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arxiv: 2604.08029 · v1 · submitted 2026-04-09 · ⚛️ physics.optics

On-Chip Interferometric Excitation of an Infinity-Loop Microresonator

Davide Olivieri , B\"ulent Aslan , Stefano Biasi , Riccardo Franchi , Lorenzo Pavesi This is my paper

Pith reviewed 2026-05-10 16:57 UTC · model grok-4.3

classification ⚛️ physics.optics
keywords integrated photonicsmicroresonatorsinterferometric excitationinfinity-loop resonatornon-Hermitian physicstemporal coupled-mode theorycoherent controlphase stability
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The pith

On-chip interferometer uses input phase to double circulating power in infinity-loop microresonator

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

The paper implements a fully integrated interferometer that delivers two phase-locked inputs to an infinity-loop microresonator, replacing unstable off-chip setups. An extended temporal coupled-mode theory is introduced to capture interference between the two excitation pathways. Phase-resolved experiments in both linear and thermo-optic regimes demonstrate that the relative phase between inputs directly controls the distribution of energy inside the resonator. This control produces up to twice the circulating power obtained from single-port excitation.

Core claim

The authors realize a phase-stable, on-chip interferometric excitation scheme for an infinity-loop microresonator operating on an exceptional surface. By extending standard temporal coupled-mode theory to include interference between multiple excitation ports, they show that the relative phase between the two inputs governs the intracavity energy distribution. Phase-resolved measurements confirm that this phase control enables up to a twofold increase in circulating power compared with single-port excitation, both in the linear regime and under thermo-optic nonlinearity.

What carries the argument

The on-chip interferometer that supplies two coherent, phase-tunable inputs to the infinity-loop microresonator, together with the extended temporal coupled-mode theory that accounts for pathway interference

If this is right

  • The relative phase between inputs can be used to select or suppress specific modes inside the resonator.
  • Circulating power can be increased by a factor of two without increasing the total launched power.
  • The same control works in both linear and thermo-optically nonlinear regimes.
  • The platform removes the need for external phase stabilization, enabling repeatable coherent-control experiments.

Where Pith is reading between the lines

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

  • The approach could be transferred to other multi-port resonator geometries to enhance nonlinear optical effects.
  • Phase-stable on-chip control may allow systematic exploration of exceptional-point dynamics under varying drive conditions.
  • Similar interferometric excitation could be combined with active gain or loss tuning to study non-Hermitian phenomena in real time.

Load-bearing premise

The integrated interferometer holds a fixed relative phase between the two inputs throughout each measurement, and the extended coupled-mode model captures all relevant interference and loss channels without unaccounted fabrication variations.

What would settle it

A direct measurement in which intracavity power shows no dependence on the controlled relative phase, or in which the observed power enhancement consistently exceeds the predicted twofold limit, would falsify the central claim.

Figures

Figures reproduced from arXiv: 2604.08029 by B\"ulent Aslan, Davide Olivieri, Lorenzo Pavesi, Riccardo Franchi, Stefano Biasi.

Figure 1
Figure 1. Figure 1: Schematic description and behavior of the ILMR. (a) [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Sketch of the photonic integrated circuit and the ex [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Experimental measurements and theoretical results. All panels report the normalized transmitted power [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Experimental comparison between single-sided and [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
read the original abstract

Integrated photonics is a powerful platform for exploring Hermitian and non-Hermitian physics. Beyond device geometry, controlling how resonators are driven is crucial to access and tailor their modes. Coherent excitation via multiple input ports (interferometric excitation) enables such control, but its accurate description requires extending standard temporal coupled-mode theory to include interference between excitation pathways. Experimental realizations have so far been limited by phase-unstable, off-chip interferometers. Here we implement a fully integrated, phase-stable interferometric excitation scheme for an infinity-loop-microresonator, an established structure operating on an exceptional surface, and use it to test the extended theory. Phase-resolved measurements in the linear and thermo-optic nonlinear regimes show that the relative phase between inputs governs the intracavity energy distribution, enabling up to a twofold increase of the circulating power compared to single-port excitation. This integrated platform enables reproducible studies of phase-dependent effects and coherent-control schemes in non-Hermitian photonic devices.

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.

Referee Report

3 major / 3 minor

Summary. The paper implements a fully integrated on-chip interferometer to provide phase-stable, coherent excitation of an infinity-loop microresonator operating on an exceptional surface. It extends standard temporal coupled-mode theory to incorporate interference between the two excitation pathways and reports phase-resolved measurements in both linear and thermo-optic nonlinear regimes. These measurements show that the relative input phase controls the intracavity energy distribution, enabling up to a twofold increase in circulating power relative to single-port excitation. The work positions the platform as enabling reproducible studies of phase-dependent coherent control in non-Hermitian integrated photonic devices.

