"""Transmissive optical components which focus or disperse light beams."""
import logging
import numpy as np
from finesse.components.general import Connector, InteractionType, NoiseType
from finesse.components.node import NodeDirection, NodeType
from finesse.parameter import float_parameter
from finesse.utilities import refractive_index
from finesse.tracing import abcd
from finesse.symbols import Matrix, Constant
from finesse.env import warn
from finesse.warnings import UnreasonableComponentValueWarning
LOGGER = logging.getLogger(__name__)
[docs]@float_parameter(
"f",
"Focal length",
validate="_check_f",
units="m",
is_geometric=True,
)
# IMPORTANT: renaming this class impacts the katscript spec and should be avoided!
class Lens(Connector):
"""Represents a thin lens optical component with an associated focal length.
Notes
-----
The specified focal length `f` is only accurate when the lens is attached to spaces with index
of refraction close to 1. This component exists so that one can use the intuitive focal length
parameter instead of having to set radii of curvature as with e.g. :class:`.Mirror`.
Parameters
----------
name : str
Name of newly created lens.
f : float, optional
Focal length of the lens in metres; defaults to infinity.
Attributes
----------
OPD_map : :class:`finesse.knm.Map`
A map that is used to describe the transverse spatial amplitude and phase
variations beyond a simple lensing. Typically the map applied is describing
the dnr/dT temperature effects in some substrate.
"""
[docs] def __init__(self, name, f=np.inf):
super().__init__(name)
self.f = f
self.OPD_map = None
self._add_port("p1", NodeType.OPTICAL)
self.p1._add_node("i", NodeDirection.INPUT)
self.p1._add_node("o", NodeDirection.OUTPUT)
self._add_port("p2", NodeType.OPTICAL)
self.p2._add_node("i", NodeDirection.INPUT)
self.p2._add_node("o", NodeDirection.OUTPUT)
# optic to optic couplings
self._register_node_coupling(
"P1i_P2o",
self.p1.i,
self.p2.o,
interaction_type=InteractionType.TRANSMISSION,
)
self._register_node_coupling(
"P2i_P1o",
self.p2.i,
self.p1.o,
interaction_type=InteractionType.TRANSMISSION,
)
[docs] def optical_equations(self):
if self._model._settings.is_modal:
return {
f"{self.name}.P1i_P2o": Matrix(f"{self.name}.K12"),
f"{self.name}.P2i_P1o": Matrix(f"{self.name}.K21"),
}
else:
return {
f"{self.name}.P1i_P2o": Constant(1),
f"{self.name}.P2i_P1o": Constant(1),
}
def _check_f(self, value):
if value == 0:
raise ValueError("Focal length of lens must be non-zero.")
# check for unreasonable focal length and suggest alternative
if abs(value) < 10e-3:
warn(
f"Lens '{self.name}' has a small focal length. The 'lens' ABCD "
"matrix is valid for focal lengths >> thickness of the lens."
"This lens may be better modelled as two mirrors and a space.",
UnreasonableComponentValueWarning,
)
return value
def _resymbolise_ABCDs(self):
self.__symbolise_ABCDs("x")
self.__symbolise_ABCDs("y")
def __symbolise_ABCDs(self, direction):
# TODO (sjr) Not using direction currently but will split
# into fx, fy soon to support astigmatic lenses
M_sym = abcd.lens(self.f.ref)
# Matrices same for both node couplings
self.register_abcd_matrix(
M_sym,
(self.p1.i, self.p2.o, direction),
(self.p2.i, self.p1.o, direction),
)
@property
def abcdx(self):
"""Numeric ABCD matrix in the tangential plane.
Equivalent to ``lens.ABCD(1, 2, "x")`` and ``lens.ABCD(2, 1, "x")``.
:getter: Returns a copy of the (numeric) ABCD matrix for this coupling (read-only).
"""
return self.ABCD(1, 2, "x")
@property
def abcdy(self):
"""Numeric ABCD matrix in the sagittal plane.
Equivalent to ``lens.ABCD(2, 1, "y")`` and ``lens.ABCD(2, 1, "y")``.
:getter: Returns a copy of the (numeric) ABCD matrix for this coupling (read-only).
"""
return self.ABCD(1, 2, "y")
[docs] def ABCD(
self,
from_node,
to_node,
direction="x",
symbolic=False,
copy=True,
retboth=False,
allow_reverse=False,
):
r"""Returns the ABCD matrix of the lens for the specified coupling.
