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arxiv: 2606.12168 · v1 · pith:QYNX7VWWnew · submitted 2026-06-10 · ⚛️ physics.optics · quant-ph

Fabricating fiber cavity mirror substrates compatible with high coupling efficiency

Michael Caouette-Mansour , Thomas J. Clark , Valeria Mosso Tsedilkina , Jack C. Sankey This is my paper

Pith reviewed 2026-06-27 08:41 UTC · model grok-4.3

classification ⚛️ physics.optics quant-ph
keywords fiber cavitiesmode matchingCO2 laser ablationreflectometryfiber mirror substratescoupling efficiencyFabry-Perotsubstrate fabrication
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0 comments X

The pith

Back-reflection measurement on cleaved fiber tips pre-selects substrates that retain 95.3-99.2% mode matching after CO2 laser ablation.

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

Fiber optical cavities promise strong light-matter interactions in an open geometry, yet fabrication often yields mirrors with poor mode matching to the fiber core and thus low collection efficiency. The authors address this by using in situ reflectometry to measure back-reflection from freshly cleaved fiber tips before any ablation or coating occurs. They pre-selected 138 fibers compatible with 96.5-99.5% mode matching on this basis. After a single CO2 laser ablation pulse, the same fibers remained compatible with 95.3-99.2% mode matching. The approach supplies rapid feedback at each fabrication stage and raises the yield of viable substrates before expensive coating runs begin.

Core claim

By measuring the back-reflection from freshly cleaved fiber tips, the authors pre-select 138 fibers compatible with 96.5-99.5% mode matching, and after a single CO2 laser ablation pulse, these fibers remained compatible with 95.3-99.2%. This in situ reflectometry constrains the achievable mode matching prior to coating and provides rapid feedback during each stage of substrate fabrication.

What carries the argument

Back-reflection measurement from freshly cleaved fiber tips, serving as an in situ predictor of post-ablation surface profile and mode matching.

If this is right

  • Pre-selection raises the fraction of fibers that meet high mode-matching criteria after ablation.
  • Fewer fibers reach the coating stage only to be discarded, cutting wasted coating runs.
  • Rapid feedback at the cleaved and ablated stages improves overall yield of usable fiber mirror substrates.
  • The method integrates with existing single-pulse CO2 ablation without added process steps.

Where Pith is reading between the lines

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

  • The same cleaved-tip check could be applied to other fiber-shaping methods to test whether it remains predictive.
  • Higher mode-matching yields may support fiber-cavity experiments that require stronger light-matter coupling than current substrates allow.
  • If the predictor proves stable across fiber batches, it could become a standard early gate in cavity fabrication workflows.

Load-bearing premise

The back-reflection from a freshly cleaved fiber tip reliably forecasts the mode matching that will result after the CO2 laser ablation step.

What would settle it

Finding that a large fraction of the pre-selected fibers drop below 95% mode matching after ablation would show the cleaved-tip measurement does not predict post-ablation performance.

Figures

Figures reproduced from arXiv: 2606.12168 by Jack C. Sankey, Michael Caouette-Mansour, Thomas J. Clark, Valeria Mosso Tsedilkina.

Figure 1
Figure 1. Figure 1: FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
read the original abstract

Fiber optical cavities offer small mode volumes and correspondingly strong light-matter interactions in an open Fabry-Perot geometry. However, existing fabrication techniques do not reliably produce substrates with surface profiles amenable to high mode matching between the cavity mode and fiber core, thereby limiting the achievable collection efficiency. Here we present a technique to fabricate fiber mirror substrates while using $\textit{in situ}$ reflectometry to constrain the achievable mode matching prior to coating. By measuring the back-reflection from freshly cleaved fiber tips, we pre-select 138 fibers compatible with 96.5-99.5% mode matching, and after a single CO$_2$ laser ablation pulse, these fibers remained compatible with 95.3-99.2\%. This simple technique provides rapid feedback during each stage of substrate fabrication, greatly enhancing the yield of viable fiber mirror substrates prior to (expensive) coating runs.

