Elliptic solid immersion lens for NFR; compensation for disk thickness variation and disk tilt

In the last decade of optical data storage development, near-field recording (NFR) technology has been suggested for achieving higher areal density. However, there remain several serious and practical issues. The major defects in NFR due to the use of a solid immersion lens (SIL) are dust and thermal problems compared to orthodox optical storage technologies. The existing SIL is delicate in an unsealed environment due to heat, dust, contamination etc. CISD released a new SIL concept called elliptic solid immersion lens (ESIL) at the last ISOM (T.S. Song et al, ISOM01 p. 130, 2001). The new ESIL is capable of resolving some critical problems that are possibly caused by the existing SIL which records on the disk surface; in addition, the ESIL does not require an objective lens and with its simple structure, it has achieved improvements in mechanical tolerances of the alignment process and in pickup actuator dynamics. Although the ESIL possesses the potential to reduce present restrictions from the conventional SIL, it is necessary to establish a focusing servo system against variation in thickness of the cover layer. Also, a gap maintenance and tilt compensation system using an optical sensor and PZT was proposed in this paper.