Objective   Enlarging the field of view of an optical system while maintaining good imaging quality is a difficult problem in modern optical design. The large field of view and high resolution of optical lenses are mutually restricted, and it is generally difficult to realize them at the same time. It requires complex structure design, expensive manufacturing, and large volume. Each surface of the monocentric lens is monocentric, and the curved imaging plane is also monocentric with each surface. The special structure enables it to achieve a large field of view and high resolution. It also has the advantages of simple structure, small size, and light weight. It is widely used in aerial remote sensing, security monitoring, photography, videography and so on, and may be first applied in miniaturized mobile phone lenses in the future. However, because the monocentric lens sets a conventional stop in the center to block the light beam of the off-axis field of view, when the field of view is larger, more light will be blocked, which causes greater vignetting, reduces the uniformity of illumination of the imaging plane, and affects the imaging quality. In order to improve the relative illuminance of the monocentric lens, a monocentric reflective mobile phone lens that uses a total reflection surface to control the light beam is designed.

  Methods   A monocentric reflective mobile phone lens structure is designed in this paper. The initial structure is obtained by calculating the optical path of two reflective monocentric lenses (Fig.4). The optimized structure consists of a meniscus lens and a hemispherical lens, which are glued together using a low-refractive-index cement (Fig.5(a)). The spot for different fields of view of monocentric reflective lenses using conventional stop and virtual stop are simulated (Fig.6, Fig.8). Under different stop conditions, the relative illuminance curves of monocentric reflective lens are drawn (Fig.9).

  Results and Discussions   The designed monocentric reflective mobile phone lens has a focal length of 2.7 mm, a maximum field of view of ±50°, a system F number of 1.8, a total length of 2.7 mm, and a maximum RMS radius of no more than 0.8 μm (Fig.5(b)). Under the conditions of conventional stop and virtual stop, the spot illuminance simulation of monocentric reflective lens is carried out. From the illumination diagrams of different fields of view, it can be seen that under the condition of conventional stop, the shape of the spot becomes ellipse when the field of view is 30°, and the minor axis of the ellipse is smaller when the field of view is 50° (Fig.6). Under the condition of virtual stop, the spot is circular in the 30° field of view, and the spot in the 50° field of view is rounder than the spot with the conventional stop. The relative illuminance curves of the mobile phone lens under the two kinds of stops are drawn, and the results show that the relative illuminance of the monocentric lens using the virtual stop is above 0.85, and the relative illuminance of the monocentric lens using the conventional stop is above 0.64 (Fig.9).

  Conclusions   A monocentric reflective mobile phone lens is designed with a total reflection surface to restrict the light. Based on the establishment conditions of the virtual stop and the requirements of the mobile phone lens, an initial structure of the mobile phone lens based on the monocentric reflective lens is calculated. The focal length of the optimized system is 2.7 mm, the maximum field of view is ±50°, the system F# is 1.8, and the total length is 2.7 mm. The illuminance analysis results show that the relative illuminance of the mobile phone lens using the conventional stop gradually decreases with the increase of the field of view, and it is only 0.64 in the 50° field of view. However, the relative illuminance of a mobile phone lens with a virtual stop remains constant at 0° to 28° and is above 0.85 in the 50° field of view. The illuminance uniformity of the full field of view of the monocentric reflective lens using the virtual stop has been significantly improved, which can effectively improve the imaging performance of the system.