A simple equation which gives the crosstalk-free condition for land/groove recording of optical discs is deduced. Making use of this equation, the groove depth which minimizes the crosstalk from adjacent tracks is easily calculated. For simultaneous suppression of both the on-groove crosstalk and the on-land crosstalk, two practical approaches are proposed for the phase modulation discs. This equation is also of use in the signal estimation of optical discs.

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We show analytically that addition of a quintic term to the positive Kerr-type nonlinearity offers a unique type of kink soliton-like solution with Fermi-Dirac profile. This type of optical kink allows, in contrast to other optical kinks discovered so far, stationary kink formation not only in the time domain but in the spatial domain. The latter could admit of a route for the first time to our knowledge to spatial kink solitons of intensified laser beams. The underlying principle of the optical kink propagation is described.

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This paper describes a change in optical spectrum on propagation in free space for a particular class of spatially partially coherent fields emanating from a polychromatic secondary source. A rectangular opening aperture in an opaque screen, illuminated with an extended incoherent polychromatic primary source, works as the secondary source. The spectral change is explored in detail theoretically and experimentally in association with spatial coherence in the secondary source as well as dispersive diffraction by the secondary source. The peak shift of the spectrum is associated with the coherence area for characterizing the secondary source. The peak shift becomes maximum if the secondary source is spatially coherent, but no shift occurs if the secondary source is spatially incoherent.

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A noise power spectrum estimation method is presented for optical disk readout signal influenced by dust on the substrate. The noise due to dust has been modeled using geometrical optics and assuming the Poisson distribution for the dust particles. The noise power spectrum consists of two components: one comes from the effect of individual dust particles passing across the light beam, and the other comes from the effect of overlapping area of a particle and the inverted image of another particle. The feasibility of a thin-substrate optical disk was studied using this model. Dust will not have a serious effect on the readout signal when a 0.6 mm-thick substrate is used in place of the conventional 1.2 mm-thick substrate.

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A new concept of three-dimensional (3D) optical storage is proposed based on a multi-layered thin-film structure and a nonlinear optical (NLO) read/write process. Theoretical analysis of the device indicates that a 20-fold increase in total volume density can be expected without any compensating primary spherical aberration, owing to the lateral superresolution and the multi-layer structure in the vertical direction.

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Spatial light modulators whose phase modulation capability (PMC) exceeds 2are 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.

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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.

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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.

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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.

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Recently, we have discovered that?besides the all-optical photo-thermal bistability in transmission?the excitation of thin CdS films with the 514.5 nm line of an argon laser causes all-optical bistability in the luminescent radiation. The emitted radiation of the CdS layers lies far enough in the infrared region of the spectrum so that all-optical bistability in luminescence can be observed through GaAs wafers, i.e. an all-optical bistable loop remains in the direction of the propagation of the incident laser beam even though GaAs is strongly absorptive at the excitation wavelength. On the basis of this penetrating feature of all-optical bistability, we present a new concept for an architecture of future optical data processing devices.

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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.

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Pumping of a rare-earth-doped double-clad fiber laser with a GaAlAs laser diode bar requires imaging the near field output of a 1 cm long one-dimensional linear array of tens of multi-mode laser diode sources onto a two-dimensional oblong cross section approximately matching the fiber's first cladding shape. This work describes the design and preliminary implementation of a device (here called a high brightness geometric transformer) that achieves this transformation with minimum brightness loss. This is done by imaging the laser diode bar near field using a fast cylindrical micro-lens onto a linear array of N (≈10) soft-glass, thin-clad rectangular fibers; in turn, the fibers' output ends are arranged to form a stack that matches the required first cladding shape. For a typical 20 W CW laser diode bar with brightness of 25 mW·μm^-2·sr^-1, the geometric transformer output brightness is 0.6 mW·μm^-2·sr^-1, i.e., there is a×40 intermediate loss of brightness. If the output of the geometric transformer is used to pump a Nd-doped double-clad fiber laser, an overall brightness gain of 40 can be achieved.

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A new CGH (computer generated hologram) common path interferometer, which can be used for testing an aspherical mirror with large aperture, is proposed. This interferometer does not have a circle of least confusion, and a spatial filter can be used effectively to stop extraneous lights so that interferograms with good contrast can be obtained. The phase shifting technique can be easily applied to the interferometer. The method of designing and making the CGH zone-plate is described.

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A new technique to measure the radius of a concave mirror is proposed, in which the radius is calculated from the difference of the two interferograms obtained before and after shifting the sample perpendicular to or along the optical axis. By comparison of these two shifting directions, it is shown that since the amount of shift can be measured accurately and the result is insensitive to the tilt during the shifting, better accuracy can be obtained by shifting the sample along the optical axis.

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The critical power of the input pulse in which spontaneous Raman scattering is not seriously disturbed by stimulated Raman scattering in a fiber optic temperature sensor has been investigated experimentally and theoretically. The critical power determines the critical distance, which is nearly equal to the distance where optical time-domain reflectometry (OTDR) signal of the stimulated Raman scattering becomes maximum. From this fact, a new method to determine the critical input power with the OTDR system has been proposed, which may be applicable to most distributed fiber optic temperature sensors. It has been determined that the critical power of the input pulse is 4 watts for an infinitely long silica fiber.

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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.

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Stellar speckle spectroscopy is a speckle interferometric method enabling us to separate point by point spectra on a stellar object with a diffraction-limited spatial resolution of a telescope. We describe observational results obtained with our system for speckle spectroscopy. Data of two binary stars, of which separations are closer than seeing disc, were taken and processed by cross-correlation method. In each object, spectral images of two component stars around the Hα line (656.3 nm) were spatially resolved with nearly diffraction-limited resolution. The separated spectra of ADS940 reveal different spectral types of the component stars. These results demonstrate the ability of the speckle spectroscopic method.

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Two studies were conducted to investigate changes which take place in the visual information processing of novel stimuli as they become familiar. Japanese writing characters (Hiragana and Kanji) which were unfamiliar to two native English speaking subjects were presented using a moving window technique to restrict their visual fields. Study time for visual recognition was recorded across repeated sessions, and with varying visual field restrictions. The critical visual field was defined as the size of the visual field beyond which further increases did not improve the speed of recognition performance. In the first study, when the Hiragana patterns were novel, subjects needed to see about half of the entire pattern simultaneously to maintain optimal performance. However, the critical visual field size decreased as familiarity with the patterns increased. These results were replicated in the second study with more complex Kanji characters. In addition, the critical field size decreased as pattern complexity decreased. We propose a three component model of pattern perception. In the first stage a representation of the stimulus must be constructed by the subject, and restricting of the visual field interferes dramatically with this component when stimuli are unfamiliar. With increased familiarity, subjects become able to reconstruct a previous representation from very small, unique segments of the pattern, analogous to the informativeness areas hypothesized by Loftus and Mackworth [J. Exp. Psychol., 4 (1978) 565].

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We examined 1) whether the perception of shape from shading is based on luminance or brightness by testing the additivity law, and 2) whether the spatial frequency contents in the stimulus affect on the spectral sensitivity. We measured the relative radiance at which shading disappeared in a simple shading figure. Results showed that 1) the additivity law holds for shading disappearance settings and that 2) the sensitivity for green to white decreased as higher spatial frequencies in the figure decreases. These results suggest that the perception of shape from shading is based on a luminance type additive mechanism and that the spectral sensitivity of the mechanism varies depending on spatial frequency.

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