The folded optics for HMD (head-mounted display), commonly referred to as pancake optics, is widely used to realize a compact HMD headset. The optics has the advantage of compactness, but also has a big drawback of lowering light efficiency. To overcome the issue, we proposed novel HMD pancake optics named “DP (double path) pancake optics” to achieve both compactness and high light efficiency simultaneously. In this paper, we introduce the principle of our “DP pancake optics” and review our prototype. We describe optical simulation results to find a highly balanced design among thickness, lens power, and magnification ratio. We also describe fabrication study of, such as polarization state and alignment accuracy. We successfully have fabricated two prototypes with 90° FOV (field of view), one of which is 20.6 mm optics thickness and the other is 25.5 mm optics thickness. The latter prototype especially shows high MTF with a 1200 ppi (pixel per inch) resolution LCD (liquid crystal display). Both prototypes have 1.8 times higher light efficiency than that of conventional one. In addition, to further expand the DP pancake optics, we also describe the improved design with wider FOV for future prototype fabrication. Therefore, we also show the optical simulation result of the improved design.

HMD（头戴式显示器）的折叠光学器件通常称为薄饼光学器件，广泛用于实现紧凑型 HMD 耳机。该光学器件具有紧凑的优点，但也有降低光效率的大缺点。为了克服这个问题，我们提出了名为“DP（双路）煎饼光学器件”的新型 HMD 煎饼光学器件，以同时实现紧凑性和高光效率。在本文中，我们介绍了“DP 薄饼光学”的原理并回顾了我们的原型。我们描述光学模拟结果，以找到厚度、镜头光焦度和放大倍率之间高度平衡的设计。我们还描述了偏振状态和对准精度等制造研究。我们成功制造了两个具有 90° FOV（视场）的原型，其中一个光学器件厚度为 20.6 毫米，另一个光学器件厚度为 25.5 毫米。后一个原型特别展示了具有 1200 ppi（每英寸像素）分辨率 LCD（液晶显示器）的高 MTF。两种原型的光效率比传统原型高出 1.8 倍。此外，为了进一步扩展 DP 薄饼光学器件，我们还描述了为未来原型制造提供更宽视场的改进设计。因此，我们还展示了改进设计的光学仿真结果。