Researching | Advances in lithium niobate photonics: development status and perspectives

Advanced Photonics, Volume. 4, Issue 3, 034003(2022)

Advances in lithium niobate photonics: development status and perspectives Article Video , On the Cover

Guanyu Chen¹, Nanxi Li², Jun Da Ng¹, Hong-Lin Lin¹, Yanyan Zhou², Yuan Hsing Fu², Lennon Yao Ting Lee², Yu Yu^3、*, Ai-Qun Liu⁴, and Aaron J. Danner^1、*

Author Affiliations

¹National University of Singapore, Department of Electrical and Computer Engineering, Singapore

²A*STAR (Agency for Science, Technology and Research), Institute of Microelectronics, Singapore

³Huazhong University of Science and Technology, School of Optical and Electronic Information, Wuhan National Laboratory for Optoelectronics, Wuhan, China

⁴Nanyang Technological University, Quantum Science and Engineering Centre, Singapore

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Fig. 1. Overview of LN photonics. Top middle inset is LN crystal structure. EO, electro-optic; SHG, second harmonic generation; SFG/DFG, sum/difference frequency generation; SCG, supercontinuum generation; OPA/OPO, optical parametric amplification/oscillation; SRS, stimulated Raman scattering; PPLN, periodically poled lithium niobate; GC, grating coupler; WL, wavelength; AO, acousto-optic.

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Fig. 2. Process flow of planar LN device fabrication. Illustration of (a) metal ion-in diffusion and (b) PE methods for planar photonic device fabrication in bulk LN crystals (dimensions are not drawn to scale). PR, photoresist.

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Fig. 3. Process flows of (a) CIS and (b) lapping and polishing technologies. Dimensions are not drawn to scale.

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Fig. 4. Heterogeneous integrated LN devices. (a) Schematic structure, (b) optical, and (c) atomic force microscopic images of an LN on silica hybrid micro-resonator. (a)–(c) Adapted from Ref. 161 © 2015 Wiley-VCH Verlag GmbH and Co. (d) 3D schematic structure, (e) cross section and optical field distribution of a ${SiN}_{x}$ on LN hybrid MZI modulator. (d) and (e) Adapted from Ref. 169; all article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.

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Fig. 5. Dry etching results of LN. (a) SEM image of the LN cross section and (b) current changed along etching depth in end point detection after ${SF}_{6}$ based etching. (a) and (b) Adapted from Ref. 182 © 2008 American Institute of Physics (AIP). (c) SEM, (d) AFM, and (e) XPS images of LN sample after Ar-based dry etching. (c)–(e) Adapted with permission from Ref. 175.

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$Wet etching results of LN. SEM images of the LN etched cross section using undiluted (a) 0% and (b) 20% of adipic acid, (c) 0% and (d) 20% of adipic acid with 0.6% of lithium benzoate, (e) 20% and (f) 30% of adipic acid with 0.3% of lithium carbonate (concentrations in percent represent mole fractions). (a)–(f) Adapted from Ref. 198 © 2006 Wiley Periodicals, Inc. (g) SEM image of photonic crystals (PhCs) using ion implantation and wet etching. Adapted with permission from Ref. 138 © 2010 American Vacuum Society.$

Fig. 6. Wet etching results of LN. SEM images of the LN etched cross section using undiluted (a) 0% and (b) 20% of adipic acid, (c) 0% and (d) 20% of adipic acid with 0.6% of lithium benzoate, (e) 20% and (f) 30% of adipic acid with 0.3% of lithium carbonate (concentrations in percent represent mole fractions). (a)–(f) Adapted from Ref. 198 © 2006 Wiley Periodicals, Inc. (g) SEM image of photonic crystals (PhCs) using ion implantation and wet etching. Adapted with permission from Ref. 138 © 2010 American Vacuum Society.

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Fig. 7. LN-based microresonators. (a) Schematic experimental setup for characterizing a mechanical polishing bulk LN whispering-gallery resonator and its corresponding measured $Q$ factor. Adapted from Ref. 227 © 2011 AIP. (b) Resonance spectra of the fabricated microdisk using ECR RIE technology in TFLN. Inset shows the microscope image of tapered fiber coupling on top of the device. Zoom in views are the details of representative resonance dips. Adapted with permission from Ref. 228 © 2014 Optical Society of America (OSA). (c) SEM (top) and microscopic images (bottom) of microring and microracetrack ring with various lengths, and (d) its measured transmission spectrum. (c) and (d) Adapted with permission from Ref. 192 © 2017 OSA. (e) Microscope image of the waveguide coupled TFLN microring and (f) its measured transmission spectrum. The Q factors for (g) TE and (h) TM modes fitted by Lorentz-shape curves. (e)–(h) Adapted with permission from Ref. 224 © 2022 Chinese Optical Society (COS).

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Fig. 8. LN-based GCs. (a) Schematic structure, (b) simulated electric field distribution and (c) measured transmission spectrum of 1D chirped GC in TFLN. (a)–(c) Adapted with permission from Ref. 259 © 2020 OSA. (d) Schematic structure of a 2D GC in TFLN. Measured and simulated (e) transmission spectra and (f) polarization dependence loss of the TFLN 2D GC. (d)–(f) Adapted with permission from Ref. 265 © 2021 OSA.

