In this article, a general theoretical framework to describe and analyze the optical properties of photonic crystals is presented. In addition to the analytical treatment of their optical response based on the method of Green's function, numerical tools to calculate the dispersion relations and the eigenfunctions of the radiation field, transmission spectra, localized midgap modes, and lasing threshold are introduced and applied to some typical examples. Group theory to analyze the symmetry of the eigenmodes is also introduced, and the existence of uncoupled modes that cannot be excited by external plane waves is shown. The presence of the enhancement effect of nonlinear optical processes and stimulated emission due to the small group velocity which is easily realized in the photonic crystals is pointed out, and the possibility of low-threshold lasing in the photonic crystals is discussed.

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We observed an electroluminescence (EL) of poly bis(p-propoxyphenyl)silane (PBPPS) from a double-layer device with an electron transport layer of 8-hydroxyquinoline aluminum (Alq₃) for the first time. The EL spectrum at 77 K consisted of a PBPPS emission at 3.0 eV, which coincided with the photoluminescence spectrum, and a broad emission band between 1.8 and 2.7 eV.

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We report for the first time a laser microfabrication and its characteristics of photonic crystal structure in vitreous silica. It is two-dimensional triangle lattices composed of hollow cylinders with a periodicity of approximately 1.2 μm. Infrared spectroscopic measurements revealed dielectric-periodicity-matched transmission valleys centering approximately at 4100 cm^-1 for H-polarization and 4000 cm^-1 for E-polarization, respectively.

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The properties of low-frequency fluctuations in semiconductor lasers with optical feedback from a long external cavity are experimentally studied. Frequency-locking of the laser light output to the injection current modulation is observed when the modulation frequency approaches the external cavity mode. The modulation frequency for the successful frequency-locking is always less than the external cavity mode frequency and the locking domains as a function of the modulation amplitude is asymmetric with respect to the frequency detuning.

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The modulation characteristics of the negative nonlinear absorption effect were investigated in an erbium nitrate solution using a 1510 nm laser diode. The reversed-phase waveform was obtained in the transmitted laser for a sample length of 3.0 mm. With decrease in the modulation degree, the reversed-phase waveforms were observed at modulation degrees smaller than 72%. With increase in the modulation frequency, the transmitted waveforms were asymmetrical. The optical signal inversion phenomenon for 1.5 μm can be explained by considering an excited state absorption in which energy transfer occurs in a system with high concentrations of the Er³⁺ ion.

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We have found that the fringes in a laser diode interferometer can be locked even in the presence of mirror vibration and injection current modulation. A theoretical analysis explains the fringe locking phenomenon. The dependence of wavelength change on both PZT (piezoelectric transducer) mirror vibration and the injection current variation are calculated using a model of coupled resonators consisting of the laser cavity and the interferometer. The fringe phase change caused by the vibration and modulation of the current is derived from this model, and was proven to be suppressed within much less than 2π in excess of an integer multiple of 2π.

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A dispersion theory for linear optical properties of two-phase layered-geometry nanocomposites is presented. Generalized dispersion relations and sum rules are stated using the results from complex analysis. The concept of Lorentzian linear susceptibility is exploited in theoretical treatment of the effective linear susceptibility of the nanocomposite. The meromorphism of total reflectance in the case of effective meromorphic nonlinear susceptibility was observed.

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In this work we propose a method for scatter compensation in single photon emission computed tomography imaging, by which we can estimate the scatter components in projections in high speed with good accuracy. The method is that we first estimate the scatter components in projections based on scatter response kernels by one time of ordered subsets expectation maximization iterative reconstruction, and then subtract the estimated scatter components from the projections and complete reconstruction by filtered back-projection method. The principle is that the image corresponding to the scatter components in projections consists largely of low-frequency components of an activity distribution; these low-frequency components will converge faster than the high ones in iterative reconstruction. Therefore, we can estimate the low-frequency component image before the image converges with the high-frequency ones, and obtain the scatter components by re-projecting the low-frequency component image with scatter response kernels. The effects of the proposed method were compared with the dual- and triple-energy window methods using experimental measurements. The results show that good accuracy in estimated scatter components, good uniformity of scatter compensation at the center and the side of an object, and good noise property can be acquired by this method.

