Reinstate defining elliptical grating coupler with period and fill factor

[danielpeace]

Removal of grating_coupler_circular removes ability to define focused grating coupler based on period, fill factor and number of periods like rectangular grating couplers.

[joamatab]

Hi Daniel,

How about using https://gdsfactory.github.io/gdsfactory/components.html#grating-coupler-elliptical-arbitrary
?

@gf.cell
def grating_coupler_elliptical_uniform(
    n_periods: int = 20,
    period: float = 0.75,
    fill_factor: float = 0.5,
    **kwargs,
) -> Component:
    r"""Grating coupler with parametrization based on Lumerical FDTD simulation.
    The ellipticity is derived from Lumerical knowdledge base
    it depends on fiber_angle (degrees), neff, and nclad
    Args:
        n_periods: number of grating periods.
        period: grating pitch in um.
        fill_factor: ratio of grating width vs gap.
    Keyword Args:
        taper_length: taper length from input.
        taper_angle: grating flare angle.
        wavelength: grating transmission central wavelength (um).
        fiber_angle: fibre angle in degrees determines ellipticity.
        neff: tooth effective index to compute ellipticity.
        nclad: cladding effective index to compute ellipticity.
        layer_slab: Optional slab.
        slab_xmin: where 0 is at the start of the taper.
        polarization: te or tm.
        fiber_marker_width: in um.
        fiber_marker_layer: Optional marker.
        spiked: grating teeth have spikes to avoid drc errors..
        bias_gap: etch gap (um).
            Positive bias increases gap and reduces width to keep period constant.
        cross_section: cross_section spec for waveguide port.
        kwargs: cross_section settings.
    .. code::
                      fiber
                   /  /  /  /
                  /  /  /  /
                _|-|_|-|_|-|___ layer
                   layer_slab |
            o1  ______________|
    """
    widths = [period * fill_factor] * n_periods
    gaps = [period * (1 - fill_factor)] * n_periods
    return grating_coupler_elliptical_arbitrary(gaps=gaps, widths=widths, **kwargs)

[joamatab]

Hi Daniel,

just released gdsfactory 5.26.0 with grating_coupler_elliptical_uniform

[danielpeace]

Hi Joaquin,

That's greatly appreciated, thank you!

Being able to define gratings using only pitch and period is very useful for non-standard wafers and other materials platforms.