{"id":"dbd0a4dc-be79-4966-8105-30d953781a7f","arxiv_id":"2505.00678","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"A hybrid SiN-on-LNOI photonic-crystal ring resonator achieves 14.6 GHz mode splitting, Q = 147,000, 0.85 pm/V EO tuning, and a 93.4 MHz/nm splitting-versus-corrugation slope.","lead":"This paper demonstrates a photonic-crystal microring resonator on a hybrid silicon nitride on lithium niobate platform, achieving a 14.6 GHz mode splitting and an intrinsic quality factor of 147,000. The platform avoids etching lithium niobate, which could enable simpler, voltage-tunable frequency converters in integrated photonics.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The two-dip spectrum in Fig. 3(a) is not proven to be a single azimuthal-mode CW/CCW supermode pair; the splitting, slope, and converter claims all depend on this identification.","rationale":"The reader identified the same load-bearing assumption: the two-dip spectrum of Fig. 3(a) being a single-mode CW/CCW supermode pair. Without this identification, the 14.6 GHz splitting bandwidth and the 93.4 MHz/nm slope are not meaningful. The main text and Supplement 1 describe a more complex split-mode spectrum arising from the anisotropic X-cut LN layer, which makes the pair near 1620 nm potentially mode-selective. Equations (1)-(2) provide the theory, but no measured or simulated mode-order verification is presented. Because this concern is already the reader's weakest assumption and the recommendation was CONDITIONAL, the stress-test does not change the verdict. The paper remains a plausible engineering contribution if the mode attribution is confirmed, but the conditional recommendation is appropriate until that is done.","tokens_in":6579,"tokens_out":4278,"duration_ms":47376,"concrete_test":"Repeat the transmission measurement of the A=150 nm device with a polarization controller before the input grating coupler and a polarizer after the output, sweeping over at least two full FSRs. If the two dips near 1620 nm both appear only for TE excitation, retain identical relative depths as polarization is varied, and are separated from neighboring pairs by the FSR of the same mode family, the supermode assignment is supported. If the two dips show different polarization responses, different linewidths, or spacing inconsistent with the FSR pattern, the assignment is falsified. Optionally, compute Eq. (2) for m=2106 with the fabricated geometry and check that the predicted 14.6 GHz splitting and 93.4 MHz/nm slope match within experimental uncertainty.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claims — 14.6 GHz supermode splitting, Qint = 1.47e5, 93.4 MHz/nm control slope, and the first PhCR-based bidirectional frequency-conversion demonstration — all require that the two transmission dips in Fig. 3(a) are the clockwise/counterclockwise supermodes of one fundamental TE azimuthal mode. The paper provides no direct evidence for this assignment. No polarization-resolved measurement, no full free-spectral-range mode mapping, and no eigenmode simulation of the anisotropic X-cut LN structure is shown; the supplement is reported to show a range of split modes due to X-cut LN anisotropy, so the clean pair near 1620 nm may be a mode-selected feature. If the two dips are adjacent azimuthal modes or TE/TM-hybrid modes, then 'mode splitting bandwidth' is not a corrugation-induced supermode splitting and Eq. (1)-(2) do not describe the data. The apparent linear slope in Fig. 5(h) also assumes the same azimuthal index m=2106 across devices, which is stated but not verified.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports a hybrid SiN-on-LNOI microring resonator with a periodic sidewall corrugation (a photonic-crystal resonator, PhCR) that is intended to lift the degeneracy of clockwise and counterclockwise modes into a pair of supermodes. The authors claim a supermode splitting bandwidth of 14.6 GHz with an intrinsic quality factor of 1.47×10^5, a voltage-driven resonance shift of 0.85 pm/V, and a linear dependence of the splitting bandwidth on corrugation amplitude with a slope of 93.4 MHz/nm. They position this as the first demonstration of precise mode-splitting control for bidirectional electro-optic frequency conversion on a hybrid SiN-on-LNOI platform, achieved without etching lithium niobate. The paper presents transmission spectra of a corrugated and an uncorrugated ring, DC electro-optic tuning of the split resonances, and a set of transmission measurements at different corrugation amplitudes to support the linear slope. It also points to Supplement 1 for additional