Optical data storage is now well into the second decade of continuing market and technology expansion. Media removability, which is the main attribute of this technology, presented the optical recording industry with unmatched opportunities and also new challenges. On the one hand, data interchange between the media and drives from different sources becomes a major concern, which can only be solved if international standards for all optical recording disk/cartridge are available. Many standards organizations, with the help of world wide industrial support, took up the challenge, and numerous international standards were established which are now being adapted. On the other hand, copy protection technology must be developed to prevent illegal copying and distribution of contents using this removable media. This need is accentuated by the proliferation of low cost CD and now DVD disks replication means and the availability of recordable and rewritable CD and DVD devices. This paper provides an update of the brief summary of the current status of the international optical disk standards published earlier and a brief review of the copy protection technology.

Several kinds of disks, such as DVD, MO and/or CD-R, for the next generation require high quality of plastic surface. Especially their flatness is very important. Here a disk inspection system is proposed using 2D birefringence distribution measurement. Small birefringence is a serious problem that is caused by internal strain, and/or residual stress. Moreover it is possible to observe its molecular orientation. The birefringence measurement is necessary to determine the relative retardation and the azimuthal angle of the fast axis in an optical disk. Several images captured by a CCD camera are enough for one birefringence distribution analysis. Experimental procedure and their results of some famous optical disks are discussed.

We present an experimental set-up for systematical studies of optical near-field coupling phenomena using a solid immersion lens (SIL) to surpass the conventional far field diffraction limit. The set-up incorporates a microscope objective lens with NA equals 0.80 in combination with a hemispherical SIL manufactured from glass with refractive index n equals 1.887 and a laser with a wavelength of 430 nm. Test samples are positioned within the evanescent decay distance from the bottom surface of the SIL using a closed- loop-controlled piezo actuator. The laser spot can be scanned over the sample enabling a study of the push-pull signal of pregrooved samples on a split photodiode. The intensity distribution and polarization state of the light reflected from the sample in the exit pupil of the microscope objective lens is studied on a CCD camera. The reflected light can be combined with a reference beam into an interferogram used for alignment purposes. We present measurements of evanescent coupling of light to a glass sample and the push-pull signal of a reflective phase grating with a groove pitch of 300 nm as a function of thickness of the air gap between de SIL and the sample. The evanescent coupling to a glass sample can accurately be described by thin-film optics theory. Experiments show that the push-pull signal amplitude depends on the polarization state of the irradiating beam.

SiN_x films were prepared by rf reactively sputtering. The refractive index of SiN_x films was affected by total pressure and sputtering power. When the total pressure increased, the refractive index decreased. The reduction of sputtering power showed similar effect to raise the total gas pressure. The residual stress and roughness of SiN_x films depended on the total pressure, sputtering power, and the thickness. The thermal cycles may result in irreversible change of residual stress of SiN_x film. The magnetic properties of TbFeCo depended on the residual stress and roughness of SiN_x in the trilayer SiN_x/TbFeCo/SiN_x samples. The coercivity of TbFeCo was enhanced in the samples with SiN_x films having low stress and large roughness.

This paper reports the perspective and future of DVD-RAM. The standardization of DVD-RAM and future technologies are described.

Brushless spindle motor is one of the most important key components used in a CD system. A stable spindle motor control loop is essential to assure reliable data integrity for a high-speed CD drive. However, DC offset is frequently observed on Hall sensors of the spindle motor used in a CD system. This spindle-motor Hall sensor offset also shows large range variation among batches from different motor suppliers. This undesired Hall sensor DC offset can induce unstable spindle-motor control loop and cause malfunction of a CD drive. Being a drive manufacturer to mass produce CD drives over one million unit per month, the problem of Hall sensor offset variation must be overcome to assure smooth operation of the mass production. As the demand on CD technology continues toward higher data transfer rate, the demand on spin rate stability of a spindle motor continues its advance. The increase of spin rate requires higher power consumption of a spindle motor and excessive heat is generated. This excessive heat aggravates the offset drifting in the Hall sensor and also induces amplitude shrinkage of Hall sensor signals. This undesired offset variation results in timing jitter of spindle-motor timing driving sequence to induce unstable spindle-motor ioop in a CD system. In this paper, a practical solution is proposed to remove the offset completely, and thus, to achieve a very stable spindle loop.

