Progress of Optical Waveguide Devices in Thin Film Lithium Niobate (Invited)

Fig. 3. LNOI ridge waveguides. (a) (b) Diced waveguide by diamond blade^[36]; (c) chemical-mechanical polished waveguide^[39]; (d) dry-etched waveguide^[44]

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Fig. 4. Grating couplers for LNOI optical waveguides. (a) Schematic structure of a grating coupler with a metal bottom reflector^[45]; (b) SEM image of a chirped grating coupler^[47]; (c) cavity-enhanced grating coupler^[49]

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Fig. 5. Edge couplers for the LNOI waveguides. (a) Bilayer tapered mode size converter and the mode field distribution at different cross sections^[57]; (b) bilayer tapered mode size converter with a cladding waveguide^[59]; (c) mode size converter with vertical tapered structure^[65]

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Fig. 6. LNOI electro-optic modulators. (a) LNOI modulator driven directly by CMOS chip^[10]; (b) modulator using T-rail electrodes^[13]; (c) DP-IQ modulator^[15]; (d) Si-LN heterogeneous integrated Mach-Zehnder modulator^[11]

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Fig. 7. LNOI tunable filters. (a) LNOI microring resonator^[9]; (b) long period waveguide grating filter^[19]; (c) 1 $\times$ 4 interleaver^[83]

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Table 1. Comparison of the propagation loss of the LNOI waveguides

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Table 1. Comparison of the propagation loss of the LNOI waveguides

Reference	Method	Waveguide width / $μ m$	Propagation loss /（dB/cm）
［26］	Proton exchange	4	0.6
［27］	Si₃N₄ rib loading	2	0.3
［29］	Si₃N₄ rib loading	1	0.86
［30］	Ta₂O₅ rib loading	1	5
［31］	Chalcogenide glasses rib loading	1.3	1.2
［34］	$α$ -Si rib loading	0.7	3
［35］	Diamond blade dicing	6	0.1
［36］	Diamond blade dicing	2.1	1.2
［38］	CMP	3	0.027
［39］	CMP	1	0.042
［7］	Dry etching	2.4	0.027
［10］	Dry etching	0.8	0.2
［12］	Dry etching	4	0.15

Table 2. Performance comparison of the grating couplers for the LNOI waveguides

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Table 2. Performance comparison of the grating couplers for the LNOI waveguides

Platform	Structure	Reflector	Efficiency /（dB/facet）	Bandwidth /nm
LNOI^［45］	Uniform	Yes	-6.90
LNOI^［46］	Uniform	Yes	-3.51
LNOI^［47］	Chirped	No	-3.60	48（3-dB）
LNOI^［48］	Chirped	Yes	-1.43
LNOI^［49］	Uniform and cavity enhanced	Yes	-0.89	45（1-dB）
Si on LNOI^［50］	Uniform	No	-2.20	81（3-dB）
Si on LNOI^［51］	Uniform	No	-3.06	55（1-dB）
Si on LNOI^［52］	Uniform	No	-18.00
Si₃N₄ on LNOI^［54］	Uniform	No	-5.82	57（3-dB）
Si₃N₄ on LNOI^［55］	Uniform	No	-4.02	>70（3-dB）

Table 3. Performance comparison of the edge couplers for the LNOI waveguides

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Table 3. Performance comparison of the edge couplers for the LNOI waveguides

Reference	structure	Clad waveguide material	Efficiency /（dB/facet）
［56］	Single taper		2.5±0.5
［57］	Bilayer taper		1.7
［58］	Bilayer taper	SiON	0.54（TE）/0.59（TM）
［59］	Bilayer taper	SU8	0.5
［60］	Tri-layer taper	SiO₂	1（1550 nm）/3（775 nm）
［61］	Bilayer taper	SiO₂	1.06
［62］	Bilayer taper	Si₃N₄	0.75
［63］	Multilayer		1.60（simulated）
［64］	Multilayer		0.47（simulated）
［65］	Vertical taper	Polymer	1.49

Table 4. Performance comparison of the LNOI modulators

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Table 4. Performance comparison of the LNOI modulators

Platform	ER /dB	$V_{π}$ L /（Vcm）	$V_{π}$ /V	L /mm	3 dB bandwidth /GHz
Ta₂O₅ on LNOI^［30］	20	4	6.8	6
Chalcogenide glasses on LNOI^［31］	15	3.8	6.3	6	1
LNOI^［9］	10	1.8	9	2	15
LNOI^［10］	30	2.2/2.3/2.8	4.4/2.3/1.4	5/10/20	100/80/45
LNOI^［13］	20	2.7	1.35	20	175
LNOI^［67］	17	1.7	3.4	5	110
LNOI^［70］	17	1.75	3.5	5	>40
LNOI^［71］		1.41	3.52	4	>67
LNOI（IQ）^［12］	>25	2.33/2.47	3.1/1.9	7.5/13	>67/48
LNOI（DP-IQ）^［15］	>20	2.35	1	23.5	110
LNOI（DP-IQ）^［75］	24	2.6	2.18	12	30
LNOI（DP-IQ）^［76］		2.25	1	22.5	67
LN on SOI^［68］	>20	6.7	13.4	5	106
LN on SOI^［11］	>40	2.22/2.55	7.4/5.1	3/5	>70
Si₃N₄ on LNOI^［6］	18	3.1	3.88	8	33
Si₃N₄ on LNOI^［28］	30	2.11	0.875	24
Si₃N₄ on LNOI^［69］	20.12	2.18	2.8	7.6	~30
LN on Si₃N₄^［77］	33	3.01	4.3	7	37

Table 5. Performance comparison of the LNOI tunable optical filters

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Table 5. Performance comparison of the LNOI tunable optical filters

Platform	Filter type	Tuning efficiency /（pm/V）	ER /dB	Q-factor	Crystal cut
Chalcogenide glasses on LNOI^［31］	Ring	3.2	15	1.2×10⁵	Y
LN on SOI^［32］	Ring	12.5	9	1.15×10⁴	Z
Si₃N₄ on LNOI^［80］	Ring	1.78	27	1.85×10⁵	X
LNOI^［78］	Ring	1.05	7	4×10³	Z
LNOI^［9］	Racetrack	7	7	5×10⁴	X
LNOI^［81］	Photonic crystal	16	11.5	1.34×10⁵	X
LNOI^［16］	Bragg grating	23.37	14		X
LNOI^［82］	Bragg grating	14.6	53.8	2×10⁵	X
LNOI^［18］	Bragg grating	25.1	10.5	1×10⁵	X
LNOI^［79］	Bragg grating	3.83	27	8×10⁴	X
LNOI^［19］	Long period grating	344	16.32		X
LNOI^［17］	Asymmetric MZI	18	18		X
Si₃N₄ on LNOI^［84］	Asymmetric MZI	26	28		X

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Hao Yao, Mengke Wang, Jiayao Deng, Yuzhe Sun, Jieyun Wu, Kaixin Chen. Progress of Optical Waveguide Devices in Thin Film Lithium Niobate (Invited)[J]. Laser & Optoelectronics Progress, 2024, 61(11): 1116017

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Paper Information

Category: Materials

Received: Jan. 5, 2024

Accepted: Mar. 21, 2024

Published Online: Jun. 5, 2024

The Author Email: Kaixin Chen (chenkx@uestc.edu.cn)

DOI:10.3788/LOP240460

CSTR:32186.14.LOP240460

Topics

laser devices and laser physics

Lasers and Laser Optics

Laser physics

laser manufacturing

Instrumentation, Measurement and Metrology