from __future__ import annotations
from functools import partial
import numpy as np
import gdsfactory as gf
from gdsfactory.component import Component
from gdsfactory.components.rectangle import rectangle
from gdsfactory.components.taper import taper as taper_function
from gdsfactory.typings import ComponentSpec, CrossSectionSpec, LayerSpec
# The default values are loosely based on Taillaert et al,
# "A Compact Two-Dimensional Grating Coupler Used
# as a Polarization Splitter", IEEE Phot. Techn. Lett. 15(9), 2003
rectangle_unit_cell = partial(
rectangle, size=(0.3, 0.3), layer="SLAB150", centered=True, port_type=None
)
[docs]
@gf.cell
def grating_coupler_dual_pol(
unit_cell: ComponentSpec = rectangle_unit_cell,
period_x: float = 0.58,
period_y: float = 0.58,
x_span: float = 11,
y_span: float = 11,
length_taper: float = 150.0,
width_taper: float = 10.0,
polarization: str = "te",
wavelength: float = 1.55,
taper: ComponentSpec = taper_function,
base_layer: LayerSpec | None = "WG",
cross_section: CrossSectionSpec = "strip",
**kwargs,
) -> Component:
r"""2 dimensional, dual polarization grating coupler.
Based on a photonic crystal with a unit cell that is usually an ellipse,
a rectangle or a circle.
Args:
unit_cell: component describing the unit cell of the photonic crystal.
period_x: spacing between unit cells in the x direction [um].
period_y: spacing between unit cells in the y direction [um].
x_span: full x span of the photonic crystal.
y_span: full y span of the photonic crystal.
length_taper: taper length [um].
width_taper: width of the taper at the grating coupler side [um].
polarization: polarization of the grating coupler.
wavelength: operation wavelength [um]
taper: function to generate the tapers.
base_layer: layer to draw over the whole photonic crystal \
(necessary if the unit cells are etched into a base layer).
cross_section: for the routing waveguides.
kwargs: cross_section settings.
.. code::
side view
fiber
/ / / /
/ / / /
_|-|_|-|_|-|___ --> unit_cells
base_layer |
o1 ______________|
top view
-------------
// | o o o |
o1 __ // | o o o |
\\ | o o o |
\\ | o o o |
-------------
\\ //
\\ //
|
o2
"""
xs = gf.get_cross_section(cross_section, **kwargs)
wg_width = xs.width
layer = xs.layer
c = Component()
_ = c << rectangle(
size=(x_span, y_span), layer=base_layer, centered=True, port_type=None
)
# Photonic crystal
num_x = int(np.floor(x_span / period_x))
num_y = int(np.floor(y_span / period_y))
x_start = -(num_x * period_x) / 2
y_start = -(num_y * period_y) / 2
unit_cell_grating = gf.get_component(unit_cell)
g = c.add_ref(
unit_cell_grating, columns=num_x, rows=num_y, spacing=(period_x, period_y)
)
g.dxmin = x_start
g.dymin = y_start
port_type = f"vertical_{polarization.lower()}"
c.add_port(
name=port_type,
port_type=port_type,
center=(0, 0),
orientation=0,
width=x_span,
layer=layer,
)
c.info["polarization"] = polarization
c.info["wavelength"] = wavelength
taper = gf.get_component(
taper,
length=length_taper,
width2=width_taper,
width1=wg_width,
cross_section=cross_section,
)
taper1 = c << taper
taper1.dxmax = -x_span / 2
taper1.dy = 0
c.add_port(port=taper1.ports["o1"], name="o1")
taper2 = c << taper
taper2.drotate(90)
taper2.dx = 0
taper2.dymax = -y_span / 2
c.add_port(port=taper2.ports["o1"], name="o2")
xs.add_bbox(c)
return c
if __name__ == "__main__":
c = grating_coupler_dual_pol()
c.show()
