Continuous Wave Second Harmonic Generation from an Etchless Lithium Niobate Resonant Metasurface

Noa Mazurski; Uriel Levy; Zetian Chen

arxiv: 2604.18501 · v1 · submitted 2026-04-20 · ⚛️ physics.optics

Continuous Wave Second Harmonic Generation from an Etchless Lithium Niobate Resonant Metasurface

Zetian Chen , Noa Mazurski , Uriel Levy This is my paper

Pith reviewed 2026-05-10 03:54 UTC · model grok-4.3

classification ⚛️ physics.optics

keywords lithium niobatemetasurfacesecond harmonic generationcontinuous waveresonant metasurfacenonlinear photonicsetchless fabricationguided mode resonance

0 comments

The pith

A hybrid etchless lithium niobate metasurface enables continuous-wave second-harmonic generation at low pump powers.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that patterning a silicon-rich nitride layer atop an unetched lithium niobate film creates a resonant structure that concentrates light in the nonlinear material for efficient frequency conversion. This design supports guided-mode resonances with quality factors near 2300 while avoiding etching damage to the lithium niobate. Under continuous-wave pumping at intensities below one kilowatt per square centimeter, clear second-harmonic signals appear with a normalized conversion efficiency of 0.156 percent square centimeters per gigawatt in the linear regime. The results also highlight that resonant operation under continuous drive produces time-dependent effects such as power-induced resonance shifts and signal overshoot, which must be accounted for in device performance.

Core claim

CW second-harmonic generation is achieved in transmission on an etchless thin-film lithium niobate platform with a patterned silicon-rich nitride metasurface, yielding a quality factor of approximately 2300 and a normalized efficiency of 0.156 % cm²/GW at sub-kW/cm² pump levels, together with the observation of transient resonance dynamics including power-dependent evolution and overshoot.

What carries the argument

Hybrid SRN-on-LN metasurface providing guided-mode resonance while confining most of the optical mode in the unpatterned lithium niobate layer.

If this is right

CW resonant SHG exhibits pronounced transient dynamics such as power-dependent resonance shifts and nonideal power scaling.
The etchless platform combines low loss, high nonlinearity, and CMOS compatibility for compact frequency converters.
Resonance dynamics are central to both the operation and the accurate evaluation of CW-driven nonlinear metasurfaces.
Sub-kW/cm² operation opens routes to narrow-linewidth, stable-frequency nonlinear sources without high-power requirements.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Transient dynamics observed here may appear in other resonant nonlinear metasurface systems and could be engineered for adaptive tuning.
Extending the hybrid design to different wavelengths or nonlinear processes could broaden applications in integrated photonics.
The avoidance of etching suggests better preservation of material properties, potentially improving long-term stability compared to etched structures.

Load-bearing premise

The hybrid design truly confines most of the optical mode in the unpatterned lithium niobate while the SRN only provides resonance without adding significant loss or nonlinearity, and the observed transient dynamics arise intrinsically from the CW resonant process.

What would settle it

Absence of any detectable second-harmonic signal when the pump is tuned to the resonance wavelength at the reported power levels, or complete disappearance of the transients when the measurement is repeated with different equipment or sample batches, would challenge the claims.

Figures

Figures reproduced from arXiv: 2604.18501 by Noa Mazurski, Uriel Levy, Zetian Chen.

**Figure 2.** Figure 2: Linear transmission spectrum. (a) Simulated spectrum of devices with different notch sizes and periods. Inset: calculated field enhancement for the small notch high-Q device at resonance, showing 44-fold enhancement confined in the LN. (b) Measured transmission spectrum. Inset shows the zoom-in of the high-Q device resonance, estimated with Q~2300. (c) Optical setup. EDFA: erbium-doped fiber amplifier, SM:… view at source ↗

**Figure 3.** Figure 3: a [PITH_FULL_IMAGE:figures/full_fig_p008_3.png] view at source ↗

**Figure 4.** Figure 4: SH power (a, c) and conversion efficiency (b, d), for the low-Q device (a, b) and high-Q device (c, d). The low-Q device shows a close to 2 logarithmic slope between the SH power and pump power up to high power, with almost constant normalized conversion efficiency. The high-Q device shows piecewise, and progressively decreased slope as pump power increases. In contrast, the high-Q device does not exhibit … view at source ↗

