In silicon photonics, optical coupling between optical fibers and silicon photonics chips still remains a big issue to be improved. Recently we have developed a new surface coupler consisting of a vertically-bent silicon waveguide using ion implantation as a bending method. This bending method enabled bending of silicon waveguide terminals to the vertical surface direction with curvature radii as small as several μm and bending of propagation direction of light to the surface direction with broadband wavelength property. In our initial studies, to couple the propagated light with optical fibers efficiently, we taper-narrowed the tips of the waveguide terminals from 440 nm to ~200 nm to expand the mode field and obtained a coupling loss of ~2 dB in TE-polarization mode for a lensed fiber with a beam diameter of 2 μm. We are now developing couplers with high coupling efficiencies for 5 μm mode field diameter fibers. Such mode field diameters are available by HNA fibers and position alignment accuracy can be mitigated to a micron level. In addition, HNA fibers can be fusion-spliced to standard single mode fibers. Using 3D-FDTD simulation we have demonstrated that <1dB coupling is possible if the tip of the bent waveguide is taper-narrowed to 50 nm and covered with a lens-shaped SiO<sub>2</sub> dome. In practice, such a structure could be fabricated successfully and 5 dB coupling with a 5 μm mode field diameter lensed fiber has been demonstrated in our initial experiment
Optical coherence tomography (OCT) is a non-invasive optical imaging technology for micron-scale cross-sectional imaging of biological tissue and materials. We have been investigating ultrahigh resolution optical coherence tomography (UHR-OCT) using fiber based supercontinuum (SC) source. Although UHR-OCT has many advantages in medical equipments, low penetration depth is a serious limitation for wider applications. Recently, we have demonstrated high penetration depth UHR-OCT by use of fiber based Gaussian shaped SC source at 1.7 μm center wavelength. However, the penetration depth has been limited by the low power of SC source. In this paper, to realize deeper penetration imaging, we have developed the high power Gaussian shaped SC source at 1.7 μm wavelength region based on the custom-made Er-doped ultrashort pulse fiber laser with single-wall carbon nanotube and nonlinear phenomena in fibers. This SC source has 43.3 mW output power, 242 nm full-width at half maximum bandwidth, and 109 MHz repetition rate. The repetition rate and average power were almost twice as large as those of previous SC source. Using this light source, 105 dB sensitivity and ultrahigh resolution of 4.3 μm in tissue were achieved simultaneously. We have demonstrated the UHR-OCT imaging of pig thyroid gland and hamster’s cheek pouch with this developed SC source and compared the images with those measured by the previous SC source. We have observed the fine structures such as round or oval follicles, epithelium, connective tissue band, and muscular layer. From the comparison of the UHR-OCT images and signals, we confirmed the improvement of imaging contrast and penetration depth with the developed SC source.
Amorphous siliceous materials with molecular dispersions of organic molecules, TPPS, TMPyP and DAQ were prepared by a sol-gel process in which Si(OC<SUB>2</SUB>H<SUB>5</SUB>)<SUB>4</SUB> was hydrolyzed in weak acid solution. Effect of ultrasonic irradiation on the sol-gel process was studied for the TPPS/a-SiO<SUB>2</SUB> system in order to attain the further molecular dispersions and shorten the sol-gel reactions. Optical properties of TMPyP doped sol-gel thin films were observed. An amorphous silica thin film which was doped with TMPyP on the order of 1 X 10<SUP>-3</SUP> mol/mol SiO<SUB>2</SUB> showed photochemical hole burning at 20 K. the TMPyP/a-SiO<SUB>2</SUB> was heat-treated at various temperatures and the changes of optical spectrum were observed as a function of temperature. It was found that the sample was comparatively stable up to 200 degree(s)C. Apparent quantum yields of PHB of porphines and quinizarin in polymer or sol-gel film and bulk were discussed.