Showing papers in "Optical Review in 1995"
TL;DR: In this article, the ability and limitation of the theory applied to estimate the performance of subwavelength relief gratings is described. But the limitation is revealed by numerical calculations using a rigorous electromagnetic grating theory and the effective medium theory.
Abstract: In the recent researches of subwavelength relief gratings, the effective refractive indices are used for calculating the coefficients of reflection and transmission of light waves. The effective refractive indices are given by the effective medium theory for light waves propagating in a bulky stratified medium. This paper describes the ability and limitation of the theory applied to estimate the performance of such subwavelength gratings. The limitation is revealed by numerical calculations using a rigorous electromagnetic grating theory and the effective medium theory. As a result, an understanding of the wave behavior in the subwavelength grating has been acquired, which explains the limitation of the effective medium theory.
78 citations
TL;DR: In this paper, the technique of using the "escape function" for global optimization in lens design is described, which includes how to identify two solutions as independent; the threshold value for this criterion can be chosen to determine how to explore local solutions.
Abstract: The technique of using the ‘escape function’ for global optimization in lens design is described. This includes how to identify two solutions as independent; the threshold value for this criterion can be chosen to determine how to explore local solutions—rough or fine. Choice of appropriate values for two parameters in the escape function is most important, since this will affect the efficiency of the automatic global optimization process. There are two problems, i.e. giving default values at the beginning of the design, and determining a default rule to change them when the escape is unsuccessful. The latter was solved by assuming a ‘saddle path’ as the best route to escape. An exact solution for the former was not found, but a hint for finding a second best solution is shown based on the statistical study of local minima.
72 citations
TL;DR: In this article, a ground speed sensor based on optical spatial filtering was designed, fabricated and evaluated, and an accuracy of 1.5 km/h was obtained with response time of 30 ms, height from ground of from 230 to 370 mm and on various road surfaces.
Abstract: The prototype for a ground speed sensor has been designed, fabricated and evaluated. It works on the principle of optical spatial filtering and uses pulse driven light emitting diodes as a source of illumination. The sensor was tested at speeds ranging from 2 to 50 km/h, and an accuracy of 1.5 km/h was obtained with response time of 30 ms, height from ground of from 230 to 370 mm and on various road surfaces. The sensor is viewed as beneficial for use in a vehicle’s antilock braking system and will contribute to traffic safety.
45 citations
TL;DR: In this paper, the theoretical improvement of the discrete dipole approximation (DDA) to provide scattering properties of clusters of spherical monomers is discussed, and the first scattering coefficient (al-term) in Mie theory is introduced to determine the dipole polarizability used in the DDA.
Abstract: This paper concerns the theoretical improvement of the discrete dipole approximation (DDA) to provide scattering properties of clusters of spherical monomers The first scattering coefficient (al-term) in Mie theory is introduced to determine the dipole polarizability used in the DDA In the al-term method, a spherical monomer in the cluster is replaced by a single dipole The accuracy of this method is tested to calculate extinction and scattering cross sections by a single sphere, two-touching spheres and three collinear touching spheres It is found that when each monomer is replaced by a dipole the al-term method is superior to the different types of DDA, eg, the Lattice Dispersion Relation (LDR), at least for the target with the volume equivalent size parameter X, 02≦X≦2 This method also allows treatment of a relatively large sub-volume element which is replaced by a dipole, ie the size parameter of the monomer Xm∼15 Furthermore, a great reduction in memory requirement and computing time are achieved, eg for two touching spheres the al-term method requires only 6% of the total memory requirement and 0008% of the total computing time for N=8448 with the LDR
37 citations
NEC1
TL;DR: In this article, an asymmetric colliding-pulse mode-locking was successfully demonstrated in an InGaAsP laser, which had a single saturable absorber section located partway along the cavity length, and showed modelocking operation at harmonics of the cavity roundtrip frequency.
Abstract: Asymmetric colliding-pulse mode-locking was successfully demonstrated in an InGaAsP laser. This laser had a single saturable absorber section located partway along the cavity length, and showed mode-locking operation at harmonics of the cavity roundtrip frequency. The method verified that optical pulse repetition up to subterahertz rates can be generated with nearly 1-mm-long mode-locked InGaAsP lasers.
32 citations
TL;DR: In this article, the authors proposed a more realistic approach based on the contents of growing water droplet clouds predicted by a sophisticated adiabatic cloud model, which are offered for use as new standard vertically-inhomogeneous cloud models.
