• Chinese Optics Letters
  • Vol. 19, Issue 9, 091301 (2021)
Jiangbing Du*, Weihong Shen, Jiacheng Liu, Yufeng Chen, Xinyi Chen, and Zuyuan He**
Author Affiliations
  • State Key Laboratory of Advanced Optical Communication Systems and Networks, Shanghai Jiao Tong University, Shanghai 200240, China
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    Historical view of microelectronics development, PIC integration (upper), and ASIC integration (lower).
    Fig. 1. Historical view of microelectronics development, PIC integration (upper), and ASIC integration (lower).
    Optical fiber transmission capacity trend with respect to all kinds of enabling technologies.
    Fig. 2. Optical fiber transmission capacity trend with respect to all kinds of enabling technologies.
    Schematic diagram of MDM optical interface, including vertical coupling with on-chip mode multiplexer (MUX) and edge coupling with 3D asymmetric waveguide. (i)–(iii) Specific progresses of the MDM interface[35,36,37].
    Fig. 3. Schematic diagram of MDM optical interface, including vertical coupling with on-chip mode multiplexer (MUX) and edge coupling with 3D asymmetric waveguide. (i)–(iii) Specific progresses of the MDM interface[35,36,37].
    Schematic diagram of integrated multimode waveguide bends: (a) the Euler curved bend for four TM modes[49], (b) the dual-mode bend with MC[54], (c) the pixelated four-mode bend structure[51], (d) four-mode bend based on a TIR mirror[56].
    Fig. 4. Schematic diagram of integrated multimode waveguide bends: (a) the Euler curved bend for four TM modes[49], (b) the dual-mode bend with MC[54], (c) the pixelated four-mode bend structure[51], (d) four-mode bend based on a TIR mirror[56].
    Schematic diagram of integrated multimode waveguide crossing: (a) two-mode crossing based on non-adiabatic tapered waveguide[58], (b) three-mode crossing based on pixelated mode MUX and single-mode crossing array[60], (c) ultra-compact multimode crossing for two TE modes[61], (d) meta-material-based dual-mode star-crossing[62].
    Fig. 5. Schematic diagram of integrated multimode waveguide crossing: (a) two-mode crossing based on non-adiabatic tapered waveguide[58], (b) three-mode crossing based on pixelated mode MUX and single-mode crossing array[60], (c) ultra-compact multimode crossing for two TE modes[61], (d) meta-material-based dual-mode star-crossing[62].
    Schematic diagram of integrated mode MUX/deMUX: (a) 10-channel mode (de)MUX with dual polarizations by adiabatic tapered ADC[15], (b) asymmetric Y-junction-based mode MUX[90], (c) MRRs serving as modulators and mode MUXs simultaneously[79], (d) four-mode MUX based on pixelated waveguides[86].
    Fig. 6. Schematic diagram of integrated mode MUX/deMUX: (a) 10-channel mode (de)MUX with dual polarizations by adiabatic tapered ADC[15], (b) asymmetric Y-junction-based mode MUX[90], (c) MRRs serving as modulators and mode MUXs simultaneously[79], (d) four-mode MUX based on pixelated waveguides[86].
    Schematic diagram of universal (a) MC[94] and (b) mode exchanger[98].
    Fig. 7. Schematic diagram of universal (a) MC[94] and (b) mode exchanger[98].
    Schematic diagram of (a), (b) integrated PBS based on mode conversion[102,103] and (c) mode-transparent PBS based on TIR mirror[110].
    Fig. 8. Schematic diagram of (a), (b) integrated PBS based on mode conversion[102,103] and (c) mode-transparent PBS based on TIR mirror[110].
    Schematic diagram of (a) Si-based MZI modulator with two branches of light propagating in one multimode waveguide[112], and (b) spatial mode recycling scheme used to reduce the required power consumption[113].
    Fig. 9. Schematic diagram of (a) Si-based MZI modulator with two branches of light propagating in one multimode waveguide[112], and (b) spatial mode recycling scheme used to reduce the required power consumption[113].
    Schematic of (a) mode switch based on two micro-rings[114] and (b) reconfigurable mode switch based on an MZI structure[115]. (c) Four-mode thermal switch by geometric-optic inspired multimode 3 dB coupler[56].
    Fig. 10. Schematic of (a) mode switch based on two micro-rings[114] and (b) reconfigurable mode switch based on an MZI structure[115]. (c) Four-mode thermal switch by geometric-optic inspired multimode 3 dB coupler[56].
