Application Cases

Experiment Name: Liquid Crystal Lens Performance Testing

Test Purpose: As a focusing element in imaging systems, the optical performance of liquid crystal lenses is crucial. Since the refractive index distribution of a liquid crystal lens changes with the electric field distribution of the control electrodes, its imaging quality also varies. Therefore, selecting an appropriate control voltage is a critical step for the practical application of liquid crystal lenses in various scenarios. Choosing suitable testing methods to evaluate the optical performance of liquid crystal lenses under different conditions and determining the optimal voltage state is one of the preparatory tasks before conducting imaging experiments with liquid crystal lenses.

Test Equipment: High-voltage amplifier, function generator, detector, liquid crystal lens, computer, etc.

Experimental Process:

Figure 1: Experimental interference optical path diagram

The experiment consists of two parts: data acquisition and data analysis. First, images containing wavefront information are obtained through the interference optical path, and then the wavefront fitting values are analyzed using software.

The Mach-Zehnder interference optical path was used to acquire the wavefront data of the liquid crystal lens. The optical path structure is shown in Figure 1. A 532 nm laser beam passes through a beam expander and a polarizer to become linearly polarized light aligned with the extraordinary light direction in the liquid crystal lens. The beam spot size is sufficient to cover the liquid crystal lens area. The beam is split into two paths by a beam splitter, each equipped with an adjustable mirror. The liquid crystal lens is placed in one of the paths. The two beams are recombined by mirrors and interfere at the beam splitter, which directs the combined beam to a CMOS detector through an imaging lens that presents a clear image of the liquid crystal lens.

The driving system of the liquid crystal lens consists of a function generator and a high-voltage amplifier. The signal from the function generator is amplified 10 times by the high-voltage amplifier and used to control the voltage of the liquid crystal lens. The function generator's signal is programmed and controlled by a computer to change in specific steps, synchronizing with the detector to capture images automatically. Ultimately, a series of wavefront state data images of the liquid crystal lens under different driving voltages are obtained.

The interference fringes of the liquid crystal lens obtained through the Mach-Zehnder interference optical path are analyzed using a program. After processing with algorithms such as filtering, envelope removal, and Zernike polynomial fitting, the wavefront fitting of each image is obtained. The optical power and root mean square (RMS) aberration of the liquid crystal lens are calculated from the coefficients of the Zernike polynomial. By analyzing the interference fringes of the liquid crystal lens under a series of different voltages, the optical power and RMS aberration under various driving conditions are derived, and the relationships between voltage, optical power, and aberration are plotted.

Experimental Results:

Figure 2: Relationship between optical power and liquid crystal lens voltage

Figure 3: Relationship between RMS aberration and liquid crystal lens voltage

The experimental results are shown in the figures below. Figure 2 is a pseudocolor map showing the trend of optical power of the liquid crystal lens with control voltage. Since the liquid crystal lens used in the experiment is controlled by two voltages, the horizontal axis represents the voltage V1 of the circular electrode outside the liquid crystal lens area, and the vertical axis represents the voltage V2 of the circular electrode inside the liquid crystal lens area. The optical power of the liquid crystal lens is indicated by the grayscale intensity. The results show that the optical power of the liquid crystal lens varies between -6.5 and +7 Diopter within the driving voltage range of 100 V. Figure 3 shows the RMS aberration under different driving voltage states. Similar to the left figure, the horizontal and vertical axes represent the effective values of the two driving voltages, and the color indicates the RMS aberration of the liquid crystal lens under the corresponding voltage distribution. The suitable working range of the liquid crystal lens is selected based on the aberration size during the experiment.

By measuring and fitting the wavefront distribution of the liquid crystal lens, the optical power and RMS aberration under different driving conditions are obtained. The experiment shows that the optical power variation range of the liquid crystal lens device is -6.5 to +7 Diopter within 100 V. When the RMS aberration is less than 0.1 wavelength, the working range of the liquid crystal lens is -6.4 to +4.1 Diopter.

High-Voltage Amplifier Recommendation: ATA-7020

Figure: ATA-7020 High-Voltage Amplifier Specifications

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