Polymer optical waveguide devices are getting popular for next generation FTTH application. In order to accelerate the development of polymer optical devices, evaluation of waveguide characteristics should be speeded up. Polymer optical chip containing a combination of 45°-angled cut waveguide, Y-splitter and S-bend structures was designed and fabricated for simple evaluation of multimode waveguides. Input launching such as light source, mode scrambler was investigated for reliable measurement.
A uniaxial refractive index anisotropy was introduced by a corona poling. And, and biaxial refractive index anisotropy was introduced by a physical film stretching with the presence of the nonlinear optical chromophore. The refractive indices of the film before poling and after the poling were nx=ny=nz=1.541 and nx=ny=1.539, nz=1.552, respectively. The mechanical stress was then applied to the film to introduce another anisotropy. The refractive indices after the stretching were nx=1.540, ny=1.538, and nz=1.551. We also proposed an in-situ film elongation technique with poling. Above the grass transition temperature, the polymer film is plasticized and can be stretched longer so that the chromophore is reoriented effectively. As a result, the decreasing of film transparency due to the stretching can be prevented by this temperature.
To introduce shock wave as a new treatment modality for the lesions in the vicinity of brain and skull, pressure-dependent brain damages after exposure of shock wave were investigated. A novel compact Ho:YAG laser-induced cavitational shock wave generator (diameter: 15 mm, weight: 20g) was used intstead of clinical lithotriptors due to their wide distribution of shock waves. In the first part, we have developed and investigated characteristics of present generator by means of high-speed photography, shadowgraphy, and pressure measurement. Generation of localized shock wave without harmful effect of laser was observed after irradiation of Ho:YAG laser in the brass tube with internal water supply. Mechanical effect of accompanying laser-induced liquid jet was mitigated after placement of latex diaphragm with acrylic water reservoir. Maximum overpressure of generated shock wave was 15 MPa before placement of diaphragm, and 5 MPa after placement of diaphragm. In the second part, shock wave-induced brain damages were investigated in 5 male Sprague-Dawley rats. While subarachnoid hemorrhage could be observed between 1 and 5 MPa, intracerebral hemorrhage, and laceration of tissue were also observed above 5 MPa. We therefore conclude that overpressure of exposing shock wave over brain surface should be managed under 1 MPa.
The paper reports an experimental study of the interaction of initially disturbed converging and diverging cylindrical shock waves with cylindrical interfaces and the resulting Richtmyer- Meshkov instability. Experiments were conducted in an annular vertical diaphragmless shock tube, in which cylindrical soap bubbles filled with He and SF6 were placed co-axially in its test section. In order to the clarify effects of initial disturbances, 10 mm dia. pins were installed in the annular section, 92 mm from the shock tube's test section and before the 90 degree smooth bend at the top of the shock tube. The inner ends of the pins were rounded to ensure completel sealing with the inner wall of the low pressure channel. Weak disturbances in the converging cylindrical shock waves were produced by inserting the pins. Double exposure holographic interferometry was used for quantitative visualization of the interfacial instability and the subsequent mixing between the interface gases. It is known that the lower mode numbers of disturbances are dominant near the converging center, therefore experiments with mode eight and mode four disturbed converging shock waves were performed and the effects of weak waves behind the shock wave on the interfacial growth rates were clarified.
A ridge waveguide of an organic salt, 4-N,N-methyl- stilbazorium tosylate, DAST, which has the largest second- order optical nonlinearities among organic materials, was fabricated for the first time to our knowledge. DAST crystal was covered by poly (methyl methacrylate) as a protect layer for a photo-resist solution, then standard photolithography and oxygen reactive ion etching (RIE) processes were applied. DAST ridge waveguide, 34x20 micrometers and 6x6 micrometers channel s with 2mm in length were successfully fabricated by this process. To reduce the refractive index of the crystal, photo bleaching was effectively applied for DAST crystal. So, photobleaching can be applied to fabricate a cladding layer for the ridge waveguide.