In this paper, error analysis and alignment for the optical head of Near Field Recording (NFR) system are presented.
Using optical systems analysis tool - CODEV, the NFR system are designed. After design, we fabricate the NFR system
and test the reading & writing performance of the NFR system. The test results show that the reading & writing
performance is not good enough. In order to find the cause of the performance drop in the NFR system, assembly
tolerances of the optical head of NFR system are simulated. The simulation results show that the tolerance in the optical
head of the NFR system is very tight. So in order to align the optical head within the tolerance limit, we design and
fabricate an alignment system which can detect the RMS wavefront aberration and align the optical head. Before the
experiment, we model the interferometer (by CODEV) and analyze the interference pattern trend. The interference
patterns will be compared with the experiment results. The system can control the position of optical head of the NFR
system using the pico-motor actuators and the capacitance type gap sensors. Using the system, we can align the objective
lens and the solid immersion lens in 5-axis. Finally, we verify the alignment performance of the optical head using the
alignment system. We can align the optical head within tolerance limit using the proposed system.
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.
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.
Evaluation results and an autoalignment method for an optical head of a near-field recoding (NFR) system are presented. The focusing unit is an optical head of a NFR system and is composed of a solid immersion lens (SIL) and an objective lens (OL). Generally, the size of the focusing unit is smaller than that of the conventional optical recording head. Hence there are difficulties in assembling the small focusing unit precisely and a novel method for an effective assembly is required. We compose an evaluation system with an interferometer and evaluate some focusing unit samples aligned and assembled manually and present the obtained results. We also propose a conceptual method of autoalignment to assemble the focusing unit well by a pattern recognition using a neural network. Using the conventional optical tool, Code V, a tolerance analysis of the assembly error between the SIL and the objective lens and an interference pattern analysis for the assembly error are executed. Then, through an analysis of the simulation results, the autoalignment methodology using a neural network approach is proposed.
The errors can cause the serious loss of the performance of a precision machine system. In this paper, we propose the method of allocating the alignment tolerances of the components and apply this method to Confocal Scanning Microscopy (CSM) to get the optimal tolerances.
CSM uses confocal aperture, which blocks the out-of-focus information. Thus, it provides images with superior resolution and has unique property of optical sectioning. Recently, due to these properties, it has been widely used for measurement in biological field, medical science, material science and semiconductor industry.
In general, tight tolerances are required to maintain the performance of a system, but a high cost of manufacturing and assembling is required to preserve the tight tolerances. The purpose of allocating the optimal tolerances is minimizing the cost while keeping the performance of the system. In the optimal problem, we set the performance requirements as constraints and maximized the tolerances.
The Monte Carlo Method, a statistical simulation method, is used in tolerance analysis. Alignment tolerances of optical components of the confocal scanning microscopy are optimized, to minimize the cost and to maintain the observation performance of the microscopy. We can also apply this method to the other precision machine system.
Tolerance analysis for focusing unit of near field recording system is presented. The assembling and manufacturing tolerances of SIL and OL are simulated using CODE V. In addition, we proposed to move collimated lens (CL) back and forth to compensate and control these tolerances, especially in optical axis direction. And we proposed, a new doublet solid immersion lens (DSIL) for near field optical system, which can minimize the tilting, decenter, defocus misalignment problems between objective lens and solid immersion lens in existing near field optical system. The objective lens, which confines the beam, and secondary lens which increases the numerical aperture, join together to make one module cemented lens system.
We propose and demonstrate a simple decision-threshold tracking technique that can minimize the PMD-induced power penalties. Using this technique, we could reduce the power penalty of RZ signal to 0.2 dB even when the DGD were as large as 40 ps.
We report on the effect of the polarization-dependent loss (PDL) on the polarization-shift-keying (PolSK) transmission system. In a PolSK system, the PDL of the fiber-optic link could generate an inband crosstalk and degrade the signal’s extinction ratio. The result shows that a 3-dB PDL could result in the 1-dB power penalty. However, unlike the effect of PMD, it is not dependent on the transmission speed.
12 In this paper, we designed and made a solid immersion lens (SIL) microscope using SIL (diameter equals 1 mm, refractive index n equals 1.83). Through the real experiment, we obtained the scanned-surface image of 700 nm and 300 nm standard specimens using SIL effect (compared with it's SEM scanning picture) an analyzed the result and error of image and system. According to this paper we can assure the capability of SIL microscope and possibility of the development of high-area density, large-capacity data storage device.
Proc. SPIE. 3740, Optical Engineering for Sensing and Nanotechnology (ICOSN '99)
KEYWORDS: Optical fibers, Stereoscopy, Optical microscopy, Near field scanning optical microscopy, Fiber characterization, 3D vision, Feedback signals, 3D image processing, Phase shifts, Near field optics
The shear force characteristics of NSOM (Near field scanning optical microscopy) probe is examined. The NSOM probe is modeled as a 2'nd order mass-spring-damper system driven by a harmonic force. The primary cause of the decrease in vibration amplitude is due to the damping force -- shear force -- between the surface and the probe. Using the model, damping constant and resonance frequency of the probe is calculated as a function of probe-sample distance. Detecting the amplitude and phase shift of the NSOM probe attached to the high Q- factor piezoelectric tuning fork, we can control the position of the NSOM probe about 0 to 50 nm above the sample. The feedback signal to regulate the probe-sample distance can be used independently for surface topography imaging. Three- dimensional view of the shear force image of a testing sample with the period of 1 micrometer will be shown.