Aiming at the precise measurement of numerical aperture which is a key optical parameter of gradient index (GRIN) lens. An incremental measurement method based on image recognition is proposed. Based on the definition of numerical aperture of GRIN lens by geometrical optics, the sinusoidal value of the maximum receiving angle is measured by imaging method. Incremental measurement means the GRIN lens images the light-emitting mesh twice, and calculates the sinusoidal value of the maximum receiving angle with the object heights of two images and the relative displacement. Two object heights are obtained by computer image recognition algorithm. According to the characteristics of mesh and the edge of field of view on the image, the complete object height in the longitudinal truncation is extracted which includes the central object height and the edge object height. The central height is determined by all the fringes on the truncation line, and the edge height that equals to the distance between the edge of field of view and the outermost fringe is determined by the extrapolation algorithm. The error analysis of the measurement system is carried out by establishing the error model, and the main source of the system error is determined. The experiment proves the stability of the sub-measurement method meets the practical needs. The measurement of the numerical aperture of a GRIN lens, which combines image recognition with incremental measurement, can reduce the measurement error caused by absolute measurement and discrimination of our eye, and it is simple, fast and accurate.
As a typical miniaturized smart device, the miniature projection system is an important part of a head-mounted display device. In the micro-projection system with a LCOS or a DMD as the display chip, the performance of the lighting system directly affects the final imaging quality. We design and simulate two lighting systems based on compound eyes and a diffuser respectively. The design shows that without considering the loss of polarized light the light energy utilization rate of the system based on compound eyes is 70.3% while that of the system based on a diffuser is 25%, and with the ANSI nine-point sampling method the calculated uniformity of the system based on compound eyes is 91%, while that of the system based on a diffuser is 88%, and the axial length of the lighting system based on the diffuser is 0.6 times that of the lighting system based on compound eyes. According to the analysis of design results, the compound eyes based system results in higher energy utilization and uniformity compared with a diffuser based one. Since the compound eyes based system needs a relay system, it nevertheless has a larger volume. Therefore, it is necessary to choose a suitable lighting method according to actual needs of a specific head-mounted display device.
At present, micro lens arrays have been widely used in the fields of infrared detection, light gathering, portable solar battery and so on. The focusing and imaging properties of micro lens arrays are closely related to the performance parameters such as point diffusion function, diffraction efficiency and optical intercept. In order to better evaluate the quality of micro lens, this paper introduces a method for accurately measuring the optical intercept of micro lens arrays, which is more precise and has less deviation than interferometry, CCD direct imaging and so on. This experiment is based on the principle of CCD imaging and image processing, and a set of testing system is established. The system is mainly composed of a laser light source, a collimation system, samples and a camera. After many experiments, The optical post intercept detection device can obtain test accuracy below 5μm
In order to meet the increasing demand for the diagnosis of household medical eye fundus, the design of a new fundus camera is proposed. The entire structure includes the imaging system and the lighting system. The optical imaging system, modeled on the Kepler telescope, matches the exit pupil of the human eye and the entrance pupil of the mobile phone camera. Thus, this system uses a mobile camera lens that owns more than 5 million pixels to take a picture of a clear fundus. A new type of fundus camera is designed with the field of 40°, the working distance of 30mm and the full length of 138 mm. The value of MTF outweighs 0.5 at the central field of view. The lighting system takes advantage of the Kohler illumination. The stray light of the reflection of corneal is effectively suppressed by adding an annular aperture on the optical path. The inner diameter of the annular light spot formed at the cornea was larger than 4mm, the outer diameter was less than 6mm, and the diameter of the evenly illuminated fundus area was 12mm.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.