spectra and gradient-design simulations. No direct frequency-conversion experiment (e.g., with an applied RF tone and detection of the converted optical frequency) is reported.","tokens_in":6742,"tokens_out":3804,"duration_ms":34558,"significance":"If the mode-splitting identification is sound, this work offers a practically appealing route to integrated electro-optic frequency conversion: it avoids etching lithium niobate, uses CMOS-compatible SiN patterning, and provides a geometric knob (corrugation amplitude) to set the conversion shift. The comparison between the Q factor of the corrugated ring (1.47×10^5) and an uncorrugated reference ring (1.69×10^5) is a useful and reassuring data point, showing that the corrugation introduces little extra loss. The EO tuning demonstration is also concrete and directly relevant to the frequency-conversion concept. However, the verification of the central physical picture is currently incomplete: the paper does not positively prove that the observed doublet is the CW/CCW supermode pair of a single azimuthal mode, and it does not demonstrate the frequency-conversion process itself. The reported four-point slope without uncertainties further weakens the quantitative control claim. The platform concept is valuable, but the current evidence is not yet sufficient to establish the advertised level of control and the converter demonstration.","major_comments":[{"comment":"The identification of the two transmission dips in Fig. 3(a) as the clockwise/counterclockwise supermodes of a single fundamental TE azimuthal mode is load-bearing for all subsequent claims, but it is not directly supported. The paper does not provide polarization-resolved transmission, a full free-spectral-range mode map, or an eigenmode simulation that includes the X-cut LN anisotropy. The manuscript itself acknowledges in the discussion of Fig. 5 that the broad transmission spectrum of the A = 150 nm device shows a range of split modes due to the anisotropic LN layer (Supplement 1, Fig. S1), which means the clean two-dip reading near 1620 nm may be mode-selective rather than representative of the entire resonator. If the two dips are adjacent azimuthal modes or TE/TM hybrid modes, then the quoted splitting bandwidth and the linear slope do not arise from corrugation-induced CW/CCW coupling, and Eqs. (1)–(2) do not describe the data. I ask the authors to either provide a full FSR trace with the azimuthal order of the split pair identified, a polarization-resolved measurement, or a simulation of the anisotropic structure that reproduces the observed doublet.","section":"Section 3 (Fig. 3) and Section 5 (Fig. 5)"},{"comment":"The linear slope of 93.4 MHz/nm is fitted to only four points (A = 0, 50, 100, and 150 nm, based on the spectra in Figs. 5(d)–(g)) and is shown without error bars. The same azimuthal index m = 2106 is asserted for all devices, but no method for determining m is given. A four-point fit without uncertainties and without verification that the same mode is tracked across devices does not establish the claimed linear relation, especially since the mode assignment is itself the concern. Please include additional corrugation amplitudes, error bars or confidence intervals from repeated measurements, and an explicit procedure for confirming the azimuthal mode index.","section":"Section 5 (Fig. 5)"},{"comment":"The paper claims to demonstrate bidirectional frequency conversion, but no frequency-conversion experiment is shown. The reported experiments are passive transmission spectra (Fig. 3), DC electro-optic tuning of the resonance wavelengths (Fig. 4), and corrugation-dependent splitting (Fig. 5). There is no application of a microwave/RF signal at the splitting frequency and no measurement of output power at the converted frequency. As written, the manuscript demonstrates the components of a converter (split modes, EO tunability, splitting control) but not the conversion process. The claim should be softened to a statement about enabling such conversion, or a direct conversion measurement with efficiency should be added.","section":"Title, Abstract, and Conclusion"}],"minor_comments":[{"comment":"The corrugation amplitudes are labeled inconsistently: the SEM images in Figs. 5(a)–(c) are described as A = 30, 60, and 150 nm, while the spectra in Figs. 5(e)–(g) are described as A = 50, 100, and 150 nm. Please harmonize the notation.","section":"Fig. 5"},{"comment":"The notation in Eq. (2) is not fully defined: the meaning of the integration variable (presumably the angle along the ring), the boundary dS, and the permittivity contrast terms