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214 lines
8.2 KiB
Python
214 lines
8.2 KiB
Python
"""


Routines for creating normalized 2D lattices and common photonic crystal


cavity designs.


"""




from typing import List




import numpy






def triangular_lattice(dims: List[int],


asymmetrical: bool=False


) > numpy.ndarray:


"""


Return an ndarray of [[x0, y0], [x1, y1], ...] denoting lattice sites for


a triangular lattice in 2D. The lattice will be centered around (0, 0),


unless asymmetrical=True in which case there will be extra holes in the +x


direction.




:param dims: Number of lattice sites in the [x, y] directions.


:param asymmetrical: If true, each row in x will contain the same number of


lattice sites. If false, the structure is symmetrical around (0, 0).


:return: [[x0, y0], [x1, 1], ...] denoting lattice sites.


"""


dims = numpy.array(dims, dtype=int)




if asymmetrical:


k = 0


else:


k = 1




positions = []


ymax = (dims[1]  1)/2


for j in numpy.linspace(ymax, ymax, dims[0]):


j_odd = numpy.floor(j) % 2




x_offset = j_odd * 0.5


y_offset = j * numpy.sqrt(3)/2




num_x = dims[0]  k * j_odd


xmax = (dims[0]  1)/2


xs = numpy.linspace(xmax, xmax  k * j_odd, num_x) + x_offset


ys = numpy.full_like(xs, y_offset)




positions += [numpy.vstack((xs, ys)).T]




xy = numpy.vstack(tuple(positions))


return xy[xy[:, 0].argsort(), ]






def square_lattice(dims: List[int]) > numpy.ndarray:


"""


Return an ndarray of [[x0, y0], [x1, y1], ...] denoting lattice sites for


a square lattice in 2D. The lattice will be centered around (0, 0).




:param dims: Number of lattice sites in the [x, y] directions.


:return: [[x0, y0], [x1, 1], ...] denoting lattice sites.


"""


xs, ys = numpy.meshgrid(range(dims[0]), range(dims[1]), 'xy')


xs = dims[0]/2


ys = dims[1]/2


xy = numpy.vstack((xs.flatten(), ys.flatten())).T


return xy[xy[:, 0].argsort(), ]




# ### Photonic crystal functions ###






def nanobeam_holes(a_defect: float,


num_defect_holes: int,


num_mirror_holes: int


) > numpy.ndarray:


"""


Returns a list of [[x0, r0], [x1, r1], ...] of nanobeam hole positions and radii.


Creates a region in which the lattice constant and radius are progressively


(linearly) altered over num_defect_holes holes until they reach the value


specified by a_defect, then symmetrically returned to a lattice constant and


radius of 1, which is repeated num_mirror_holes times on each side.




:param a_defect: Minimum lattice constant for the defect, as a fraction of the


mirror lattice constant (ie., for no defect, a_defect = 1).


:param num_defect_holes: How many holes form the defect (perside)


:param num_mirror_holes: How many holes form the mirror (perside)


:return: Ndarray [[x0, r0], [x1, r1], ...] of nanobeam hole positions and radii.


"""


a_values = numpy.linspace(a_defect, 1, num_defect_holes, endpoint=False)


xs = a_values.cumsum()  (a_values[0] / 2) # Later mirroring makes center distance 2x as long


mirror_xs = numpy.arange(1, num_mirror_holes + 1) + xs[1]


mirror_rs = numpy.ones_like(mirror_xs)


return numpy.vstack((numpy.hstack((mirror_xs[::1], xs[::1], xs, mirror_xs)),


numpy.hstack((mirror_rs[::1], a_values[::1], a_values, mirror_rs)))).T






def ln_defect(mirror_dims: List[int], defect_length: int) > numpy.ndarray:


"""


Nhole defect in a triangular lattice.




:param mirror_dims: [x, y] mirror lengths (number of holes). Total number of holes


is 2 * n + 1 in each direction.


:param defect_length: Length of defect. Should be an odd number.


:return: [[x0, y0], [x1, y1], ...] for all the holes


"""


if defect_length % 2 != 1:


raise Exception('defect_length must be odd!')


p = triangular_lattice([2 * d + 1 for d in mirror_dims])


half_length = numpy.floor(defect_length / 2)


hole_nums = numpy.arange(half_length, half_length + 1)


holes_to_keep = numpy.in1d(p[:, 0], hole_nums, invert=True)


return p[numpy.logical_or(holes_to_keep, p[:, 1] != 0), ]






def ln_shift_defect(mirror_dims: List[int],


defect_length: int,


shifts_a: List[float]=(0.15, 0, 0.075),


shifts_r: List[float]=(1, 1, 1)


) > numpy.ndarray:


"""


Nhole defect with shifted holes (intended to give the mode a gaussian profile


in real and kspace so as to improve both Q and confinement). Holes along the


defect line are shifted and altered according to the shifts_* parameters.