Abstract: Although it has long been recognized that the effects of photon multiple scattering generally need to be accounted for in the analysis of lidar cloud returns, this is a difficult problem and current approaches are still rudimentary. The multiple scattering process is controlled by the size of the lidar beamwidth and the distance to the cloud, which jointly determine the lidar footprint, but cloud microphysical content (i.e., particle size, concentration, and shape) exerts a strong influence on the range distribution and depolarization of the returned energy. Since clouds are inherently inhomogeneous with height, it is our premise that vertically homogeneous cloud simulations based on idealized particle size distributions lead to misleading results. We offer a more realistic approach based on the contents of growing water droplet clouds predicted by a sophisticated adiabatic cloud model, which are offered for use as new standard vertically-inhomogeneous cloud models. Lidar returned signal and depolarization profiles derived from our analytical double-scattering method are given for inter-comparison purposes.
30 citations
TL;DR: An optimal solution for the modal reconstruction of wavefronts distorted by Kolmogorov turbulence is described and the maximum a posteriori (MAP) estimate for the Karhunen-Loeve expansion coefficients is calculated.
Abstract: We describe an optimal solution for the modal reconstruction of wavefronts distorted by Kolmogorov turbulence. The approach is Bayesian and calculates the maximum a posteriori (MAP) estimate for the Karhunen-Loeve expansion coefficients.
22 citations
TL;DR: In this paper, a stochastic model for the transfer of polarized light is presented, which is necessary for the exact determination of the scattering distribution for polarized light, and results of variance reduction Monte Carlo simulations based on that model with measurements taken with the DLR-Microlidar.
Abstract: In this paper we shall present our stochastic model for the transfer of polarized light. We introduce the polarized phase function which is necessary for the exact determination of the scattering distribution for polarized light. Finally, we compare results of variance reduction Monte Carlo simulations based on that model with measurements taken with the DLR-Microlidar. This LIDAR is designed especially for cloud and fog measurements and has two fields of view with two polarization channels each; see W. Krichbaumer et al. (Opt. Laser Technol. 25 (1993) p. 283).
21 citations
NEC1
TL;DR: In this paper, a synchronized mode-locking of monolithic mode-locked diode lasers was demonstrated by injecting the light output from a master monolithic diode laser, which is a 10 GHZ hybridly mode-lock two-section InGaASP quantum well laser.
Abstract: Synchronized mode-locking of monolithic mode-locked diode lasers has been demonstrated by injecting the light output from a master monolithic mode-locked diode laser. The master diode laser is a 10 GHZ hybridly mode-locked two section InGaASP quantum well laser. The slave lasers are a 10 GHz two section laser which is similar to the master laser, and a 20 GHz three section colliding pulse mode-locking laser. Both the slave lasers were greatly stabilized at 10 GHz frequency by a synchronous mode-locking mechanism under the injection of master laser pulses.
21 citations
TL;DR: In this article, optical diffraction tomography (ODT) is applied to reconstruct the cross-sectional, complex refractive index distribution of cylindrical objects, and the results demonstrate that ODT can be used for quantitative imaging of semitransparent fibers.
Abstract: Optical diffraction tomography (ODT) is applied to reconstruct the cross-sectional, complex refractive index distribution of cylindrical objects. Experimental reconstructions showing noticeable image contrast for refractive index variations of about 0.001, and having a spatial resolution of about 2 μm, are obtained for objects with cross-sectional diameters of about 100 μm. The results demonstrate that ODT can be used for quantitative imaging of semitransparent fibers.
21 citations
TL;DR: In this paper, a Monte Carlo simulation of enhanced backscatterings from the disordered dense media is investigated by means of the Rayleigh-Debye scattering theory, and numerical simulations demonstrate the dependences of the peak, width and spatial anisotropy of enhanced intensity distributions on the size of scattering particles.
Abstract: Enhanced backscatterings from the disordered dense media are investigated by means of the Monte Carlo simulation. On the basis of the Rayleigh-Debye scattering theory, numerical simulations demonstrate the dependences of the peak, width and spatial anisotropy of enhanced intensity distributions on the size of scattering particles. Discussions are made by decomposing the backscattering intensity to the contributions with different scattering orders. As a result, it is shown that the particle-size dependence of the peak and width is described by the probability density function of the scattering order and the mean free pathlength. It is also shown that the spatial anisotropy of the intensity peak is described by the depolarization at each scattering event and the extinction in propagation within the random media.
