It was reported recently that optical pulses propagating through a tapered fiber (TF) immersed in heavy water (D2O) or
photonic crystal fiber (PCF) of special design yield a broad and flat supercontinuum (SC) spectrum because the fiber
dispersion characteristics are of low dispersion: around 1000 nm. This work was undertaken to investigate spectral
intensities and phase distributions of SC pulses generated in low-dispersion fibers. Results show that PCF with group
velocity dispersion (GVD) distributions having an extremum value of zero dispersion can be used at short fiber length
for applications where the phase distribution is a concern.
A use of liquid crystal panels (LCPs) as a random phase modulator in the optical encryption system based on
the double random phase coding (DRPC) [Optics Letters, Vol.20, 767(1995)] is considered in the present paper.
Required phase modulation property of LCPs as random phase modulators in the DRPC are investigated by
computer simulations. It is found from simulation results that the required number of independent patches for
phase modulations must be greater than 128 × 128 pixels for LCPs with the maximum phase modulation of
1.55π radians. It is also found that the required maximum phase modulation can be reduced to 1.25π radians by
increasing the number of independent patches to 1024 × 1024 pixles. Experimental study using a commercially
available LCP (EPSON, HTPS LCP, L3P14Y-55G00) verified partially these simulation results.
Phase-shifting digital holography based on the spatial carrier interferometry makes available for snap-shot recording
and reconstruction of three-dimensional objects in dynamic motion without erroneous signals. Key point of
the method is an introduction of tilt in the reference plane wave in recording a hologram so that relative phase
difference between sequential pixels of image sensors becomes 2π/3 or π/2. This requires theoretically rigorous
alignment in the angle of incidence of the reference wave, and therefore, it seems to make the method impractical.
In the present paper, the tolerance of the incident angle of the plane reference wave in the method is analyzed
theoretically and verified by computer simulations. It is found from these studies that the rigorous alignment of
the incident angle of the plane reference wave is very important requirement to reconstruct the correct complex
amplitude of the object wave. However, it is also found that in the case of miss-alignment, we can derive the
correct object waveform by compensating the linear phase due to miss-alignment.
Mechanism of supercontinuum(SC) spectrum generation due to cross-phase modulation(XPM) in a dispersionflattened/decreasing fiber(DFDF) with low birefringence has been investigated theoretically and experimentally. By using a XPM, the measured SC spectum width becomes 33.6 % broader than that obtained by using only self-phase modulation (SPM). This fact implys that effectiveness and validity of the sc generation using XPM method. Furthermore, dependence of generated sc spectrum broadening on incident power, polarization angle of the input pulses, and modal birefringence are investigated. consequently, it was velifid that when a polarization angle of the input pulses is 45 degrees with regard to the principal axes of the fiber and incident average power is less than 0.147 mW, soliton trapping takes place due to a balance between soliton pulse powers and modal
birefringence value. In addition, it was shown experimentally that for a polarization angle of the input pulses of 22.5 degrees, the sc spectrum is enlarged by the same amount as in the case of 45 degrees.
Phase-shifting property of moire patterns which constitute spatially sampled data set of single interferograms with a linear carrier is revealed. Based on this property, a phase reconstruction method using the phase-shifting algorithm is proposed for single interferograms with a linear carrier. Limits of a carrier frequency and a phase slope being reconstructed are given.
Dynamics and light-scattering properties of the Brownian particles in colloidal suspensions under an influence of the radiation pressure force of an illuminating laser beam are investigated by means of computer simulations using the Fokker-Planck equation and the generalized Lorenz-Mie theory. Dynamic behavior of the particles and a temporal correlation function of intensity fluctuations of the light scattered by these particles are calculated for various factors of particle size and power of the illuminating laser beam. Results of the simulations support the experimental observations of deformations in the temporal correlation functions of the scattered light and their dependencies on a size of the particles and a power of the laser. From simulation results of the dynamics of particles, it is found that these changes in the correlation function come from suppression in the radial direction of the laser beam and an acceleration in the axial direction of the beam, of a random motion of the particles.
An extended method is described for continuous measurements of the size and two-dimensional (2-D) motion of single spherical particles using an image sensor. It is based on two-fold principles: the formation of a streak image of the particle from light scattered into an off-axis forward direction and the scanning detection of the streak image by a 2-D MOS imager which employs the X-Y addressing format. Unlike conventional video camera methods, all time-resolved information of the particle size and motion can be determined by evaluating the intensity distribution of one frame image with an attainable time resolution of 63.5 μs.
Since a proposal and pioneering experiments by Ashkin et all for trapping a small dielectric particle by using the laser radiation pressure (RP), this technique has been applied in wide fields of chemistry and biology, known as optical tweezers, and in new-type optical microscopy. By considering the laser trapping from the viewpoint of optical particle sizing based on the laser light scattering, e.g. photon correlation spectroscopy2' 3 (PCS), in which the Brownian motion of particles plays an important role, the radiation pressure of an illuminating laser beam may affect the motion of particles under investigation in despite of the unsuspected assumption that the illuminating laser beam does not distort the particles' motion.
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