Variable-focus Lens Research Articles

42 mm large aperture variable-focus lens based on the liquid-membrane-liquid structure

42 mm large aperture variable-focus lens based on the liquid-membrane-liquid structure

High-speed all-in-focus 3D imaging method based on liquid lens focus scanning

A large open aperture in an optical system can capture high-resolution images but yields a shallow depth of field. To overcome this issue, we propose a method for retrofitting microscopy imaging systems by using a variable-focus liquid lens to achieve 3D focus scanning. Specifically, the focal length of the imaging system was changed by controlling the liquid lens, and a sequence of images was captured at different focal planes in milliseconds. The image scale and phase were corrected. Then the in-focus pixels were abstracted by employing the Laplacian operator. These pixels were marked in the index table. According to the index table, the focused parts of multiple images were merged, and an all-in-focus image was generated. At the same time, a depth map was constructed based on the image number in the index table and the extracted depth information. Additionally, we have optimized the image processing flow; the processing speed was improved to around 6.5 fps.

Analysis of the zoom system of a microscope condenser and its modification using variable focus lenses

A detailed theoretical analysis and optimization of the classical three-element zoom (pancratic) microscope condenser according to a patent from the 1930s [Reichspatentamt Nr. 713188 (29 10 1936)] is performed and formulas are derived for calculating basic parameters and the displacement of lenses during zooming. Furthermore, the modification of the classical zoom microscope condenser is investigated using a simpler optical system of two lenses with variable focal lengths and fixed positions. The relations for the calculation of the focal lengths of both variable focus lenses and the basic parameters of the zoom system have been described. The proposed two-element zoom system consisting of a system of two lenses with variable focal lengths maintains a constant distance between the object and image planes and fixed position of both lenses during zooming. The basic parameters and third-order aberration coefficients of such a system are calculated using an example.

Measurement method of virtual image distance for a head-mounted display based on a variable-focus liquid lens

The distance from the virtual image to the human eye is an important factor in measuring the comfort of a head-mounted display (HMD). However, accurately measuring their distance is challenging due to the dynamic changes in virtual presence and distance. In this paper, we proposed a virtual image distance measurement prototype based on a variable-focus liquid lens and derived a virtual image distance calculation model. We built a variable-focus liquid lens experimental platform to verify the method’s correctness. In addition, we proposed an improved optimization algorithm that can efficiently and accurately search for the optimal focal length corresponding to the maximum sharpness moment of the virtual image within the focal length value space. Verified in an experimental scene of 0.5 m to 3.5 m, we observed that the error between the object image distance and the virtual image distance at the same focal length is about 5 cm. The proposed virtual image distance measurement method can accurately measure the distance value of the virtual image in the HMD. This method can be widely used in virtual and augmented reality, especially in the task of constructing realistic scenes.

Dynamic projection mapping for non-planar objects with a variable focus lens and visual feedback.

Dynamic projection mapping for moving objects has attracted much attention in recent years. However, conventional approaches have faced some issues, such as the target objects being limited to the moving speed of the objects, the limitation of the narrow depth-of-field optics, and the planar shape objects. This work proposed an adaptive three-dimensional projection prototype, and it could project an always in-focus image on a non-planar object based on liquid lens optics. The location of the non-planar object could be detected, and the mapped projection contents calculated; as a result, a stable "printed" projection mapping should be viewed on a moving object.

