We present the design and experimental demonstration of multilayer etched CMOS-compatible grating couplers with high efficiency on a heterogeneous silicon-lithium niobate platform. The dual-level grating coupler comprises 90 nm-thick Si waveguides and 220 nm-thick Si grating with a linear chirped structure without etching LN. The design changes the grating diffraction properties, which not only reduce back reflection but also improve directionality and fiber-to-chip mode match. In comparison with existing studies, this work achieves high coupling efficiency solely through CMOS-compatible etching without additional bottom reflectors or high-index overlays. Theoretical calculations predict a fiber-to-chip coupling efficiency of −1.76 dB and an off-chip diffraction efficiency of −1.1 dB for the TE mode. The experimental measurement of the peak coupling efficiency is −2.84 dB with the back reflection as low as −26 dB. The grating coupler paves the way for monolithic integration of Si and LN.

1.
D.
Zhu
,
L.
Shao
,
M.
Yu
,
R.
Cheng
,
B.
Desiatov
,
C. J.
Xin
,
Y.
Hu
,
J.
Holzgrafe
,
S.
Ghosh
,
A.
Shams-Ansari
,
E.
Puma
,
N.
Sinclair
,
C.
Reimer
,
M.
Zhang
, and
M.
Lončar
, “
Integrated photonics on thin-film lithium niobate
,”
Adv. Opt. Photonics
13
(
2
),
242
(
2021
).
2.
M.
He
,
M.
Xu
,
Y.
Ren
,
J.
Jian
,
Z.
Ruan
,
Y.
Xu
,
S.
Gao
,
S.
Sun
,
X.
Wen
,
L.
Zhou
,
L.
Liu
,
C.
Guo
,
H.
Chen
,
S.
Yu
,
L.
Liu
, and
X.
Cai
, “
High-performance hybrid silicon and lithium niobate Mach–Zehnder modulators for 100 Gbit s−1 and beyond
,”
Nat. Photonics
13
(
5
),
359
364
(
2019
).
3.
A. N. R.
Ahmed
,
S.
Shi
,
A.
Mercante
,
S.
Nelan
,
P.
Yao
, and
D. W.
Prather
, “
High-efficiency lithium niobate modulator for K band operation
,”
APL Photonics
5
(
9
),
091302
(
2020
).
4.
J.
Wang
,
H.
Yang
, and
W.
Zou
, “
Engineering a sandwiched Si/I/LNOI structure for 180-GHz-bandwidth electro-optic modulator with fabrication tolerances
,”
Opt. Express
30
(
20
),
35398
(
2022
).
5.
Y.
Liu
,
X.
Huang
,
H.
Guan
,
Z.
Yu
,
Q.
Wei
,
Z.
Fan
,
W.
Han
, and
Z.
Li
, “
C-band four-channel CWDM (de-)multiplexers on a thin film lithium niobate–silicon rich nitride hybrid platform
,”
Opt. Lett.
46
(
19
),
4726
(
2021
).
6.
M.
Zhang
,
K.
Chen
,
M.
Wang
,
J.
Wu
, and
K. S.
Chiang
, “
Electro-optic reconfigurable two-mode (de)multiplexer on thin-film lithium niobate
,”
Opt. Lett.
46
(
5
),
1001
(
2021
).
7.
D.
Yin
,
Y.
Zhou
,
Z.
Liu
,
Z.
Wang
,
H.
Zhang
,
Z.
Fang
,
W.
Chu
,
R.
Wu
,
J.
Zhang
,
W.
Chen
,
M.
Wang
, and
Y.
Cheng
, “
Electro-optically tunable microring laser monolithically integrated on lithium niobate on insulator
,”
Opt. Lett.
46
(
9
),
2127
(
2021
).
8.
Z.
Wang
,
Z.
Fang
,
Z.
Liu
,
W.
Chu
,
Y.
Zhou
,
J.
Zhang
,
R.
Wu
,
M.
Wang
,
T.
Lu
, and
Y.
Cheng
, “
On-chip tunable microdisk laser fabricated on Er3+-doped lithium niobate on insulator
,”
Opt. Lett.
46
(
2
),
380
(
2021
).
9.
N.
Yao
,
J.
Zhou
,
R.
Gao
,
J.
Lin
,
M.
Wang
,
Y.
Cheng
,
W.
Fang
, and
L.
Tong
, “
Efficient light coupling between an ultra-low loss lithium niobate waveguide and an adiabatically tapered single mode optical fiber
,”
Opt. Express
28
(
8
),
12416
(
2020
).
10.
C.
Hu
,
A.
Pan
,
T.
Li
,
X.
Wang
,
Y.
Liu
,
S.
Tao
,
C.
Zeng
, and
J.
Xia
, “
High-efficient coupler for thin-film lithium niobate waveguide devices
,”
Opt. Express
29
(
4
),
5397
(
2021
).
11.
P.
Ying
,
H.
Tan
,
J.
Zhang
,
M.
He
,
M.
Xu
,
X.
Liu
,
R.
Ge
,
Y.
Zhu
,
C.
Liu
,
C.
Liu
,
X.
Cai
, and
X.
Cai
, “
Low-loss edge-coupling thin-film lithium niobate modulator with an efficient phase shifter
,”
Opt. Lett.
46
(
6
),
1478
1481
(
2021
).
12.
X.
Zhou
,
Y.
Xue
,
F.
Ye
,
Z.
Feng
,
Y.
Li
,
X.
Sun
,
K. M.
Lau
, and
H. K.
Tsang
, “
High coupling efficiency waveguide grating couplers on lithium niobate
,”
Opt. Lett.
48
(
12
),
3267
(
2023
).
13.
S.
Yang
,
Y.
Li
,
J.
Xu
,
M.
Wang
,
L.
