Continuous optical zoom telescopic system based on liquid lenses.

Telescopes play an essential important role in the fields of astronomical observation, emergency rescue, etc. The traditional telescopes achieve zoom function through the mechanical movement of the solid lenses, usually requiring refocusing after magnification adjustment. Therefore, the traditional telescopes lack adaptability, port-ability and real-time capability. In this paper, a continuous optical zoom telescopic system based on liquid lenses is proposed. The main components of the system consist of an objective lens, an eyepiece, and a zoom group composed of six pieces of liquid lenses. By adjusting the external voltages on the liquid lenses, the zoom telescopic system can achieve continuous optical zoom from ∼1.0× to ∼4.0× operating with an angular resolution from 28.648" to 19.098", and the magnification switching time is ∼50ms. The optical structure of the zoom telescopic system with excellent performance is given, and its feasibility is demonstrated by simulations and experiments. The proposed system with fast response, portability and high adaptability is expected to be applied to astronomical observation, emergency rescue and so on.

Large viewing angle integral imaging 3D display system based on a symmetrical compound lens array.

We propose a large viewing angle integral imaging 3D display system based on a symmetrical compound lens array (SCLA). The display system comprises a high-resolution 2D display panel, an SCLA, and a light shaping diffuser. The high-resolution 2D display panel presents an elemental image array, the SCLA modulates the light rays emitted from the 2D display panel to form 3D images in space, and the light shaping diffuser eliminates the gaps between 3D pixels of the 3D images. We find that the lateral aberration is a crucial factor that affects the resolution of the reconstructed 3D image. The symmetrical structure of the SCLA enables a reduced focal length and the elimination of lateral aberration, improving the viewing angle and the 3D image resolution simultaneously. The experimental results confirm that the proposed display system increases the viewing angle to 68.6°, achieving a comparable resolution of the full field of view while maintaining a simple structure.

Dual interface trapezium liquid prism with beam steering function.

In this paper, a dual interface trapezium liquid prism with beam steering function is implemented and analyzed. The electrowetting-on-dielectric method is used to perform the desired beam steering function without mechanical moving parts. This work examines deflection angles at different applied voltages to determine the beam steering range. The deflection angle can be experimentally measured from 0° to 3.43°. The proposed liquid prism can be applied in the field of optical manipulation, solar collecting system and so on.

3D microscope image acquisition method based on zoom objective.

Microscopy is being pursued to obtain richer and more accurate information, and there are many challenges in imaging depth and display dimension. In this paper, we propose a three-dimensional (3D) microscope acquisition method based on a zoom objective. It enables 3D imaging of thick microscopic specimens with continuous adjustable optical magnification. The zoom objective based on liquid lenses can quickly adjust the focal length, to expand the imaging depth and change the magnification by adjusting the voltage. Based on the zoom objective, an arc shooting mount is designed to accurately rotate the objective to obtain the parallax information of the specimen and generate parallax synthesis images for 3D display. A 3D display screen is used to verify the acquisition results. The experimental results show that the obtained parallax synthesis images can accurately and efficiently restore the 3D characteristics of the specimen. The proposed method has promising applications in industrial detection, microbial observation, medical surgery, and so on.

Three-phase electrowetting liquid lens with deformable liquid iris.

Inspired by the arrangement of iris and crystalline lens in human eyes, we propose a three-phase electrowetting liquid lens with a deformable liquid iris (TELL-DLI). The proposed electrowetting liquid lens has three-phase fluid: air, conductive liquid, and dyed insulating liquid. The insulating liquid is distributed on the inner wall of the chamber in a ring shape. By applying voltage, the contact angle is changed, so that the dyed insulating liquid contracts towards the center, which is similar to the contraction of iris and the function of crystalline lens muscle in human eyes. The variation range of focal length is from -451.9 mm to -107.9 mm. The variation range of the aperture is from 4.89 mm to 0.6 mm. Under the step voltage of 200 V, the TELL-DLI can be switched between the maximum aperture state and the zero aperture state, and the switching time is ∼150/200 ms. Because of the discrete electrodes, TELL-DLI can regionally control the shape and position of the iris, and switch between circle, ellipse, sector, and strip. The TELL-DLI has a wide application prospect in imaging systems, such as microscopic imaging system, and has the potential to be applied in the field of complex beam navigation.

Method of color holographic display with speckle noise suppression.