Long-distance optical-conveyor-belt transport of ultracold Cs133 and Rb87 atoms

We report on the transport of a thermal cloud of ultracold cesium and rubidium atoms over about 37 cm in under 25 ms using an optical conveyor belt formed by two counterpropagating beams with a controllable frequency difference that generate a movable optical lattice. By carefully selecting the waists and focus positions, we are able to use two static Gaussian beams for the transport, avoiding the need for a Bessel beam or variable-focus lenses. We characterize the transport efficiency for both species, including a comparison of different transport trajectories, gaining insight into the loss mechanisms and finding the minimum jerk trajectory to be optimum. Using the optimized parameters, we are able to transport up to 7×106 cesium or rubidium atoms with an efficiency up to 75%. To demonstrate the viability of our transport scheme for experiments employing quantum gas microscopy, we produce Bose-Einstein condensates of either species after transport and present measurements of the simultaneous transport of both species. Published by the American Physical Society 2024

Deployable optics for the Buccaneer Main Mission (BMM)

AbstractDefence Science and Technology Group (DSTG) is currently preparing for the launch of the Buccaneer Main Mission (BMM) satellite, the successor to the Buccaneer Risk Mitigation Mission (BRMM). BMM hosts a high-frequency (HF) antenna and receiver to contribute to the calibration of the Jindalee Operational Radar Network (JORN). Verification of the successful deployment and stability of the large HF antenna is critical to the success of the mission. A bespoke deployable optics payload has been developed by DSTG to fulfil the dual purpose of direct verification of the deployed state of the HF antenna and capturing images of the Earth through a rotatable, dual-surfaced mirror and a variable-focus liquid lens. The payload advances research at DSTG in several fields of space engineering, including deployable mechanisms, precision actuation devices, radiation-tolerant electronics, advanced metal polishing and optical metrology. This paper discusses the payload design, material selection, trade-offs considered for the deployable optics payload and preliminary test results.

Schistosomiasis enteropathy diagnosed by real-time endocytoscopy.

Fourth-generation endocytoscopy (EC) integrates a variable-focus lens and provides up to 520× continuous zoom-focus magnification. A single endoscope enables white-light imaging, narrow-band imaging, and cellular-level observation. The so-called virtual histology or optical biopsy has shown promising diagnostic ability in GI malignancies or premalignant lesions. Here, we report unexpected findings in the diagnosis of a rare benign disease. A 43-year-old man without a significant medical history underwent a colonoscopy because of abdominal distension. The colonoscopy showed patchy areas of multifocal white miliary spots in the hyperemic mucosa of the descending colon, with no features of polypoid tissue (A). Endocytoscopic ultramagnified images were obtained after staining with 1% methylene blue and 0.05% crystal violet. The microsurface structure of the gland was obviously destroyed, and a large number of seedlike oval structures were notable under endocytoscopy (CF-H290ECI endocytoscope; Olympus, Tokyo, Japan) (B). The on-site pathologist confirmed these structures to be schistosome eggs. Histologic examination of the targeted biopsy specimen also revealed numerous eggs of schistosome organisms (C, H&E, orig. mag. ×200). We hope that this first reported endocytoscopic observation of schistosomiasis enteropathy may enrich the understanding and application of this novel technique, and we believe that maximum diagnostic yield can be achieved under the guidance of an on-site pathologist, although a trained endoscopist can make the diagnosis in most cases.

Dynamic performance of a membrane-based variable focus lens with a large aperture.

Dynamic performance is one of the most important characteristics of a variable focus lens. However, there are few studies investigating the dynamic response of a membrane-based variable focus lens. In this paper, we present a mathematical model to describe spring-damping phenomena in theory. The first order natural frequencies with different scales were confirmed via finite element analysis. We also built a dynamic response experiment platform with changeable optical apertures, which was driven by a high-speed piezo stack actuator. A photodiode module was placed behind the lens to measure the variation of light luminance as the lens changed, and a laser displacement sensor was used to measure the deformation of the membrane. A series of data was collected with different optical apertures (20mm, 30mm, 50mm) and different pre-stretching ratios (200%, 300%) under different driving frequencies (from 5Hz to 25Hz in every 5Hz step). The experimental results were consistent with the mathematical model, which showed that the first order natural frequency increased as the aperture decreased or the membrane stiffness increased. This frequency-dependent characteristic of the variable focus lens provides a basis for further research on its dynamic performance.