**Figure 4.** Figure 4: When the device is illuminated directly from the dark at 𝜆max𝑆𝐻 , the SH signal exhibits only a slow and relatively weak increase (green curve), remaining far below the optimized value. For red-detuned excitation, i.e., at 𝜆max𝑆𝐻 + 0.1 nm, the response is even weaker. In contrast, for blue-detuned excitation at 𝜆max𝑆𝐻 − 0.3 nm and 𝜆max𝑆𝐻 − 0.4 nm, the SH signal first builds up with time and can temporarily… view at source ↗

**Figure 5.** Figure 5: Transient dynamic of the high-Q device SH response. (a) under constant pump power, and (b) under constant pump wavelength. 𝝀𝒎𝒂𝒙𝑺𝑯 denotes the pump wavelength that yields the maximum SH signal at quasi-steady state under 270 mW, as determined using the resonance-tracking protocol. The yellow curves with markers indicate the same measurement for direct comparison. The dashed lines are included only as guides… view at source ↗

read the original abstract

Nonlinear metasurfaces provide a route to compact frequency conversion by replacing phase matching and long interaction lengths with resonantly enhanced light matter interaction in subwavelength structures. Extending this capability to continuous wave (CW) operation is particularly important for applications requiring narrow linewidth, stable frequency, and stationary optical fields, but remains extremely challenging. Here, we demonstrate CW second-harmonic generation on a transmission mode, etchless thin film lithium niobate platform enabled by a patterned silicon rich nitride metasurface. This hybrid design combines guided mode resonance coupling, low optical loss, and CMOS compatible processing while keeping most of the optical mode confined in the unpatterned lithium niobate, yielding a measured quality factor of ~2300. Clearly resolved SHG is achieved under sub-kW/cm^2 CW pumping, with a normalized conversion efficiency of 0.156 % cm^2/GW in the low power regime. Interestingly, our work reveals that CW resonant SHG in metasurfaces can exhibit pronounced transient dynamics, including power dependent resonance evolution, overshoot, and nonideal scaling. These findings establish etchless LN SRN metasurfaces as a promising platform for compact CW nonlinear photonics, and show that resonance dynamics are central to the operation and evaluation of CW driven nonlinear metasurfaces.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

They've shown working CW second-harmonic generation in an etchless LN platform with an SRN resonant layer on top, plus some transient dynamics worth noting.

read the letter

The main takeaway is that this experiment demonstrates continuous-wave second-harmonic generation from a lithium niobate metasurface without etching the LN film itself. They pattern silicon-rich nitride to create the resonance while leaving the nonlinear material intact, which keeps most of the mode in the LN layer and supports a measured Q around 2300. The normalized efficiency hits 0.156 % cm²/GW at low powers with sub-kW/cm² CW pumping, and they report clear SHG in transmission mode. The hybrid stack is CMOS-compatible, which is a practical plus for integration. They also call out transient effects under CW drive—power-dependent resonance shifts, overshoot, and scaling that deviates from ideal quadratic behavior. That observation is new enough to matter for anyone trying to run these devices steadily rather than with pulsed pumps. The work is straightforward experimental demonstration with directly measured quantities and no obvious circular derivations or free parameters. The platform choice and the dynamics both look like genuine additions to the etchless LN literature. The soft spots are limited but real. The abstract gives no error bars, no explicit baseline comparisons, and no detailed checks on whether the transients come from thermal drift, fabrication variation, or the resonance itself. If the full paper has solid controls and statistics on those points, the claims hold; otherwise the transients remain plausible but not fully nailed down. The central efficiency number is credible on its face but would benefit from clearer uncertainty reporting. This paper is for researchers working on compact nonlinear frequency conversion and integrated photonics platforms. Anyone building CW metasurface devices or looking for etchless LN routes will find the design and the dynamics useful to consider. I would send it for peer review. The experiment is concrete, the platform is new, and the results are relevant enough that referees can give targeted feedback on the data and the transients.

Referee Report

1 major / 2 minor

Summary. The manuscript demonstrates continuous-wave second-harmonic generation (SHG) from an etchless thin-film lithium niobate resonant metasurface enabled by a patterned silicon-rich nitride (SRN) layer in a hybrid design. The structure achieves a measured quality factor of ~2300 with most of the optical mode confined in the unpatterned LN layer. Clearly resolved SHG is reported under sub-kW/cm² CW pumping, with a normalized conversion efficiency of 0.156 % cm²/GW in the low-power regime. The work additionally reports pronounced transient dynamics during CW resonant operation, including power-dependent resonance evolution, overshoot, and nonideal scaling.