In this paper, a method of color holographic display with speckle noise suppression is proposed. Firstly, the intensity information of the object is extracted according to the red, green and blue (RGB) channels. The band-limited phase is calculated and used as the initial phase for each color channel. Secondly, the double-step Fresnel diffraction algorithm is used to calculate the computer-generated holograms (CGHs), and a filter plane that dynamically adjusts the position of the filter in the optical path is designed. Then, a divergent spherical phase factor is added to the CGHs. Finally, the time average method is used to further reduce the speckle noise. When the CGHs of the RGB channels are loaded on the digital micromirror device and illuminated by the RGB lights emitting in a temporal sequence, the color reconstructed images with speckle noise suppression can be displayed. The validity of the proposed method is verified.

Real scene acquisition and holographic near-eye display system based on a zoom industrial endoscope.

In this paper, we propose a real scene acquisition and holographic near-eye display system based on a zoom industrial endoscope. By controlling the driving current of the liquid lens, the working distance and focal length of the zoom industrial endoscope can be tuned accordingly. Thus, the object at different depths can be captured. Then, the sub-sampling algorithm is used to generate the hologram. By adjusting the hologram sampling rate of the objects with different depths, the holographic near-eye 3D display can be realized. Experimental results demonstrate that the working distance of the zoom industrial endoscope can be tuned from 20 mm to 200 mm with the driving current changing from 80 mA to 190 mA. With the proposed system, the human eye can intuitively see the depth relationships among the real objects. The proposed system is expected to be applied to 3D display and industrial inspection fields.

Holographic near-eye display system with large viewing area based on liquid crystal axicon.

In this paper, a liquid crystal axicon based holographic near-eye display system with large viewing area is proposed. The viewing area of the system is extended by implementing the liquid crystal axicon. The error diffusion algorithm is used to calculate the computer-generated hologram (CGH). When incident on the liquid crystal axicon placed at the back focal plane of Fourier lens, the reconstruction light modulated by the CGH is deflected into two directions resulting in a viewing area extension. Meanwhile, to illustrate the potential of the proposed system, two-dimensional viewing area extension is demonstrated. It combines the frequency spectrum shift with the proposed system and achieves a double expansion of the horizontal viewing area and three-times expansion of the vertical viewing area. Feasibility of the proposed system is verified by optical experiments. The proposed system has potential applications in holographic augmented reality (AR) display.

Color curved hologram calculation method based on angle multiplexing.

In this paper, a method of color curved hologram calculation based on angle multiplexing is proposed. The relationship between the wavelength, center angle and sampling interval of the curved holograms is analyzed for the first time by analyzing the reconstruction process of the curved holograms with different wavelengths. Based on this relationship, the color curved holograms are calculated by compensating phase to the complex amplitude distribution of the planar holograms. To eliminate the chromatic aberration, the curved holograms of different objects with the same color channel are respectively used for angle multiplexing and phase compensation, and then the color composed curved hologram is generated. Different color objects without chromatic aberration can be reconstructed by bending the composed curved hologram into different central angles. The experimental results verify the feasibility of the proposed method. Besides, the application of the proposed method in augmented reality display is also shown.

Depth of field and resolution-enhanced integral imaging display system.

Depth of field (DOF) and resolution are mutually restricted in integral imaging (II) display. To overcome the trade-offs, we propose an II display system that simultaneously enhances the DOF and resolution. The system consists of a transmissive mirror device (TMD), a semi-transparent mirror (STM), and two II display units. Each II display unit consists of a 4K display screen and a micro-lens array (MLA). Benefiting from the parallel placement of the TMD and the STM, two central depth planes are reconstructed, which effectively enhances the DOF. Meanwhile, the resolution in the overlapping DOF region is increased to two times due to the interpolation of the light field information from two II display units. The impact of the distance between the two II display units and the TMD on the 3D image quality is analyzed. In geometric optics, a distance between the II two display units and the TMD is optimized to eliminate ghost images. In wave optics, a distance is optimized to eliminate 3D pixel gaps by exploiting the diffraction effect of the TMD. Both the geometric and wave optics are considered simultaneously to obtain a high-quality 3D image without ghost images and 3D pixel gaps. A DOF and resolution-enhanced II display system is developed, and the experimental results verify its feasibility.

System to eliminate the graininess of an integral imaging 3D display by using a transmissive mirror device.

We propose a system to eliminate the graininess of an integral imaging 3D display by using a transmissive mirror device (TMD). The proposed system consists of a 2D display, a micro-lens array (MLA), and a TMD. The TMD comprises square apertures with mirror-reflective inner wall. The light rays pass through the square aperture to form a diffraction spot, and the diffraction light intensity has a Sinc-function distribution. Therefore, the TMD can be used as an optical low-pass filter. In a certain imaging range, the mainlobe of the Sinc-function distribution is almost unchanged. The TMD has the property of a volumetric optical low-pass filter. It can interpolate the interval between discrete 3D pixels. Therefore, the TMD can be used to eliminate the graininess. The resolution of the 3D image is improved by 2.12 times. The experimental results verify the feasibility of the proposed system.

