Integrated photonics on thin-film lithium niobate

In the paper

“Broadband absorption spectra were measured that is consistent with a reference bulk crystal.”

In the paper

“Additionally, the dispersion can be carefully tailored with small variations in the geometry”

In the paper

“The effect of different cladding configurations on the TE mode dispersion of TFLN waveguides, including uncladded, 1 μm SiO 2 top cladding, and suspended/free standing structure.”

In the paper

“We compare the TE mode GVD for thin-film LN waveguides with different widths (b), etch depths (b), and initial film thicknesses (d) against LN's intrinsic material dispersion (a).”

• Also stated in: § 8. Conclusion · plain

  “We evaluate the effect of different geometric parameters, including waveguide width, etch depth, initial LN film thickness, and the etch angle on the dispersion curve.”

In the paper

“it can be seen that in the case of thin-film LN, the GVD curve takes on a larger range of 𝛽𝛽 2 value than for bulk crystal.”

In the paper

“We note that there exist discrepancies of Raman oscillation strength among the work in thinfilm LN devices [27,174,175].”

What the sources say

• Not checked yetcites [27] He, 2019, Optica source
• Not checked yetcites [174]
• Not checked yetcites [175] Holzgrafe, 2020, Optica source

In the paper

“The development and refinement of the "Smart Cut" technology [53], commonly used to generate SOI wafers, has emerged as a the standard technique for producing high-quality LN thin films [35,54].”

What the sources say

• Not checked yetcites [53] Bruel, 1995, Electron. Lett. source
• Not checked yetcites [35] Poberaj, 2012, Laser Photon. Rev. source
• Not checked yetcites [54] Levy, 2004, Single-crystal lithium niobate films by crystal ion slicing source

In the paper

“some of these thin-film LN devices, such as optical modulators and nonlinear wavelength converters, have already outperformed their legacy counterparts realized in bulk LN crystals.”

What the sources say

• Not checked yetcites [21][22][23][24][25]
• Not checked yetcites [29][30][31]

In the paper

“With breakthroughs in fabrication techniques, ultra-low-loss, high index-contrast, nanophotonic LN waveguides have been realized [11][12][13][14][15][16][17][18][19][20].”

What the sources say

• Not checked yetcites [11][12][13][14][15][16][17][18][19][20]

In the paper

“The other challenge with Ar + etching is that it forms nonvertical sidewalls due to redeposition.”

In the paper

“First, it has low etch selectivity with respect to the available lithography resists (usually around 1:1), resulting in limited etch depth.”

In the paper

“With the optimization of lithography, etching, and post-etch cleaning, the propagation loss of dry-etched LNOI waveguides has improved from > 6 dB/cm [55] in 2007 to 0.027 dB/cm in 2017 [11].”

What the sources say

• Not checked yetcites [55] Guarino, 2007, Nat. Photonics source
• Not checked yetcites [11] Zhang, 2017, Optica source

In the paper

“One disadvantage, however, is that only a portion of the optical mode is in the LN which results in weaker nonlinear and EO interactions.”

In the paper

“This means that the thin-film LN platform is not only able to guide photons, but also phonons.”

In the paper

“Followed by foundational works laid around the early 2000s [8][9][10], high-quality thin-film LN wafers prepared from ion slicing and wafer bonding have recently been made commercially available.”

What the sources say

• Not checked yetcites [8][9][10]

In the paper

“Despite great progress, these material platforms cannot simultaneously support ultra-low propagation loss, fast and low-loss optical modulation, and efficient all-optical nonlinearities.”

What the sources say

• Not checked yetcites [1] Jalali, 2006, J. Lightwave Technol. source
• Not checked yetcites [2] Smit, 2019, APL Photon. source
• Not checked yetcites [3] Moss, 2013, Nat. Photonics source

In the paper

“While traditional diffusion-based photonic devices in bulk LN have played an important role in optical and RF signal processing, they have several important limitations, predominately originating from the large optical mode due to the low index contrast.”

In the paper

“Combining this with large piezoelectric coefficients (for example, 𝒹𝒹 22 = 21 pC/N and 𝒹𝒹 33 = 16 pC/N for Rayleigh waves, and 𝒹𝒹 15 = 74 pC/N for shear waves) and photoelastic coefficients (e.g., p 13 = 0.133 and p 44 = 0.146) of LN, it is possible to realize a wide variety of novel piezo-optomechanical devices, in addition to more traditional surface-acoustic-wave (SAW) microwave filters.”

In the paper

“Within the past few years, a complete set of integrated optical components have been developed on the thin-film LN platform with unprecedented performances.”

What the sources say

• Not checked yetcites [21][22][23][24][25]
• Not checked yetcites [26][27][28]
• Not checked yetcites [29][30][31]

In the paper

“The major loss mechanism in dry-etched LNOI waveguide is the contribution from sidewall roughness.”

In the paper

“The success of manufacturing wafer-scale, high-quality, thin films of LN on insulator (LNOI), accompanied with breakthroughs in nanofabrication techniques, have made high-performance integrated nanophotonic components possible.”

In the paper

“It, however, presents a significant challenge in optical packaging due to the mode mismatch between the waveguides and standard optical fibers.”

