We present advanced methods to improve the performance of the near field system. Using the RF signal, the near field
system can detect a tilt error and find the best tilt condition for more wide range. The 2-step approach process can
shorten the pull-in time and decrease the possibility of a collision.
Certain ideas and techniques are being developed outside the field of optical/magnetic/
electronic recording, but the storage community could benefit from these developments once we become
sufficiently familiar with the new concepts and methodologies. Developments in the areas of nano- and
bio-photonics, fluorescence microscopy, quantum-dots, optical tweezers, micro- and nano-fluidics,
femtosecond lasers, etc., have the potential to influence future generations of data storage systems.
We experimentally demonstrated improvement in optical disc readout signal quality by homodyne detection. We
introduced an optical phase servo system as an alternative to the phase-diversity detection scheme for stabilization of the
interference signal in homodyne detection, which resulted in further enhancement of readout signal quality.
Experimental results indicate that at least a 16-layer recordable disc can be reliably read out with a jitter of less than 8%
at a 1-mW read power by homodyne detection. The estimated amplification of signal amplitude was 13 times.
We propose a method of optical data storage that exploits the small dimensions of metallic nano-particles
and/or nano-structures to achieve high storage densities. The resonant behavior of these particles (both individual and in
small clusters) in the presence of ultraviolet, visible, and near-infrared light may be used to retrieve pre-recorded
information by far-field spectroscopic optical detection. In plasmonic data storage, a femtosecond laser pulse is focused
to a diffraction-limited spot over a small region of an optical disk containing metallic nano-structures. The digital
information stored in each bit-cell modifies the spectrum of the femtosecond light pulse, which is subsequently detected
in transmission (or reflection) using an optical spectrum analyzer. We present theoretical as well as preliminary
experimental results that confirm the potential of plasmonic nano-structures for high-density optical storage applications.
Multilevel recording technology is used to improve the recording density without changing the optical and mechanical
units. A new modulation code scheme for signal waveform modulation multilevel (SWM) read-only optical disc has
been implemented. The proposed scheme is composed of run-length limited (RLL) modulation and level modulation two
steps. RLL modulation is employed to meet the requirements of channel. To acquire higher code rate, the parameter d of
RLL(d, k) is decreased to 0, which makes the presented scheme difference from other modulation codes of the optical
storage systems. Increasing the number of k also contributes to the high code rate. Decreasing d and increasing k will
respectively introduce more inter-symbol interference (ISI) and timing recovery error (TRE) to SWM optical system.
Level modulation is used to resolve these problems. The decoding rule is simple and easy for implementation. The signal
waveform of SWM disc adopted the proposed code is also described. The information bits per 400nm are 2.19, which is
46% higher than that of DVD.
By using conventional MEMS processes, we have successfully developed a high accuracy and easily controllable
deformable mirror with simple structure. Our deformable mirror is driven by a single actuator different from a
conventional deformable mirror of multi-actuator type. The deformed shape is controlled by giving strength
distribution on the reverse side of the mirror. Furthermore, we have obtained a reflective film of low stress which had
previously been a challenge.
Axicon produces a deep focused Bessel beam whose transverse focal spot is smaller than the size of an airy disk
produced by conventional lens with the same numerical aperture. Rieko Arimoto et al. applied axicon to a beamscanning
system and established the beam-scanning imaging system which is free from need of precise positioning.
Meanwhile, the allowed amount of rotation is severely restricted due to the unwanted tilt in the focused ring. We analyze
the tilt in the focused ring quantitatively and suggest an appropriate method of designing the aberration corrected lens.
An exemplary lens design for 1° tilt in the scanning mirror is presented and it is shown that the amount of degradation is
clearly suppressed in the optimized system.
We present an overview of the main properties and the emerging implementations corresponding to a photopolymerizable glass modified with high refractive index species (HRIS) incorporated at molecular level. The study concerns to transmission and reflection holograms in Bragg and Raman-Nath regimens and polarization properties of
gratings with high spatial frequencies are also analyzed demonstrating a strong dependence of the refractive index
modulation with the polarization state of the reading beam. Not limited to the study of the optical properties of the
photopolymerizable glass we propose two applications of the holographic material. The first one is the fabrication of
polarizers elements with high performance at low cost such us holographic polarizers and holographic polarizers beam splitters. The second application concerns to the holographic recording of stables modes exhibiting high diffraction efficiency. Also, we have recently extended our studies to ultrashort pulse lasers in femtosecond regime. The photopolymerizable gratings are good candidates as optic elements to beam manipulation of ultrashort pulse lasers.
The optical constants including the refraction index n and extinguished coefficient k of the variety of materials are
calculated from their reflection and transmittance measurements with measured wavelengths. We derive the reflectance
and transmittance equations associated to the material film optical constants. The organic and inorganic materials used
for optical recording medium materials are examined. The organic dyes show that significant optical constants vary with
the laser wavelength, in comparison to the inorganic phase-change materials. This is an evidence to indicate the
complicated bonding structure in the organic dyes within the measured wavelength ranges.
In Micro-Reflector optical disc systems, multi-layer index modulation distribution causes wavefront fluctuation in the
light beam passing through the layers. Generally, the Merecial's criterion 0.07λrms is widely used as a figure of merit
for the wavefront quality of a light beam for readout. However, due to the fine structure of the wavefront fluctuation by
the recorded marks, the decay of readout signal is less comparing to the general case.
In this paper, it is experimentally verified that the refractive-index modulation of the existing gratings continues to
increase with uniform exposure or when a current grating is being recorded. And it is reasonable to assume that the effect
of a sequential recording on an existing grating can be equivalent to the uniform exposure. Our simplified model for
grating formation in photopolymers is extended to describe the effects of uniform post-exposure on an existing hologram,
and further to deduce a new model of holographic multiplexing in detail for calculating the exposure schedule for
multiplexed gratings with uniform diffraction efficiency. Twenty gratings were multiplexed using the exposure schedule
calculated with the uniform post-exposure model.