Spiral with Tapered Waveguides and Spline Bends

If you want to reduce losses you can use spline bends and broader waveguide for the straight sections.

# Importing si_fab's technology and IPKISS

from si_fab import all as pdk
from ipkiss3 import all as i3
from picazzo3.wg.spirals import FixedLengthSpiral

Defining the Spline Rounding Algorithm

We use a rounding algorithm i3.SplineRoundingAlgorithm that will result in Bezier bends

RA = i3.SplineRoundingAlgorithm(adiabatic_angles=(45, 45))

Defining the trace template

We take a basic template from the picazzo and derive a TaperedWaveguideTemplate version of it, which does two things:

flaring out to a different width, with a specified taper length and minimum lengths for the narrow and wider waveguides.
creating bends using a given rounding algorithm

wg_tmpl = pdk.SiWireWaveguideTemplate()
wg_tmpl.Layout(
    core_width=0.450,
    cladding_width=2 * 2.0 + 0.45,
)

wg_tmpl_wide = pdk.SiRibWaveguideTemplate()
wg_tmpl_wide.Layout(core_width=0.85)

tapered_wg_tmpl = i3.TaperedWaveguideTemplate(
    name="tapered_wg_tmpl",
    trace_template=wg_tmpl,
    straight_trace_template=wg_tmpl_wide,
)

tapered_wg_tmpl.Layout(
    bend_radius=5.0,  # shortest radius of curvature in the bend
    rounding_algorithm=RA,  # use splines instead of circular arcs: smoother transition
    taper_length=10.0,  # length of the taper between the regular waveguide and the expanded waveguide
    # min_expanded_length=1.0, # minimum length of the expanded section. If shorter, don't expand
)

Defining a spiral

Now we build the spiral using the TaperedWaveguideTemplate. By using this specific trace template, the resulting generated waveguide will be of the i3.TaperedWaveguide type.

spiral = FixedLengthSpiral(
    total_length=4000.0,
    n_o_loops=4,
    trace_template=tapered_wg_tmpl,
)
spiral_lo = spiral.Layout(
    incoupling_length=10.0,
    spacing=6,
    stub_direction="V",  # either H or V
    growth_direction="V",
)

spiral_lo.visualize(annotate=True)
print(f"The length of the spiral is {spiral_lo.trace_length()} um")

The length of the spiral is 4000.0000000000005 um