TL;DR: In this article, a radially and homogeneously aligned LC cell as a polarization controlling device is fabricated using a memory effect in an axially symmetric electrical field, and the conversion property of the polarization states of the cell is discussed in detail from the molecular orientation in the cell.
Abstract: A radially and homogeneously aligned LC cell as a polarization controlling device is fabricated using a memory effect in an axially symmetric electrical field. Optical properties and the molecular orientation of the LC cell are investigated and the conversion property of the polarization states of the cell is discussed in detail from the molecular orientation in the cell.
TL;DR: In this article, an equation which estimates the transmittance change of the mask layer was derived and a numerical simulation based on the equation showed that the reflectance increase of the layer by photo-irradiation is nonlinear when the optical density of layer is high.
Abstract: The possibility of a super-resolution optical memory using a photochromic mask layer was theoretically discussed. An equation which estimates the transmittance change of the mask layer was derived. The numerical simulation based on the equation showed that the reflectance increase of the layer by photo-irradiation is nonlinear when the optical density of the layer is high. The nonlinear response decreased the crosstalk in adjacent recording tracks and improved the MTF (modulation transfer function) characteristics, resulting in a higher recording density.
TL;DR: In this paper, a green light-emitting diodes (LEDs) were fabricated employing a ZnCdSe/ZnSSe triple quantum-well active region surrounded by ZnMgSSe cladding layers grown on an n-type (100) GaAs substrate by molecular beam epitaxy (MBE).
Abstract: Green light-emitting diodes (LEDs) were fabricated employing a ZnCdSe/ZnSSe triple quantum-well (TQW) active region surrounded by ZnMgSSe cladding layers grown on an n-type (100) GaAs substrate by molecular beam epitaxy (MBE). A 3.5 mW pure green emission was observed for the surface-emitting LED device at a peak wavelength of 513.3 nm (2.415 eV) with a spectral half-width of 11.7 nm (55 meV) under a 20 mA (4.6 V) direct current at room temperature (25°C). These correspond to an external quantum efficiency of 7.2%, a power conversion efficiency of 3.8%, a luminous current efficiency of 66 lm/A, and a luminous efficiency of 14 lm/W.
TL;DR: In this article, the main features of a Monte Carlo code developed to deal with polarization of lidar returns from water clouds in multiple scattering regime are described, and an example of results pertaining to a stratified cloud structure, and a series of comparisons of calculation results with measurements carried out in the laboratory is also given.
Abstract: The main features of a Monte Carlo code developed to deal with polarization of lidar returns from water clouds in multiple scattering regime are described. The paper presents an example of results pertaining to a stratified cloud structure, and a series of comparisons of calculation results with measurements carried out in the laboratory. For double scattering a comparison of Monte Carlo results with those of an analytical formula is also given.
TL;DR: In this paper, an experimental verification of the reflection properties of non-cooperative targets for a time-of-flight laser rangefinder is proposed, where the useful reflection coefficient (RC) is contained at between 0.6 and 0.7 at the wavelength λlD (=820 nm, polar diagrams presenting almost a lambertian shape for incident angles lower than 60°.
Abstract: An experimental verification of the reflection properties of non-cooperative targets for a time-of-flight laser rangefinder is proposed. Indeed, knowing the light scattering physical properties of usual targets is necessary to determine the optical power budget of such a device. The useful reflection coefficient (RC) is contained at between 0.6 and 0.7 at the wavelength λlD (=820 nm), polar diagrams presenting almost a lambertian shape for incident angles lower than 60°. The useful RC thus corresponds to the value of the lambertian RC increased by the contribution of the specular RC.
TL;DR: In this article, the nonlinear refractive index coefficient n2 of bacteriorhodopsin suspensions in water is measured by the Z-scan technique with a low power continuous wave laser at 647.1 manometer wavelength.
Abstract: Nonlinear refractive index coefficient n2 of bacteriorhodopsin suspensions in water is measured by the Z-scan technique with a low power continuous wave laser at 647.1 manometer wavelength. Our results indicate that both the magnitude and the sign of n2 depend strongly on the light intensity. Negative values for n2 are obtained for on axis laser irradiance at the focus above 3 W/cm2. The observed self-defocusing phenomena can be attributed to the index change due to the light induced transition between the photochromic states. The results elucidate the origin of n2 and offer a plausible explanation for the differences in the reported n2 measurements.
TL;DR: In this article, the absolute longitudinal distance between two points can be determined by the corresponding correlation peaks of two light-waves from a broad-band light source, which can be applied to measurement of thickness of a few hundred microns.
