Theoretical and experimental investigations into the use of a liquid crystal lens with a variable focal length for spherical aberration compensation in an optical pickup are presented. Spherical aberration is induced when the cover-layer thickness of the optical disc deviates from its nominal value. A convex liquid crystal lens is integrated into a Blu-ray standard conform optical pickup and tested with a 50 Gbyte dual-layer ROM disk. Excellent jitter values on the upper (6.8%) and on the lower (6.4%) data layer are achieved

Liquid crystal lens for spherical aberration compensation in a Blu-ray disc system

A new optical design inclusive of Blue-Ray Pickup head system and liquid crystal optics is proposed in this paper. With
electrode pattern and the differential biased circuit, the gradient of the electric field distribution inside the liquid crystal
sample cell are able to vary through the adjustment of driving voltage. Optical power of liquid crystal lens can be
determined by changing the polarity of gradient within the sample cell which posses the homogeneous alignment, then
deliver convergence or divergence of specific light beams. This design is capable of correcting aberrations fast with
liquid crystal optics scheme when any misalignment errors occur. According to specification from Blue-ray Disc White
paper, there are several kinds of pick up head system with LC liquid optics are designed and discussed in this paper.
Different tolerance such as de-focus, tilt, de-center and their related compensation are further analyzed in this research.
The simulation results show that optical design using liquid crystal optics with aperture stop setup as a compensation
device can eliminate up to 46% compared to traditional ones.

A study of blue-ray pickup head optical system with liquid crystal optics module

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.

Shin-ya Hasegawa

Papers

Optical Pickup with a Spherical Aberration Compensator Using a Crossed-Stripe Liquid Crystal Device