    Schematic diagram of Si optical phased array based on multi-pass recycling structure by mode multiplexing[119].
    Fig. 11. Schematic diagram of Si optical phased array based on multi-pass recycling structure by mode multiplexing[119].
    Schematic diagram of integrated interconnect system hybrid multiplexed by WDM, MDM, and PDM.
    Fig. 12. Schematic diagram of integrated interconnect system hybrid multiplexed by WDM, MDM, and PDM.
    Schematic diagram of on-chip switching networks ROADM for multiplexing: (a) on-chip typical multimode optical switching system[125], (b) on-chip ROADM system for hybrid WDM and MDM[129].
    Fig. 13. Schematic diagram of on-chip switching networks ROADM for multiplexing: (a) on-chip typical multimode optical switching system[125], (b) on-chip ROADM system for hybrid WDM and MDM[129].
    (a) Optimized step-index profiles of different FMFs[133], (b) core-cladding difference for seven-LP-mode fibers with step-index and depressed-inner-core profiles[134], (c) refractive index profile of ring-assisted four-mode fiber[135], (d) refractive index profile of ring-assisted seven-LP-mode fiber with trench structure[136].
    Fig. 14. (a) Optimized step-index profiles of different FMFs[133], (b) core-cladding difference for seven-LP-mode fibers with step-index and depressed-inner-core profiles[134], (c) refractive index profile of ring-assisted four-mode fiber[135], (d) refractive index profile of ring-assisted seven-LP-mode fiber with trench structure[136].
    (a) Refractive index profile of two-mode graded-index fiber[137], (b) refractive index profile of nine-mode graded-index fiber with trench-assisted structure[138], (c) geometry and parameter definitions of the elliptical core fiber[142].
    Fig. 15. (a) Refractive index profile of two-mode graded-index fiber[137], (b) refractive index profile of nine-mode graded-index fiber with trench-assisted structure[138], (c) geometry and parameter definitions of the elliptical core fiber[142].
    Schematic of a multi-core super-mode fiber[143].
    Fig. 16. Schematic of a multi-core super-mode fiber[143].
    (a) Flow chart of the proposed NN-assisted inverse design method. (b) The inverse design frame of the NN[145].
    Fig. 17. (a) Flow chart of the proposed NN-assisted inverse design method. (b) The inverse design frame of the NN[145].
    Schematic diagram of mode MUX based on free-space beam combiner[148].
    Fig. 18. Schematic diagram of mode MUX based on free-space beam combiner[148].
    Directional fiber-coupler-based (a) mode MUX and (b) mode deMUX supporting LP01, LP11a, and LP11b modes[148].
    Fig. 19. Directional fiber-coupler-based (a) mode MUX and (b) mode deMUX supporting LP01, LP11a, and LP11b modes[148].
    LPFBG-based (a) mode MUX and (b) mode deMUX supporting LP01 and LP11a modes. MC is achieved by LPFBG[148].
    Fig. 20. LPFBG-based (a) mode MUX and (b) mode deMUX supporting LP01 and LP11a modes. MC is achieved by LPFBG[148].
    Schematic diagram of a photonics lantern[151].
    Fig. 21. Schematic diagram of a photonics lantern[151].
    (a) Ring-shaped erbium doping profile[154]. (b) Refractive index and doping profile (shaded region) of the four-mode EDF[155]. (c) Overlaps between mode fields and gain media in a small doped area (left) and a large doped area (right)[156]. (d) Schematic of dual-core fiber with dual-core doping and colored shadings representing erbium doping[157]. (e) Schematic description of micro-structure[158].
    Fig. 22. (a) Ring-shaped erbium doping profile[154]. (b) Refractive index and doping profile (shaded region) of the four-mode EDF[155]. (c) Overlaps between mode fields and gain media in a small doped area (left) and a large doped area (right)[156]. (d) Schematic of dual-core fiber with dual-core doping and colored shadings representing erbium doping[157]. (e) Schematic description of micro-structure[158].
    Schematic principle of DRA for mitigating the nonlinear distortion and noise over EDFA[148].
    Fig. 23. Schematic principle of DRA for mitigating the nonlinear distortion and noise over EDFA[148].
    Quasi-lossless transmission with bidirectional high-order pump[166].
    Fig. 24. Quasi-lossless transmission with bidirectional high-order pump[166].
