# 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 silicon_photonics technology and IPKISS

import technologies.silicon_photonics
from ipkiss3 import all as i3
from picazzo3.wg.spirals import FixedLengthSpiral
from picazzo3.traces.rib_wg.trace import RibWaveguideTemplate
from picazzo3.traces.wire_wg.trace import WireWaveguideTemplate


## Defining the Spline Rounding Algorithm¶

In order to create a custom rounding algorithm we need to inherit from spline import ShapeRoundAdiabaticSpline and override the defaults of the bend radius and the adiabatic angles.

class RA(i3.ShapeRoundAdiabaticSpline):

return 5.0

return (45.0, 45.0)


## 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 = WireWaveguideTemplate()
wg_tmpl.Layout(
core_width=0.450,
core_process=i3.TECH.PROCESS.WG
)

wg_tmpl_wide = RibWaveguideTemplate()
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)

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("The length of the spiral is {} um".format(spiral_lo.trace_length()))


Out:

The length of the spiral is 4000.0 um