:param mirror_dims: [x, y] mirror lengths (number of holes). Total number of holes


is 2 * n + 1 in each direction.


:param defect_length: Length of defect. Should be an odd number.


:param shifts_a: Percentage of a to shift (1st, 2nd, 3rd,...) holes along the defect line


:param shifts_r: Factor to multiply the radius by. Should match length of shifts_a


:return: [[x0, y0, r0], [x1, y1, r1], ...] for all the holes


"""


if not hasattr(shifts_a, "__len__") and shifts_a is not None:


shifts_a = [shifts_a]


if not hasattr(shifts_r, "__len__") and shifts_r is not None:


shifts_r = [shifts_r]




xy = ln_defect(mirror_dims, defect_length)




# Add column for radius


xyr = numpy.hstack((xy, numpy.ones((xy.shape[0], 1))))




# Shift holes


# Expand shifts as necessary


n_shifted = max(len(shifts_a), len(shifts_r))




tmp_a = numpy.array(shifts_a)


shifts_a = numpy.ones((n_shifted, ))


shifts_a[:len(tmp_a)] = tmp_a




tmp_r = numpy.array(shifts_r)


shifts_r = numpy.ones((n_shifted, ))


shifts_r[:len(tmp_r)] = tmp_r




x_removed = numpy.floor(defect_length / 2)




for ind in range(n_shifted):


for sign in (1, 1):


x_val = sign * (x_removed + ind + 1)


which = numpy.logical_and(xyr[:, 0] == x_val, xyr[:, 1] == 0)


xyr[which, ] = (x_val + numpy.sign(x_val) * shifts_a[ind], 0, shifts_r[ind])




return xyr






def r6_defect(mirror_dims: List[int]) > numpy.ndarray:


"""


R6 defect in a triangular lattice.




:param mirror_dims: [x, y] mirror lengths (number of holes). Total number of holes


is 2 * n + 1 in each direction.


:return: [[x0, y0], [x1, y1], ...] specifying hole centers.


"""


xy = triangular_lattice([2 * d + 1 for d in mirror_dims])




rem_holes_plus = numpy.array([[1, 0],


[0.5, +numpy.sqrt(3)/2],


[0.5, numpy.sqrt(3)/2]])


rem_holes = numpy.vstack((rem_holes_plus, rem_holes_plus))




for rem_xy in rem_holes:


xy = xy[(xy != rem_xy).any(axis=1), ]




return xy






def l3_shift_perturbed_defect(mirror_dims: List[int],


perturbed_radius: float=1.1,


shifts_a: List[float]=(),


shifts_r: List[float]=()


) > numpy.ndarray:


"""


3hole defect with perturbed hole sizes intended to form an upwardsdirected


beam. Can also include shifted holes along the defect line, intended


to give the mode a more gaussian profile to improve Q.




:param mirror_dims: [x, y] mirror lengths (number of holes). Total number of holes


is 2 * n + 1 in each direction.


:param perturbed_radius: Amount to perturb the radius of the holes used for beamforming


:param shifts_a: Percentage of a to shift (1st, 2nd, 3rd,...) holes along the defect line


:param shifts_r: Factor to multiply the radius by. Should match length of shifts_a


:return: [[x0, y0, r0], [x1, y1, r1], ...] for all the holes


"""


xyr = ln_shift_defect(mirror_dims, 3, shifts_a, shifts_r)




abs_x, abs_y = (numpy.fabs(xyr[:, i]) for i in (0, 1))




# Sorted unique xs and ys


# Ignore row y=0 because it might have shifted holes


xs = numpy.unique(abs_x[abs_x != 0])


ys = numpy.unique(abs_y)




# which holes should be perturbed? (xs[[3, 7]], ys[1]) and (xs[[2, 6]], ys[2])


perturbed_holes = ((xs[a], ys[b]) for a, b in ((3, 1), (7, 1), (2, 2), (6, 2)))


for row in xyr:


if numpy.fabs(row) in perturbed_holes:


row[2] = perturbed_radius


return xyr
