Design of an ultralight and compact projection lens

Comprehensive defect-detection method for a small-sized curved optical lens

During quality-assurance procedures in the mass production of small-sized curved optical lenses, fine defects are usually detected via manual observation, which is not recommended owing to the associated drawbacks of high error rate, low efficiency, and nonamenability to quantitative analysis. To address this concern, this paper presents a comprehensive defect-detection system based on transmitted fringe deflectometry, dark-field illumination, and light transmission. Experimental results obtained in this study reveal that the proposed method demonstrates efficient and accurate detection of several microdefects occurring in small-sized optical lenses, thereby providing valuable insights into the optimization of parameters concerning the mass production of optical lenses. The proposed system can be applied to the actual mass production of small-sized curved optical lenses.

Effect of assembling errors on the diffraction efficiency for multilayer diffractive optical elements

Based on the expression function of diffraction efficiency, and the phase delay function of diffractive optical elements (DOEs), the diffraction efficiency for multilayer diffractive optical elements (MLDOEs) is described with tilt and decenter assembling errors. A mathematical model of the relationship between diffraction efficiency and assembling errors of MLDOEs is proposed to analyze the effect of assembling errors on the diffraction efficiency of MLDOEs. The analyzed results from the mathematical model provide a range of values for the effect of assembling errors on the diffraction efficiency of MLDOEs. Assembling errors are important parameters for hybrid diffractive refractive optical systems, including MLDOEs, and so the proposed model will be useful for guiding the design and fabrication of such optical systems.

Diffractive-refractive correction units for plastic compact zoom lenses

A method of designing a plastic zoom lens with a diffractive-refractive hybrid corrector, comprising one diffractive lens and one refractive lens, is described. The efficiency of this method is demonstrated by designing a compact zoom lens for a mobile phone. This zoom design, incorporating lenses made only of two commercial optical plastics (polymethylmethacrylate and polycarbonate), provides high optical performance.

Effects of manufacturing errors on diffraction efficiency for multilayer diffractive optical elements

The effect of manufacturing errors on diffraction efficiency for multilayer diffractive optical elements (MLDOEs) used in imaging optical systems is discussed in this paper. The relationship of diffraction efficiency and depth-scaling errors are analyzed for two different cases: the two relative depth-scaling errors change in the same sign and in the opposite sign. For the first condition, the corresponding diffraction efficiency decreases more slowly. The effect of periodic width errors on diffraction efficiency is also evaluated. When the two major manufacturing errors coexist, the magnitude of the decrease of diffraction efficiency is analyzed for MLDOEs. The result can be used for analyzing the effects of the manufacturing errors on diffraction efficiency for MLDOEs.

Design of achromatic and apochromatic plastic micro-objectives

The possibility and the efficiency of using a single diffractive lens to achromatize and apochromatize micro-objectives with plastic lenses are shown. In addition, recommendations are given on assembling the starting configurations of the objectives and calculating the design parameters required for subsequent optimization. It is also shown that achievable optical performance of achromatic and apochromatic micro-objectives with plastic lenses satisfy the qualifying standards for cell-phone objectives and closed-circuit television (CCTV) cameras.

Automatic image performance balancing in lens optimization

In the final stage of lens design, it is usually a critical step to balance the optical performance of a lens system across the sampled fields, which is achieved by adjusting the weights to these fields. Because the current optical design software packages use fixed weights in the optimization process, the task of weight adjustment is left to the optical designer, who has to change the weights manually after each optimization trail. However, this process may take a very long time to finish, especially when many fields of the lens system are sampled, and the results are subjectively affected by the designer's design experience. In this paper, we propose an automatic performance balancing method. An automatic outer loop is added in the optimization process. The weight for each sampled field and azimuth is calculated appropriately according to the actual performance of the current design and the system requirements, and it is applied to the corresponding field and azimuth automatically in the next optimization trial. The method is successfully implemented in CODE V, and design examples show that it is very effective.

Design of an optical see-through head-mounted display with a low f-number and large field of view using a freeform prism

It has been a challenge to design an optical see-through head-mounted display (OST-HMD) that has a wide field of view (FOV) and low f-number (f/#) while maintaining a compact, lightweight, and nonintrusive form factor. In this paper, we present an OST-HMD design using a wedge-shaped freeform prism cemented with a freeform lens. The prism, consisting of three freeform surfaces (FFSs), serves as the near-eye viewing optics that magnifies the image displayed through a microdisplay, and the freeform lens is an auxiliary element attached to the prism in order to maintain a nondistorted see-through view of a real-world scene. Both the freeform prism and the lens utilize plastic materials to achieve light weight. The overall dimension of the optical system per eye is no larger than 25 mm by 22 mm by 12 mm, and the weight is 8 g. Based on a 0.61 in. microdisplay, our system demonstrates a diagonal FOV of 53.5 degrees and an f/# of 1.875, with an 8 mm exit pupil diameter and an 18.25 mm eye relief.