The application of aberration compensation devices can support the trend to higher information densities in optical data storage. The information content of a disc may be increased while maintaining acceptable tolerance levels. For example, disc tilt dependence may require coma compensation, whereas double layer formats require spherical aberration compensation. Liquid crystals (LCs) can be successfully applied in such devices. The design of two practical implementations is discussed; a coma compensating LC-cell with special electrode-design for optimized tolerances w.r.t. decentering, and a lens made of photopolymerizable LC, which can be used to compensate for spherical aberration.

Multi-level recording has advantage of increasing the recording density without extensively altering the current optic configuration. In this paper, a new four-level recording phase-change disk using three-recording layers was demonstrated. By modulating the intensity of the laser pulse, marks were chosen to record in any of recording layers, to form four recording regions. Utilizing the property of the phase change media whose amorphous and crystalline states differ largely in refractive indices, each recording region corresponds to different reflectance. For the four-level recording disk, each recording region represents two-bit data, then the recording density of the four-level disk is a factor of two higher than that of a conventional disk recorded by adopting the pulse position modulation.

The performance of a CD-RW drive is evaluated mainly in terms of recording data rate, access time, and power consumption. Constant linear velocity (CLV) recording technology is broadly employed in almost all the commercially available CD-RW drives today. In the CLV mode, the spindle motor which is driven by the real-time linear velocity of the disc will always be braked while seeking outwards or accelerated for inward-oriented seeks. Since the motor driver is driven in saturation, additional power dissipation will occur. This is undesirable in a CD-RW drive especially during data recording and accessing and huge power consumption will thus take place. When a long sequence of recording and seek actions are taking place, the spindle motor keeps braking and accelerating to result in excessive heat generated. Further, with even higher than 16X CD-RW drives on the horizon, the CLV would not only cause over heating but also induce larger vibration to distort the system. A feasible approach to avoid the excessive heat and vibration is to employ constant angular velocity (CAV) to record the data in a CD-RW drive. Since CAV recording would require the on-the-fly optical power calibration (OPC), this imposes a totally new generation of technology requirement on the chipset and system design which are not currently available yet to the mass market. A quasi-CAV recording technique is thus proposed in this paper. This quasi-CAV recording algorithm can not only effectively reduce the heat dissipation in a CD-RW drive during recording but also avoids the complicated interaction of on-the-fly write strategy adjustment. In this paper, both experimental results and software implementation technique are presented.

3D optical memory with photorefractive materials is discussed for ultra-high density/capacity memory exceeding the classical limit of a conventional optical recording system. Bit data are recorded as highly localized refractive index variations in 3D volume using a focused laser beam. We show recording and reading results using various recording materials and optical configurations. A multi-structured optical recording medium using a photoisomerization polymer and a transparent films has been developed for reflection confocal reading. Two-photon recording is also demonstrated.

Readout characteristics of light-scattering-mode super- resolution near-field structure (super-RENS) disks are described in detail. Readout intensities in reflected and transmitted signals are compared. Both signals showed mostly the same carrier-to-noise ratios (CNRs) using objective lenses with NA of 0.6. The formation mechanism of light scattering centers in the super-RENS disks ia also described in comparison with several different disks. As increasing oxygen ratio during the deposition of silver oxide (AgOx) layers, two different chemical reactions were identified. It was found that the super-RENS disks with oxygen-rich AgOx films have both characteristics of transparent and light- scattering apertures in one disk. Further study also revealed that the AgOx dynamic nonlinearity is not so high and less than 6% by the film itself; however, it is enhanced to 12% in super-RENS. It is supposed that the imaginary refractive index k of the films is less than 0.1; therefore, it is hard to heat itself to the decomposition temperature without a heat source (GeSbTe film) underneath. This result would be a hint to further increase CNRs in a light- scattering-mode super-RENS disks.

