"""Direct probing of coupling coefficients."""
from finesse.detectors.general import Detector
from finesse.detectors.compute.amplitude import (
KnmDetectorWorkspace,
knm_detector_scalar_output,
knm_detector_mode1_output,
knm_detector_mode2_output,
knm_detector_matrix_output,
)
from finesse.cymath.homs import field_index
[docs]class KnmDetector(Detector):
"""Direct probe of coupling coefficients at a component.
This detector has several "modes" which depend upon the values
given for the mode indices `n1`, `m1` and `n2`, `m2`. If:
* all of `n1`, `m1`, `n2`, `m2` are specified then the detector
will output a single complex coefficient corresponding to the
coupling from ``(n1, m1) -> (n2, m2)``,
* just `n1` and `m1` are specified then it will output a vector
of complex coefficients corresponding to each coupling from
``(n1, m1) -> (n, m)`` for each mode ``(n, m)`` in the model,
* only `n2` and `m2` are specified then it will output a vector
of complex coefficients corresponding to each coupling from
``(n, m) -> (n2, m2)`` for each mode ``(n, m)`` in the model,
* none of `n1`, `m1`, `n2`, `m2` are specified then the detector
outputs the full matrix of complex coupling coefficients.
.. hint::
When using this detector in "full-matrix" mode (i.e. by not giving
the values for any of the mode indices), it can be useful to combine
the output with the :class:`.KnmMatrix` object to obtain a more
convenient representation of the scattering matrix.
An example of this is shown below, where the output of a detector
of this type is wrapped using :meth:`.KnmMatrix.from_buffer`.
.. jupyter-execute::
import finesse
finesse.configure(plotting=True)
from finesse.knm.matrix import KnmMatrix
IFO = finesse.Model()
IFO.parse('''
l L0 P=1
link(L0, ITM)
m ITM R=0.99 T=0.01 Rc=-2090 xbeta=0.3u
s LARM ITM.p2 ETM.p1 L=4k
m ETM R=0.99 T=0.01 Rc=2090
cav ARM ITM.p2
modes(x, maxtem=6)
knmd K_itm_r ITM 22
''')
out = IFO.run()
# Make a KnmMatrix wrapper around the output from the detector
k_mat = KnmMatrix.from_buffer(out["K_itm_r"], IFO.homs)
# Now we can perform operations such as plotting the scattering matrix
k_mat.plot(cmap="bone");
See :ref:`arbitrary_scatter_matrices` for some examples on the utility that
the :class:`.KnmMatrix` object provides.
Parameters
----------
name : str
Name of newly created KnmDetector.
comp : :class:`.Connector`
A component which can scatter modes.
coupling : str
Coupling direction string, e.g. "11" for coupling coefficients on reflection from the front
surface of a mirror.
n1, m1, n2, m2: int or None
From (n1, m1) and To (n2, m2) mode indices of the coupling coefficient(s) to retrieve.
See above for the options.
"""
def __init__(self, name, comp, coupling, n1=None, m1=None, n2=None, m2=None):
Detector.__init__(self, name, label="Coupling coefficient", needs_trace=True)
self.__comp = comp
self.__coupling = str(coupling)
if not self.__coupling.startswith("K"):
self.__coupling = f"K{self.__coupling}"
int_or_none = lambda x: None if x is None else int(x)
self.n1 = int_or_none(n1)
self.m1 = int_or_none(m1)
self.n2 = int_or_none(n2)
self.m2 = int_or_none(m2)
if any(k < 0 for k in (self.n1, self.m1, self.n2, self.m2) if k is not None):
raise ValueError("Mode indices cannot be negative.")
for n, m in (("n1", "m1"), ("n2", "m2")):
sn = getattr(self, n)
sm = getattr(self, m)
if (sn is None and sm is not None) or (sm is None and sn is not None):
raise ValueError(f"Both of {n}, {m} must either be integers or None.")
self.__mode1_given = self.n1 is not None
self.__mode2_given = self.n2 is not None
def _get_workspace(self, sim):
# TODO (sjr) Move this block to a separate method which should get called
# whenever number of modes in model changes, otherwise
# querying self.dtype_shape or self.dtype_size will give
# incorrect result until simulation performed. Not a big
# problem though, as these are typically never accessed by user.
if self.__mode1_given and self.__mode2_given:
shape = ()
elif self.__mode1_given or self.__mode2_given:
shape = (sim.model_settings.num_HOMs,)
else:
shape = (sim.model_settings.num_HOMs, sim.model_settings.num_HOMs)
self._update_dtype_shape(shape)
for n, m in [(self.n1, self.m1), (self.n2, self.m2)]:
if n is None:
continue
index = self._model.mode_index_map.get((n, m))
if index is None:
raise ValueError(f"The mode ({n},{m}) is not in the model!")
ws = KnmDetectorWorkspace(self, sim)
if self.__mode1_given:
ws.from_idx = field_index(self.n1, self.m1, sim.model_settings.homs_view)
if self.__mode2_given:
ws.to_idx = field_index(self.n2, self.m2, sim.model_settings.homs_view)
comp_ws = list(filter(lambda x: x.owner == self.__comp, sim.workspaces))
if not comp_ws:
raise RuntimeError(
f"Could not find {self.__comp.name} in simulation workspace"
)
ws.knm_matrix = getattr(comp_ws[0], self.__coupling, None)
if ws.knm_matrix is None:
raise ValueError(
f"Connector {self.__comp.name} has no scattering "
f"matrix coupling {self.__coupling}"
)
if self.__mode1_given and self.__mode2_given:
ws.set_output_fn(knm_detector_scalar_output)
elif self.__mode1_given:
ws.set_output_fn(knm_detector_mode1_output)
elif self.__mode2_given:
ws.set_output_fn(knm_detector_mode2_output)
else:
ws.set_output_fn(knm_detector_matrix_output)
return ws