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A system for optical digital fast Fourier transform (FFT) is proposed. Data exchange, adder, and multiplier circuits required for the optical FFT system are designed. Each circuit contains the same basic element of an optical beam switch composed of a polarization rotator and a birefringent plate. In the FFT algorithm, butterfly switching for data exchange is important and the method of optical switching networks is very suitable for such operations. FFT calculation for one-dimensional data of a sinusoidal signal is experimentally demonstrated using the optical system. The throughput of the proposed system is estimated and its future perspective is discussed.

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An interpolation method for reconstructed images of computer-generated holograms (CGHs) enables one to synthesize CGHs with a large space bandwidth product (SBWP) from CGHs with a small SBWP. The phase information of objects is regarded as constant because the method is based on digital image processing techniques. Therefore, diffraction efficiency is low due to the saturation effect in the recording process. To improve the diffraction efficiency, a random phase technique is employed for the interpolation method to the CGH. Effects of the random phase in the reconstructed image are discussed in several interpolation types. The interpolation method is also applied to a kinoform. Some computer simulations and optical experiments are presented.

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Based on the rate-equations of quasi-three-level lasers, we analyzed the threshold and the output power of longitudinally pumped Tm:YAG lasers in an active mirror configuration. In contrast to one-pass pumping, two-pass pumping in this configuration will result in a 24% decrease in threshold and 16% increase in slope efficiency. Using a 3-W diode-laser pumping in the active mirror configuration, we demonstrated a CW Tm:YAG laser and obtained 735 mW output power with a slope efficiency up to 49%. Using a Ti:sapphire laser to pump the same device, the threshold power was further reduced and the slope efficiency reached 59%.

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This paper describes heterodyne interferometers using orthogonally polarized and two-frequency shifted light sources of two types with super-high extinction ratio to reduce non-linearity of the interferometer due to polarization cross-talk. The acousto-optic modulators are used to shift light frequency. In the first interferometer the light source with Glan-Thomson prisms of very high extinction ratio (50 dB) is used to make the polarization cross-talk very small. In the second interferometer the light source of two-frequency shifted beams with small crossing angle (2.5 mrad~10 mrad) is used to completely exclude non-linearity of the interferometer due to polarization cross-talk. By measuring the thickness of vacuum evaporation film, it was demonstrated that the interferometers are useful to measure thickness of a thin film in nanometer order.

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A fringe analysis method, which combines the Fourier transform with the fractional fringe order method for measuring the absolute thickness of a block gauge, is presented. An approximate integer part of the fringe order is estimated by mechanical measurements, and the fractional part is determined by Fourier analysis of the interferometric fringe patterns. The fringe patterns are obtained with a Michelson interferometer by illumination of several selected wavelengths, respectively. The use of the fractional fringe order method can determine accurately more than 2π phase jumps. The measured thickness of a block gauge is 5999115.0±0.7 nm, which is comparable with the standard thickness of 6 mm. The influence of wavelength and approximate integer part of fringe order on the measurement accuracy is discussed.

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We propose dispersive coherence spectrotomography with white-light continuum to extract both range and spectral properties inside a medium. The main feature is that the dispersive coherence spectrotomography has a high dynamic range in depth and high signal-to-noise ratio making the most of the extreme brightness of the white-light continuum.

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Static characteristics of two different structured InAlGaAs/InAlAs superlattice avalanche photodiodes (SLAPDs) cooled by liquid nitrogen were evaluated at a wavelength of 1.5 μm. The dark current of the SLAPD having a thick superlattice layer of 0.504 μm was 5×10^-13 A. This was successively reduced by four orders of magnitude compared to that of the thin layer SLAPD of 0.231 μm at a breakdown voltage of around 20 V. The thickened layer was effective in suppressing tunneling dark current. An output current of 1.7×10^-12 A at a bias voltage of 15 V was measured for an optical input with a wavelength of 1.5 μm and a signal power of 1×10^-12 W. This showed a sharp distinction from the dark current.

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Improvement of an infrared light detection and ranging (IR-lidar) system for a short range (0-1000 m) and with high resolution is studied to enhance a geometrical form factor. Theoretical modeling of Mie scattering echo signals agrees with the experimental results. Introduction of a lens in front of the detector is effective for increasing the geometrical form factor, and a significant improvement in the received signal intensity is achieved, especially for short-range measurements around 100 m. This is useful for the IR-lidar system with a detector diameter of less than 1 mm. In the theoretical model, a ray-tracing technique was applied and a transmitting laser beam with Gaussian profile was considered for better accuracy.

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