Optical integrated aperture imaging involves an array of objects in a certain form based on multiple small aperture sub-mirrors arranged in a certain form. Its imaging resolution can be equivalent to that of a large-aperture lens, which is widely used in astronomy, medicine, commerce, military scientific research, and other fields. Resolving the problems of loading error and environmental engineering requires independent static or dynamic phase compensatory adjustment for each sub-mirror to meet the phase modulation accuracy requirement of 0.1λ (λ is the wavelength of incident light)or the higher requirement. Liquid optical devices have potential application prospects owing to their compact structure, light weight, and low price, and they do not require mechanical devices. A piezoelectric ceramic tube has the advantages of high sensitivity, good linearity, strong integration, and easy control. Furthermore, the tube can be filled with clear liquid and its length is adjustable, providing a new approach for the preparation of liquid optical phase modulators. Much research has been conducted on magnesium alloy liquid optical devices and good results have been achieved. However, further research is necessary to make practical engineering applications possible and new liquid optical phase modulators must be developed.

Transparent liquid is filled into the cavity of a piezoelectric ceramic tube. The length of the liquid produces a micrometer-level displacement change because of the inverse piezoelectric effect. Then, encapsulation and illumination are performed in the cavity length direction and the optical phase produces little change. A piezoelectric ceramic tube with an inner diameter of 15 mm, outer diameter of 20 mm, and height of 12 mm is filled with methyl silicone oil and encapsulated with a gasket, an upper cover sheet, and an lower cover sheet. Finally, a Michelson interferometer is used to observe and analyze the accuracy, range, response time, and other performance characteristics of the phaser.

First, integer fringes are detected using fixed-line grayscale values. Alignment gray value detection involves making a horizontal reference line in the middle of the interference image and recording all gray values on the reference line. These gray values can reflect the intensity change trend of the interference fringes. Then, the curve is detected and recorded once at a certain voltage interval, and a series of curves of the relationship between the gray values and the position of the fringes are obtained. The differences between the positions of the dark and bright fringes are compared; as a result, the phase shift can reflect the relationship between the shift of phase and the voltage (Fig. 6). The interference fringes are recorded, and an extreme value of the grayscale curve appears every 7.0 V interval, which can be understood as a first-order shift of the interference fringe, indicating that the optical path is adjusted by λ/2 (Fig. 7). Moreover, the fixed-line grayscale values are used to detect the fractional fringes, and the interference fringes can move in one direction under the driving voltage. The fractional counting of interference fringe can be achieved by comparing the movement of the fringes in a single cycle and calculating the movement of a fringe relative to the previous position (Fig. 8). The variation curve of the optical path of phase modulator with the applied voltage measured at 0-28 V shows the good linear relationship (Fig. 9). The measured phaser response time is 7 ms (Fig. 10).

To meet the high-precision requirements and achieve a large adjustment range, a liquid optical phase modulator is constructed by filling the transparent liquid into a piezoelectric ceramic tube. Optical phase adjustment is performed through a small electric displacement generated by the piezoelectric effect in the light-transmitting direction. The piezoelectric ceramic tube filled with transparent liquid is used as the core structure of transmissive optical phase modulator. The optical phase modulation devices in this study are not only compact and significantly reduced in cost but also have high precision and a wide range. An experiment is conducted using the fixed-line grayscale values and a Michelson interferometer with a wavelength of 632.8 nm. Under a voltage of 0-28 V, the phase modulator can reach a modulation range of 0-4π and an accuracy of λ/36. When the applied voltage is 150 V, the modulation range can be expanded to 20π. This meets the requirements of optical synthetic aperture subaperture phase modulation.