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Fig. 9. LN-based edge coupler. (a) Schematic structure of the bilayer edge coupler and its corresponding mode profiles at different positions. (b) Simulated and measured coupling efficiency versus different tip widths in the tapered slab region. (c) Additional insertion loss with respect to coupling misalignment (TE mode). (a)–(c) Adapted with permission from Ref. 246 © 2019 OSA.

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Fig. 10. TFLN EO tunable microring resonator. (a) Schematic structure (top), cross section (bottom left), and SEM images of the Z-cut TFLN microring modulator, and (b) its EO resonance shift curve. (a) and (b) Adapted with permission from Ref. 181 © 2007 Nature Publishing Group.

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Fig. 11. TFLN-based modulators. (a) Microscopic image of TFLN MZI modulator (inset is its schematic cross section). (b) Measured transmission spectrum of a 2-cm long device. (c) Measured high speed data transmission results of $100 Gb / s$ NRZ, $140 Gb / s$ 4-ASK, and $210 Gb / s$ 8-ASK signals. (a)–(c) Adapted with permission from Ref. 31 © 2018 Springer Nature Limited (SNL). (d) SEM images (top: full SEM image; bottom: zoom-in image of the PhC details). (e) Schematic structure of the TFLN PhC modulator. (d) and (e) Adapted with permission from Ref. 241. (f) Schematic structure of the MIM, and insets are cross section mode profiles at different positions. Adapted from Ref. 276. (g) Schematic structure of the TFLN DBR modulator, and SEM images of the (h) DBR and (i) modulation region. (g)–(i) Adapted with permission from Ref. 242 © 2021 COS. (j) Schematic structure and (k) measured $S_{21}$ curves of the TFLN-based DP-IQ modulator. X and Y represent two orthogonal polarization states, I and Q represent in-phase and quadrature branches. (j) and (k) Adapted with permission from Ref. 294 © 2022 Optica.

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Fig. 12. EO tunable interleaver in TFLN. (a) Schematic structure of TFLN waveguide interleaver, and its measured tunable transmission spectra for (b) TE and (c) TM polarized input light. (a)–(c) Adapted with permission from Ref. 297 © 2018 OSA.

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Fig. 13. TFLN-based EO devices for optical frequency controlling. (a) False colored SEM image of an EO tunable coupled microring resonator. (b) The programmable photonic molecule consists of a pair of identical coupled rings (resonant frequency $ω_{1} = ω_{2}$ ). Such a system has two distinct energy levels: symmetric (blue/blue shading) and antisymmetric (red/blue) optical modes are spatially out of phase by $π$ . The microwave field interacts with the two-level system through the large EO effect of TFLN. (a) and (b) Adapted with permission from Ref. 298 © The Author(s), under exclusive license to SNL 2018. (c) SEM image of a reconfigurable electro-optic frequency shifter. (d) Upshift and (e) downshift under 12.5 GHz microwave frequency and at 1601.2 nm wavelength ( $ω_{1}$ ) show measured 80% CE and >0.99 shift ratio (defined as the ratio of the output power at the shifted frequency and the output power inside the bus waveguide). Inset shows the directions of energy flow and the spectra in dB scale. (c)–(e) Adapted with permission from Ref. 299 © The Author(s), under exclusive license to SNL 2021.

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Fig. 14. EO-based microwave to optical transducer in TFLN. (a) Microscopic image of a TFLN-based transducer, and (b) its corresponding measured maximum transduction efficiency with respect to optical pump powers. (a) and (b) Adapted with permission from Ref. 300 © 2020 OSA. (c) Microscopic image of a triply resonant LN on sapphire transducer (zoom in: device details), and (d) its measured photon count rate versus microwave drive frequency with respect to different input microwave powers. (c) and (d) Adapted with permission from Ref. 301 © 2020 OSA. (e) Schematic of an EO converter in TFLN based on two coupled microring resonators (red) and a cointegrated superconducting resonator (yellow). DC bias is applied for optical mode tuning. (f) False color SEM image of the EO converter detail. Inset is the electric field distribution. (e) and (f) Adapted with permission from Ref. 302.

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Fig. 15. EO waveguide spectrometer in TFLN. Microscopic image and device details of an EO TFLN waveguide spectrometer. Adapted with permission from Ref. 171 © The Author(s), under exclusive license to SNL 2019.

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Fig. 16. LN-based nonlinear and quantum photonic devices. (a) Schematic structure of the TFPPLN microring. (b) False-color SEM images of the device cross section and coupling region detail. (c) Experimentally measured SHG power versus pump power. (a)–(c) Adapted with permission from Ref. 63 © 2019 OSA. (d) False color SEM image of TFLN PIC containing Kerr comb and EO add-drop filter. Adapted with permission from Ref. 76. (e) Measured transmission spectrum of the EO comb. Left inset shows a magnified view of several comb lines. Right inset shows measured transmission spectrum for several different modulation indices. Adapted with permission from Ref. 77 © The Author(s), under exclusive license to SNL 2019. (f) Measured transmission spectra with respect to different waveguide width. Adapted with permission from Ref. 79 © 2019 OSA. (g) Principle of OPA in dispersion engineered PPLN waveguide and simulated relative gain spectrum for three dispersion cases. Adapted with permission from Ref. 70 © 2022 OPTICA. (h) Schematic structure of the PPLN microring. Insets are the SEM images of the device details. Measured (i) PGR and (j) CAR. (h)–(j) Adapted with permission from Ref. 81 © 2020 American Physical Society (APS).

