This article describes how to use and integrate Corning® Varioptic® Liquid Lenses into an optical design in Ansys Zemax OpticStudio. There are different liquid lenses available with various clear apertures, yet they all have a similar construction to the example detailed in this document.
Authored By Xavier Berthelon, PhD (Optical Engineer with Corning)
What Systems Use Liquid Lenses?
Corning Varioptic lenses are optical devices that adjust voltage to change the shape of a liquid interface. This technology is used in high-demand industrial imaging applications that require focus adjustment to image objects at different depths. While traditional autofocus systems rely on the mechanical movement of the lens module to adjust the back focal length, liquid lens-based systems have no moving parts. The bulky and fragile motors are replaced by a single opto-electrical component that can endure hundreds of millions of cycles and perform autofocus at great speed with high optical quality. Liquid lenses can be found in many markets such as barcode readers, consumer devices, lasers, machine vision, biometrics, or even AR/VR.
General Presentation
A typical Zemax model of an adjustable lens is provided as an attachment to this article. It is composed of 8 surfaces, namely the two glass windows (shown below: a Schott glass D263T eco, Surface 3 and 7), the conductive phase (Surface 4), the oil phase in the conical part of the liquid lens (Surface 5) and the oil phase in the cylindrical part (Surface 6). Surface 2 is a virtual surface that represent the package top surface. Surface 9 is the package bottom surface.
Corning uses ZPL macros to fully describe the liquid lens behaviour as a function of its optical power. The ZPL macros are applied to the lens as a ZPL Solve. More information about ZPL Solves may be found in the Zemax help file "The Programming Tab...About the ZPL...Using ZPL Macro Solves."
The optical power of these lenses is described using three different macros. The macros are applied to the Radius (C), the conductive phase Thickness (T) and the Clear Semi-Diameter (U). Additionally, a Thickness Solve is applied to solve for oil thickness. Its value is given as a function of the conductive phase thickness and the total thickness between the windows. It is used to ensure the distance between the two glass windows (thickness 4 + thickness 5) remains the same when the variable thickness for conductive phase changes.
Note: For liquid lenses’ model with variable astigmatism, an additional ZPL macro (A) drives the cylindrical power of the liquid-liquid interface.
Changing Adjustable Lens Optical Power
To change the optical power, the designer must change the variable optical power used by the macros which is set by the Multi Configuration Editor (MCE). In Figure 3, the optical power is set to 5. This is aligned with the power described in the Comment cell of Surface 1 (coincident with surface 2, as shown in Figure 2).
After changing the value and pressing enter, the four solves described above will be updated along with the optical power.
ZPL Macro
The ZPL Macro solves used by the model are provided within the Zemax Project (ZPRJ) file attached to the article. Upon opening the ZPRJ file, the macros will either be placed in the Zemax\Macros folder or the <Your project directory>\Macros folder, depending on the settings you apply when opening the file. For more information on how to use a Zemax Project file, see this article: Using Project Directories to organize OpticStudio files.
Each of the macro names can be found by clicking on the Z letter next to the numerical value (Figure 4 below). In the example below, the macro name for radius of curvature is “C_A25H0_PO”.
Details of each command used within the macros can be found in the Zemax help file under "The Programming Tab...About the ZPL."
Note: Two additional lines of code are present in the curvature macro. Their purpose is to paste the optical power set from the Multi Configuration Editor into one of the Comment cells.
SOLVEBEFORESTOP
p = parm(0,0)
A$ = "Conductive phase"
SURF1 = SURC(A$)
C$ = "Oil bodycone"
SURF2 = SURC(C$)
n1 = INDX(SURF1)
n2 = INDX(SURF2)
n = n2 - n1
b$ = "Lens power: "+$str(p)+" Diopters"
q = p / (1000 * n)
SURP 1,1,b$
SOLVERETURN(q)
Building an optical system with a liquid lens
There are two ways to design an optical system with a variable focus liquid lens. The best practice is to position the liquid lens at the STOP aperture of the optical system. For front-aperture systems, the liquid lens can be placed on top of an existing stack of lenses. Such systems are called add-on designs. When the STOP aperture is located inside the optical stack, then the liquid lens should be positioned between front and rear groups. Such designs are called add-in designs.
Below is an example of add-in design with the A-39N0-A1 liquid lens:
The materials used by the sample file are custom, so are not provided as part of a standard Zemax installation. More information on the materials can be found in the Materials Catalog provided with the liquid lens file. Optical indices are fitted on the range 365nm to 950nm.
Optimizing a system containing a liquid lens
To optimize an optical system with a liquid lens, the radius of curvature of the liquid/liquid meniscus can be set as variable. In the Multi-Configuration Editor, it is recommended to define multiple focus positions for the object (THIC operand for surface 0) and set the liquid lens’ optical power (PRAM 0/0) as a variable for each focus position.
The user can then define any Merit Function target using the Optimization Wizard and perform an optimization to find the best optical power for each focus position.
Below is an example of the MTF chart before (top) and after (bottom) the lens optimization for an optical system containing a liquid lens.
Conclusion
In this article, a method for simulating Corning's Varioptic Liquid Lenses was introduced and a sample file was provided. All product documentation regarding these lenses may be found on the Corning website, here: https://www.corning.com/worldwide/en/products/advanced-optics/product-materials/corning-varioptic-lenses.html
For additional information on Corning liquid lenses and related products, or specific requests for a custom design, you can contact us by email at varioptic@corning.com. At Corning Varioptic, we offer different level of support for your projects: from simple assistance during your design phase to a complete all-inclusive solution that covers design, prototyping and mass production.