Monocular vision ranging method based on small liquid adjustable focus lens

An experimental setup used to measure the important optical properties of electrowetting liquid lens is proposed. The simple and precise method of measuring dynamic responses and focal lengths of liquid lens under different excitation signals is based on Gaussian beam transmission theory. The measurement method can be widely used in all kinds of zoom lens systems. The device is simple and economical, and also has the advantages of convenient operation, high measurement precision and wide range measurement. This work provides a new way to study the dynamic response of electrowetting liquid lens and the the mechanism of electrowetting liquid lens. The fabrication process and some relevant noticeable points for the homemade liquid lens are introduced. The testing device of dynamic process of lens consists of a He-Ne laser, an electrowetting lens, a circular diaphragm, a phototube, a digital storage oscilloscope and a computer. The change of the focal length of liquid lens due to the applied voltage will affect the flux detected by the photoelectric receivers. It is proved according to Gaussian beam transmission theory that the light flux received by the phototube changes with time, which represents the relationship between the focal length and time and the dynamic characteristics of the liquid lens. Therefore, the intensity of output signal of photoelectric receiver reflects the focal length of liquid lens. A dynamic changing process of the focal length of a self-regulating varifocal liquid lens based on electrowetting technology is tested under alternating current signal. It shows that the focal length of the liquid lens changes with the corresponding amplitude and polarity of the sine voltage. In one cycle, 4 peak signals of 50 Hz appear in turn, and the peak amplitude increases with the increase of voltage. Peaks 1 and 2 are caused by the voltage polarity, while peaks 3 and 4 by the oscillation modes. This is due to the fact that the liquid surface changes with time in the spherical shape under low voltage, but it will generate new oscillation mode when the amplitude is high.

Inspired by crystalline lenses in human eyes, liquid lenses have a simple yet elegant working principle, and result in compact optical systems. Recent numerical studies showed that membranes with variable thicknesses could affect the lens profile. However, fabrication and assembly of a liquid lens with an inhomogeneous membrane is difficult. There is also a lack of experimental studies about the changes of a lens profile during deformation. In this paper, we provided a new experimental approach for characterizing the performance of a liquid lens with an inhomogeneous membrane. A 2D axisymmetric lens model was built in finite element analysis software to theoretically study the non-linear deformation behavior of the inhomogeneous membrane. Then we provided a new approach to fabricate inhomogeneous membranes using a pre-machined aluminum mold. An optical coherence tomography (OCT) system was used to dynamically measure the changes of a lens profile without contact. Both simulation and the experiments indicated that the variation of the thickness of the membrane could affect the lens profile in a predictable manner. A negative conic constant was achieved when a plano-concave membrane was adopted in a liquid lens. Larger increments of the thickness of the membrane in the radial direction resulted in a larger contribution of a conic constant to the lens profile. The presented study offers guidance for image-quality analysis and optimization of a liquid-lens-based optical system.

A novel design of a wavefront coded compact camera system with liquid lens is presented. The point spread function must remain practically constant over a wide range of defocus in order to create an image which is sharp over a large depth of field. Therefore, the trade-off between the effect of extended depth of field and reduction in the signal to noise ratio of the restored image become critical. By combining liquid lens and wavefront coding, the system can deliver much greater depth of field without the restoration problems caused by the similarity of point spread function. This could improve the overall image performance.

Integral microscopy is a 3D imaging technique that permits the recording of spatial and angular information of microscopic samples. From this information it is possible to calculate a collection of orthographic views with full parallax and to refocus computationally, at will, through the 3D specimen. An important drawback of integral microscopy, especially when dealing with thick samples, is the limited depth of field (DOF) of the perspective views. This imposes a significant limitation on the depth range of computationally refocused images. To overcome this problem, we propose here a new method that is based on the insertion, at the pupil plane of the microscope objective, of an electrically controlled liquid lens (LL) whose optical power can be changed by simply tuning the voltage. This new apparatus has the advantage of controlling the axial position of the objective focal plane while keeping constant the essential parameters of the integral microscope, that is, the magnification, the numerical aperture and the amount of parallax. Thus, given a 3D sample, the new microscope can provide a stack of integral images with complementary depth ranges. The fusion of the set of refocused images permits to enlarge the reconstruction range, obtaining images in focus over the whole region.