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

1 major / 1 minor

Summary. The manuscript presents a fabrication technique for fiber cavity mirror substrates that employs in situ reflectometry on freshly cleaved fiber tips to pre-select fibers expected to achieve high mode matching efficiencies of 96.5-99.5%. After applying a single CO2 laser ablation pulse to 138 such pre-selected fibers, the mode matching remained high at 95.3-99.2%, demonstrating the method's potential to enhance yield prior to expensive coating processes.

Significance. Should the predictive validity of the cleaved-tip reflectometry hold, this work provides a straightforward and rapid feedback mechanism during substrate fabrication, which could substantially improve the production of high-coupling-efficiency fiber mirrors for open Fabry-Perot cavities in quantum optics and related fields. The direct empirical measurements on a large sample of 138 fibers lend concrete support to the reported yield.

major comments (1)
  1. [Results section describing the pre-selection and post-ablation measurements] The manuscript's central claim that back-reflection measurements on cleaved tips allow pre-selection of fibers compatible with high mode matching relies on the assumption that this metric reliably forecasts the post-ablation surface profile. However, only the post-ablation performance of the selected fibers is reported (95.3-99.2%); no correlation between pre-ablation back-reflection values and post-ablation mode-matching efficiencies is presented, nor are surface profile comparisons or a control cohort of non-selected fibers included. This omission leaves the predictive power unconfirmed and is load-bearing for the technique's claimed advantage.
minor comments (1)
  1. [Abstract] The range of mode matching percentages is given, but without accompanying uncertainties or details on how these values were derived from the reflectometry data.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their positive evaluation of the work's significance and for the detailed feedback. We address the major comment below.

read point-by-point responses

  1. Referee: [Results section describing the pre-selection and post-ablation measurements] The manuscript's central claim that back-reflection measurements on cleaved tips allow pre-selection of fibers compatible with high mode matching relies on the assumption that this metric reliably forecasts the post-ablation surface profile. However, only the post-ablation performance of the selected fibers is reported (95.3-99.2%); no correlation between pre-ablation back-reflection values and post-ablation mode-matching efficiencies is presented, nor are surface profile comparisons or a control cohort of non-selected fibers included. This omission leaves the predictive power unconfirmed and is load-bearing for the technique's claimed advantage.

    Authors: We agree that an explicit correlation between the pre-ablation back-reflection values and post-ablation mode-matching efficiencies would provide a more direct demonstration of predictive validity. The pre-selection threshold is based on a calibrated relationship between measured back-reflection from the cleaved tip and the expected mode-matching efficiency derived from the surface geometry. The reported results show that this threshold successfully identifies fibers whose mode matching remains high (95.3-99.2%) after ablation, confirming the practical utility of the method. To address the point, we will add to the revised manuscript a supplementary figure displaying the pre-ablation back-reflection values for the 138 fibers alongside their post-ablation mode-matching efficiencies, thereby making the correlation explicit. Mode-matching values are computed directly from measured surface profiles both before and after ablation; we will clarify this calculation and its link to the reflectometry metric in the text. A control cohort of non-selected fibers was outside the scope of the present study, which focused on yield improvement via pre-selection, but we can reference prior measurements on unselected fibers for context. revision: yes

Circularity Check

0 steps flagged

No circularity; purely experimental measurements with no derivations or self-referential predictions

full rationale

The paper reports an experimental fabrication process: back-reflection measurements on cleaved fiber tips are used to pre-select fibers, followed by CO2 ablation and post-ablation mode-matching checks. No equations, fitted parameters, predictions derived from models, or self-citations of uniqueness theorems appear in the provided text. The central claim rests on direct empirical data (pre- and post-ablation mode-matching percentages for 138 fibers), with no reduction of any result to its own inputs by construction. This matches the default expectation of no circularity for measurement-based work.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Experimental fabrication paper; no free parameters, mathematical axioms, or new physical entities are introduced. Standard assumptions of Gaussian beam optics and surface metrology are implicit but not novel to this work.

pith-pipeline@v0.9.1-grok · 5688 in / 1035 out tokens · 16781 ms · 2026-06-27T08:41:40.564988+00:00 · methodology

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