172 lines
6.1 KiB
Python
172 lines
6.1 KiB
Python
"""
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Example code for running an OpenCL FDTD simulation
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See main() for simulation setup.
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"""
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import sys
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import time
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import numpy
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import h5py
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from fdtd.simulation import Simulation
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from masque import Pattern, shapes
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import gridlock
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import pcgen
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def perturbed_l3(a: float, radius: float, **kwargs) -> Pattern:
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"""
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Generate a masque.Pattern object containing a perturbed L3 cavity.
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:param a: Lattice constant.
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:param radius: Hole radius, in units of a (lattice constant).
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:param kwargs: Keyword arguments:
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hole_dose, trench_dose, hole_layer, trench_layer: Shape properties for Pattern.
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Defaults *_dose=1, hole_layer=0, trench_layer=1.
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shifts_a, shifts_r: passed to pcgen.l3_shift; specifies lattice constant (1 -
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multiplicative factor) and radius (multiplicative factor) for shifting
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holes adjacent to the defect (same row). Defaults are 0.15 shift for
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first hole, 0.075 shift for third hole, and no radius change.
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xy_size: [x, y] number of mirror periods in each direction; total size is
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2 * n + 1 holes in each direction. Default [10, 10].
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perturbed_radius: radius of holes perturbed to form an upwards-driected beam
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(multiplicative factor). Default 1.1.
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trench width: Width of the undercut trenches. Default 1.2e3.
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:return: masque.Pattern object containing the L3 design
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"""
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default_args = {'hole_dose': 1,
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'trench_dose': 1,
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'hole_layer': 0,
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'trench_layer': 1,
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'shifts_a': (0.15, 0, 0.075),
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'shifts_r': (1.0, 1.0, 1.0),
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'xy_size': (10, 10),
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'perturbed_radius': 1.1,
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'trench_width': 1.2e3,
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}
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kwargs = {**default_args, **kwargs}
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xyr = pcgen.l3_shift_perturbed_defect(mirror_dims=kwargs['xy_size'],
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perturbed_radius=kwargs['perturbed_radius'],
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shifts_a=kwargs['shifts_a'],
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shifts_r=kwargs['shifts_r'])
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xyr *= a
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xyr[:, 2] *= radius
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pat = Pattern()
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pat.name = 'L3p-a{:g}r{:g}rp{:g}'.format(a, radius, kwargs['perturbed_radius'])
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pat.shapes += [shapes.Circle(radius=r, offset=(x, y),
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dose=kwargs['hole_dose'],
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layer=kwargs['hole_layer'])
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for x, y, r in xyr]
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maxes = numpy.max(numpy.fabs(xyr), axis=0)
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pat.shapes += [shapes.Polygon.rectangle(
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lx=(2 * maxes[0]), ly=kwargs['trench_width'],
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offset=(0, s * (maxes[1] + a + kwargs['trench_width'] / 2)),
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dose=kwargs['trench_dose'], layer=kwargs['trench_layer'])
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for s in (-1, 1)]
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return pat
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def main():
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max_t = 8000 # number of timesteps
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dx = 40 # discretization (nm/cell)
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pml_thickness = 8 # (number of cells)
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wl = 1550 # Excitation wavelength and fwhm
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dwl = 200
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# Device design parameters
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xy_size = numpy.array([10, 10])
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a = 430
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r = 0.285
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th = 170
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# refractive indices
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n_slab = 3.408 # InGaAsP(80, 50) @ 1550nm
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n_air = 1.0 # air
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# Half-dimensions of the simulation grid
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xy_max = (xy_size + 1) * a * [1, numpy.sqrt(3)/2]
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z_max = 1.6 * a
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xyz_max = numpy.hstack((xy_max, z_max)) + pml_thickness * dx
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# Coordinates of the edges of the cells. The fdtd package can only do square grids at the moment.
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half_edge_coords = [numpy.arange(dx/2, m + dx, step=dx) for m in xyz_max]
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edge_coords = [numpy.hstack((-h[::-1], h)) for h in half_edge_coords]
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# #### Create the grid, mask, and draw the device ####
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grid = gridlock.Grid(edge_coords, initial=n_air**2, num_grids=3)
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grid.draw_slab(surface_normal=gridlock.Direction.z,
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center=[0, 0, 0],
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thickness=th,
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eps=n_slab**2)
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mask = perturbed_l3(a, r)
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grid.draw_polygons(surface_normal=gridlock.Direction.z,
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center=[0, 0, 0],
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thickness=2 * th,
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eps=n_air**2,
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polygons=mask.as_polygons())
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print(grid.shape)
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# #### Create the simulation grid ####
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sim = Simulation(grid.grids)
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# Conducting boundaries and pmls in every direction
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c_args = []
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pml_args = []
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for d in (0, 1, 2):
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for p in (-1, 1):
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c_args += [{'direction': d, 'polarity': p}]
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pml_args += [{'direction': d, 'polarity': p, 'epsilon_eff': n_slab**2}]
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sim.init_conductors(c_args)
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sim.init_cpml(pml_args)
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# Source parameters and function
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w = 2 * numpy.pi * dx / wl
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fwhm = dwl * w * w / (2 * numpy.pi * dx)
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alpha = (fwhm ** 2) / 8 * numpy.log(2)
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delay = 7/numpy.sqrt(2 * alpha)
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def field_source(i):
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t0 = i * sim.dt - delay
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return numpy.sin(w * t0) * numpy.exp(-alpha * t0**2)
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# #### Run a bunch of iterations ####
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# event = sim.whatever([prev_event]) indicates that sim.whatever should be queued immediately and run
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# once prev_event is finished.
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output_file = h5py.File('simulation_output.h5', 'w')
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start = time.perf_counter()
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for t in range(max_t):
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event = sim.cpml_E([])
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sim.update_E([event]).wait()
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sim.E[1][tuple(grid.shape//2)] += field_source(t)
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event = sim.conductor_E([])
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event = sim.cpml_H([event])
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event = sim.update_H([event])
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sim.conductor_H([event]).wait()
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print('iteration {}: average {} iterations per sec'.format(t, (t+1)/(time.perf_counter()-start)))
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sys.stdout.flush()
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if t % 20 == 0:
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r = sum([(f * f * e).get().sum() for f, e in zip(sim.E, sim.eps)])
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print('E sum', r)
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# Save field slices
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if (t % 20 == 0 and (max_t - t <= 1000 or t <= 2000)) or t == max_t-1:
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print('saving E-field')
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for j, f in enumerate(sim.E):
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a = f.get()
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output_file['/E{}_t{}'.format('xyz'[j], t)] = a[:, :, round(a.shape[2]/2)]
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if __name__ == '__main__':
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main()
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