We propose a new laser lithography technique using the effect of thermal-induced super resolution and demonstrate that the technique can effectively reduce the exposed spot size on the photoresist layer, thus allowing disk mastering toward higher density by using exiting light source and optics. A mask layer, whose nonlinear optical properties result in formation an aperture in high temperature area near to the center of the laser spot, is deposited on the top of the photoresist layer. Usually, the aperture size is much smaller than the laser spot, thus, achieving thermal- induced super resolution. The simulation and experimental results reveal that the line width on the photoresist layer could be shrunk by more than 40%.

A thin ferroelectric interferometer (TFI) structure for light modulating devices is presented. It was fabricated entirely with thin film techniques on sapphire and silicon substrates. The ferroelectric layer in this structure was the lanthanum-modified lead zirconate titanate electrooptic materia, deposited from a chemical precursor solution onto an ITO-coated dielectric mirror stack. Light intensity modulation in both transmission and reflection modes, and phase modulation in the reflection mode were demonstrated. Experimental and simulation data show that TFI devices can be fast switching with a low driving voltage. Variations of the basic TFI structure can be used for phase tunable spatial light modulators and laser beam steering devices. Design principles, fabrication procedure and the preliminary performance of the devices are described.

We propose a new stream cipher technique for 2D image data which can be implemented by iterative optical transformation. The stream cipher uses a pseudo-random number generator (PRNG) to generate pseudo-random bit sequence. The proposed method for the PRNG is composed of iterative operation of 2D affine transformation achieved by optical components, and modulo-n addition of the transformed images. The method is expected to be executed efficiently by optical parallel processing. We verify performance of the proposed method in terms of security strength and clarify problems on optical implementation by the optical fractal synthesizer.

Because they produce small spot size, near-field techniques are applied to optical data storage systems in order to increase recording density. For data storage, the optical near field is defined in terms of evanescent coupling between the system used to read data and the recording layer. Two practical implementations that use evanescent energy are aperture probes and solid immersion lenses (SILs). In this paper, the basic characteristics of these systems are reviewed, and some considerations for improving performance are discussed. Combinations of SILs and apertures could produce data storage systems with ultra-fine resolution and good detection characteristics.

High numerical aperture vector diffraction theory is used to analyze a near field optical system using a solid immersion lens. The amplitude and phase of the transmitted light through the system changes as a function of the air gap height as well as indices of refraction, incident angle, etc. We call these `amplitude apodization' and `phase apodization'. The characteristics of those are done using supergaussian form. The effects of amplitude and phase apodization on irradiance are investigated for various index of refraction and air gap height.

The modulation of the irradiance in the exit pupil of an optical data storage scanning system is described by analyzing the behavior of scan-dependent interference fringes. These fringes are grouped into three independent irradiance components. The variation of the exit pupil irradiance pattern as a function of groove depth is discussed.

Comprehensive analyses based on rigorous vector diffraction theory have been presented to simulate the readout signal contrast using SIL in reading phase change recording disk. De-polarized reflected light (y-polarized from x-polarized incident beam) results in the reduction of total signal contrast, and becomes more obvious for high numerical aperture systems. Due to the signal degradation from de- polarized reflected light, filtering de-polarized light is applied to signal detection. The x-polarized contrast is a factor 1.0 to 1.35 higher than the conventional detection contrast (x+y polarized) at different gap widths, at a cost of 0 to 25 percent total intensity reduction.

We present a new technique for Chinese seal recognition using constrained energy minimization joint transform correlator (CEMJTC). Either optical or digital correlation is one of the most powerful operations for detecting the presence/absence of the seal image. The CEMJTC is proposed to improve the discrimination capability for shift- invariance and rotational-invariant seal recognition. By minimizing the average correlation energy with respect to all training seal images, while constraining the correlation peak value to a constant, a filter function is constructed. The main emphasis is to design a filter for good discriminate ability. Numerical results are presented to demonstrate the improvements. Furthermore, experimental results show the sharp correlation output profile when the seal image is correct, otherwise the correlation peak will be obviously reduced. The new technique for seal recognition shows a significant increase in high speed and detection ability.

We present a study of the grating detuning effect on the volume holographic data storage using photopolymer recording material. By using the Bragg matching condition, the angle shift and the decay of the diffraction efficiency of the reconstructed beam is obtained. Then the distortion of the readout page is described. And a method for pre-compensation of the incident angles of the reading beam is presented.

