Freeform Lens Research Articles

Improved optical camera communication systems using a freeform lens.

Optical camera communication (OCC) systems, which utilize image sensors embedded in commercial-off-the-shelf devices to detect time and spatial variations in light intensity for enabling data communications, have stirred up researchers' interest. Compared to a direct OCC system whose maximum data rate is strongly determined by the LED source size, a reflected OCC system can break that limitation since the camera captures the light rays reflecting off an observation plane (e.g., a wall) instead of those light rays directly emanated from the light source. However, the low signal-to-noise ratio caused by the non-uniform irradiance distribution produced by LED luminaire on the observation plane in current reflected OCC systems cannot be avoided, hence low complexity and accurate demodulation are hard to achieve. In this paper, we present a FreeOCC system, which employs a dedicatedly tailored freeform lens to precisely control the propagation of modulated light. A desired uniform rectangular illumination is produced on the observation plane by the freeform lens, yielding a uniform grayscale distribution within the received frame captured by the camera in the proposed FreeOCC system. Then, the received signal can be easily demodulated with high accuracy by a simple thresholding scheme. A prototype of the FreeOCC system demonstrates the high performance of the proposed system, and two pulse amplitude modulation schemes (4-order and 8-order) are performed. By using the freeform lens, the packet reception rate is increased by 35% and 32%, respectively; the bit error rate is decreased by 72% and 59%, respectively, at a transmission frequency of 5 kHz. The results clearly show that the FreeOCC system outperforms the common reflected OCC system.

Freeform optical design of beam shaping systems with variable illumination properties.

Freeform optics constitutes a new technology that is currently driving substantial changes in beam shaping. Most of the current beam shaping systems are elaborately tailored for fixed optical properties, which means the output light distribution of a beam shaping system usually cannot be changed. What we present here is a class of beam shaping systems, the optical properties of which can be changed to meet the requirements for different applications. The proposed beam shaping system is composed of a freeform lens and a non-classical zoom system which is designed by ray aiming and the conservation of energy instead of aberration control. The freeform lens includes two elaborately designed freeform optical surfaces, by which both the intensity distribution and wave-front of an incident light beam are manipulated in a desired manner. The light beam after propagating through the non-classical zoom system produces an illumination pattern on a fixed observation plane with a variable pattern size and an unchanged irradiance distribution at different zoom positions. Two design examples are presented to demonstrate the effectiveness of the proposed beam shaping systems.

Freeform beam splitting system design for generating an array of identical sub-beams.

Laser beam splitting by freeform optics is promising but less studied. Instead of directly forming a target spot array, we propose to first convert the input beam into a closely connected Gaussian sub-beam array. All the Gaussian sub-beams have the same optical field distributions which thus can produce identical discrete spots on the target plane. Such a design concept is very beneficial to ensure the consistency for laser processing. Importantly, the introduction of an intermediate Gaussian sub-beam array can reduce diffraction effects when the size of each Gaussian sub-beam is sufficiently larger than that of the corresponding sub-area within the input beam. The desired transformation can be achieved by two typical systems. The first system consists of two plano-freeform lenses. The second system is composed of a plano-freeform lens and a lens with an entrance freeform surface and an exit surface of freeform lens array. The two freeform beam splitting systems can be determined based on appropriate ray mappings among the input, intermediate and target irradiance distributions and a subsequent double-surface construction. Geometrical and physical simulations verify the effectivenesses of the two beam splitting systems.

Material removal profile prediction and experimental validation for obliquely axial ultrasonic vibration-assisted polishing of K9 optical glass

