From a6a2925ca8417ceafc3dfac946102394ece0d2f5 Mon Sep 17 00:00:00 2001
From: Joaquin Matres <4514346+joamatab@users.noreply.github.com>
Date: Thu, 26 Feb 2026 23:28:20 -0500
Subject: [PATCH] add lumerical from sax

---
 .../write_sparameters_lumerical_from_sax.py   | 122 ++++++++++++++++++
 1 file changed, 122 insertions(+)
 create mode 100644 gplugins/lumerical/write_sparameters_lumerical_from_sax.py

diff --git a/gplugins/lumerical/write_sparameters_lumerical_from_sax.py b/gplugins/lumerical/write_sparameters_lumerical_from_sax.py
new file mode 100644
index 00000000..c1fbd5ba
--- /dev/null
+++ b/gplugins/lumerical/write_sparameters_lumerical_from_sax.py
@@ -0,0 +1,122 @@
+"""Convert SAX S-parameter models to Lumerical Interconnect DAT format."""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any, Callable
+
+import numpy as np
+
+SPEED_OF_LIGHT = 299792458.0  # m/s
+
+
+def sax_to_lumerical_dat(
+    model: Callable[..., dict[tuple[str, str], Any]],
+    filepath: str | Path,
+    port_names: list[str] | None = None,
+    port_map: dict[str, str] | None = None,
+    wavelength_start: float = 1.2,
+    wavelength_stop: float = 1.6,
+    wavelength_points: int = 500,
+    **model_kwargs,
+) -> Path:
+    """Write a SAX model's S-parameters in Lumerical Interconnect DAT format.
+
+    Evaluates a SAX model over a wavelength sweep and writes the resulting
+    S-parameters to a .dat file readable by Lumerical Interconnect.
+
+    Args:
+        model: SAX model callable that accepts ``wl`` and returns an SDict.
+        filepath: output .dat file path.
+        port_names: ordered port names for the DAT file header.
+            If None, inferred from the model output keys.
+        port_map: mapping from SAX port names to Lumerical port names,
+            e.g. ``{"o1": "W0", "o2": "N0", "o3": "E0", "o4": "N1"}``.
+            Applied after evaluating the model.
+        wavelength_start: start wavelength in micrometers.
+        wavelength_stop: stop wavelength in micrometers.
+        wavelength_points: number of wavelength points.
+        **model_kwargs: extra keyword arguments forwarded to the SAX model.
+
+    Returns:
+        Path to the written .dat file.
+    """
+    filepath = Path(filepath).with_suffix(".dat")
+
+    wl = np.linspace(wavelength_start, wavelength_stop, wavelength_points)
+    sdict = model(wl=wl, **model_kwargs)
+
+    # Apply port renaming
+    if port_map:
+        sdict = {
+            (port_map.get(p1, p1), port_map.get(p2, p2)): v
+            for (p1, p2), v in sdict.items()
+        }
+
+    # Determine unique port names preserving order of first appearance
+    if port_names is None:
+        seen: set[str] = set()
+        port_names = []
+        for p1, p2 in sdict:
+            for p in (p1, p2):
+                if p not in seen:
+                    seen.add(p)
+                    port_names.append(p)
+
+    n_wl = len(wl)
+
+    # wavelength (um) -> frequency (Hz), reversed so frequency is ascending
+    frequencies = SPEED_OF_LIGHT / (wl[::-1] * 1e-6)
+
+    lines: list[str] = []
+
+    # Port declarations
+    for name in port_names:
+        lines.append(f'["{name}",""]')
+
+    # S-parameter blocks: iterate source then destination
+    for src in port_names:
+        for dst in port_names:
+            key = (src, dst)
+            if key in sdict:
+                values = np.asarray(sdict[key], dtype=complex)
+            else:
+                # Missing entries (e.g. reflections) default to zero
+                values = np.zeros(n_wl, dtype=complex)
+            # Reverse to match ascending-frequency order
+            values = values[::-1]
+            magnitudes = np.abs(values)
+            angles = np.angle(values)
+
+            lines.append(f'("{src}","mode 1",1,"{dst}",1,"transmission")')
+            lines.append(f"({wavelength_points}, 3)")
+            for f, m, a in zip(frequencies, magnitudes, angles):
+                lines.append(f"{f:.16e} {m:.16e} {a:.16e}")
+
+    filepath.write_text("\n".join(lines) + "\n")
+    return filepath
+
+
+if __name__ == "__main__":
+    from sax.models import coupler
+
+    out = sax_to_lumerical_dat(
+        model=coupler,
+        filepath="coupler_test.dat",
+        port_map={"o1": "W0", "o2": "N0", "o3": "E0", "o4": "N1"},
+        wavelength_start=1.2,
+        wavelength_stop=1.6,
+        wavelength_points=500,
+        length=15.7,
+        coupling0=0.0,
+        dn=0.02,
+    )
+    print(f"Wrote {out}")
+
+    # Verify by reading back
+    from gplugins.lumerical.read import read_sparameters_file
+
+    port_names, F, S = read_sparameters_file(filepath=str(out), numports=4)
+    print(f"Ports: {port_names}")
+    print(f"Frequencies: {F.shape}, S-matrix: {S.shape}")
+    print(f"Frequency range: {F[0]:.6e} - {F[-1]:.6e} Hz")