The improved scheme of data recording process on an optical disc based on a substrate made of high-stable materials has been proposed. Information layer with depth of 115nm and width of 600nm has been obtained on sapphire substrate by ion-beam etching using improved scheme. These experimental results allow to create the sapphire optical discs for long-term data storage.
The non-homogeneous multilayer medium was proposed for laser thermal recording. The mathematical model of laser thermal recording based on the phase transition of non-homogeneous medium (such as melting, ablation, evaporation) to simulate and optimize was developed. It was shown that in multilayer recording medium can be performed narrower structures than in monolayer films on similar conditions. It was shown that for getting small structures the thermoconduction of recording medium should be much smaller than the thermoconduction of substrate on which a medium is deposited. It was demonstrated that in the case of strong light absorption in recording layer its thermal conductivity must be sufficiently large to ensure the transfer of heat on a distance that equals to the thickness of the layer during a time interval equals to the difference in time for warming up to the phase transition temperature of the central part of the light spots and area that separated from a center of light spot on a distance equals to the thickness of layer.
Results of numerical simulation of near-field optical data storage using microstrip probe are presented. Simulation is
carried out on the basis of the finite-difference time-domain method. Features of the information reading process from
the ROM and RW (based on the phase transmissions of Ge2Sb2Te5 film) formats of optical discs under illumination and
illumination-collection mode are analyzed and considered. Mathematical modeling has shown that the signal from the
ROM-format disc under illumination mode, despite the fact that the probe has a significant far-field transmission
coefficient, has a large crosstalk and small spatial resolution (significantly worse than a size of probe aperture). Unlike
illumination mode, signal under illumination-collection mode (pure near-field method) has a resolution close to the size
of the aperture, good amplitude and contrast, as well as relatively low crosstalk. However, information reading under
illumination-collection mode from RW-format disc is not able to get the same good quality signal. Therefore the further
optimization of the method is required to improve the signal quality of RW format.
Results of implementation of technical solution for long term data storage technology on the basis of single crystal
sapphire are presented. The effect of birefringence on the distribution of the focused laser beam through a uniaxial
birefringent medium having a vertical orientation of the optical axis is analyzed. An expression for the calculation of the
geometric aberrations of the focused laser beam in single-crystal substrate of the optical disc has been presented. It is
shown that the problem of data reading through a substrate of negative single crystal sapphire can be solved by using for
reading a special optical system with a plate of positive single crystal materials. The experimental results confirm the
efficiency of the proposed technical solution.
Microprism diagnostic set KK-42 for ophthalmology application comprises 42 separate microprism elements - strabismus optical compensators and it is designed for the image displacement at vision diagnostics.
The main requirement for optical compensators is high quality of observed images. However, strong diffraction
phenomena and chromatic aberrations due to light dispersion exist for microprisms similar to any other prismatic
systems. Structure simulation was carried out to minimize the acuity degradation and to avoid observed image
discretization. The simplest method to diminish aberrations is the application of filters and colour plastics. Experiments
and calculations were performed which showed the opportunity to diminish twice the chromatism zone by filters to the
value of 20-25 angular minutes.
Another method of decreasing chromatic aberrations is application of additional prism microrelief - saw tooth
diffractive optical element. In optical compensators the first microrelief with the pitch of 600-800 μm serves as a
refractive prism. Diffractive element with the pitch of 15-20 μm operating in first diffractive order is optimized in such a
way that dispersion of the first diffractive order compensates dispersion of the compensator. This method allows to
compensate dispersion totally at any spectrum zone.
Diffractive spatial optical modulators (SOM) employing a fine-pitch pixel array were introduced. The micromechanical designs of the lead zirconate titanate (PZT) actuator and mirror ribbon structure were optimized for a small volume while maintaining the same level of performance. The same design rule and fabrication equipment were used for a new 10-µm-pitch and conventional 16-µm-pitch SOM. The optical efficiency of the new SOM was 78% (zeroth-order diffraction), which is an improvement over that of the 16-µm-pitch SOM (73%). The full on/off contrast ratio showed no differences, and a high displacement of 500 nm was achieved. The stress of the Pt/PZT/Pt actuating layer was the main parameter affecting the initial gap height and displacement of the ribbon. The required ribbon flatness could be achieved by applying a stress gradient on the SiN layer. The temperature-sensitive characteristics, which degrade image quality, could be minimized by a mechanical compensation method that takes advantage of the thermal expansion effect of Si substrates. The estimated lifetime of the device is >4000 h. The developed fine-pitch SOM device has sufficient response time and ribbon displacement to be suitable for high-quality embedded laser-projection displays. The VGA optical module was successfully demonstrated in a mobile laser projection display.