In the paper

“The state-of-the-art quality factors of these resonators are listed in Table 2, with the highest intrinsic Q-factor achieved to date ~10 7 .”

In the paper

“This approach has demonstrated coupling efficiency as high as ~-3 dB per coupler with a 1-dB bandwidth of 55 nm [122] (see Figure 8(c)).”

What the sources say

• Not checked yetcites [122] Qian, 2020, Proc. SPIE source

In the paper

“However, due to the mismatch between the spot size of the lensed fiber (~2 μm diameter) and waveguide mode (~1 μm), typical fiber-to-chip coupling efficiencies are between -4 to -6 dB [32].”

What the sources say

• Not checked yetcites [32] Chen, 2019, OSA Continuum source

In the paper

“Using this approach, fiber-to-chip coupling loss of 1.7 dB per facet has been achieved [120] (see Figure 8(a)).”

What the sources say

• Not checked yetcites [120] Krasnokutska, 2019, Opt. Express source

In the paper

“More recently, fiber-to-chip coupling loss as low as 0.54/0.59dB per facet for TE/TM mode has been demonstrated by adding a SiON cladding waveguide to the LNOI adiabatic taper [128].”

What the sources say

• Not checked yetcites [128] Chen, 2017, Opt. Mater. Express source

In the paper

“Thus, two-step tapering is needed.This is accomplished by tapering down both the rib and slab that gradually pushes the mode to the oxide cladding.”

In the paper

“Solc-type polarization control and wavelength filtering have also been demonstrated utilizing this off-diagonal EO coefficient in PPLN waveguides [14,189].”

What the sources say

• Not checked yetcites [14] Ding, 2019, J. Lightwave Technol. source
• Not checked yetcites [189] Savchenkov, 2009, Opt. Lett. source

In the paper

“In cavity-EO, this offdiagonal EO coefficient can couple two resonances with different polarizations [190,191].”

What the sources say

• Not checked yetcites [190] Alferness, 1982, IEEE Trans. Microw. Theory Tech. source
• Not checked yetcites [191] Wooten, 2000, IEEE J. Sel. Top. Quantum Electron. source

In the paper

“This indicates that the current cavity Q-factors using the LNOI platform are likely still largely limited by surface scattering.”

In the paper

“On LNOI substrates, both 1D and 2D photonic crystal cavities have been demonstrated (see Figure 9(b) and (d)) [142,143,170,181,182].”

What the sources say

• Not checked yetcites [142] Li, 2019, Laser Photon. Rev. source
• Not checked yetcites [143] Wang, 2018, Opt. Lett. source
• Not checked yetcites [170] Luo, 2019, Phys. Rev. Appl. source
• Not checked yetcites [181] Li, 2019, Optica source
• Not checked yetcites [182] Li, 2020, Nat. Commun. source

In the paper

“On-chip microdisks support whispering gallery modes with ultra-high quality-factors (Qfactor) and compact mode volumes.”

In the paper

“Benefiting from LNOI technology, an on-chip dual-comb spectrometer in the telecommunication region with a resolution of ~10 GHz were demonstrated using a pair of cavity-based EO comb microring sources [250].”

What the sources say

• Not checked yetcites [250] Yan, 2017, Light Sci. Appl. source

In the paper

“Electrodes with such length will have a large capacitance.”

In the paper

“In general, a device with thicker slab, wider waveguide, and a dielectric cladding would have lower 𝑉𝑉 𝜋𝜋 .”

In the paper

“Dynamical EO modulation of these resonators can induce optical transition between these energy levels.”

In the paper

“In non-traveling-wave modulators, the EO bandwidth is mainly restricted by the RC (resistancecapacitance) limit of the electrode.”

In the paper

“By forming hybrid modes, coupled resonators host resonance modes with energy splittings that are different from their intrinsic FSR.”

In the paper

“Therefore, one can inject two CW lasers that are spectrally distant and generate two separate combs in a single device.”

In the paper

“The output spectrum consists of equidistant spectral elements with spacing 𝜔𝜔 𝑚𝑚 around the center frequency of the input field, 𝜔𝜔 𝑐𝑐 .”

In the paper

“Compared to other dual-comb spectrometers based on Kerr combs [254,255], this platform has the potential of increasing the resolution i.e. the repetition rate of the comb sources with more versatility.”

What the sources say

• Not checked yetcites [254] Shams-Ansari, 2020, Low-repetition-rate integrated electro-optic frequency comb sources source
• Not checked yetcites [255] Bayer, 1998, Phys. Rev. Lett. source

In the paper

“It is shown that employing an intermediate cavity between the input coupler and the EO-comb cavity can increase the output comb power [248].”

What the sources say

• Not checked yetcites [248]

In the paper

“In bulk LN modulators, the microwave index is mainly restricted by the permittivity of LN, which is very high ( 𝜖𝜖 𝑟𝑟,𝑧𝑧 = 28 and 𝜖𝜖 𝑟𝑟,𝑥𝑥/𝑦𝑦 = 44 ) and hard to match the optical index ( 𝜖𝜖 𝑟𝑟,𝑧𝑧 = 4.6 and 𝜖𝜖 𝑟𝑟,𝑥𝑥/𝑦𝑦 = 4.9).”