80‐1: Invited Paper: Tunable liquid crystal lens for dynamic Prescription (Rx) correction and Accommodation‐Convergence (AC) conflict correction in AR/VR/3D HMDs

While the near‐to‐eye HMDs are advancing in display resolution, there are active challenges related to accommodation‐convergence (AC) conflict correction as well as prescription correction (Rx). Many approaches are reported previously to solve AC conflict using variable focal lenses, however, very few of them included dynamic Rx correction. While AC correction requires only adjustment of focal plane, Rx correction requires simultaneous correction of focal length and astigmatism. In this report, we have shown concept, design, fabrication, and demonstration of liquid crystal based tunable lens that is capable of dynamic correction of both the issue without needing any mechanical moving parts. The device is lightweight, thin, flat, low voltage driven and has potential to replace the eyeglasses worn by the users with the HMDs.

How to fix an ultrasonic variable-focus liquid crystal lens for substrate-mountable applications

This paper proposed a board-mounted ultrasonic variable-focus liquid crystal (LC) lens. The lens controls the focus using the acoustic radiation force generated by the resonant flexural vibration mode. The LC lens was fixed to an aluminum substrate with a hole whose aperture corresponded to the inner diameter of the transducer. The part of the LC lens attached to the substrates functioned as a fixed condition, and the flexural vibration mode was successfully generated. The fixed lens exhibited a gradual focal change with current, confirming that fixing the condition affected the rate of focal change.

Dynamic depth-of-field projection mapping method based on a variable focus lens and visual feedback.

Dynamic projection mapping is an interactive display technology, which is capable with multiplayers with naked eyes for augmented reality. However, the fixed and shallow depth-of-field of the projector optics limits its potential applications. In this work, a high-speed projection mapping method with a dynamic focal tracking technology based on a variable focus lens will be illustrated. The proposed system included a high-speed variable focus lens, a high-speed camera, and a high- speed projector, so that the depth and rotation information would be detected and then served as feedback to correct the focal length and update the projection information in real time. As a result, the information would be well-focused projected even on a 3D dynamic moving object. The response speed of the high-speed prototype could reach around 5 ms, and the dynamic projection range covered from 0.5 to 2.0 m.

A note on “Variable-focus liquid lens based on electrically responsive fluid”

A note on “Variable-focus liquid lens based on electrically responsive fluid”

Dynamic Adaptive Beam Control System Using Variable Focus Lenses for Laser Inter-Satellite Link

One of technical challenges in laser inter-satellite link (ISL) is the mitigation of performance degradation caused by pointing errors and angle-of-arrival (AoA) fluctuations arising unavoidably from satellite movements and vibrations. In this paper, we propose the dynamic adaptive beam control (ABC) technique implementable by using variable focus lenses (VFLs) at both the transmitter and receiver. In this technique, we monitor the instantaneous pointing error and AoA fluctuation induced by satellite vibrations and then provide feedback corrections to the VFL-based ABC system. The VFLs at the transmitter and receiver adjust their focal lengths adaptively to the amount of pointing error and AoA fluctuation, respectively, to minimize the link loss. VFLs operated by electro-wetting or electromagnetic actuator are fast enough to respond to the vibrations. We design the proposed dynamic ABC system for laser ISL by using the double-lens configuration and VFLs. An exemplary system design is presented when commercially available VFLs are utilized. Our simulation study shows that the proposed dynamic ABC technique offers improved transmission performance, compared to the static and the dynamic ABC technique applied to either the transmitter or receiver.

Relationship between liquid crystal layer thickness and variable-focusing characteristics of an ultrasound liquid crystal lens

The effect of the liquid crystal (LC) layer thickness on the optical characteristics of an ultrasound LC lens was explored. Three LC lenses with differing LC layer thicknesses (100, 200, and 300 μm) were fabricated, and the optical focal lengths were measured by an optical microscope with a varying driving voltage. For the lens with a 200 μm thick LC layer, a larger change in the focal length was observed for a smaller driving voltage compared with that of the other two lenses, indicating that the LC layer thickness is appropriate for a variable-focus lens.

