A new wide-band laser noise cancel technique

Abstract

ABSTRACT We propose a new wide-band laser noise ca ncel technique which is especially eff ective in Blu-ray Disc system because of its laser noise increasing compared with conventional optical disc systems. Laser noise cancellation method has already been available, but it is difficult to extend the noise suppression bandwidth for high-speed reading. So we examined the realization possibility of wide-band noise canceling and developed a new photo diode IC (PDIC) with noise cancel function based on our princi ple examinations. Big advantages in resp ect of the cost and space are expected to be obtained by adopting this technology. Keywords: Blu-ray Disc, wide-band laser noise cancel, subtraction circuit, delay difference, one chip CMOS-LNC-PDIC 1. INTRODUCTION In the latest optical disc systems, shorter wave length laser diode (LD) and higher numerical aperture of objective lens are used to make beam spot size smaller to achieve high record ing density. At the same time, it is needed to keep as same optical power density on a disc as the existing formats for recorded data reliability, so LD emission power during playback has to be reduced. It makes the laser noise contribution to the total system tolerance much bigger. There are two kinds of solution for this problem, one is to lower the optical coupling efficiency only during read by using a movable neutral density filter or a liquid crystal attenuator, and the other is electrical active noise cancellation. The latter, which has already applied in the first generation Blu -ray Disc recorder (BDZ-S77) for consumer market in Japan [1], has a big advantage to get much lower noise floor and sa ve much cost and space than those of the former. But there is a disadvantage that is difficult to achieve noise suppression over wide bandwidth because of its plural chip configuration. In this paper, we propose a new electrical active noise canceling method, wide-band laser noise cancel (LNC). This technique is realized with a new multi beam PDIC in which all of the photo diodes and the circuits for LNC are implemented and with a new optics which leads both of RF and monitor light to the same PDIC chip. And we also discuss about new subtracting LNC circuit, which is necessary for one chip LNC PDIC because of its simple composition, instead of big and complex conventional multiplying type. Finally we show the experimental result.