In the paper

“In Ref [26], injecting a continuous-wave (CW) laser into a high-Q optical race-track cavity (Figure 17(a)) (FSR~10 GHz), which is modulated at a microwave frequency equal to the FSR, a frequency comb spectrum consisting of 900 lines in the telecommunication region was generated (Figure 17(b)).”

What the sources say

• Not checked yetcites [26] Zhang, 2019, Nature source

In the paper

“At frequencies 𝜔𝜔 > 1/𝐹𝐹𝑅𝑅, the capacitor (which is the electrode) has low impedance so the voltage would not drop across it.”

In the paper

“The low-repetition-rate output spectrum was achieved by densifying the original 10-GHz spectrum with a filling factor set by the nonresonant EO-comb.”

What the sources say

• Not checked yetcites [256] Lukens, 2017, Optica source

In the paper

“It is observed that DC response of LN modulators sometimes tends to be inefficient, unstable, and drift over time due to photorefraction, photoconduction, and surface charge accumulation [206,207].”

What the sources say

• Not checked yetcites [206] Spickermann, 1996, In traveling wave modulators which velocity to match? source
• Not checked yetcites [207] Aoki, 2006, Jpn. J. Appl. Phys. Part 1 source

In the paper

“Benefiting from the push-pull configuration, an MZM has a 𝑉𝑉 𝜋𝜋 that is half of a phase modulator.”

In the paper

“The key idea here is to realize that the driving microwave field of the phasemodulator must be resonant with the free spectral range (FSR) of the optical cavity to maximize the efficiency of the cascaded side-band generation.”

In the paper

“In dual-comb setups with EO comb sources, the mutual coherence can be achieved by driving with phase-locked microwave sources and shared optical pump laser [252].”

What the sources say

• Not checked yetcites [252] Suh, 2016, Science source

In the paper

“Velocity matching allows microwave and optical signals to co-propagate at the same speed so that the modulation accumulates constructively.”

In the paper

“Using a single CW laser source to feed both microrings resulted in a coherence time of 5×10 -3 seconds.”

What the sources say

• Not checked yetcites [250] Yan, 2017, Light Sci. Appl. source

In the paper

“With the advent of ultra-low-loss LNOI waveguides and resonators [11], resonant-based EO combs have been realized on-chip with unprecedented performance [26].”

What the sources say

• Not checked yetcites [11] Zhang, 2017, Optica source
• Not checked yetcites [26] Zhang, 2019, Nature source

In the paper

“Such a spectrometer can potentially probe transitions that are spectrally far apart with an optimized signal to noise ratio.”

In the paper

“A unique property of these comb sources is their ability to generate the spectrum at multiples of the optical FSR (defined by the size of the race-track cavity) by changing the microwave driving frequency, as shown in Figure 17(c).”

In the paper

“To accumulate a 𝜋𝜋 phase shift, the modulator requires millimeter-or even centimeter-scale length given a reasonable driving voltage.”

In the paper

“By cascading a cavity-based and a non-resonant EO-comb, a 3-GHz comb was achieved on an X-cut LNOI platform [256].”

What the sources say

• Not checked yetcites [256] Lukens, 2017, Optica source

In the paper

“To achieve an EO bandwidth of tens to hundreds of GHz, traveling-wave modulators are necessary, where the electrode is a transmission line.”

In the paper

“As it was discussed earlier, EO-comb sources can be operated over different center frequencies due to the flexible operating frequency and natural phaselocking established by the microwave driving field.”

In the paper

“As a practical example, Xu et al. use 1 μm waveguide when routing the optical signals while tapering up to 4 μm wide waveguides in the phase modulation region to reduce 𝑉𝑉 𝜋𝜋 [16].”

What the sources say

• Not checked yetcites [16] Xu, 2020, Nat. Commun. source

In the paper

“Moreover, the dispersion engineering of the LNOI waveguides would help to overcome the fundamental limitation of the comb bandwidth for resonant EO-combs based on bulk elements.”

In the paper

“Using this concept, for the first time, the authors demonstrated a spectrally-tailored dual-comb interferometer which could probe two different regions at telecommunication wavelengths that are 6.6 THz apart.”

In the paper

“First, current efficiency and output power of LNOI EO comb are relatively low compared to Kerr combs.”

In the paper

“One of the requirements for dual-comb spectroscopy is the need for mutual coherence time between the two comb sources.”

In the paper

“Therefore, the phase velocity of the microwave should match the group velocity of the optical signal [209,210].”

What the sources say

• Not checked yetcites [209] Pozar, 2005
• Not checked yetcites [210] Shin, 2005, IEEE Trans. Microw. Theory Tech. source

In the paper

“Besides periodic poling, periodically perturbing the waveguide width in the form of grooves can also achieve quasi-phase matching [117,321].”

What the sources say

• Not checked yetcites [117] Wang, 2017, Opt. Express source
• Not checked yetcites [321] Guo, 2016, Optica source

In the paper

“Dielectric metasurface can be used to achieve phase-matching-free SHG [320].”

What the sources say

• Not checked yetcites [320] Boes, 2019, Opt. Express source

In the paper

“With this configuration, both the optical pump and modulation sideband were resonantly enhanced.”

