fouriax.KSpacePropagator#

class KSpacePropagator(distance_um=None, refractive_index=1.0, na_limit=None, include_evanescent=False, precomputed_transfer_stack=None)#

Bases: OpticalLayer

Diagonal k-space propagator using the angular-spectrum phase advance.

Requires k-space-domain input. Multiplies each frequency component by exp(j * kz * distance_um) where kz is derived from the dispersion relation. Supports scalar and Jones fields.

All length quantities are in micrometers.

Parameters:

  • distance_um (float | None) – Propagation distance in micrometers.

  • refractive_index (float) – Refractive index of the medium.

  • na_limit (float | None) – Optional numerical aperture cutoff applied as a hard k-space mask.

  • include_evanescent (bool) – If True, evanescent modes are included (complex kz). If False (default), evanescent modes are zeroed out.

  • precomputed_transfer_stack (Array | None)

__init__(distance_um=None, refractive_index=1.0, na_limit=None, include_evanescent=False, precomputed_transfer_stack=None)#
Parameters:

  • distance_um (float | None)

  • refractive_index (float)

  • na_limit (float | None)

  • include_evanescent (bool)

  • precomputed_transfer_stack (Array | None)

Return type:

None

Methods

__init__([distance_um, refractive_index, ...])

forward(field)

Propagate a k-space field by diagonal transfer multiplication.

parameters()

Return trainable parameters exposed by this layer.

transfer_function(field, wavelength_um, ...)

Build the diagonal k-space transfer function for one wavelength.

validate_for(field)

Check that field is compatible with this layer.

Attributes

distance_um

include_evanescent

na_limit

precomputed_transfer_stack

refractive_index

distance_um: float | None = None#
refractive_index: float = 1.0#
na_limit: float | None = None#
include_evanescent: bool = False#
precomputed_transfer_stack: Array | None = None#
transfer_function(field, wavelength_um, distance_um)#

Build the diagonal k-space transfer function for one wavelength.

Parameters:

  • field (Field) – K-space field whose grid defines the sampled frequency axes.

  • wavelength_um (float) – Wavelength to propagate in micrometers.

  • distance_um (float) – Propagation distance in micrometers.

Returns:

Complex array with shape (ny, nx) matching the sampled k-space grid.

Raises:

ValueError – If the distance, refractive index, or NA limit is invalid.

Return type:

Array

parameters()#

Return trainable parameters exposed by this layer.

Return type:

dict[str, Array]

forward(field)#

Propagate a k-space field by diagonal transfer multiplication.

Parameters:

field (Field) – K-space input field with scalar or Jones data layout.

Returns:

K-space field with the same shape, batch axes, and sampling metadata as the input.

Raises:

ValueError – If the input domain is wrong or propagation parameters are invalid.

Return type:

Field