We propose an all-optical logic device made of a bent waveguide with a Kerr-like nonlinear interface. It could provide an OR gate, exclusive-OR (XOR) gate and AND gate. We could obtain different transmission results by modifying the bending angle. The numerical simulation results show that the device functions as OR, XOR and AND gates.

Recently, the applications of diffractive optical element (DOE) for commerce and research have become more and more popular. DOE itself has a lot of advantages like small volume, low weight, ease of reproduce and low cost. A DOE actually can be considered as a wavefront modulator, and its performance can also be described as a complex amplitude transmittance. In the past, we usually design a DOE by quantizing the phase of DOE from Gerchberg-Saxton algorithm or other methods with equal etching-depth and etching-width because of the ease of process. In this paper, we present a novel approach for design DOE. We change the element's etching-depth and etching-width nonuniformly. The reason why we strike out this approach is that one who can control the timing within the etching process can make any depth and width after all. Therefore, we have more components of etching-depth and etching-width that can be produced to reach the better diffractive efficiency on output diffraction plane than the conventional etching method. In terms of our proposed method, the conventional method of DOE design will become a special case of our new approach. According to the minimum etching-depth, we try all possible combinations to find a set of DOEs phases that have better diffractive efficiency than the conventional method can achieve. The DOE design with the proposed method has higher efficiency on output diffraction plane than those achieved by the conventional method.

Comparison of the frequency responses of two high-speed optical fiber processing elements is reported. The two filters we considered are a two-loops optical infinite impulse response (IIR) filter and a three-loops optical IIR filter. The theoretical models of these two kinds of optical IIR band pass filters are built up. Some suitable coupling coefficients are searched for simulating the narrow band- pass filters. The frequency responses under different conditions are analyzed. The theoretical models can provide parameter evaluation for experimental design. A higher design flexibility can be given by the three-loops optical IIR filter. These filters can be implemented with PIC (photonic PIC) techniques and applied for optical data signal processing.

This paper addresses the design and construction of an interesting polarization-switched diffractive optical element (DOE) that generates multiple beams incident on the disk and acts as a beamsplitter and servo-generating element for light returning from the disk. In this way, data speed is increased proportional to the number of beams on the disk, and, by combining three functions into a single optical element, allows a more compact and lightweight pickup to be realized. The polarization-switched DOE is constructed as a sandwich of two pieces of some birefringent material, with one rotated by 90 degrees relative to the other so that the ordinary and extraordinary axes are interchanged, and with a common index-match layer between them. A diffractive pattern is etched into each of the two birefringent pieces. Linearly polarized light traveling from the laser towards the disk is diffracted into multiple beams by one of the diffractive patterns while experiencing no diffraction from the other. Travelling the roundtrip from the DOE to the disk and back to the DOE, the light traverses a quarter-wave retarder two times thereby rotating its polarization direction by 90 degrees. It now experiences no diffraction from the multiple beam diffraction layer, but is diffracted by the second diffraction layer, which steers it onto the photodetectors and alters the beam to create useful focus and tracking error signals. This design is important in that it provides a way for two diffractive surfaces, each acting independently with high efficiency on orthogonal polarizations of light, to be combined into a single element. Implementation and application to a multiple-beam holographic pickup head module are presented.

A diffractive phase element (DPE) reducing the diameter of main-lobe of a focal light spot has been developed. A light spot focused by an optical system spreads due to the light diffraction from a limited aperture of lens. The developed DPE reduces the main-lobe diameter by modulating the incident wave-front of the focusing lens. Although the DPE increases the side-lobe intensity of the focal spot, appropriate design can reduce its magnitude enough not to affect the photoresist in lithography process. An iterative method based on the Gerchberg-Saxton algorithm combined with new constraints was applied to design a DPE. A rotation symmetrical binary DPE was designed, which reduces the main- lobe diameter to 74% and makes the side-lobe intensity under 2.7% of the main-lobe. The designed DPE was fabricated with the laser beam lithography system developed by the authors, and its performance was measured by mounting it on this system. The minimum line width obtained with the DPE becomes 1.0 micrometers while it is 1.2 micrometers without the DPE. It is also shown by a computer simulation that the focal depth of the focusing system with the DPE becomes wider than that without the DPE when both systems produce the same focal spot size.

