In an attempt to apply the fuzzy set theory to optics a fuzzy entropy [A. De Luca and S. Termini: Inf. Control 20 (1972) 301] is used as a measure of optical field concentration in transverse dimensions. Unlike the Shannon's information entropy, the fuzzy entropy is based on a nonprobabilistic concept and therefore can be used for characterizing the strength of classical wave localization.

View full abstract

Thin film waveguides of germanosilicate glass are fabricated by rf-sputtering. Second-order nonlinearity of d₃₃=3.2 pm/V is obtained from electrically poled film, and the lifetime of the nonlinearity is found to be 310 years. The poled channel-waveguide is prepared and the Cerenkov-type phase-matched frequency doubling is successfully observed.

View full abstract

A wave-front folded interferometer consisting of a Kters prism and an image forming lens provides an excellent way to make a precision measurement of correlation-induced spectral changes. Experiments are successfully made by incorporating a primary spectral source of super-luminescent diodes. The diode emits a Gaussian-like spectrum. Theoretical background for the measurement is given in the framework of geometric optics. It is shown theoretically and experimentally that the spectral changes are induced by two causes: one is the complex degree of spectral coherence of the secondary source, and the other the time delay between the interfering optical waves. No spectral change takes place if the secondary source satisfies a spatially incoherent condition at particular optical frequency, whereas the spectrum changes most clearly if a spatially coherent condition is satisfied.

View full abstract

Binary subtracted joint transform correlator (BSJTC) provides sharp autocorrelation peaks and better discrimination for similar targets even though many reference images are arranged regularly in an input scene. The effects of the number of reference patterns, the quantization levels and truncation of the Fourier power spectra on the performance of BSJTC are investigated. The number of effective quantization levels to obtain sharp and clear autocorrelation peaks is estimated by computer simulations using the input scenes with many binary images (alphabetic characters) and halftone images (human portraits). Experimental results of BSJTC are also shown using a hybrid system with a Bi₁₂SiO₂₀ spatial light modulator and a personal computer.

View full abstract

We have built an optical VanderLugt-type correlator that uses two Epson liquid crystal televisions (LCTVs) separately generating the amplitude and phase modulation properties. The input scene is displayed in amplitude-mostly regime on the first LCTV. Thereafter a phase-only filter with a different level of phase quantization is addressed in phase-mostly regime on the second LCTV. To characterize this device, the phase and amplitude modulations were experimentally measured and investigated in pattern recognition application where the grey-level input scenes and multilevel kinoforms are displayed on the LCTVs.

View full abstract

Pure phase correlation with improved discrimination capability is proposed. The improvement is achieved by designing a region of support based on the discrimination capability (DC). We propose four approaches for designing this region; some of them consider the input scene in the design, while others are input scene invariant. The performances of these approaches are compared by numerical simulation. The DC is improved significantly for the multi-object scenes even when using an input scene invariant region of support design.

View full abstract

This paper deals with segmentation of noisy images using Gibbs random field (GRF) with an emphasis on modeling of the region process. For noisy image segmentation using the multi-level logistic (MLL) model with the second-order neighborhood system, which is commonly used in image processing, the segmentation performance is degraded significantly in case of low signal to noise ratio. By comparison with the Ising model that explains the magnetic properties of ferromagnetic material, it is evident that the characteristics of the region process modeled using the MLL model with the second-order neighborhood system are different in nature from the expected characteristics of a region. To solve this problem we added the term of the magnetic energy associated with the magnetic field of a spin system (or image) to the energy function of GRF. Using the modified model for the region process, the result of image segmentation was improved and did not depend on the cooling schedule in simulated annealing.

