# Mode Settings

The Mode Settings tab contains the definitions for the set of optical modes calculated by the mode solver. Here, you should specify, for example, the mode plane, bend radius, polarization, frequencies, or direction.

# Plane

Definition of the structure cross-section containing the geometry and medium information to calculate the optical modes.

# Background Medium

Simulation background medium.

Options:

# Center + size

Constructs the mode plane using a center position and size.

center: Center of the mode plane in x, y, and z-directions.

Type: floating-point number

  • Unit: m, μm (default), or nm
  • Default: (0, 0, 0)

size: Size of the mode plane in x, y, and z-directions.

Use Infinity to define a geometry extending to infinity in both directions along an axis.

Type: floating-point number

  • Unit: m, μm (default), or nm
  • Constraint: greater than or equal to 0
  • Required field

# Bounds

Constructs the mode plane from minimum and maximum coordinate bounds.

min: Values of the x, y, and z coordinates defining the mode plane lower corner.

Type: floating-point number

  • Unit: m, μm (default), or nm
  • Required field

max: Values of the x, y, and z coordinates defining the mode plane upper corner.

Type: floating-point number

  • Unit: m, μm (default), or nm
  • Required field

# Specification

Stores specifications for the mode solver to find an electromagnetic mode.

Note, the planar axes are found by popping the injection axis from {x, y, z}. For example, if injection axis is y, the planar axes are ordered {x, z}.

# Number of Modes

num_modes: Number of modes returned by the mode solver.

Type: integer

  • Unit: unitless
  • Constraint: greater than 0
  • Default: 1

# Target Effective Index

target_neff: Guess for effective index of the mode.

Type: floating-point number

  • Unit: unitless
  • Constraint: greater than 0
  • Default: None

# Number of PML Layers

num_pml: Number of standard pml layers to add in the two tangential axes.

Type: integer

  • Unit: unitless
  • Constraint: greater than or equal to 0
  • Default: (0, 0)

# Polarization Filtering

filter_pol: The solver always computes the num_modes modes closest to the given target_neff. If filter_pol=None, they are simply sorted in order of decresing effective index. If a polarization filter is selected, the modes are rearranged such that the first n_pol modes in the list are the ones with the selected polarization fraction larger than or equal to 0.5, while the next num_modes - n_pol modes are the ones where it is smaller than 0.5 (i.e. the opposite polarization fraction is larger than 0.5). Within each polarization subset, the modes are still ordered by decreasing effective index.

te-fraction is defined as the integrated intensity of the E-field component parallel to the first plane axis, normalized to the total in-plane E-field intensity. Conversely, tm-fraction uses the E field component parallel to the second plane axis.

Options:

  • None
  • te
  • tm

Default: None

# Polar Angle

angle_theta: Polar angle of the propagation axis from the injection axis.

Type: floating-point number

  • Unit: rad or degree (default)
  • Default: 0

# Azimuth Angle

angle_phi: Azimuth angle of the propagation axis in the plane orthogonal to the injection axis.

Type: floating-point number

  • Unit: rad or degree (default)
  • Default: 0

# Single or Double Precision in Mode Solver

precision: The solver will be faster and using less memory under single precision, but more accurate under double precision.

Options:

  • single
  • double

Default: single

# Bend Radius

bend_radius: A curvature radius for simulation of waveguide bends.

Can be negative, in which case the mode plane center has a smaller value than the curvature center along the tangential axis perpendicular to the bend axis.

Type: floating-point number

  • Unit: m, μm (default), or nm
  • Default: None

# Bend Axis

bend_axis: Index into the two tangential axes defining the normal to the plane in which the bend lies.

This must be provided if bend_radius is not None.

For example, for a ring in the global xy-plane, and a mode plane in either the xz or the yz plane, the bend_axis is always 1 (the global z axis).

Options:

  • None
  • 0
  • 1

Default: None

# Track Mode Frequency

track_freq: Parameter that turns on/off mode tracking based on their similarity. Can take values 'lowest', 'central', or 'highest', which correspond to mode tracking based on the lowest, central, or highest frequency. If 'None', no mode tracking is performed.

Options:

  • None
  • central
  • lowest
  • highest

Default: central

# Group Index Computation Control

group_index_step: Control the computation of the group index alongside the effective index. If set to a positive value, it sets the fractional frequency step used in the numerical differentiation of the effective index to compute the group index. If set to True, a value of 0.15 is used.

Options:

  • False: The mode solver will not calculate the group index.
  • True: The mode solver will calculate the group index using a fractional frequency step of 0.15 or other user input value.

Default: True

# Frequencies

Definition of the mode wavelengths/frequencies.

Options:

  • Wavelengths: Definition of mode wavelengths in units of m, μm (default), or nm.
  • Frequencies: Definition of mode frequencies in units of Hz (default) or THz.

Default: Wavelengths

# Enter wavelength/frequency range

Create an evenly spaced list of wavelength/frequency points between a minimum and a maximum value.

min: Minimum wavelength/frequency value.

  • Required field Default: None

max: Maximum wavelength/frequency value.

  • Required field Default: None

number of points: Number of wavelength/frequency points.

  • Required field Default: None

# Custom wavelength/frequency list

Create a custom list of wavelength/frequency points. Click the Edit list button to include, edit, or exclude wavelength/frequency values from the list.

# Direction

direction: Specifies propagation in the positive or negative direction of the injection axis.

Options:

  • +: Propogate in the positive direction of the injection axis.
  • -: Propogate in the negative direction of the injection axis.

# Field Components

fields: Collection of field components to store in the monitor. Note that some methods like flux, dot require all tangential field components, while others like mode_area require all E-field components.

Options: select one or more of

  • Ex
  • Ey
  • Ez
  • Hx
  • Hy
  • Hz

Default: [Ex, Ey, Ez, Hx, Hy, Hz]

← Configuration →