Wu
,
X.
Quan
,
M.
Liu
,
L.
Fu
, and
X.
Cheng
, “
Low loss ridge-waveguide grating couplers in lithium niobate on insulator
,”
Opt. Mater. Express
11
(
5
),
1366
(
2021
).
14.
L.
Cai
and
G.
Piazza
, “
Low-loss chirped grating for vertical light coupling in lithium niobate on insulator
,”
J. Opt.
21
(
6
),
065801
(
2019
).
15.
J.
Jian
,
P.
Xu
,
H.
Chen
,
M.
He
,
Z.
Wu
,
L.
Zhou
,
L.
Liu
,
C.
Yang
, and
S.
Yu
, “
High-efficiency hybrid amorphous silicon grating couplers for sub-micron-sized lithium niobate waveguides
,”
Opt. Express
26
(
23
),
29651
(
2018
).
16.
I.
Krasnokutska
,
R. J.
Chapman
,
J.-L. J.
Tambasco
, and
A.
Peruzzo
, “
High coupling efficiency grating couplers on lithium niobate on insulator
,”
Opt. Express
27
(
13
),
17681
(
2019
).
17.
B.
Chen
,
Z.
Ruan
,
X.
Fan
,
Z.
Wang
,
J.
Liu
,
C.
Li
,
K.
Chen
, and
L.
Liu
, “
Low-loss fiber grating coupler on thin film lithium niobate platform
,”
APL Photonics
7
(
7
),
076103
(
2022
).
18.
S.
Kang
,
R.
Zhang
,
Z.
Hao
,
D.
Jia
,
F.
Gao
,
F.
Bo
,
G.
Zhang
, and
J.
Xu
, “
High-efficiency chirped grating couplers on lithium niobate on insulator
,”
Opt. Lett.
45
(
24
),
6651
(
2020
).
19.
Z.
Chen
,
Y.
Ning
, and
Y.
Xun
, “
Chirped and apodized grating couplers on lithium niobate thin film
,”
Opt. Mater. Express
10
(
10
),
2513
(
2020
).
20.
Y.
Tan
,
S.
Niu
,
M.
Billet
,
N.
Singh
,
M.
Niels
,
T.
Vanackere
,
J.
Van Kerrebrouck
,
G.
Roelkens
,
B.
Kuyken
, and
D.
Van Thourhout
, “
Micro-transfer printed thin film lithium niobate (TFLN)-on-silicon ring modulator
,”
ACS Photonics
11
(
5
),
1920
1927
(
2024
).
21.
Z.
Chen
,
Y.
Wang
,
H.
Zhang
, and
H.
Hu
, “
Silicon grating coupler on a lithium niobate thin film waveguide
,”
Opt. Mater. Express
8
(
5
),
1253
(
2018
).
22.
A.
Bozzola
,
L.
Carroll
,
D.
Gerace
,
I.
Cristiani
, and
L. C.
Andreani
, “
Optimising apodized grating couplers in a pure SOI platform to −0.5 dB coupling efficiency
,”
Opt. Express
23
(
12
),
16289
(
2015
).
23.
D.
Vermeulen
,
S.
Selvaraja
,
P.
Verheyen
,
G.
Lepage
,
W.
Bogaerts
,
P.
Absil
,
D.
Van Thourhout
, and
G.
Roelkens
, “
High-efficiency fiber-to-chip grating couplers realized using an advanced CMOS-compatible silicon-on-insulator platform
,”
Opt. Express
18
(
17
),
18278
(
2010
).
24.
G.
Roelkens
,
D.
Van Thourhout
, and
R.
Baets
, “
High efficiency silicon-on-insulator grating coupler based on a poly-silicon overlay
,”
Opt. Express
14
(
24
),
11622
(
2006
).
25.
A. G.
Gad
, “
Particle swarm optimization algorithm and its applications: A systematic review
,”
Arch. Comput. Methods Eng.
29
(
5
),
2531
2561
(
2022
).
26.
F.
Van Laere
,
T.
Claes
,
J.
Schrauwen
,
S.
Scheerlinck
,
W.
Bogaerts
,
D.
Taillaert
,
L.
O'Faolain
,
D.
Van Thourhout
, and
R.
Baets
, “
Compact focusing grating couplers for silicon-on-insulator integrated circuits
,”
IEEE Photonics Technol. Lett.
19
(
23
),
1919
1921
(
2007
).
27.
Y.
Tong
,
W.
Zhou
, and
H. K.
Tsang
, “
Efficient perfectly vertical grating coupler for multi-core fibers fabricated with 193 nm DUV lithography
,”
Opt. Lett.
43
(
23
),
5709
(
2018
).
28.
X.
Han
,
Y.
Jiang
,
A.
Frigg
,
H.
Xiao
,
P.
Zhang
,
A.
Boes
,
T. G.
Nguyen
,
J.
Yang
,
G.
Ren
,
Y.
Su
,
A.
Mitchell
, and
Y.
Tian
, “
Single-step etched grating couplers for silicon nitride loaded lithium niobate on insulator platform
,”
APL Photonics
6
(
8
),
086108
(
2021
).
29.
Y.
Liu
,
X.
Huang
,
Z.
Li
,
H.
Guan
,
Q.
Wei
,
Z.
Fan
,
W.
Han
, and
Z.
Li
, “
Efficient grating couplers on a thin film lithium niobate–silicon rich nitride hybrid platform
,”
Opt. Lett.
45
(
24
),
6847
(
2020
).
30.
J.
Wang
,
N.
Xiong
, and
W.
Zou
, “
Loss compensation of an ultra-wideband electro-optic modulator in heterogeneous silicon/erbium-doped lithium niobate
,”
Opt. Lett.
48
(
13
),
3399
(
2023
).
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