.. _fig_abcd_lens_transmission:
.. figure:: ../images/abcd_lenst.*
:align: center
This is given by,
.. math::
M = \begin{pmatrix}
1 & 0 \\
-\frac{1}{f} & 1
\end{pmatrix},
where :math:`f` is the focal length of the lens.
See :meth:`.Connector.ABCD` for descriptions of parameters, return values and possible
exceptions.
"""
return super().ABCD(
from_node, to_node, direction, symbolic, copy, retboth, allow_reverse
)
[docs] def actuate_f(self, dioptres, direction=("x", "y")):
r"""Actuate on the focal length of the lens with a specified dioptre shift.
Sets the focal length to a new value, :math:`f_2`, via,
.. math::
f_2 = \frac{1}{d + \frac{1}{f_1}},
where :math:`f_1` is the current focal length and :math:`d` is the dioptre shift (i.e.
the `dioptre` argument).
By default, both focal planes are shifted. To shift, e.g., only the
tangential plane, specify ``direction="x"``.
Parameters
----------
dioptres : float
Shift in lens focal length in dioptres.
direction : tuple or str, optional; default: ("x", "y")
Focal plane to shift, defaults to both tangential and sagittal.
"""
fnew = lambda x: 1 / (dioptres + 1 / x)
if "x" in direction: # TODO (sjr) Change to fx
self.f = fnew(self.f.value)
if "y" in direction: # TODO (sjr) Change to fy
self.f = fnew(self.f.value)
def _fill_optical_matrix(self, ws, matrix, connections):
for freq in matrix.optical_frequencies.frequencies:
with matrix.component_edge_fill3(
ws.owner_id,
connections.P1i_P2o_idx,
freq.index,
freq.index,
) as mat:
mat[:] = ws.K12.data
with matrix.component_edge_fill3(
ws.owner_id,
connections.P2i_P1o_idx,
freq.index,
freq.index,
) as mat:
mat[:] = ws.K21.data
def _fill_carrier(self, ws):
self._fill_optical_matrix(ws, ws.sim.carrier, ws.carrier.connections)
def _fill_signal(self, ws):
self._fill_optical_matrix(ws, ws.sim.signal, ws.signal.connections)
def _get_workspace(self, sim):
from finesse.simulations.sparse.simulation import SparseMatrixSimulation
if isinstance(sim, SparseMatrixSimulation):
from finesse.components.modal.lens import LensWorkspace, lens_fill_qnoise
_, is_changing = self._eval_parameters()
refill = sim.is_component_in_mismatch_couplings(self) or len(is_changing)
ws = LensWorkspace(self, sim)
# This assumes that nr1/nr2 cannot change during a simulation
ws.nr1 = refractive_index(self.p1)
ws.nr2 = refractive_index(self.p2)
# TODO ddb refractive index should be equal on
# both sides of the lens as we are using the thin
# lens approximation
assert ws.nr1 == ws.nr2
ws.carrier.add_fill_function(self._fill_carrier, refill)
ws.signal.add_fill_function(self._fill_signal, refill)
if sim.is_modal:
ws.abcd_x = self.ABCD(self.p1.i, self.p2.o, "x", copy=False)
ws.abcd_y = self.ABCD(self.p1.i, self.p2.o, "y", copy=False)
# Set the coupling matrix information
# ABCDs are same in each direction
ws.set_knm_info(
"P1i_P2o",
abcd_x=ws.abcd_x,
abcd_y=ws.abcd_y,
nr_from=ws.nr1,
nr_to=ws.nr2,
is_transmission=True,
apply_map=self.OPD_map,
map_phase_factor=1,
map_fliplr=False,
)
# TODO nr reversed here for now until it's forced to be same on both sides
ws.set_knm_info(
"P2i_P1o",
abcd_x=ws.abcd_x,
abcd_y=ws.abcd_y,
nr_from=ws.nr2,
nr_to=ws.nr1,
is_transmission=True,
apply_map=self.OPD_map,
map_phase_factor=1,
map_fliplr=True,
)
if sim.signal:
ws.signal.set_fill_noise_function(
NoiseType.QUANTUM, lens_fill_qnoise
)
return ws
else:
raise Exception(f"Lens does not handle a simulation of type {sim}")