K9 optical glass is one of the typical components in optical systems. However, because of its poor fracture resistance, it is difficult to polish it with ultra-precision and high-efficiency and without any surface damage simultaneously. The emergence of the obliquely axial ultrasonic vibration-assisted polishing (UVAP) method can solve this problem which encounters in polishing efficiency and shape accuracy. However, due to the unclear material removal profile (MRP) mechanism, obliquely axial UVAP is not widely used in the processing field. This paper introduces the obliquely axial UVAP method in research processes, mainly focusing on the fixed point MRP analysis of the obliquely axial UVAP. Based on Hertz's contact theory, polishing pressure, the length of the semi-long axis (LLA) and the length of the semi-short axis (LSA) of the contact area are calculated under ultrasonic vibration conditions. Meanwhile, the relative linear velocity distribution of the oblique polishing tool in the instantaneous contact area is modeled by mathematical geometry method. A novel model of the MRP distribution for obliquely axial UVAP is proposed following the Preston equation. Subsequently, a series of polishing experiments were carried out to verify this model. The results show that the numerical model has good agreement with the experimental results on MRP, LLA, LSA, material removal depth and material removal rate (MRR). In addition, the material removal capability can be significantly improved by larger ultrasonic amplitude and larger oblique angle. This model not only more clearly elucidates the processing mechanism of obliquely axial UVAP, but also provides theoretical support for the polishing of free-form optical lenses.

Iterative freeform lens design for optical field control

It is still very challenging to determine a freeform lens for converting a given input beam into a prescribed output beam where not only the irradiance distribution but also the phase distribution hardly can be expressed analytically. Difficulties arise because the ray mapping from the input beam to the output beam is not only intertwined with the required double freeform surfaces but also intertwined with the output phase distribution, whose gradient represents the directions of the output rays. Direct determination of such a problem is very difficult. Here, we develop a special iterative wavefront tailoring (IWT) method to tackle this problem. In a certain iteration, the current calculation data of the double freeform surfaces and the output phase gradient are used to update the coefficients of a Monge–Ampère equation describing an intermediate wavefront next to the entrance freeform surface. The solution to the wavefront equation could lead to an improved ray mapping to be used to update the corresponding phase gradient data and reconstruct the double freeform surfaces. In a demonstrative example that deviates much from the paraxial or small-angle approximation, the new IWT method can generate a freeform lens that performs much better than that designed by a conventional ray mapping method for producing two irradiance distributions in the forms of numerals “1” and “2” on two successive targets, respectively.

High-contrast ratio and high-efficiency anamorphic DLP illumination system design with a freeform surface lens.

In this paper, an anamorphic digital light processing illumination system design with a freeform surface lens is described. A lens with a freeform surface lens is combined with the achromatic total internal reflection prism set for application in a relay lens system. In order to achieve a high contrast ratio without sacrificing illumination system efficiency, the novel, to the best of our knowledge, design uses an x-y polynomial surface for the freeform surface lens to reduce the overlap angle of the anamorphic angular distribution in angular space. Moreover, there is no need to use a baffle at the aperture stop in this novel design. We can reach a half-cone angle of 17.49° in the y direction of the angular distribution in angular space. The overlap angle is only 0.98°. Finally, with this novel design, we can achieve a high contrast ratio of 9128:1 and an illumination system efficiency is 66.4%. The four-corner average spot size at the active area of the digital micromirror device chip is controlled at about 240 µm, and the optical distortion is less than 1%. The corresponding lateral color aberration is 3.61 µm.

Design of a phosphor-converted LED based lighting system considering both the lighting and color uniformity

In this work, a scheme of combining an aspheric reflector and a primary packaging freeform lens in phosphor-converted lighting-emitting diode (pc-LED) based lighting system design was developed. In contrast to most of previous works in which the color and illumination uniformity of the pc-LED lighting systems were improved one by one, the developed scheme can improve both indicators simultaneously. To demonstrate the feasibility of the developed design scheme, an initially designed pc-LED optical model, with an average correlated color temperature (CCT) of about 5000 K, was constructed as the light source of the illumination system. The key ingredient to the color uniformity of the illumination system was investigated at first, and then several instances with the cut-off angle ranging from 40 to 60 degrees were further discussed. Detailed analysis shows: for each case, the CCT variation decreases from over 4000 K to smaller than 300 K and the illumination uniformity increases from a very low level to better than 80% on the target region.