should be stated explicitly for readers who do not have access to ref. [18].","section":"Eq. (2)"},{"comment":"The reported EO tuning rate of 0.85 pm/V is the average shift of the two split resonances. Please report the shift of each resonance separately and indicate whether the response is linear over the full voltage range; this is relevant for the later claim of controllable frequency-conversion operation.","section":"Section 4 (Fig. 4)"},{"comment":"The phrase 'photonic-crystal resonator' is used for a sidewall-corrugated ring, which is a specific subclass; a brief comment on how this relates to conventional 2D photonic-crystal cavities would improve clarity for a general optics readership.","section":"General"}],"recommendation":"major_revision","confidential_remarks":"The central concern is that the claimed supermode identification is not verified despite being load-bearing, and the supplement (referenced for Fig. S1–S3) is not included with the manuscript for review. The authors' own text admits a range of split modes due to X-cut LN anisotropy, which makes the clean two-dip reading near 1620 nm appear mode-selective. In addition, the term 'demonstration' is used for a frequency converter without showing any conversion experiment. These issues are fixable with additional measurements or careful rewording, but they are not merely cosmetic. The relationship to the authors' prior work (ref. [18]) should be clarified so the novelty of the present letter over the earlier conference paper is explicit."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The useful thing here is the platform: a photonic-crystal ring patterned in SiN on top of an X-cut LNOI substrate, without etching the LN. That is worth reporting. The device shows a decent Q of 1.47e5, a large split of 14.6 GHz, and a voltage tuning rate of 0.85 pm/V. The corrugation-versus-splitting slope of 93.4 MHz/nm is consistent with what was already known from Si and SiN rings, so the concept is not new; the new part is the hybrid material platform and the first demonstration that you can electro-optically tune the split modes without touching the LN.\n\nThe soft spots are real, and they mostly reduce to one load-bearing assumption. The two dips in Fig. 3(a) are read as the CW/CCW supermodes of a single azimuthal TE mode. There is no polarization-resolved measurement, no full FSR mode map, and no eigenmode simulation of the anisotropic X-cut stack. The paper itself admits in the text that the broader spectrum shows a range of split modes due to the X-cut LN anisotropy, which makes the clean pair near 1620 nm look mode-selective rather than typical. If those two dips are actually adjacent azimuthal modes or TE/TM hybrids, then the \"supermode splitting bandwidth\" and the Eq. (1)-(2) fit have little meaning. The stress-test note is right, and the burden is on the authors to show the identification.\n\nAlso, the slope is fitted to four points with no error bars, and the claim that all resonances share m = 2106 is asserted, not verified. The frequency-converter language is stronger than the evidence: the paper shows static transmission and DC tuning, not microwave-driven conversion. The supplement is said to contain a gradient design and a near-unity efficiency calculation, but that material is not visible to this review and should be checked.\n\nThat said, the paper is honest in its own way: it flags the anisotropy issue, it provides the no-corrugation control, and it does not hide the complexity. The engineering is plausible, and the Q is well measured. This is not a desk-reject; it needs a serious referee who can push on the mode identification and demand either a conversion measurement or a rewritten abstract.\n\nThe reader's conditional verdict and the stress-test concern both land. Send it to peer review, but ask for evidence—raw spectra, polarization checks, error bars—before the claims about bidirectional frequency conversion are accepted.","headline":"A plausible engineering first for PhCRs on SiN-on-LNOI, but the central mode-splitting claim rests on an unresolved mode identification and the paper overstates its frequency-conversion readiness.","tokens_in":7340,"tokens_out":1470,"would_cite":false,"duration_ms":17395,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"A periodic corrugation on a silicon-nitride microring over lithium niobate creates a 14.6 GHz split between two optical supermodes, tunable by voltage at 0.85 pm/V.","keywords":["photonic crystal resonator","microring resonator","lithium niobate","silicon nitride","electro-optic effect","mode splitting","frequency