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Fig. 17. Cavity optomechanics devices in LN. (a) Schematic of a band structure engineered surface acoustic resonator on TFLN. Inset is the microscopic image of the fabricated device. (b) Measured $Q$ factor with respect to different resonator frequencies. (a) and (b) Adapted with permission from Ref. 311 © 2019 APS. Unit cell geometries of the (c) nanobeam optomechanical crystal and (d) 1D photonic shield. (e) SEM image of a 1D PhC cavity resonator for optomechanical mode generation. Left: full view of the device. Middle: top view of one device. Top right: top view of the 1D photonic shield region. Bottom right: SEM image of the nanobeam reflector coupling region. (c)–(e) Adapted with permission from Ref. 310 © 2019 OSA.

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Fig. 18. Design of IDTs. Schematics of (a) straight and (b) concentric IDTs. (a) and (b) Adapted with permission from Ref. 315 © 2005 IEEE.

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Fig. 19. LN-based AO modulators. Schematics of (a) MZI and (b) microring type AO modulators. (c) Cross section of the AO modulator. (a)–(c) Adapted with permission from Ref. 16 © 2019 Chinese Laser Press (CLP). (d) Microscopic image of a suspended AO MZI. (e) $S_{11}$ and $S_{21}$ spectra of microwave to optical conversion. The optical power detected by photodetector (PD) is 0.25 mW. (d) and (e) Adapted with permission from Ref. 17 © 2019 OSA. (f) Principal illustration of one AO modulator without resonator cavity. (g) Measured $S_{11}$ and $S_{21}$ spectra. (f) and (g) Adapted with permission from Ref. 312 © 2021 CLP. (h) Schematic of AO frequency shifter based on photonic BIC. Adapted with permission from Ref. 320 © 2021 American Chemical Society (ACS).

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Fig. 20. LN-based ADL. (a) Microscopic image of the fabricated ADL. (b) Microscopic image of zoomed in view of the device. (c) Extracted IL and FBW of ADLs with respect to cell numbers. (a)–(c) Adapted with permission from Ref. 321 © 2018 IEEE.

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Fig. 21. Rare-earth-doped devices in LN. (a) Schematic structure of a ${Tm}^{3 +}$ doped TFLN device. Measured (b) photoluminescence spectra and (c) time-resolved photoluminescence in ${Tm}^{3 +}$ doped bulk LN and TFLN, respectively. (a)–(c) Adapted with permission from Ref. 94 © 2019 ACS. (d) Top left: SEM images of GC and microring patterned in TFLN. Top right: the stopping and range of ions in matter (SRIM) simulation of ${Er}^{3 +}$ implantation depth distribution. Bottom: schematic electrical field distribution. (e) Transmission spectrum of a TFLN microring. (f) Measured fluorescence decay when the pumping frequency is detuned from the ring resonance. (d)–(f) Adapted from Ref. 95. (g) Schematic structure of an ${Er}^{3 +}$ doped TFLN waveguide-based amplifier. Gain characterization with respect to different pump power when signal wavelength is (h) 1530 nm and (i) 1550 nm. (g)–(i) Adapted with permission from Ref. 33 © 2021 Wiley-VCH GmbH. (j) Signal power and (k) mode linewidth with respect to different pump powers. (j) and (k) Adapted with permission from Ref. 330 © 2021 OSA. (l) Modulated wavelength of microdisk laser with respect to pump power. Adapted with permission from Ref. 93 © 2021 OSA.

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Fig. 22. TFLN-based pyroelectric infrared detector. (a) SEM image of the metamaterial top surface. (b) Schematic of the unit cell. (c) Microscopic image of the pyroelectric PD. (d) Measured detector response and optical absorption of pyroelectric PD with and without metamaterial structure. (a)–(d) Adapted with permission from Ref. 18 © 2017 OSA.

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$Nonlinear metasurface devices in LN. (a) Schematic structure of TFLN metasurface for SHG. (b) Measured SHG power with respect to fundamental harmonic average power. (a) and (b) Adapted with permission from Ref. 341 © 2020 ACS. (c) Schematic structure of the diffraction mechanism in the metasurface. SEM images of the (d) full view metasurface (scale bar is 3 μm) and (e) zoom in nanopillars. (f) SHG CE of the diffraction orders with respect to pump power. (c)–(f) Adapted with permission from Ref. 342.$

Fig. 23. Nonlinear metasurface devices in LN. (a) Schematic structure of TFLN metasurface for SHG. (b) Measured SHG power with respect to fundamental harmonic average power. (a) and (b) Adapted with permission from Ref. 341 © 2020 ACS. (c) Schematic structure of the diffraction mechanism in the metasurface. SEM images of the (d) full view metasurface (scale bar is $3 μ m$ ) and (e) zoom in nanopillars. (f) SHG CE of the diffraction orders with respect to pump power. (c)–(f) Adapted with permission from Ref. 342.

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Fig. 24. TFLN modulator operated at visible wavelength range. (a) Microscopic image of the TFLN EO modulator. (b) Measured transmission spectrum and (c) $S_{21}$ curve. (a)–(c) Adapted with permission from Ref. 42 © 2019 OSA.

