Apply Optical Coatings

Optical coatings are stacks of thin films made from specific optical materials, designed to control reflection and transmission of light within an optical system. You can design, edit, and apply optical coatings to lens and mirror surfaces in an optical system using the Optical Design and Simulation Library for Image Processing Toolbox™. You can perform reflectance, transmittance, and absorbance analysis for optical coating design with specific wavelength, incident light angle, and polarization requirements.

To apply optical coatings, follow these steps:

  1. Use Optical Coating Materials

  2. Create Custom Optical Coatings

  3. Manage Optical Coating Library

  4. Visualize Coating Optical Response

  5. Apply Coating to Surfaces

You can install the Optical Design and Simulation Library for Image Processing Toolbox from the Add-On Explorer. For more information about installing add-ons, see Get and Manage Add-Ons.

Use Optical Coating Materials

You can select an existing optical coating material from the coating material library, or create a custom optical coating material, and add it to the library.

Use Material from Coating Library

To use an optical coating material from the default coating material library, use the coatingMaterialLibrary object. The default materials in the coating library are Al2O3, GdF3, HfO2, MgF2, SiO2, TiO2, Al, Ag, and Au.

Load the default coating library.

cml = coatingMaterialLibrary
cml = 

  CoatingMaterialLibrary with properties:

    CoatingMaterialCatalogTable: [2×3 table]
               CoatingMaterials: [10×1 opticalMaterial]

Inspect the properties of a material in the default coating material library, by extracting it using the pickCoatingMaterial function.

ocm = pickCoatingMaterial("TiO2")
ocm = 

  opticalMaterial with properties:

   Main Properties
                               Name: "TiO2"
                            Catalog: "RefractiveIndex.INFO"
                                 Nd: 2.3247
                                 Vd: 12.5465
                    WavelengthRange: [0 Inf]

   Extended Properties
              RefractiveIndexMethod: "LookupTable"
           RefractiveIndexParameter: [609×2 double]
    ExtinctionCoefficientParameters: [609×2 double]
                     RawCatalogData: [1×1 struct]

Create Custom Coating Material

Create a custom coating material by using an opticalMaterial object. Set the optical properties by specifying the index of refraction and Abbe number, make the material retrievable using pickCoatingMaterial function by setting the Name property, and add the material to a material catalog by setting the Catalog property.

newMat = opticalMaterial([1.43 95.23],Name="CaF2",Catalog="New")
newMat = 

  opticalMaterial with properties:

   Main Properties
                        Name: "CaF2"
                     Catalog: "New"
                          Nd: 1.4300
                          Vd: 95.2300
             WavelengthRange: [0 Inf]

   Extended Properties
       RefractiveIndexMethod: "AbbeNumber"
    RefractiveIndexParameter: [1.4300 95.2300]
      TransmissionParameters: [587.5618 1 1]
              RawCatalogData: [1×1 struct]

Add Custom Optical Material to Coating Material Library

To use a custom material for optical coating layers, you must first add the material to the coating material library. Use the addCoatingMaterial function to add the custom optical material to the coating material library.

addCoatingMaterial(cml,newMat)

To inspect the properties of the custom optical material after you have added it to the coating material library, you can use the pickCoatingMaterial function. Note that the catalog matches the coating material catalog specified when creating the material.

ocm_CaF2 = pickCoatingMaterial("CaF2")
ocm_CaF2  = 

  opticalMaterial with properties:

   Main Properties
                        Name: "CaF2"
                     Catalog: "New"
                          Nd: 1.4300
                          Vd: 95.2300
             WavelengthRange: [0 Inf]

   Extended Properties
       RefractiveIndexMethod: "AbbeNumber"
    RefractiveIndexParameter: [1.4300 95.2300]
      TransmissionParameters: [587.5618 1 1]
              RawCatalogData: [1×1 struct]

Once you have the coating materials required for your application in the coating library, you can create your optical coating.

Create Custom Optical Coatings

You can use the opticalCoating object to create a multilayer coating. Create a custom Bragg reflector coating by specifying the coating layer materials using the CoatingMaterials property, the design wavelength using the PrimaryWavelength property, and the layer thicknesses using the LayerThickness property. Specify the units of the optical coating layer thicknesses using the ThicknessUnit property.

The opticalCoating object also has properties that enable you to specify the incident light angle range, ambient medium type, substrate type, and operational wavelength range.

ocBragg = opticalCoating(Name="Bragg_500nm", ...
    CoatingMaterials=["CaF2","TiO2"], ...
    PrimaryWavelength=500, ...
    LayerMaterialIndex=repmat([1 2],[1 6]), ...
    ThicknessUnit="quarterWavelength", ...
    LayerThickness=ones(1,12));

This coating has 12 layers, with bilayer stacks of CaF2 and TiO2, materials with low and high indices of refraction, respectively, each repeating 6 times. Each layer is exactly a quarter of the primary wavelength, or λ/4 at 500 nm, in optical thickness. This figure shows the structure of the layer stacks that comprise the coating.

Optical coating stack schematic, showing alternating layers of CaF2 and TiO2 thin film coatings.

Create another custom coating, a broadband anti-reflective (AR) optical coating that consists of two alternating SiO2 and TiO2 bilayer stacks.

ocBBAR = opticalCoating(Name="BBAR_4l", ...
    CoatingMaterial = ["TiO2","SiO2"], ...
    LayerMaterialIndex = [1 2 1 2], ...
    ThicknessUnit = "nm", ...
    LayerThickness = [14.6 36.5 129.1 95.5]);

Manage Optical Coating Library

Use coatingLibrary to load and manage the library of available optical coatings. You can add or remove a custom coating from the coating library using the addCoating or removeCoating object function of the coatingLibrary object, respectively. To delete all custom coatings and restore the coating library to its default state, you can use the restoreDefaultCoatingLibrary function.

