Mikitaka Itoh

OPTICAL AND ELECTRICAL PROPERTIES OF AG-AS-S GLASSES

Physical properties of Ag2S‐As2S3 glassy alloys have been studied as a function of the Ag atomic concentration x. With an increase in x, the optical‐absorption edge exhibits a red shift, while the steepness of the Urbach tail changes little. In the glasses with x≥15, the electrical conductivity is governed by Ag+ ionic conduction. The ionic conductivity exponentially increases with x, and in contrast the hole conductivity hardly changes with x; however, the activation energies for the ionic and the hole conductivity are nearly the same at about 0.4 eV for compositions with 15 ≤x≤35. These observations are discussed on the basis of atomic and electronic structures in Ag2S‐As2S3 glasses.

Mobility of Ag ions in AgAsS glasses

Abstract The drift mobility and the carrier density of Ag ions in AgAsS glasses with the Ag content of 15 – 45 at.% have been measured over a temperature range of 20 – 100 °C using a time-of-flight method. With an increase in the Ag content, the mobility increases exponentially, while the carrier density remains nearly constant. These two results are in quantitative agreement with electrical conductivity data. The observations are discussed in light of structural models.

Electronic structures of Ag(Cu)–As–Se glasses

Abstract Fundamental physical properties of Ag(Cu)–As–Se glasses along Ag(Cu)–As2Se3 tie lines have been investigated in order to obtain knowledge of electronic structures. Optically, Ag and Cu addition to As2Se3 induce red shifts of the absorption edges, in which the shift in the Ag–As–Se system is smaller than that in the Cu–As–Se system. In X-ray photoelectron spectra, Ag 4d and Cu 3d states gradually appear at an upper valence band with increasing Ag(Cu) content. Further, a transient photocurrent study shows that the localized states Nt(E) at E≃0.5 eV from the valence band are distributed exponentially, Nt(E)∝exp(−E/kT0), in Ag(Cu)–As–Se glasses, in which the Ag–As–Se system possesses a greater characteristic temperature T0. On the bases of these observations, electronic structures of Ag(Cu)–As–Se glasses are considered from a unified point-of-view.

Photoelectric properties of Ag–As–S glasses

Photoconductive and photovoltaic responses in glassy Ag–As–S ion‐conducting semiconductors have been studied. The ac conductivity of the glass increases with illumination, while the increase is ascribed to enhanced ionic conduction caused by temperature rise and to interfacial photoeffects. Bulk photocurrent is not detected. By contrast, photovoltages appear in Ag–As–S samples having sandwich and floating electrodes. The photovoltaic characteristics are discussed in terms of classical electrodynamics assuming interaction between electronic carriers and Ag+ ions.

Ionic Conduction in Glasses

The activation energy of ionic conductivity in a variety of glasses has been studied from a unified point of view. A plot of the activation energy as a function of the cation-anion distance manifests that the glass can be divided into two groups; the examples being chalcogenide and oxide glasses. In the chalcogenide the activation energy becomes smaller with the increase in the cation-anion distance, while in the oxide the opposite trend exists. Origins of these features are discussed in connection with carrier and mobility activations.

High-Sensitivity Detection of Fiber Bends: 1-μm-Band Mode-Detection OTDR

We propose a measurement system based on optical time-domain reflectometry (OTDR) that offers high-sensitivity detection of bend location in a standard single-mode (SM) fiber. This technique, which employs 1-μm-band probe pulse, i.e., below the cut-off wavelength of SM fiber, enables us to individually observe the fundamental (LP01) and the second-order (LP11) modes of the backscattered light generated in the two-mode region of the SM fiber, using a key technical advance is a mode-selective coupler designed for optimal 1-μm-band operation. Analyzing the loss distribution of the backscattered LP11 mode realizes the high-sensitivity detection of the fiber bend location without suffering degradations from the modal dispersion. We perform experiments for the four kinds of widely-used SM fibers, and demonstrate the proof-of-concept; a comparison is made with the conventional OTDR operating at the wavelength of 1650 nm.

Wide passband tandem MZI-synchronized AWG employing mode converter and multimode waveguide

We have successfully demonstrated an AWG with a wide and rectangular passband by introducing a new concept using 0th and 1st order modes. An interference circuit consisting of a tandem MZI and a mode converter at the entrance of the 1st slab waveguide perturbs the input light field, thus attaining a 0.5-dB bandwidth of 69% relative to its channel spacing.

Heterogeneously Integrated PLC With Low-Loss Spot-Size Converter and Newly Developed Waveplate PBS for DC-DP-16QAM Receiver

Digital coherent transmission systems with multilevel and multicarrier modulation formats have been moving beyond 100-G systems. In this paper, we report a one-chip 400-G coherent receiver founded on a silica-based planar lightwave circuit (PLC) integration platform. To integrate a polarization beam splitter (PBS), two polarization rotators, four-optical hybrids, and 16 high-speed photodiodes (PDs) in one chip, we employed a 5%-Δ waveguide with a minimum bending radius of 300 μm, and the heterogeneous integration of InP-PDs. To achieve a compact receiver without any degradation in optical passive performance, we also investigated a three-branched spot size converter with a low loss and a high-fabrication tolerance and a waveplate type PBS with a high-polarization extinction ratio. Using these techniques, we fabricated a dual-carrier dual-polarization (DP) 16-level quadrature amplitude modulation (QAM) receiver PLC, and successfully demonstrated 32-Gbaud DP-16QAM signal demodulation for each channel.

Low loss 1 × 8 silica-based phased array switch with low power consumption

We demonstrated a low loss 1 × 8 silica-based phased array switch with low power consumption by optimizing the number of arrayed waveguides. To reduce the single-mode fiber coupling loss and to obtain a large coupling tolerance, we introduced triple-branched spot-size converters designed with the wavefront matching method. In addition, heat insulating grooves and a 2π shift-controlled procedure were adopted to reduce the switching power. As a result, we obtained a low insertion loss of 3.6–6.8 dB and a low power consumption of 1.6 W. The polarization dependence, extinction ratio and switching time were 0.1 dB, 17.4–38.6 dB, and 1.2 ms, respectively.

Loss Cause Identification by Evaluating Backscattered Modal Loss Ratio Obtained With 1-μm-Band Mode-Detection OTDR

We propose a novel diagnostic technique that uses 1-μm-band mode-detection optical time domain reflectometry (1 μm-OTDR) to identify the loss causes such as macrobends and fusion splices, of single-mode fibers. 1 μm-OTDR, which employs 1-μm-band probe pulses and a mode selective coupler operating in the same band, enables us to individually observe the fundamental (LP01) and the second-order (LP11) modes of the backscattered light generated in the two-mode region of single-mode fibers. Evaluating the ratio of losses occurring in the LP01 to LP11 modes of the backscattered light allows us to determine whether the cause of loss is a macrobend or a fusion splice. A proof-of-concept demonstration is performed for two kinds of widely used single-mode fibers, and the results show that macrobending and fusion splice losses can be clearly identified.