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Fig. 25. Integrated SNSPD in LN. (a) Schematic structure of Ti diffused LN waveguide integrated with five in-line SNSPDs. Inset shows the detail of single SNSPD, which has $400 μ m$ length and 160 nm width. (b) Measured response time of an integrated SNSPD. (c) Measured signal and dark counts of the integrated SNSPD under different bias current. (a)–(c) Adapted with permission from Ref. 347. Published by IOP Publishing Ltd. (d) Top: schematic of a TFLN GC coupling light into an integrated U-shaped NbN SNSPD. Bottom left: device cross section. Bottom right: SEM image of the device detail. (e) Measured OCDE, (f) DCR and NEP with respect to $I_{b} / I_{S W}$ for a $250 - μ m$ long detector. $I_{SW}$ , switching current; $I_{b}$ , bias current. (d)–(f) Adapted from Ref. 172. (g) Microscopic image of the on-chip integrated circuit containing one TFLN EO modulator and two NbTiN SNSPDs. (h) Measured count rates collected from the SNSPDs with a time tagging module (bottom) when EO modulator is driven with a ramp function with an amplitude of $20 V_{pp}$ and frequency of 1 kHz (top). (g) and (h) Adapted with permission from Ref. 349.

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Fig. 26. Integrated Si PD onto LN passive circuit. (a) Schematic structure and (b) false colored SEM image of a TFLN waveguide with integrated Si PD. (a) and (b) Adapted from Ref. 34.

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Table 1. Material property summary of LN.

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Table 1. Material property summary of LN.


Category	Typical values/characteristics	Reference
Crystal structure	Trigonal	38
Refractive index	$n_{o} / n_{e}$ : 2.341/2.2547 @ 500 nm	41
Transparency window	400 to 5000 nm	42
Bandgap	4.71 eV	45
Electro-optic coefficients	$r_{13} = 9.6 pm / V$ ; $r_{22} = 6.8 pm / V$ ;	41
$r_{33} = 30.9 pm / V$ ; $r_{42} = 32.6 pm / V$
Second-order nonlinear susceptibility	$d_{22}$ $(1.058 μ m) = 2.46 \pm 0.23 pm / V$ ;	46
$d_{31}$ $(1.058 μ m) = - 4.64 \pm 0.66 pm / V$ ;
$d_{33}$ $(1.058 μ m) = - 41.7 \pm 7.8 pm / V$
Third-order nonlinear susceptibility	$χ^{(3)} = (0.61 \pm 0.092) \times 10^{4} {pm}^{2} / V^{2}$ @ $1.047 μ m$	47
Photo-elastic constants	$p_{11} = - 0.026$ ; $p_{12} = 0.09$ ; $p_{13} = 0.133$ ; $p_{14} = - 0.075$ ; $p_{31} = 0.179$ ; $p_{33} = 0.071$ ; $p_{41} = - 0.151$ ; $p_{44} = 0.146$ (dimensionless)	2
Pyroelectric coefficient	$- 4 \times 10^{- 9} C \cdot {cm}^{- 2} \cdot ° C^{- 1}$ at 25°C	48
Thermal conductivity	$\sim 5.234 W / (m \cdot K)$ (a- or c-oriented)	49
Thermo-optic coefficient	$\sim 2.5 \times 10^{- 6} K^{- 1}$ (337 K, 1523 nm, ordinary)	50
$\sim 4 \times 10^{- 5} K^{- 1}$ (337 K, 1523 nm, extraordinary)^a
Piezoelectric strain coefficients	$d_{15} = 6.8 \times 10^{- 11} C \cdot N^{- 1}$ ; $d_{22} = 2.1 \times 10^{- 11} C \cdot N^{- 1}$ ; $d_{31} = - 0.1 C \cdot N^{- 1}$ ; $d_{33} = 0.6 C \cdot N^{- 1}$	51

Table 2. Summaries of metal ion-in diffusion method. T, temperature; TE, transverse electric; TM, transverse magnetic; N.A., not available/applicable; Zn, Zinc.

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Table 2. Summaries of metal ion-in diffusion method. T, temperature; TE, transverse electric; TM, transverse magnetic; N.A., not available/applicable; Zn, Zinc.


Year	Metal	Depth (Å)	Atmosphere	Time (h)	$T$ (°C)	$Δ n_{o} / n_{e}$	Loss	Ref.
1974	Ti/V/Ni	500	Argon (Ar)	6	960/970/800	Ti: 0.01/0.04	1 dB/cm at 630 nm	19
V: 0.0005/0.004
Ni: 0.0095/0.006
1975	${TiO}_{2}$	200	Oxygen	10	900 to 1150	0.002	TE: 0.8 dB/cm	98
TM: 0.7 dB/cm
1977	Co, Ni, Cu, Zn	10,000	Air	N.A.	900 to 1100	N.A.	N.A.	101
1978	Ti	400 to 600	Air	5	1050	N.A.	2 dB/cm at 633 nm	102
1978	Ti	500	Air	10	1000 to 1100	0.0077/0.0105	N.A.	103
1979	Ti	500	N.A.	5.5	1060	N.A.	1.25 dB/cm	104
1979	Ti	75	Ar	4.5	940	N.A.	N.A.	105
1980	Ti	500	Air	5	975 to 1075	0.005	0.5 dB/cm	113
1982	Ti	740	Ar	6	1050	0.00051/0.00049	0.62 dB/cm at $1.3 μ m$	114
1983	Ti	950	$O_{2}$ and $H_{2} O$	6	1050	N.A.	N.A.	106
1984	${TiO}_{2}$	50 to 150	Oxygen	5 to 10	1000	N.A.	N.A.	107
1994	Ti/Ni	200/180	N.A.	8/2.5	1050/960	N.A.	N.A.	108
1995	Ni	220	N.A.	1.5	800	0.0112	N.A.	109
1996	Ni	100	N.A.	4 to 6	900	$\sim 0.002$ to 0.016	TE: 0.7 dB/cm	110
TM: 1.4 dB/cm
1999	Zn	N.A.	N.A.	N.A.	700 to 800	$\sim 0.0033$ to 0.0077	N.A.	111
2006	Zn	N.A.	Zn	2	500	0.0012	N.A.	112
2019	Ti	700	Wet oxygen	Several	1010	N.A.	0.5 dB/cm	115

Table 3. Summary of heterogeneous integration of LN with other material systems. ALD, atomic layer deposition; N.A., not available/applicable; a-Si, amorphous silicon.