The volume holographic optical data storage has been an important and exciting area of research. Recently the more interested study for a high-density holographic memory is focused on the speckle wave used as a coded reference wave in various multiplexing techniques. In this paper, a novel speckle holographic storage scheme is proposed, which a random phase diffuser is added in the front of storage medium along the reference optical path of the original 90 degree storage geometry. In this scheme the incident angle of the reference beam and the place of the random phase diffuser illuminated by the reference beam can be changed simultaneously. The joint action of these changes generated a dynamic speckle wave for the reference beam in holographic storage. A theoretical model has been derived to describe the storage properties of this scheme based on the cross- correlation of dynamic speckle and the diffractive theory. The storage density influenced by the properties of the speckle patterns has been analyzed and experimentally confirmed. The results indicate that this scheme allows an increase in the data storage density with simple storage- retrieval architecture.

In this paper, a new two-way measurement method of optical signal processing elements is presented. The proposed method can decrease testing time and reduce human errors induced by disconnection in conventional one-way testing method. We can measure the scattering parameters of optical devices with fast two-way measurement when applying the new probes in conventional network analyzers. We demonstrated using our designed opto-electronic probes can measure the frequency responses of S₂₁ and S₁₂ of optical information processing component simultaneously. No reverse connections are needed for transfer functions measurement. In the future, this system can be applied to measure the characteristics of broadband optical signal processing elements for system applications. The theoretical model we built is very match to the experimental results.

Dual-layer optical disks comprised of two data layers were developed to study readout/write/erase characteristics. This disk was composed of recording layer 1 and 2, of high transmittance and high reflectivity, respectively. Layer 1 and 2 of 15 and 20 nm increase transmittance and reduce writing power for recording. Only 1.5 mW laser power was sufficient for readout, 9 and 16 mW was required for recording on recording layer 1 and 2, respectively. This dual-layer disk can double data capacity on a disk substrate.

We describe the design of a single diffractive LCD element placed adjacent to the objective lens that can be addressed to provide the required spherical aberration (SA) compensation for a plurality of disk substrate thicknesses. It is now commonplace that optical disk drives must be able to handle disks of more than one substrate thickness. The major problem is compensating for the SA introduced when the highly corrected objective lens is used with a disk substrate thickness other than that which it was specifically designed for. An abundance of methods for solving this problem in the specific case of CD/DVD backward compatibility exist in the literature; we use an active device to extend this to include HD-DVD as well.

The technology of infrared wireless local area network is one branch of the IEEE802.11 protocol's access network technology. As a medium for short-range or indoor communication, infrared radiation offers several significant advantages over radio. Infrared emitters and detector capable of high-speed operation are available at low cost. The infrared spectral region offers a virtually unlimited bandwidth that is unregulated worldwide.

The single-phase DC motor has the low-cost advantage over 3- phase DC motor owing to its easy-assembling and high yield- rate, however, it has larger torque ripple and cogging torque. Single-phase DC motor is currently applied to low profit margin products such as cooling fan. In order to utilize single-phase DC motor to high precision system, for instance, DVD (Digital Versatile Disk), the vibration caused by torque ripple and cogging torque needs to be solved. In this paper, focusing error, tracking error, seeking ability and some velocity control performances are studied when single-phase DC motor is used in DVD related products.

An optical scanning technique of dactylogram (fingerprint) has been developed by using plural LED's with different wavelength as emitting elements and a color CCD or CMOS area image sensor was receiving element. Owing to the R/G/B filters built in that color area image sensor, if the above LED's have wave lengths corresponding to those peak sensing wavelengths of the R/G/B outputs of that color area image sensor, and if the above mentioned LED's are installed to emit light on the surface of finger from different directions, then it will be effective to get a 3D picture by using a single color area image sensor. Moreover, the time needed to obtain a 3D picture is only that for single exposure.

As we approach the new millennium, the ongoing aim of human society is not only for promoting scientific technology but also creating new industries. To achieve this goal, each person in industry must recognize anew that the real meaning of science is to explore the absolute truth. It is also important that people recognize that there are unlimited matters which we humans do not yet know.