{
  "title": "Air-cladded feedthrough coupling (FDTD convergence)",
  "device": "air-cladded Si nanobeam (Quan\u2013Lon\u010dar v2 campaign)",
  "updated_at": "2026-07-27T17:34:09.887060+00:00",
  "definition": "eta_x = (P_+x + P_-x) / sum_faces P  (closed-surface free-decay power fraction)",
  "converged": true,
  "initial": {
    "eta_x": 0.8220629653986832,
    "eta_x_spectral_pole": 0.82180804671482,
    "Q_this_run": 13125.227033696221,
    "wavelength_nm": 1503.674992956754,
    "te0_valid": false,
    "te0_neff": 2.58731480679194,
    "runtime_key": "T96",
    "window_etas": {
      "last_50pct": 0.8220707419244612,
      "last_40pct": 0.8220609944784374,
      "last_30pct": 0.822052256878272,
      "last_20pct": 0.82205129272186,
      "last_10pct": 0.8220629609171829,
      "mid_50_75": 0.822071537209508,
      "last_25pct": 0.8220629653986832,
      "early_25_50": 0.8220487965603379
    },
    "runtime_spread_pp": 0.0009594286368486138,
    "by_runtime": {
      "T48": {
        "eta_x_last25": 0.8220533711123147,
        "Q": 13125.671652081568,
        "wl_nm": 1503.6749919991294
      },
      "T96": {
        "eta_x_last25": 0.8220629653986832,
        "Q": 13125.227033696221,
        "wl_nm": 1503.674992956754
      }
    }
  },
  "final": {
    "eta_x": 0.5957042700637071,
    "eta_x_spectral_pole": 0.5964850873305084,
    "Q_this_run": 426541.63038577675,
    "wavelength_nm": 1492.5234588748901,
    "te0_valid": false,
    "te0_neff": 2.597027644467322,
    "runtime_key": "T128",
    "window_etas": {
      "last_50pct": 0.5957171155804968,
      "last_40pct": 0.5957098070126496,
      "last_30pct": 0.5957083724727673,
      "last_20pct": 0.5957089860522924,
      "last_10pct": 0.5956820894454836,
      "mid_50_75": 0.5957288090818027,
      "last_25pct": 0.5957042700637071,
      "early_25_50": 0.5957243804749829
    },
    "runtime_spread_pp": 0.004476562055955036,
    "by_runtime": {
      "T48": {
        "eta_x_last25": 0.5957490356842666,
        "Q": 426806.39546037116,
        "wl_nm": 1492.5234594038352
      },
      "T128": {
        "eta_x_last25": 0.5957042700637071,
        "Q": 426541.63038577675,
        "wl_nm": 1492.5234588748901
      },
      "T96": {
        "eta_x_last25": 0.5957232969836275,
        "Q": 426381.5066710446,
        "wl_nm": 1492.523458394152
      }
    }
  },
  "te0_mode_monitor": {
    "trustworthy": false,
    "reason": "ModeMonitor TE0 fails validation (incoming/outgoing ~0.26\u20130.33; seed P_net/P_x > 1). Longer runtime and pole tuning do not fix it."
  },
  "convergence": {
    "runtimes_ps": [
      48,
      96,
      128
    ],
    "mesh_steps_per_wvl": 12,
    "initial_eta_x_runtime_spread_pp": 0.0009594286368486138,
    "final_eta_x_runtime_spread_pp": 0.004476562055955036,
    "window_stability": "flat to <0.01 pp across late windows",
    "spectral_vs_time": "agree to ~0.1 pp at ResonanceFinder pole"
  },
  "cost_flexcredits_total": 0.6733056358994289,
  "cost_flexcredits_prior_48ps": 0.1552273495773751,
  "cost_flexcredits_convergence_suite": 0.5180782863220538,
  "reports": {
    "markdown": "coupling_fdtd/CONVERGENCE_REPORT.md",
    "full_json": "coupling_fdtd/convergence_results.json",
    "summary_json": "coupling_fdtd/convergence_summary.json"
  },
  "notes": [
    "FDTD eta_x is NOT the same quantity as analytical guided_external_decay_fraction (~99%).",
    "Optimization raised Q while lowering end-face power fraction (82.2% \u2192 59.6%).",
    "Not shown on the team presentation slides (held back by request)."
  ]
}