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Table 3. Summary of heterogeneous integration of LN with other material systems. ALD, atomic layer deposition; N.A., not available/applicable; a-Si, amorphous silicon.


Year	Cut	Structure	Thickness	Device	Integration method	Ref.
2009	X-cut	${As}_{2} S_{3} / Ti : LN$	470 nm/N.A.	Ring	Magnetron sputtering	155
2011	Z-cut	$LN / Si / {SiO}_{2}$	$\sim 1 μ m / 250 nm / 2 μ m$	Ring	Bonding	156
2012	Z-cut	$LN / Si / {SiO}_{2}$	$600 nm / 250 nm / 2 μ m$	Ring E-field sensor	Bonding	157
2013	Y-cut	${Ta}_{2} O_{5} / LN / {SiO}_{2}$	$200 nm / 400 nm / 1.6 μ m$	Ring modulator	Bonding and deposition	158
2014	X-cut	a-Si:H/LN	90 nm/N.A.	MZI modulator	PECVD	159
2014	Z-cut	$LN / Si / {SiO}_{2}$	$1 μ m / 250 nm / 1 μ m$	Ring modulator	Bonding	160
2015	N.A.	LN/silica	$290 nm / 2 μ m$	Whispering-gallery-mode resonator	Excimer laser ablation	161
2015	X-cut	${SiN}_{x} / LN / {SiO}_{2}$	$260 nm / 700 nm / 2 μ m$	MZI modulator	PECVD	162
2015	Z-cut	${TiO}_{2} / LN / {SiO}_{2}$	95 nm/600 nm/N.A.	Waveguide	Magnetron sputtering	163
2015	Y-cut	${Ge}_{23} {Sb}_{7} S_{70} / LN / {SiO}_{2}$	$350 nm / 400 nm / 2 μ m$	MZI modulator	Bonding and E-beam evaporation	164
2016	X-cut	$SiN / LN / {SiO}_{2}$	$390 nm / 700 nm / 2 μ m$	PPLN waveguide	Magnetron sputtering	54
2016	Y -cut	$SiN / LN / {SiO}_{2}$	$500 nm / 400 nm / 2 μ m$	MZI modulator	Bonding and PECVD	165
2017	X-cut	$LN / {Si}_{3} N_{4} / {SiO}_{2}$	300 nm/850 nm/N.A.	Waveguide	LPCVD and Bonding	166
2017	X-cut	Si/LN	145 nm/N.A.	Resonator	Bonding	167
2019	X-cut	$a - Si / LN / {SiO}_{2}$	$100 nm / 300 nm / 2 μ m$	Photodetector	PECVD	34
2020	X-cut	${SiN}_{x} / LN / {SiO}_{2}$	$220 nm / 300 nm / 4 μ m$	MZI modulator	PECVD	168
2020	X-cut	${SiN}_{x} / LN / {SiO}_{2}$	$200 nm / 300 nm / 4.7 μ m$	MZI modulator	LPCVD	169
2020	X-cut	$LN / {SiN}_{x} / {SiO}_{2}$	200 nm/225 nm/N.A.	MZI modulator	Bonding	170
2020	X-cut	${Si}_{3} N_{4} / LN / {SiO}_{2}$	200 nm/300 nm/N.A.	Spectrometer	PECVD	171
2020	Z-cut	$NbN / {HfO}_{2} / LN / {SiO}_{2}$	$5 nm / 10 nm / 615 nm / 2 μ m$	Superconducting SPD	ALD	172
2020	N.A.	$Polymer / LN / {SiO}_{2}$	500 nm/400 nm/N.A.	Mode (de)multiplexer	Spin coating	35

Table 4. Summary of LN dry etching technologies. PMMA, polymethyl methacrylate; HSQ, hydrogen silsesquioxane; MMA, methyl methacrylate; N.A., not available/applicable; RIE, reactive ion etching; ICP, inductively coupled plasma.

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Table 4. Summary of LN dry etching technologies. PMMA, polymethyl methacrylate; HSQ, hydrogen silsesquioxane; MMA, methyl methacrylate; N.A., not available/applicable; RIE, reactive ion etching; ICP, inductively coupled plasma.


