## Ray Optics Module

### New App: Distributed Bragg Reflector (DBR) Filter

A distributed Bragg reflector (DBR) consists of multiple alternating layers of two materials. Each material has a different refractive index, resulting in a repeating pattern of high and low refractive index in the direction perpendicular to the DBR layers. As light propagates through this structure, reflections occur at each interface between the layers. This application computes the reflectance of a DBR filter for a distribution of free-space wavelengths. Either a band-stop filter or a notch filter can be analyzed. The user inputs include the refractive index of each layer, the number of periods in the DBR, and the threshold reflectance within the stopband.

*Reflectance of a DBR filter as a function of free-space wavelength. The user inputs include the refractive index of each layer, the number of periods in the DBR, and the threshold reflectance within the stopband.*

Reflectance of a DBR filter as a function of free-space wavelength. The user inputs include the refractive index of each layer, the number of periods in the DBR, and the threshold reflectance within the stopband.

### Part Library for the Ray Optics Module

In order to facilitate fast and efficient geometry set-up for ray optics modeling, the Ray Optics Module includes a part library with predefined geometry components. The part library includes a variety of cylindrical and spherical lenses, cemented doublets, a beam splitter, paraboloidal reflectors, prisms, and a corner cube retroreflector. All parts are fully parameterized, making them easy to use in simulations of large-scale industrial applications.

*Ray propagation in a system of three spherical equiconvex lenses and a beam splitter. Each of these entities is available as a fully parameterized part from the Part Library.*

Ray propagation in a system of three spherical equiconvex lenses and a beam splitter. Each of these entities is available as a fully parameterized part from the Part Library.

### Polarization Ellipses

It is now possible to plot ellipses along trajectories in the Ray Trajectories plot. When the ray intensity is computed, the default expressions for the semi-major and semi-minor axes are predefined variables to indicate the polarization ellipse. The ellipse will appear as a line for linearly polarized rays and will not appear at all for completely unpolarized rays. When elliptically or circularly polarized rays are shown, arrows around the perimeter of the ellipse can be used to distinguish between left- and right-handed polarization.

*Linear wave retarder: An unpolarized ray passes through two linear polarizers and a quarter-wave retarder. The transformations to linearly and circularly polarized light can be seen by plotting polarization ellipses along the ray.*

Linear wave retarder: An unpolarized ray passes through two linear polarizers and a quarter-wave retarder. The transformations to linearly and circularly polarized light can be seen by plotting polarization ellipses along the ray.

### Ray Heating Multiphysics Interface

The new* Ray Heating* interface is a dedicated Multiphysics interface that uses the *Geometrical Optics* and *Heat Transfer in Solids* interfaces to compute temperature changes as rays propagate through absorbing media. It automatically adds the new *Ray Heat Source* Multiphysics coupling and applies the computed heat source to the temperature computation.

### New Study for Bidirectional Ray-Thermal Coupling

Simulation of ray heating requires a two-way coupling between ray tracing and temperature calculation. As the rays are attenuated, they contribute to a heat source that affects the temperature. Conversely, as the temperature changes, the ray trajectories may change if the domains undergo thermal deformation or if the refractive index depends on temperature or strain. A two-way coupling between ray tracing and temperature can be set up using an iterative solver loop in which the ray trajectories and temperature are computed in alternating steps. This solver loop can now be set up automatically via the *Bidirectionally Coupled Ray Tracing* study step. This study step computes all ray variables using one solver and all other variables using another solver. These two solvers are arranged in a loop that runs for a user-defined number of iterations.

*Ray trajectories and temperature (left) and deformation (right) in two lenses that focus a high-powered laser beam. Thermally induced focal shift can be simulated more easily by using the Ray Heat Source Multiphysics coupling and the Bidirectionally Coupled Ray Tracing study step.*

Ray trajectories and temperature (left) and deformation (right) in two lenses that focus a high-powered laser beam. Thermally induced focal shift can be simulated more easily by using the Ray Heat Source Multiphysics coupling and the Bidirectionally Coupled Ray Tracing study step.

### Improved Accumulators

The domain-level* Accumulator* feature is faster, more accurate, and is no longer sensitive to the size of the time steps taken by the solver. As a result, simulations of thermal deformation in high-powered laser focusing systems may be more than ten times faster in some cases, as compared to similar models in version 5.0, while also becoming more accurate. In addition, new options are available for determining how the accumulated variables are computed when a ray crosses over a large number of mesh elements.

### Release Rays from a Text File

The initial positions and directions of rays can now be imported from a text file by using the* Release from Data File* node.

### Intensity in Graded Media

It is now possible to compute the intensity of rays in graded media. The intensity in a graded medium can be computed by selecting a new *Intensity computation* option from the *Geometrical Optics* settings window. The following options are now available:

*None*– Do not compute intensity.*Using principal curvatures*– The most accurate intensity computation method, but only applicable to homogeneous (i.e., constant refractive index) media.*Using principal curvatures and ray power*– Like*Using principal curvatures*, but creates additional variables that can be used to compute deposited ray power on domains or boundaries.*Using curvature tensor*– Can be used to compute intensity in both homogeneous and graded media. In completely homogeneous media, the option*Using principal curvatures*is slightly more accurate.*Using curvature tensor and ray power*– Like*Using curvature tensor*, but creates additional variables that can be used to compute deposited ray power on domains or boundaries.

### New Options for Applying Thin Dielectric Films

The options for specifying the properties of thin dielectric films at material discontinuities have been greatly expanded. It is now possible to automatically generate a single-layer dielectric film such that the reflectance or transmittance for rays of a given frequency, polarization, and direction can be obtained. There is also a new shortcut for creating anti-reflective coatings at boundaries between different media. When setting up a multilayer film by adding *Thin Dielectric Film* subnodes to a surface, it is possible to make some layers periodic, allowing complex multilayer films containing hundreds of layers to be set up with only a small number of *Thin Dielectric Film* subnodes.

*With improvements to the treatment of multilayer films, it is now possible to parameterize the number of layers in a distributed Bragg reflector. As the number of layers increases, the reflectance within the stopband approaches 100%.*

With improvements to the treatment of multilayer films, it is now possible to parameterize the number of layers in a distributed Bragg reflector. As the number of layers increases, the reflectance within the stopband approaches 100%.

### Improved Support for Frequency-Dependent Material Properties

In geometrical optics models, it is now possible to specify material properties that are dependent on the ray frequency or another ray property directly in the *Material* settings window, instead of the* Medium Properties* settings window. To do so, all ray properties must be contained within the new noenv() operator, which allows quantities that exist only on rays to be included in expressions defined on domains.

### New Tutorial: Transparent Light Pipe

Light pipes are structures that can be used to transport light between different locations. In general, they can be divided into two major groups: tubes lined with a reflective coating and transparent solids that contain light via total internal reflection. In this example, light is transported through a bent light pipe by total internal reflection. The effect of the pipe shape on the transmittance is investigated.