Monocular Real Time Full Resolution Depth Estimation Arrangement with a Tunable Lens

This work introduces a real-time full-resolution depth estimation device, which allows integral displays to be fed with a real-time light-field. The core principle of the technique is a high-speed focal stack acquisition method combined with an efficient implementation of the depth estimation algorithm, allowing the generation of real time, high resolution depth maps. As the procedure does not depend on any custom hardware, if the requirements are met, the described method can turn any high speed camera into a 3D camera with true depth output. The concept was tested with an experimental setup consisting of an electronically variable focus lens, a high-speed camera, and a GPU for processing, plus a control board for lens and image sensor synchronization. The comparison with other state of the art algorithms shows our advantages in computational time and precision.

Fabrication and characterization of variable-focus liquid lens based on coil

This paper presents a coil-based liquid lens (CLL) with a mature and simple fabrication process. A tunable focal length is achieved by changing the liquid–liquid interface curvature using electrowetting on dielectric (EWOD). The lens cavity is a coil wound or stacked by a particular structure named EWOD wire, which is made by coating a soft insulating dielectric layer on a flexible conductive core. As a result, requirements for different lens designs can be achieved, and coating an insulating dielectric layer in complex cavities is not required. The optical performance of the CLL is measured with a clear aperture of 8 mm, which shows that the tunable range for the focal length is (−∞, −35 mm] ∪ [78 mm, +∞) at a voltage of 0–235 V, and the response time is less than 40 ms.

A liquid lens-based optical sensor for tactile sensing

Tactile sensing plays a crucial role in robot manipulation, robot interaction, and health monitoring. Because of high sensitivity, simple structure, and superior interference immunity, optical tactile sensors based on optical imaging or optical conduction have been one of the most active research. Herein, a novel liquid lens-based optical sensor (LLOS) is presented. Different with existed optical tactile sensors, the main body of the proposed sensor belongs to a variable-focus optical lens with a liquid-membrane structure, and its focal length is changed with the contact force, thereby changing the propagation direction of light and affecting the perceived light intensity of the photosensitive element. By conducting some testing experiments, the LLOS demonstrates fast response (about 0.021 s), stable dynamic response characteristics, and good linearity (R-squared is about 0.99), repeated measurement accuracy (<0.006 V), and measurement accuracy (<0.2 N). Hence, the LLOS provides a new and promising method to measure tactile and has potential application in robotics nondestructive grasping and interactive input devices.

Variable-focus liquid lens based on electrically responsive fluid.

In this work, an adaptive liquid lens using a novel transparent electrically responsive fluid, dibutyl adipate (DBA), is demonstrated. The DBA liquid lens with a hemispherical plano-convex shape can change its curvature according to the application of various input voltages. More specifically, when an external direct current (DC) electric field is applied to the DBA liquid, the charges that are injected from the cathode move along with the DBA molecules toward the anode and accumulate on the surface of the anode. When the DC electric field is removed, the shape of the DBA liquid is recovered to its original state. This electrostatic force induces the deformation of the DBA liquid lens within a concentric annular anode electrode. In addition, the focal length of our system is increased from a value of approximately 7.5 mm to 13.1 mm when the voltage is changed from 0 to 100 V. Interestingly, the resolution of our DBA liquid lens can reach a value of ∼28.5 lp/mm. The proposed DBA liquid lens exhibits high optical transmittance (∼95%), good thermal stability (20-100°C), simple structure, and an excellent imaging property, which implies that the DBA liquid is a promising candidate for fabricating novel adaptive liquid lenses.

2E2-4 Board-mounted ultrasonic variable-focus liquid crystal lens

2E2-4 Board-mounted ultrasonic variable-focus liquid crystal lens