Design of a miniature anamorphic lens with a freeform front group and an aspheric rear group

We propose a miniature anamorphic lens design that records wide-screen videos on an ordinary CMOS format. The front group consists of two freeform lenses, which achieve different focal lengths in the two orthogonal directions and thus enable the anamorphic characteristics. The rear group is made of rotationally symmetric aspheric elements that relay the image on the sensor. The annularly stitched extreme-point-based polynomial surface description is proposed to control the extreme point position and the air clearance between elements in the optimization process. An optimization method based on surface upgrade and conversion is adopted in the design. The design result offers an anamorphic ratio of 1.33 and an f-number (f / #) of ∼2, with a field of view of 65.3 deg × 35 deg. The overall length of the lens is 9.5 mm, which shows an advantage for integration into pocket devices.

Asymmetric Double Freeform Surface Lens for Integrated LED Automobile Headlamp.

We propose a design method of asymmetric double freeform surface lens for an integrated LED automobile headlamp and develop an integrated LED automobile optical system. A single asymmetric double freeform surface lens is designed to redistribute rays emitting from the light source for realizing both low and high beams. Moreover, a freeform surface reflector is used to improve the energy efficiency of high beams. The prism placed in the optical path can suppress chromatic dispersion on the edge of the target plane. Simulation and experimental results show that the illumination values and color temperature of the key points can fully meet the requirements of United Nations Economic Commission for Europe vehicle regulations (ECE) R112, 48, and 128. The volume of the whole optical system comprised of freeform surface elements is smaller than that of the low beam system of a traditional headlamp, resulting in saved space, in which other electronic devices can be installed for the safety of the driver, which indicates that the proposed method is practical in the field of automobile lighting.

Short Free-Standing Pole LED Luminaire and Lens Design for Road Lighting

Road luminaries are required to provide the luminance specified in the standards according to the road characteristics. For this reason, the light from the light source should be directed according to the desired conditions. While the range of minimum average road surface luminance recommended for different classes of road are provided; at the same time, it is desirable to be economical. In this study, a freeform lens and LED luminaire design with high luminous efficacy, low glare and uniform luminance distribution with a height of 1.5 m and a distance of 7 m between poles were designed for M3 road standards. First of all, lens design was made by using optical and illumination design software. Also, lens manufacturing and luminaire production were made as a result of the success of the design simulation test. The success of the LED luminaire in providing CIE standards has been measured on the designed road. In addition, the advantages and disadvantages have been determined by comparing with High Pressure Sodium Vapor (HPS) lamps.

Comparison of physiognomy and frame angle parameters using different devices to prescribe progressive addition lenses

ABSTRACT Clinical relevance Accurate measurement of several physiognomy parameters (interpupillary, nasopupillary and fitting height distances) and frame angles (pantoscopic and frame wrap angles) is essential for prescribing progressive addition lenses for presbyopic patients. Background Few reports have described the repeatability of different devices commonly used to conduct essential measurements for prescribing progressive addition lenses. Methods Interpupillary, nasopupillary (at far and near distances) and fitting point heights were measured three consecutive times in 21 healthy volunteers with four devices (traditional frame ruler, PD-5 interpupilometer, OptiCenter, and VisiOffice). Pantoscopic and wrap frame angles were also measured three times with Essilor standard pantoscopic ruler, Opticenter and VisiOffice. Results The frame ruler, PD-5 and Opticenter showed better repeatability for interpupillary and nasopupillary distance (co-efficient of variation close to 1%, within-subject standard deviation or Sw < 0.50 mm) measurements at far and near distances than Visioffice (co-efficient of variation > 2%, Sw > 0.50 mm). Fitting point heights measurements showed worse repeatability with all devices (frame ruler: co-efficient of variation close to 5%, Sw = 0.46 mm; Opticenter co-efficient of variation > 5%, Sw > 0.80 mm; Visioffice co-efficient of variation > 10%, Sw > 1.50 mm). Pantoscopic angle measurements showed very low repeatability with the ruler and Opticenter (co-efficient of variation > 25%, Sw > 1.90 mm). The frame wrap angle showed unacceptable repeatability values with the ruler (co-efficient of variation > 10%, Sw = 0.49º) and Visioffice (co-efficient of variation > 60%, Sw > 2.50º), but acceptable repeatability with Opticenter (co-efficient of variation < 1%, Sw = 0.05º). Conclusions Interpupillary and nasopupillary distance measurement showed acceptable repeatability with all the assessed methods; however, these measurements alone are no longer sufficient for free-form progressive addition lens prescription, which requires fitting point heights and pantoscopic and frame wrap angle measurement. Such measures display a lack of repeatability that could induce centration errors and could affect vision and/or adaptation of the user.