Year	Cut	Type	Etch gas	Resist	Mask	Etch rate	Selectivity^a	Etch type	Ref.
1981	X-cut	Bulk	${CCl}_{2} F_{2}$ , Ar, $O_{2}$	AZ 1350-J	Ni/Cr	55 nm/min	$\sim 4$ ^b	RIE	178
1998	Z-cut	Bulk	${CF}_{4}$	N.A.	Ni	$800 nm / h$	N.A.	Plasma etching	179
2000	X-cut	Bulk	${CF}_{4}$	N.A.	${SIO}_{2}$	$\sim 60 nm / \min$ ^c	N.A.	Plasma etching	180
2007	Z-cut	TFLN	Ar	SU-8	N.A.	N.A.	N.A.	Plasma etching	181
2008	X/Y/Z-cut	Bulk	${CF}_{4}$ , $O_{2} / {SF}_{6} / {SF}_{6}$ , $O_{2}$	N.A.	Ni/NiCr	2 to 3/10 to 53/37 to $195 nm / \min$	3–10	RIE/ICP/ICP	182
2009	Y-cut	Bulk	${SF}_{6}$	TI09 XR	Ni	20 to 50 nm/min	20	RIE	183
2009	Z-cut	TFLN	Ar	OIR 907-17	N.A.	7.67 nm/min^c	N.A.	ICP	184
2010	X-cut	Bulk	${CHF}_{3}$ , Ar	AZ5214	Cr	97.5 nm/min	8.1–16	ICP	185
2010	X-cut	Bulk	${CHF}_{3}$ , Ar	N.A.	Cr	92.5 nm/min	N.A.	ICP	186
2011	X-cut	Bulk	${SF}_{6}$ , ${CF}_{4}$ , He	PMMA	Cr	280 nm/min	N.A.	ICP	187
2012	Z-cut	Bulk	${SF}_{6}$ , Ar	AZ5214E	Cr	98.6 nm/min	12	ICP	188
2015	Z-cut	Bulk	${BCl}_{3}$ , Ar	N.A.	Ni	100 nm/min	7	ICP	189
2016	X-cut	TFLN	Ar	S1828	N.A.	12 nm/min	N.A.	ICP	190
2018	Z-cut	TFLN	${CHF}_{3}$ , Ar	N.A.	Cr	N.A.	7	Plasma etching	191
2018	X-cut	TFLN	Ar	N.A.	N.A.	N.A.	N.A.	RIE	192
2019	Z-cut	TFLN	${Cl}_{2}$ , ${BCl}_{3}$ , Ar	PMMA	${SIO}_{2}$	$200 nm / \min$	0.69	RIE	193
2019	X-cut	TFLN	Ar	HSQ	N.A.	N.A.	N.A.	ICP	52
2019	Z-cut	Bulk	${SF}_{6}$ , $O_{2}$	N.A.	Cr/Cu	812 nm/min	77	ICP	194
2021	X/Z-cut	TFLN	Ar	ma-N 1400	Cr	15 to 30 nm/min	1.4	ICP	175
2021	X-cut	TFLN	${CF}_{4}$ , Ar; ${Cl}_{2}$ , Ar; Ar	MMA/PMMA	Cr	35 to 50 nm/min; 20 to 33 nm/min; 12 to 18 nm/min;	N.A.	ICP	195

Table 5. Summary of LN-based EO modulators. HI, heterogeneous integration; DMT, discrete multitone; APE, annealed proton exchange; N.A., not available/applicable.

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Table 5. Summary of LN-based EO modulators. HI, heterogeneous integration; DMT, discrete multitone; APE, annealed proton exchange; N.A., not available/applicable.