Imaging quality of a retroreflective screen in head-mounted projection displays

A retroreflective screen composed of miniature corner cube reflectors (CCRs) or microbeads redirects an incident ray in the reverse direction. Recently the retroreflective screen was utilized as a key element in head-mounted projection displays (HMPDs). Most prior efforts in developing the HMPD technology have been focused on optimizing the optical design of the projection optics, neglecting the imaging artifacts caused by the screen. Few efforts have been attempted to analyze and evaluate the overall image quality of the HMPD system with the presence of a retroreflective screen. This paper first applies a ray-tracing method to examine the imaging properties of a single CCR. Through the combination of both the geometrical imaging effect and the diffraction effect, the imaging properties of a CCR-based retroreflective screen are analyzed and characterized. Based on these analytical results, the paper further evaluates how the imaging artifacts of a retroreflective screen degrade the spatial resolution of an HMPD system and limit the tolerance range of the distance from an HMPD user to the screen. Finally, a discussion is employed to illustrate potential techniques in minimizing the image quality degradation through the optimization of the corner cube size in a retroreflective screen.

Design of a polarized head-mounted projection display using ferroelectric liquid-crystal-on-silicon microdisplays

It has been a common problem in optical see-through head-mounted displays that the displayed image lacks brightness and contrast compared with the direct view of a real-world scene. This problem is aggravated in head-mounted projection displays in which multiple beam splitting and low retroreflectance of a typical retroreflective projection screen yield low luminous transfer efficiency. To address this problem, we recently proposed a polarized head-mounted projection display (p-HMPD) design where the polarization states of the light are deliberately manipulated to maximize the luminous transfer efficiency. We report the design of a compact p-HMPD prototype system using a pair of high-resolution ferroelectric liquid-crystal-on-silicon (FLCOS) microdisplays. In addition to higher resolution, the FLCOS displays have much higher optical efficiency than a transmissive-type liquid crystal display (LCD) and help to further improve the overall light efficiency and image quality. We detail the design of a compact illumination unit for the FLCOS microdisplay, also commonly referred to as the light engine, and a projection lens, both of which are key parts of the p-HMPD system. The performances of the light engine and projection lens are analyzed in detail. Finally, we present the design of a compact p-HMPD prototype using the custom-designed light engine and projection optics.

Design of a bright polarized head-mounted projection display

In optical see-through head-mounted displays, it has been a common challenge that the displayed image lacks brightness and contrast compared with the direct view of a real-world scene. Consequently, such displays are usually used in dimmed lighting conditions, which limits the feasibility of applying such information displays outdoors or in scenarios where well-lit environments, such as in operation rooms, are required. The lack of image brightness is aggravated in the design of a see-through head-mounted projection display (HMPD). For instance, the overall flux transfer efficiency of existing HMPD designs is less than 10%. The design of a polarized head-mounted projection display (p-HMPD) is presented. The images of a p-HMPD system can potentially be three times brighter than those in existing HMPD designs. It is further demonstrated that the p-HMPD design is able to dramatically improve image brightness, contrast, and color vividness with experimental results. Finally, the design of a compact optical system and helmet prototype is described.

Analysis of multimask fabrication errors for diffractive optical elements

As design algorithms for diffractive optical elements improve, the limiting factor becomes the fabrication process. It is hoped a better understanding of fabrication errors will allow elements with greater tolerance to be designed. This is important for high-power laser fiber coupling, where hot spots lead to failure. We model seven different fan-out gratings applying misetch, misalignment, and feature rounding. Our main findings are that misetch can lead to improved results, misalignment is strongly asymmetric, and both the pi and pi/2 masks can dominate misalignment. Rounding has a r(2) dependence and potentially can be incorporated into the design stage. Finally we present some experimental data for misalignment.

Diffractive-refractive hybrid corrector for achro- and apochromatic corrections of optical systems

The possibility is shown of achro- and apochromatic correction of an optical system with any residual chromatism by completing the system with a diffractive-refractive hybrid corrector comprising one diffractive lens and one or two refractive lenses.

Analysis of the effects of bias phase and wavelength choice on the design of dual-wavelength diffractive optical elements

Diffractive optical elements (DOEs) are often used in pattern formation for display purposes. Constructing these images from two or more colors greatly enhances their visual effect. To achieve this with DOEs is not simple, as they are inherently wavelength specific. We discuss an algorithm for designing quantized elements that produce distinct intensity patterns in the far field for two wavelengths. The benefits of applying bias phase to the dual-wavelength problem are investigated. The difference between the best and the worst choice of bias phase is shown to produce a variation of up to 2% in the efficiency. The mean square error can vary by up to a factor of 2 between the best and the worst case. It is also critically important to understand how the values of the two wavelengths affect the result. We present an analysis of how choosing different pairs of wavelengths in the design process affects the quality of our results.