Asymmetric freeform lens design for a light-emitting diode front fog lamp

With the rapid advancement of light-emitting diodes (LEDs), front fog lamps using LEDs have become a main emphasis for vehicle lighting. For vehicle lighting, the front fog lamps should provide a bar-shaped beam of light with a sharp cutoff at the top and are designed to increase the illumination directed toward ground at a sharp angle. In this study, an innovative lens design based on a freeform surface responding to the requirements of the vehicle lighting is proposed. The design of the two-axis asymmetric freeform lens for LED front fog lamp can meet ECE R19 class F3 regulation without any other lens or reflector.

Further support for a trio of mass-to-light deviations in Abell 370: free-form grale lens inversion using BUFFALO strong lensing data

ABSTRACT We use the Beyond Ultra-deep Frontier Fields and Legacy Observations (BUFFALO) strong lensing image catalogue of the merging galaxy cluster Abell 370 to obtain a mass model using free-form lens inversion algorithm grale. The improvement of the strong lensing data quality results in a lens plane rms of only 0.45 arcsec, about a factor of two lower than that of our existing HFF v4 reconstruction. We attribute the improvement to spectroscopic data and use of the full reprocessed HST mosaics. In our reconstructed mass model, we found indications of three distinct mass features in Abell 370: (i) a ∼35 kpc offset between the northern BCG and the nearest mass peak, (ii) a ∼100 kpc mass concentration of roughly critical density ∼250 kpc east of the main cluster, and (iii) a probable filament-like structure passing N-S through the cluster. While (i) is present in some form in most publicly available reconstructions spanning the range of modelling techniques: parametric, hybrid, and free-form, (ii) and (iii) are recovered by only about half of the reconstructions. We tested our hypothesis on the presence of the filament-like structure by creating a synthetic cluster – Irtysh IIIc – mocking the situation of a cluster with external mass. We also computed the source plane magnification distributions. Using them, we estimated the probabilities of magnifications in the source plane, and scrutinized their redshift dependence. Finally, we explored the lensing effects of Abell 370 on the luminosity functions of sources at zs = 9.0, finding it consistent with published results.

Optimized Design of a Pump Laser System for a Spin Exchange Relaxation Free Inertial Measurement Device.

In order to improve the precision and beam quality of a pump laser for a spin exchange relaxation free inertial measurement device, we applied one scheme to achieve the square wave modulation and power stability control of the pump laser and another one to obtain the uniform intensity distribution of the laser beam, in which the acousto-optic modulator (AOM) and proportion integration differentiation (PID) controller were used to achieve the former, and the freeform surface lens was designed and optimized to achieve the latter based on the TracePro software. In experiments, the first-order diffraction light beam coming through the AOM had a spot size of about 1.1 × 0.7 mm2, and a spherical vapor cell with a radius of 7 mm was placed behind the freeform surface lens. Results show that the uniformity of the reshaped intensity distribution is higher than 90% within the target area with a radius of 7 mm both in the simulation and the experiment, which ensure that the uniform laser beam covers the area of cell. On the other hand, the power stability of the pump laser is controlled to be less than 0.05%. Compared with traditional methods, the complicated calculation process in optical design is better solved, and a higher uniformity with slight energy loss is achieved.

Extended aperture line-scanning Hartmann wavefront sensor.

We first propose a line-scanning Hartmann wavefront sensor (LS-HWS) with extended aperture. In the LS-HWS, a line-scanning imaging sensor was driven by a motor and scanning behind a large-area Hartman mask. Compared to the traditional Hartman wavefront sensor with two-dimensional imaging sensors, our method can significantly enlarge the aperture because of the larger imaging area with line-scanning imaging sensors. Cross correlation registration was adopted to reduce the scanning error. Experiments on two single spherical lenses and a free-form lens were performed to demonstrate the capability of the LS-HWS method. The results show that our method can achieve an aperture of 17.5×37.5mm2 with the prototype system, which could be further extended easily and is limited only by the size of the line-scanning imaging sensor and the scanning range of the motor. We believe that the LS-HWS method is promising for many wavefront sensing applications where a large aperture is preferred.

