feat: add FiberSource for grating coupler simulation#23
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feat: add FiberSource for grating coupler simulation#23
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Add Gaussian beam source support to gsim.meep for simulating fiber-to-chip coupling through grating couplers. New API: - FiberSource model (beam_waist, angle_theta, z_offset, polarization) - FiberSourceConfig with discriminated union on SimConfig.source - CouplingResult with from_csv(), plot(), peak_ce - Notebook example using UBC PDK ebeam_gc_te1550 Runner changes: - build_fiber_source() creates mp.GaussianBeamSource - build_incident_flux_monitor() for normalization - extract_coupling_efficiency() with CE = |alpha|^2 / |incident_flux| - Cell z-range includes dielectrics (not just layer_stack) - Source z references core layer (highest n), not topmost metal - Use abs() on incident flux (downward beam gives negative flux) 179 meep tests passing.
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- Format long pydantic import line - Add docstring to TestFiberSource class (interrogate) - Add isinstance narrowing for ty type checker - Wrap long lines in ROADMAP.md
…nimation helper Support xz cross-section animations for grating coupler sims, render fiber source metadata in 2D plot overlays, and add CouplingResult.show_animation() for inline Jupyter playback.
Draw the Gaussian beam on plot_2d slices: cone with arrow on XZ/YZ side views, dashed circle footprint on XY top-down view.
Replace GaussianBeamSource with the proven gplugins approach: launch EigenModeSource from waveguide port, measure coupling into fiber mode via get_eigenmode_coefficients with oblique kpoint and NO_DIRECTION. Fixes grating coupler CE from -37 dB to physically meaningful values. Also fix animation frame saving to use MEEP's native HDF5 output (mp.output_efield_y) instead of get_array, avoiding MPI vol mismatch crashes and OOM kills on multi-rank cloud runs.
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Summary
FiberSourceAPI for Gaussian beam excitation (grating coupler fiber-to-chip coupling)CouplingResultmodel withfrom_csv(),plot(db=True), andpeak_cepropertymp.GaussianBeamSourcewith incident flux normalization:CE = |alpha|² / |flux|ebeam_gc_te1550Key design decisions
FiberSource.z_offsetreferences the core layer top (highest refractive index), not the topmost metal layer, so the source is always near the waveguideabs()since a downward beam produces negative flux through a +z-normal plane (MEEP convention)SimConfig.sourceis a discriminated union (source_type: "mode" | "fiber") for backward compatibilityTest plan
uv run pytest tests/meep/)z_offset >= margin_z_above