Efficient mode coupling/(de)multiplexing between a few-mode fiber and a silicon photonic chip

Xiaolin Yi; Weike Zhao; Long Zhang; Yaocheng Shi; Daoxin Dai

doi:10.1364/PRJ.508099

Photonics Research, Volume. 12, Issue 12, 2784(2024)

Efficient mode coupling/(de)multiplexing between a few-mode fiber and a silicon photonic chip

Xiaolin Yi^1、†, Weike Zhao^1、†, Long Zhang¹, Yaocheng Shi^1,2, and Daoxin Dai^1,2,3、*

¹State Key Laboratory for Modern Optical Instrumentation, Center for Optical & Electromagnetic Research, College of Optical Science and Engineering, International Research Center for Advanced Photonics, Zhejiang University, Zijingang Campus, Hangzhou 310058, China

²Ningbo Research Institute, Zhejiang University, Ningbo 315100, China

³Jiaxing Key Laboratory of Photonic Sensing & Intelligent Imaging, Intelligent Optics & Photonics Research Center, Jiaxing Research Institute, Zhejiang University, Jiaxing 314000, China

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Figures & Tables(13)

Fig. 1. Illustration of the proposed multimode coupling scheme working with six mode-channels.

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Fig. 2. Illustration of the PLC chip. (a) Schematic configuration of the mode (de)multiplexer. (b) MWS-based multimode edge coupler. (c) Coupler #a or #b used in the mode (de)multiplexer. (d) Mode rotator.

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Fig. 3. Design of the MWS-based multimode edge coupler. Calculated mode mismatch losses between the FMF and the MWS structure for the LP01 (a), LP11a (b), and LP11b (c) modes as a function of f1 when choosing different waveguide widths wm. Calculated overall coupling losses for the LP01 (d), LP11a (e), and LP11b (f) modes as the segment period Λ varies at the wavelength of 1550 nm. Calculated overall coupling losses for the LP01 (g), LP11a (h), and LP11b (i) modes with/without the MWS structure, respectively.

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Fig. 4. Design of couplers #a and #b. Calculated effective indices neff of the silica optical waveguide as the core width varies for the cases with different core heights of (a) 6.5 μm and (b) 4 μm. Simulated transmissions for couplers #a (c)–(f) and #b (g)–(j) when the LP01 and LP11a modes are launched, respectively.

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Fig. 5. Design of the mode rotator. (a) Illustration of the PLC-based mode rotator. (b) Normalized mode conversion efficiency of the mode rotator as the length Lr varies. Simulated light propagation (c) and transmission (d) for the launched LP11b mode. Simulated light propagation (e) and transmission (f) for the launched LP01 mode.

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Fig. 6. Simulation results of the PLC mode (de)multiplexer. Simulated light propagation of the mode (de)multiplexer for the LP01-x/y (a), LP11a-x/y (b), and LP11b-x/y (c) modes at the wavelength of 1550 nm. Simulated transmissions of the mode (de)multiplexer when the LP01-x/y (d), LP11a-x/y (e), and LP11b-x/y (f) modes are launched, respectively. Fabrication tolerance analysis of the designed PLC-based mode (de)multiplexer working with the LP01-x/y (g), LP11a-x/y (h), and LP11b-x/y (i) modes when assuming that the core width has a variation from −0.5 to +0.5 μm.

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Fig. 7. Design of the SSC. (a) 3D schematic configuration of the bi-level multicore polarization-insensitive SSC. (b) 2D view of the SSC with key parameters. Calculated mode field overlap as a function of the tip width w and the gap g for (c) TE and (d) TM polarizations. Simulated coupling loss of the SSC and the 4 μm×4 μm silica optical waveguide for (e) TE and (f) TM polarizations when choosing different buffer layer thicknesses (hBOX). Simulated light propagation for (g) TE and (h) TM polarizations. Analysis of the alignment tolerance in the (i) horizontal and (j) vertical directions.

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Fig. 8. Image of the fabrication chips. The scanning electron microscope (SEM) images of (a) the MWS and (b) the mode rotator on the fabricated PLC chip. (c) The microscope image of the polished facet at the input end of the mode multiplexer. (d) The microscope image of the silicon photonic chip with high-performance PBSs and SSCs. (e) The picture of the butt-coupled fiber array (FA), the silicon photonic chip, the PLC chip, and the FMF.

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Fig. 9. Measured results of the coupling loss for each part. (a) PLC-based MWS, (b) bi-level multicore SSC on silicon, and (c) overall coupling loss of the proposed FMF-chip coupler.

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Fig. 10. Near-field pattern observation and MDM transmission experiment. (a) Near-field patterns of the light emitted from the FMF. (b) Measured crosstalk matrices when different modes are launched.

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Fig. 11. Experimental setup for the mode field pattern measurement and the MDM transmission.

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Table 1. Structure Parameters of the SSC (in μm)
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Table 1. Structure Parameters of the SSC (in μm)
Parameter $w_{g}$ $w_{1}$ $w_{2}$ $w$ $g$ $L_{1}$ $L_{2}$ $L_{t}$
Value 0.14 0.14 0.14 0.11 1.1 30 50 20

Table 2. Comparison for the FMF-Chip Couplers Reported Previously

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Table 2. Comparison for the FMF-Chip Couplers Reported Previously

Reference	Type	Method	Mode Order	Coupling Loss (dB)		Crosstalk (dB)
Reference	Type	Method	Mode Order	Sim.	Exp.	Sim.	Exp.
[12]	Grating	Spot excitation	01-x/y, 11a-x/y, 11b-x/y	$> 5.3$	25	–	–
[13]	Grating	Spot excitation	01-x/y, 11a-x/y, 11b-x/y	7.6	10.6	–	–
[16]	Grating	Double-part grating	11a-x	3.61	3.68	–	$< - 15$
[17]	Grating	2D grating	01-x/y, 11a-x, 11b-y	4.3/5.0	4.9/6.1	–	$< - 6$
[18]	Grating	2D grating	01-x/y, 11a-x/y, 11b-x/y	3.3/3.6	5.2/9.0	–	–
[22]	Edge	Double inverse taper	01-x, 11a-x	2.8–3.3	4.9–7.5	–	$< - 15$
[23]	Edge	Inverse taper array	01-x, 11a-x	3.2–5.2	6.3–7.0	$< - 25$	$< - 10$
[24]	Edge	Inverse taper, MMI	01-x, 11a-x	8.8–10.1	12.5–13.2	$< - 11.9$	$< - 7.3$
[30]	Edge	Tapered FMF	01-x/y, 11a-x/y, 11b-x/y	0.7	–	$< - 19$	–
This work	Edge	PLC-SOI	01-x/y, 11a-x/y, 11b-x/y	0.77–1.39	1.36–2.48	$< - 27.2$	$< - 14.2$

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Xiaolin Yi, Weike Zhao, Long Zhang, Yaocheng Shi, Daoxin Dai, "Efficient mode coupling/(de)multiplexing between a few-mode fiber and a silicon photonic chip," Photonics Res. 12, 2784 (2024)

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