Abstract: The absolute longitudinal distance between two points can be determined by the corresponding correlation peaks of two light-waves from a broad-band light source. Using this technique, the height of three-dimensional objects can be measured without 2π phase ambiguity. We can also detect the absolute position of scattering seeds in sub-surface or bulk materials such as defects, dislocations or impurities of high purity materials. The wavelet analysis is used to determine the correlation peaks. This technique can be applied to measurement of thickness of a few hundred microns.
TL;DR: In this paper, a new type element that can implement perfect shuffle (PS) network of free spatial optical interconnection is presented, which is a microoptics array element consisting of a series of sub-blazed gratings with different spatial frequency.
Abstract: In this paper a new type element that can implement perfect shuffle (PS) network of free spatial optical interconnection is presented. It is a microoptics array element consisting of a series of sub-blazed gratings with different spatial frequency. The array has highly efficient light energy and a very simple setup. It can realize 1-D, 2-D PS networks and their inverse transforms. Also, the array can conveniently realize microminiaturization and multilevel interconnection and other forms of interconnections.
TL;DR: In this paper, the authors measured curves of time-resolved transmittance of the pulse through the media were used to estimate the optical properties of the media, and the estimated absorption coefficients were in good agreement with those measured in a nonscattering case by a spectrophotometer.
Abstract: Absorption coefficient measurements of strongly scattering and weakly absorbing media have been performed using time resolved transmittance of a 100 fs pulse through a 30 mm slab containing latex spheres suspended in water and absorbing ink solutions. The scattering and absorption coefficients were selected so that the optical properties of the media were similar to those of biological tissues. Measured curves of time-resolved transmittance of the pulse through the media were used to estimate the optical properties of the media. The experiment was made at two different wavelengths, 784 nm and 810 nm. Estimated absorption coefficients were in good agreement with those measured in a nonscattering case by a spectrophotometer.
TL;DR: In this article, the optical length between the two mirrors was set according to the scale of the luminescent wavelength in order to compose a microcavity structure for organic thin films sandwiched between two mirrors.
Abstract: The luminescent characteristics of organic thin films sandwiched between two mirrors were measured. The optical length between the two mirrors was set according to the scale of the luminescent wavelength in order to compose a microcavity structure. Photoluminescence (PL) and electroluminescence (EL) from tris(8-hydroxyquinoline)aluminum (ALQ) were enhanced at distinct resonating wavelengths, and suppressed in other regions. Then, narrow and enhanced luminescent peaks were observed from the devices with the microcavity structure. Based on their injection current dependence, the primary cause of these spectra was speculated to be spontaneous emission. An EL sample with the microcavity structure for multicolor emissions was fabricated.
TL;DR: In this paper, the optical multistability of a Fabry-Perot semiconductor laser is analyzed when multi-optical inputs detuned from the cavity-resonant wavelength of a semiconductor LIDAR are injected.
Abstract: Optical multistability of a Fabry-Perot semiconductor laser is analyzed when multi-optical inputs detuned from the cavity-resonant wavelength of a semiconductor laser are injected. Many split branches are shown to be produced in the optical output versus optical input characteristics for different detuned optical inputs. It is also shown that optical outputs can be switched in any one of the optical input wavelengths by optical input pulses, based on the optical output versus input characteristics with multi-split branches.
TL;DR: In this article, a comparison between the nonlinear optical coefficients of (±)2-(α-methylbenzylamino)-5-nitropyridine ((±)MBANP) single crystals has been comprehensively investigated and compared with those of the enantiomorph (−) 2-(α-,methylbenzenylmethyl-methyl-labeled)-5-(α)-nibyridine (β)-methylbenzylmethyl)-labeled (β-MBANp) crystals.
Abstract: Linear and nonlinear optical properties of racemic (±)2-(α-methylbenzylamino)-5-nitropyridine ((±)MBANP) single crystals have been comprehensively investigated and compared with those of the enantiomorph (–)2-(α-methylbenzylamino)-5-nitropyridine ((–)MBANP) crystals. (±)MBANP crystal exhibits very high chemical and physical stability, but relatively small nonlinear optical coefficients (d31 = 6.8 pm/V, d32 = 4.7 pm/V, d33 = 0.84 pm/V). A comparison between the nonlinear optical coefficients of (±)MBANP and (–)MBANP demonstrates the validity of the oriented-gas model in molecular crystals that neglects all the contributions from intermolecular interaction.
