Large Focal Length Research Articles

Computer simulation of the effect of focusing X rays by means of refractive-diffractive lens

The features of focusing X rays using a refractive-diffractive lens (RDL), which is a system of two asymmetrically reflecting crystals with asymmetry factors, the product of which is equal to unity, and a refractive lens with a large focal length, are theoretically studied. Crystals make it possible to shorten the focal length of the lens by b2 times, where b is the asymmetry factor of the second crystal. A detailed numerical simulation of the effect of radiation focusing using the RDL has been performed. The universal computer program XRWP was used which is created to calculate the effects of coherent X-ray optics. Analytical formulas are obtained for the optimal aperture and radius of curvature of the lens, as well as for the width of the radiation spectrum that can be focused.

Far-field sub-diffraction focusing and controlled focus shaping of circularly polarized light using a dielectric phase plate

In recent years, sub-diffraction focusing has received substantial attention due to its versatility. However, achieving a flexible sub-diffraction focusing in the far field remains stimulating. Existing techniques either require complex fabrication facilities or are limited to the short focal length and high numerical aperture (NA) of the imaging system. Here, we introduce an optimization method for sub-diffraction focusing of a circularly polarized beam in the far field with a lens of large focal length. A cost-effective dielectric phase plate serves the purpose. By employing a phase plate composed of a thin layer of dielectric Si3N4, the phase of the propagating beam is modulated in the beam’s cross-section, which is divided into two regions of the opposite phase by the plate. A sub-diffraction focusing is achieved for a proper tunning between the two regions. In addition to sub-diffraction focusing, the phase plate is also capable of shaping the focus into a doughnut-shaped and a flat-top profile in the far field. This design provides a simple solution for sub-diffraction focusing and focus shaping that will find potential applications in optical imaging, optical trapping, and material processing.

Soft lenses with large focal length tuning range based on stacked PVC gel actuators

A novel tunable lens with large focal length change and driven by stacked polyvinyl chloride (PVC) gel actuators is designed and characterized in this study. The lens rigid parts are 3D-printed and commercially available, whereas the PVC gel membrane is in volume production. Under electrical actuation, the lens attains focal length ranges from 30 to 217 mm within 400 V. A manual regulating mechanism is proposed for the finished lens that dexterously adjusts the initial focus and focal length ranges. In the compound actuation mode, large focus variation over 950% is achieved within 250 V. Under 250 V step input, the lens exhibits practical response time around 291 ms. Focal length tuning ability of the lens is also demonstrated by capturing the images of objects placed in different positions. This tunable lens is promising for various smart optics.

Large focal length planar focusing of Dyakonov polaritons in hyperbolic metamaterial

Achieving subwavelength optical focusing is of great importance in nanophotonics. However, achieving focusing with both a small focal spot size and a large focal length remains elusive so far. Here, a large focal length planar focusing device is presented, utilizing highly oriented Dyakonov polaritons in hyperbolic metamaterial with periodic silver rings as the excitation source. Experimental results show that by controlling the size of the excitation sources, the focal length can reach 6λ0 (where λ0 is the illumination wavelength), and the focal spot size can be reduced to λ0/10. This method provides new prospects for planar polariton optical applications.

Design of an Integrated Optical System for Detection and Imaging of Large Aperture and Long Focal Length Based on Continuous Zoom

Design of an Integrated Optical System for Detection and Imaging of Large Aperture and Long Focal Length Based on Continuous Zoom

Optical computation of Laplace operator using Pancharatnam-Berry lens of large focal length

We propose an optical Laplace operator consisting of a large-focal-length Pancharatnam-Berry lens placed on the Fourier plane of an optical imaging system and sandwiched with two orthogonal linear polarizers. Theoretical analysis reveals that the isotropic second-order differentiation derives from the quadratic phase attached to the left-handed and right-handed circularly polarized light. The Pancharatnam-Berry lens made of liquid crystal with high transmittance and diffraction efficiency is integrated into different imaging systems to realize edge detection for both amplitude and phase objects, and the results conform to the theory well. This work paves the way to implement Laplace operator in practical applications such as image processing and high-contrast microscopy.

Nanocolloidal Lenses with Tunable Focal Length for an Augmented Reality System

A flat lens with a tunable focal length that does not require mechanical movement is highly desirable in augmented reality (AR) or virtual reality (VR) systems, but its development poses significant challenges. A colloidal lens that uses dielectrophoretic (DEP) manipulation of nanoparticle density in a colloid can be a good solution for achieving tunability in flat lenses. In this study, we investigated the optical properties of a nanocolloidal lens containing two-dimensional (2D) α-zirconium phosphate (α-ZrP) nanoparticles and optimized the lens design parameters to achieve low image distortion and large focal length tunability. We simulated the nanoparticle distribution function as a function of applied voltage for various lenses with different electrode designs, and the simulation results matched well with experimental observations. Additionally, we identified a condition for lower power consumption. Finally, we identified specific design parameters that allow for wide focal length control without image deformation and utilized them to fabricate lenses for a simple AR system. This study clearly demonstrates the potential of tunable nanocolloidal lenses, particularly in AR systems, by optimizing their design and performance.

