Route profiles

A route profile is the cross-section recipe for a waveguide: which layers to stamp, what width each is, where periodic features (gratings, periodic claddings, slot rails, electrical stitching) sit. Once a profile exists, you stop thinking about per-stroke geometry and just point at the profile.

Using a profile

The demo PDK ships several ready-made profiles in pdk.RP. Attach one to a port and every Route from that port adopts it:

"""Route profiles — cross-section recipes for waveguides.

A route profile bundles everything that varies along a route: layers,
strokes, widths, periodic teeth (gratings, tapers, periodic claddings).
Attach one to a port and every Route from that port adopts it.
"""
import lumicron as lm
import lumicron.pdks.elyon_demo.all as pdk


@lm.pcell
def ProfileDemo():
    c = lm.CELL("ProfileDemo")

    # The PDK ships ready-made profiles in `pdk.RP`. Here we route with
    # the silicon-nitride strip — the profile stamps SiLN at the right
    # width and inherits its bend radius.
    c.add(lm.PORT(
        "in", position=(0, 0), direction=0,
        route_profile=pdk.RP.siln_strip,
    ))
    c.add(lm.PORT(
        "out", position=(500, 200), direction=180,
        route_profile=pdk.RP.siln_strip,
    ))

    c.Route(c.ports["in"], radius=15).to(c.ports["out"])
    return c


if __name__ == "__main__":
    ProfileDemo().to_gds("profile_demo.gds")

Three things happen automatically:

1. The route is stamped on the profile’s primary layer (here, SiLN) at the profile’s width.
2. The bend radius defaults to the profile’s radius if you don’t pass radius= on the Route(...) call.
3. Any sibling strokes the profile defines (claddings, slot rails) are emitted as parallel FlexRoutes alongside the primary.

What a profile contains

A profile is built from two kinds of strokes:

• Layer strokes: continuous parallel bands at fixed widths and offsets. Used for the core, claddings, exclusion zones, slot-mode rails.
• Tooth strokes: periodic PCells laid along the route. Used for grating teeth, periodic deep-etch features, periodic electrical contacts, photonic-crystal slabs.

Together they let one profile describe geometry as exotic as “core + cladding + exclusion + grating teeth every 0.32 µm” in a single Route() call.

When to override at the call site

Two override knobs on Route(...):

• profile=... overrides any port-attached profile for this one route.
• radius=... overrides the layout radius. Width changes use the chain’s .width(...) or .style(width=...) methods; width is not a Route constructor argument.

# Use an explicit layout radius compatible with the PDK curvature rule.
chip.Route(a, b, radius=15)

# Pin a different profile for this one route.
chip.Route(a, b, profile=pdk.RP.silc_rib)

For section-level overrides inside a single Route, see .style(profile=...) in the previous chapter.

Auto layer transitions

When port_a.layer != port_b.layer, the router consults a transition registry. If the layer pair has a registered transition PCell (e.g. a PhotonicElevator for SiLC-to-SiLN), the router inserts it automatically and continues on the new layer.

"""Auto layer transitions — cross-layer routes, no manual PCells.

When port_a is on one layer and port_b is on another, the router checks
the registered TransitionRegistry. If a transition PCell exists for the
pair (e.g. `PhotonicElevator` for SiLC ↔ SiLN), the router drops it in
automatically and continues on the new layer.

`transition_offset` controls where along the route the transition sits.
"""
import lumicron as lm
import lumicron.pdks.elyon_demo.all as pdk


@lm.pcell
def LayerTransition():
    c = lm.CELL("LayerTransition")

    # Input on silicon, output on nitride.
    c.add(lm.PORT(
        "in", position=(0, 0), direction=0,
        route_profile=pdk.RP.silc_strip,
    ))
    c.add(lm.PORT(
        "out", position=(600, 0), direction=180,
        route_profile=pdk.RP.siln_strip,
    ))

    # The router consults pdk's default transition registry for the
    # SiLC → SiLN pair and inserts the elevator at offset=300 µm.
    c.Route(c.ports["in"], transition_offset=300).to(c.ports["out"])
    return c


if __name__ == "__main__":
    LayerTransition().to_gds("layer_transition.gds")

transition_offset=300 places the transition PCell 300 µm in from port_a. PDK imports populate the default transition registry, so this works with no extra setup. To override, pass transitions= with a custom TransitionRegistry.

Where profiles come from

Every profile in this guide is built into the elyon_demo PDK. To define your own - including custom strokes, periodic teeth, and slot-mode rails - see the PDK Authoring Guide, which has a dedicated chapter on the @route_profile builder.

For now, treat profiles as a black box: pick one from your PDK’s RP namespace, assign it to ports, and routes will inherit it.