Year	Cut	Type	$V_{π} L$	Performance	Process	IL^a/ $Q$ factor	Ref.
2002	X-bulk	MZI	$\sim 12 V \cdot cm$	$S_{21}$ : 30 GHz; ER: 25 dB; data: $40 Gb / s$ (NRZ)	Ti diffusion	5.4 dB^b	289
2007	Z-bulk	Ring	N.A.	EO shift: $1.565 nm / V$ (TM); $0.6912 nm / V$ (TE)	Ti diffusion and wet etch	N.A.	43
2007	Z-TFLN	Ring	N.A.	EO shift: $0.105 pm / V$ (TM)	HI and Ar etch	$Q$ : $4 \times 10^{3}$	181
2009	Z-bulk	MZI	$5.35 V \cdot cm$	ER: 20 dB	Ti diffusion and wet etch	0.5/0.15 dB/cm (TM/TE)	290
2014	X-bulk	PhC	$0.0063 V \cdot cm$	EO shift: $0.6 nm / V$ ; ER: $\sim 11.2 dB$ ; $S_{21}$ : $\sim 1 GHz$	APE and FIB	21 dB^b	291
2018	Y-TFLN	Ring	N.A.	$S_{21}$ : 4 GHz; EO shift: $0.32 pm / V$ ; ER: >10 $dB$	${Cl}_{2}$ ICP	2.3 dB/cm	292
2018	X-TFLN	MZI	$2.2 V \cdot cm$ ^c	$S_{21}$ : 100 GHz (length: 5 mm);	Ar ICP-RIE	<0.5 $dB / 0.2 dB / cm$	31
data: $210 Gb / s$ (8-ASK)
2018	X-TFLN	MZI Ring	$1.8 V \cdot cm$ (MZI) $7 pm / V$ (ring)	$S_{21}$ : 15 GHz (MZI); $S_{21}$ : 30 GHz (ring)	Ar ICP-RIE	MZI: 2 dB; ring: 1.5 dB	272
2019	X-TFLN	MZI	$2.2 V \cdot cm$	$S_{21}$ : > $70 GHz$ ; data: $100 Gb / s$ (NRZ)	HI and Ar ICP	2.5 dB	52
2019	X-TFLN	MIM	$1.4 V \cdot cm$	$S_{21}$ : 12 GHz; data: $35 Gb / s$ (NRZ)	Ar ICP	4 dB	273
2019	X-TFLN	MZI	$5.3 V \cdot cm$	ER: > $53 dB$	ICP	3 dB/cm	274
2019	X-TFLN	MZI	7 to $9 V \cdot cm$	$V_{π}$ : 3.5 to 4.5 V at 5 to 40 GHz	Ar RIE	$\sim 1 dB$	275
2019	X-TFLN	MIM	$1.2 V \cdot cm$	$S_{21}$ : 17.5 GHz; data: $40 Gb / s$ (NRZ); ER: 6.6 dB	HI and Ar ICP	3.3 dB	276
2019	X-TFLN	MZI	$7.2 V \cdot cm$	$S_{21}$ : 20 GHz	Ti-diffusion	9 dB^d	293
2020	X-TFLN	PhC	N.A.	EO shift: $16 pm / V$ ; $S_{21}$ : 17.5 GHz; data: $11 Gb / s$ (NRZ)	Ar ICP	2.2 dB	241
2020	X-TFLN	DBR-FP	N.A.	$S_{21}$ : 60 GHz; data: $100 Gb / s$ (NRZ); ER: 53.8 dB	Ar ICP	0.2 dB	243
2020	X-TFLN	MZI	$2.7 V \cdot cm$	$S_{21}$ : > $70 GHz$ ; data: $128 Gb / s$ (PAM4); ER: $\sim 40 dB$	Ar ICP	1.8 dB	277
2020	X-TFLN	MZI	$2.47 V \cdot cm$ ^c	$S_{21}$ : >67 GHz (7.5 mm arm); data: $320 Gb / s$ (16 QAM)	Ar ICP	1.8 dB	88
2021	X-TFLN	MZI	$2.74 V \cdot cm$	$S_{21}$ : 55 GHz	ICP	8.5 dB	278
2021	X-TFLN	MIM	$1.06 V \cdot cm$	$S_{21}$ : 40 GHz; data: $70 Gb / s$ (NRZ)	HI with SiN	4.1 dB	279
2021	X-TFLN	WG	$1.91 V \cdot cm$	Operating at 1064 nm	${CF}_{4}$ and Ar ICP	7.7 dB	280
2021	X-TFLN	MZI	$0.64 V \cdot cm$	$S_{21}$ : 3 GHz	Ion milling	1.77 dB/cm	281
2021	X-TFLN	MZI	$2.3 V \cdot cm$	$S_{21} :$ > $50 GHz$ ; ER: 20 dB	Ar RIE	<1 dB	282
2021	X-TFLN	MZI	$1.7 V \cdot cm$	$S_{21}$ : > $67 GHz$	Ar RIE	17 dB^b	283
2021	X-TFLN	MZI	$1.75 V \cdot cm$	$S_{21}$ : > $40 GHz$	Ar ICP	0.7 dB/cm	284
2021	X-TFLN	MZI	$3.67 V \cdot cm$	$S_{21}$ : 22 GHz; data: $25 Gb / s$ (NRZ); ER: > $20 dB$	Ar ICP	6 dB ( $2 μ m$ )	285
2021	X-TFLN	DBR-FP	N.A.	EO shift: $15.7 pm / V$ ; $S_{21}$ : 18 to 24 GHz; data: $56 Gb / s$ (NRZ)	ICP	<1.65 dB	242
2021	X-TFLN	MZI	$3.068 V \cdot cm$	$S_{21}$ : 60 GHz; data: $200.4 Gb / s$ DMT data	Ar ICP	3 dB^b	287
2022	X-TFLN	MZI	$2.35 V \cdot cm$	$S_{21}$ : 110 GHz (1 V); data: 1.96 Tb/s (400 QAM)	Ar ICP	6.5 ± 0.5 dB	294

Table 6. Summary of LN-based devices for nonlinear and quantum photonic applications. MgLN, MgO-doped lithium niobate; ZnLN, Zn-doped lithium niobate; ZnOLN, ZnO-doped lithium niobate; PE, proton exchange; HI, heterogeneous integration; PIC, photonic integrated circuit; N.A., not available/applicable.

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Table 6. Summary of LN-based devices for nonlinear and quantum photonic applications. MgLN, MgO-doped lithium niobate; ZnLN, Zn-doped lithium niobate; ZnOLN, ZnO-doped lithium niobate; PE, proton exchange; HI, heterogeneous integration; PIC, photonic integrated circuit; N.A., not available/applicable.