Significance. If the experimental results hold, the work is significant for establishing a CMOS-compatible, etchless platform for compact CW nonlinear photonics. The hybrid SRN-on-LN approach combines guided-mode resonance with low loss and mode confinement in LN, addressing key challenges in achieving stable, narrow-linewidth frequency conversion at low powers. The observation of transient dynamics provides new insight into the time-dependent behavior of CW-driven resonant metasurfaces, which has implications for device operation and characterization. The direct experimental measurements of Q-factor and efficiency constitute concrete, falsifiable performance benchmarks.

major comments (1)

[Results (transient dynamics subsection)] The claim that the observed transient dynamics (power-dependent resonance evolution, overshoot, and nonideal scaling) are intrinsic to CW resonant SHG rather than arising from fabrication variations or the measurement setup is central to the interpretation but rests on the hybrid platform design. The results section should provide additional supporting evidence, such as repeated measurements across multiple devices or comparisons with simulations of the expected dynamics, to substantiate this assertion.

minor comments (2)

[Abstract] The abstract reports specific numerical values (Q ~2300, efficiency 0.156 % cm²/GW) without error bars, uncertainty estimates, or baseline comparisons; including these would improve assessment of the quantitative claims.
Clarify the exact definition and calculation of the normalized conversion efficiency, including the assumed mode area and any power-dependent corrections applied in the low-power regime.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive assessment of our work and the constructive comment on strengthening the evidence for the intrinsic nature of the observed transient dynamics. We address the major comment below and will incorporate revisions accordingly.

read point-by-point responses

Referee: [Results (transient dynamics subsection)] The claim that the observed transient dynamics (power-dependent resonance evolution, overshoot, and nonideal scaling) are intrinsic to CW resonant SHG rather than arising from fabrication variations or the measurement setup is central to the interpretation but rests on the hybrid platform design. The results section should provide additional supporting evidence, such as repeated measurements across multiple devices or comparisons with simulations of the expected dynamics, to substantiate this assertion.

Authors: We agree that additional supporting evidence would strengthen the central claim regarding the intrinsic character of the transient dynamics. The hybrid SRN-on-LN platform is designed to minimize fabrication-induced variations by keeping the LN layer unpatterned and confining most of the mode there, while the SRN provides the resonance without etching LN. In the revised manuscript, we will add (i) repeated measurements on multiple devices fabricated on the same wafer showing consistent power-dependent resonance shifts, overshoot, and nonideal scaling, and (ii) comparisons with time-dependent simulations of the expected thermo-optic and nonlinear dynamics based on the measured Q-factor and mode overlap. These additions will directly address the possibility of setup or fabrication artifacts and confirm the dynamics arise from the CW resonant SHG process itself. revision: yes

Circularity Check

0 steps flagged

No significant circularity; pure experimental demonstration

full rationale

The paper is an experimental report of CW SHG in a hybrid SRN-on-LN metasurface. All headline results (Q~2300, normalized efficiency 0.156 % cm²/GW, power-dependent transients) are stated as directly measured quantities from fabricated devices and optical characterization. No equations, ansatzes, or predictive derivations appear in the provided text that could reduce to fitted inputs or self-citations by construction. The hybrid-mode-confinement description is a design rationale, not a load-bearing derivation. This matches the default case of a self-contained experimental paper with no circularity.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

Experimental paper relying on established material properties and resonance principles with no new free parameters, axioms beyond standard optics, or invented entities.

axioms (2)

domain assumption Guided-mode resonances can be engineered in hybrid thin-film dielectric stacks to enhance fields in an unpatterned nonlinear layer.
Underpins the metasurface design choice and mode confinement claim.
standard math Lithium niobate possesses intrinsic second-order optical nonlinearity suitable for second-harmonic generation.
Standard property invoked to interpret the observed frequency conversion.

pith-pipeline@v0.9.0 · 5534 in / 1388 out tokens · 73302 ms · 2026-05-10T03:54:24.688368+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

9 extracted references · 9 canonical work pages

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Continuous Wave Second Harmonic Generation Enabled by Quasi-Bound-States in the Continuum on Gallium Phosphide Metasurfaces

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47 Qu L, Wu W, Cai W, Ren M, Xu J. Second Harmonic Generation in Lithium Niobate on Insulator. Laser Photon Rev 2025; 19: 2401928. 48 Goldberg O, Gherabli R, Engelberg J, Nijem J, Mazurski N, Levy U. Silicon Rich Nitride Huygens Metasurfaces in the Visible Regime. Adv Opt Mater 2024; 12: 2301612. 20 Supporting Information Supporting Information is Attache...