In the paper

“Such frequency shifter and beam splitter allow coherent frequency control of photons, which are of particular interest to frequency-domain quantum computing [258].”

What the sources say

• Not checked yetcites [258] Tsang, 2010, Phys. Rev. A source

In the paper

“By engineering the density of states of, and coupling between, optical modes in LNOI waveguides and ring-resonators, an EO frequency shifter that works with CW optical input and continuous sinusoidal microwave drive was demonstrated, featuring a shift efficiency of ~99% and an on-chip device insertion loss of 0.45 dB [177].”

What the sources say

• Not checked yetcites [177] Jiang, 2020, Nat. Commun. source

In the paper

“In a type-I second harmonic generation (SHG) process, there are four positions along the ring which the phase matching can be achieved.”

What the sources say

• Not checked yetcites [317] Fürst, 2016, Opt. Express source
• Not checked yetcites [318] Wang, 2017, Nat. Commun. source
• Not checked yetcites [319] Rao, 2017, Appl. Phys. Lett. source

In the paper

“Cavity EO devices are particularly promising for this application because of their direct conversion mechanism (i.e. they do not rely on an intermediate form of energy, such as a mechanical excitation), which may enable higher efficiency and lower noise operation.”

In the paper

“Indirect optical poling diagnostic methods have also been exploited by monitoring the output optical signal from the waveguides while poling.”

What the sources say

• Not checked yetcites [309] Niu, 2020, Appl. Phys. Lett. source

In the paper

“The average poling duty cycle can be inferred from the change in phase of the out-coupled light.”

In the paper

“A key component of such an interconnect is a quantum transducer that can convert single photons between microwave and optical frequencies.”

In the paper

“Quantum interconnects [267] based on optical fiber links offer a way around this restriction, because they provide relatively weak attenuation and negligible thermal noise due to the high optical carrier frequency.”

What the sources say

• Not checked yetcites [267] Lambert, 2020, Adv. Quantum source

In the paper

“The efficiency of the aforementioned parametric frequency conversion processes is greatly enhanced in nanophotonic PPLN waveguides compared to in bulk PPLN waveguides.”

In the paper

“In the former case, high normalized conversion efficiency of 1160%/W•cm 2 was achieved in a 5 mm SiN x loaded waveguide on PPLN through engineering the waveguide cross section to limit leakage of the fundamental TE mode to TM slab modes [322].”

What the sources say

• Not checked yetcites [322] Minkov, 2019, Optica source

In the paper

“The resonant enhancement of microwave power creates stronger optical modulation at the cost of a reduced bandwidth set by the linewidth of the microwave resonator.”

In the paper

“In the latter case, ultra-high normalized conversion efficiency of 4600%/W•cm 2 was achieved in a 300 μm long LN ridge waveguide through the use of active monitoring of the second harmonic signal to achieve optimal poling [310].”

What the sources say

• Not checked yetcites [310] Zhao, 2020, J. Appl. Phys. source

In the paper

“This is because the normalized conversion efficiency of, for instance, SHG, scales as 2 where 𝜁𝜁 is the mode overlap between the fundamental frequency and second harmonic modes, and 𝐴𝐴 1 and𝐴𝐴 2 are the mode areas of the fundamental frequency and second harmonic, respectively; details on calculating 𝜁𝜁, 𝐴𝐴 1 , and 𝐴𝐴 2 can be found in Ref. [299].Since mode areas 𝐴𝐴 1 and 𝐴𝐴 2 can be more than an”

What the sources say

• Not checked yetcites [299] Gopalan, 1998, Appl. Phys. Lett. source

In the paper

“Additionally, this splitting can be tuned by a DC bias capacitor.”

In the paper

“The main motivation for the development of such modulators is to achieve an efficient transducer between microwave and optical fields to couple microwave-frequency superconducting qubits to optical networks.”

In the paper

“Under the generalized critical coupling condition, light injected at one frequency can be efficiently coupled from one frequency mode to another without back conversion.”

What the sources say

• Not checked yetcites [177] Jiang, 2020, Nat. Commun. source

In the paper

“When the crystallographic axis is not the symmetry axis, for example, on a X/Y-cut LN thin film, the effective nonlinearity and the refractive index of in-plane polarized light is changing as light propagates in the microring resonator ([317-319]).”

What the sources say

• Not checked yetcites [317] Fürst, 2016, Opt. Express source
• Not checked yetcites [318] Wang, 2017, Nat. Commun. source
• Not checked yetcites [319] Rao, 2017, Appl. Phys. Lett. source

In the paper

“Recently, cavity EO transducers in thin-film LN, shown in Figure 19(d) and (e) have demonstrated microwaveto-optical photon conversion efficiency as high as 2×10 -5 [178,179].”

What the sources say

• Not checked yetcites [178] Diziain, 2013, Appl. Phys. Lett. source
• Not checked yetcites [179] Jiang, 2018, Appl. Phys. Lett. source

In the paper

“It is also possible to achieve type-0 effective quasi-phase matching in such a cyclic fashion.For example, all participating waves can be in quasi-TE modes inside an X-cut microdisk [151].”

What the sources say

• Not checked yetcites [151] Ye, 2020, Opt. Lett. source

In the paper

“Recently, a photonic two-level system was achieved using a pair of evanescently coupled LNOI microring resonators”

In the paper

“A normalized conversion efficiency as high as 1,660% W -1 cm -2 has been achieved at telecom wavelengths.”