Deep Learning Enables Optofluidic Zoom System with Large Zoom Ratio and High Imaging Resolution

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.

Investigating the effect of turbulence on IPI in a vehicular OCC system using PSF analysis

Optical camera communication (OCC) has emerged as a promising technology for wireless communication owing to its enormous potential benefits. However, turbulence conditions can restrict the feasibility of OCC systems that employ multiple-input multiple-output (MIMO) techniques. In this work, we consider a vehicular MIMO-OCC system model in which the traffic light LEDs transmit data streams separately in parallel channels to the camera of a vehicle. We analyze the effect of turbulence on the inter-pixel interference (IPI) and bit error rate (BER) of the low speed vehicular MIMO-OCC system using the point spread function (PSF) of the optical channel. We introduce two performance metrics, i.e., digital number difference (DND) and the percentage of separable LEDs (PSLED) for strong and very strong turbulence conditions, respectively. The parameters of the camera and traffic light LEDs can affect the IPI caused by turbulence. It is shown that the DND of MIMO-OCC systems with larger focal length and LED size less affected by turbulence. In addition, smaller f-number and pixel size reduce the effect of turbulence on DND. It is also demonstrated that very strong turbulence can reduce PSLED for links longer than 20 m. Moreover, if turbulence reduces PSLED, increasing the LEDs’ intensity cannot efficiently reduce the BER in the MIMO-OCC system.

Holographic optical elements with a large adjustable focal length and an aberration correction.

Holographic optical element (HOE) has the advantages of light weight, small volume and multiple functions, but the fixed focal length limits its application. The current methods of adjusting focal length suffer from the disadvantages of small adjustable range and the introduction of aberration. This paper proposes a design method for HOE, and it can compensate the aberrations of the reconstructed image for each distance in a large adjustable range. The focal length of HOE is adjusted by modulating the incident light through the wavefront modulator, and the aberration of the reconstructed image is corrected by optimizing the phase distribution of HOE and superimposing different compensation phases for different reconstruction distances. The reconstructed image experimentally moves without aberration in a large range, which demonstrates the feasibility of the proposed method. It is expected to be widely used in various optical fields where the focal length of HOE needs to be dynamically tuned.

Forced convection method for optical testing system with large aperture and long focal length

Forced convection method for optical testing system with large aperture and long focal length

Coaxial double-hole PEDOT: PSS electrodes achieving tunable terahertz zoomable convergence.

The local wavefront modulation technique in the terahertz band is an important basis for the development of terahertz modulation technology. Here, an electrically controlled convergent tunable device based on patterned transparent electrode poly (3, 4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) is realized to locally tune the terahertz wavefront. The device consists of two substrates with circular-hole electrodes and liquid crystal sandwiched between them. The refractive index gradient of liquid crystal in the device can be generated by the coaxial double-hole electrodes, which realize continuous control of significant focusing of the terahertz wave. The test results show that the focal length can be modulated in the range of 3-12 cm with varied external voltage; when it varies from 3 to 8 V, the 1/e2 radius of the spot decreases to 1.3 mm, 0.27 times the initial state, and the spot central intensity magnification increases gradually with the change, up to 3.31 times. The acquisition of the large tunable focal length range of the continuous terahertz zoom device shows that the construction of the gradient refractive index is an important method to regulate the terahertz wavefront by optical means, which greatly promotes the research of terahertz imaging devices.

Tunable Soft Lens of Large Focal Length Change.

Tunable lens technology inspired by the human eye has opened a new paradigm of smart optical devices for a variety of applications due to unique characteristics such as lightweight, low cost, and facile fabrication over conventional lens assemblies. The fast-growing demands for tunable optical lenses in consumer electronics, medical diagnostics, and optical communications require the lens to have a large focal length modulation range and high compactness. Herein, for the first time, an all-solid tunable soft lens driven by highly transparent dielectric elastomer actuators (DEAs) based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and waterborne polyurethane (PEDOT:PSS/WPU) transparent electrodes is developed. The deformation of the tunable soft lens is achieved by the actuation of DEAs, mimicking the change of the surface profile of the human eye to achieve remarkable focal length variations. Upon electrical activation, this tunable soft lens can vary its original focal length by 209%, which is one of the highest among current tunable soft lenses and far beyond that of the human eye. This study demonstrates that transparent DEAs are capable of achieving focus-variation functions, and potentially useful in artificial robotic vision, visual prostheses, and adjustable glasses, which will induce significant effects on the future development of tunable optics.

A compact and high-precision method for active beam stabilization system

An active beam stabilization system with high-precision correction and fast response with a small size is developed. By completely separating the correction of positional (x, y) and angular (α, β) deviations, this system avoids the coupling effect which increases the errors caused by the nonlinear, hysteresis, and creep characteristics of the piezoelectric actuators in conventional dual fast steering mirrors (FSMs) control system. And a combination of lenses is designed to achieve a large focal length in a small space, which is advantageous for high-precision and strong anti-interference ability. The experimental results show that the peak and valley (PV) values of the positional and angular deviations over 60 min are smaller than 0.58μm and 1.07 μrad which are less than 8% of the deviations without control, the standard deviation (STD) values are smaller than 0.07μm and 0.09 μrad. The regulating time is reduced to 38 ms. Moreover, the results from a series of experiments show that the STD values of the deviations over 10 h are smaller than 0.09μm and 0.13 μrad. Thus, the proposed system is effective for many laser applications, especially those involving high-precision optical systems.

