add_route_astar finds a path from one port to another that avoids the listed obstacle layers — useful when you don't want to dictate the route shape but the wire has to navigate around existing components (waveguides, bond pads, MMIs, fences, …).

This is optical routing, so we route on a waveguide cross-section and use bend_euler for the bends — sharp corners would scatter the mode and break the loss budget. The bend radius must be ≥ the PDK's minimum; here we use 5 µm for cspdk.si220.cband.

The grid the A* algorithm searches over is set by grid_unit (in dbu). A finer grid finds tighter paths but costs more solve time; coarser is faster but can miss valid routes through narrow gaps.

Imports

import doroutes as dr
import gdsfactory as gf
from cspdk.si220.cband import PDK

PDK.activate()

Single Route on a Test Field

dr.pcells.field1() is a small example layout with in and out named instances and a handful of waveguide stubs scattered between them as obstacles — a stand-in for the kind of crowded floorplan you might be routing through. A* finds a path on the WG (waveguide) layer that doesn't cross any of those obstacles.

c = gf.Component()
ref = c << dr.pcells.field1()
dr.add_route_astar(
    c=c,
    start=ref.cell.insts["in"].ports["o2"],
    stop=ref.cell.insts["out"].ports["o1"],
    straight="straight",
    bend={"component": "bend_euler", "settings": {"radius": 5}},
    layers=["WG"],  # obstacles to avoid
    grid_unit=500,  # A* grid pitch (dbu) — smaller = tighter paths, more solve time
)
dr.util.show_cell(c)

API key for organization 'DoPlayDo' found.

Next steps

• Need to route N parallel waveguides as a single bundle? See A* Bundle Routing.
• Want full control over the route shape instead of an algorithmic search? See Corners Routing and Steps Routing.
• Build whole circuits from a YAML description that calls into A*? See Circuit From Netlist.