Bridging the gap between resonance and adiabaticity: a compact and highly tolerant vertical coupling structure

Chunhui Yao; Qixiang Cheng; Günther Roelkens; Richard Penty

doi:10.1364/PRJ.465765

Photonics Research, Volume. 10, Issue 9, 2081(2022)

Bridging the gap between resonance and adiabaticity: a compact and highly tolerant vertical coupling structure

Chunhui Yao¹, Qixiang Cheng^1、*, Günther Roelkens², and Richard Penty¹

¹Centre for Photonic Systems, Electrical Engineering Division, Department of Engineering, University of Cambridge, Cambridge CB3 0FA, UK

²Department of Information Technology (INTEC), Photonics Research Group, Ghent University-imec, 9052 Ghent, Belgium

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Fig. 1. (a) Schematic of the cross section of a III-V-on-silicon vertically coupled waveguide system. (b)–(d) Calculated maps of γ for different width combinations of the III-V and Si waveguide when the misalignment is 0, 0.5, and 1.0 μm, respectively. The dashed white lines and the orange dots represent the width combinations for, respectively, the linearly tapered structure and the multisegmented tapered structure.

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Fig. 2. (a) 3D schematic diagram of the proposed III-V-on-silicon vertical coupler. (b) and (c) Top view of the vertical couplers with, respectively, a linear taper structure and a multisegmented taper structure.

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Fig. 3. Simulated coupling efficiency versus the length L of the linear taper vertical couplers with different lateral misalignments. The theoretical calculation for a perfectly phase-matched conventional resonant coupler when Δm is 1.0 μm is also presented for reference.

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Fig. 4. (a) Waveguide widths of the vertical coupler with multisegmented taper structure along the propagation direction z. (b) Simulated coupling efficiency versus the lateral misalignment. (c) Normalized power of the two supermodes (even and odd) along the propagation direction when Δm is 1.0 μm. Insets show their simulated transverse electric field profiles at z=57 μm. (d) Simulated electric field profiles at the input cross section and the output cross section when Δm is, respectively, 0, 0.5, and 1.0 μm.

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Fig. 5. (a) Simulated map of the coupling efficiency with different width variations of the III-V and Si waveguide when the coupler is 1.0 μm misaligned. (b) Simulated coupling efficiency versus the thickness of the BCB bonding layer with different misalignments. (c) Simulated coupling efficiency versus wavelength with different misalignments.

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Fig. 6. (a) Cross section schematic of a heterogenous coupled waveguide system based on 220 nm SOI platform with poly-Si overlay. (b) Waveguide widths of the multisegmented vertical coupler along the propagation direction. (c) FDTD simulated coupling efficiency versus the lateral misalignment.

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Fig. 7. Simulated coupling efficiency of the optimized couplers with different numbers of taper segments when Δm is ±1.0 μm. Inset shows the coupling efficiency of a three-segmented coupler versus the lateral misalignment.

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Table 1. Comparison of Several Different Vertical Couplers^a

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Table 1. Comparison of Several Different Vertical Couplers^a

References	Principle	Materials	Length	Efficiency	Alignment Tolerance	Tolerance of Width Variation ( $> 80 %$ )	Bandwidth
[23]	Adiabatic	AlGaInAs/Si	210 μm	98%	$\pm 1.0 μm$ ( $> 93 %$ )	N.A.	N.A.
[43]	Adiabatic	InGaAsP/a-Si:H	224 μm	93%	$\pm 1.0 μm$ ( $> 75 %$ )	N.A.	N.A.
[39]	Adiabatic	InGaAsP/InP	180 μm	83%	N.A.	$\pm 0.4 μm$	N.A.
[40]	Adiabatic	InGaAsP/InP	293 μm	90%	N.A.	$\pm 0.125 μm$	N.A.
[34]	Resonant	AlGaInAs/Si	8 μm	95%	$\pm 0.1 μm$ ( $> 90 %$ )	N.A.	1.5–1.6 μm ( $> 95 %$ )
[35]	Resonant	AlGaInAs/Si	5 μm	98%	N.A.	N.A.	1.5–1.6 μm ( $> 90 %$ )
[32]	Resonant	InGaAsP/InP	24 μm	97%	N.A.	$\pm 0.125 μm$	N.A.
[44]	Resonant	AlGaInAs/InP	55 μm	96%	$\pm 0.3 μm$ ( $> 90 %$ )	$\pm 0.25 μm$	1.23–1.4 μm ( $> 80 %$ )
This work	Hybrid	AlGaInAs/Si	87 μm	98%	$\pm 1.0 μm$ ( $> 94 %$ )	$\pm 0.5 μm$	1.44–1.74 μm ( $> 90 %$ )

Table 2. Comparison to an Adiabatic Coupler

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Table 2. Comparison to an Adiabatic Coupler

Performance Metrics	Adiabatic Coupler	Multisegmented Tapered Coupler
Device length	237 μm	87 μm
Alignment tolerance	1.0 μm ( $> 91 %$ )	1.0 μm ( $> 94 %$ )
Tolerance of width variation	$\pm 0.3 μm$ ( $> 75 %$ )	$\pm 0.5 μm$ ( $> 80 %$ )
Tolerance of BCB thickness variation	$\pm 10 nm$ ( $> 86 %$ )	$\pm 50 nm$ ( $> 90 %$ )
Bandwidth	1.49–1.58 μm ( $> 90 %$ )	1.44–1.74 μm ( $> 90 %$ )

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Chunhui Yao, Qixiang Cheng, Günther Roelkens, Richard Penty, "Bridging the gap between resonance and adiabaticity: a compact and highly tolerant vertical coupling structure," Photonics Res. 10, 2081 (2022)

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