Panoramic Annular Lens System Research Articles

Athermal panoramic annular lens design with a thermal analysis method

An athermal 360∘×(30∘−100∘) and F/3.5 panoramic annular lens (PAL) system is designed. Through the optical mechanical thermal analysis results based on finite element analysis (FEA), it is expected that the system will have excellent performance under extreme temperature fluctuations. Simulation shows that the system is thermally insensitive in the temperature range from −40∘C to 60°C, consistently providing great imaging capability with the modulation transfer function (MTF) value at 133 lp/mm greater than 0.3. The proposed design and analysis workflow contains an evaluation of thermal optical performance with a higher accuracy, thus having significance in future athermal optical design. We expect the designed PAL system to have a broad application prospect in the field of outdoor applications, including automatic navigation of vehicles and all-weather surveillance systems.

General design algorithm for stray light suppression of a panoramic annular system.

In this work, a universal algorithm for designing a panoramic annular lens (PAL) system free from stray light is proposed. The impact of a given stray light path to the optical system could be estimated without running a full stray light analysis process, which allows designers to eliminate troublesome stray light paths by optimizing lens parameters at an early stage of optical design. A 360° ×(40°-100°) PAL system is designed and implemented to verify the proposed method. Simulation shows that the point source transmittance (PST) decreases by 2 orders of magnitude at a specific field-of-view (FoV) range after optimizing the system. Experimental results show perfect consistency with the simulation predictions, which indicate that two types of stray light are totally eliminated in the demonstrated system. This stray light analysis and suppression method provides a promising approach for the research and development of ultra-wide angle high performance optical systems.

Design of a panoramic annular lens system with an ultra-wide angle via an annular Gaussian radial basis function freeform surface.

The panoramic annular lens (PAL) system can capture plentiful scene information in real time. The locally described freeform surface can provide more degrees of freedom for the optical system design than the globally described one. In this paper, we propose a locally described annular Gaussian radial basis function freeform surface that enables a high-performance yet compact PAL system. The designed PAL system achieves an ultra-wide field of view (FOV) of (30∘∼125∘)×360∘. The F-theta distortion of the system is less than 3%, and the modulation transfer function across the whole FOV is greater than 0.5 at 100lp/mm. The proposed system can be implemented for various applications such as video conferencing or robotic navigation.

Compact and lightweight panoramic annular lens for computer vision tasks.

We propose a focal power distribution theory for the design of a compact panoramic annular lens (PAL) system based on Petzval sum correction. The system has a large field of view (FoV) of 360° ×(25°-100°). Its total length is 29.2 mm and weight is only 20 g. The proposed compact PAL system achieves large FoV and loose tolerances while maintaining small volume and low cost. It solves the shortcomings of traditional PAL systems that cannot be mounted on miniaturized portable devices due to their large volume and weight. We equip the compact PAL system with a novel and customized image enhancement model: PAL-Restormer to achieve better imaging quality. The produced images are further evaluated in various panoramic environment perception tasks. Extensive experiments show the promising potential of our proposed compact PAL system for the applications in wearable devices and mobile robots.

Design of a compact varifocal panoramic system based on the mechanical zoom method.

A compact varifocal panoramic annular lens (PAL) system based on the four-component mechanical zoom method is proposed, which solves the problem that the traditional PAL system cannot zoom in to the region of interest. By moving the zoom group and the compensation group, our design achieves continuous zooming, in which the focal length changes from 3.8 to 6 mm. It can keep the position of the image surface unchanged while maintaining a compact structure. The system has a field of view (FoV) of 25°-100° in wide-angle mode and an FoV of 25°-65° in telephoto mode. The modulation transfer function of the wide-angle view is higher than 0.22 at 147 lp/mm. The F-theta distortion is less than 3%, and the relative illuminance is higher than 0.9 in the zoom process. Compared with the zoom PAL system with multiple free-form aspheric surfaces, the proposed system uses multiple spherical lenses and only one Q-type asphere lens to achieve outstanding panoramic zoom imaging results. It is practical and straightforward, easy to manufacture, detect, and mass produce.

Design of a compact dual-channel panoramic annular lens with a large aperture and high resolution.

We propose a compact dual-channel panoramic annular lens (PAL) with a large aperture and high resolution to solve three major shortcomings of conventional PAL systems: resolution, imaging quality, and compactness. Using polarization technology, the system integrates two optical channels to eliminate the central blind area. Using our PAL aperture ray-tracing model, the large aperture PAL system with a low F-number of 2.5 and a diameter ratio of 1.5 is realized. The field of view (FoV) of the front channel is 360∘×(0∘-45∘), and the FoV of the side channel is 360∘×(45∘-100∘). Both channels apply Q-type aspheres. The Airy radii of the front channel and the side channel are 1.801 and 1.798 µm, respectively. It indicates that they match the 1.8 µm pixel sensor and can form a great image on the same sensor. The modulation transfer function at 157 lp/mm is greater than 0.4 over the entire FoV. The F-θ distortion is less than 5%, and the relative illuminance is higher than 0.78 in the two channels. The excellent imaging results prove the feasibility of our PAL design method and the advantages of the compact dual-channel PAL system for space-constrained scenes.

Design of a panoramic annular lens with ultrawide angle and small blind area.

A panoramic annular lens (PAL) comprises a panoramic annular head unit (PAHU) and a relay lens group. Due to the properties of annular imaging, single-channel PAL systems contain a blind area in the central field of view (FOV), which is difficult to reduce in a traditional optical system structure. Therefore, we propose a novel reflective PAHU structure, using two mirrors to replace the traditional single-lens- or multilens-cemented PAHU, to achieve a smaller blind area and ultrawide-angle imaging. In this paper, we present the design of an ultrawide-angle PAL with a FOV of (22∘∼120∘)×360∘ using our proposed method. The resulting optical system achieves a blind area ratio of less than 3.67%. Compared with the traditional PAL system with the lowest blind area ratio, the blind area ratio of our system is reduced by half, demonstrating the feasibility of the proposed method.

Non-blind area PAL system design based on dichroic filter.

An inevitable problem of Panoramic Annular Lens (PAL) System is the blind area in the central part of image plane, which vastly reduces the pixel efficiency of detector. Here we present a design of PAL system based on dichroic filter, which can combine two channels of rays in different bands and image them on the same detector. The dichroic filter in this paper is designed to make ultraviolet rays reflect and visible rays transmit, and the ultraviolet rays are imaged on the PAL imaging area while the visible rays are imaged on the blind area of conventional PAL image plane. In order to image both bands of rays on the same plane, we add a correcting lens group in front of PAL system. As a result, the FOV of ultraviolet channel is ranging from 30°~90° and the one of visible channel is ranging from 0°~10°.

Design of a panoramic annular lens with a long focal length

A new method to improve the design of the panoramic annular lens (PAL) optical system with long focus is introduced. Cemented lenses are used in a PAL block to improve the design freedom. A multilayer diffractive optical element (MDOE) is used in relay optics to simplify the structure of the system and to increase diffractive efficiency of the design spectral range. The diffractive efficiency of MDOE in a wide spectral range is investigated theoretically. A seven piece PAL system with a total effective focal length of 10.8 mm is realized, and the diffractive efficiency of the whole design wavelength is above 99.3%. A PAL system with all spherical surfaces is described as a comparison.