Design of Star Sensor Optical Lens with Large Aperture and Long Focal Length

Design of Star Sensor Optical Lens with Large Aperture and Long Focal Length

Endless Single-Mode Photonics Crystal Fiber Metalens for Broadband and Efficient Focusing in Near-Infrared Range.

The advent of the ‘lab-on-fiber’ concept has boosted the prosperity of optical fiber-based platforms integrated with nanostructured metasurface technology which are capable of controlling the light at the nanoscale for multifunctional applications. Here, we propose an endless single-mode large-mode-area photonic crystal fiber (LMA-PCF) integrated metalens for broadband and efficient focusing from 800 to 1550 nm. In the present work, the optical properties of the substrate LMA-PCF were investigated, and the metalens, consisting of dielectric TiO2 nanorods with varying radii, was elaborately designed in the fiber core region with a diameter of 48 μm to cover the required phase profile for efficient focusing with a high transmission. The focusing characteristics of the designed metalens were also investigated in detail over a wide wavelength range. It is shown that the in-fiber metalens is capable of converging the incident beams into the bright, symmetric, and legible focal spots with a large focal length of 315–380 μm depending on the operating wavelength. A high and average focusing efficiency of 70% was also obtained with varying wavelengths. It is believed the proposed fiber metalens may show great potential in applications including fiber laser configuration, machining, and fiber communication.

Biomimetic curved compound-eye camera with a high resolution for the detection of distant moving objects.

In this Letter, we demonstrate the design and fabrication of a biomimetic curved compound-eye camera (BCCEC) with a high resolution for detecting distant moving objects purpose. In contrast to previously reported compound-eye cameras, our BCCEC has two distinct features. One is that the ommatidia of the compound eye are deployed on a curved surface which makes a large field of view (FOV) possible. The other is that each ommatidium has a relatively large optical entrance and long focal length so that a distant object can be imaged. To overcome the mismatch between the curved focal plane formed by the curved compound eye and the planar focal plane of the CMOS image sensor (CIS), an optical relay subsystem is introduced between the compound eye and the CIS. As a result, a BCCEC with 127 ommatidia in the compound eye is designed and fabricated to achieve a large FOV of up to 98∘×98∘. The experimental results show that objects with a size of 100 mm can be clearly resolved at a distance of 25 m. The capture of the motion trajectories of a moving object is also demonstrated, which makes it possible to detect and track the moving targets in a huge FOV for security surveillance purposes.

Multi-aperture imaging for flat cameras.

Imaging with high angular resolution requires large apertures and long focal lengths. This has prevented the integration of telephoto lenses into thin devices such as modern mobile phones. We report a camera module employing multiple rotated rectangular apertures and folding of the optical system into the plane of the camera, enabling an order-of-magnitude reduction in depth compared to traditional telephoto lenses. Multiple images are fused in the frequency domain to yield a single high-resolution image equivalent to that yielded by a single circular aperture. The diameter of this equivalent aperture may be several times wider than the depth of the camera module. We propose two architectures and present illustrative optical designs to demonstrate the concept. Simulations of raytraced image acquisition and computational image reconstruction demonstrate the potential for high-quality, high-resolution imaging from thin, flat lens modules.

Electrowetting lens with large aperture and focal length tunability

The electrowetting lenses has attracted researchers in many fields, such as biology, beam shaping, and drug delivery. Previous research on electrowetting lens has focused on neither expanding the dynamic focal length range nor reducing the wavefront aberration. However, the properties with large numerical aperture and low aberration are also essential properties of lenses, and can promote their application. Therefore, we calculated the meniscus of the lens with different optical apertures, and subsequently, analyzed the relations among the focal length, wavefront aberration, and optical aperture. To expand the focal length range, we designed an electrowetting-based triple-liquid lens with a root-mean-square wavefront aberration error of less than 1/4 waves.

Self‐Contained Focus‐Tunable Lenses Based on Transparent and Conductive Gels

AbstractFocus‐tunable lenses have found wide applications in optical communications, medical diagnostics, and consumer electronics. However, many focus‐tunable lenses have complex architecture, slow response, and low focal length variation, due principally to the separate design of optical path and activation mechanism and the use of liquid medium. Herein, a new self‐contained focus‐tunable lenses based on transparent and conductive gels are developed. The plano‐convex gels, acting both as lens and electrodes of actuator, with desirable curvature are precisely patterned by inkjet 3D printing. When a voltage is applied to the gel lenses, the elastomer membrane is stretched radially by Maxwell force, resulting in a reduction of lens thickness that corresponds to an increase of curvature radius. Therefore, a large focal length variation of 32–81% and a fast response speed of 80–153 ms are obtained. It is believed that this self‐contained focus‐tunable gel lenses can find many applications in portable optical devices, particularly suitable for space‐constrained tasks.