conversion","integrated photonics"],"falsifier":"Drive the fabricated $A = 150$ nm PhCR with an over-coupled waveguide, inject light at one split resonance, apply a microwave tone at the 14.6 GHz splitting frequency, and look for converted light at the other split resonance. If no bidirectional sideband appears under the matching conditions the paper cites from its reference [16], or if the two dips do not remain a single constant-separation pair across the full spectrum, then the mode-splitting claim is not sufficient for the intended frequency converter.","tokens_in":6351,"feed_emoji":"🔁","tokens_out":8631,"duration_ms":80870,"temperature":0.7,"pith_summary":"This paper proposes a single, corrugated microring as the working element of a microwave-assisted optical frequency converter. It claims that a periodic ripple on the inner edge of a silicon-nitride ring sitting on lithium niobate splits each resonance into two supermodes whose frequency separation is set by the ripple depth, and that an applied voltage shifts the pair together through the lithium-niobate electro-optic effect. The measured device shows a 14.6 GHz splitting with an intrinsic quality factor of 1.47e5, a voltage tuning rate of 0.85 pm/V, and a splitting-versus-corrugation slope of 93.4 MHz/nm, all achieved without etching the lithium niobate. If the claims hold, this is a simpler, CMOS-compatible route to bidirectional frequency conversion than paired coupled resonators, because the corrugation replaces the mode-matching and gap-control needed in a two-resonator converter.","feed_headline":"Corrugated microring splits light modes by 14.6 GHz","feed_subtitle":"Voltage-tunable ring on lithium niobate enables precise bidirectional frequency conversion without etching the LN.","key_machinery":"The central object is the photonic-crystal resonator (PhCR): a microring whose radius is modulated as $r = r_0 + A_n \\cos(n\\phi)$, where $n$ is the number of corrugation periods. This ripple couples the otherwise degenerate clockwise and counterclockwise modes of the ring, splitting them into two supermodes separated by $\\beta_m = k\\,\\omega_m A_n$, with $k$ an overlap integral over the corrugation boundary. That linear dependence is what lets the device designer choose the conversion frequency by picking $A_n$. The active mechanism is the X-cut lithium-niobate layer underneath the unetched silicon nitride: electrodes spaced along the crystal $c$-axis use the largest electro-optic coefficient ($r_{33} = 30$ pm/V) to shift both supermodes together at 0.85 pm/V while leaving $\\beta_m$ essentially unchanged.","core_discovery":"The central discovery is that the hybrid silicon-nitride-on-lithium-niobate platform can support a high-quality photonic-crystal resonator whose mode splitting is both large and precisely controlled by geometry. The authors report the first PhCR on this platform that lifts the degeneracy of clockwise and counterclockwise modes to form a pair of supermodes, demonstrating a splitting bandwidth of 14.6 GHz while keeping the intrinsic quality factor at 1.47e5, close to the 1.69e5 of an unperturbed ring on the same chip. They further show that the split resonances shift together under an applied DC voltage at 0.85 pm/V, giving voltage control of the converter operating frequency, and that the splitting grows linearly with corrugation amplitude at 93.4 MHz/nm so the intended frequency shift can be designed in advance. The platform avoids etching lithium niobate altogether, patterning only the deposited silicon-nitride layer, which sidesteps the poor sidewall angles of etched LNOI waveguides.","pith_inferences":["If the linear scaling in $\\beta_m = k\\,\\omega_m A_n$ holds beyond $A = 150$ nm, narrower waveguide widths or deeper corrugations should push the splitting well past 14.6 GHz; the paper hints at this route but does not measure it.","Because the X-cut lithium niobate's anisotropy produces a range of split modes at large $A$, a practical broadband converter will likely need the gradient-compensated PhCR design described in the supplement, not the plain periodic device measured in the main text.","The same corrugation-on-silicon-nitride recipe could be transferred to other electro-optic films beneath the silicon nitride, such as thin-film aluminum nitride or barium titanate, to trade the 0.85 pm/V tuning rate for different material properties; this is an extension the paper does not pursue.","A direct microwave-driven conversion experiment at $\\beta_m$ would be the decisive test of the bidirectional frequency-converter claim, since the reported measurements demonstrate the