What the sources say

• Not checked yetcites [320] Boes, 2019, Opt. Express source

In the paper

“Cyclic phase matching (CPM) [317] is often used in ring or microdisk cavities to achieve type-I phase matching.”

What the sources say

• Not checked yetcites [317] Fürst, 2016, Opt. Express source

In the paper

“To date, ultrahigh normalized conversion efficiencies have been achieved in both SiN x loaded waveguides and monolithic LN ridge waveguides via type-0 quasi-phase matching.”

What the sources say

• Not checked yetcites [322] Minkov, 2019, Optica source
• Not checked yetcites [310] Zhao, 2020, J. Appl. Phys. source

In the paper

“Jankowski et al. reported an achieved 𝜒𝜒 eff (3) ~200 times higher than the 𝜒𝜒 Kerr (3) of LN at 2050 nm using an integrated PPLN waveguide [295].”

What the sources say

• Not checked yetcites [295] Jankowski, 2020, Optica source

In the paper

“Most 𝜒𝜒 (2) processes demonstrated in Z-cut LN microdisks rely on modal phase matching [141,150,161], where the largest nonlinear tensor element 𝑑𝑑 33 are not used.”

What the sources say

• Not checked yetcites [141] Liang, 2017, Optica source
• Not checked yetcites [150] Lin, 2019, Phys. Rev. Lett. source
• Not checked yetcites [161] Hao, 2020, Photon. Res. source

In the paper

“Furthermore, a soliton microcomb spanning > 200 nm at 1.5 μm (Figure 30 (c)) > 300 nm at 2 μm have been achieved by avoiding Raman scattering effects (Figure 30 (d)).”

What the sources say

• Not checked yetcites [27] He, 2019, Optica source
• Not checked yetcites [174]

In the paper

“In the same year, Lu et al. demonstrated radially poled, Z-cut microring [31] (see Figure 28(b)).A single pulley waveguide was designed to efficiently couple both the infrared and visible frequency bands.Due to the fabrication limit on the poling period, TE 00 -to-TM 00 SHG was adopted, utilizing the 𝑑𝑑 31 coefficient.Nonetheless, an ultra-high on-chip SHG efficiency of 250%/mW was achieved.”

What the sources say

• Not checked yetcites [31] Lu, 2019, Optica source

In the paper

“More importantly, in lithium niobate, 𝜒𝜒 eff 3) can be tuned to either a positive or negative value by engineering the quasi-phase matching (QPM) condition in periodically poled lithium niobate waveguides ( 𝛥𝛥𝛥𝛥 = 𝛥𝛥 SH -2𝛥𝛥 FW -𝛥𝛥 QPM ).”

In the paper

“In addition to the intrinsic cubic third order nonlinearity, phase-mismatched second order processes can induce an effective Kerr nonlinearity due to back-action of the second harmonic (SH) wave at 2𝜔𝜔 on the fundamental wave (FW) at 𝜔𝜔.It originates from the occurrence of two successive second order nonlinear processes: upconversion to SH at 2𝜔𝜔 via second harmonic generation (SHG) and then down”

What the sources say

• Not checked yetcites [328] Bache, 2007, J. Opt. Soc. Am. B source

In the paper

“For example, group velocity mismatching (GVM, 𝛥𝛥𝛥𝛥′) or the temporal walk-off between the FW and SH is the dominant factor of the SHG bandwidth (𝛥𝛥𝜆𝜆 ∼ 1/|𝛥𝛥𝛥𝛥′|𝐿𝐿, where L is the PPLN waveguide length).”

In the paper

“Optical cavities can strongly enhance these parametric conversion processes given the same optical pump power.”

In the paper

“For example, in Z-cut microrings, the fundamental wave is usually at fundamental quasi-TM (TM 00 ) mode, and the second harmonics can be at higher order quasi-TM (TM 20 ) mode.This conversion thus utilizes the largest nonlinear coefficient 𝑑𝑑 33 .”

What the sources say

• Not checked yetcites [172] Yu, 2020, Light Sci Appl source
• Not checked yetcites [173] Zhang, 2019, Nat. Photonics source

In the paper

“Kerr combs spanning 700 nm were demonstrated on the LNOI platform on X-cut lithium niobate wafers [28].”

What the sources say

• Not checked yetcites [28] Wang, 2019, Nat. Commun. source

In the paper

“Recent demonstration [295] reports a multi-octave spanning supercontinuum spectrum with a few pJ pulse energy.”

What the sources say

• Not checked yetcites [295] Jankowski, 2020, Optica source

In the paper

“High coincidence-to-accidental ratio (CAR) of 668 ± 7 has been achieved at a pair generation rate of 12 MHz in Ref. [34] in a 5 mm PPLN waveguide on X-cut LNOI.”

What the sources say

• Not checked yetcites [34] Zhao, 2020, Phys. Rev. Lett. source

In the paper

“Longer PPLN ridge waveguides up to 4 mm have also been demonstrated [29,32], albeit with lower normalized conversion efficiencies (<3000%/W•cm 2 ) due to nonoptimal poling duty cycle (i.e.<50% duty cycle) and non-uniform poling.”

