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We present a flow type single-mode microwave (MW) reactor that forms a uniform electromagnetic field along a tubular reactor (quartz glass, i.d. 1.5 mm × 100 mm) located in the center of a cylindrical MW cavity. The temperature of liquid flow in the reactor tube was controlled precisely by a resonance frequency autotracking function. This MW reactor system is useful for rapid heating of liquid flow at pressures up to 10 MPa. Continuous flows of polar solvents including water, ethylene glycol, and ethanol were heated instantaneously beyond their boiling points by application of pressure. Acceleration of the reaction was exemplified in continuous synthesis of Cu nanoparticles by elevation of the reaction temperature beyond the boiling point of solvent (ethylene glycol) at 2 MPa.

Amorphous Si (a–Si) films, sputter deposited under lower Ar pressure conditions, include numerous Ar atoms and exhibit high refractive indices, higher even than that of crystalline Si (c–Si), notwithstanding their lower Si densities. Such behavior in the refractive indices of the films was inconsistent with the conventional explanation considering only the density term in the Clausius–Mossotti relation. In the present study, the contribution of the polarizability changes of the films is proposed in order to account for the result in the refractive index. The molecular orbital (MO) calculations and experiments reveal that the polarizability of the a–Si film is sensitive to change in the angular distortion of the Si–Si bonds brought on by changing deposition conditions. The incorporated Ar atoms are found to cause the distortion in the Si network, leading to higher refractive indices for the less densified films.

Silicon oxide films deposited by Ar-H 2 sputtering exhibited significantly smaller internal stresses than conventional films deposited by Ar-O 2 sputtering. This phenomenon was found to be caused by the introduction of Si-H bonds into the Si-O-Si network structure. As a result of hydrogenation, the number of planar ring type defects in the network was successfully reduced, and the Si-O bonding force constant seemed to decrease, judging from Raman and IR spectroscopy. These results suggest that the hydrogenation produced a structural relaxation of the Si-O-Si network, leading to the reduction in stress.

Thick Si/SiO2 multilayered films with flat interfaces are needed to achieve optical devices with low optical propagation losses, such as a laminated polarization splitter operating at a 1 550 nm wavelength. Such films can be realized by a sputtering method using an Ar/H2 gas mixture because of the successful reduction of internal stress and surface roughness of films compared with those of conventional ones. We fabricate 350 μm thick Si:H/SiO2-x:H multilayered films having flat interfaces by such a hydrogenation technique. The absorption losses at 1 550 nm wavelengths of both films measured separately are negligibly small.

The relation between stresses of sputtered a-Si: H films and the film deposition conditions are investigated. The film stresses change from a large compressive stress of 1000 MPa to an almost stress-free one. They arise from distortions of the Si network via the following two mechanisms. The first results from the inclusion of the Ar-sputtering gas into the films, which provides volume expansion of the film network. The other is due to structural disorders, such as a deviation of the Si bond angle which is generated during the deposition processes. Moreover, it is found that Si–H terminations in the films contribute to reducing the film stresses because the Si–H termination breaks and relaxes the Si network. These effects can be realized as long as the Si–H terminations are homogeneously distributed in the films.

The compressive internal stresses of sputtered silicon oxide films are remarkably reduced by use of an Ar/H2 gas mixture instead of the conventional Ar/O2 one. The film deposition rates are also found to be larger than those using an Ar/O2 gas mixture. The effect is thought to be caused mainly by structural relaxation of Si‐O‐Si network via partial Si‐H terminations. The oxygen deficiency in films leads to optical absorption loss at short wavelengths (

Lensless in-line bandpass filters with low insertion losses and high backreflection losses are achieved with expanded-core fibers. It has been experimentally shown that using a large modal-field diameter of expanded-core fibers can resolve the problem of the trade-off between the insertion loss and backreflection. The reduction in the outer diameter, usually occurring when the modal-field diameter is enlarged to an extent, was suppressed at an optimized heating condition.

A laminated polarizer (LAMIPOL) is smaller in size and has a higher extinction ratio and lower insertion loss than the conventional polarizer. Therefore, it is suitable for optical integration. However, when a LAMIPOL with a conventional continuous metallic film is used in a short wavelength region, the property is not sufficiently good. On the other hand, we fabricated a Cu/SiO2 LAMIPOL and achieved an extinction ratio of 46 dB and insertion loss of 0.3 dB, which are better than theoretical values for the device with a continuous film. After detailed investigation of this particular device, it was found that the metal film had granular structure. To investigate the superior characteristic of a LAMIPOL with granular metallic films, a simple model for a granular Cu film was proposed, and the film parameters were estimated using the wavelength dependence of the optical transmittance and reflectance. Using these parameters, the wavelength dependencies of the attenuation constants of LAMIPOL for TE and TM waves were calculated. The agreement between the experimental and calculated results were excellent.

Ar/H2 sputtering of a SiO2 target can produce thick silicon oxide films with significantly reduced internal stresses compared with those of conventional films prepared by an Ar/O2 sputtering method. As an origin of the stress reduction, we proposed previously the structural relaxation model of the Si–O–Si network via partial Si–H termination. This model is experimentally supported here by the Raman spectroscopy measurements which show a large decrease of planar three‐ and four‐fold ring‐type defects in the hydrogenated Si–O–Si network structure.

Continuous synthesis of silver nanoparticles based on a polyol process was conducted using a microwave-assisted flow reactor installed in a cylindrical resonance cavity. Silver nitrate (AgNO(3)) and poly(N-vinylpyrrolidone) (PVP) dissolved in ethylene glycol were used respectively as a silver metal precursor and as a capping agent of nanoparticles. Ethylene glycol worked as the solvent and simultaneously as the reductant. Silver nanoparticles of narrow size distributions were synthesized steadily for 5 h, maintaining almost constant yield (93%) and quality. The reaction was achieved within 2.8 s of residence time, although nanoparticles were not formed under this flow rate by conventional heating. A narrower particle size distribution was realized by the increased flow rate of the reaction solution. Nanoparticles of 9.8 nm average size with a standard deviation of 0.9 nm were synthesized at the rate of 100 ml h(-l).

Ge laminated polarizers (Ge-LAMIPOLs) consist of Ge/SiO2 multilayers which are designed to absorb the TE mode of the light wave at 850 nm wavelength. Such Ge-LAMIPOLs facilitate the miniaturization of optical components, but they usually break during the fabrication processes because of their low mechanical strength. This problem is solved by insertion of Si binding layers at Ge and SiO2 interfaces. Further improvement is also achieved by reduction of the internal stresses in SiO2 layers, using the hydrogenation technique. The optical properties of the Ge-LAMIPOLs can be optimized by adjustment of the film deposition parameters. As the result, 250-µm-thick Ge/Si-LAMIPOLs with 54.0 dB extinction ratio and 0.37 dB insertion loss are successfully fabricated.