High-Density Near-Field Readout Using Solid Immersion Lens Made of KTaO₃ Monocrystal

We developed solid immersion lenses made of a KTaO 3 monocrystal. The refractive index of KTaO 3 is 2.382 at a wavelength of 405 nm. Using KTaO 3 as the raw material of a solid immersion lens, we could design an effective numerical aperture of 2.20. We observed an eye pattern of a 150 GB capacity with a 130 nm track pitch and a 47.6 nm bit length. The areal density is 104.3 Gbit/in. 2 .