View full abstract

A novel method using a phase modulator is proposed for the nondestructive measurement of propagation loss in a channel waveguide. The phase modulator was fabricated on a Ti-diffused LiNbO₃ crystal. Tuning the effective optical length of a waveguide by application of an electrical field on the phase modulator, the contrast of the resultant Fabry-Perot resonator in a channel waveguide device can be measured. The associated propagation attenuation coefficients are determined from the experimental results. Coordination of the phase modulator with an optical channel waveguide device not only allows measurement of the bending loss, but improvement in the relative intensity noise owing to the reduction of the reflected power.

View full abstract

A single-mode frequency stabilized laser with modulation-free and moderate power is desired as a light source for an ultra-high resolution interferometer system and/or a rapid laser calibration system. For this purpose, we developed a new stabilized laser system that utilizes intermittent control of a 2 mW transverse Zeeman stabilized He-Ne laser (Zeeman laser) with an iodine stabilized He-Ne laser (I₂ stabilized laser). Because of the intermittent control, working time of the I₂ stabilized laser is reduced. The Zeeman laser has two operational modes: independent and slave mode. In the independent mode, the Zeeman laser is stabilized through control of Zeeman beat frequency. Temperature dependent drift of the oscillation frequency during the independent mode is periodically corrected by the slave operation utilizing frequency offset locking to the I₂ stabilized laser. Frequency instability of the Zeeman laser in independent and slave modes is 7.70^-11 and 2.00^-11, respectively, at the sampling time of 100 s.

View full abstract

Combining one stable resonator with a concave mirror and a coupling-hole plane mirror, and another unstable resonator having a concave mirror and a convex mirror, a new hybrid optical resonator type laser has been proposed by overlapping the concave mirror as a common one and fitting the convex mirror exactly to the coupling-hole. Using the ABCD law, the so-called g-parameters are first found for beam confinement. Then, based on the eigen-equation, the field distribution on the plano-convex mirror is obtained with the g-parameters above. Knowing this field distribution results in an effective transmittance _e. Finally, the ratio of the inner convex to outer plane mirror radii can be determined for an optimum coupling in both the limiting cases of homogeneously and inhomogeneously broadened gain media. Some numerical examples will also be given for a CO₂ laser having the proposed hybrid resonator.

View full abstract

A grating interferometer composed of two transmission gratings in tandem irradiated incoherently was studied for an atom interferometer. Determination of its interference effect was made with consideration of the optical transfer function. An atom beam had a velocity distribution, which made the influence on the interference phenomenon. The calculated results show that the fringe (grating image) with relatively high contrast is obtained under a certain grating arrangement even if the interferometer is irradiated by a spatially incoherent polychromatic atom beam.

View full abstract

We analyzed the chemical composition of K⁺-exchanged glass optical waveguides (OWGs) by secondary ion mass spectroscopy. Extensive condensation of impurity halide ions took place at the surface of the OWGs in the ion-exchanging and annealing processes. The condensation of Cl^- ions is likely a cause of the abnormal behavior observed for soda-lime glass OWGs; that is, a guided mode having appeared during the annealing did not disappear even after long annealing. Moreover, it was suggested that a space charge layer was formed at the OWG surfaces owing to the condensation of the halide ions.

View full abstract

The cause of the change in the optical path length (nd) of the saturable absorbing dye-doped polymer films under laser irradiation is investigated using polyvinyl alcohol and gelatin films doped with erythrosin B. The temperature rise of the dye-doped films, the changes in optical path length, film thickness, the refractive index and the optical density of the dye-doped films are measured under laser irradiation. The thermal expansion due to the temperature rise of the dye-doped films caused by the irradiation has greater effect on the (nd) than the fading of dye molecules due to the irradiation of laser beams.

View full abstract

A Mie scattering laser radar with a powerful flashlamp-pumped dye laser has been developed to measure “Yamase” fog which is caused by very cold air intrusion as a result of Okhotsk high pressure. The inner structure of the “Yamase” fog-height profile, horizontal distribution, speed, thickness of the fog layer and its time development, periodic movement and dominant periods were observed and analyzed for the first time by laser radar of our institute.

View full abstract