[OPTICAL REVIEW Vol. 7, No. 2 (2000) 138-143]
Optical Pickup with a Spherical Aberration Compensator Using a Crossed-Stripe Liquid Crystal Device
Hiroyasu YOSHIKAWA,1 Shin-ya HASEGAWA2 and Tatsuo UCHIDA1
1Department of Electronics, Graduate School of Engineering, Tohoku University, 05, Aoba, Aramaki, Sendai, Miyagi, 980-8579 Japan, 2Fujitsu Laboratories LTD. 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0197 Japan
(Received November 9, 1999; Accepted December 22, 1999)
To increase recording density in an optical disk system, a two-lens system which enlarge its numerical aperture (NA) has been developed. When NA becomes larger, however, the spherical aberration due to disk thickness error increases. We propose an optical pickup with a spherical aberration compensator using nematic liquid crystal (LC). Our LC device is composed of two LC cells each of which has X and Y stripe electrodes, respectively. We discussed how the spherical aberration due to the disk thickness error can be compensated by combination of two crossed cylindrical phase distributions induced by the LC cells, and confirmed the compensation effect in a design example by simulation. We have also fabricated the crossed-stripe LC device actually, and have obtained the experimental result which shows that amount sufficient to compensate the aberration is achieved.
Key words : optical disk, high numerical aperture, liquid crystal, compensation, wavefront aberration, multi-layer disk, mass fractal, surface fractal, combined fractal, self-similarity, power law, fractal dimension