PyNJ 0.1.1

Time-reversal FDFD solver for photonic nanojet (PNJ) generation

PyNJ

A time-reversal FDFD solver for generating photonic nanojets (PNJ) with dielectric lenses.

Installation

pip install PyNJ

Quick start

from timereversal import Solver

solver = Solver(
    lambda0=532e-9,   # wavelength in meters
    n_bg=1.0,         # background refractive index
    n_lens=1.5,       # lens refractive index
    Lx=10e-6,         # simulation domain width (m)
    Ly=10e-6,         # simulation domain height (m)
    ppum=20,          # pixels per micrometer
    R_lens=2e-6,      # lens radius (m)
    x0_lens=0.0,      # lens center x (m)
    y0_lens=0.0,      # lens center y (m)
    shape="circle",   # lens shape
)

result = solver.solve(x=0.0, y=3.0)  # target PNJ position in micrometers

Lens shapes

The following shapes are supported via the shape parameter:

Shape	Description
"circle"	Circular lens
"square"	Square lens
"superformula"	Gielis superformula shape (parametric)
"triangle"	Triangular SVG mask
"triangle_flipped"	Flipped triangle
"triangle_rounded"	Rounded triangle
"square_concave"	Square with concave sides
"square_convex"	Square with convex sides
"clepsidra"	Hourglass shape
"clepsidra_flipped"	Flipped hourglass
"clepsidra_rounded"	Rounded hourglass
"hz"	Arbitrary SVG mask (Hz mode)

Custom SVG masks can be loaded by passing svg_folder pointing to a directory of .svg files and setting shape to the filename stem.

Result fields

solver.solve() returns a SimulationResult dataclass with:

• Hz, Ex, Ey — complex field arrays
• Iz — normalised intensity |Hz|
• x, y — coordinate axes (meters)
• x_pnj, y_pnj — snapped PNJ target coordinates
• entrance, src_line — aperture fields used for the time-reversed source
• eps_r — permittivity map
• i_pnj, j_pnj, j_src — grid indices

License

MIT