At the beginning of this century, lighting technology has been shifted from discharge lamps, fluorescent lamps and electric bulbs to solid-state lighting. Current solid-state lighting is based on the light emitting diodes (LED) technology, but the laser lighting technology is developing rapidly, such as, laser cinema projectors, laser TVs, laser head-up displays, laser head mounted displays, and laser headlamps for motor vehicles. One of the main issues of laser displays is the reduction of speckle noise1). For the monochromatic laser light, speckle is random interference pattern on the image plane (retina for human observer). For laser displays, RGB (red-green-blue) lasers form speckle patterns independently, which results in random distribution of chromaticity, called color speckle2).
The recording density limit of the collinear holographic memory purely determined by the optical system, that is under
the assumption that the recording material is ideal, is estimated. Signal to noise ratio is decreasing with the increase of
the number of overlapped hologram pages because of the increase of the off- and degenerated-Bragg diffraction from the
gratings in the holograms increases. The signal to noise ratio is calculated with the plane wave model accompanied with
statistical considerations. It is shown that 5 Tbyte recording in a compact disc size is possible in ideal case.
Inverse Faraday effect and optical Kerr effect are measured in antiferromegnetic NiO using pump-probe method.
The magnetic field is induced by the illumination of 100 fs intense circularly polarized wave, which is detected
by the Faraday rotation of probe beam.
Non-periodic structure of optical pattern can assign distinctive potential landscape to multiple micro particles
according to their sizes, and enables optical sorting using only optical gradient force. We have theoretically
and experimentally investigated the dependence of success rate of sorting as a function of time on beam
power in non fluidic flow system. In the experiment, polystyrene spheres suspended in water were used as
samples, and the radii were 0.49 μm, 1.03 μm, and 1.61 μm, respectively. We used multiple optical lines in
the experiment, and placed it non-periodically with increasing peak intensities. The experimental result
qualitatively agreed with the theoretical one, and the success rate of sorting was more than 90 % with
sufficient beam power. We demonstrated our method in the system with flow by placing optical pattern such
that optical gradient force acted on particles orthogonal to the flow. In the experiment with flow, triangle
optical pattern was used to lift up micro particles onto the top surface where image of optical pattern was
formed and to carry the particles to starting position for sorting. Our sorting system can in principle work in
broad range of particle velocity with sufficient beam power.
We experimentally demonstrate that adiabatic compression of femtosecond pulse can be achieved by employing the
management of quadratic cascading nonlinearity in quasi-phase-matching gratings. Cascading nonlinearity is not a
simple analogy with third-order optical nonlinearity in term of the engineering properties of the magnitude and focusing
(or defocusing) nonlinearity. Femtosecond pulse compression is investigated based on type-I (e: o + o) collinear QPM
geometry of aperiodically poled MgO-doped LiNbO3 (MgO: LN). Group-velocity-matching condition is chosen to
generate quadratic femtosecond soliton consisting of fundamental (FF) and second harmonic (SH) pulses. Adiabatic-like
compression process is observed in the length of 50 mm linearly chirped QPM. Cascading nonlinearity is local managed,
instead of dispersion management used in fiber adiabatic soliton compression. Quadratic soliton including FF and SH
pulses are obtained from the compression of 95 fs FF pulse in the initial experiments. Dependence on the phase
mismatch and group velocity mismatch, cascading nonlinearity has a flexible property and presents a new challenge for
exploring femtosecond pulse shaping and control. The demonstrated pulse compression and control based on cascading
nonlinearity is useful for generation of shorter pulses with clean temporal profiles, efficient femtosecond second
harmonic generation and group-velocity control.
Holographic Versatile Disc (HVDTM) using CollinearTM Technologies is proposed by OPTWARE Corporation, in which
the information and reference beams are displayed co-axially by the same SLM. With this unique configuration the
optical pickup can be designed as small as the DVD's, and can be placed on one side of the recording disc. In HVDTM
structure, the pre-formatted meta-data reflective layer is used for the focus/tracking servo and reading address
information, and the dichroic mirror layer is used for detecting holographic recording information without interfering
with the preformatted information. A 2-dimensional digital page data format is used and the shift-multiplexing method
is employed to increased recording density of HVDTM. Experimental and theoretical studies suggest that the holographic
material is very effective to increased recording density of the system. As the servo technology is being introduced to
control the objective lens to be maintained precisely to the disc in the recording and the reconstructing process, a
vibration isolator is no longer necessary. HVDTM will be compatible with existing disc storage systems, like CD and
DVD, and enable us to expand its applications into other optical information storage systems.
