Shuichiro Asakawa

ARROW-B type polarization splitter with asymmetric Y-branch fabricated by a self-alignment process

We have proposed and demonstrated a polarization splitter based on an ARROW-B type waveguide. This device has an asymmetric Y-branch configuration, connecting a waveguide with a large modal birefringence to a low-birefringent waveguide which is channeled by a stripe lateral confinement structure. The device can achieve a high extinction ratio without precise mask alignment, since these two waveguides are connected by a self-alignment process. In addition, a low insertion loss is achieved because of adiabatic Y-branching. We designed this device at the wavelength of 1.55 /spl mu/m and fabricated it using RF sputtering. As a result, high extinction ratios of -19.4 dB for TE mode and -19.0 dB for TM mode were achieved.

ARROW-type polarizer utilizing form birefringence in multilayer first cladding

A waveguide polarizer using an ARROW (antiresonant reflecting optical waveguide) structure, of which the first cladding consists of three thin layers, is proposed. Theoretical calculation shows that this polarizer can achieve isolation over 30 dB/cm with an insertion loss of 0.01 dB/cm at 1.3 mu m. Isolation of 83 dB/cm with insertion loss of 4.3 dB/cm was experimentally obtained at 0.633 mu m. This structure is suitable for the integration of a polarization splitter and photodetector.<<ETX>>

Fiber fuse generation in single-mode fiber-optic connectors

The evolution of the fiber fuse phenomenon in a single-mode fiber-optic connector was studied theoretically. A narrow air gap of the order of 1 /spl mu/m was assumed to be formed between the fiber end-faces in the connector as a result of the adhesion of dust to both the ferrule and the fiber end-faces. It was assumed that there was a thin water layer in the gap because condensable water molecules in the air could easily be trapped by the SiOH groups on the silica-glass surface. The water layer exhibited a large absorption coefficient of about 850 cm/sup -1/ at 1.48 /spl mu/m. The temperature distributions near the air gap were numerically calculated by using the explicit finite-difference method. When a high-power laser operating at 1.48 /spl mu/m was input into the connector, the temperature along the fiber-core center increased abruptly at the thin water layer. The air gap was heated above 4/spl times/10/sup 5/ K when the optical power was 2 W and the gap was 1 /spl mu/m. The heat in the air gap gradually diffused into the neighboring optical fiber over time. The temperature of the heated fiber reached over 1/spl times/10/sup 4/ K, which is high enough to initiate the fiber fuse phenomenon.

Fiber fuse terminator

We developed a fiber fuse terminator to ensure the safe operation of high power optical network systems. The performance of this fiber fuse terminator was satisfactory as regards an optical input of 2 W.

120.7-Tb/s MCF-ROPA Unrepeatered Transmission of PDM-32QAM Channels Over 204 km

We demonstrate the unrepeatered transmission of over 100 Tb/s by employing a multicore-fiber-based remote optically pumped amplifier. We establish 120.7-Tb/s, 204-km seven-core fiber transmission with the aggregate spectral efficiency (SE) of 53.6 b/s/Hz, a record capacity per fiber and the highest SE for unrepeatered transmission. We also realized the highest capacity per core of 17.2 Tb/s (180 × 95.8 Gb/s) and SE of 7.6 b/s/Hz by using the polarization-division-multiplexed 32-quadrature amplitude modulation format for unrepeatered transmission.

A versatile design of selective radiation wavelength filter using multilayer cladding waveguide

A novel selective radiation-wavelength filter based on a multilayer cladding waveguide was proposed and analyzed. Light with a passband wavelength is selectively radiated into a photodetector on substrate, partially using a vertical coupling between the core and one of cladding layers. Narrow and sideband-free filtering characteristic and compact size are achievable with low insertion loss.<<ETX>>

ARROW-B type polarizer utilizing birefringence in multilayer stripe lateral confinement

A novel TM-mode transmission waveguide polarizer based on a three-dimensional ARROW-B waveguide was proposed and demonstrated. This polarizer can achieve a high extinction ratio over 30 dB with small insertion loss less than 0.1 dB and short device length less than a thousand wavelengths. The extinction ratio of 14.8 dB with the insertion loss of 1.1 dB was experimentally obtained with the device length of 400 /spl mu/m at the wavelength of 0.633 /spl mu/m. This structure can easily be extended to polarization splitters.<<ETX>>

PLC connector with PLC-fiber physical contact for multichannel receptacle PLC modules for optical circuit board integration

We describe a novel waveguide-fiber connector, namely, the planar lightwave circuit (PLC) connector, designed to realize a receptacle interface in PLC-based optical modules for economical optical circuit board integration. This connector can provide stable high-density multiple connection between a PLC and single-mode fibers. Moreover, this connector is inexpensive to produce because it utilizes physical contact (PC) connection between a PLC and fibers by employing the elastic force generated by the fibers themselves rather than by a ferrule and spring. We fabricated a duplex PLC connector and a multiple PLC connector for an optical transceiver module and multichannel optical modules, respectively, and successfully obtained low average connection losses of 0.2 and 0.33 dB, and high average return losses of 43 and 43 dB, respectively. In addition, we confirmed that the connectors had sufficient environmental durability. We also realized 2- and 34-channel receptacle interfaces in the transceiver module and a thermooptic switch module by equipping the modules with the duplex connector and three of the multiple connectors.

Compact multi-fiber receptacle interface for on-board optical interconnection

We have developed a new type of receptacle interface that enables us to achieve dense multi-fiber connection between a planar lightwave circuit based optical device and single-mode fibers on a printed circuit board. To obtain both a small size and good optical performance with this interface we devised a small fiber guide for aligning the fibers with waveguides, and also developed a refractive-index-matching gel that maintains stable optical performance. We fabricated sufficiently small (5 mm long) 32-fiber interfaces, and successfully obtained low connection and high return losses with average values of 0.17 and 60 dB, respectively. We also demonstrated that the interface can provide sufficient environmental durability. Our new interface eliminates the need for pigtail fibers on the board, and this will lead to the development of dense and low-cost optical interconnection on a board for advanced optical network systems.

SPring-8 X-Ray Micro-Tomography Observations of Zirconium Inclusions in CO

Laser fusion splicing has been realized for the simple splicing of optical fibers in a small board area, and for accommodating the increasing number of optical fibers that must be mounted on a board. For the splicing, zirconia ceramics are conventionally used to fabricate V-groove substrates because of their high machining performance. In this study, the existence of zirconium inclusions between the spliced optical fibers could be clarified with SPring-8 micro-computed tomography (SP-μCT) for the first time. The large inclusion size was found to increase the splicing loss. Moreover, the average splicing loss could be reduced from 0.18 dB to 0.15 dB by the adoption of a cleaning process to remove the zirconium inclusions that originate from the V-groove substrate used for the fiber.