To add a custom coating to the coating library, first load the default coating library by creating a coatingLibrary object. The default optical coating library contains two Bragg reflector coatings. 

cl = coatingLibrary
cl = 
  CoatingLibrary with properties:

    CoatingCatalogTable: [1×3 table]
               Coatings: [2×1 opticalCoating]

Add the custom Bragg reflector and broadband AR coatings to the coating library.

addCoating(cl,[ocBragg ocBBAR])

Inspect the properties of the custom Bragg coating using the pickCoating function.

pickCoating("Bragg_500nm")
ans = 

  opticalCoating with properties:

                  Name: "Bragg_500nm"
    IncidentAngleRange: [0 15]
       WavelengthRange: [300 800]
     PrimaryWavelength: 500
                Medium: [1×1 opticalMaterial]
             Substrate: [1×1 opticalMaterial]
      CoatingMaterials: [2×1 opticalMaterial]
    LayerMaterialIndex: [1 2 1 2 1 2 1 2 1 2 1 2]
        LayerThickness: [1 1 1 1 1 1 1 1 1 1 1 1]
         ThicknessUnit: "quarterWavelength"
             NumLayers: 12
        TotalThickness: 827.0304

Visualize Coating Optical Response

To create spectral response plots for your optical coating, you can compute the reflectance (R), transmittance (T), and absorbance (A), as well as the reflection (r) and transmission (t) amplitude coefficients, using the fresnelCoefficients object function. Then, use these quantities to create custom spectral response visualizations.

For example, compute the optical response coefficients for the custom coating ocBragg at an incident light angle of 21 degrees.

coeffs = fresnelCoefficients(ocBragg,IncidentAngles=21);

Define the operational wavelength range for the coating.

lambda = ocBragg.WavelengthRange(1):ocBragg.WavelengthRange(2);

Plot the spectral response of the coating as a function of wavelength.

figure
hold on
plot(lambda,coeffs.Rs,"r-",LineWidth=2)
plot(lambda,coeffs.Rp,"r--",LineWidth=2)
plot(lambda,coeffs.Ra,"r:",LineWidth=2)
plot(lambda,coeffs.As,"k-",LineWidth=2)
plot(lambda,coeffs.Ap,"k--",LineWidth=2)
plot(lambda,coeffs.Ta,"b:",LineWidth=2)
plot(lambda,coeffs.Ts,"b-",LineWidth=2)
plot(lambda,coeffs.Tp,"b--",LineWidth=2)

xlabel("\lambda")
ylabel("T/R/A")
text(550,0.8,"\theta_{incident}=21\circ",FontSize=14)

legend({"Rs","Rp","Ra","As","Ap","Ta","Ts","Tp"}, ...
    Orientation="horizontal",Location="southoutside")

xlim([min(lambda),max(lambda)])
ylim([0 1])
hold off

Spectral response plot for custom Bragg reflector coating.

Apply Coating to Surfaces

When you are satisfied with the optical performance of your coating, you can apply it to all lens elements in an optical system simultaneously, or select specific mirror or lens element surfaces to which to apply the optical coating.

First, create an optical system that contains refractive surfaces. Alternatively, you can load an optical system into the workspace using the zmximport function.

opsys = opticalSystem;
addRefractiveSurface(opsys,Radius=10,DistanceToNext=4,Material="N-BK7")
addRefractiveSurface(opsys,Radius=-10,DistanceToNext=2,Material="F2")
addRefractiveSurface(opsys,DistanceToNext=10)
addRefractiveSurface(opsys,Radius=10,DistanceToNext=4,Material="N-BK7")
addRefractiveSurface(opsys,Radius=-10)
addGap(opsys,2)
addImagePlane(opsys)

Display a 2-D visualization of the optical system with labeled surfaces by using the view2d object function.

view2d(opsys,Labels="surface");

Sample optical system to which to add coatings.

Apply Coating to All Lens Elements

To apply a coating to all lens elements in the optical system, use the addCoating object function of the opticalSystem object.

Apply the custom Bragg reflector coating to the back surfaces of all the lens elements in the optical system, surfaces S3 and S5.

addCoating(opsys,ocBragg,CoatingSide="back")

Apply Coatings to Individual Components or Surfaces

To apply a coating to one or both surfaces of a specific lens element or mirror, you must set the Coatings property of that LensElement or Mirror object.

Apply the custom Bragg reflector coating to the first component in the sample optical system opsys, a doublet lens. The function applies the coating to the front surface, S1, of the lens element. The back surface, S3, remains uncoated.

Lens1 = opsys.Components(1);
Lens1.Coatings = ocBragg;

To instead apply different coatings to the front and back surfaces of a lens element with only two surfaces, set the Coatings property as a 2-element row vector of the form [frontCoating backCoating], where frontCoating and backCoating are the front and back coatings of the lens element, respectively, specified as opticalCoating objects.

Apply the Bragg reflector coating to the front surface, S4, and the AR coating to the back surface, S5, of the second lens element in the optical system.

Lens2 = opsys.Components(2);
Lens2.Coatings = [ocBragg ocBBAR];

For a lens with N surfaces, the first N – 1 coatings in the Coatings property apply to the front of each corresponding surface, and the Nth coating applies to the back of surface N.

See Also

Functions

Topics