Researchers, Developers and Staffs
Yohei  NISHIDATE Yohei NISHIDATE


Research Themes

Development of a ray-tracing procedure and attendant software which can take into account form errors, optical anisotropy, and inhomogeneity
Physics based modeling and visualization of continua to atomic-scale phenomena

Research Subjects and Results

Even an optical system is carefully designed to satisfy its precision requirements, the system consists of the fabricated lenses and the fabricated mirrors in reality may attain the precision poorer than expected. The modern plastic lenses are fabricated by the injection molding procedures, but the optical path of incident lights deviate due to the form errors, the inhomogeneous optical property distributions, and the optical anisotropy induced by thermal effects. In order to improve the form errors, numerous experiments using the fabricated lens are performed, and the results are feed back to find better molding conditions and the process is repeated. During this adjustment process, ray-tracing simulation is hardly employed since it is considered as difficult to reproduce the real surface and the real medium).
In order to reproduce the fabricated lens/mirror surfaces, the data must be taken from measurement of the real thing or from the simulation results of injection molding procedure. Accordingly, the input to the ray-tracing simulation is a point set, and hence the fabricated lens/mirror surfaces should be reconstructed from the discrete input.
The Nagata patch, invented by senior researcher Nagata of VCAD system research program, mathematically assures C0 continuity across neighbor patch boundaries even the patch nodes are assigned multiple normal vectors, and a closed-form solution exsits for intersection problem of lines with the patch. The ray-tracing simulation is not necessary to be more precise than the diffraction limit. Therefore, the Nagata patch representation is effective since it simultaneously ensures sufficient precision and simplicity for the optical design. The ray-tracing simulation using the Nagata patch has been implemented as the user defined surface of the commercial optical design software ZEMAX (V-Opt-S).
Optical systems are usually designed under the assumption that the medium is optically isotropic homogeneous. However, the optical anisotropy and inhomogeneity arise due to residual stresses. The inhomogeneity leads to the changes in the path of lights transmission, and the anisotropy induces birefringence. A ray-tracing procedure taking into account the form errors, the optical anisotropy, and the inhomogeneity has been developed. Also, the ray positions and energy distributions at focal planes can be calculated using a computer program (will be released as V-Opt2).


A screen shot of V-Opt2

VCAD Public Software

V-Opt-S
V-Opt2

Software Block Page


Selected Publications

【Papers】
Y. Nishidate
"Evaluation of stress birefringence in fabricated lenses, by using a ray-tracing method for anisotropic inhomogeneous media"
Procs. of VCAD symposium 2010, Wako, Japan, Mar. 2-3, 2011, pp. 189-192.

Y. Nishidate, T. Nagata, S. Morita, Y. Yamagata, and C. Teodosiu
"Ray-tracing simulation procedure for general GRIN media"
Frontiers in Optics 2010/Laser Science XXVI (FiO/LS 2010), Rochester, NY, USA, Oct. 24-28, 2010, OSA Technical Digest (Optical Society of America, 2010), PDPA6.

Selected Publications Page