"""Superconducting nanowire single photon detector geometries."""
# can be removed in python 3.14, see https://peps.python.org/pep-0749/
from __future__ import annotations
import qnngds as qg
import phidl.geometry as pg
import numpy as np
from qnngds.typing import LayerSpec
from qnngds import Device
from typing import Tuple
[docs]@qg.device
def basic(
wire_width: float = 0.2,
wire_pitch: float = 0.6,
size: Tuple[int | float | None, int | float | None] = (5, 5),
num_squares: int | None = None,
turn_ratio: int | float = 4,
num_pts: int = 50,
extend_terminals: bool = True,
terminals_same_side: bool = False,
layer: LayerSpec = (1, 0),
) -> Device:
"""Creates an optimally-rounded SNSPD.
Modification of gdsfactory's and phidl's implementations
Args:
wire_width (float): Width of the nanowire.
wire_pitch (float): Pitch of the nanowire.
size (tuple of Optional[int or float]): Size of the detector.
num_squares (int | None): Number of squares in the detector.
turn_ratio (int or float): Specifies how much of the SNSPD width is
dedicated to the 180 degree turn. A turn_ratio of 10 will result in 20%
of the width being comprised of the turn.
num_pts (int): number of polygon points to use for turn
extend_terminals (bool): If True, bring ports flush to edges of device
terminals_same_side (bool): If True, both ports will be located on the
same side of the SNSPD.
layer (LayerSpec): GDS layer specification
Returns:
(Device): optimally-rounded SNSPD, as provided by
Phidl but renamed and unified.
"""
# check parameters constrains
if wire_pitch <= wire_width:
print(
"Warning, wire_pitch cannot be smaller than wire_pitch. "
"Choosing wire_pitch = 2*wire_width."
)
wire_pitch = 2 * wire_width
if num_squares is not None and (
(size is None) or ((size[0] is None) and (size[1]) is None)
):
xy = np.sqrt(num_squares * wire_pitch * wire_width)
size = [xy, xy]
num_squares = None
if [size[0], size[1], num_squares].count(None) != 1:
raise ValueError(
"SNSPD requires that exactly ONE value of "
"the arguments ``num_squares`` and ``size`` be None "
"to prevent overconstraining, for example:\n"
">>> snspd(size = (3, None), num_squares = 2000)"
)
if size[0] is None:
ysize = size[1]
xsize = num_squares * wire_pitch * wire_width / ysize
elif size[1] is None:
xsize = size[0]
ysize = num_squares * wire_pitch * wire_width / xsize
else:
xsize = size[0]
ysize = size[1]
num_meanders = int(np.ceil(ysize / wire_pitch))
half_size = xsize / 2
SNSPD = Device()
hairpin = qg.geometries.optimal_hairpin(
width=wire_width,
pitch=wire_pitch,
turn_ratio=turn_ratio,
length=half_size,
num_pts=num_pts,
layer=layer,
)
if not terminals_same_side and (num_meanders % 2) == 0:
num_meanders += 1
elif terminals_same_side and (num_meanders % 2) == 1:
num_meanders += 1
if extend_terminals:
start_nw = SNSPD.add_ref(
pg.straight(size=(wire_width, half_size), layer=qg.get_layer(layer))
)
hp_prev = SNSPD.add_ref(hairpin)
hp_prev.connect(1, start_nw.ports[2])
else:
start_nw = SNSPD.add_ref(hairpin)
hp_prev = start_nw
alternate = True
last_port = None
for _n in range(2, num_meanders):
hp = SNSPD.add_ref(hairpin)
if alternate:
hp.connect(2, hp_prev.ports[2])
else:
hp.connect(1, hp_prev.ports[1])
last_port = hp.ports[2] if terminals_same_side else hp.ports[1]
hp_prev = hp
alternate = not alternate
if extend_terminals:
finish_se = SNSPD.add_ref(
pg.straight(size=(wire_width, half_size), layer=qg.get_layer(layer))
)
if last_port is not None:
finish_se.connect(2, last_port)
SNSPD.add_port(port=finish_se.ports[1], name=2, layer=layer)
else:
SNSPD.add_port(port=last_port, name=2, layer=layer)
SNSPD.add_port(port=start_nw.ports[1], name=1, layer=layer)
SNSPD.info["num_squares"] = num_meanders * (xsize / wire_width)
SNSPD.info["area"] = xsize * ysize
SNSPD.info["xsize"] = xsize
SNSPD.info["ysize"] = ysize
SNSPD.flatten()
SNSPDu = Device("snspd_basic")
SNSPDu << pg.union(SNSPD, layer=qg.get_layer(layer))
SNSPDu.add_ports(SNSPD.ports)
SNSPDu.move(SNSPDu.center, (0, 0))
return SNSPDu
[docs]@qg.device
def vertical(
wire_width: float = 0.2,
wire_pitch: float = 0.6,
size: Tuple[int | float, int | float] = (5, 5),
num_squares: int | None = None,
extend: float | None = 1,
num_pts: int = 50,
layer: LayerSpec = (1, 0),
) -> Device:
"""Creates an optimally-rounded SNSPD, with terminals in its center instead
of the side.
Args:
wire_width (float): Width of the nanowire.
wire_pitch (float): Pitch of the nanowire.
size (tuple of int or float): Size of the detector.
num_squares (int | None): Number of squares in the detector.
extend (bool | None): Whether or not to extend the ports.
num_pts (int): number of points to use for optimal hairpin.
layer (LayerSpec): GDS layer specification
Returns:
(Device): The vertical SNSPD device.
"""
# check parameters constrains
if wire_pitch <= wire_width:
print(
"Warning, wire_pitch cannot be smaller than wire_pitch. "
"Choosing wire_pitch = 2*wire_width."
)
wire_pitch = 2 * wire_width
D = Device()
S = basic(
wire_width=wire_width,
wire_pitch=wire_pitch,
size=size,
num_squares=num_squares,
extend_terminals=False,
terminals_same_side=False,
layer=layer,
num_pts=num_pts,
)
D << S
T = pg.optimal_90deg(width=wire_width, layer=qg.get_layer(layer))
t1 = D << T
t1.move(np.subtract(S.ports[1].center, t1.ports[2].center))
t1.movex(T.xsize - wire_width / 2)
t2 = D << T
t2.rotate(180)
t2.move(np.subtract(S.ports[2].center, t2.ports[2].center))
t2.movex(-T.xsize + wire_width / 2)
ports = []
if extend is not None:
E = pg.straight(size=(wire_width, extend), layer=qg.get_layer(layer))
e1 = D << E
e1.connect(port=e1.ports[1], destination=t1.ports[1])
e2 = D << E
e2.connect(port=e2.ports[1], destination=t2.ports[1])
ports.append(e1.ports[2])
ports.append(e2.ports[2])
else:
ports.append(t1.ports[1])
ports.append(t2.ports[1])
Du = Device("snspd_vert")
Du << pg.union(D, layer=qg.get_layer(layer))
Du.flatten()
for p, port in enumerate(ports):
Du.add_port(
name=p + 1,
port=port,
layer=layer,
)
return Du