Improved gap servo system using a brake pulse for a SIL-based near-field recording system

A mode-switching servo is widely used in solid immersion lens (SIL)-based near-field recording (NFR) systems to control the air gap between the bottom surface of the SIL and the top surface of the rotating media. In the mode-switching servo, it is very important to reduce the initial overshoot in the near field region, as this overshoot can cause collisions between the SIL and the media, and increase the settling time required for the SIL to be initially moved to the final air gap. In this paper, the mode-switching servo with a brake pulse is proposed to reduce the initial overshoot and settling time. The effectiveness of the proposed method is proved by experiments of which results show that the minimum air gap due to the initial overshoot is improved from 6.86 to 18.73 nm and the settling time is reduced from 30 to 4.5 ms.