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Nonlinear Optics

1 Boyd RW, Gaeta AL, Giese E. Nonlinear Optics. In: Drake GWF (ed). Springer Handbook of Atomic, Molecular, and Optical Physics. Springer International Publishing: Cham, 2023, pp 1097–1110. 2 Boyd GD, Kleinman DA. Parametric Interaction of Focused Gaussian Light Beams. J Appl Phys 1968; 39: 3597–3639. 3 Zhang X, Cao Q-T, Wang Z, Liu Y, Qiu C-W, Yang L et ...

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Second harmonic generation microscopy: principles and applications to disease diagnosis

6 Campagnola PJ, Dong C-Y. Second harmonic generation microscopy: principles and applications to disease diagnosis. Laser Photon Rev 2011; 5: 13–26. 7 Fejer MM, Magel GA, Jundt DH, Byer RL. Quasi-phase-matched second harmonic generation: tuning and tolerances. IEEE J Quantum Electron 1992; 28: 2631–2654. 8 Trovatello C, Ferrante C, Yang B, Bajo J, Braun B...

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Nonlinear nonlocal metasurfaces

13 Cotrufo M, Carletti L, Overvig A, Alù A. Nonlinear nonlocal metasurfaces. eLight 2026; 6:

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Continuous Wave Second Harmonic Generation Enabled by Quasi-Bound-States in the Continuum on Gallium Phosphide Metasurfaces

14 Anthur AP, Zhang H, Paniagua-Dominguez R, Kalashnikov DA, Ha ST, Maß TWW et al. Continuous Wave Second Harmonic Generation Enabled by Quasi-Bound-States in the Continuum on Gallium Phosphide Metasurfaces. Nano Lett 2020; 20: 8745–8751. 15 Zhang X, He L, Gan X, Huang X, Du Y, Zhai Z et al. Quasi-Bound States in the Continuum Enhanced Second-Harmonic Gen...

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Efficient second harmonic generation by harnessing bound states in the continuum in semi-nonlinear etchless lithium niobate waveguides

22 Li X, Ma J, Liu S, Huang P, Chen B, Wei D et al. Efficient second harmonic generation by harnessing bound states in the continuum in semi-nonlinear etchless lithium niobate waveguides. Light Sci Appl 2022; 11:

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Multiple High-Q Optical Modes in a Polymer-Lithium Niobate Integrated Metasurface

23 Fang C, Kanyang R, Ji Y, Zhang Y, Yang J, Wang D et al. Multiple High-Q Optical Modes in a Polymer-Lithium Niobate Integrated Metasurface. Laser Photon Rev 2024; 18: 2300900. 24 Chakkoria JJ, Aoni RA, Dubey A, Ren G, Nguyen TG, Boes A et al. Efficient Poling- Free Wavelength Conversion in Thin Film Lithium Niobate Harnessing Bound States in the Continu...

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11 Proust J, Bedu F, Gallas B, Ozerov I, Bonod N

doi:doi:10.1515/nanoph-2024-0454. 33 Shoji I, Kondo T, Kitamoto A, Shirane M, Ito R. Absolute scale of second-order nonlinear-optical coefficients. Journal of the Optical Society of America B 1997; 14: 2268–2294. 34 Chen Z, Mazurski N, Engelberg J, Levy U. Tunable Transmissive Metasurface Based on Thin-Film Lithium Niobate. ACS Photonics 2025; 12: 1174–11...

work page doi:10.1515/nanoph-2024-0454 2024

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Optica Publishing Group: Munich, 2025, p eh_5_2

and European Quantum Electronics Conference (EQEC 2025). Optica Publishing Group: Munich, 2025, p eh_5_2. 37 Klopfer E, Delgado HC, Dagli S, Lawrence M, Dionne JA. A thermally controlled high-Q metasurface lens. Appl Phys Lett 2023; 122: 221701. 38 Moretti L, Iodice M, Della Corte FG, Rendina I. Temperature dependence of the thermo-optic coefficient of li...

work page 2025

[9] [9]

Second Harmonic Generation in Lithium Niobate on Insulator

47 Qu L, Wu W, Cai W, Ren M, Xu J. Second Harmonic Generation in Lithium Niobate on Insulator. Laser Photon Rev 2025; 19: 2401928. 48 Goldberg O, Gherabli R, Engelberg J, Nijem J, Mazurski N, Levy U. Silicon Rich Nitride Huygens Metasurfaces in the Visible Regime. Adv Opt Mater 2024; 12: 2301612. 20 Supporting Information Supporting Information is Attache...

work page 2025