Shigekuni Sasaki

Fluorinated polyimide waveguides with low polarization-dependent loss and their applications to thermooptic switches

Fluorinated polyimide waveguides with low polarization dependent loss (PDL) and thermooptic (TO) switches made from them were demonstrated. The waveguides showed loss of less than 0.3 dB/cm at the wavelength of 1.3 /spl mu/m and 0.6 dB/cm at 1.55 /spl mu/m for both TE and TM polarizations. The PDLs were less than 0.1 dB/cm. Extinction ratios of Y-branching-type TO switches fabricated from these waveguides were larger than 20 dB when over 160 mW of electric power was applied at 1.3 /spl mu/m, and over 150 mW at 1.55 /spl mu/m. The switching speed was faster than 8 ms.

Single-mode optical waveguides fabricated from fluorinated polyimides

Buried channel optical waveguides were fabricated from fluorinated polyimides. They operated in single mode and showed an optical loss of less than 0.3 and 0.7 dB/cm for TE and TM polarizations, respectively, at a wavelength of 1.3 mum. Moreover, these waveguides had high heat and moisture resistance; the optical loss did not significantly change after heating at 380 degrees C for 1 h or after exposure to 85% relative humidity at 85 degrees C for over 200 h.

Heat-resistant flexible-film optical waveguides from fluorinated polyimides

Heat-resistant flexible-film optical waveguides were fabricated from fluorinated polyimides. These waveguides operated in single mode and had low optical loss (0.3 dB/cm) at a wavelength of 1.3 microm for TE and TM polarizations. They also had good flexibility: The optical loss did not significantly change above a minimum radius of curvature of less than 20 mm. The birefringence of 9 x 10(-5) between the TE and TM polarizations is 2 orders of magnitude smaller than that for a waveguide upon a substrate. Moreover, these waveguides had high thermal stability and moisture resistance: The optical loss and single-mode behavior changed little after heating the waveguides at 420 degrees C for 1 h or after their exposure to 85% relative humidity at 85 degrees C for more than 350 h.

Embedded channel polyimide waveguide fabrication by direct electron beam writing method

A new embedded channel polyimide waveguide fabrication process by a direct electron beam writing method (DEBWM) is described. The new technique uses an electron-beam induced effect to directly alter the refractive indices of the two-layer polyimide. Both the core and the lower cladding have been fabricated at the same time in two-layer polyimides using electron beam with 25 keV energy. The obtained embedded channel waveguide was made of two kinds of polyimides, one for lower cladding and one for core and other claddings. Guide losses are 0.3 dB/cm for both TE and TM polarized incident lights and guiding mode is single-mode for TE. The optical properties of the waveguide and a relationship between the doses of electron beam and optical losses or loss dependence on wavelength are also mentioned. >

Directional couplers using fluorinated polyimide waveguides

Optical properties of directional couplers using a fluorinated polyimide waveguide were demonstrated. At a wavelength of 1.3 /spl mu/m, directional couplers with the refractive index difference of 0.3% between the core and cladding have a maximum power coupling ratio of more than 97 and 96% for TE and TM polarisations, respectively. The excess loss for a 3-dB coupler was as low as 0.3 dB. Moreover, the change in the coupling ratio of the 3-dB couplers remained within 0.5% between 25 and 100/spl deg/C.

Optical anisotropy of uniaxially drawn and silver-dispersed polyimide films

Distinct anisotropy in optical transmittance in the visible and near-infrared region for uniaxially drawn and silver-dispersed polyimide films was observed. The films were prepared in a one-step operation that involves thermal curing and simultaneous uniaxial drawing of poly(amic acid) (PAA) films, which were made by dissolving silver nitrate in the PAA solution at a 1:4 mol ratio. The polyimide molecular chains with a rod-like structure were oriented along the drawing direction during curing, and this orientation accompanied the generation of silver nanoparticles with elongated shapes. An anisotropy in the optical transmittance of 5:1 was obtained for a 22-μm-thick film at 850 nm with transmittance of 68% perpendicular to the drawing direction. The optical and mechanical properties of this film were retained after annealing at 300 °C for 1 h.

Property Control Of New Fluorinated Copolyimides And Their Applications

New fluorinated copolyimides are synthesized with 2,2′-bis(trifluoromethyl)-4,4′- diaminobiphenyl (TFDB) and a mixture of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and pyromellitic dianhydride (PMDA). The thermal expansion coefficient decreases with decreasing 6FDA content, because the hexafluoroisopropylidene group makes the main chain flexible. The refractive index decreases with increasing 6FDA content, because the fluorine content increases. The thermal expansion coefficient can be controlled between -0.5 × 10 −5 and 8×10 −5 /°C, and the refractive index can be controlled between 1.556 and 1.647 at 589.3 nm, by changing the 6FDA content. The polyimides and copolyimides from TFDB can be used in optical filters because of their high optical transparency and low thermal expansion coefficient. They are expected to be used in optical waveguides because of their high optical transparency and refractive index control.

Synthesis and Properties of Perfluorinated Polyimides

Silica-based single-mode optical fibers are used as the transmission medium in current optical telecommunication systems.1 The transmission light is near-IR. Degradation of communication quality under transmission is minimized by using a 1.3 μm wavelength because the refractive index dispersion of these optical fibers is zero at this wavelength, which is thus called the zero-dispersion wavelength. On the other hand, this optical fiber has a minimum transmission loss at 1.55 μm. Techniques have been developed to shift the zero-dispersion wavelength of silicabased optical fibers to 1.55 μm. Future telecommunication subscriber systems will use both 1.3 and 1.55 μm as communication wavelengths2 (e.g., 1.3 μm for communication service and 1.55 μm for one-directional video service). The refractive index of the core of the optical fibers is made slightly higher than that of the cladding in order to confine the transmitted optical signals. A small amount of GeO2 is doped into the core of the commonly used silica-based optical fibers in order to increase the refractive index. Since doping into the core is undesirable from the point of view of decreasing the transmission loss, fluorine is doped into the cladding of optical fibers to achieve very low transmission loss. The

Ultrathin (5 µm) Flexible Reflective Waveplate of Fluorinated Polyimide and Elimination of Polarization Sensitivity in Titanium-Diffused Lithium Niobate Waveguide Circuits

An ultrathin, flexible reflective half-waveplate, consisting of a 5-µm-thick polyimide quarter-waveplate sputtered with a thin gold film, was fabricated, and its property of eliminating polarization sensitivity in titanium-diffused lithium niobate waveguide circuits was investigated. Transverse electric/transverse magnetic mode-conversion ratios of 15–20 dB at 1.55 µm were obtained, and a polarization-insensitive intensity modulator with a low half-wave voltage of 4.5 V was successfully fabricated using a titanium-diffused lithium niobate waveguide. The excess loss of the polyimide reflective waveplate (1 dB) was much smaller than that using a conventional quartz waveplate (6 dB).

In situ mass and photoemission studies of fluorinated polyimide films irradiated with an electron beam

Fluorinated polyimide films were irradiated in an ultrahigh vacuum with an electron beam. In situ mass analysis was carried out simultaneously and in situ photoemission studies were performed on surfaces modified by electron exposure at various electron beam energies and various sample currents. Based on the present data, the irradiation of electrons produces a fluorine-poor surface and an imide-ring opening, and the production rate was accelerated by raising the electron beam energy. An electron beam with low energy and low density is effective for changing the refractive index of the surface of fluorinated polyimide films with small strength change.