Zhao-Qi Wang

Effects of error in radius of curvature on the corneal power measurement before and after laser refractive surgery for myopia

Citation information: Liu Y, Wang Y, Wang Z & Zuo T. Effects of error in radius of curvature on the corneal power measurement before and after laser refractive surgery for myopia. Ophthalmic Physiol Opt 2012, 32, 355–361. doi: 10.1111/j.1475‐1313.2012.00921.x

Head-mounted display with LCOS using diffractive optical element

Summary We designed a 60° hybrid refractive-diffractive eyepiece for head mounted display (HMD), and applied it in micro-display of liquid crystal on silicon (LCOS) by introducing a relay system. The hybrid eyepiece design is based on a traditional Erfle eyepiece. It has a 10mm exit pupil and a 22mm eye relief, which satisfies the requirements of HMD used in computer entertainment and visual reality. Moreover, the proposed eyepiece possesses better performances with a considerable reduction in physical size and weight compared to the traditional refractive type. The relay system can solve the matching problem between micro-display device and eyepiece, and provides the space for illuminating light source. The whole optical system is suitable for display of 18 mm-diagonal LCOS with a VGA resolution.

Study on chromatic aberration in a population of Chinese myopic eyes by means of optical design

Two kinds of individual eye models, involving and without involving the angle between visual axis and optical axis, are established by means of optical design. We use them to study the properties of the transverse chromatic aberration (TCA) and longitudinal chromatic aberration (LCA) over the visible spectrum. Then the effects of the LCA and TCA on the visual quality of human eyes are evaluated. The statistical averages of TCA and LCA over the visible spectrum for Chinese myopic eyes are obtained. Results show that both TCA and LCA restrict the visual performance, and LCA is more detrimental than TCA.

Hybrid diffractive-refractive ultra-wide-angle eyepieces

Summary Two kinds of hybrid diffractive-refractive ultra-wide-angle (70°) eyepieces are designed which are with considerably reduced apparent size and weight and with comparable or improved aberrations as compared with the conventional refractive countertype. The designing strategy including the consideration and the steps of the optimization, the most important specification of the diffractive efficiency, and the manufacture issues is presented. The structures and the performance merits of the designed systems are given in a comparison of the traditional Scidmore eyepiece. The designed eyepieces have potential applications in various kinds of modern head-mounted displays.

Hybrid diffractive-refractive 40° head-mounted display

Summary The design of a head-mounted display with a field of view of 40 degrees and suitable for use with a micro display of 17.5 mm diagonal is presented. It is a combination of a diffractive-refractive eyepiece with an appropriate reflective relay system. The eyepiece design is based on a Kellner eyepiece. By replacing the cemented-doublet of the traditional eyepiece with a diffractive-refractive element (a plano-convex lens with the plane surface as the diffractive surface) an improved eyepiece is obtained. The proposed eyepiece shows a considerable reduction in physical size (which is particularly important for binocular systems) and weight, and exhibits superior performance compared to the traditional refractive type. It is emphasized that the proposed design has a performance that is well matched to a micro display with SXGA resolution.

Study of an athermal infrared dual band optical system design containing harmonic diffractive element

A harmonic diffractive element (HDE) is first successfully introduced to the athermal system of infrared dual band in this paper. In this system, there are only three lens and two materials, silicon and germanium. When the temperature ranges from −70 °C to 100 °C in the dual band, it can simultaneously accomplish the rectification of the longitudinal aberration in the big field of view, as well as the wave front aberration less than 1/4 wavelength. Modulation transfer function of dual band approaches or attains the diffraction limit. The calculation results show that the spectral properties of the HDE are between refractive and diffractive elements, so we can design a simple dual-band and athermal optical system by selecting the thickness and central wavelength of the HDE exactly. Compared with a conventional refractive optical system, this system not only reduces the demand for high technical levels, but also has a compact structure, few elements, a high transmittance better aberrations performances and athermal character. At the same time, the use of the HDE also offers a new element for the infrared optics design.

Aspheric spectacles for correcting presbyopia with myopia and astigmatism

The aim of this paper is to propose a method for designing aspheric spectacles capable of realizing good optical performance at both far and near vision for presbyopia. We have experimentally measured wavefront aberrations and axial lengths for eight myopic eyes. In consideration of the field of view (FOV), the rotation of the eyeball, and a small amount of accommodation retained for presbyopia, we constructed individual eye models and optimized all the spectacle-eye systems for visible wavelengths by Zemaxs simulation. Finally, we evaluated the image quality by the modulation transfer function (MTF) and visual acuity (VA) with different pupil sizes (2, 2.8, 4 mm). Results show that when the pupil size is 2 mm or 2.8 mm, the spectacles designed for the full FOV (0° and ±4° FOV) provide a strong ability to transfer low contrast at both far and near vision, and the VA for all reaches 0.8, and up to 1.1 for eyes NO. 1, NO. 5, NO. 6, and NO. 8 for the 0° FOV. As the pupil size increases to 4 mm, the VA for all comes to 0.6 for the full FOV, indicating that presbyopia is able to acquire a good visual resolution at both far and near vision by the designed aspheric spectacles. Furthermore, we verified the visual continuity of the spectacle-eye systems by studying intermediate vision, which demonstrates that the method used in our design is accurate and practicable.

Passively athermalised hybrid Petzval objective for high resolution MWIR detector arrays

Abstract To meet the requirement of extensive temperature adaptability of infrared optical systems, diffractive optics is applied to a high resolution Petzval objective in the 3-5 μm waveband and a hybrid Petzval objective, which is passively athermalised over the temperature range −20 °C to +50 °C, is designed. Only two materials Si and Ge are used. The theoretical polychromatic MTF is above 0.80 at 20 cycles/mm and near diffraction-limited, the geometrical spot diameter is controlled to within 20 μm over the range of temperature. The lens is compatible with a latest generation Middle Wave Infrared (MWIR) staring array imager with the pixel size of 25 μm. The manufacturing issues related to the diffractive surface are also described.

Design of refractive/diffractive objective for head-mounted night vision goggle

Summary A refractive/diffractive objective for head-mounted night vision goggle was designed. This objective consists of six elements, including one binary surface and two hyperboloids. It has a 40° field of view, a 1.25 f-number, and a 18 mm image diameter, with a compact structure and a light weight. All optical specifications reach proposed designing targets. Besides, we considered fabrication issues about special surfaces of the system.

Simple 40° head-mounted display

Summary A simple 40° eyepiece matched with the micro-display device is designed. It consists of two elements, including a binary surface and an aspheric surface. With satisfactory performance, the eyepiece can be used in display with a SXGA resolution sized 1.1 inches diagonal. Because no other relay system is needed, the HMD system could be made more compact with much less weight.