add lumerical from sax

[joamatab]

Summary by Sourcery

Add a utility to export SAX S-parameter models to Lumerical Interconnect DAT files.

New Features:

• Introduce sax_to_lumerical_dat helper to sweep a SAX model over wavelength and write S-parameters in Lumerical DAT format.
• Support optional port renaming and automatic port ordering when generating Lumerical-compatible S-parameter data.

Tests:

• Add a simple main script example that generates a coupler DAT file and verifies it by reading it back with the existing Lumerical reader.

[sourcery-ai]

Reviewer's Guide

Adds a utility to export SAX S-parameter models into Lumerical Interconnect .dat format, including wavelength sweep, optional port remapping, and correct frequency-ordered S-parameter serialization plus a small CLI-style example/verification block.

Sequence diagram for sax_to_lumerical_dat example execution

sequenceDiagram
    actor User
    participant sax_to_lumerical_dat
    participant SAXModel
    participant FileSystem
    participant LumericalReader

    User->>sax_to_lumerical_dat: call sax_to_lumerical_dat(model, filepath, port_map, wavelength_start, wavelength_stop, wavelength_points, model_kwargs)
    activate sax_to_lumerical_dat

    sax_to_lumerical_dat->>sax_to_lumerical_dat: build wl array (linspace)
    sax_to_lumerical_dat->>SAXModel: model(wl, model_kwargs)
    activate SAXModel
    SAXModel-->>sax_to_lumerical_dat: sdict[(port_src, port_dst)] -> complex array
    deactivate SAXModel

    sax_to_lumerical_dat->>sax_to_lumerical_dat: apply port_map to sdict (optional)
    sax_to_lumerical_dat->>sax_to_lumerical_dat: infer port_names if None
    sax_to_lumerical_dat->>sax_to_lumerical_dat: compute frequencies from wl (reversed)

    loop for each src in port_names
        loop for each dst in port_names
            sax_to_lumerical_dat->>sax_to_lumerical_dat: get sdict[(src, dst)] or zeros
            sax_to_lumerical_dat->>sax_to_lumerical_dat: reverse values, compute magnitude and angle
            sax_to_lumerical_dat->>sax_to_lumerical_dat: append DAT header and data lines
        end
    end

    sax_to_lumerical_dat->>FileSystem: write_text(joined lines) -> filepath.dat
    deactivate sax_to_lumerical_dat
    sax_to_lumerical_dat-->>User: return Path(filepath.dat)

    User->>LumericalReader: read_sparameters_file(filepath.dat, numports)
    activate LumericalReader
    LumericalReader->>FileSystem: open and parse DAT file
    FileSystem-->>LumericalReader: raw DAT content
    LumericalReader-->>User: port_names, F, S
    deactivate LumericalReader

Loading

File-Level Changes

Change	Details	Files
Introduce sax_to_lumerical_dat helper to sweep a SAX model over wavelength and write Lumerical Interconnect-compatible DAT S-parameter files.	Define SPEED_OF_LIGHT constant and compute wavelengths and corresponding ascending frequencies from user-specified sweep parameters. Evaluate the provided SAX model over the wavelength grid, optionally apply a port mapping, and infer ordered port names when not explicitly provided, preserving first-seen order from the S-dict keys. Generate full S-parameter blocks for all source/destination port combinations, defaulting missing entries to zero, reverse data to match ascending-frequency ordering, and write frequency/magnitude/phase triplets in Lumerical DAT text format. Write port declarations and S-parameter data lines to the target .dat file path and return it as a pathlib.Path object.	gplugins/lumerical/write_sparameters_lumerical_from_sax.py
Add a simple executable example for manual testing and verification of the written DAT file.	Use sax.models.coupler as an example model and call sax_to_lumerical_dat with a realistic port mapping and coupler parameters. Read the generated .dat file using gplugins.lumerical.read.read_sparameters_file to verify port names, frequency/S-matrix shapes, and printed frequency range.	gplugins/lumerical/write_sparameters_lumerical_from_sax.py

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[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• Consider adding basic validation (e.g., that wavelength_start < wavelength_stop, wavelength_points > 0, and that the arrays returned in sdict all match len(wl)) to fail fast on misconfigured sweeps or inconsistent model outputs rather than silently producing malformed DAT files.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider adding basic validation (e.g., that `wavelength_start < wavelength_stop`, `wavelength_points > 0`, and that the arrays returned in `sdict` all match `len(wl)`) to fail fast on misconfigured sweeps or inconsistent model outputs rather than silently producing malformed DAT files.

## Individual Comments

### Comment 1
<location path="gplugins/lumerical/write_sparameters_lumerical_from_sax.py" line_range="81-82" />
<code_context>
+    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
</code_context>
<issue_to_address>
**issue (bug_risk):** Validate that each S-parameter vector length matches `wavelength_points` to avoid silent shape mismatches.

`values` is implicitly assumed to have length `n_wl`. If the model returns a different-length array (e.g., from wavelength sweep rounding or a model bug), the output will be malformed without any error. Please add a check like `assert values.shape[0] == n_wl` (or at least log a warning) before reversing and writing so these issues fail fast instead of silently corrupting the DAT file.
</issue_to_address>

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[sourcery-ai]

issue (bug_risk): Validate that each S-parameter vector length matches wavelength_points to avoid silent shape mismatches.

values is implicitly assumed to have length n_wl. If the model returns a different-length array (e.g., from wavelength sweep rounding or a model bug), the output will be malformed without any error. Please add a check like assert values.shape[0] == n_wl (or at least log a warning) before reversing and writing so these issues fail fast instead of silently corrupting the DAT file.