Numerical simulations of the signal decay with media shift were performed. Principle of the shift selectivity of the
data pages are explained with our simple numerical model. Decay of the diffracted signal is calculated with the shift of
the media. The dependencies of the shift selectivity on the reference pixel patterns, radius and width of the of the
reference pixel area, and the media thickness. Shift selectivity of the page does not depend on the media thickness or
reference pixel patterns. It is mainly determined by the radius and the width of the reference pixel area.
Photorefractive properties of Fe, Mn, and Rh doped 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 (0.91PZN-0.09PT) are investigated. Relaxor ferroelectric crystals are expected to show large photorefractive effect due to its large piezoelectric effect near morphotropic phase boundary (MPB). Crystals are grown by flux solution method, then cut, polished, and poled along  direction. Absorption spectrum, photorefractive two-beam coupling gain, and response speed were measured as functions of the grating period, and light intensity, at several wavelengths for each doped and undoped samples. Photoconductivity and photochromism in Fe doped crystal were estimated. Fe doping enhanced the photorefractive effect and net two-beam coupling gain of 19 cm-1was obtained. Rh doping increased the gain at 633 nm compared to the undoped sample. From the intensity dependence of the two-beam coupling gain, two-center model is suitable for explaining the photorefractive properties of Fe doped samples. For all samples, doping of the ions slowed down the response speed because of the decrease of the photoconductivity.
Some characteristics of photorefractive semiconductor multiple quantum well devices are discussed from the point of view of a material for the vibration measurement system using two-wave mixing. Device structure and device fabrication is explained, and some results of the measurements on the characteristics of the device are presented and discussed. Finally, the system of vibration measurements is described and some results are discussed. The smallest detectable amplitude of the vibration is 0.4 nm and the signal is linear up to 25 nm. Cut off frequency is 34 kHz at the incident intensity of 90mW/cm2.
An optical interconnection technique using photorefractive segmented waveguides is reviewed. The photorefractive segmented waveguide consists of many localized high refractive-index regions that are fabricated by illuminating a focused laser beam. The waveguide interconnections can be adaptive by changing the spatial arrangement of the high refractive-index regions. Fabrication results of straight, curved, and Y-branch waveguides are presented. In the straight waveguides, the transmitted power of a guided beam as a function of the period of segmentation and the dark decay time are measured. The tolerance due to fabrication error is also investigated experimentally. Waveguide structures can be optically modified to implement adaptive interconnections. As an example, a curved structure was transformed into a Y-branch structure by optical illumination. We numerically show that a novel structure of a segmented waveguide can work as a waveguide, where average refractive index of the core is the same as that of surrounding material.
A beam profile monitoring system for the synchrotron radiation is designed to evaluate distribution of a cross section of the electron beam in a high-energy accelerator storage ring in real-time. The Shack-Hartmann wavefront sensor is adopted for the measurement of the wavefront error caused by deformation of an extraction beryllium mirror for the visible synchrotron radiation. The correction of the measured wavefront distortion is also described.
Single longitudinal mode operation of 1 W class broad-area diode lasers are achieved with phase conjugate injection locking technique. We adopted two stage injection scheme because the final output power is limited by the power of the injection beam. First, we locked a broad-area laser by the output beam from a single mode diode laser of the output power of 40 mW. We obtain 550 mW output from the broad-area laser with single longitudinal mode. Spatial pattern of the slave lasers are greatly improved by mode selection with the spatial filters at the far field between the lasers and phase conjugate mirrors. We also analyze the transverse oscillation modes in broad-area laser under locking conditions by numerical modeling. We can explain the near field and far field pattern in our experiment with our model.
The phase conjugate reflectivity and the transmission in mutually pumped phase conjugators are investigated as a function of input bema power ratio in order to find out the optimum operating condition for high reflectivity and for high transmission with mutually incoherent and coherent beams. In our experimental results we show that we have the highest transmission at the ratio more than one in the modified bridge phase conjugator.
A novel method to measure a short light pulse using the photorefractive effect is proposed. Since photorefractive crystals are volume holograms, if we assign one axis to time, we can use them as materials which record the change of spatially two dimensional information. We recorded 3.5 ps pulses of a mode-locked Nd:YAG laser in a Fe:LiNbO3 crystal and read out the information by cw He-Ne laser by measuring the amplitude and phase of the diffracted wave.