Akira Saitoh

Self-developing aspherical chalcogenide-glass microlenses for semiconductor lasers

A principle of self-developing microlenses for semiconductor lasers has been demonstrated using a photosensitive glass, As2S3. The glass film is placed in front of a semiconductor laser, the light from which increases the refractive index and thickness of the film. If its position and thickness are properly selected, the illuminated film operates as an aspherical microlens which can focus an elliptical laser beam to a circular spot.

Chalcogenide-glass microlenses for optical fibers

Abstract Three types of As2S3 microlenses attached onto end surfaces of optical fibers have been fabricated, and their characteristics are evaluated. These lenses are formed through photostructural transformations induced by He–Ne laser light, which is propagated in the fibers, so that the lenses are automatically positioned at the center of fiber cores. The lenses can be used at red to infrared wavelengths, and a minimal focal length is about 10 μm.

Chalcogenide-glass microlenses attached to optical-fiber end surfaces

Convex microlenses of As(2)S(3) glass have been fabricated on oxide-glass fiber ends by use of a photolithographic technique. As(2)S(3) film evaporated on the end surface of an optical fiber is exposed to light through the opposite end surface, and the film etching is observed under a microscope. This process produces a lens that is automatically positioned on the fiber core. The As(2)S(3) film possesses a high refractive index, which is favorable for production of microlenses with short focal lengths of ~10 mum.

Zero photoelastic zinc tin phosphate glass without lead oxide

The photoelastic constant (PEC) is evaluated for 15 zinc tin phosphate glasses in a series of xZnO-(67-x)SnO-33P(2)O(5) where x is 0-30 mol. % at 0.5-7 mol. % intervals. The phase retardation of polarized light, passing through a disk sample with applying various uniaxial loads, was measured for PEC determinations by using a frequency stabilized transverse Zeeman He-Ne laser as a polarized light source. The substitution of ZnO for SnO results in the increase of PEC from negative to positive values in the range of -1.43 and +1.45×10(-12) Pa(-1). The minimum PEC value of 0.04±0.02×10(-12) Pa(-1) was experimentally obtained in the 18.5 mol. % ZnO-48.5 mol. % SnO-33 mol. % P(2)O(5) glass.

Zero photoelastic and water durable ZnO–SnO–P2O5–B2O3 glasses

We report properties of zero birefringent xZnO–(67–x)SnO–(33–y)P2O5–y B2O3 glasses, within 18.5 ≤ x ≤ 22 and y = 0, 3, and 10 mol. %. These compositions of boro-phosphate glasses provide both zero photoelastic constant (PEC) and improved water durability. x = 19 and y = 3 compositions show minimum PEC of −0.002 × 10−12 Pa−1, which can contribute to candidate material for fiber current sensor devise without lead. The structures of zero photoelastic glasses were investigated by Raman scattering and nuclear magnetic resonance spectroscopies. Compositions of zero PEC glasses are explained by the empirical model proposed by Zwanziger et al. [Chem. Mater. 19, 286-290 (2007)].

Optical nonlinearities of Se-loaded zeolite (ZSM-5): A molded nanowire system

Nonlinear optical properties of Se-loaded ZSM-5 single crystals have been studied comparatively with those of glassy Se. Two-photon absorption coefficients and intensity-dependent refractive-index of the Se-zeolite are higher by three orders of magnitude than those of glassy Se. The enhancements can be ascribed to electron confinement in single Se chains.

Surface crystallization behavior during thermal processing of low-photoelastic ZnO–SnO–P2O5 glasses

Pb-containing glasses such as the PbO–SiO2 series are useful in optical devices because of their low-photoelastic constants (PECs); however, the toxic Pb component in these glasses is problematic. Transparent ternary ZnO–SnO–P2O5 glasses are potential substitutes for low-PEC Pb-containing glasses, but their thermal behavior is not well understood, which inhibits their ability to be drawn into fibers. Herein, we report the surface crystallization behavior of transparent ternary ZnO–SnO–P2O5 glasses, including those with low-PEC compositions, heated under isothermal conditions to temperatures above their glass-transition temperatures. The crystallization conditions for low-PEC phosphate glasses during their thermal processing into shapes of optical modules were deduced. The crystalline compounds precipitated on the surfaces were investigated via X-ray diffraction analysis, micro-Raman spectroscopy, and microscopic observations. A time–temperature–transformation diagram was constructed on the basis of the thermal stability of the glasses. We expect that this enhanced understanding of the crystallization behavior induced by the reshaping process will enable fabrication of precise polarization control devices with low PECs, such as optical-fiber current sensors, optical lenses, and filters.

Low photoelastic and optical properties in RO-SnO-P2O5 (R = Zn, Ba, Sr) glasses.

We report transparent RO-SnO-P2O5 (R=Zn, Ba, Sr) glasses with low photoelastic constant less than ∼1  B (1×10(-12)  Pa(-1)) and high refractive index more than ∼1.65. The BaO or SrO substitution effect of SnO on optical properties is nearly the same as ZnO substitution of the ternary zinc tin-phosphate glass without hazardous oxide. A new series of BaO-SnO-P2O5 glass characterized with a very low photoelastic constant of ∼0.08  B, high refractive index (∼1.66), and better water durability is a candidate for precise polarization control devices such as optical filters and beam splitters.

Study of the properties and structure of binary tin silicate glasses with zero photoelastic constant

Sn-containing silicate glasses with zero photoelastic constant (PEC) can potentially substitute zero-PEC Pb-containing glasses as optical fiber current sensor components based on the Faraday effect. These compounds allow monitoring of the electric power by measuring the electric current in high-voltage conductors operated with a 1550-nm light. The toxicity of Pb in these glasses still remains an important issue. However, replacing Pb in the sensors while minimizing the PEC of the resulting device would represent a significant breakthrough. We report a 43.5SnO–56.5SiO2 glass in molar% with zero PEC of + 0.01 × 10−12 Pa−1 observed with a wavelength of 632.8 nm.

Structure and properties of barium tin boro-phosphate glass systems with very low photoelastic constant

Glasses in the BaO–SnO–P2O5–B2O3 system were prepared and evaluated in order to formulate preform glasses suitable for the fabrication of fiber cores with a very low photoelastic constant. A first glass system (I: xBaO–(60–x)SnO–40P2O5) was designed with a constant P2O5 content and various BaO contents (0–40 mol. %). Introduction of 3 mol. % of B2O3 to enhance the glass stability leads to the second glass system (II: x′BaO–(57–x′)SnO–40P2O5–3B2O3) with 33–38 mol. % BaO. The structure of both systems was investigated by 1D/2D magic-angle spinning nuclear magnetic resonance, Raman, and Fourier transform infrared spectroscopic techniques. 31P NMR showed the presence of Q2 and Q1 units in the first system and correlation 11B/31P NMR indicated that boron enters into the network as B(OP)4 structural units. The photoelastic constant was determined and the stability of the best formulations as well as their refractive index dispersion was established. The drawing temperature and isothermal heating time (without c...