What the sources say

• Not checked yetcites [29] Wang, 2018, Optica source
• Not checked yetcites [32] Chen, 2019, OSA Continuum source

In the paper

“In the presence of phase mismatch 𝛥𝛥𝛥𝛥 between the FW and SH, this effective third order nonlinearity 𝜒𝜒 eff 3) is approximately proportional to -[𝜒𝜒 (𝟐𝟐) ] 𝟐𝟐 /𝛥𝛥𝛥𝛥.”

In the paper

“Since there is almost no acoustic contrast between the region with and without Ti indiffusion, the optical waveguides defined by Ti indiffusion do not reflect SAW or scatter SAW into bulk acoustic waves.”

In the paper

“This approach drastically simplified the conventional approach for f-2f interferometry, which consists of a bulk periodically-poled lithium niobate (PPLN) with a temperature controller and a delay line for compensation of the temporal walk-off between the f and 2f spectral components”

In the paper

“there has been a demonstration of a novel approach for broadband SCG in an integrated PPLN waveguide via cascaded nonlinearities [295].”

What the sources say

• Not checked yetcites [295] Jankowski, 2020, Optica source

In the paper

“Unlike the aforementioned Rayleigh mode, shear modes create strain from top to bottom of the thin film with the same sign, and thus the induced optical index change adds constructively in the overlap with the optical mode.”

In the paper

“The choice of crystal orientation significantly changes the performance of piezo-optomechanical devices.”

In the paper

“Optomechanics [386] provides an efficient interface between light and elastic waves, via the photoelastic and moving boundary interactions.”

What the sources say

• Not checked yetcites [386] Mirhosseini, 2020, Nature source

In the paper

“As both the optical and acoustic indices (inverse phase velocities) of LN are higher than the underneath silicon dioxide layer, thin-film LN on oxide can simultaneously confine optical and acoustic modes.”

In the paper

“With optical waveguides defined by etching thin-film LN, waveguide-based acousto-optic modulators have been demonstrated (Figure 35(f)(g)) [398-400].”

What the sources say

• Not checked yetcites [398]
• Not checked yetcites [399] Tellekamp, 2016, J. Electron. Mater. source
• Not checked yetcites [400] Dahmani, 2020, Phys. Rev. Appl. source

In the paper

“An acousto-optic frequency shifter has been built employing Ti indiffused optical waveguides on bulk LN substrate [395].”

What the sources say

• Not checked yetcites [395] Mahmoud, 2018, Opt. Express source

In the paper

“Since the acoustic contrast between LN and oxide is small, thin-film LN on oxide only confines a few acoustic wave modes, for example the Rayleigh-like modes.”

In the paper

“However, it is challenging to form a high-Q acoustic resonators using this approach, since the top optical waveguide inevitably scatters the SAW into bulk acoustic waves, especially when the acoustic wavelengths are comparable to the size of optical waveguides.”

In the paper

“This configuration provides an opportunity to achieve overall efficient piezo-optomechanical coupling by using materials with high photoelastic coefficients as top optical waveguides.”

In the paper

“where an ultrabroadband supercontinuum generation spanning 0.35 to 4.1 µm with 240 pJ pulse energy [297].”

What the sources say

• Not checked yetcites [297] Luo, 2018, Optica source

In the paper

“The LN platform allows for on-chip f-2f interferometry due to the large intrinsic 𝜒𝜒 (2) and 𝜒𝜒 (3) nonlinearities.”

In the paper

“Such large nonlinearities allow for the generation of a supercontinuum spectrum spanning 2.5 octaves with pulse energies as low as 10 pJ.”

What the sources say

• Not checked yetcites [295] Jankowski, 2020, Optica source

In the paper

“the presence of both 𝜒𝜒 (2) and 𝜒𝜒 (3) nonlinearities allows for the extension of the spectral bandwidth even further through a combination of supercontinuum via dispersive wave generation, harmonic generation, and difference frequency generation (DFG)”

In the paper

“Since the acoustic velocity of sapphire is much higher than LN, LN on sapphire supports more interesting acoustic modes than LN on oxide [394].”

What the sources say

• Not checked yetcites [394] Cai, 2019, Photon. Res. source

In the paper

“Coherent two-octave-spanning supercontinuum generation and f CEO detection through the spectral overlap of the second harmonic component with the generated supercontinuum spectrum was achieved in a single LN waveguide [65].”

What the sources say

• Not checked yetcites [65] Wang, 2019, Quantum Eng. source

In the paper

“Since the piezoelectricity of LN is strong, the secondary electro-optic effect, which is caused by the electric field generated by the elastic wave via piezoelectricity, plays a significant role in the overall coupling from microwaves to light.”

In the paper

“An integrated LN f-2f interferometer is demonstrated for stabilizing the f CEO of a mode-locked fiber laser [296].”

What the sources say

• Not checked yetcites [296] Luo, 2019, Laser Photon. Rev. source

In the paper

“The contribution of this secondary electrooptic effect can be more than one third of the overall coupling.”

In the paper

“For example, X cut LN on sapphire supports shear waves (Love waves) propagating in the crystal Y direction.”