Year	Cut	Type	Application	Performance	Fabrication	Ref.
1993	Z-cut	Bulk PPLN WG	SHG	CE: $600 % / (W \cdot {cm}^{2})$	PE and electrical poling	12
1996	Z-MgLN	Bulk PPLN WG	SHG	CE: $4.5 % / (W \cdot {cm}^{2})$ ^a	Wet etching and electrical poling	13
2002	N.A.	Bulk PPLN WG	Photon-pair	CE: $2 \times 10^{- 6}$	PE and electrical poling	80
2004	N.A.	Bulk PPLN WG	SFG	CE: $330 \pm 10 % / (W \cdot {cm}^{2})$	PE	67
2006	Z-ZnLN	TFPPLN ridge	SHG	CE: $370 % / (W \cdot {cm}^{2})$	Lapping and polishing, dicing	29
2009	Z-MgLN	Bulk PPLN disk	THG	CE: $1.5 % / W^{2}$	Mechanical polishing	69
2010	Z-ZnOLN	TFPPLN ridge	SHG	CE: 2400%/W	Lapping and polishing, dry etching	30
2016	Y-MgLN	TFPPLN ridge	SHG	CE: $189 % / (W \cdot {cm}^{2})$ ;	Lapping and polishing	152
output power: 0.86 W
2016	X-cut	TFPPLN WG	SHG	CE: $160 % / (W \cdot {cm}^{2})$	HI and electrical poling	54
2016	ZnLN	TFPPLN ridge	Photon-pair	Rate: $1456 Hz / μ W$ ;	Lapping and polishing	149
efficiency: 64.1%
2016	Z-cut	TFPPLN ridge	SHG	CE: 204%/W	Lapping and polishing, dicing	148
2017	Z-MgLN	TFPPLN	SFG	CE: 3.3%/W; BW: 15.5 nm	HI and bonding	305
2017	X-cut	TFLN WG	SHG	CE: $1660 % / (W \cdot {cm}^{2})$ ;	Ar ICP-RIE	55
phase matching free
2017	X-cut	TFLN WG	SHG	CE: $41 % / (W \cdot {cm}^{2})$	Ar ICP-RIE	56
2018	N.A.	TFPPLN ridge	Comb	Mid-infrared span	Lapping and polishing	150
2018	X-MgLN	TFPPLN WG	SHG	CE: $2600 % / (W \cdot {cm}^{2})$	Ar ICP-RIE and electrical poling	58
2019	X-cut	TFLN WG	SHG	CE: $1160 % / (W \cdot {cm}^{2})$	HI	59
2019	X-MgLN	TFPPLN ring	SHG	CE: 230,000%/W	Ion-milling and electrical poling	60
2019	X-cut	TFLN WG	SHG	CE: $2200 % / (W \cdot {cm}^{2})$	Ion-milling and electrical poling	61
2019	X-cut	TFLN disk	SHG; THG	SHG: 9.9%/mW; THG: $1.05 % / {mW}^{2}$	Femtosecond-laser ablation and FIB polishing	62
2019	Z-cut	TFPPLN ring	SHG	CE: 250,000%/W	Ar etching and electrical poling	63
2019	Z-cut	TFLN WG	SCG	Span: 1.5 octaves	Ar ICP	78
2019	Z-cut	TFPPLN ridge	SFG	CE: 85%/W	Lapping and polishing, dicing	151
2019	X-cut	TFLN PIC	Comb	Comb generation and modulation (PIC)	Ar ICP-RIE	76
2019	X-cut	TFLN WG	SCG	Span: 2.58 octaves	Ar ICP-RIE	79
2019	X-cut	TFLN ring	Comb	Span: >80 nm	Ar ICP-RIE	77
2019	MgLN	TFPPLN ridge	SHG	CE: $6.29 % / (W \cdot {cm}^{2})$ ; output power: 1.1 W	Lapping and polishing, dicing	154
2020	N.A.	TFLN disk	SHG	CE: $10^{- 2} %$ (282.7 nm)	Simulation	306
2020	Z-cut	TFPPLN ring	Photon-pair	PGR: 36.3 MHz; CAR: >100	Ion-milling and electrical poling	81
2020	X-cut	TFLN WG	SHG	CE: $3061 % / (W \cdot {cm}^{2})$	ICP and electrical poling	65
2020	Z-cut	TFLN disk	SFG	CE: $2.22 \times 10^{- 6} / mW$	FIB and wet etching	68
2020	X-cut	TFLN ring	SRS	Pump-to-Stokes CE: 46%	Ar ICP-RIE	73
2020	X-MgLN	TFPPLN WG	Photon-pair	PCR: 11.4 MHz; CAR: 668	Electrical poling	82
2021	X-MgLN	TFPPLN WG	OPA	Amplification: > $45 dB / cm$	Ar etching and electrical poling	70
2021	Z-cut	TFPPLN ring	OPO	Threshold: $\sim 30 μ W$ ; CE: 11%	Ar ICP-RIE and electrical poling	71
2021	Z-cut	TFPPLN ridge	SHG	CE: $22 % / (W \cdot {cm}^{2})$ ; output power: 1 W	Lapping and polishing, dicing	153
2021	X-MgLN	TFPPLN WG	DFG	CE: $200 % / (W \cdot {cm}^{2})$	Ar etching and electrical poling	44
2021	X-cut	TFPPLN WG	SHG	CE: $435.5 % / (W \cdot {cm}^{2})$	ICP and electrical poling	66
2021	X-cut	TFPPLN WG	Photon-pair	Rate: $2.79 \times 10^{11} Hz / mW$ ; SHG: $2270 % / (W \cdot {cm}^{2})$	ICP and electrical poling	83

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Guanyu Chen, Nanxi Li, Jun Da Ng, Hong-Lin Lin, Yanyan Zhou, Yuan Hsing Fu, Lennon Yao Ting Lee, Yu Yu, Ai-Qun Liu, Aaron J. Danner, "Advances in lithium niobate photonics: development status and perspectives," Adv. Photon. 4, 034003 (2022)

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Paper Information

Category: Reviews

Received: Jan. 16, 2022

Accepted: Apr. 26, 2022

Published Online: Jun. 9, 2022

The Author Email: Yu Yu (yuyu@mail.hust.edu.cn), Danner Aaron J. (adanner@nus.edu.sg)

DOI:10.1117/1.AP.4.3.034003

Topics

laser devices and laser physics

Lasers and Laser Optics

laser manufacturing

Instrumentation, Measurement and Metrology