A f-theta laser scanning optical system with wide scanning angle, high resolution and compactness is proposed. Specifications of the system are analyzed and calculated. To simplify the optical layout and improve the optical performance, freeform surfaces are used to describe the shape of the lens. The method about how to create a user-defined surface in the optical design software is introduced. The optimization strategy and implementation method of freeform surface are mentioned. The design result achieves a f-theta laser scanning optical system with a field-of-view of ±55.6°, a resolution higher than 600 dots per inch, and a total length less than 150mm. The modulation transfer function of the system is close to the diffraction limit and the linear distortion is less than 3μm.
With the advent of high brightness microdisplay, augmented reality head mounted display (AR-HMD) has rapidly developed and applied. Various optical schemes emerge one after another. However, it is still a huge challenge to realize large field of view (FOV), high resolution and keep the compact form of head mounted display. We propose a novel free-form prism tiling optical system, which can simultaneously realize large field of view, high resolution and compact optical see-through augmented reality HMD. It can overcome the FOV/resolution invariant and solves the problem that the optical axes of the display channels don’t coincide with the visual axis of the human eye. The optical system consists of two microdisplays, two free-form prisms and a compensation lens which are attached together. The prisms are partially overlapped to provide the same field of view and reduce the seam at the transition region of adjacent FOV. The optical see-through system we designed achieves large FOV of 52.8°×52.8° (70° diagonally) and resolution of 33.7 pixels/degree, and has good optical performance. We emulated the system with distortion and illuminance pre-conditioning and discussed the remaining problems and future work.
Stitched surfaces have the advantages of high degrees of freedom and flexibility, which can improve the performance of imaging optical system while reducing volume and weight. In this paper, a new type of surface, called annularly stitched aspheric surface (ASAS), is demonstrated. Firstly, the definition of ASAS is given, and it meets the C1 continuity condition. Then, a high-precision conversion method from traditional aspherical surface to ASAS is proposed to establish the initial system with this novel surface. The optimization strategy and implementation method are explained. Special constraints that are needed when optimize the system with ASAS is also mentioned. Finally, the ASAS is applied to the design and an ultra-short throw (UST) ratio projector objective lens is optimized. The total length of the optimized system is only 155mm, the maximum distortion value is only 1.36%, and MTF value of full field of view at 66lp/mm is higher than 0.3. The result shows that this new surface type can increase the degrees of freedom and flexibility to optical system, verifying the feasibility of ASAS.
Virtual image distance (VID) is a key parameter in augmented reality (AR) or virtual reality (VR) systems and has a great influence on product performance and user experience. Therefore, it is very necessary to measure the VID accurately and efficiently. In this paper, we develop a VID measurement system which needs no mechanical scanning in the measurement process. The VID can be measured in a short period of time based on one single image generated by the AR/VR system. An image-telecentric lens is designed which is used to capture the virtual image. A diaphragm with two pinholes is placed at the entrance pupil plane of the imaging lens. When the imaging lens is not focused on the virtual image, the captured image contains two copies of the virtual image with a certain interval which is proportional to the VID in units of diopters. By calculating the interval, we can obtain the VID. A simulation is performed in LightTools to verify the effectiveness of the measurement system, and the result indicates that the measurement error is 5 mm when the virtual image is at 3 m.
It has been a challenge to design an automotive head-up display (HUD) that has large eyebox while maintain a compact structure. In this paper, we present a combiner-type HUD design using freeform mirrors. The HUD is an off-axis fourmirror system consisting of 4 mirrors, which are enclosed in a box to achieve a compact form. The tilt angle of the combiner is adjustable, which can be adapted to different heights of exit pupil. We initially propose an off-axis, fourmirror system which only uses spherical surfaces, then we optimize it by replacing with freeform surfaces, which enables us to balance the residual asymmetrical aberrations. Finally, we obtain an HUD system with good imaging performance. The virtual image is projected at 5 meters away from observer, and the eye box is 106 × 66 mm2 .
The compound eye optical system has attracted much recent attention, owing to its large field-of-view, compact structure, and rapid imaging capabilities. We designed a compact image scanner (cross-section 36.5 mm × 17 mm) based on the compound eye system. A single imaging unit is mainly composed of two freeform mirrors and a flat mirror, and its field-of-view in object space reaches 10 mm. The modulation transfer function of the system is greater than 0.6 at 12 cycles/mm corresponding to Nyquist spatial frequency of 600 dots per inch in depth-of-field of 0~4 mm. Furthermore, a larger field-of-view is achieved by splicing multiple imaging units with 1-mm overlap in object space. An object-side telecentric system is used to obtain constant magnification at different object distances and the distortion (<1 μm) is controlled by freeform mirrors. The final image is obtained by image splicing. The imaging quality of the scanner is further improved by eliminating stray light.
With the widespread use of AR/VR head-mounted displays, there is an increasing demand for pinhole cameras to test their image quality. However, it has been a challenge to design a pinhole camera with a wide field of view (FOV), high image performance and low distortion while maintaining compact and lightweight. In this paper, a pinhole camera optical system is designed. Based on a 1 in. sensor, the pinhole lens has a FOV of 100° and an entrance pupil diameter of 4mm. In our final design, the distortion is limited within 2.5% and the modulation transfer function values across the entire field are above 0.3 at 161 line pairs/mm (lps/mm). The spherical aberration, color aberration and field curvature are corrected. The design result shows that the optical system of the pinhole camera is compact and meets the requirements of the VR/AR image quality test system.
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