1. Field of the Invention
The present invention relates to an optical waveguide device having an optical waveguide such as optical waveguide layer for optically coupling signals between electronic chips on an electric circuit board or between electric circuit boards, for example. The present invention also relates to a layered substrate made up of such a device integrated with an electric circuit board, and an electronic equipment using the same.
2. Related Background Art
In recent years, there has been rapid progress in performance of portable devices such as personal computers, cellular phones and personal digital assistants (PDA), and digital audio/video (AV) apparatuses. These devices are interconnected at any frequency band using a combination of wireless and wired connections. There is, therefore, an urgent need to address any faulty operation of digital devices due to, for example, electromagnetic interference (EMI) from circuit boards, interference by external electromagnetic radiation, and signal integrity (SI) disturbance by faulty connections. These problems associated with electromagnetic waves require the products to satisfy the regulatory standards imposed by the Radio Law before shipment, and the developing costs to fulfill the requirement is increasing year by year. It is expected that the optical wiring, which inherently induces no electromagnetic radiation, may essentially eliminate the bottleneck. With the prospect that a high-speed connection environment such as FTTH will be available even at home in the future, faulty operation, noise disturbance and the like of high-speed electronics must be avoided taking into account the fact they may be connected to different types of ground environment. The optical connection is one potential solution, because it provides electrical isolation from the ground in a simple manner.
To this end, a variety of ways have been proposed for optical wiring means. Among them, a method of using an optical waveguide sheet to make a bus connection among a plurality of electric circuit boards in an information processing apparatus 1100 has been disclosed in Japanese Patent Application Laid-open Nos. 09-270751 and 10-206677. In those disclosures, an optical waveguide sheet 1101 and electric circuit boards 1120 are coupled together independently and vertically, as shown in FIG. 8A. Optical elements 1132, 1142 are mounted at input and output ports 1130, 1140 on an electric circuit board 1120, and are adapted to couple with the optical waveguide sheet 1101 via mirrors 1133s inclined at an angle of 45 degrees. In this example, the optical waveguide sheet 1101 constitutes a planar slab waveguide and multiplexes signals in a direction along the layers. In FIG. 8B, reference numeral 1123 denotes an electronic circuit, 1131 and 1141 denote circuits for optical elements, 1133 denotes an input for signal light, and 1134 denotes an output for signal light.
Although an optical waveguide sheet as shown in FIGS. 8A and 8B leads to cost savings, because it mitigates the problems of fabrication and alignment, it requires one sheet for each bit of a bus. This limits its application, because a parallel-to-serial conversion and/or multilayer sheet is required to accommodate a multi-bit bus. Although several systems to multiplex multi-bit signals using one single sheet have been studied, they resulted in a complex system, because signals are separated according to the signal strength or wavelength.