Makoto Nakai

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.”

Frequency tunable compact antenna for digital terrestrial radio reception

A varactor-loaded folded dipole antenna has been proposed for digital terrestrial radio reception. From calculation using ldquoFEKOrdquo, the proposed antenna maintains a VSWR of less than 1.6 and a figure-of-eight radiation pattern between frequency ranges of 187 MHz to 230 MHz. The proposed antenna has a compact structure of 332 mm by 30 mm which is suitable for sealing on vehiclespsila window. It will be used for digital terrestrial radio reception on vehicles.

Using system simulation to evaluate design choices for automotive ethernet over plastic optical fiber

The growing bandwidth demands of advanced driver assistance systems (ADAS) and infotainment technologies make Gigabit Ethernet over plastic optical fiber (POF) a natural choice for next-generation automotive data networks, especially in light of the recent approval of the IEEE 802.3bv standard for Gigabit Ethernet transmission over POF. POF-based transmission provides the advantages of low cost, light weight, easy termination, durability, and immunity to electromagnetic interference (EMI), while Gigabit Ethernet extends the current maximum data rate of 150 Mb/s provided by Media Oriented Systems Transport (MOST). Thus, we examine important design choices that impact the performance of POF-based automotive data links for data rates up to and beyond 1 Gb/s and different choices of modulation format, including NRZ and PAM-n. Because simulation is an efficient and cost-effective solution for studying the complex interplay of multiple design choices without requiring physical prototypes, we base our analysis on a comprehensive modeling framework for optical communication systems incorporating large-core step-index fiber and fiber-to-fiber connectors. We study anticipated system performance in terms of bandwidth and BER for different choices of link length and connector count, including the IEEE 802.3bv targets of 15 meters with four connectors and 40 meters with no connectors. In addition, we consider the impact of connector misalignments (both lateral and longitudinal) and source launch profile (measured in terms of its encircled angular flux, or EAF), which also directly affect link bandwidth.