Polymeric, birefringent reflective polarizers have been used to produce compact, mid-field-of-view eyepieces and wide field-of-view optics for virtual reality (VR) head-mounted displays using the “pancake” lens configuration. Multiple configurations for pancake lens systems are discussed as are their advantages and disadvantages relative to refractive systems. Polarization control is an important consideration and the polarizing effects of different components are discussed. Designs for mid-FOV and wide FOV are presented and additional benefits of using folded optics for virtual reality systems are explored.
Over the past decade, 3M has developed a number of mobile projectors, with a goal towards providing the world’s smallest, most efficient projection systems. Compact size and efficiency are required characteristics for projection systems used in mobile devices and more lately, in augmented reality systems. In this paper we summarize the main generations of 3M light engine optical designs. We present the optical architectures of four light engines, including the rationale behind the illumination designs and the projection systems. In particular, we describe various configurations relating to the 3M polarizing beam splitter (PBS) which is key to enhanced efficiency of the miniature projection systems.
Eyepieces are a part of visual optical systems. Because of their wide field of view and long eye-relief, it is difficult to further improve the existing eyepieces using all-refractive surfaces. Since diffractive elements demonstrate unique characteristics: negative dispersion and non-field curvature, the eyepiece design can be improved by using refractive-diffractive hybrid surfaces. In this paper, several design examples using refractive-diffractive hybrid surfaces to design moderate field of view (FOV) eyepieces were studied. Firstly, a design example using a diffractive surface to replace the negative piece in the cement doublet of a conventional Kellner type eyepiece is presented. Then a design example is given by employing two diffractive elements to replace the negative elements used in the conventional symmetrical eyepiece. For the above examples the eyepiece aberration correction techniques were also analyzed.
In both design and fabrication, diffractive optical elements (DOEs) are more flexible and powerful than traditional refractive/reflective optical elements, hence an optical system with one or more diffractive elements may provide better optical performance at lower cost with small, light and compact structure. However due to its inherent large spectral dispersion, a DOE is generally designed and fabricated for one specific wavelength or a narrow spectral bandwidth. In the case of a wide band light source, chromatic aberration and loss of diffraction efficiency will occur. In this paper, the chromatic dispersion of DOE is discussed, and four achromatic strategies, namely hybrid diffractive/refractive strategy, harmonic diffraction strategy, multi-material strategy, and bi-blazed strategy are introduced and analyzed respectively. A comparison has also been made among them to guide the application.
In planar diffractive imaging system, extra-axial imaging elements are frequently used. Since the elements have large off-axial aberrations such as coma, astigmatism, field curvature and distortion, it seems a little difficult to design a practical aberration-free element. In this paper, we reviewed the axial imaging diffractive element design procedure. Referring to designing axial elements, we present a semianalytical approach that enables one to determine the exact surface profile of an extra-axial element based on geometrical optics according to design and aberration-free requirements. The design procedure of the element can be divided into two steps: firstly, to obtain the zone boundaries and then to solve the exact surface profile. Finally, a schematic is given to test and evaluate small size diffractive elements.
Compared to the holographic elements, the binary optical element (BOE) is more flexible and powerful in its design, functionality and fabrication. Better optical performance, with the advantages of compactness, lightweight, and low cost, is possible if the BOE based optical system is made monolithic. In this paper a monolithic planar-binary integrated optical visor with two couplers is proposed, designed and analyzed. One of the couplers directs the light into the glass slide substrate so that the light can travel within a planar passage via total internal reflection; the other couples the light out of the optical plate and into the wearer's eyes. Meanwhile, a binary lens array is adopted on the surface of the input end, so the visor can serve its imaging function with minimal geometrical aberrations. A bi- blazed diffractive structure of BOL is proposed to correct the chromatic aberrations and achieve achromatic imaging over the visible range.
The study of planar imaging system is an interesting topic because its compact structure and lightweight are consistent with the trend of production miniaturization. This paper presents our study of designing and fabricating planar imaging elements. Theoretical analysis of grating and off- axis imaging diffractive elements was conducted. A low- aberration symmetrical imaging optical system was designed and evaluated with CODE V. Using a variable intensity laser- writing system, diffractive surface relief patterns were written on photoresist and were later transferred to a fused quartz plate.
A novel planar-binary optical see-through visor, in which three binary optical elements, namely two couplers and one compensator, are designed to be fabricated on a planar glass slide substrate, is presented in this paper. One binary focusing coupler serves to image and couple the light into the optical plate so that the light can travel within the planar passage via total internal reflection. The other coupler directs the light out of the plate, and the compensator makes it possible for the user to see directly through the visor at the same time. Harmonic diffractive technology is employed to reduce the chromatic displacement in the visible range. The schematic of the structure and simulation results are given in this paper. Our results indicate that it is promising to utilize the planar-binary optics to cover the visible band.