In the paper

“For high frequency applications, with the acoustic frequency in GHz range, the acoustic wavelength is <1 μm which results in reduced interaction between the optical and the acoustic waves, due to the limited mode overlap.This limits the efficiency of the acousto-optic devices.”

In the paper

“In addition, the spectrum extends into the mid-infrared (mid-IR) regime via DFG.”

What the sources say

• Not checked yetcites [297] Luo, 2018, Optica source

In the paper

“The spectral generation of UV to the mid-IR in a single LN device offers promise towards the development of an integrated ultrabroadband source for spectroscopy applications.”

In the paper

“Numerical modeling of the pulse propagation [296] dynamics in the LN waveguide showed that the system can be modeled using a reduced scalar nonlinear envelope equation with both quartic and cubic nonlinearities [379-381]”

What the sources say

• Not checked yetcites [296] Luo, 2019, Laser Photon. Rev. source
• Not checked yetcites [379] Efimov, 2005, Phys. Rev. Lett. source
• Not checked yetcites [380] Webb, 2013, Opt. Lett. source
• Not checked yetcites [381] Okawachi, 2017, Opt. Lett. source

In the paper

“Acoustic waves generated on LN have been used to measure the elasto-optic coefficients of the arsenic trisulfide thin film overlaying on the LN [389].”

What the sources say

• Not checked yetcites [389] Shao, 2019, Phys. Rev. Appl. source

In the paper

“offers promise towards the realization of a fully-integrated frequency comb source.”

In the paper

“Using IDTs, >80% microwave power has been successfully delivered to the suspended LN slabs (Figure 35(d)) [404].”

What the sources say

• Not checked yetcites [404] Kittlaus, 2021, Nat. Photonics source

In the paper

“Through acousto-optic interactions, a travelling acoustic wave can thus result in a strong nonreciprocity between light travelling in opposite directions.”

In the paper

“They are suitable for heterogeneous integration with photonic waveguides as they only require a single layer of material.”

In the paper

“However, the frequency shifting efficiencies are only a few percent, which is still quite low compared to the mature commercial bulk AOFS.”

In the paper

“Hybrid LN/Si modulators can combine the scalability of silicon photonics with the excellent EO performance of LN.”

In the paper

“Very recently, direct integration of SNSPDs on thin-film LN waveguides have been successfully demonstrated [420,421] by overcoming a number of fabrication challenges.”

What the sources say

• Not checked yetcites [420] Sayem, 2020, Appl. Phys. Lett. source
• Not checked yetcites [421] Cheng, 2019, Appl. Phys. Lett. source

In the paper

“Later, LN/SOI hybrid traveling-wave modulators with 3 dB EO bandwidth exceeding 100 GHz were demonstrated [23].”

What the sources say

• Not checked yetcites [23] Weigel, 2018, Opt. Express source

In the paper

“The state of the art implementation demonstrates a single microwave photon to optical photon conversion efficiency of 5% using piezo-optomechanical crystals (Figure 35(c)) [170].”

What the sources say

• Not checked yetcites [170] Luo, 2019, Phys. Rev. Appl. source

In the paper

“However, the optomechanical coupling rate is compromised due to the large mode volumes.”

In the paper

“Due to the strong piezoelectricity, LN devices demonstrate efficient microwave to mechanical conversion even without an electromagnetic resonator.”

In the paper

“The optical waveguides do not cause acoustic losses in the suspended structures.”

In the paper

“Beyond standard EO modulators used for telecommunication, integrated EO Fourier transform spectrometer has also been demonstrated based on SiN x -loaded thin-film LN modulators [410].”

What the sources say

• Not checked yetcites [410] Gol’tsman, 2001, Appl. Phys. Lett. source

In the paper

“On the other hand, efficient microwave-to-mechanical conversion has been demonstrated on suspended LN slabs with optical waveguides [167].”

What the sources say

• Not checked yetcites [167] Lu, 2020, Optica source

In the paper

“Since the acoustic velocity is about 5 orders of magnitude smaller than the electromagnetic wave velocity, acoustic waves at microwave frequencies have wave numbers, k, that are 5 orders of magnitude larger than their EM counterparts.”

In the paper

“It was first implemented in hybrid ring modulators [111-113] by bonding pieces of LN thin films prepared from ion slicing onto Si ring resonators.”

What the sources say

• Not checked yetcites [111] Lee, 2011, Opt. Lett. source
• Not checked yetcites [112] Chen, 2013, Opt. Express source
• Not checked yetcites [113] Chen, 2014, Optica source

In the paper

“Among the integrated devices, LN acousto-optic frequency shifters (AOFS) [396,401] demonstrate frequency shifting efficiencies that are 10-100 times higher than those of the pioneering integrated AOFS developed on thin film AlN (Figure 35(b)).”

What the sources say

• Not checked yetcites [396] Cai, 2019, Low-loss waveguides in Y-cut thin film lithium niobate for acousto-optic applications source
• Not checked yetcites [401] Shao, 2020, Acoustically mediated microwave-to-optical conversion on thin-film lithium niobate

In the paper

“Integrating thinfilm LN through flip-chip or wafer bonding can complement their functionality while leveraging their existing fabrication/manufacturing processes.”