We demonstrated a fast response and large tunable focusing imaging system consisting of a lens module and a liquid crystal (LC) lens based on the switching of two modes of a LC lens: the negative LC lens and positive LC lens. By discarding the conventional operation of a positive LC lens only in the imaging system, large tunable focusing range can be achieve from 300 to 10 cm owning to the phase change between the positive and the negative LC lens; meanwhile, the response time is fast (∼433 ms). The potential applications are autofocused cell phones, and cameras.

The microscope system in combination with a digital image processing is developed for determining all-focused images and depth mapping properties of microscopic objects by using a liquid crystal (LC) lens with variable focal length. Three-dimensional distributions of the microscopic objects are determined by applying voltages to the electrodes of the LC lens and tuning a focal plane in a depth direction.

A liquid lens is used to realize an adaptive interferometric particle imaging system. The defocus parameter of the system can be changed instantaneously by adjusting the voltage applied to the lens. This enables adjusting the imaging conditions in real time. The setup is first tested on programmable rough particles generated by a digital micromirror device (DMD), and then with real glass particles under nanosecond pulse illumination.

Due to the relatively low optical power of a liquid lens, it is usually difficult to achieve a large zoom ratio and a high-resolution image simultaneously in an optofluidic zoom imaging system. We propose an electronically controlled optofluidic zoom imaging system combined with deep learning, which achieves a large continuous zoom change and a high-resolution image. The zoom system consists of an optofluidic zoom objective and an image-processing module. The proposed zoom system can achieve a large tunable focal length range from 4.0 mm to 31.3 mm. In the focal length range of 9.4 mm to 18.8 mm, the system can dynamically correct the aberrations by six electrowetting liquid lenses to ensure the image quality. In the focal length range of 4.0-9.4 mm and 18.8-31.3 mm, the optical power of a liquid lens is mainly used to enlarge the zoom ratio, and deep learning enables the proposed zoom system with improved image quality. The zoom ratio of the system reaches 7.8×, and the maximum field of view of the system can reach ~29°. The proposed zoom system has potential applications in camera, telescope and so on.

Due to the limitations of spatial bandwidth product and data transmission bandwidth, the field of view, resolution, and imaging speed constrain each other in an optical imaging system. Here, a fast-zoom and high-resolution sparse compound-eye camera (CEC) based on dual-end collaborative optimization is proposed, which provides a cost-effective way to break through the trade-off among the field of view, resolution, and imaging speed. In the optical end, a sparse CEC based on liquid lenses is designed, which can realize large-field-of-view imaging in real time, and fast zooming within 5 ms. In the computational end, a disturbed degradation model driven super-resolution network (DDMDSR-Net) is proposed to deal with complex image degradation issues in actual imaging situations, achieving high-robustness and high-fidelity resolution enhancement. Based on the proposed dual-end collaborative optimization framework, the angular resolution of the CEC can be enhanced from 71.6" to 26.0", which provides a solution to realize high-resolution imaging for array camera dispensing with high optical hardware complexity and data transmission bandwidth. Experiments verify the advantages of the CEC based on dual-end collaborative optimization in high-fidelity reconstruction of real scene images, kilometer-level long-distance detection, and dynamic imaging and precise recognition of targets of interest.

In this paper the focusing effect of flat metallic-slit array in micro-meter scale area is discussed and the role of surface plasmons waves inside slits is recognized. A proximate relationship between the equivalent focal length and slit material, slit geometrical parameters is built. The theoretically derived focal length and that from Finite Difference Time Domain (FDTD) simulation is proved to be in good agreement. Additionally, FWHM of focal point, focal depth and intensity of focal point for the slit array with invariant slit width and the slit array with variant slit width are compared as well. The slit array with varied slit width is found to have the better performance than slit array with invariant slit width.