Diffractive spatial optical modulators (SOM) with fine pitch pixel array were introduced for the mobile applications of
laser projection display which requires the small volume, low power consumption and high optical efficiency.
Micromechanical designs of piezoelectric (PZT) actuator and mirror ribbon structure were optimized for small volume,
but keeping the same level of the other performance. Even though the same design rule and fabrication equipment were
used for 10 um pitch SOM and 16 um pitch SOM, the optical efficiency of the fine pitch SOM was 78 % for the 0th order
diffraction and is better than that of 16 um pitch SOM (73%). The full on/off contrast ratio has no difference between 10
um pitch and 16 um pitch SOM. All the optical characteristics coincide well with the theoretical estimations. High
displacement of 500nm, which is enough to modulate the three Red, Green and Blue colors were achieved by the control
of the thicknesses and stresses of constituent structural layers. It was found that the stress of Pt/PZT/Pt actuating layer
was the main parameter affecting the initial gap height of the ribbon and also its displacement. For improving the optical
properties of the SOM devices, the required ribbon-flatness could be achieved by applying a stress gradient on the SiN
layer to compensate for the stress unbalance between Al mirror and SiN supprting layer. The temperature sensitive
characteristics of the SOM device, which degrades the image quality, could be minimized by a mechanical compensation
method using a thermal expansion effect of Si substrates. This concept could be applied in most of the bridge type
MEMS structure. The most critical parameter which limit the SOM device lifetime was found to be the ribbon
displacement degradation. By using a temperature accelerating lifetime measurement method based on the displacement
degradation the estimated lifetime was more than 4,000 hrs and is of acceptable level in the mobile application. In short,
the developed fine pitch SOM device, for making small volume of optical module, has sufficient response time and
ribbon displacement for modulating the red, blue and green colors with one SOM chip and is suitable for high quality
embedded laser projection displays. Optical module with VGA is successfully demonstrated for its potential applications
in mobile laser projection display such as a embed projection cellular phone.
A diffractive optical modulator has been fabricated based on a micromachining process. Novel
properties of its fast response time and dynamics were fully understood and demonstrated for the
strong potentials in embedded mobile laser display. Bridged thin film piezo-actuators with so called
open mirror diffraction structure has been designed. Optical level package also was achieved to
successfully prove its display application qualities. Display circuits and driving logic were developed
to finally confirm the single-panel laser display at a 240Hz VGA (640×480). With its efficiency of
more than 75% and 13cc volume optical engine with the MEMS-based VGA resolution SOM
showed 7 lm brightness at a 1.5W electrical power consumption. Detailed design principle,
fabrication, packaging and performances of the invented SOM are described.
A new type of diffractive spatial optical modulators, named SOM, has been developed by Samsung Electro-Mechanics
for laser projection display. It exhibit inherent advantages of fast response time and high-performance light modulation,
suitable for high quality embedded laser projection displays. The calculated efficiency and contrast ratio are 75 % and
800:1 respectively in case of 0th order, 67 % and 1000:1 respectively in case of ±1st order. The response time is as fast as
0.7 &mgr;s. Also we get the displacement of 400 nm enough to display full color with single panel in VGA format, as being
10 V driven. Optical module with VGA was successfully demonstrated for its potential applications in mobile laser
projection display such as cellular phone, digital still camera and note PC product. Electrical power consumption is less
than 2 W, volume is less than 13 cc. Brightness is enough to watch TV and movie in the open air, being variable up to 6
lm. Even if it's optimal diagonal image size is 10 inch, image quality does not deteriorate in the range of 5 to 50 inch
because of the merit of focus-free. Due to 100 % fill factor, the image is seamless so as to be unpleasant to see the every
pixel's partition. High speed of response time can make full color display with 24-bit gray scale and cause no scan line
artifact, better than any other devices.
