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stencil.focused_grating

focused_grating(
    wavelength,
    period,
    n_sin,
    focal_length,
    length,
    width=None,
    angle=None,
    input_width=None,
    fill_factor=0.5,
)

Create a focused grating.

The geometry is based on the work by F. Van Laere et al., “Compact Focusing Grating Couplers for Silicon-on-Insulator Integrated Circuits,” in IEEE Photonics Technology Letters, vol. 19, no. 23, pp. 1919-1921, Dec.1, 2007, doi: 10.1109/LPT.2007.908762.

Args

  • wavelength (float): Central wavelength for the grating design.
  • period (float): Grating period (distance between adjacent teeth centers).
  • n_sin (float): Product n0sin⁡θn_0 \sin\theta between the free-space index and the sine of the input wave angle measured from the grating surface normal (such that a value of 0 indicates normal grating illumination).
  • focal_length (float): Distance between the focal point and the start of the grating.
  • length (float): Length of the grating, proportional to the number of teeth.
  • width (float | None): If set, a rectangular-shaped grating is created with the specified width. Only one of width and angle must be set.
  • angle (float | None): If set, the grating is created with the shape of a circular section with the specified angle. Only one of width and angle must be set.
  • input_width (float | None): If set, the input taper region is added to the grating terminating with this dimension.
  • fill_factor (float | str | Expression): Ratio between the grating teeth and the grating period. An string parametrized by "u" or an expression of a single parameter (varied from 0 to 1) can be used to vary the fill factor along the grating.

Returns

list[Circle | Polygon]: Grating structures.

Example

>>> # Pie-slice, apodized grating
>>> grating1 = pf.stencil.focused_grating(
...     wavelength=1.55,
...     period=0.6,
...     n_sin=np.sin(np.pi / 18),
...     focal_length=12.5,
...     length=10,
...     angle=60,
...     input_width=0.5,
...     fill_factor="0.8 - 0.3 * u^0.5",
... )
>>> # Rectangular-shaped grating
>>> grating2 = pf.stencil.focused_grating(
...     wavelength=1.55,
...     period=0.6,
...     n_sin=np.sin(np.pi / 18),
...     focal_length=12.5,
...     length=12,
...     width=16,
...     input_width=0.5,
...     fill_factor=0.6,
... )
>>> grating2 = [s.translate((30, 0)) for s in grating2]
>>> component = pf.Component().add(*grating1, *grating2)

focused_grating