguide,” Photonics and Nanostructures-Fundamentals and Applications, vol 35, pp 100709, 2019 91 DISSERTATION CONCLUSION AND FUTURE WORKS Conclusion Silicon photonics technology, especially SOI waveguide has proven to be one of the core technologies in designing and manufacturing Photonics Integrated Circuits This technology has significant advantages such as: stability, wide bandwidth, low insertion loss, cross talk, high fabrication tolerance, as shown in our designs mentioned in chapter 2, and 4, and highly compatible with current CMOS technology for low cost and mass producing ability The dissertation had proposed new designs for coupling, sorting and converting high-order modes to fundamental mode, which can be used in MDM silicon photonics technology Our schematic structures are designed by applying Eigen Mode Solver with Effective Index Method and optimizing by numerical simulation, namely Beam Propagation Method st Our design published in the International Conference on Advanced Technologies for Communications (ATC) 2016 is based on asymmetric directional coupler using coupling mode phenomenon due to near field interaction This design structure was newly introduced and optimized, hence achieved better optical performance nd compared to other proposals using similar mode coupling principles Our design published in Journal of Optical and Quantum Electronic 2017 is constructed from cascaded multimode interference coupler with phase shifter and trident coupler This design can (de)multiplex three modes, in contrast to two modes (de)multiplexed by all previous works Trident coupler was also introduced to sort and convert mode as rd well as split power according to predetermined ratio at the same time Our design published in Journal of Photonics and Nanostructures-Fundamentals and Applications 2018 is built based on multi-junction coupler Phase matching conditions are applied to sort and convert higher-order mode from bus waveguide to lower-order mode in branch waveguide rather than to merely fundamental modes of all previous works using the same mode coupling principles, which is a promising result for developing a universal principles of arbitrary mode sorting and converting from bus to branched waveguide Moreover, our proposal design had better optical performance operating in a wider bandwidth compared to other designs built from similar structure and material The design procedures were derived from theories, reference from previous works, verified by matrix transfer function then optimized using numerical simulation methods Designs performance were investigated by BPM simulation regarding important parameters that affect performance the most Performance tolerances regarding devices’ geometric shape and surface roughness fabrication and bandwidth 92 of input signal were also examined The simulation results presented that all of our designs have low signal loss, low signal cross effect, good fabrication tolerance and wide bandwidth working region Future works Although this dissertation had proposed new designs with MDM function, providing better performance and compactness compared to existing and conventional designs, all of our proof-of-concept designs are built from theoretical knowledge and simulation and lack of experimental and practical applications It is our next task to manufacture prototypes and execute corresponding actual measurements to verify the designs performance and characteristics Those works will be carried by cooperating with universities having advanced technology or high-tech companies with all required infrastructures The manufacturing and actual measurement phase is very important for demonstrating the high relevance between simulation and practice Another important future research field is to continue developing and optimizing performance of mode division multiplexing active devices, such as switch components, routers, mode cross connectors via controllable phase shifters using mechanic-optic effect, thermal-optic effect, carrier effect or electro-optic effect, rather than passive devices proposed in this dissertation Those works require different approaches and different materials as non-linear effects will be considered Finally, designs based on silicon photonics still have relatively large footprint (around few hundred nanometer) In the future, integrated circuits will be designed at scale of subwavelength or nanoscale Photonics crystal (PhC), which is unlike conventional waveguides that depend of total internal reflection for guidance of optical field in region of high refractive index surround by lower refractive index environment, provides guide modes appear within the photonic band gap or plasmonics structure due to surface oscillating PhCs are good candidate for decreasing the size of integrated photonics components with reasonable performance regarding simple structures such as Y-branches, power splitters However, manufacturing cost is still a major concern in PhCs and hence showing a good further research fields for a promising technology of PICs in the future 93 PUBLICATIONS DURING PHD COURSE [1] T A Tran, Y V Vu, D H Tran, C D Truong, “Two mode division (De) multiplexer based on an MZI asymmetric silicon waveguide”, International Conference on Advanced Technologies for Communications (ATC), 2016 [2] T A Tran, D C Truong, H T Nguyen, Y V Vu “A new simulation design of three-mode division (de)multiplexer based on a trident coupler and two cascaded × MMI silicon waveguides”, Optical and Quantum Electronics, vol 49, pp 426, 2017 [3] H D T Nguyen, T A Tran, D H Ta, T P Bui, Q N Le, T M Nguyen, D C Truong, “A low loss mode division (de)multiplexing device based on soi waveguide in the form of a branched bus,” Journal of Science and Technology – University of Danang, vol 132, no 11, pp 25-28, 2018 [4] T A Tran, H D T Nguyen, D C Truong, H T Nguyen, Y V Vu and D H Tran, “Three-mode multiplexed device based on tilted- branch bus structure using silicon waveguide,” Photonics and Nanostructures-Fundamentals and Applications, vol 35, pp 100709, 2019 UNDER REVIEW PAPER H D T Nguyen, D H Ta, T T T Tran, N K D Hoang, T A Tran, C D Hoang, D C Truong, “Four Mode Demultiplexer Based on Branched Silicon Waveguides For Photonics Interconnects,” Submitted to Optik: International Journal for Light and Electron Optics PUBLICATIONS BEFORE PHD COURSE C D Truong, D H Tran, T A Tran, and T T Le, “3 x Multimode interference optical 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DECLARATION OF AUTHORSHIP I, Tran Tuan Anh, declare that this dissertation entitled, "Design and simulation of wideband photonic integrated circuits for multi -mode (de)multiplexing and conversion", and. .. (nm) and ΔW (nm) of the bus waveguide when four modes are excited (a), (b), (c), (d) for mode TE 0; (e), (f), (g), (h) for mode TE1; (i), (j), (k), (l) for mode TE2 and (m),(n),(o),(p) for mode