High-density near-field optical recording with a solid immersion lens, conventional actuator, and a robust air gap servo

We present a near-field optical recording system with a solid immersion lens (SIL) in a conventional biaxial actuator. We manufactured a super-hemispherical aplanatic SIL with a numerical aperture (NA) of NA = 1.9. Our system utilizes a gap error signal (GES) and a digital servo system to drive a conventional actuator in order to maintain a constant air gap of 25 nm between the SIL and a spinning optical disc.