In the paper

“Compared to LN cavity electro-optic implementations, LN piezo-optomechanical implementations [167,170] demonstrate higher microwave-to-optical conversion efficiencies by taking advantage of higher Q factors and smaller mode volumes of the mechanical resonances.”

What the sources say

• Not checked yetcites [167] Lu, 2020, Optica source
• Not checked yetcites [170] Luo, 2019, Phys. Rev. Appl. source

In the paper

“The microwave return loss from the acoustic resonator can be less than -10 dB [404].”

What the sources say

• Not checked yetcites [404] Kittlaus, 2021, Nat. Photonics source

In the paper

“Indeed, the ability to perform fast modulation of light makes thin-film LN a very promising platform for time-and frequency-encoded quantum operations.”

In the paper

“Photorefractive effects are particularly prominent in LNOI devices operating at visible wavelengths [15].”

What the sources say

• Not checked yetcites [15] Desiatov, 2019, Optica source

In the paper

“These charge carrier effects typically manifest as bias or detuning drift when operating electro-optic devices in LNOI, with timescales typically on the order of milliseconds to hours or longer [457].”

What the sources say

• Not checked yetcites [457] Surya, 2021, Opt. Lett. source

In the paper

“First, reciprocity can be broken through optical nonlinearity, such as wavelength conversion [485].”

What the sources say

• Not checked yetcites [485] Shi, 2015, Nat. Photonics source

In the paper

“LNOI PPLN waveguides are well suited for this approach.”

In the paper

“Such strong power-dependent detuning can make it more challenging to operate LNOI devices at high powers or where stable phase tuning is required [168,178,179].”

What the sources say

• Not checked yetcites [168] Wolf, 2018, Optica source
• Not checked yetcites [178] Diziain, 2013, Appl. Phys. Lett. source
• Not checked yetcites [179] Jiang, 2018, Appl. Phys. Lett. source

In the paper

“It is well known that such relaxation can lead to drift in the bias voltage required for electro-optic devices [456,464-466].”

What the sources say

• Not checked yetcites [456] Sun, 2017, Opt. Express source
• Not checked yetcites [464] Korotky, 1996, J. Lightwave Technol. source
• Not checked yetcites [465] Holzgrafe, 2020, Toward efficient microwave-optical transduction using cavity electro-optics in thin-film lithium niobate source
• Not checked yetcites [466] Sun, 2020, Photon. Res. source

In the paper

“recent works have observed bias drift consistent with dielectric relaxation [467].”

What the sources say

• Not checked yetcites [467] Zhong, 2020, Science source

In the paper

“Because it has both 𝜒𝜒 (2) and 𝜒𝜒 (3) optical nonlinearities, thin-film LN is a promising platform for both Kerr (produced via 𝜒𝜒 (3) ) [339] and Pockels (produced via 𝜒𝜒 (2) ) [481] soliton generation.”

What the sources say

• Not checked yetcites [339] Xu, 2021, Opt. Express source
• Not checked yetcites [481] Etrich, 1997, Phys. Rev. Lett. source

In the paper

“The combined effects of Raman scattering, four-wave mixing, and electro-optic modulation can result in a broad spectrum of small EO combs around lines formed by Raman and Kerr effects [484].”

What the sources say

• Not checked yetcites [484] Zhang, 2019, Microresonator frequency comb generation with simultaneous Kerr and electro-optic nonlinearities

In the paper

“The use of electro-optic switches and phase shifters enables additional functionalities going further than reducing the power consumption and heat generation of thermal phase shifters.”

In the paper

“Indeed, resonance tuning of photonic crystal cavities in LNOI has been demonstrated using optical powers corresponding to just a few photons inside the cavity [183].”

What the sources say

• Not checked yetcites [183] Boyd, 2019

In the paper

“Efforts to reduce photorefractive effects in LNOI have shown that photorefractive shifts can be reduced by annealing and using uncladded waveguides [342], but further work is required to understand the impact of material properties and device geometry on photorefraction in LNOI devices.”

What the sources say

• Not checked yetcites [342] Sanna, 2015, Phys. Rev. B source

In the paper

“Recent work has shown that the photorefractive effect in LNOI is stronger and responds at faster timescales than in bulk devices, especially in high-quality factor resonant photonic devices [457,458].”

What the sources say

• Not checked yetcites [457] Surya, 2021, Opt. Lett. source
• Not checked yetcites [458] Günter, 2006 source

In the paper

“Recently, such an optical isolator was achieved based on difference frequency generation in PPLN waveguides (see Figure 42(a)) [486].”

What the sources say

• Not checked yetcites [486] Abdelsalam, 2020, Optica source

In the paper

“Cavity EO transducers using thin-film lithium niobate resonators and superconducting LC resonators [178,179].”

What the sources say

• Not checked yetcites [178] Diziain, 2013, Appl. Phys. Lett. source
• Not checked yetcites [179] Jiang, 2018, Appl. Phys. Lett. source

In the paper

“PPLN waveguide frequency converters.”

What the sources say

• Not checked yetcites [29] Wang, 2018, Optica source
• Not checked yetcites [310] Zhao, 2020, J. Appl. Phys. source

In the paper

“Group velocity engineering for second harmonic generation (SHG).”

What the sources say

• Not checked yetcites [295] Jankowski, 2020, Optica source