Ray Optics Module Updates

For users of the Ray Optics Module, COMSOL Multiphysics® version 5.5 brings multiscale modeling with new features to couple frequency-domain electromagnetics with the RF Module or Wave Optics Module to ray optics, a dedicated Spot Diagram plot that makes postprocessing much easier, and improvements to the Grating boundary condition, including a dedicated Cross Grating feature. Learn about these and other Ray Optics Module updates in more detail below.

Multiscale Electromagnetics Modeling

Two new ray release features enable multiscale electromagnetics modeling with the Ray Optics Module in combination with the RF Module or the Wave Optics Module. The functionality is seamless and fully integrated in the Model Builder workflow.

The Settings window for the Release from Electric Field feature in COMSOL Multiphysics. Release from Electric Field feature settings The combined ray tracing and full wave modeling settings in the Model Builder.

In this case, multiscale means that waves are modeled over length scales comparable to the wavelength as well as length scales that could be much larger. The finite element method (FEM) is used at the wavelength scale and a ray tracing approach is used for modeling propagation over long distances.

Use the new Release from Electric Field feature to launch rays from a surface; the initial intensity and polarization of the rays are taken from the electric field in an adjacent region. This allows you to first model electromagnetic wave propagation over a distance comparable to the wavelength, using the Electromagnetic Waves, Frequency Domain interface or Electromagnetic Waves, Beam Envelopes interface, and then extend the model over a much longer distance via ray tracing. Similarly, you can use the new Release from Far-Field Radiation Pattern feature to launch rays outward from a point, or grid of points, based on a far-field function defined in a previous study. When releasing rays, you can transform the radiation pattern by specifying Euler angles. This allows you to release rays from many different antenna orientations, without having to recompute the radiation pattern.

A model of a Gaussian beam visualized as a grayscale slice plot and released rays visualized as arrows and polarization ellipses. Gaussian beam and released rays A Gaussian beam is modeled for a small number of wavelengths using the Electromagnetic Waves, Beam Envelopes interface (grayscale slice plot). Then, rays are released from the boundary of the modeling domain. Polarization ellipses are drawn along the rays.
A dipole antenna is modeled with rays released outward in every direction. Dipole antenna with released rays A dipole antenna, modeled in the frequency domain, and its far-field radiation pattern are shown at the center. Then, rays are released in every direction, taking their intensity and polarization from this radiation pattern.
Four models of a dipole antenna with rays released at different combinations of Euler angles. Dipole antenna with rays released at different Euler angles Dipole antenna with its far-field radiation pattern, shown with rays released at the default Euler angles (top-left). Rays are released from three other points with different combinations of Euler angles.

You can see this new functionality in the following models:

Spot Diagram Plot

With the dedicated Spot Diagram plot, you can more easily plot the intersection points of rays with a surface, significantly speeding up the postprocessing of ray optics models. The surface can either be a physical boundary in the geometry or a virtual boundary created by the Intersection Point 3D dataset.

The Spot Diagram plot includes dedicated tools for customizing and organizing the plot, such as:

  • Filtering rays out so they do not appear in the plot
  • Sorting the rays based on wavelength or field angle so they appear as an array of distinct spots
  • Automatically locating the plane of minimal root mean square (RMS) spot size and creating a dataset there
  • Displaying text annotations such as spot size, wavelength, and position
A spot diagram of a double Gauss lens system shown in rainbow coloring. Spot diagram: Nominal image plane Spot diagram in the nominal image plane of a double Gauss lens system. From the Double Gauss Lens tutorial in the Application Libraries.
A spot diagram in the best focus of a double Gauss lens system. Spot diagram: 'Best focus' plane Spot diagram in the "best focus" plane of the double Gauss lens system. The position of the intersecting plane was automatically computed to minimize the RMS spot size.
A collage of nine spot diagrams where the spots are sorted by wavelength. Spot diagrams for a white pupil échelle spectrograph Spot diagram array from the White Pupil Échelle Spectrograph model in the Application Libraries. The spots are sorted by wavelength.

