Freeform Refractive Surface Research Articles

3D-printed facet-attached optical elements for beam shaping in optical phased arrays.

We demonstrate an optical phased-array equipped with a 3D-printed facet-attached element for shaping and deflection of the emitted beam. The beam shaper combines freeform refractive surfaces with total-internal-reflection mirrors and is in-situ printed to edge-emitting waveguide facets using high-resolution multi-photon lithography, thereby ensuring precise alignment with respect to on-chip waveguide structures. In a proof-of-concept experiment, we achieve a grating-lobe free steering range of ±30∘ and a full-width-half-maximum beam divergence of approximately 2∘. The concept opens an attractive alternative to currently used grating structures and is applicable to a wide range of integration platforms.

Cancelling lidar echo signal 1/range2 dependence and geometrical form factor shaping by the application of freeform optics

Due to three-dimensionality of the surrounding space, power of the optical echo in laser rangefinders, scanners and variety of lidar systems shows a well-known range−2 dependence. It creates demanding requirements for the receiving electronics in terms of extremely high dynamics of the detected signal. In order to meet these requirements, specific solutions have to be implemented, the side effect of which may be a signal distortion and corresponding precision degradation. In this paper, it is shown, that it is possible to design freeform optical component, which can compensate 1/range2 effect. The aim of this study was to design such a freeform lens which makes laser tele-detection system receiving the same level of optical echo power, no matter of the distance to the target. From simple energy-conservation rules, the required ray mapping for collecting optics can be deduced, which appears however to be non-integrable. To overcome this problem, the modified fully integrable ray mappings were calculated, based on functional minimization method and Monge-Ampere equation, which enabled to obtain smooth freeform refractive surface.

Interpolation equations of freeform refractive surfaces

Active studies on freeform optical surfaces have only begun very recently. Currently, such surfaces are widely used in illuminators, concentrators, hybrid systems, and other optical devices. In this paper, a method for modeling freeform surfaces is proposed for a given source type and illumination distribution, which can be described by a line, arc, circle, or a complex shape. The interpolation of the resultant freeform surface point array obtained via modeling allows for the determination of the equation of the refracting freeform surface.

Cloaking of metal grid electrodes on Lambertian emitters by free-form refractive surfaces.

We discuss invisibility cloaking of metal grid electrodes on Lambertian light emitters by using dielectric free-form surfaces. We show that cloaking can be ideal in geometrical optics for all viewing directions if reflections at the dielectric-air interface are negligible. We also present corresponding white-light proof-of-principle experiments that demonstrate close-to-ideal cloaking for a wide range of viewing angles. Remaining imperfections are analyzed by ray-tracing calculations. The concept can potentially be used to enhance the luminance homogeneity of large-area organic light-emitting diodes.

Catadioptric freeform optical system design for LED off-axis road illumination applications.

The aim of this paper is to develop a new composite structure of catadioptric optical system containing both freeform refractive surface and freeform total internal reflective (TIR) surface for LED road illumination applications. The role of freeform refractive part is to generate the shifted general rectangular illumination pattern to optimally match the shape of the road surface. The application of TIR mechanism is aimed to control the stray light in the sidewalk direction of the road luminaire and maximize the efficient energy efficiency. In this paper, we use the "double pole" ray mapping technique to design the refractive optical surface and the θ-φ coordinate ray mapping technique to derive the freeform TIR surface. The simulation shows that the novel catadioptric design has relatively high collection efficiency, thus high average illuminance level inside the effective illumination area. This lens also has good control of stray light on the backside of the road luminaire.

Numerical Modeling of Freeform Refractive Surfaces Forming Line Radiation Pattern

The original purpose of the study is to solve the inverse problem of synthesis of freeform optical elements. This article describes a numerical approach for synthesis of freeform refracting surfaces forming a line radiation pattern.

Free-form illumination of a refractive surface using multiple-faceted refractors.

We report a design method based on multiple-faceted refractors for free-form illumination of a refractive surface. The free-form surface is constructed as a set of primitive surface elements, which provide flexibility to satisfy the requirements of practical design problems. An extended light source can be considered, and a smooth free-form refractive surface can be established by adding feedback to the design process for a point source. Moreover, the performance can be improved by iterating this feedback process. Illumination systems with a point source and an extended source are designed and analyzed, resulting in uniform illuminance distribution, which demonstrates the validity of the method.

Freeform illumination lens design using composite ray mapping

We develop a new ray mapping approach to address the surface error and hot spot issues in designing a freeform total internal reflection (TIR) lens for nonrotational uniform illumination. Our proposed ray mapping approach partitions the source intensity distribution in the peripheral regions using the traditional spherical coordinate system to design the freeform TIR surfaces and in the central regions using the modified spherical coordinate system to design the freeform refractive surface. This new design method will reduce the surface error in the current ray mapping methods, therefore improving the illumination uniformity significantly. In addition, the freeform lens designed with this approach is much more robust than the lenses designed using other ray mapping methods.

LED surgical lighting system with multiple free-form surfaces for highly sterile operating theater application.

Although the ventilation system is widely employed in the operating theater, a strictly sterile surgical environment still cannot be ensured because of laminar disturbance, which is mainly caused by the surgical lighting system. Abandoning traditional products, we propose an LED surgical lighting system, which can alleviate the laminar disturbance and provide an appropriate lighting condition for surgery. It contains a certain amount of LED lens units, which are embedded in the ceiling and arranged around the air supply smallpox. The LED lens unit integrated with an LED light source and a free-form lens is required to produce a uniform circular illumination with a large tolerance to the change of lighting distance. To achieve such a dedicated lens, two free-form refractive surfaces, which are converted into two ordinary differential equations by the design method presented in this paper, are used to deflect the rays. The results show that the LED surgical lighting system can provide an excellent illumination environment for surgery, and, apparently, the laminar disturbance also can be relieved.

Efficient optimal design of smooth optical freeform surfaces using ray targeting

An optimization design method is proposed for generating smooth freeform reflective and refractive surfaces. In this method, two optimization steps are employed for ray targeting. The first step aims to ensure the shape of the target illumination, and the second step is employed to further improve the irradiance uniformity. These two steps can provide significant savings of time because the time consuming Monte Carlo raytracing is not used during the optimization process. Both smooth freeform reflective surfaces and smooth freeform refractive surfaces can be designed, and the target illumination could be achieved just by controlling the positions of several hundred predefined rays on the target plane with these two steps. The simulation results and the experimental tests show that this optimization design method is robust and efficient.

Freeform surface design for a light-emitting diode–based collimating lens

A freeform collimating lens is designed to project light rays emitted from an LED light source to a far target plane. Generally, the projection distance is assumed to be more than 100 m, and the light beam to have negligible divergence. The lens consists of a total internal reflection (TIR) side surface, a spherical surface in the rear, a vertical plane surface in the outer part of the front, and a freeform refractive surface in the central part of the front. Light rays emitted from the LED source with large spread angles hit the TIR surface and are redirected parallel to the light axis, and those having small spread angles will be collimated by the freeform refractive surface, which is designed with a simple approximation method, and then travel parallel to the light axis. Computer simulation results show that an optical efficiency of 81.5% is achieved under a view angle of ±5 deg and for a 1 mm×1 mm LED source.