Near-Field Induced Polarization Imaging for Optical Data Storage Metrology
It is shown that when the induced polarization is used to acquire near-field induced polarization images, both a high-resolution near-field image and height information of the object are obtained
Gap Servo System for a Biaxial Device Using an Optical Gap Signal in a Near Field Readout System
A readout method using a near field optical head has been proposed as a technique to read out over 30 Gbytes on a 12 cm disc. For the purpose of reading out the RF signal in the system, a gap servo is required to maintain a constant air gap between the solid immersion lens (SIL) and the disc. In this paper, we propose a practical near field readout system with a similar system to an ordinary optical disc, where a biaxial device is used as an optical head actuator and the gap error is detected optically. First, we explain the gap servo system by which it is possible to control the air gap from a far field initial position to a near field target position at a relatively high speed without a head colliding with a disc. Second, we report the result of applying this gap servo system to a 30 Gbyte and a 50 Gbyte ROM disc. Finally, its performance is confirmed by comparing simulated signal with an observed signal.
Readout Method for Read Only Memory Signal and Air Gap Control Signal in a Near Field Optical Disc System
We describe a method of obtaining an optical air gap control signal for near-field optical disc systems. Because of the total reflection on the surface of a solid immersion lens (SIL), the polarization state of the reflected light differs from that of the incident light. However, when the SIL is close to a disc surface, the polarization state difference between the reflected and the incident light becomes small. We used this difference to obtain an air gap control signal. Both observed and calculated results show that this signal is negligibly affected by the pits on the disc. Thus, our air gap servo system is stable. We show the observed readout signals of a 40 GB ROM disc (with a 12 cm diameter) obtained by an optical head with a 1.4 NA objective lens and a 405nm wavelength GaN LD. Comparisons between observed and calculated results are made.