You can see this new functionality in the following models:

Improvements to the Optical Aberration Plot

The Optical Aberration plot has new settings that make it easier to compute the Zernike polynomial coefficients that describe monochromatic aberrations. There are built-in filter options to remove rays based on wavelength, number of reflections, or release feature. There is also a new command to automatically define a reference hemisphere centered at the rms focus. You can see this new functionality in the Double Gauss Lens and Newtonian Telescope Structural Analysis models.

An optical aberration plot for the sum of all Zernike polynomials. Optical aberration plot: All Zernike polynomials Sum of all Zernike polynomials in the RMS focus of the double Gauss lens system. The dataset was generated automatically by the COMSOL Multiphysics® software.
An optical aberration plot without the piston and defocus terms. Optical aberration plot: Excluding piston and defocus terms Sum of all Zernike polynomials except for the piston (Z00) and defocus (Z20) terms. It is now easier to see the effect of spherical aberration (Z40).

Cross Grating Feature

Use the new Cross Grating feature to treat a boundary as a periodic substructure with two different directions of periodicity. In contrast, the existing Grating node allows one direction of periodicity and treats the substructure as homogeneous in the orthogonal direction. You can see this new functionality in the Cross Grating Échelle Spectrograph model.

The Cross Grating feature settings in COMSOL Multiphysics with the Equation section open. Cross Grating feature settings Equation display in the Settings window for the new Cross Grating feature.

Grating Improvements

The Grating feature has been significantly upgraded in version 5.5. You can now click an Add Diffraction Orders button to automatically create subnodes for all of the diffraction orders that the grating might release, based on the wavelengths of rays used in the model. Alternatively, you can specify relative diffraction orders for the grating. This is particularly useful in blazed gratings, where the absolute diffraction orders with the lowest relative order numbers are those that show the smallest deviation from the blaze angle. You can see this new functionality in the White Pupil Échelle Spectrograph model.

Air Model for Exterior and Void Domains

You can now treat the empty space outside the geometry, and in unmeshed domains, as air using the built-in Edlen model, which accurately expresses the refractive index of air as a function of temperature and pressure. This allows you to easily model optical systems that have been optimized for atmospheric, rather than vacuum, conditions. As always, exterior and unmeshed domains must be homogeneous. The exterior temperature and pressure are scalar inputs that must apply over the entire region.

The Settings window for the Geometrical Optics feature in COMSOL Multiphysics showing that the Air, Edlen dispersion model has been selected. Geometrical Optics feature settings The Air, Edlen (1953) optical dispersion model can be used in exterior and unmeshed domains.

You can see this new functionality in the following models:

New Release Type: Hexapolar Cone

When you release rays in a cone, a new type of Conical distribution is available: Hexapolar. For the Hexapolar cone option, rays are released at uniformly distributed angles from the cone axis, with each ring having six more rays than the previous one.

Rays released in a cone shape visualized with arrows of rainbow coloring, seen from the side so the arrows point to the right. Hexapolar cone: Side view Hexapolar-cone-based release, side view.
Rays released in a cone shape visualized with arrows of rainbow coloring, seen from the front so the arrows point at the viewer. Hexapolar cone: Front view Hexapolar-cone-based release, front view.

You can see this new functionality in the following models:

Renamed Ray Release Features

Ray release features have been renamed in COMSOL Multiphysics® version 5.5. The Inlet is now called Release from Boundary, and the Inlet on Axis (in 2D axisymmetric models) is now called Release from Symmetry Axis.

The COMSOL Multiphysics UI in version 5.5 showing the Release from Boundary and Release from Symmetry Axis ray release features. Showing the updated ray release feature names Choice of boundary features in the Geometrical Optics interface in a 2D axisymmetric geometry.