TL;DR: In this paper, the authors proposed to use an escape function as an additional operand of the lens system, to be controlled by the optimization algorithm, and experimented on simple models of merit function and the advantage of this technique was ascertained.
Abstract: In designing lenses with the damped least squares method, the solution obtained by optimization routine is a local minimum of the merit function. To get out of this and seek a different solution, we propose to use an ‘escape function’ as an additional operand of the lens system, to be controlled. Experiments were made on simple models of merit function and the advantage of this technique was ascertained. We also planted this algorithm into OSLO SIX (lens design software by Sinclair Optics) by means of CCL (C-compatible language) and applied it to actual lens design. Experiments convinced us that the method would be an effective tool for global optimization.
TL;DR: In this paper, a double-pass configuration was evaluated to enhance the phase modulation capability of twisted nematic liquid crystal panels, and it was proved that phase modulation is exactly doubled when the panel is sandwiched by two polarizers.
Abstract: Spatial light modulators whose phase modulation capability (PMC) exceeds 2π are strongly desirable. A double-pass configuration was evaluated to enhance PMC of twisted nematic liquid crystal panels. Theoretical analysis using Jones calculus is given, and it is proved that phase modulation is exactly doubled when the panel is sandwiched by two polarizers. Experiments to measure the PMC were carried out and results coincide well with the theory.
TL;DR: In this article, the possibility of a super-resolution optical memory using a saturable absorption dye mask layer has been discussed and an equation which estimates the transmittance change of the mask layer was derived.
Abstract: The possibility of a super-resolution optical memory using a saturable absorption dye mask layer is theoretically discussed. An equation which estimates the transmittance change of the mask layer has been derived. The numerical simulation shows that an efficient super-resolution is performed when the initial optical density of the mask layer is high.
TL;DR: In this article, a novel method of modifying photorefractive waveguides in a lithium niobate crystal by a guided beam was investigated experimentally and numerically, and it was shown that the transmitted power or peak intensity of the probe beam decreases exponentially as a function of total exposure energy of the modification beam.
Abstract: We investigate experimentally and numerically a novel method of modifying photorefractive waveguides in a lithium niobate crystal by a guided beam. The guided beam with a strong optical power can change the refractive index of the photorefractive waveguide because of the photorefractive effect. The modification of waveguide structure can be utilized for optical dynamic interconnection. Changes of optical characteristics of a probe beam caused by a modification beam are investigated. Experimental results show that the transmitted power or the peak intensity of the probe beam decreases exponentially as a function of total exposure energy of the modification beam. We also numerically analyze the refractive index change caused by the modification beam in the photorefractive waveguide. The numerical results show good agreement with the experimental results.
TL;DR: In this paper, the correlation function of image speckle decreases with the change of illumination angle, so for a static object, scan the incident angle within the plane of the light sheet and get a sparse image, with the time-integration effect of a CCD camera.
Abstract: In laser triangulation, the determination of the centroid is limited by the image speckle. In this article we present a new method to reduce image speckle. We find the correlation function of image speckle decreases with the change of illumination angle, so for a static object we scan the incident angle within the plane of the light sheet and get a speckle-reduced image, with the time-integration effect of a CCD camera. An analytical description is presented and is experimentally verified.
TL;DR: In this article, the spatial frequency response of bR in gelatin films is described and an experimental investigation into the photo-induced anisotropy of the bR films is also presented.
Abstract: In this paper, we present new results describing the spatial frequency response in bacteriorhodopsin (bR), immobilised in gelatin films. It is shown that the spatial frequency response is flat, as compared to bR contained in solution form. An experimental investigation into the photoinduced anisotropy of bR films is also presented. It is shown that the anisotropy can be induced using two wavelengths (632.8 nm and 454 nm) and is dependent on the pH of the gelatin matrix, the 454 nm laser polarisation and the 454 nm pump power. The mechanisms producing the anisotropy are briefly discussed.
TL;DR: In this article, the important role of how aerosols play in light scattering in the earth's atmosphere and how their characteristics can be retrieved was addressed. But the authors did not consider the effect of the type of aerosols on light scattering.
Abstract: This paper addresses the important role of how aerosols play in light scattering in the earth’s atmosphere and how their characteristics can be retrieved. It is shown here, by referring to typical aerosol types, that more than a half of the atmospheric light is scattered by aerosols, and the aerosol optical properties can be estimated in terms of the scattering behavior. It is also confirmed that aerosol retrieval can be accurately determined by combining polarization and radiance data.