Low vision aids used in the spectacle plane may be either plus lenses or telescopes focused for near. The plus lens has a shorter working distance than a near point telescope of the same equivalent power. A relationship between the anterior focal length (fv) of the near point telescope and the equivalent focal length (fe) of a thin lens of equal power can be derived from the formula fv = (mag) (fe). This formula provides a basis for determining what equivalent powers are equal and interchangeable between the two types of aids. Furthermore, the advantages of the increased working distance afforded by the near point telescope can be defined.

The use of effective and radii of curvature permits the well-known formulae relating the tangential and sagittal centres of curvature of a wavefront element before and after refraction to be put into a form which yields formulae and computing schemes identical with those customarily used for computing the paraxial focus, magnification, and equivalent focal length. Simple expressions follow for the T- and S-magnifications and oblique equivalent focal lengths. After being in use for a few months, the computing schemes have now been adopted as standard calculations.

The focal track sensor is a monocular and computationally efficient depth sensor that is based on defocus controlled by a liquid membrane lens. It synchronizes small lens oscillations with a photosensor to produce real-time depth maps by means of differential defocus, and it couples these oscillations with bigger lens deformations that adapt the defocus working range to track objects over large axial distances. To create the focal track sensor, we derive a texture-invariant family of equations that relate image derivatives to scene depth when a lens changes its focal length differentially. Based on these equations, we design a feed-forward sequence of computations that: robustly incorporates image derivatives at multiple scales; produces confidence maps along with depth; and can be trained endto- end to mitigate against noise, aberrations, and other non-idealities. Our prototype with 1-inch optics produces depth and confidence maps at 100 frames per second over an axial range of more than 75cm.

The position and the size of the Gaussian image of an object formed by an optical imaging system is determined by using its Gaussian imaging equations. We have stated in Chapter 1 that the quality of the diffraction image depends on the aberrations of the system. A spherical wave originating at a point object is incident on the system. The image formed by the system is aberration free and perfect if the wave exiting from the system is also spherical. In this case, the rays originating at the point object and traced through the system all pass through the Gaussian image point. If the optical wavefront exiting from the exit pupil is not spherical, its optical deviations from a spherical form represent its wave aberrations. These wave aberrations play a fundamental role in determining the quality of the aberrated image. The rays traced from the object point through the system, instead of passing through the Gaussian image point, intersect the image plane in its vicinity. The distance of the point of intersection of a ray in the image plane from the Gaussian image point is called the transverse ray aberration, and the distribution of the rays is referred to as the spot diagram. In this chapter, we define the wave and ray aberrations and give a relationship between them. We relate the longitudinal defocus of an image to the defocus wave aberration, and its wavefront tilt to the wavefront tilt aberration. Next, the possible aberrations of an imaging system that is rotationally symmetric about its optical axis are described. The aberration function of the system is expanded in a power series of the object and pupil coordinates, and primary (or Seidel), secondary (or Schwarzschild), and tertiary aberrations are introduced. We also discusss briefly how the aberrations may be observed using a Twyman–Green interferometer and what the fringe pattern of a primary or Seidel aberration looks like. A short summary of the chapter is given at the end.

Gradient index (GRIN) lenses are used both in imaging and beam shaping optical systems. Usually, to design a GRIN lens system, we would find the equivalent lens effective focal length and the principal planes position. Then if we design an imaging system the Newton formula gives the image position or, if we design a beam shaping system the Kogelnik's ABCD law gives the Gaussian beam waist size and position. The Hamilton's phase plane approach gives the same result as these sets of formulas, but is more spectacular and clearer. Hamilton's phase plane approach gives a vivid and clear illustration of GRIN lens imaging and beam shaping properties and does not require substitution by an equivalent lens. Hamilton's phase plane approach allows easy derivation of transparent and simple direct formulas for a GRIN lens created image and beam transformation, including Gaussian beams and multimode fiber beams. These formulas and graphical illustrations facilitate solving, and give a clearer understanding of practical problems.