Lenses

Lenses are fundamental optical components used to focus or diverge light, making them essential for constructing imaging systems. The BeamletOptics.AbstractRefractiveOptic type provides a general definition of components that refract light. This package includes a variety of rotationally symmetric lens models to simulate simple imaging setups. All lens models provided as part of this package are based on SDFs. Refer to the Signed Distance Functions (SDFs) section for more information.

A concrete implementation is provided by the Lens type.

Lens{T, S <: AbstractShape{T}, N <: RefractiveIndex} <: AbstractRefractiveOptic{T, S, N}

Constructing lens shapes

In practice, a great variety and mixture of different lens shapes exists – e.g. spherical and aspherical lenses surfaces and all combinations thereof. Usually a lens is a block of a transparent, dielectric material with two optically active surfaces (fancy special cases using the sides of the lens as well exist, e.g. for HUD displays). It is common to describe such a lens by specifying the properties of the two surfaces and the material in between. This package, however, works with closed volume shapes for all of its optical elements and any erroneous (i.e. non-watertight) SDF might result in unphysical behaviour. Refer to the Geometry representation section for more information.

Surface based lens construction

To make it easier to specify lenses similar to established optical simulation frameworks, e.g. Zemax, the BeamletOptics.AbstractSurface API can be used. This is a helper interface for surfaces specifications and interprets them to the corresponding SDF-based volume representation.

Currently the following surface types are implemented:

julia> BeamletOptics.list_subtypes(BeamletOptics.AbstractSurface);└── BeamletOptics.AbstractSurface
    ├── BeamletOptics.AbstractCylindricalSurface
    │   ├── BeamletOptics.AbstractAcylindricalSurface
    │   │   └── AcylindricalSurface
    │   ├── CylindricalSurface
    │   └── RectangularFlatSurface
    └── BeamletOptics.AbstractRotationallySymmetricSurface
        ├── CircularFlatSurface
        ├── EvenAsphericalSurface
        └── SphericalSurface

At least 9 types have been found.

A Lens can be then constructed with the following function call:

 Lens(front_surface::AbstractRotationallySymmetricSurface, back_surface::AbstractRotationallySymmetricSurface, center_thickness::Real, n::RefractiveIndex)

Lens constructor example

In practice, this works as follows: the bi-convex LB1811 lens consists of two spherical surfaces and can be constructed like this:

# refractive index of NBK7 for 532 and 1064 nm
NBK7 = DiscreteRefractiveIndex([532e-9, 1064e-9], [1.5195, 1.5066])

# lens diameter
d = BeamletOptics.inch

# lens types
r1 = 34.9e-3
r2 = -34.9e-3
l = 6.8e-3
LB1811 = Lens(
    SphericalSurface(r1, d),
    SphericalSurface(r2, d),
    l,
    NBK7
)

SDF-based spherical lenses

In order to model the lens surfaces shown above, the following SDF-based spherical lens shapes have been implemented:

• BeamletOptics.ConvexSphericalSurfaceSDF
• BeamletOptics.ConcaveSphericalSurfaceSDF
• BeamletOptics.MeniscusLensSDF
• BeamletOptics.PlanoSurfaceSDF

The BeamletOptics.AbstractSurface will translate surface specifications into volume representations using the sub-volumes above. This is achieved by combining the sub-volumes via the BeamletOptics.UnionSDF-API in order to enable the quasi-surface-based design of spherical lens systems. Additional distance functions have been implemented in order to model aspherical and cylinder lenses.

Spherical lenses

Spherical lenses are characterized by surfaces with constant curvature, making them straightforward to model and ideal for basic imaging applications. The SphericalLens constructor can be used in order to define this lens type in a concise manner.

SphericalLens(r1, r2, l, d=1inch, n=λ->1.5)

Below, several spherical lenses are recreated from manufacturer data.

• GaussianBeamlet parameters
  • $w_0 = 5~\text{mm}$
  • $\lambda=532~\text{nm}$
• Lenses (in order of appearance)
  • LD1464
  • LB1811
  • LC1715
  • LE1234
  • LA1805

The spherical lenses are shown below. To recreate this figure, refer to the Spherical lens example.

Aspherical lenses

Aspherical lenses offer more advanced control over aberrations, enabling higher performance in specialized optical systems. The package offers surface support for rotationally symetrical aspheric lenses that adhere to the DIN ISO 10110 convention with even terms.

To construct a lens with any possible combination of convex/concave, spherical/aspherical surfaces you can use the Lens constructor with the EvenAsphericalSurface surface specification type.

A complex example of such a lens might look like the following example. This lens has the following peculiarities:

• The front surface is an aspherical convex surface with a clear diameter smaller than the full mechanical diameter
• The back surface is an aspherical concave surface which first curves outwards before change slope and curving invards, giving a more "convex" like character while still beeing a concave lens by definition. Also this surface extends towards the full outer diameter.

L3 = Lens(
    EvenAsphericalSurface(
        3.618e-3,               # r
        3.04e-3,                # d
        -44.874,                # conic
        [0,-0.14756*(1e3)^3, 0.035194*(1e3)^5, -0.0032262*(1e3)^7,
        0.0018592*(1e3)^9, 0.00036658*(1e3)^11, -0.00016039*(1e3)^13,
        -3.1846e-5*(1e3)^15]    # coeffs
    ),
    EvenAsphericalSurface(
        2.161e-3,               # r
        3.7e-3,                 # d
        -10.719,                # conic
        [0,-0.096568*(1e3)^3, 0.026771*(1e3)^5, -0.011261*(1e3)^7,
        0.0019879*(1e3)^9, 0.00015579*(1e3)^11, -0.00012433*(1e3)^13,
        1.5264e-5*(1e3)^15]     # coeffs
    ),
    0.7e-3,                     # center_thickness
    n -> 1.580200               # refractive index
)

Cylindrical lenses

Cylindrical lenses are non-rotationally symmetric lenses where a spherical or aspherical curvature is present only in one dimension, i.e. leading to a cylindrical shape. Thus, they focus or collimate light only in one dimension. This package currently supports convex/concave cylindrical and acylindrical lenses with an even aspheric deviation from the cylindrical shape.

A plano-convex cylindrical lens can be constructed in the following way. Note that for this lens type a plano-surface can be constructed by passing a RectangularFlatSurface to the lens constructor:

r = 5.2e-3  # radius
d = 10e-3   # diameter/width of the cylindric portion
h = 20e-3   # height/length of the cylinder
ct = 5.9e-3 # center thickness
lens = Lens(
    CylindricalSurface(r, d, h),
    ct,
    n -> 1.517
)

An acylindrical lens can easily be constructed using the AcylindricalSurface surface type:

radius = -15.538e-3
diameter = 25e-3
height = 50e-3
conic_constant = -1.0

lens = Lens(
    BeamletOptics.AcylindricalSurface(
            radius,
            diameter,
            height,
            conic_constant,
            [0, 1.1926075e-5*(1e3)^3, -2.9323497e-9*(1e3)^5, -1.8718889e-11*(1e3)^7, -1.7009961e-14*(1e3)^9, 3.5481542e-17*(1e3)^11, 6.5241296e-20*(1e3)^13]
        ),
        7.5e-3,
        n -> 1.777
    )

Doublet lenses

The DoubletLens is an example for a multi-shape object as mentioned in the Multi-shape objects section. For spherical doublet lenses the following constructor can be used.

SphericalDoubletLens(r1, r2, r3, l1, l2, d, n1, n2)

The following image shows the AC254-150-AB doublet lens for 488 and 707 nm. It has been created using the SphericalDoubletLens constructor shown above.