Three-dimensional lattice deformation of blue phase liquid crystals under electrostriction.

In this work, we investigate the three-dimensional lattice deformation of blue phase (BP) liquid crystals under electrostriction. Using the in situ measurement of light diffraction signals from a twinned crystal, we propose a method to experimentally determine the lattice constants of BPs under an electric field; the overlap angle in the diffraction pattern of BP twinning domains gives the ratio of lattice constants in the lateral direction of the field, which can be analyzed together with the Bragg reflection peak wavelength along the field direction to yield three-dimensional lattice constants. The obtained values are confirmed to show good agreement with the diffraction data measured from a converging monochromatic light. Furthermore, by applying the method to BPs in a thin cell and specifying the transitions of azimuthal orientation, three-dimensional lattice deformation of BP I crystals and evolution of the azimuthal orientation are clarified under the electrostriction. Results reveal that the BPs confined to thin films undergo discrete elongation along the field direction and the BP I crystal undergoes larger lattice deformation in the field-perpendicular directions than that along the field. Our work allows a relatively easy determination of three-dimensional lattice constants of deformed BP crystals under an electric field, and the obtained results provide important insights into the understanding of the electrostriction behaviour of BPs towards improvement of the electro-optical performance of BP devices in practical applications.

Continuous optical zoom microscopy imaging system based on liquid lenses.

In this paper, a continuous optical zoom microscopy imaging system based on liquid lenses is proposed. Compared with traditional microscopes, which have discrete magnification, requiring manual conversion of the objective lens to change the magnification, the proposed microscope can continuously change the magnification of the targets in real-time. An adaptive zoom microscope, a liquid lens driving board, a microscope bracket, an adjustable three-dimensional stage and a light source are stacked to form the main framework of the continuous optical zoom microscopy imaging system. The adaptive zoom microscope which is composed of four electrowetting liquid lenses and six glass lenses form the main imaging element of the microscope. By changing the driving voltage which is applied to the four liquid lenses, the focal length of the liquid lenses can be modulated to achieve continuous zooming. By contrast, in traditional microscopes, the zooming process can only be achieved by rotating the eyepieces at different magnifications. At a fixed working distance, the magnification of the proposed microscope can change continuously from ∼9.6× to ∼22.2× with a response time of ∼50ms. Moreover, an axial depth scanning of ∼1000µm can be achieved without any mechanical movement. Our experiments proved that the microscope has stable performance and high consistency during zooming. Therefore, the proposed microscope has obvious advantages over the traditional microscopes in observing dynamic samples with different magnifications and can be commercialized for further expanding the applications in biochemical and pathological analysis.

Continuous zoom compound eye imaging system based on liquid lenses.

In this paper, a continuous zoom compound eye imaging system based on liquid lenses is proposed. The main imaging part of the system consists of a liquid compound eye, two liquid lenses and a planar image sensor. By adjusting the liquid injection volumes of the liquid compound eye and liquid lenses, the system can realize continuous zoom imaging without any mechanical movement of imaging components. According to the results of experiments, the paraxial magnification of the target can range from ∼0.019× to ∼0.037× at a fixed working distance. Moreover, the system can realize continuous focusing at a fixed paraxial magnification when the working distance ranges from ∼200mm to ∼300mm. Compared with the traditional artificial compound eye imaging systems, the proposed system increases the adjustability and matches the variable image surfaces of the liquid compound eye to a planar image sensor. The aspherical effects of the liquid compound eye and liquid lenses are also considered in the design of the system. The system is expected to be used for imaging in various scenes, such as continuous zoom panoramic imaging, 3D scanning measurement and so on.

Zoom liquid lens employing a multifocal Fresnel zone plate.

We propose a zoom liquid lens employing a multifocal Fresnel zone plate. The proposed lens has two optical surfaces: liquid-liquid interface and Fresnel zone plate. The Fresnel zone plate is designed to have a multifocal point and an increased depth of focus. Therefore, the proposed lens has two obvious advantages. Due to increased depth of focus, the proposed lens can realize zooming using only one tunable liquid-liquid interface, which is not available for conventional liquid lens. Thus, it is possible to remove conventional zooming mechanisms from cameras. Besides, the focal length tuning range is also increased, and a lens system based on the proposed lens can simultaneously collect two images with different magnifications. We present the design, fabrication and characterization of the proposed lens. The shortest positive and negative focal length are ∼17.5mm and ∼-34.5mm and the diameter is 5mm. The zoom ratio of the proposed lens reaches ∼1.48×. Our results confirm that the proposed lens has widespread applications in imaging system.