    Inverse design based on NN for FM-DRA[170].
    Fig. 25. Inverse design based on NN for FM-DRA[170].
    Recent-year MDM experiments and progresses.
    Fig. 26. Recent-year MDM experiments and progresses.
     SOISiNChGLNInP
    Index3.42.02–32.63.2
    Loss (dB/cm)0.1<0.010.050.0270.3
    Window (µm)1.1–3.70.4–2.41.5–120.4–51.3, 1.5
    LasingNoNoNoNoYes
    PDYesNoNoNoYes
    ModulationYesNoNoYesYes
    Extra doping//Standard processStandard process
    CMOS compatibilityYesYesNoNoNo
    Table 1. Photonic Integration Platforms
    PropertiesVertical CouplingEdge Coupling
    Ref. [35]Ref. [36]Ref. [37]
    Mode number642
    Coupling loss20–25 dB4.9–6.1 dB10.77 dB
    Crosstalk/6dB−7.3 to −11.9 dB
    Bandwidth30nm20 nm>100nm
    Footprint/lengthmm-scale622μm×622μm<300μm
    Table 2. Cutting-Edge Performance of MDM Interface on SOI
    PropertiesEuler Bend[49]SWG Bend[50]Pixelated Bend[51]
    Structure and principleWaveguide curve optimizationSWG for mode convertingInverse design of pixelated structure
    Mode number4 TM modes6 modes with dual polarizations4 TE modes
    Bending radius45 µm10 µm3.9 µm
    Loss<0.5dB<0.23dB<1.8dB
    Crosstalk<20dB<26.5dB<17dB
    ScalabilityYesYesYes
    Table 3. Benchmark Performance of MDM Bend
    Ref.YearL (μm)ILmax (dB)CTmax (dB)BW (nm)ChannelStructureE / Sa
    [9]201280140502 (TE)MMI + PSS
    [68]201448.80.3221002 (TE)Symmetric Y junction + PS + MMIS
    [69]20207.240.74–1.215502 (TE)Shallow-etched MMIE
    [70]2013500.3161002 (TE)Adiabatic tapered ADCE
    [72]2016680.8–1.326652 (TE)Taper-etched ADCE
    [15]201815–500.2–1.8−15 to −259010 (PM)Adiabatic tapered ADCE
    [71]2019751.5/7512 (TE)Adiabatic ADC using SWGE
    [73]201310001.591002 (TE)Asymmetric Y junctionE
    [74]20165105.7−9.7 to −31.5293 (TE)Cascaded asymmetric Y junctionE
    [12]20133000.3361002 (TE)Adiabatic couplerE
    [75]2016200120752 (TE)Adiabatic coupler + Y junctionE
    [76]20171801.519902 (TE)Adiabatic coupler + Y junctionE
    [77]2014253–16−12 to −22/3 (TE)Micro-ringE
    [78]20151001.5–3.5−20 to −32/3 (TE)Micro-ringE
    [79]2019402.119.7/4 (TE)Micro-ringE
    [81]201390–2500.2–0.34−22 to −303.7–11.84 (TE)Grating-assisted contra-DCS
    [82]2015//22/2 (TE)Grating-assisted tapered contra-DCE
    [83]20203006.618.744 (PM)SWG-based contra-DCE
    [84]20162.6×4.21.2121002 (TE)Topology optimized structureE
    [85]20183.6×4.81.2–2.519603 (TE)Pixelated structureE
    [86]20205.4×61.514.6604 (TE)Pixelated structureE
    [87]20181000413.7402 (TE)Triple waveguide couplerE
    [88]20187.50.3215352 (TM)Triple waveguide coupler with hybrid plasmonic waveguideS
    Table 4. The Summary of Mode MUX/deMUX
    Copy Citation Text
    Jiangbing Du, Weihong Shen, Jiacheng Liu, Yufeng Chen, Xinyi Chen, Zuyuan He. Mode division multiplexing: from photonic integration to optical fiber transmission [Invited][J]. Chinese Optics Letters, 2021, 19(9): 091301
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    Category: Integrated Optics
    Received: Dec. 29, 2020
    Accepted: Feb. 26, 2021
    Published Online: Aug. 26, 2021
    The Author Email: Jiangbing Du (dujiangbing@sjtu.edu.cn), Zuyuan He (zuyuanhe@sjtu.edu.cn)