Akari Kawasaki

A polymer optical waveguide with out-of-plane branching mirrors for surface-normal optical interconnections

We have developed a simultaneous fabrication method using temperature control reactive ion etching (RIE) for channel optical waveguides incorporating plural out-of-plane branching mirrors made from polymer film. By using this method, the etching rate can be adjusted locally by controlling the temperature. This technology also enables the formation of trenches of various depths on the same polymer optical waveguide. We noted from scanning electron microscope (SEM) observations that simultaneous control of the mirror tilt angle and a smooth core surface could be achieved. To be specific, a heat treatment temperature of 130-135/spl deg/C appears to be the optimum to maintain a rectangular cross section and to achieve a sufficiently smooth core surface for a polymethyl methacrylate (PMMA) waveguide. The measured propagation loss is small, in spite of the presence of a high-/spl Delta/ waveguide (/spl Delta/=5.4%). For example, losses of 0.1, 0.3, and 0.7 dB/cm are measured at wavelengths of 650 nm, 850 nm, and 1.3 /spl mu/m, respectively. From far-field pattern (FFP) measurements, we found that the mirror plane was almost rectilinear, and that the reflected light can be captured efficiently by a photodiode. In operational temperature tests, we showed that intensity fluctuations of the coupling light can be reduced to less than 1.5 dB for the temperature range between -25/spl deg/C and +85/spl deg/C by adopting a sandwich structure with glass plates.

Polymer waveguide module for visible wavelength division multiplexing plastic optical fiber communication

We report a polymer waveguide module that provides bidirectional communication over a single plastic optical fiber (POF) with dual visible wavelength LEDs. The module is constructed using light-induced self-written waveguides, which enables a three-dimensional optical circuit for visible wavelength division multiplexing to be fabricated by an extremely simple process. We demonstrated 250 Mbits/s communication using a pair of these modules that each contained one green (lambda = 495 nm) and one red (lambda = 650 nm) LEDs by measuring the bit error rates. The results indicate that the system could transmit over more than 20 m of POF in full duplex mode.

Encircled Angular Flux Representation of the Modal Power Distribution and its Behavior in a Step Index Multimode Fiber

The optical properties of inline optical components inserted at the input to a multimode optical fiber (MMF) strongly affect the propagating modal power distribution (MPD). To realize stable systems with predictable reproducible performance and to encourage widespread use of MMF systems, improvements to the system design process and to the characterization process need to be made and new interface standards need to be defined. To this end, we have developed a new reproducible MPD measurement and representation together with its theoretical definition. By modifying the encircled flux (EF) representation, which is based on the near-field pattern of a graded-index multimode optical fiber (GI-MMF), we define the encircled angular flux (EAF) for step-index multimode optical fibers (SI-MMFs) based on their far-field patterns (FFPs). Using a SI-MMF, which is used for low cost short distance interconnects, as an example, we show the changes in the MPD along the fiber, reveal an unusual insertion loss-increasing phenomenon due to the evanescent tails of the core modes extending into the cladding, and characterize the equilibrium mode distribution (EMD) in the fiber. The EAF representation enables these phenomena to be quantified. We also propose an EAF template that consists of the target EMD and its tolerance. If device system designers use the EAF template to set the launch conditions, they can perform a fair assessment of the components, and they can design the system performance even if some components are replaced with others from a different supplier manufactured by a different method. We call this concept “Total MPD Management.”

Modal power distribution in short reach optical communications using step-index-type multimode optical fibers

In an optical communication system using Step Index type Multi-Mode optical Fiber (SI-MMF), the propagating modal power distribution (MPD) in the fiber is strongly influenced by the transmission characteristics. In most cases the MPD launched from the optical transmitter is significantly transformed before reaching the receiver due to a number of factors, i.e. mode conversion and mode dispersion along the fiber and the various components inserted in the optical path. In order to secure the minimum received optical power and desired bandwidth at the receiver, we propose using the concept of “Total MPD management” for all interfaces in the transmission line. To implement this concept, a method of specifying requirements to the device side from the specifications on the system side is needed. Although rapid changes in MPD arise, especially in SI-MMFs, there is no universal means of quantifying this. In this paper, we define a simple quantification method for MPD which we have named the “encircled angular flux (EAF)”, and which can be used to accurately design optical systems (FFP-based). Moreover, this EAF acts as a fundamental parameter for the design, mounting and evaluation of optical components and can provide the specifications required for connecting to a network. We expect the use of “Total MPD management” and “IEC standardization” will generate interest in related institutions and suppliers worldwide.

Shape control of Self-Written Waveguide

Recently, drastic increase of information flow has become a serious problem in information and communication technology, because of a data transmission rate limit in metallic wiring. To solve this problem, we have paid a special interest to optical interconnection by SWW (Self-Written Waveguide). We studied about a mutual relationship between the SWW shape and fabrication parameters, such as the laser irradiation power and the optical mode. We examined the SWW by simulation using the ray tracing method. Experimentally we fabricated SWWs under several beam divergence angles. From these results we confirmed that it seems possible to control the SWW shape with specific parameters.

Light-Induced Self-Written three-dimensional polymer optical waveguide for module fabrication and interconnection

Light-induced self-written (LISW) technology is a unique and simple method of forming low-loss 3-dimensional optical circuits in a photopolymer solution. By using this technology, we fabricated and tested a WDM optical module.

Three-dimensional WDM optical module using a light-induced self-written (LISW) waveguide technology

We developed the bidirectional optical transceiver module that combined the two LED light sources of different wavelength and three-dimensional (3-D) optical waveguides. By using a light-induced self-written (LISW) technique, we fabricated and tested 3-D optical waveguide circuits for a plastic optical fiber (POF) WDM full-duplex communication module. Because of the large diameter of the POF, an optical waveguide has the advantages, as compared to conventional lens based modules, of a small size and optical low-loss features. The LISW waveguide enables optical components to connect automatically even if the circuit in the module is complex. In this paper, we demonstrate newly developed bidirectional WDM optical module containing 3-D optical circuits, i.e. a branching waveguide and a reflection waveguide, and their optical properties. The module using commercially available green and red LED was constructed and the two-way communication on IEEE1394-S100 (125Mbps) protocol was verified through 10m-length of POF.

An optical scanner based on beam switching method fabricated on silicon photonics circuit

We have demonstrated an optical scanner based on beam switching method fabricated on silicon photonics integrated circuit. Scanner is based on beam switching method. Scanner is composed of ring resonator multiplexer and grating array. Multiplexer determines the optical path and one of grating is selected for emitter. The scanning angle was 6 degree. Solid state scanner is suitable for Laser intensity direction and ranging (LIDAR) because of reliability and small factor. We fabricated and demonstrated an optical scanner based on beam switching method fabricated on silicon photonics integrated circuit. Scanner is all solid state and movement-free. Scanner is composed of ring resonator multiplexer and grating array. Multiplexer determines the optical path and one of grating is selected for emitter. LIDAR is promising sensor for automated cruising for automotive application and this report is considered to be a remarkable technology.

Light-induced self-written polymeric waveguides for low-cost integration of single-mode devices

We demonstrate the feasibility of optical interconnection waveguides, including a Bragg grating and EO waveguides, formed by a self-trapping effect into a novel photopolymer. These technologies are useful for the integration of chip-scale photonic devices.

Light-induced self-written waveguide for optoelectronic integration devices

We show the feasibility of optical interconnection waveguides formed by self-trapping effect with 0.85μm light irradiation into photopolymer. Self-written waveguides as extensions of both a single-mode fiber and a VCSEL chip were demonstrated. These technologies are useful for integration of chip-scale photonic device.