Design and evaluation of a freeform lens-array for a structured light illumination

In illumination applications, freeform lens design starts by modeling the light source intensity, then determining the lens surface. Therefore, any change in the source intensity distribution directly impacts the created illuminance. Freeform lens-array could reduce the dependency between the illuminance pattern and the source intensity distribution. It divides the light source energy into separate beams; each creates the same illuminance pattern. All separated beams are superimposed at a distant target to generate the final illuminance pattern. This paper explains the design procedures of a freeform lens-array in detail, simulates the optical performance, and experimentally evaluates the working principle. Experiments evaluate using different light sources and using a variable illuminated aperture. Moreover, simulations compare the freeform lens-array to a traditional freeform lens.

Generating-function approach for double freeform lens design.

Many LED lighting applications involve the design of multiple optical surfaces. A prime example is a single lens with two refractive surfaces. In this paper, we consider an LED light source approximated as a point and a far-field target intensity. Using Hamilton's characteristic functions, the design problem is converted into two generalized Monge-Ampère equations by deriving a generating function for each optical surface. The generating function is a generalization of the cost function in optimal transport theory. The generalized Monge-Ampère equations are solved using an iterative least-squares algorithm. To compute the first optical surface, we choose an intermediate far-field target intensity. By choosing different intermediate target intensities based on the source and target intensity, we develop a "knob" to distribute the refractive power over both surfaces of the lens. We apply the algorithm on two example problems and show it is capable of producing complicated target distributions.

A Freeform Lens System Design and Simulation in the Polar Coordinate

In the field of illumination engineering, freeform technology is playing a more and more important role. Several methods have been reported in recent papers. The paper introduce a design method to generate an ellipse spot in the polar coordinate using the polar grids based on flux transportation mapping. In this method, the source is a point and the point is divided along the azimuth angle and zenith angle in the polar coordinate system. Then we divided the flux target in the polar coordinate, the grids of the target are achieved by the mapping between the source and the target. Based on the mapping and energy conservation, we can derive a set of the first-order PDE according to Snell’s law. We can acquire a points cloud after solving the PDE numerically, then we will construct a smooth freeform using Rhino. Finally, we will test the freeform using Light Tools. With this method, we can design a lens with the light utilization efficiency over 0.8. Keywords: LED; Freeform; Mapping; Polar coordinate.

Free-form broadband flat lenses for visible imaging

The resolution of a conventional lens is governed by its numerical aperture (NA) while its light-concentration ability is governed by its f-number (f/#), both of which are dependent on the diameter and focal length of the lens. Hence, these properties for a conventional lens are inherently coupled. Here, we show that by utilizing the principle of free-form broadband diffractive optical elements (BDOEs), we can create ultra-flat optical elements that are able to concentrate incoming light over a fixed aperture to different sized focal spots engineered in the shape of a square. Hence, we are able to decouple the NA and f/# of a lens by being able to independently control the size of the input aperture and the resolution of these devices. Specifically, we designed, fabricated, and characterized three BDOE lenses operating in the visible band (450nm–750nm), each having f/# of 11.25, but with NAs of 0.00075, 0.0067, and 0.054, respectively. We further use simulations to emphasize that such decoupling is possible even at much higher NAs. Experiments confirm achromatic focusing and broadband imaging. One of the lenses exhibited a depth-of-focus almost 2 orders of magnitude larger than the diffraction limit. Such BDOE lenses can eliminate the need for anti-aliasing filters and could also be very useful in focal-plane arrays with large pixel sizes, where light collection efficiency needs to be maintained. Furthermore, by abandoning rotational symmetry, one can achieve free-form geometries in the focal spot, such as a square that can more closely match the geometry of the sensor pixel.

用于LED均匀照明的自由曲面菲涅耳TIR透镜光学设计

用于LED均匀照明的自由曲面菲涅耳TIR透镜光学设计