split modes and their voltage tuning but stop short of showing converted output light."],"forward_implications":["A designer can set the converter frequency shift in advance by choosing the corrugation amplitude, using the measured 93.4 MHz/nm slope.","Voltage tuning at 0.85 pm/V lets the same device be re-centred onto different input wavelengths without changing the ring geometry.","Because only silicon nitride is etched, the fabrication stays CMOS-compatible and avoids the sloped-sidewall loss of etched lithium-niobate waveguides.","The splitting of 14.6 GHz with an intrinsic quality factor near 1.47e5 is large enough for practical bidirectional frequency conversion, and the near-unity efficiency condition identified for coupled-resonator converters transfers to a single PhCR."],"supporting_citations":[{"why":"Supplies the coupled-resonator frequency-converter architecture and the over-coupling, zero-detuning, matched-microwave-power conditions that the single PhCR aims to reproduce.","marker":"[16]"},{"why":"Gives the perturbation formula $\\beta_m = k\\,\\omega_m A_n$ and the overlap integral $k$ that predicts linear splitting versus corrugation amplitude.","marker":"[17]"},{"why":"Earlier PhCR mode-splitting demonstration by the same group; anchors the corrugation-to-supermode mechanism that this paper moves to the silicon-nitride-on-lithium-niobate platform.","marker":"[18]"},{"why":"Documents the sloped sidewalls of etched LNOI waveguides, motivating the hybrid approach where lithium niobate is left unetched.","marker":"[19,20]"},{"why":"Reported linear splitting-versus-amplitude scaling on silicon-nitride PhCRs, providing the baseline for the 93.4 MHz/nm slope measured here.","marker":"[21]"}],"fun_headline_variants":["Voltage-tuned ring splits modes by 14.6 GHz","Precise 14.6 GHz mode split in hybrid photonic crystal ring","Hybrid nitride-niobate ring: record 14.6 GHz split","Voltage-controlled frequency shift in high-Q hybrid ring","First photonic crystal ring on hybrid LNOI: 14.6 GHz split"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing assumption is that the two dips seen near 1620 nm are the two split directions of one and the same ring mode; if they are instead two unrelated modes or a polarization artefact, then the reported splitting does not describe a usable supermode pair.","fun_headline_variants_meta":{"raw":{"variants":["Voltage-tuned ring splits modes by 14.6 GHz","Precise 14.6 GHz mode split in hybrid photonic crystal ring","Hybrid nitride-niobate ring: record 14.6 GHz split","Voltage-controlled frequency shift in high-Q hybrid ring","First photonic crystal ring on hybrid LNOI: 14.6 GHz split"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001271,"raw_usage":{"total_tokens":5192,"prompt_tokens":931,"completion_tokens":4261,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":547,"completion_tokens_details":{"reasoning_tokens":4163}},"tokens_in":547,"tokens_out":4261,"duration_ms":27800,"temperature":1.0,"reasoning_tokens":4163,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-16T04:36:04.161914+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Drive the fabricated $A = 150$ nm PhCR with an over-coupled waveguide, inject light at one split resonance, apply a microwave tone at the 14.6 GHz splitting frequency, and look for converted light at the other split resonance. If no bidirectional sideband appears under the matching conditions the paper cites from its reference [16], or if the two dips do not remain a single constant-separation pair across the full spectrum, then the mode-splitting claim is not sufficient for the intended frequency converter.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the coupled-resonator frequency-converter architecture and the over-coupling, zero-detuning, matched-microwave-power conditions that the single PhCR aims to reproduce."},{"cited_title":"Lu, Silicon and Silicon Carbide Photonics and the Applications (University of Rochester, 2016)","cited_arxiv_id":null,"evidence_quote":"Gives the perturbation formula $\\beta_m = k\\,\\omega_m A_n$ and the overlap integral $k$ that predicts linear splitting versus corrugation amplitude."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Earlier PhCR mode-splitting demonstration by the same group; anchors the corrugation-to-supermode mechanism that this paper moves to the silicon-nitride-on-lithium-niobate platform."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reported linear splitting-versus-amplitude scaling on silicon-nitride PhCRs, providing the baseline for the 93.4 MHz/nm slope measured here."}],"review_version":1}