KEYWORDS: Metals, Transmission electron microscopy, Near field scanning optical microscopy, Dielectrics, Wave propagation, Magnetism, Near field optics, Near field, Spatial resolution, Distance measurement
The optical characteristics of probe of near-field optical microscope operating on TEM-wave based on two trapeziform metallic strips on the surface of a dielectric cone are investigated by mathematic simulation. It was shown that this probe has large near-field and far-field transmission coefficient. The mathematic simulation also shown that this probe has large electrical field enhancement and broad bandwidth. The theoretical modeling of field structure of quasi TEM in optical waveband has shown that spatial resolution of 10 nm can be achieved. The probe design with low background radiation is proposed. The method of distance measurement from scanned surface based on detection of amplitude of microwave radiation excited by mechanical vibration of contrarily charged part of bifurcate probe apex is proposed. Large transmission coefficient, high spatial resolution and broad bandwidth of operation make this probe promising for using it in data storage, spectroscopy and nonlinear optic of nano-object. The characteristics of bulk metal were used in digital simulation. The obtianed theoretical results must be validated by experiments.
KEYWORDS: Near field optics, Near field, Microscopes, Near field scanning optical microscopy, Waveguides, Magnetism, Absorption, Optical microscopes, Transmission electron microscopy, Dielectrics
A near-field optical microscope on the basis of two trapeziform metallic strips on the surface of a dielectric cone is investigated1. It is shown that such construction of a near-field probe significantly improved the optical efficiency of a near-field microscope.
The field distribution in the vicinity of probe apex is investigated for this probe and for the usual SNOM probe. On the basis of mathematical simulation it was shown that this type of a near-field microscope is promising for use in optical information recording with pit length less than 200 nm and also for using as optical heating element in magnetic information recording. The construction of a near field microscope for information recording is proposed on the basis of this near-field microscope and a solid immersion lens2.
The model of a near field strips probe with cleaved apex is proposed. A method of checking the distance between a probe and the surface on the basis of exciting mechanical vibration of cleaved apex by voltage step is offered. The oscillation amplitude and their attenuation are determined by measuring high-frequency electromagnetic oscillation, which are excited by oscillation of opposite charges at the apex of a probe.
The investigation was carried out on the basis of a mathematical model and an experiment is needed for full investigation.
Three-dimensional vector diffraction analysis for optical disc systems is described. The geometrical form of information pits and tracts is simplified to rectangular form. The disc surface and side wall of pits are perfect conductive. We considered two physical model of the pits: (1) in the bottom of pits the partial waves of rectangular waveguide satisfy impedance condition; (2) bottom of pits are connected to semi-infinite dielectric space. In the first case we obtained two-dimensional integral equation for electrical field in upper end of pit. In the second case we obtained two integral equation for upper and lower pit ends. The diffraction of laser beam by information pits was regarded in Fourier optics approach. We use the most exact theory of diffracted vector field to evaluate Fourier transform function for Gaussian beam. This approach gave us possibility to investigate the diffraction fields in the case of the lens with big aperture and small linear size. The obtained mathematical algorithm was applied then to the study of diffraction linear polarized Gaussian laser beam by disc information surface and to the diffraction laser beam by small rectangular aperture in infinite shield. The digital results showed that to obtain accuracy for integral characteristic of fields less than one percent it is necessary to take eight Fourier members for every coordinate on every pit end.
To overcome the limitation of the current memories some authors developed method for storing data throughout a volume of memory material using two-photon absorption effect. In this work we represent the three-dimensional vector analysis of diffraction laser beam by the simple model of this volume data storage. We represent the volume data storage as homogeneous dielectric in which three- dimensional grating of spheres with complex (epsilon) , (mu) are located. To evaluate scattering field of partial wave we used Lorenz-Mie theory. The total scattering field is sum of partial scattering fields and some small addition field of re-radiation. The addition field of re-radiation was evaluated in first approach of perturbation theory. The investigation results were used for the determination of recording information limits into the memory material.
The process of optical recording on ablation mechanism carriers shows a peculiar microrelief. The peculiarity of the latter is in the presence of an annular rim around the pit, of the carrier material arising by action of surface tension. This force on the liquid phase of microregion was subjected to the thermal action of a laser beam. During reading for increasing the signal- to-noise ratio, it is necessary to achieve optimal relations for parameters of reading laser beam, and geometrical pit dimensions surrounded by the annular rim. The method of scalar theory of diffraction did not allow to investigate the influence of geometrical sizes rims of pits on scattering characteristics of the laser beam from pits. In this connection, the mathematical simulation problem of the informaiton reading process from the surface with such form of units is of current concern.
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