Yusuke Nasu

Low-loss waveguides written with a femtosecond laser for flexible interconnection in a planar light-wave circuit

We describe a low-loss single-mode waveguide in planar light-wave circuit (PLC) glass doped with boron and phosphorus, which is more difficult to write than pure-silica glass. The written waveguide has a rectangular core, a symmetric near-field pattern, and a propagation loss of 0.35 dB/cm. The loss that originates from the mode-field mismatch between the mode-field diameters of the written and the PLC waveguides is less than 0.1 dB/point. In addition, we successfully connected PLC waveguides with a 500-microm-long waveguide written with a laser. The laser-written waveguide can flexibly connect PLC waveguides with a low coupling loss.

Densification of sampled fiber Bragg gratings using multiple-phase-shift (MPS) technique

The authors recently proposed the multiple-phase-shift (MPS) technique, in which multiple phase shifts are introduced in sampled fiber Bragg gratings (SFBGs) to realize dense channel spacing. In this paper, the MPS technique is studied in detail, and it is shown that it can densify SFBGs both spectrally and spatially. Then, the paper presents that the MPS technique is applicable to densify the spectra of not only simple SFBGs but also various kinds of complex SFBGs, such as apodized, sinc-, and chirped SFBGs.

Ultralow Power Consumption Silica-Based PLC-VOA/Switches

We have achieved a silica-based PLC thermooptic switch with a power consumption of only 30 mW without any deterioration in the optical properties by using a tapered narrow ridge structure. To reduce the power consumption further, we propose a novel structure, the suspended narrow ridge structure, which has the advantages of both the tapered narrow ridge structure and the already reported suspended-bridge structure. As a result, we achieved PLC-VOA/switches with excellent heat design flexibility and a power consumption of 20 mW. In addition, using the proposed the suspended narrow ridge structure, we demonstrate a 16-channel V-AWG with a compact size of 20 times 17 mm and a low total power consumption of 320 mW.

Planar waveguide-type saturable absorber based on carbon nanotubes

The authors propose and demonstrate a planar waveguide-type optical device based on carbon nanotubes (CNTs). They realize saturable absorbers utilizing the interaction between the evanescent field of guiding mode and the CNTs. Saturable absorption characteristics are observed and insertion loss decreases ∼3% by high power pulsed laser. The device shows that polarization dependence originated from the asymmetric structure of their device and over 15dB polarization dependent loss. The saturable absorption is observed only in the polarization state that shows a maximum loss caused by the CNTs.

A multiplexing technique for fibre Bragg grating sensors with the same reflection wavelength by the synthesis of optical coherence function

We propose a technique for multiplexing fibre Bragg grating (FBG) sensors with the same Bragg wavelength. We have already developed a technique for the synthesis of an optical coherence function, in which we can select one signal among various reflections along an optical path in an interferometer. By applying the technique, the reflection spectrum of each FBG in arrayed FBGs can selectively be obtained, even if the array is composed of FBGs with the same Bragg wavelength. In this paper, we first describe the principle of the proposed system, and then show the experimental results.

Silica-based, compact and variable-optical-attenuator integrated coherent receiver with stable optoelectronic coupling system

We demonstrate a compact and variable-optical-attenuator (VOA) integrated coherent receiver with a silica-based planar lightwave circuit (PLC). To realize the compact receiver, we integrate a VOA in a single PLC chip with polarization beam splitters and optical 90-degree hybrids, and employ a stable optoelectronic coupling system consisting of micro lens arrays and photodiode (PD) subcarriers with high-speed right-angled signal lines. We integrate a VOA and a coherent receiver in a 27x40x6 mm package, and successfully demodulate a 128-Gbit/s polarization division multiplexed (PDM) quadrature phase shift keying (QPSK) signal with a VOA-assisted wide dynamic range of more than 30 dB.

Temperature insensitive and ultra wideband silica-based dual polarization optical hybrid for coherent receiver with highly symmetrical interferometer design.

We designed temperature-insensitive dual-polarization optical hybrids for the coherent receivers, and firstly demonstrated temperature-insensitive performance with a polarization extinction ratio over 25 dB and phase errors within 3 degrees over fully C-and L-bands.

Silica-based PLC with heterogeneously-integrated PDs for one-chip DP-QPSK receiver.

We fabricated a DP-QPSK receiver PLC by the heterogeneous integration of eight high-speed PDs on a compact silica-based PLC platform with a PBS, 90-degree optical hybrids and a VOA. 32 Gbaud DP-QPSK signal demodulation was successfully demonstrated.

In Situ Characterization of Bak Clusters Responsible for Cell Death Using Single Molecule Localization Microscopy

Apoptosis plays a pivotal role in development and tissue homeostasis in multicellular organisms. Clustering of Bak proteins on the mitochondrial outer membrane is responsible for the induction of apoptosis by evoking a release of pro-apoptotic proteins from mitochondria into cytosol. However, how the protein cluster permeabilizes the mitochondrial membrane remains unclear because elucidation of the cluster characteristics such as size and protein density has been hampered by the diffraction-limited resolution of light microscopy. Here, we describe an approach to quantitatively characterize Bak clusters in situ based on single molecule localization. We showed that Bak proteins form densely packed clusters at the nanoscale on mitochondria during apoptosis. Quantitative analysis based on the localization of each Bak protein revealed that the density of Bak protein is uniform among clusters although the cluster size is highly heterogeneous. Our approach provides unprecedented information on the size and protein density of Bak clusters possibly critical for the permeabilization and is applicable for the analysis of different cluster formations.

Ultrasmall 100 GHz 40-Channel VMUX/DEMUX Based on Single-Chip 2.5%-

The extension of optical add/drop multiplexing (OADM) systems to metro-core and metro-access networks has led to the need for economical and compact OADM devices. In this paper, we demonstrate a 1-in.2 100 GHz spacing 40-channel (ch) single-chip variable attenuator multiplexer/demultiplexer based on a monolithic 2.5%-Delta silica planar lightwave circuit (PLC) and stacked photodiode arrays. We also investigate the particular issues raised by monolithic integration with such high Delta waveguides. One is the loss increase caused by high index contrast of the waveguides. Performance fluctuation and thermal interference between the integrated circuits are also inherent issues. By utilizing effective solutions, we have successfully overcome such problems and confirmed that a 2.5%-Delta silica PLC is effective for use in monolithic integration.