From the viewpoint of assembly, evaluation results and an autoalignment method for the focusing unit (FU) of a near-field recording (NFR) system are proposed. Generally, the size of the focusing unit composed of the objective lens and the solid immersion lens is smaller than that of the conventional focusing unit. Hence there are difficulties in the precise assembly of the small focusing unit. We developed an evaluation system with an interferometer and evaluated some focusing unit samples, then a tolerance analysis of the assembly error between the SIL and the objective lens and an interference pattern analysis of the assembly error were carried out. A pattern recognition method using a neural network is presented with features, which were extracted from interference patterns due to errors in the FU.

The swing-arm-type voice coil motor (VCM) is widely used as an actuator in rotating data storage devices. Recently, it has been found that to achieve a faster data transfer rate and a higher data storage areal density, a high performance actuator is required. Moreover, a small form factor has become desirable for portable devices. In this paper, a novel magnetic circuit of VCM with multisegmented magnet array (MSMA) is proposed. Both the magnetic circuits of the conventional VCM and the MSMA VCM are optimized using the 3D finite element method. Sample magnetic circuits are fabricated with optimally designed parameters and a comparative analysis is carried out. The performances of magnetic circuits are evaluated and the experimental results prove the effectiveness of the proposed magnet array.

Near field recording (NFR) has been introduced as a new optical data storage method to realize higher data density beyond the diffraction limit. As the data density increases, the track pitch is remarkably reduced to about 400nm. Thus, more precise actuator is required and we propose a dual servo actuator to improve the accuracy of actuator. The proposed dual servo actuator consists of a coarse actuator and a fine actuator, multisegmented magnet array (MSMA) voice coil motor (VCM) and PMN-PT actuator. In design of VCM actuator, a novel magnetic circuit of VCM with MSMA is proposed. It can generate higher air gap flux density than the magnetic circuit of VCM with the conventional magnet array. In design of fine actuator, the fine actuator including PMN-PT single crystal instead of the conventional PZT is proposed. The displacement gain of PMN-PT fine actuator is 26 nm/V and that of PZT fine actuator is 17 nm/V. The displacement gain is increased by 53 %. To evaluate tracking performance of the manufactured dual servo actuator and to assign the proper role to each actuator, the PQ method is selected. From experiment results, the total bandwidth of the dual servo actuator is increased to 2.5kHz and the resolution is 25 nm. Comparing with the resolution of one servo actuator, 70 nm, we can find that the accuracy of actuator is remarkably improved. And the proposed dual servo actuator shows satisfactory performances to be applied to NFR and it can be applied to other future disk drives.

In this paper, error analysis and tolerance allocation methods for the optical head of NFR (Near Field Recording) system are presented. We fabricate the NFR system and test the reading & writing performance of the NFR system. The test results show that the performance is not good enough. In order to find the cause of the performance drop in the NFR system, assembly and manufacturing tolerances in the optical head of NFR system are simulated. The tolerances analysis result shows that it needs to allocate the tolerances of the optical head of NFR system. So we proposed optimal compound tolerance allocation method using WOW (worst on worst) method and Monte-Carlo method base on sensitive analysis of the optical system. We used two tolerance allocation methods to allocate the compound tolerance in the optical head of NFR system. The results show that WOW method is an over-design method and the Monte-Carlo method is the optimal method of tolerance allocation in optical system.

From the viewpoint of assembly, an autoalignment method and experimental verification results for the focusing unit (FU) of a near-field recording (NFR) system are proposed. Generally, the size of focusing unit composed of an objective lens and a solid immersion lens is smaller than that of the conventional focusing unit. Hence there are difficulties in the precise assembly of the small focusing unit. We composed an autoalignment system with an interferometer and carried out an experimental verification of the proposed methodology using some focusing unit samples. Excluding manufacturing errors of optical components, we could make the alignment error of FU less than wavefront error of 0.03λ by the proposed method.