Multi-depth hologram generation using stochastic gradient descent algorithm with complex loss function.

The stochastic gradient descent (SGD) method is useful in the phase-only hologram optimization process and can achieve a high-quality holographic display. However, for the current SGD solution in multi-depth hologram generation, the optimization time increases dramatically as the number of depth layers of object increases, leading to the SGD method nearly impractical in hologram generation of the complicated three-dimensional object. In this paper, the proposed method uses a complex loss function instead of an amplitude-only loss function in the SGD optimization process. This substitution ensures that the total loss function can be obtained through only one calculation, and the optimization time can be reduced hugely. Moreover, since both the amplitude and phase parts of the object are optimized, the proposed method can obtain a relatively accurate complex amplitude distribution. The defocus blur effect is therefore matched with the result from the complex amplitude reconstruction. Numerical simulations and optical experiments have validated the effectiveness of the proposed method.

High stability liquid lens with optical path modulation function.

In this paper, a high stability liquid lens with optical path modulation function is designed and fabricated. The liquid lens has an outer chamber and an inner chamber, and the inner chamber has a structure with three annular anchoring layers. This structure can limit the sliding of the three-phase contact line under electrowetting effect and anchor the position of contact angle with a limited distance. The feasibility of this structure is verified by simulation and practice. The zoom imaging, contact angle, focal length and response time of the liquid lens are analyzed. The structure with three annular anchoring layers provides six anchored precision optical path modulation gears, and the optical path difference can be changed by mechanical hydraulic control, up to 1.17 mm. Widespread applications of the proposed liquid lens are foreseeable such as microscopic imaging and a telescope system, etc.

Optofluidic lenticular lens array for a 2D/3D switchable display.

In this paper, we propose an optofluidic lenticular lens array (OLLA) for a two-dimensional/three-dimensional (2D/3D) switchable display. The OLLA includes a bottom substrate layer with lenticular lens structure, a microfluidic layer with microchannels, and a top substrate layer with inlets as well as outlets. A micro gap is formed between the lenticular lens of the bottom substrate layer and the top substrate layer. When air is in the micro gap, the OLLA behaves as a lenticular lens array, which can realize 3D display. When fluid is filled in the micro gap, because the refractive index of the fluid is the same with the lenticular lens structure, the OLLA equivalents to a transparent flat panel, which can realize a 2D display. Experiments verify that a switchable 2D/3D display prototype based on this OLLA and a smartphone achieves both high-resolution 2D display and high-quality 3D display.

Four-mode 2D/3D switchable display with a 1D/2D convertible liquid crystal lens array.

A four-mode 2D/3D switchable display using a 1D/2D convertible liquid crystal (LC) lens array is proposed in this paper. The LC lens array is composed of two orthogonal LC lens arrays, with a λ/2 film in the middle to rotate the polarization by 90°. Based on the LC lens array, a four-mode 2D/3D switchable display is realized, which is switchable between the turn-off and turn-on states: when the operating voltage V1 = 0, V2 = 0, the display operates in mode I, which is 2D display; when the operating voltage V1 = 0, V2 = 0, the display operates in mode II, and the 3D display effect is in x direction; when the operating voltage V1 = 0, V2 = 0, the display operates in mode III, and the 3D display effect is in y direction; when the operating voltage V1 = 0, V2 = 0, the display operates in mode IV, the 3D display effect is in x-y plane. Experimental results indicate that the LC lens array has simple fabrication process, low operating voltage (∼5.4V), and short focal length. Moreover, based on the designed LC lens array, the 2D/3D switchable display shows no moiré pattern.

Fast responsive 2D/3D switchable display using a liquid crystal microlens array.

A fast responsive two-dimensional/three-dimensional (2D/3D) switchable display is demonstrated based on an active liquid crystal (LC) microlens array and a twisted nematic (TN) cell. Compared with the traditional LC microlens array, the fabricated LC microlens array has more ideal phase profile and better focusing effect. The TN cell can switch the polarization direction of the incident light with a very short switching time (4.3 ms) and a small driving voltage (5Vrms). By introducing the tilted elemental image arrays and tilted LC lens array, the moiré patterns are eliminated. The fast switching of the 2D/3D display can be realized by applying or removing voltage to the TN cell. The fast responsive 2D/3D switchable display with the LC microlens array and the TN cell is thin and compact without moiré pattern compared with other 2D/3D switchable display devices.