New Polygonal Mirror Parts

You can now add polygonal mirrors to the geometry using the Part Libraries for the Ray Optics Module. The new polygonal mirrors are named Spherical Polygonal Mirror 3D, Conic Polygonal Mirror On Axis 3D, and Conic Polygonal Mirror Off Axis 3D. You can see the Conic Polygonal Mirror Off Axis 3D part used in the Keck Telescope model.

Sixteen polygonal mirror parts shown in yellow and gray. Polygonal mirror parts The new polygonal mirror parts are similar to the existing mirror parts. The number of sides and the orientation of the resulting polygon can be specified. Spherical, on-axis conic, and off-axis conic polygonal mirrors are all possible.

Aspheric Lens and Mirror Parts

The aspheric lenses and mirrors in the Part Libraries for the Ray Optics Module have been revised, and several new parts are available:

  • Aspheric Even Lens 3D (improved replacement for the Aspheric Lens 3D, which has moved to legacy parts)
  • Aspheric Even Mirror 3D
  • Aspheric Odd Lens 3D
  • Aspheric Odd Mirror 3D
  • Aspheric Q-type Qbfs Lens 3D
  • Aspheric Q-type Qbfs Mirror 3D
  • Aspheric Q-type Qcon Lens 3D
  • Aspheric Q-type Qcon Mirror 3D

Here, "Q-type" indicates a type of orthogonal polynomial basis that is used to define the lens or mirror surface sag. "Qbfs" and "Qcon" indicate that the polynomials describe the deviation from a "best-fit sphere" and a conic, respectively. The advantage of defining Q-type aspheres over the even and odd aspheres is that all of the polynomial coefficients have about the same order of magnitude, so there is less risk of numerical error due to roundoff. You can see the Aspheric Even Lens 3D used in the Compact Camera Module and Schmidt Cassegrain Telescope models.

Doublet and Triplet Lens Parts

Two new multiplet lens parts are now available in the Part Libraries for the Ray Optics Module: Spherical Doublet Lens 3D and Spherical Triplet Lens 3D. For both of these parts, you can specify whether the individual lenses are cemented together or if there is an air gap between them. You can see the Spherical Doublet Lens 3D in the Cross Grating Échelle Spectrograph model.

The 3D spherical doublet lens part shown in gray alongside a diagram. Doublet lens part The Spherical Doublet Lens 3D part.
The 3D spherical triplet lens part shown in gray alongside a diagram. Triplet lens part The Spherical Triplet Lens 3D part.

Preview Grid Release Positions

When you release particles from a grid of points using the Release from Grid feature, you can now preview the initial particle positions in the Graphics window. In the Initial Coordinates section of the Settings window, click the Preview Initial Coordinates button to view the initial particle coordinates as a grid of points. Click the Preview Initial Extents button to view the spatial extents of the initial coordinates as a bounding box. These buttons allow you to check the initial particle positions before running a study.

In addition, when you right-click a Study node and click Get Initial Value, you can preview the initial particle positions and velocities for all release types.

The COMSOL Multiphysics UI showing a model where the initial particle coordinates are viewed as a grid of points. Initial particle coordinates viewed as a point grid Graphics window after clicking the Preview Initial Coordinates button.
The COMSOL Multiphysics UI showing a model where the spatial extents of the initial particle coordinates are shown as a bounding box. Initial particle coordinates' spatial extents Graphics window after clicking the Preview Initial Extents button.

Isotropic Scattering Wall Condition

You can now select Isotropic scattering as the wall condition when particles hit boundaries in the geometry. Like the Diffuse scattering condition, the Isotropic scattering condition causes particles to be reflected with randomly sampled velocity directions around the surface normal. However, whereas the Diffuse scattering condition uses a probability distribution based on the cosine law, the Isotropic scattering condition follows a probability distribution that gives equal flux across any differential solid angle in the hemisphere.

The diffuse scattering wall condition is compared to the isotropic scattering wall condition. Scattering wall condition comparison Comparison of the diffuse (left) and isotropic (right) scattering wall conditions. Each side shows a distribution of 1000 particles.

New Tutorial Models and Applications

Version 5.5 brings several new tutorial models and applications.