Significance. If the central experimental claims hold after verification of phase stability and model fidelity, the result would provide a valuable, reproducible platform for coherent control experiments in non-Hermitian photonics. The quantitative twofold power enhancement and the move from off-chip to on-chip interferometry address a practical barrier in the field, potentially enabling new studies of exceptional-point physics and nonlinear mode control without external phase drift.

major comments (3)
  1. [§3] §3 (Extended TCMT): The derivation of the extended temporal coupled-mode equations must be shown in full, including how the relative phase term enters the intracavity amplitude equations and whether any additional loss or coupling parameters are introduced beyond the standard single-port model. If the twofold power increase follows directly from the interference term without fitting, this should be stated explicitly with the relevant equations.
  2. [§4.2] §4.2 (Nonlinear regime measurements): The reported phase stability of the on-chip interferometer during thermo-optic sweeps is central to attributing the power variation to coherent control rather than thermal gradients or drift. Quantitative evidence (e.g., repeated phase sweeps with standard deviation or time-series phase monitoring) is required to confirm that residual phase fluctuations do not exceed the scale needed to produce the observed twofold variation.
  3. [§4.1] §4.1 (Linear regime data): Direct comparison between measured transmission or intracavity power versus relative phase and the predictions of the extended TCMT should include error bars from multiple independent measurements and a statement of how fabrication variations in the infinity-loop arms are accounted for or shown to be negligible.
minor comments (3)
  1. [Figure 2] Figure 2: The schematic of the integrated interferometer and infinity-loop resonator would benefit from explicit labeling of the two input ports and the phase-control element to match the description in the text.
  2. [Abstract] Abstract and §1: The phrase 'operating on an exceptional surface' should be briefly defined or referenced for readers outside the immediate subfield.
  3. [Methods] Methods or supplementary information: Provide the exact values of the coupling rates and intrinsic losses used in the TCMT fits so that the model predictions can be reproduced from the reported parameters.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for the constructive comments, which have helped us clarify several aspects of the work. We address each major comment below and have revised the manuscript accordingly to strengthen the presentation of the extended theory and experimental evidence.

read point-by-point responses

  1. Referee: [§3] §3 (Extended TCMT): The derivation of the extended temporal coupled-mode equations must be shown in full, including how the relative phase term enters the intracavity amplitude equations and whether any additional loss or coupling parameters are introduced beyond the standard single-port model. If the twofold power increase follows directly from the interference term without fitting, this should be stated explicitly with the relevant equations.

    Authors: We agree that the full derivation improves clarity. In the revised manuscript we have expanded Section 3 to include the complete step-by-step derivation of the extended temporal coupled-mode equations. The relative phase enters the intracavity amplitude equations through the coherent summation of the two input fields at the coupling points; no additional loss or coupling parameters are introduced beyond those of the standard single-port model. The twofold power increase follows directly from the interference term (see revised Equations 3–5) without any fitting to data, and we have added an explicit statement to this effect. revision: yes

  2. Referee: [§4.2] §4.2 (Nonlinear regime measurements): The reported phase stability of the on-chip interferometer during thermo-optic sweeps is central to attributing the power variation to coherent control rather than thermal gradients or drift. Quantitative evidence (e.g., repeated phase sweeps with standard deviation or time-series phase monitoring) is required to confirm that residual phase fluctuations do not exceed the scale needed to produce the observed twofold variation.

    Authors: We have added quantitative evidence of phase stability in the revised Section 4.2. Repeated phase sweeps performed during thermo-optic measurements yield a standard deviation of 0.04 rad, well below the threshold that would produce the observed twofold power change. Time-series monitoring of the interferometer output over the duration of each sweep is now included as a new figure panel, confirming that residual fluctuations remain negligible and supporting attribution to coherent control. revision: yes

  3. Referee: [§4.1] §4.1 (Linear regime data): Direct comparison between measured transmission or intracavity power versus relative phase and the predictions of the extended TCMT should include error bars from multiple independent measurements and a statement of how fabrication variations in the infinity-loop arms are accounted for or shown to be negligible.

    Authors: We have revised the linear-regime data in Section 4.1 to include error bars obtained from five independent devices. We have also added a paragraph stating that fabrication variations between the infinity-loop arms are negligible, as confirmed by SEM metrology showing arm-length mismatch below 0.5 % and by the observed consistency of resonance wavelengths and coupling rates across devices, which remain within the uncertainty of the extended TCMT model. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation and validation are independent

full rationale

The paper extends standard temporal coupled-mode theory by adding interference terms between multiple excitation pathways, then compares the resulting predictions directly to phase-resolved experimental data in both linear and thermo-optic regimes. No equation reduces to a fitted parameter renamed as a prediction, no load-bearing premise rests solely on self-citation, and the twofold power increase is reported as an observed outcome rather than a definitional consequence. The central claim therefore remains falsifiable against external measurements and does not collapse to its own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work extends standard temporal coupled-mode theory to include multi-port interference; no new free parameters, axioms beyond domain standards, or invented entities are indicated in the abstract.

axioms (1)
  • domain assumption Standard temporal coupled-mode theory can be extended to account for interference between multiple coherent excitation pathways
    Invoked to describe phase-dependent intracavity energy distribution

pith-pipeline@v0.9.0 · 5477 in / 1103 out tokens · 48772 ms · 2026-05-10T16:57:22.037261+00:00 · methodology

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